USDA - SOIL CONSERVATION SERVICE
SOUTH CAROLINA IRRIGATION GUIDE
Foreword
This guide contains information for planning, design, and operation of
irrigation systems consistent with sound irrigation principles. The
guide is designed to supplement, but not to supercede national or
state standards, specifications, or other requirements of the USDA
Soil Conservation Service (SCS). It was prepared in South Carolina by
SCS under the leadership of W. Burton Wells, State Conservation
Engineer, with assistance from other Government and University person-
nel using South Carolina data and applicable material obtained from
out-of-state, SCS Irrigation Guides. It is anticipated that this
guide will be used primarily by SCS and Extension personnel, private
engineers, and others who are qualified to provide irrigation planning
and design assistance to landowners and operators.
Grateful acknowledgement is given to the American Association for
Vocational Instructional Materials (AAVIM) for allowing the use of
several drawings from the book, "Planning for an Irrigation System."
Appreciation is also expressed to staff members of Clemson University
Departments of Agricultural Engineering and Agronomy, the South
Carolina Cooperative Extension Service, Agricultural Research Service,
U, S. Geological Survey, S. C. Water Resources Commission, and the SCS
South National Technical Center who assisted in reviewing the irriga-
tion guide and provided many helpful comments and suggestions for its
improvement.
Parlicular appreciation is expressed to the following individuals, who
in addition to reviewing certain chapters, coordinated the review of
other chapters among personnel in their agencies: Mr. Charles
Privette, Extension Agricultural Engineer, Clemson University; Mr.
Gary Speiran, Hydrologist, U.S. Geological Survey, Columbia, South
Carolina; and Dr. Carl Camp, Agricultural Engineer, Coastal Plains
Soil & Water Conservation Research Center, Florence, South Carolina.
The primary coordinator of the irrigation guide was SCS Assistant State
Conservation Engineer Remer Dekle.
This guide is a complete revision of the South Carolina Sprinkler
Irrigation Guide originally prepared in the 1950's and revised in the
sixties and seventies.
January 1987
[ Assistance from the U. S. Department of Agriculture is available
I without regard to race, creed, color, sex, age, handicap, or national
origin.
SOUTH CAROLINA IRRIGATION GUIDE
CONTENTS
Chapter 1 Introduction
Chapter 2 Soils
Chapter 3 Crops
Chapter 4 Irrigation Water Requirements
Chapter 5 Irrigation Method Selection
Chapter 6 Irrigation System Components
Chapter 7 Conservation Irrigation Planning
Chapter 8 Irrigation Energy Use
Chapter 9 Irrigation Economic Evaluation
Chapter 10 Irrigation Method Design
Chapter 11 Irrigation Water Management
Chapter 12 Irrigation Water Measurement
Appendix
A. Measuring Soil Water Content
B. Irrigation Evaluation Procedures
C. Design Aids
D. Glossary
E. Chemical Treatment to Inhibit Clogging of Low Pressure
Irrigation Systems
F. TR 21 Input Data For Table 4-2
G. References
SOUTH CAROLINA IRRIGATION GUIDE
CHAPTER 1. INTRODUCTION
Contents
Page
Purpose and Objective ----- ......... 1-1
Rainfall in South Carolina- ----------- 1-1
Average Rainfall- --------------- 1-1
Seasonal Distribution of Rainfall ------- 1-3
Year-to-Year Variability of Rainfall- ..... 1-3
Temperature ------------------- 1-4
Average and Seasonal Distribution ------- 1-4
Daily Range of Temperature ...... _--__ 1-4
Growing Season and Degree Days- -------- 1-5
Wind
M I | | W
Surface Water --------- ......... 1-10
Average Streamflow -------------- 1-lQ
Seasonal Distribution of Streamflow ------ 1-10
Low Flows ------------------- l-lo
Withdrawals - ......... -------- 1-10
Water Quality ..... ----- ....... 1-11
Ronpr^l -. .. _ _ - _ _ _ _ ~, - 1-11
ucut-i ai j. j. j.
Temperature -------- ...... -_- i-ii
Dissolved Solids and Acidity ........ 1-11
Ground Water- ........ - ......... 1-12
Water-Bearing Formations (Aquifers) ...... 1-12
Water Availability ............... 1-12
Well Depths ............ ------ 1-12
Well Yield and Water Levels .......... 1-12
Withdrawals ----------- ....... 1-15
Water Quality - ................ 1-16
General ................... 1-16
Temperature ------- ........ -- 1-16
Dissolved Solids and Acidity ......... 1-16
Sand and Minerals .............. 1-19
Trickle Irrigation Concerns ......... 1-19
Waste Water Applications ............. 1-20
Figures
Figure 1-1 Average Annual Rainfall- -------- 1-2
Figure 1-2 Seasonal Distribution of
Monthly Rainfall 1-3
Figure 1-3 Seasonal Distribution of
Temperature- ------------- 1-4
Figure 1-4 Average Length of Growing Season - - - - 1-6
Figure 1-5 Average Date Last Frost- -------- 1-7
Figure 1-6 Average Date First Frost -------- 1-8
Figure 1-7 Average Annual Runoff- --------- l~g
Figure 1-8 Principal Acquirers in South Carolina- - 1-14
Figure 1-9 Ground Water Project Areas 1-18
n
SOUTH CAROLINA IRRIGATION GUIDE
CHAPTER 1. INTRODUCTION
PURPOSE AND OBJECTIVE
This irrigation guide is for the entire state of South
Carolina. The guide has been prepared by the Soil
Conservation Service with assistance from other Federal and
State Agencies for use by trained personnel in planning
and designing irrigation systems and use in irrigation water
management. The basic data will assure the irrigator that the
irrigation system will be capable of supplying the quality and
quantity of water needed by plants for optimum production and
that with proper seasonal adjustments, irrigation water can be
applied efficiently. Recommendations included in this guide
are for the most common types of irrigation systems now used
in the state.
Some basic data for economic evaluation are included. However,
it must be kept in mind that the economics of irrigation are
usually an individual field or farm determination in which
various other factors may enter.
Many principles of conservation irrigation are basic for other
aspects of planning such as drainage and erosion control. The
guide should form a sound basis for collecting and evaluating
needed additional information.
RAINFALL IN SOUTH CAROLINA
AVERAGE RAINFALL
The average annual rainfall of the Southeast River Basins is
about 50 inches. The United States average is about 30
inches. Figure 1-1 shows the average annual rainfall over
South Carolina.
Based on 90 years of record, the mean is about 48 inches with
extremes ranging from 33 inches in 1954 to 72 inches in 1964.
1-1
Figure 1-1
1-2
SEASONAL DISTRIBUTION OF RAINFALL
Figure 1-2 shows the normal seasonal distribution of monthly rainfall for
three climatic zones in South Carolina for the period 1951-1980 (see ch. 4
for zone boundaries) .
Normal Precipitation (Inches)
Season Zone 1 Zone 2 Zone 3
I/
Winter 12.87 11.07
y
Spring 13.93 11.98
I/
Summer 12.77 15.24
4/
10.47
11.42
17.04
Fall
Annual
10.21
49.78
9.02
47.31
9.88
48.81
I/ December, January, February
2J March, April , May
y June, July, August
4/ September, October, November
Figure 1-2
In general, the rainfall is fairly well distributed throughout an average
year, with most of the rain occurring during the growing season. Variations
in seasonal and especially monthly rainfall from year to year are often
significant. For example, the standard deviation of the normal monthly
rainfall varies from about 40 to 55 percent. This means that about 32 per-
cent of monthly rainfall measurements would vary more than 40 to 55 percent
from the normal .
The summer peak, which is more prominent in the southeaster
state, is a product of thunderstorms which produce a large F
summer rainfall. The climatic effect of hurricane rainfall
insignificant because hurricanes occur infrequently at any 1
their aggregate rainfall is small compared with the scatter*
frequent, thunderstorm rainfall .
YEAR-TO-YEAR VARIABILITY OF RAINFALL
The variation in total annual rainfall from year to year car
Extremes of 50 percent more an 50 percent less than average
most records. Significantly, the annual rainfall is rarely
United States average of 30 inches.
1-3
TEMPERATURE
AVERAGE AND SEASONAL DISTRIBUTION
Figure 1-3 shows the average daily temperature in degrees
Fahrenheit for 3 climatic zones in South Carolina (see
chapter 4 for zone boundaries). In general, the average
daily temperature at the height of summer is slightly below
80.
most
July temperatures averaging
of the United States.
about 75 are typical of
Average Daily Temperatures (F)
Season Zone 1
Zone 2 Zone 3
I/
Winter
44.0
46.5
47.6
u
Spring
61.1
63.4
63.6
11
Summer
77.7
79.1
79.0
4/
Fall
62.3
64.2
65.0
I/ December, January, February
21 March, April, May
3/ June, July, August
37 September, October, November
Figure 1-3
In January, the average daily temperature in South Carolina
is about 40F in the mountains, 45 over much of the Piedmont
province, and 50 over much of the Coastal Plain.
DAILY RANGE OF TEMPERATURE
The average daily temperature range is about 20F, with the
minimum usually at sunrise and the maximum usually early in
the afternoon. Exceptions to this regime occur, of course,
with a frontal passage and a change in air mass; strong wind
and mixing; and dense clouds. With unusually long duration
of cloudiness or with dense coulds, the daily temperature
range may be less than 10; and with clear skies, dry air,
and light wind the range frequently exceeds 30.
1-4
On an average January day the temperature rises to more than
50F in the mountains, the low 60' s in the central part of
the state, and reaches 70 in the extreme southeast part, the
minimum temperature during an average January day is 30 in
the mountains, 40 in the central part, and nearly 50 in the
extreme southern portion.
In July the average daily maximum temperature is about 90F
over most of South Carolina and somewhat less in the moun-
tains. During a typical July night the temperature falls to
about 70 over most of the state. In the mountains, the
minimum is about 60, and the coast is in the low 70' s.
GROWING SEASON AND DEGREE DAYS
Growing season is defined as the period between the last
occurrence in spring and the first occurrence in autumn of
temperatures below a given base. This base is different for
different plants, some being much hardier than others.
Tomatoes are damaged at temperatures below 32F, wheras peas
and cabbage can withstand temperatures as low as 24 for
brief periods. Figure 1-4 shows the average frost-free
period or length of growing season for sensitive plants. The
number of days range from 200 in the mountains to 290 in the
extreme southeast, with most of the state having about 230.
These values vary, of course, from year to year. In the
north, the length of growing season is within about 20 days
of the average two-thirds of the years, and in the south it
is within about 30 days two-thirds of the years.
Figure 1-5 shows the average date of the last freeze in
spring, and Figure 1-6 shows the average date of the first
freeze in autumn. Both figures apply to sensitive plants.
For hardy plants, the average growing season limits would be
about 25 days earlier in spring and about 20 days later in
autumn.
WIND
winds are predominantly southwesterly and northeasterly over
most land areas. Average wind speeds are 5 to 10 mph for the
state.
Physiographic influences in South Carolina are important. Stations
such as Charleston, which are near the open coast, have average wind
speeds of 7 to 10 miles per hour; stations, such as Anderson, on
ridges or plateaus, have average wind speeds of 8 to 10 miles per
hour; and at relatively sheltered valley stations such as Columbia,
the winds average 5 to 7 miles per hour.
1-5
I
I
ro
-a
o
i
s-
a
c
s-
4-
CJ
Figure 1-5
1-7
Figure 1>-6
1-8
Figure 1-7
1-9
SURFACE WATER
AVERAGE STREANFLOW
The average annual streamflow in South Carolina represents
about 22 inches average depth over the State (U.S.
Geological Survey, 1985), compared to the United States
average of about 8 inches. The range of annual streamflow is
from about 10 inches in the lower Coastal Plain and lower
Piedmont to about 45 inches in the Blue Ridge (mountains).
SEASONAL DISTRIBUTION OF STREAHFLOU
Regardless of variations in the seasonal rainfall pattern,
the average streamflow, except in certain coastal areas, is
high in early spring and recedes to a low in late autumn.
This average seasonal regime is typical even of most small
streams in the rural areas. The summer rainfall peak does
not ordinarily produce a summer runoff peak because summer
showers usually fall on relatively dry soil and because much
moisture is transpired by vegetation or evaporates directly to
the air in summer, thus leaving relatively little contribution
to runoff.
LOU FLOWS
Streams in the lower Coastal Plain and lower Piedmont nor-
mally have poorly-sustained base flows and some streams
periodically go dry during late summer and fall. This is in
contrast to the Blue Ridge province and upper Coastal Plain
(figure 1-8, B) where base flows are well-sustained.
More information on low flows of streams in South Carolina
may be obtained from the following publications of the South
Carolina Water Resources Commission by Bloxham (1976, 1979, 1981
Bloxham, W. M. 1979. Low-Flow Frequency and Flow Duration
of South Carolina Streams. South Carolina Water Re-
sources Commission, Report No. 11. 90 pp.
Bloxham, W. M. 1976. Low-Flow Characteristics of Streams
in the Inner Coastal Plain of South Carolina.
South Carolina Water Resources Commission, Report No.
5. 28 pp.
Bloxham, W. M. 1981. Low-Flow Characteristics of Ungaged
Streams in the Piedmont and Lower Coastal Plain of
South Carolina. South Carolina Water Resources Com-
mission, Report No. 14. 48 pp.
WITHDRAWALS
The average surface water discharge from South Carolina is
about 33 billion gallons per day (U.S. Geological Survey,
1985). Between 1970 and 1980, total offstream water use in
South Carolina nearly doubled to 5,780 million gallons per
day (Mgal/d). This amount is projected to increase to about
8,550 Mgal/d by the year 2020 (South Carolina Water Resources
Commission, 1983).
1-10
WATER QUALITY
General
The quality of South Carolina's surface water is generally
excellent and suitable for most uses. The water is soft and
has a low buffering capacity. There are no known significant
quality problems concerning irrigation of surface water.
Temperature
The natural temperature in large streams is near the average
monthly air temperature. In smaller streams, day-to-day
fluctuations in water temperature are greater than for the
larger streams and in the smallest streams, hour-to-hour
variations are evident with the daily range of temperature
being nearly as great as for the nearby air.
Dissolved Solids and Acidity
The range of dissolved solids for surface water in South
Carolina is from less than 15 to more than 100 mg/L with
values generally ranging from 20 to 80 mg/L. The ph of sur-
face water generally will be in the range from about 5.0 to
7.5 with alkalinity ranging from about 1 to 40 mg/L.
1-11
GROUND MATER
HATER-BEARING FORMATIONS (Aquifers)
The areal distribution of the principal aquifers in South
Carolina are shown in figure 1-8. The Piedmont and Blue Ridge
aquifers occur in alluvial deposits of sand and gravel; in
weathered saprolite; and in joints, fractures and fault zones of
cystalline bedrock.
The Coastal Plain aquifers occur in a wedge shaped area con-
sisting of sand, clay and limestone sediments overlaying meta-
morphic and sedimentary rocks. The wedge, thickening from the
Fall Line toward the coastline, can be divided into aquifers
and confining units based on reldtive permeabilites, and other
factors (figure 1-8, C) Water generally moves laterally within
each aquifer with confining units inhibiting but not preventing
vertical movement of water between aquifers. (Ancott and
Speiran, 1984)
Ancott and Speiran, 1984. Ground Water Flow in the
Coastal Plain Aquifers of South Carolina, U. S.
Geological Survey.
WATER AVAILA&ILHY
In general, the Blue Ridge and Piedmont Provinces have limited
ground water supplies because of their geology. The underlying
igneous and metamorphic rock (overlain by a weathered surface) is
dense and crystalline and water is available only in the thin
soil mantle and fracture zones of the rock itself.
Within the Coastal Plain, thick sedimentary aquifers provide
substantially greater supplies of generally good quality water.
Ground water can be obtained nearly everywhere by drilling a well
and pumping,
UELL DEPTHS
Most water is stored in the top several hundred feet in the
Piedmont and Blue Ridge Provinces, thus well depths usually stay
within this range. Wells in the Coastal Plains often produce
adequate yields at depths less than 500 feet (ft) but it is not
rare for depth to be 1000 ft or greater.
WELL YIELD AND UATER LEVELS
In the Piedmont and Blue Ridge, typical wells yield 10 to 30
gallons per minute Cgpm) with water levels generally less than
100 ft but sometimes exceeding 200 ft from the ground surface.
Water levels in most deep Coastal Plain wells (several hundred
ft.) prior to development usually are within 50 ft. beneath the
surface and sometimes above land surface in the lower Coastal Plain due to
artesian conditions. In upland areas of the upper Coastal Plain, water
levels prior to development may be deeper than 200 feet, (personal com-
munication, Gary Speiran, 1986)
Most large capacity wells in the Coastal Plain are screened in the Black
Creek or the Middendorf (Tuscaloosa) Aquifer. Potential yields range from
several hundred to greater than 2000 gpm. Little decline in water levels is
being experienced except in heavily pumped areas of Florence, Myrtle Beach,
and Savannah. Declines in the Florence area are reported to be greater than
100 ft. since 1930 for selected wells. (Ancott & Speiran, 1985a, 1985b)
After development, water levels in wells screened in the Black Creek and
Middendorf aquifer are commonly in the range from 50 to more than 250 ft.
from the soil surface at the pumping well, (personal communication, Gary
Speiran, 1986) The actual water level at any particular well during pumping
is dependent on many factors including static water level prior to pumping,
permeability of in-place materials and the gravel pack or filter at the
screened sections, the well screen itself, transmissibility of the aquifer,
and the discharge of the well.
Screens or perforated casings are utilized in unconsolidated sand and gravel
aquifers to allow water to enter the well and to stabilize the aquifer
material. Consolidated rock aquifers often may be completed without per-
forated casing or screen. Due to the cost of screens, usually only the
higher yielding zones are screened, resulting in some wells being multi-
screened. Zones of poor quality water should not be screened if ample quan-
tity of good quality water is available at different depths-
1-13
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I
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80
EXPLANATION
COASTAL PLAIN AQUIFERS
Shallow aquifers
Floridan aquifer system
Tertiary sand aquifer
Black Creek aquiler
Middendorf aquifer
NON-COASTAL PLAIN AQUIFERS
Piedmont and Blue Ridge aquifers
Confining beds
100 MILES
B
NORTHWEST
SOUTHEAST
Charleston
^- Sea leva I
B, Fenneman, 1938; Raisz, 1954.)
1-14
For more information, see South Carolina Technical Note
Engineering 2 (Geology) on file in SCS county offices, S.C. Water
Resources Publications, or U.S. Geological Survey Reports as
referenced.
Aucott and Speiran. 1984. Water Level Measurements for
the Coastal Plain aquifers of South Carolina prior
to development. U. S. Geological Survey Open-File
Report 84-803.
Aucott, W. R. and G. K. Speiran. 1984a. Potentiometric
surfaces of the Coastal Plain aquifers of South Carolina,
prior to development. U. S. Geological Survey Water-
Resources Investigations Report 84-4208.5 sheets.
Aucott, W. R. and G. K. Speiran. 1984b. Potentiometric
surfaces for November 1982 and declines in the potentio-
metric surfaces between the period prior to development
and November 1982 for the Coastal Plain aquifers of
South Carolina. U. S. Geological Survey Water-Resources
Investigations Report 84-4215.7 sheets.
WITHDRAWALS
The 1980 withdrawal of ground water in South Carolina was
slightly less than 210 mgal/d (Lonon & Others, 1983). This is
equivalent to about two-sevenths inch average depth per year over
the southeastern half of the state. A question to be considered
is what rate of withdrawal could be sustained. As indicated by
water level declines in areas where ground water pumpage is great-
est (Myrtle Beach, Florence, Sumter, and Savannah, withdrawals
may be approaching maximum sustainable yields locally. In other
areas of the Coastal Plain, ground water is relatively undevel-
oped thus significant increases in withdrawals over present rates
should be sustainable in most situations.
Ground-water withdrawals for irrigation are seasonal, usually are
spaced widely, and are located mostly in the upper part
Dlain
VIATER QUALITY
General
Ground water quality as related to irrigation is generally good to
excellent in South Carolina. At points along the coast, salt-water
intrusion is a problem; and inland there are scattered places where
salinity or sulfur limit use. Probably the most widespread problem
concerns acidity (alkalinity) and dissolved solids and their effect
upon metal parts of irrigation systems. In the Middendorf aquifer
along the coast, concentrations of boron of as little as 8 mg/L may
cause problems with certain irrigation uses.
Temperature
In general, temperature of ground water is about the same as
mean annual air temperature at the water table and increases to more
than 100 F at depths greater than 2500 feet. Temperature of water
from very shallow wells or from very small springs varies seasonably
but temperature of water from deeper aquifers changes very little.
Temperature of shallow ground water ranges from about 64 to 69 F in
the Coastal Plain and slightly cooler north of the Fall Line to
below 60 F in the mountains (Personal Communication, G. Patterson,
USGS, Columbia, SC)
Dissolved Solids and Acidity
The ph and alkalinity increases going from the West toward the coast
within the range from about 4.0 to 9.0 (ph) with alkalinity less than
1 to greater than 1,000 mg/L. Values of ph are generally between 6.0
and 8.6. (personal communication-Glenn Patterson, USGS, Columbia, SC)
At the lower end of the pH range, (acid) damage may occur to well
casings, screens, pumps, and the metal parts of the irrigation system.
Both acidity and low total dissolved solids, which are known causes of
corrosion, are recognized problems in several center pivot systems in
Lee and Sumter Counties. Some steel pipes have been severely corroded
and have failed after only two to five years use. Results of chemical
testing, provided by the Water Resources Commission to irrigators,
indicate the probable cause of deterioration of pipes in this area to
be a combination of these two problems (acidity and low total
dissolved solids). However 5 there may be some other contributing
source not yet investigated,
At present, one recommended action for existing steel pipe systems is
to inject lime containing adequate calcium carbonate to neutralize the
acid and provide a substance that the water can dissolve instead of
dissolving the pipes. The lime is normally injected on the discharge
side of the pump. This slows down the attack and depending on the
condition of the pipe, it may add many years of life to the- system
1-16
(personal communication, L. lagmon, Chemist, SC Water Resources
Commission, Columbia, SC). The screen should be of fiberglass, high
quality stainless steel, or other material resistant to attack.
The water source for the known problem sites is primarily the
Tuscaloosa (Middendorf) aquifer. The suspect area is a strip along
the fall line including the upper Coastal Plains from Augusta,
Georgia, through Chesterfield, South Carolina. Future ground-water
investigations to be conducted by the Water Resources Commission will
provide additional data to better define the area and refine treat-
ment procedures.
It is recommended that irrigators have their water supply analyzed to
determine the water quality, whether surface or subsurface source is
being used.
For new systems, a water quality analysis should be made at the test
well stage. It is advisable to use PVC or other approved pipe when
possible rather than steel pipe for sites where this problem is iden-
tified or is likely to develop. Otherwise, the owner should be pre-
pared to replace damaged components or treat as needed for pro-
tection. The South Carolina Water Resources Commission currently
will obtain samples, do the testing and provide recommendations for
treatment on a request basis at no charge for agricultural use when
the site is located within one of the Commission's study areas. The
Geology-Hydrology divisions Ground-Water Project areas map is shown on
Figure 1-9.
For specific information about water quality at a particular location,
landowners should address inquiries to the following address:
Water Resources Commission
P. 0. Box 4440
Columbia, South Carolina 29240
Phone: 758-2514
1-17
Figure 1-9
No.
1
2
3
4
5
Ground-Water Project Areas - Water Resources Commission
Name No. Name
Appalachia
Catawba
Pee Dee
Upper Savannah
Central Midlands
6 Waccamaw
7 Lower Savannah
8 Trident
9 Low Country
SCAlt -JTtrvK
10 10 10 10 SO
L
1-18
Technical personnel are encourages to discuss the acidity and
dissolved solid problems with irrigators to make them aware of the
known potential problem areas and the need to have their water
analyzed.
Sand and Minerals
When pumping from ponds, streams, or wells with suspended sand, the
pump and irrigation equipment orifices need to be checked regularly
for wear. Sand content does not have to be high enough to make the
water unclear for it to cause severe wear. A good indication of pump
or orifice wear is a reduction in system pressure at the usual
operating speed and water level.
The hardness (mineral content) of the water can cause equipment
problems due to mineral deposits closing orifices, freezing sprinklers
and mineral encrustation in pipes.
Trickle Irrigation Concerns
Trickle irrigation systems with their small emitter openings and more
intricate labyrinth-type internal structures are more easily clogged
than other types of irrigation. Clogging seems to be less of a
problem in those types of emitters through which the water moves at
higher velocities.
Particulate matter and bacterial slimes are the usual causes of these
clogging problems. Filtration will take care of the particulate
matter problem, but with a high particulate matter content cleaning
filters can become a problem.
A combination of chlorine and filters will control the bacteria
problem. It should be used a preventive rather than a corrective
treatment, because it is very difficult to clean out systems once they
are clogged. Chlorine should be metered according to need rather than
just "dumped" into the system. Chlorine injection should result in a
free residual chlorine level of 0.5 to 1.0 ppm at the end of the
system. This level should be maintained for a period of 30-45 minutes
and should be applied periodically depending on the quality of the
water supply.
Surface water may be suitable for trickle irrigation if chlorine is
injected at the pump and a sand filter is used to trap the algae and
particulate matter before they enter the lines and emitters.
Before installing a trickle irrigation system, the landowner should
have tests run for pH, iron, sulfides and dissolved solids and get
advice from experts in the field of chlorine treatment. The sulfides
and iron stimulate slime growth.
1-19
HASTE HATER APPLICATIONS
Waste water includes water that contains waste from municipal waste treat-
ment plains, industrial plants, food processing facilities, dairies, and
livestock operations. This waste water will contain various amounts of
nutrients, organic material, and possibly heavy metals.
These waste waters can be used for irrigation, but the amount of this waste
water that can be applied and the crops to which it can be applied will be
determined by its quality. Irrigation with waste water containing heavy
metals is very restricted. The fertility balance of the soil should be
maintained by supplementing the waste applications with appropriate commer-
cial fertilizers.
Waste water can be very corrosive causing system life to be limited and
maintenance increased. Also, consideration should be given to the solids
content of waste water. Large orifices are needed to pass the larger solids
without clogging. A pump that chops up the solids nnay be required,
depending on orifice and solid
Water containing human or animal waste should not be applied to crops that
are consumed raw by humans.
For more information on irrigating with agricultural waste see Engineering
Standards and Specifications Code 633 - Waste Utilization, the Agricultural
Waste Management Field Manual, and Animal Waste Utilization on Cropland and
Pastureland (USOA Utilization Research Report No. 6).
SOUTH CAROLINA IRRIGATION GUIDE
CHAPTER 2. SOILS
Contents
Page
General 2-1
Available Water Capacity and Soil Moisture Tension 2-1
Texture 2-5
Irrigation Restrictive Features 2-6
Site Selection and Erosion Control 2-7
USDA Land Capability Classification System 2-7
Erosion Control 2-8
Maximum Irrigation Application Rates 2-10
Figures
Figure 2-1 Soil Moisture Content - Kinds of
Water in the Soil 2-1
Figure 2-2 Moisture Release Curves for Three Soils. .2-2
Tables
Table 2-1 Water Retention Versus Suction for
Soil -Texture Groupings 2-4
Table 2-2 Available Water Capacity for
Selected Textures 2-5
Table 2-3 Features Affecting Irrigation 2-6
Table 2-4 Land use Capability Subclasses 2-7
Table 2-5 Conservation Practices 2-8
Table 2-6 Maximum Sprinkler Irrigation Application
Rates (In/Hr) for Row Crops 2-11
SOUTH CAROLINA IRRIGATION GUIDE
CHAPTER 2. SOILS
GENERAL
A knowledge of soil properties is necessary for the efficient use of water
for crop produc tion. Soil survey maps and special request maps are available
to all field offices. The different kinds of soils and their distribution are
identified on these maps, and important physical and chemical characteristics
of each kind of soil are recorded in the SCS technical guides. Some charac-
teristics of soils important to understanding soil-moisture plant rela-
tionships are discussed in this guide. They include permeability, intake
rate, slope, depth to water table, and texture. All of these help determine
the potential available water capacity. Also, organic matter content and bulk
density help determine available water capacity.
AVAILABLE WATER CAPACITY AND SOIL MOISTURE TENSION
The available water capacity (AWC) of a soil is a measure of its capacity to
make water available for plant growth. The AWC is the amount of water held
between field capacity (FC) and the permanent wilting point (WP) as shown in
Figure 2-1. AWC is expressed as the water retained between 1/3 bar and 15
bars tension for fine to medium textured soils and between 1/10 bar and 15
bars for moderately coarse to very coarse textured soils.
Ovendr
Ultimate
^wilting point
WILTING
RANGE
Unavailable
to plants HYGROSCOPIC
WATER
Available moislur
for sandy loam
Saturation
Limited amt,
avallobla GRAVITATIONAL
OR FREE
N N WATER
T
30 40
10 SO
Soil Moisture Content (Percent by Dry Weight)
Figure 2-1. Soil Moisture Content - Kinds of Water in the Soil
2-1
There are a number of methods used to determine when to irrigate. One method
is based on soil-moisture tension. The relationship between this concept and
AWC is shown by the moisture release curves for three soils ^"2 2. In
this figure moisture content is expressed as a percentage of AWC rather than
as percentage by weight. FC is 100 percent of AWC and the WP (15 bars) is
^ lll of AWC/ taSion at any moisture level is dif ferent for the three
soils. At the 50 percent level, for example, moisture tension for the clay is
about 4.3 bars (atmospheres); for the loam, 2.0 bars; and for the sand 0.6
bars. (These values shown for comparison only and do not represent any par-
ticular soil.)
100
Field Copoclly
5 6 7 8 $ 10 11
SOIL-MOISTURE TENSION, BARS
12 13 14 15
Figure 2-2. Moisture Releaae Curves for Three Soils
2-2
Moisture is more readily available to plants at low soil moisture tension
(near field capacity). Since tension values are so different in the three
soils shown in Figure 2-2, it is possible that crop response would be dif-
ferent if the soils were irrigated when tension reaches a given value rather
than when available moisture is depleted to a given value. See Chapter 3
(Crops) and Chapter 11 (Water Management) for information on when to irrigate
or
The SCS Field Office Technical Guide, Section II-B, Soils Descriptions,
either a published soil survey can be used to obtain the AWC for South
Carolina soils. For example, the available water capacity of the top 18
inches in a Faceville soil in Aiken County is:
Sandy loam 0"- 6", 0.075 in. /in. x 6 in. = 0.45 in.
Sandy clay 6"-18", 0.150 in. /in. x 12 in. = 1.80 in.
Total AWC for 18 in. depth = 2.25 in.
Water retention values for various soil water tension levels are shown in
Table 2-1 for Southern Piedmont and Coastal Plain soil texture groupings.
From this table, water retention for a Faceville soil (coastal plain soil
Aiken County at the indicated soil moisture tensions may be estimated as
follows:
in
Depth
0- 6"
6-18"
Texture
Sandy loam
Sandy clay
.10 bar tension
0.20 inches/inch
0.27 inches/inch
0.5 bar tension
0.15 inches/inch
0.23 inches/inch
Difference
0.05 in/in
0.04 in/in
The water retention capacity in the 18 inch depth for this range of tension
is:
6(0.05) + 12(.04) = .78"
The 2.25 inches of AWC represents the differences in the amount of water held
between about 0.1 bar and 15 bar tension whereas the 0.78 inches represents
the differences in water retention between 0.1 bar and 0.5 bar (the latter
being the range measurable by a tensiometer).
2-3
Table 2-1. Water Retention Versus Tension for soil-texture groupings V
Southern Piedmont Soils
Water retention, inch/inch,
at tension of-
Layer
Soil Texture
0.03
bar
0.06
bar
0.25
bar
0.50
bar
0.75
bar
1.0
bar
Surface, .
.Loamy sand or coarse
0.22
0.17
0.125
0.11
0.105
0.10
sandy loam.
Subsoil . .
.Sandy clay loam, clay
.36
.34
.32
.30
.29
loam, or clay.
Surface. .
.Sandy loam.
,28
.23
.17
.165
.155
.15
Suhsni 1
Sand clav loam clav
.36
.34
32
.30
.29
+J \JIJ mj \J 1 1 1
"vJl-llfl^J* \^ I \AJ IV "Jl > * \^ 1 tl T
loam, or clay.
* J\J
\J L.
Surface. .
.Loam to clay loam.
.35
.34
.32
.31
.30
,295
Subsoi 1 . .
.Sandy clay loam, clay
.36
.34
.32
.30
.29
loam, or clay.
* *j \j
Coastal
Plain
Soils
Water
retention, inch/inch,
at tension of-
0.025 0.05
0.10
0.25
0.50
1.0
Layer
Soil Texture
bar
bar
bar
bar
bar
bar
Surface.
..Sand and loamy sand.
0.29
0.20
0.13
0.10
0,08
0.07
Subsoil .
..Sand and loamy sand.
.29
.20
.13
.10
.08
.07
Surface,
..Sand and loamy sand.
.29
.20
.13
.10
.08
.07
Subsoil .
. .Sandy loam and fine
.31
.26
.20
.17
.15
.13
sandy loam.
Surface,
...Sand and loamy sand.
.29
.20
.13
.10
.08
,07
Subsoil .
. . .Sandy clay loam and
....
.30
.27
.25
.23
.22
sandy clay.
Surface,
. . .Loamy fine sand.
.29
.25
.18
.13
.11
.09
Subsoil
...Sandy clay loam and
r t
,30
,27
.25
.23
.22
sandy clay.
Surface
. . .Loamy fine sand.
.29
.25
.18
.13
.11
.09
Subsoil
...Sandy loam and fine
.31
.26
.20
.17
.15
.13
sandy loam.
Surface
. . .Sandy loam and fine
.31
.26
.20
.17
.15
.13
sandy loam.
Subsoil
. . , Sandy clay loam and
. . .
.30
.27
.25
.23
.22
sandy clay.
TT" From Irrigation of Crops in Southeast US ARM 5-9/May 1980 p. IS" and 19.
2-4
TEXTURE
Texture is shown for all map units in the SCS Technical Guide, Section II-G,
Engineering Interpretations. The following abbreviations are used:
Sand S
Coarse sand CUS
Fine sand FS
Loamy coarse sand LCDS
Loamy sand LS
Loamy fine sand LFS
Loamy very fine sand LVFS
Coarse sandy loam COSL
Sandy loam SL
Fine sandy loam FSL
Very fine sandy loam VFSL
Loam L
Silt loam SIL
Clay loam CL
Sandy clay loam SCL
Silty clay loam SICL
Silty clay SIC
Sandy clay SC
Clay C
Muck or peat MK or PT
Additional textural modifiers are:
Channery CN
Gravelly GR
Shaley SH
As a guide and quick reference for general planning, estimated available water
capacity for selected textures is given in Table 2-2.
Table 2-2. Generalized Available Water Capacity for Selected Textures
Texture
Average
AWC
(in/in)
Suggested
Range in AWC
(in/in)
Sand
0.05
0.03
- 0.07
Fine sand
0.06
0.03
- 0.09
Loamy sand
0.08
0.06
- 0.10
Loamy fine sand
0.10
0.07
- 0.13
Sandy loam
0.12
0.09
- 0.15
Fine sandy loam
0.13
0.10
- 0.16
Silt loam
0.18
0.14
- 0.22
Sandy clay loam
0.16
0.13
- 0.19
Clay loam
0.17
0.14
- 0.20
Silty clay loam
0.18
0.14
- 0.22
Sandy clay
0.16
0.13
- 0.19
Clay
0.17
0.14
- 0.20
2-5
IRRIGATION RESTRICTIVE FEATURES
Table 2-3 contains a listing of features affecting irrigation. For information
on features affecting irrigation for a particular map unit, see the SCS
Technical Guide, Section II.
Table 2-3. Features Affecting Irrigation
PROPEfUY
1. Fraction >3 in (wt pet) I/
2. Depth to high water table
(ft)
3. Available water capacity _!/
(in/in)
4. USDA texture
(surface layer)
5. USDA texture
(surface layer)
6. Wind credibility group
7. Permeability (in/hr) (0-60")
8. Depth to bedrock (in)
9. Depth to cemented pan (in)
10. Fragipan (great group)
11. Bulk density (g/cit|3) (0-40")
12. Slope (pet)
13. Erosion factor (K)
(surface layer)
14. Flooding
15. Sodium absorption ratio
(great group)
16. Salinity (mmhos/cnO (0-40")
IZ.! JPIJ faction (pH)
UMTTS
>25
<3
<0,10
COS, FS, VFS, LCDS,
LS, LFS, LVFS
SIC, C, SC
123
I , C. , J
<0.2
<40
All fragi
>3
>,35
Common
(Natric, Halic)
>4
<3.6
RESTRICTIVE
FEATURES
Large stones
Wetness
Ponding
Droughty
Fast intake
Slow intake
Soi 1 blowing
Peres slowly
Depth to rock
Cemented pan
Rooting depth
Rooting depth
Slope
Erodes easily
Floods
Excess sodium
Excess salt
Too acid
I/ Weighted average to 40 inches.
2-6
SITE SELECTION AND EROSION CONTROL
USDA LAND CAPABILITY CLASSIFICATION SYSTEM
The USDA Land Capability Classification System is a general guide in selection
of sites suitable for irrigation systems. The capability groupings are based
on the limitations of soils, the risk of damage, and the way soils respond to
treatment when used for cropland.
Soils are grouped into eight capability classes from I through VIII. Class I
soils have the fewest limitations, widest range of uses and the least risk of
damage when row cropped continuously. Soils in higher classes have progress-
ively greater natural limitations.
Within each class of II to VIII, there
designated by the letters "e," "w," or
of each class.
can be as many as three
"s." Table 2-4 defines
subclasses
the limitations
TABLE 2-4. LAND USE CAPABILITY SUBCLASSES
Subclass
e
w
Major Limitation
Risk of erosion unless a close-
growing plant cover is maintained
Water in or on the soil interferes
with plant growth or cultivation;
artificial drainage may eliminate
or reduce wetness problems
Soils are limited by shallowness,
droughty or stony conditions
The subclasses are further divided into capability units. The capability
units are similar groups of soils that are suited to the same crops and forage
plants. These soils require similar management and have similar yields.
Capability units are available through county Soil Conservation Service
offices (see S. C. Technical Note Soils-3).
Land used for irrigation and continuous row crops should fall in Classes I -
III for best results. Erosion control measures are needed on Class II and
Class III with a subclass of "e." Planning and installation for erosion
control practices should be done prior to installation of an irrigation
system. Wetness problems can be expected on soils with a subclass of "w."
Surface and/or subsurface drainage may partially correct wetness problems.
Droughty conditions occur on many soils with a subclass of "s." Irrigation
will reduce this limitation in many cases. Low fertility, excessive leaching,
and erosion problems may also occur on these soils.
2-7
Soils with marginal or very little potential for crop production fall in
Classes IV-VIII. These soils have severe natural limitations and some may
produce low yields under the best management. Irrigation on some Class iv-s
land has been successful in the Coastal Plain. This land requires better than
average management and the cost per unit of production is generally higher A
careful site by site evaluation is needed before irrigating Class iV-s land.
Land in Classes IV through VIII is normally better suited for hayland, pasture-
land, woodland, wildlife land or other uses where a permanent cover can be
maintained.
The USDA Land Capability Classification System is a useful tool for
planning. Site specific information is necessary to plan the best
system.
EROSION CONTROL
general
irrigation
Soil and water conservation needs for an irrigated area may influence the
design of an irrigation system. Table 2-5 lists conservation practices
that may have the most impact, Other practices including waterways, field
ditches, water and sediment control basins, field borders, and filter strips
should be considered as appropriate.
Conservation Practice
Contour Farming
Crop Residue Use
TABLE 2-5
Major Benefits
-reduction of runoff
from low to medium
intensity storms
-more infiltration of
rain and irrigation
water
-significant reduction
of soil loss at
minimum cost
-reduction of wind and
water erosion when
residue is left on
soil surface
-increased tilth due to
increased organic
matter
-increases water in-
filtration, reduce
runoff and micro-
organism activity
-reduce evaporation
from soil surface
Limitations
-not effective on 3-8%
slopes
-minimum 4" bed needed
for effective water
control
-row alignment may be
difficult to follow on
steep or nonuniform
slopes
-intensive rain or
irrigation rates can
cause row breakovers
and gully erosion
-may require minimum
tillage equipment
-may not be compatible
with all cropping ro-
tations
2-8
TABLE 2-5 (Continued)
Conservation Practice
Contour Stripcroppi ng
Terrace Systems
Conservation Tillage
Furrow Diking
Major Benefits
-simi lar benefits to
contour farming
-reduce sediment,
reduce runoff, and
increase infiltra-
tion
-reduction of runoff
which improves water
conservation
-increase in
infiltration
-reduction of field
sediment loss
-enduring conservation
practice
-reduces runoff
and sediment loss
-increases infil-
tration and reduces
crusting prob-
lems
-reduces evapora-
tive losses from
soil surface
-allows more versatile
double-cropping
systems
-effective in wind
erosion control
-reduces ponding in
low areas
-reduction of runoff
and sediment losses
-reduced erosion
-reduction of wind
erosion
-can reduce pumping
cost due to use of
low pressure sys-
tems
-increase in infil-
tration
Limitations
difference crops under
the same irrigation
system may have
different water needs
-chemigation generally
not feasible
-row alignment may not
fit large equipment
-grassed waterways and
pipe outlets may be
needed for water
control
-expensive
-requires grassed water-
ways or pipe outlets
for water disposal
-layout may not fit
large equipment
-requires annual
maintenance
-usually requires
specialized equipment
-not compatible wi th
all cropping systems
-requires expert
management and weed
control emphasis
-requires specialized
equipment
-dikes may interfere
with cultural or har-
vesting operations
unless they are plowed
out
-limited mostly to
slopes less than 2 per-
cent or to contouring
operations
2-9
MAXIMUM IRRIGATION APPLICATION RATES
Sprinkler irrigation application rates and amount should be related to the
temporary surface storage available and to a soil's capacity to absorb irriga-
tion water from the surface, and move it into and through the soil profile.
The amount of moisture already in the soil greatly influences the rate at
which water enters the soil. The soil takes in and absorbs irrigation water
rapidly when water is first applied to the field surface. As the irrigation
application continues, the surface soil gradually becomes saturated and the
intake rate decreases until it reaches a nearly constant value. Any excess
water accumulates for a period of time in soil pores in the surface layer and
in surface depressions. When this temporary storage is filled to capacity,
runoff begins. Proper management can increase retention time by increasing
surface storage capacity on or near the soil surface. A greater amount of_
excess water is stored, and more time is allowed for water to enter the soil
profile. This can be accomplished by several practices including surface
residue cover, tillage-induced surface roughness (such as furrow diking), and
contour or cross-slope farming. These measures also help to improve infiltra-
tion rates and to slow velocity of surface runoff.
The intake of any soil is limited by any restriction to the flow of water into
or through the soil profile. The soil layer within the soil water control
zone with the lowest transmission rate, either at the surface or directly
below it, usually has major effect upon the intake rate. Important general
factors that influence intake rates and thus application rates are the physi-
cal properties of the soil and, in sprinkler irrigation, the plant cover.
Irrigation application rates in Table 2-6 are to be used as a guide in
arriving at maximum application rates for sprinkler applications in South
Carolina. The values given are estimates based upon data published in S. C.
Agricultural Experiment Station Technical Bulletin 1022, recommendations from
NEH-15, Chapter 11, and results and observations obtained from recent irriga-
tion evaluation tests made in South Carolina. Higher application rates may be
used with smaller applications due to the higher initial intake rate and sur-
face storage* etc. For trickle systems, see Chapter 7 of the SCS National
Engineering Handbook, Section 15 (copy maintained by SCS Engineers), until
such time that trickle information is added to this guide.
2-10
Table 2-6. Maximum Sprinkler Irrigation Application Rates (In/Hr)
For Row Crops I/
Group
No.
Soil Texture in
Soil -Water Control Zone
Land
Slope
(%)
Net Application Depth
0.5"
1.0"
1.5"
2.0' r
1
Sand
under 2
2-5
over 5
2/
11
2/
2/
21
3.0
3.0
2.5
2.0
2.0
1.5
1.0
2
Sand and loamy sand
under 2
2-5
over 5
21
21
3.0
3.0
2.5
2.0
2.0
1.5
1.0
1.5
1.0
.8
3
Sand and loamy sand over
sandy loam or fine sandy
loam
under 2
2-5
over 5
21
3.0
2.5
2.0
1.5
1.0
1.5
1.0
.8
1.0
.8
.6
4
Loamy fine sand over sandy
loam or fine sandy loam
under 2
2-5
over 5
3.0
2.5
2.0
1.5
1.2
.8
1.0
.8
.5
.7
.5
.4
5
Loamy fine sand, or loamy
sand over sandy clay loam
or sandy clay
under 2
2-5
over 5
2,0
1.5
1.0
1.2
.8
.6
.8
.5
.4
.6
.4
.3
6
Sandy loam, fine sandy
loam, or loam over sandy
clay loam or sandy clay
under 2
2-5
over 5
1.5
1.0
.8
" 1.0
.6
.5
.6
.5
.4
.5
.4
.3
7
Sandy clay loam, loam,
silt, or clay loam over
silty clay, clay loam, or
clay
under 2
2-5
over 5
1.2
.8
.5
.6
.5
.4
.5
.4
.3
.4
.3
.2
I/ Use of some cultural practices such as bedding and contouring, row diking,
and possibly others may warrant that application rate not be a limiting
factor in design. These practices shall be documented to support planning
and design.
For grasses or minimum tillage crops with approximately 50% or more ground
cover, tabular values may be increased 25%.
For some crops and gun sprinklers, factors other than soil texture, slope,
and application depth may dictate that application rates be less than
shown. These include but are not limited to crop type, lack of ground
cover, droplet impact, and hydrologic condition of the soil. As a guide
use approximately 0.8 inch/hour as the maximum allowable gun sprinkler
application rate. Adjust lesser values downward as experience dictates.
21 For soils with these textures, slopes, and application depths, soil intake
rates are usually not the limiting factor in system design. Other factors
including crop type and droplet impact should be considered to arrive at an
application rate. For interpolation between other values in this table, a
value of 4.0 inches per hour may be used except for gun sprinklers as noted
above.
2-11
SOUTH CAROLINA IRRIGATION GUIDE
CHAPTER 3. CROPS
Contents
Page
General 3-1
Rooting Depth and Moisture Extraction 3-1
Irrigation and Crop Production 3-2
Irrigation Needs of Specific Crops 3-5
Alfalfa 3-5
Blueberries 3-5
Corn 3-5
Cotton 3-5
Grapes 3-5
Peacheb 3-6
Peanuts 3-6
Pecans & Walnuts 3-6
Small Grains 3-8
Sorghum 3-8
Soybeans 3-8
Strawberries 3-9
Tobacco 3-9
Vegetables 3-9
Tables
Table 3-1 Recommended Soil Water Control
Zones for Selected Crops 3-3
Table 3-2 Critical Moisture Periods of
Major Crops 3-10
SOUTH CAROUNA IRRIGATION GUIDE
Most of the irrigated cropland in South Carolina is planted to corn, cotton,
and soybeans. Irrigation is of greatest economic importance, however, on
specialty or high value crops including vegetables, strawberries, blueberries,
tobacco, nurseries, and orchards.
For full benefits from irrigation, other inputs should be supplied in ample
amounts. Special attention should be given i;o proper fertilization; selection
of adapted varieties that are capable of producing high yields; control of
weeds; insects, and diseases; and use of cultural practices such as row
spacing and increased plant population.
Deep soils with low available -,>oil water moisture during periods of peak crop
water moisture use commonly show the greatest response to irrigation.
Information on the suitability of soiU for different crops and for irrigation
is provided in Uie SCS Technical Guides,
Erosion and wetness problems commonly are intensified by irrigation.
Consequently, consideration of the physiographic features of the soils is cri-
tical to selection of a satisfactory system of irrigation. Conservation
tillage, buffer strips of perennial vegetation, vegetated terraces and diver-
sions, contour farming, and grassed waterways are effective erosion control
practices which are compatible with most systems of irrigation. Conservation
tillage and windbreaks provide effective control of soil blowing. However,
attention should be given to height c au! location of windbreaks so as not to
create a barrier to irrigation equipment and cause excessive shading of crops.
See Table 2-5 for the major benefits and limitations of soil conservation
practices. To drain wet soils, use of subsurface drainage with surface inlets
and grassed waterways should be maximized to avoid creating barriers to irri-
gation.
ROOFING DEPTH AND MOISTURE EXTRACTION
The rooting depth of the crop determines the size of the soil moisture reser-
voir (soil water control zone) to be managed- The rooting depth depends on
the crop being grown and soil conditions. Table 3-1 gives the recommended
soil water control zone of common crops grown in most soils in South Carolina.
However, examination of crop rooting depths should always be made to determine
the proper depths for water management in a particular system. Soils with
shallow depths to bedrock, gravel, hardpans, high water tables and other
restrictions to root development limit the rooting depth of crops. On these
soils, the potential for increased yields and profitability with irrigation is
limited by the shallow rooting depth. Because of the limited soil moisture
reservoir, these soils require frequent irrigation. The rooting depths on
soils with hardpans and on soils with high water tables can be increased by
subsoiling and drainage respectively, tf the water table is very high over
most of the season, a water table management system should be considered since
the irrigation requirements would be reduced due to the availability of stored
water.
3-1
In uniform soils with ample available moisture, plants use water rapidly from
the upper part of the root zone and slowly from the lower part. Most plants
have similar moisture extraction patterns. The usual extraction pattern for
soils with a uniform texture is as follows: about 40 percent from the upper
quarter of the root zone, 30 percent from the second quarter of the root zone,
20 percent from the third quarter, and 10 percent from the bottom quarter (see
figure 1). Thus, if 50 percent of the total root zone available moisture has
been used, the upper portion will be at less than 50 percent available
moisture, and the lower portion will be at greater than 50 percent available
moisture.
Frequent shallow irrigations will maintain a high moisture level (i.e., low
soil moisture tension) in the upper portion of the root zone. If, however,
irrigations are scheduled too frequently, excessive evaporation will occur,
excessively shallow root zone will result, or, in the extreme, water applica-
tion depths may be too small to effectively penetrate the crop root zone.
With heavy irrigations, losses through runoff, nutrient leeching out of root
zone, and risks of overwetting are increased. Thus, a planned method of sche-
duling irrigation is essential for effective use of irrigation (see
Irrigation Water Management Chapter 11 in this Guide for more information on
scheduling irrigations).
IRRIGATION AND CROP PRODUCTION
For maximum production and the most efficient use of water, plants must have
ample moisture throughout the growing season. For most crops there are criti-
cal periods in the growing season when a high moisture level must be main-
tained for high yields. Except for germination and transplanting, the
critical periods are periods of peak moisture use. The peak moisture use
period can best be defined as that time when soil moisture stress can most
reduce' yield in an otherwise healthy crop. This is not the only time in the
life of the crop that moisture stress reduces yield, but it is the time when
moisture stress has the greatest effect,
If there is enough moisture for germination and for the development of an ade-
quate stand, the critical moisture period is almost always in the latter part
-* *!.. g row -j ng season during the reproductive growth stage. Although plants
e moisture stress by various symptons, yields will usually be reduced
time the plants show stress. Time of irrigation should be determined
-xamination of the soil moisture content, Maintaining soil moisture
Mature control zone at or above the 60% level (40% management
" "- 4 --- 1 in Chapters 2 and 11 will normally provide adequate
sandy soils this corresponds generally to main-
^ow the 35 to 40 centibar range in the middle of
..MC OMI i a^c IOJTCI . i ui must, adndy clay soils in South Carolina, the
corresponding tension is in the range of 60 to 80 centibars or greater.
Critical moisture periods and specific information for various crops are shown
in Table 3-2 at the end of this chapter.
With most crops, maximum yields are attained by maintaining a high soil
moisture level along with other needed inputs throughout the growing season.
However, more profit may be realized by limiting irrigations to the particular
crop's critical moisture use periods in some situations.
3-2
Many South Carolina f-inns have limited water supplies for i.rirjdcion. Farmers
relvt.if] on ,uri act; '-lu^ed vmtcr (in ponds) may run short 01 water during
extended ury periods, Selection of crops showing the mo si; response to irriga-
tion mtl ' irnmi) irrin.'Mun treatments to meet critical w ( u.er needs of the crop
is Assent i A! ,
lahlo 3-J . Recommended Soil -Water Control Zone -for Selected Mature Crops
Crop
Corn. *......
Cotton
Cucumbers.
Peaches ........
i'eanuti.. . . . .
Pecans, .......:
Southern Ppas...
Soyhean'i. ,
Tomatoes .......
Tobacco
Sorghum
Watermelon .....
Pasture
Alfalfa
Blue Berries . .
Strawberries .,
Small Vegetable
Depth of Soil -Water
Control Zone
Inches
18-24
30-24
9
18
18
1.0-24
12
18-24
12
18
18
12
24
24
12
9
9
Note: Depths given are for soils without restrictive layers and
Tor soils with restrictive layers which have been loosened
by subsoiling. Use lesser depth as applicable for soils
with restrictive layers that limit deep root development.
Where two values are given, the depths shown are for
Piedmont and Coastal Plains soils respectively.
3-3
Uj
cc
d ^
O ^"
to 12
o
03
^
CC
t2 &
2: >-
0. G,
u. 3
o ">
Q: Jj
K O
^ Uj
2
2: ^
o ^
o:
K
x
UJ
Q
o
Q -J K
2
LU 2! o:
e> K
t^ O UJ
i. . QC i^.
<0
o:
K
o
o
a-Hld30 NOI10VH1X3
3NOZ 100H
IRRIGATION NEEDS OF SPECIFIC CROPS
ALFALFA
Alfalfa uses a lot of water for high production. However, Clemson University
agronomists have found that the length of life of alfalfa is reduced by irri-
gation without greatly increasing yields. Consequently, Irrigation commonly
is not recommended. If alfalfa is to be irrigated, the normal procedure is to
irrigate 3 to 5 days after each cutting. However, irrigation should also be
considered in the early spring before cutting and in the fall. These are
critical periods of growth. Thus irrigation at these times will aid in
maintenance of a highly productive stand.
BLUEBERRIES
The root system of a blueberry plant begins to grow before the top. If the
winter has been dry, irrigation should begin 3 to 4 weeks before the top
starts to grow. From bloom until harvest is a critical moisture period for
blueberries. After harvest, the blueberry continues to make new growth to
support next season's crop. Water and adequate fertility are critical during
this stage of growth.
CORN
Corn is shallow rooted until it nears tasseling. Consequently, the effective
soil moisture reservoir before tasseling is not as deep as from tasseling to
maturity. Demand for water from 60 days to maturity is high, and is especially
high and important during the tasseling and grain filling period. During this
period, maintaining soil moisture below the 0.25 - 0.4 tension range in medium
to coarse textured soils will normally provide adequate water for high yields.
While moisture use is high and moisture supply is most critical during this
period, moisture stress during any time from germination through maturity can
significantly reduce yields. Thus, irrigation schedules should allow for
irrigation throughout the life of the corn as needed.
COTTON
Cotton has significant drought tolerance; however, timely irrigation may
increase yields considerably. The critical moisture period is from first
bloom through boll maturing. High moisture levels after the boll forming
stage will delay the crop, increase the amount of immature fibers, and can
cause boll rots. High moisture levels early in the season can cause seedling
blight and damping off.
GRAPES
The year of planting is a critical moisture period for grapes. After the
first year, critical moisture period is during sizing of the fruit.
3-5
PEACHES
The fruit growth pattern of peaches is referred to as a double sigmoid growth
curve. There Is an initial period of rather rapid fruit enlargement followed
by a pit hardening period during which fruit enlargement is slight. Finally,
the flesh of the fruit thickens, and total enlargement is very rapid. During
this final swell, moisture stress reduces yields to the greatest extent.
Research findings are not conclusive on the proper available soil moisture to
maintain for peaches. But, data on cling peaches shows that the growth rate
during final swell is reduced when the soil moisture tension in the lower por-
tion of the soil-water control zone approaches 5 bars.
Excessive wetness contributes to short life. Thus, the soil moisture tension
in the soil-water control zone should not be below about 0.10 bar for any
appreciable period of time for sprinkler irrigation when the entire root zone
is wetland.
Irrigation recommendations for peaches are similar to those for pecans given
in a later section in this chapter, Therefore, refer to the pecan section for
more information.
PEANUTS
Peanuts respond well to irrigation with the greatest increases in yield
coming on sandy textured soils. Commonly, sprinkler irrigation commenced
at 50 percent moisture depletion or less during the peak growing season
(beginning a,t about 80 to 100 days of age) will provide adequate water for
high yields. Research results ("Peanut Irrigation in Georgia" by L. E.
Samples) with use of tensiometers on a loamy sand indicate sprinkler irriga-
tion should commence when the topsoil tensiometer set at the four inch depth
reads 25 centibars (approximately 45 percent depletion of AHC as per Figure
A-2 of Appendix A) or more. Tensiometers at the 12 and 20 inch depth would
typically each read about 45 centibars in relation to the 25 reading at the 4
a -:h depth.
Sprinkler irrigation commencing at the 50 percent AWC level is generally
recommended to ensure minimum plant stress. Research by Jeff Daniell in
Georgia has shown that about 1.5 net inches of water should be applied at each
irrigation on most soils utilized for pecans. (Do not exceed the AWC or the
intake capacity of the soil, however.)
Drip irrigation research in South Carolina and Georgia (Jim Aitken and Jeff
Daniell respectively) indicate that about 2,400 net gallons of water per day
per acre should be supplied to mature pecan trees in 12 hours or less at high
moisture stress periods. This volume is applicable to a tree canopy area of
about 70 to 75 percent or greater. Areas with significantly less tree canopy
(as with a young orchard) should be supplied with proportionally less water.
Research by Daniell indicates that excess water in the Southeast may decrease
yield and pecan quality.
During high moisture stress periods, pan evaporation normally reaches 0.3 to
0.35 inches per day in the Southeast (extreme values as high as 0.5 inches/day
were recorded in the summer drought of 1986). A rule of thumb suggested by
Daniell for scheduling drip irrigation using pan evaporation is to vary the
application amount in proportion to the pan evaporation approximately as
follows:
Average Daily Pan Evaporation
During Previous Week Application Amount
(Inches) (Gallons/Acre/Day)
.33 2,400
.25 1,800
.15 1,100
When approximately 0.5 or more inches of rainfall occur, Daniell recommends
turning off the system for 3 days. The system is not turned off if less than
0.5 inches of rain are received.
A method of scheduling drip irrigation recommended by Jim Aitken is to use
tensiometers placed 9 inches from 1 GPH emitters in sandy soils at depths from
12 to 24 inches. Aitken's results for young trees on Lakeland sand indicate
maximum tree growth with maximum yield and nut quality were obtained by main-
taining soil moisture below 5 centibars at the tensiometer locations as com-
pared to the 14 centibar level.
Operators should provide a check on either of the above methods of scheduling
by visually observing the trees to note signs of stress and by using the feel
and appearance method of determining soil moisture as given in this Guide.
These methods used in combination should provide good water management.
Information given in this section for pecans was obtained primarily from
publications noted in Appendix E and from personal communications with the
authors. Persons giving planning and/or design assistance for pecan irriga-
tion are encouraged to refer to the noted printed materials and utilize appli-
cable information. Also, verbal communication with the authors is encouraged.
3-7
SMALL SRAIMS
Commonly, small grains are most responsive to Irrigations at the preplant and
boot stage. However, moderate to high small grain yields can be obtained in
SORGHUM
Grain sorghum is a drought tolerant plant but one that responds well to irri-
gation. Commonly, the most important irrigation is at preplanting. However,
Irrigation at the boot to early heading stage can significantly improve
yields.
SOYBEANS
Inadequate moisture during germination and early seedling growth can prevent
establishment of a uniform stand. However, after establishment of the stand,
ARS research has shown little benefit from irrigation until blooming.
Soybeans use large amounts of water in the reproductive phase. Particularly
during pod growth and seed fill, lack of water will significantly reduce
yields. Water stress early in the reproductive stage may result in higher
than normal levels of flower abortion, leading to reduced numbers of pods per
plant. Moisture deficiencies during the seed filling stage result in smaller
than normal seeds.
Research in South Carolina has shown that soybean yields may be enhanced an
average of 10 to 15 bushels per acre with irrigation. This assumes good man-
agement with non-irrigated yields in the 30-bushel range. For irrigated
double-crop soybeans planted behind wheat, yields are predictably five bushels
or so below the potential for full season plantings. However, irrigated
double-crop yields have consistently been in the 35 to 50-bushel range,
depending on the soil and other management factors.
For irrigated full-season soybeans, high-yielding varieties from maturity
groups V, VI, and VII are suggested. Varieties with good branching habit and
lodging resistance are preferred. When selecting varieties for double
cropping under irrigation behind wheat, maturity groups VII and VIII are
recommended since they will have more time to develop vegetatively before
bloom. Varieties with yield potential and good branching habit and lodging
resistance are preferred. Take care to select varieties which have good
disease and nematode resistance. Check Extension Circular 545, Soybean
Varieties for South Carolina, for details concerning resistance to disease
along with suitability for double-cropping and irrigation.
Soybeans should have adequate soil moisture for optimum growth and develop-
ment through R7 growth stage, which is physiological maturity. This is
defined as the stage at which there is one normal pod with mature pod color
(e.g. tan) on the main stem. Usually, at least half the leaves have dropped
and the remaining leaves are yellow.
In general, other management considerations for irrigated soybeans are not
different than for non-irrigated soybeans. Examples are tillage, row spacing
plant population, fertilization, pest management, and harvesting.
0. H. Palmer, Extension Agronomist, Clemson University, Clemson, SC
3-8
STRAWBERRIES
The strawberry plant is shallow-rooted with 80-90 percent of its roots in the
top 12 inches of soil. In the matted row cultural system, moisture is
necessary in the surface soil to permit runner plants to set and make maximum
growth. Irrigation is needed at transplanting, during fruit bud formation in
the fall and fruit enlargement. Irrigation begun at 50 percent of available
soil moisture appears to provide adequate moisture for high yields.
Solid set sprinkler irrigation is recommended as a means of providing frost
protection for strawberries in South Carolina. See Chapters 5 and 10 of this
guide for more information on frost control applications.
TOBACCO
Irrigation of tobacco at transplanting will greatly improve survival and early
growth. An analysis of moisture uptake by tobacco has shown the main moisture
uptake zone to be the top 6 inches from transplanting to 3 weeks of age, the
top 12 inches during the next two weeks, and 18 inches for the remainder of
the growing period. Thus, the depth to which the soil is irrigated should be
adjusted for the age of the tobacco. Under limited irrigation, the critical
time other than at transplanting is from the knee-high stage until the top
leaves are filled out. Light irrigation during harvesting may be needed to
avoid premature firing, improve body, and reduce wilting.
Tobacco is especially sensitive to overly wet soils. Thus, the soil moisture
tension should not be reduced below 8 to 10 centibars for any appreciable
period, i.e. 24 hours. Over-irrigation at early growth stages can increase
damage by cool temperatures and limit root development.
VEGETABLES
Vegetables are 80-95 percent water. Consequently, their yield and quality
suffer rapidly from drought. Moisture shortages early in the crop's develop-
ment can delay maturity and reduce yields. Moisture shortages later in the
growing season commonly reduce quality and yields.
Most vegetables have small seeds which are planted 3/4 inch deep or less, with
the rapid drying of the upper layer of soil, these shallow planted seeds can
be left with -enough moisture to begin germination but not enough to complete
germination. Thus, a poor stand results. Sprinkler irrigation of 1/2 to 3/4
inch immediately after planting will settle the soil and provide adequate
moisture for germination. Sprinkler irrigation should be applied slowly to
avoid crusting of the surface. For larger seeds, irrigation prior to seeding
is desired.
A transplanter will not apply adequate water for vegetable transplants in dry
soil. A light sprinkler irrigation of 1/2 to 3/4 inch will provide a ready
supply of water for the transplants and will help set the transplants firmly
in the soil. Fruits such as tomatoes and peppers are injured by large fluc-
tuations in soil moisture. When soil moisture is not maintained at the proper
level, fruit cracking results, yields decrease, and diseases are encouraged.
3-9
Research results (ASAE Paper No. 82-2518 by Camp, Rabbins, & Karlen) indicate
tomato yield and fruit size are enhanced when soil water tension at the
lower edge of the soil-water control zone (12 inch depth) is maintained in the
5 to 40 centibar range for a silt soil in the South Carolina coastal plain.
(The 40 centibar tension corresponds to approximately the 15 percent depletion
level of AWC as per Figure A-2 of Appendix A.) Accordingly, optimun tension
range for tomatoes on sandy or clayey soils should be slightly lower or higher
respectively. It is important to note however that there is no conclusive
data to prove there is one best soil moisture level for tomatoes. It is
expected that most other vegetables would respond similiarly to the above
noted management schedule for tomatoes,
CROP
TABLE 3-2 CRITICAL MOISTURE PERIODS OF MAJOR CROPS
CRITICAL MOISTURE PERIOD
Alfalfa
Blueberries
Corn
Cotton
Fruit trees
Grapes
Sorghum
Pasture
Peanuts
Pecans
Small grain
Soybeans
Strawberries
Tobacco
Vegetables
Beans (Dry, lima,
pole, snap)
Broccoli
Start of flowering and immediately after cutting
When fruit and leaf bud is forming and sizing of
the berry
Tasseling through grain filling
First bloom through boll maturing
Fruit development
Sizing of the fruit
Boot, bloom, and dough stages
After grazing \J
First bloom through nut forming
During nut set {April -May) and nut fill
(August-September)
Boot, bloom and early head stage
First bloom to seed enlargement
Bud set and fruit enlargement
Knee high to full bloom 2/
Flowering
Head development I/
3-10
TABLE 3-2 CRITICAL MOISTURE PERIODS OF MAJOR CROPS (CONT'D.)
ROP
Cabbage
Carrot
Cantalopes
Celery
Col lards
Cucumber
Eggplant
Greens (turnip and
mustard)
Lettuce (head)
Okra
Onion
Peas, Green
Southern
Peppers
Potato, Irish
Potato, Sweet
Pumpkin
Rutabagas
Squash
Tomato
Turnip
Watermelon
_ CRITICAL MOISTURE PERIOD
Head development
Root expansion I/
Flowering and fruit development
Continuous
Continuous
Flowering and fruiting
Flowering and fruiting
Continuous
Head expansion I/
Flowering
Bulbing and bulb expansion I/
Flowering
Flowering and pod swelling
Transplanting, flowering up to
After flowering
First and last 40 days 2/
Fruiting
Root expansion
Fruit sizing
Fruit expansion 2J
Root expansion
Fruit expansion
fruit
/ Moisture is also critical during seed germination.
/ Moisture is also critical in the seedling'and transplanting stages
3-11
S and S are the plant and row spacings, ft
I is the gross depth per irrigation, in
o
F. is the irrigation interval (frequency), days
Application Efficiencies
A concept called potential application efficiency (of the low quarter),
PE, , is useful for estimating how well a system can perform. It is a
, ,
funct
ion of the peak use transpiration ratio, T , the leaching requirement,
LR, and EU* . When the unavoidable water losses are greater than the
leaching water requirements., T >!/(!. - LR ) :
FE
lq
and where T r <1/(1,0 - LR C ):
PE-L = EU 1 Ceq.
The values for T are given in conjunction with eq. B ~8 an ^ LR by eq. B-12
Leaching requirement, LR . In arid regions where salinity is a major
importance, most of the natural precipitation is accounted for in R ,
W , nonbeneficial consumptive use, and/or runoff. There is usually very
little additional natural precipitation, D > that can add to deep
percolation and consequently help satisfy Ene leaching requirements.
Furthermore, since only a portion of the soil area is wetted and needs
leaching under trickle irrigation, the effective additional precipitation
is reduced to (P /100) D ; therefore, it can almost always be neglected.
P is the average horizontal area wetted in the top part (6 to 12 in) of
tKe crop root zone as a percentage of the total crop area.
Calculating the leaching requirement for trickle irrigation, LR is
greatly simplified by neglecting (P /100)D rw and
EC dw
in which
LR is the leaching requirement under
L and L, are the net per irrigation a]
requirements, in
B-47
SOUTH CAROLINA IRRIGATION GUIDE
CHAPTER 4. IRRIGATION WATER REQUIREMENTS
GENERAL
Water requirements for irrigation are based on several factors including the
crop, climatic factors, soil texture and fertility, and the quality of irriga-
tion water. The method of irrigation also affects water requirements by
changing the efficiency and perhaps the consumptive use rate (trickle
irrigation).
Soils and crops are respectively covered in Chapters 2 and 3. Climatic fac-
tors and water quality concerns are included in this chapter.
CONSUMPTIVE WATER USE AND IRRIGATION NEEDS
CLIMATIC ZONES
Several climatic factors influence the quantity of water needed for irriga-
tion. Because of the effects of climate and the variation of climate, crops,
and planting dates within the state, South Carolina was divided into three
climatic zones. These zones are shown on page 4-6.
MODIFICATIONS FOR TRICKLE IRRIGATION SYSTEMS
Trickle irrigation systems are designed and managed to deliver light, frequent
applications of water that wet only a portion of the soil. The irrigation
procedures given in Chapters 2 and 3 of this Guide must be adjusted for
trickle application. To meet the objective of trickle irrigation, water
application is based on moisture replacement in a small area of the soil.
This requires determining the wetted area, wetting pattern, and vertical and
horizontal water movement in the soil. The values of water requirements, con-
sumptive use, and frequency of irrigation are adjusted accordingly. See
Chapter 10-D of this Irrigation Guide and Chapter 7 of the SCS National
Engineering Handbook, Section 15 (copy maintained by SCS Engineers), for
detailed procedures for trickle irrigation.
CONSUMPTIVE USE
Consumptive use is the amount of water required to meet evapotranspiratl
needs so that plant production is not limited due to lack of water.
Evapotranspiration and consumptive use are usually expressed in inches f
day (in. /day) and are used interchangeably in this publication.
The consumptive use of crops in this Guide has been calculated by crite*
given in SCS Technical Release 21, dated April 1967 and revised Septembt
1970. Normal monthly temperature, precipitation, and annual rainfall fc
period 1951-1980 were used as input data to determine water requirement;
various crops. Table 4-2 lists the average monthly, and seasonal
4-1
consumptive use of crops and effective rainfall for the different zones and
irrigation water needs based upon 0.75 inches net depth of applications.
Slight adjustments may be made for net application depths other than 0.75
inch, but for normal use (0.5 inch to 1.5 inches applied) no adjustments are
required .
Input data used in calculating values for the tables in this chapter are in
the appendix. Because South Carolina is located in the humid region, the
seasonal consumptive-use coefficient (K) used for each crop was the lower
value given in Table 2 of SCS Technical Release 21 (Revised September 1970).
EFFECTIVE RAINFALL
Effective rainfall is that portion of the total rainfall which does not eva-
porate, run off, or percolate below the root zone and is available to the
plant to meet its consumptive use requirements.
Since there are no effective rainfall records available, total rainfall
records are used and an estimate made of the percent of the total which is
effective.
NET IRRIGATION APPLICATION
The net irrigation application is dependent upon the capacity of the soil pro-
file in the root zone to store available moisture and the moisture deficit
allowed. The moisture deficit is the percent of the total available moisture
in the soil that evapotranspiration is allowed to remove before it is replaced
by irrigation. Usually this amount is 40-50%.
Research has shown that irrigating when the moisture deficit is only 40% may
significantly increase yields above that of a 50% deficit for some crops.
Net Irrigation Application =
(available soil moisture in the managed root zone) X percent deficit managed.
Example: 2,0 inches X 0.40 = 0.80 inches
GROSS IRRIGATION APPLICATION
The gross irrigation application is the net irrigation application plus the
water "wasted" due to evaporation, deep percolation, non-uniform distribution,
etc,
Net Irrigation Application
Gross Irrigation Application ~ Irrigation Efficiency (usually 70-8050
0.8 inches
Example: 0.70 = 1.14 inches
The irrigation system must pump 1,14 inches of water to get 0.8 inches of
water to the managed root zone.
4-2
IRRIGATION EFFICIENCY
The irrigation (system) efficiency is defined as the product of the
application eff. x pattern eff. where
application eff. = weighted average catch (system) x 100
Gross Application
and
pattern eff. = weighted average (Low 25%) x 100
Weighted Average (System)
PRE-IRRI6ATION REQUIREMENTS
All values given in this chapter assume that the soil is at field capacity at
the beginning of the growing season. For most of South Carolina, this is true
in the early spring but late season crops may need irrigation before or
shortly after planting to bring the soil moisture up to field capacity. This
irrigation is not included in the values in this chapter.
PEAK CONSUMPTIVE USE RATE
The peak consumptive use rate is the highest daily amount of evapotranspira-
tion that a crop has during its growing season. It is measured in inches per
day. The duration of this peak may be days or weeks.
Design peak use rates are values based on the peak consumptive use rates from
TR-21, research information, or various other state guides.
The design peak use rates should be used to determine the required flow capac-
ity of the system. These rates are shown in the table 4-1.
IRRIGATION FREQUENCY
Irrigation frequency refers to the number of days from the beginning of one
irrigation cycle to the beginning of the next cycle, assuming no effective
rainfall between irrigations.
Example: Irrigate when 40& of the available moisture is depleted.
Available moisture in the root zone (18 in.) is 2.0 inches.
Crop; Corn, Peak daily consumptive use 0.33 in.
Net Irrigation Application
Irrigation Frequency = Peak Daily Consumptive Use
0.4x2.0 in.
Irrigation Frequency = 0.33 in. /day = 2.42 days or 2 days and 10 hours
This means that with no effective rainfall the system must be started at the
beginning point every 2 days and 10 hours. When the use rate is less than th
peak period use, the irrigation cycle will be longer.
4-3
IRRIGATION PERIOD
The irrigation period is the time that it takes the system to complete one
irrigation cycle on the designed area. The irrigation period should be less
than the irrigation frequency to allow for regular equipment maintenance anc
the repair of equipment breakdowns.
SEASONAL NET IRRIGATION REQUIREMENT
The seasonal net irrigation requirement is the amount of water needed to
satisfy crop consumptive use requirements in excess of the effective rainfall
during the growing season. This amount is expressed in inches and is given in
the tables in this chapter. These values are computed using the TR-21 com-
puter program based upon an 80% chance of occurrence of effective rainfall.
If actual planting dates differ significantly from those indicated in the
tables, water use and irrigation requirements within each month must be
adjusted accordingly.
SEASONAL GROSS IRRIGATION REQUIREMENT
The seasonal gross irrigation requirement is the amount of water that must ^e
pumped during the growing season to get the net irrigation requirement in the
root zone,
Net Irrigation Requirement
Seasonal Gross Irrigation Requirement - Irrigation Efficiency
The values given in the tables in this chapter are based on 70% irrigation
system efficiency and should provide an adequate water supply 8 out of 10
years on an average. (Measurement of overall system efficiencies of several
centerpivot systems in South Carolina yielded efficiencies ranging from 32 to
76 percent with an average near 70. System efficiency is defined as the pro-
duct of application eff. x pattern eff.)
IRRIGATION STORAGE REQUIREMENTS
In computing the required water storage volume for irrigation, the number of
irrigations desired, the gross irrigation amount per application, recharge,
insoak, and evaporation must be considered. Measurements of recharge should
be during a dry period of the irrigation season if possible.
4-4
EXAMPLE COMPUTATIONS
Example No. 1:
Crop - 100 acres of corn for grain In Newberry County, South Carolina, planted
in period 3/10 to 4/21 to be irrigated by sprinkler irrigation. Assume system
efficiency = 70 percent.
Determine the following:
Climatic Zone - from page 4-6 = Zone 1
Design peak use rate - from page 4-7 = 0.30 inches/day
Seasonal gross irrigation requirement from page 4-8 = 16.2 inches.
Seasonal gross storage requirement needed to be available for irrigation
100 ac. X 16.2 inches = 135 acre feet
12 in. /ft.
Seasonal gross storage volume needed assuming 80# efficiency of the storage
reservoir = 135 = 169 acre ft.
78
Find the pumping rate needed if irrigating 18 hours/day
during the peak use period -
453 AD
Q = H Where Q = flow rate, gallons/min. (GPM)
A = Area irrigated = 100 ac.
D = Peak use rate/ eff .=0.30/0.7*0.43
H - Hours of pumping = 18
453(100) (0.43) ~~
18
1082 GPM
Example No. 2: Same system as example 1. Assume only a two week supply t
water is desired by the landowner to be available during 1
peak use period. Find the gross storage needed assuming
80% efficiency of the storage reservoir.
(1QO acres) X (0.43 inch/day) X (14 days) = 63 ac. ft.
Volume = (0,80) 12 in. /ft, "~
4-5
Figure *t-1
Recommended Design Peaks For South Carolina Crops
Table 4-1, Recommended Design Peaks For South Carolina Crops
Cultivated Row Crops
Inches/Day
Corn (includes silage) 30
Cotton 30
Soybeans 30
Grain Sorghum .28
Peanuts 25
Tobacco .21
Sunflowers 21
Smal 1 Gr ai ns 20
Vegetables
Onions, Lettuce 13
Cabbage, Turnips, Greens 13
Strawberries 15
Cucumbers, Cantaloupes, Squash,
Snap beans, Peppers, Eggplant,
Watermelon, Okra 18
Sweet Corn 28
Sweet Potatoes 23
Tomatoes 26
Orchard Crops!
Apples 24
Peaches, Plums 24
Pecans, Walnuts 24
Hay and Forage Crops
Alfalfa
Pasture Grasses
Winter annuals
Ipor trickle irrigation of these orchard crops, only 2,400 gallons per
acre applied daily within the root zone area are recommended for the design
peak. This is equivalent to approximately 0.13 inches/day/acre at 70 per-
cent coverage by tree canopy, [i.e., 2,400/(0.7 x 27,154) = 0.126 in/day].
4-7
Consumptive Use and Irrigation Water Requirements
Table 4-2. Consumptive Use and Irrigation Water Requirements - Inches
Climatic Zone 1
Crop
Da
Plant
te
Maturity
Month
Consump-
tive Use
Effec-
tive
Rainfall
Irriga
Require
Net
tion
ments
1 Gross
Corn, Grain
4/1
7/20
April
1.91
1.17
May
4.94
1.74
3.19
4.6
June
7,03
1.99
5.04
7.2
p.
July
4.44
"^"K" " __ _
1.36
3.08
4.4
oe
ason Totals
TO?
6.26
11.31
T672
Corn, Silage
4/1
7/20
April
1.81
1.11
May
4.47
1.70
2.73
3.9
June
7.15
2.00
5.15
7.4
July
4.89
1.41
3.47
5.0
Se
ason Totals
18.32
6.22
ITT35
TO"
Corn, Sweet
4/1
6/30
April
2.05
1.22
.08
.1
May
5.46
1.80
3.66
5.2
June
7.03
1.99
5.04
7.2
Se
ason Totals
14.54
5TM
OS
T2TF
Soybeans,
5/10
9/30
May
.97
.60
Early
June
2.82
1.52
.93
1.3
July
5.61
1.96
3.65
5,2
August
7.60
1.99
5.61
8.0
September
4.57
1.74
2.83
4.0
Se
:ason Totals
21-57
778T
13.02
TO
Soybeans,
6/10
10/28
June
1.29
.79
Late
July
3.50
1.75
1.50
2.1
August
5.89
1.81
4.07
5.8
September
6.31
1.91
4.40
6.3
October
2.88
1.08
1.08
2.6
Sc
aason Totals
W^T
73B"
TOT
TO"
Small
2/20
4/21
February
.21
.13
Vegetables
March
2.63
1.61
.35
.5
April
2.60
1.13
1.48
2.1
Si
sason Totals
5.44
2.86
1.83
2.6
Small
3/20
5/19
March
.42
.26
Vegetables
April
3.58
1.60
1.39
2.0
May
2.68
1.03
1.64
2.3
Sc
sason Totals
6.67
2.89
3TM
4.3
Small
4/20
6/19
April
.52
.32
Vegetables
May
4.47
1.70
2.22
3.2
June
2.95
1.10
1.85
2.6
Season Totals
7.94
3.12
4.07
5.8
4-8
Table 4-2. Consumptive Use and Irrigation Water Requirements
Climatic Zone 1
Inches
Crop
Da
Plant
te
Maturity
Month
Consump-
tive Use
Effec^
tive
Rainfall
Irriga
Require
Net
tion
ments
Gross
Small
4/20
7/19
April
.44
.27
Vegetables
May
3.70
1.62
1.50
2.1
June
5.57
1.83
3.74
5.3
July
2.72
1.13
1.59
2.3
Se
ason Totals
12.44
"O6
6.83
9.7
Small
8/1
10/15
August
3.94
1.58
1.61
2.3
Vegetables
September
4.42
1.72
2.70
3.9
October
.97
.54
.43
0.6
Sc
ason Totals
9.32
3.84
4.73
6.8
Tomatoes
5/1
8/20
May
2.27
1.30
.22
.3
June
4.47
1.72
2.74
3.9
July
6,92
2.11
4.81
6.9
August
4.93
1.64
3.29
4.7
Se
ason Totals
TO9
6.77
11.07
iinr
Sorghum
6/1
9/30
June
2.89
1.53
.61
.9
July
6.96
2.12
4.84
6.9
August
6.57
1.88
4.68
6.7
September
3.45
1.63
1.82
2.6
Se
ason Totals
I9T86
77I6~
TO5
T77I
Peanuts
5/1
9/18
May
1.06
.65
June
4.21
1.70
2.17
3.1
July
7.87
2.23
5.64
8.1
August
4.32
1.66
2.66
3.8
September
,54
.33
.21
.3
Se
ason Totals
17.99
6716
TO8
15.3
Wheat
11/1
5/31
November
2.34
1.
December
.62
*
January
C
February
.99
,
March
3.76
2.
April
5.28
1.
May
2.56
1.
Se
ason Totals
T5755
T.
Snap Beans
4/20
6/19
April
.54
May
3.61
1.
June
3.78
1,
Se
ason Totals
7.94
3.
4-9
Table 4-2. Consumptive Use and Irrigation Water Requirements - Inches
Climatic Zone 1
Crop F
Date
lant 1 Maturity
Month
Consump-
tive Use
Effec-
tive
Rainfall
Irriga
Require
Net
tion
nents
Gross
1 .- _- . , __ ^v__ _
Grapes
4/1 9/15
April
1.38
.84
1*"i
May
2.97
1.55
1.20
.7
June
4.20
1.70
2.50
3.6
July
4.73
1.87
2.86
4.1
August
4.16
1.64
2.52
3.6
September
1.35
.82
.52
.7
__- .. ...
|
Season Totals
TO9"
O3
_^
T377
Pasture
3/15
9/15
March
.87
.53
Grasses 1
April
3.10
1.56
1.14
1.6
1
May
4.80
1.73
3.07
4.4
June
6.05
1.88
4.17
6.0
July
6.77
2.10
4.68
6.7
August
6,19
1.84
4.34
6.2
September
2.23
1.31
.92
1.3
Season Totals
30.01
10.95
TO?
26.2
Alfalfa
3/15
9/15
March
.91
.56
April
3.22
1.57
1.26
1.8
May
5.18
1.77
3.41
4.9
June
6.64
1.95
4.69
6.7
July
7.30
2.16
5.14
7.3
August
6.50
1.88
4.62
6.6
Septembe
2.27
1.32
.95
1.4
Season Total
32.01
11,19,
20.07
28.7
Pecans &
4/1
10/10
April
1.35
,83
Walnuts
May
3.25
1.59
1.44
2.1
June
5.37
1.81
3.56
5.1
July
6.45
2.06
4.39
6.3
August
5.31
1.76
3.56
5.1
September
3.13
1.60
1.53
2.2
1
October
.46
.28
.18
.3
Season Totals
25.32
9.92
14.65
2O"
Deciduous
3/20
6/15
March
.32
.20
Orchards
April
2.29
1.32
.35
,5
(w/o cover)
May
4,63
1.71
2.92
4.2
June
3.21
1.60
1.60
2.3
S
eason Totals
10.45 ]_
4.83
4.87
7.0
Deciduous
3/20
7/15
March
.28
.17
o
n
Orchards
April
2.00
1.22
.13
u
?
(w/o cover)
May
4.05
1.66
t j. \j
2.39
C-
3.4
June
5.60
1.84
3.76
5.4
c
July
/\-\ r T-. i ^ l *
3.01
1.70
1.32
1.9
6.58
7 . 60
10.9
Table 4-2. Consumptive Use and Irrigation Water Requirements - Inches
Climatic 'Zone 1
Crop
Da
Plant
te
Maturity
Month
Consump-
tive Use
Effec-
tive
Rainfall
Irriga
Require
Net
tion
ments
Gross
Deciduous
3/20
8/15
March
,21
.16
Orchards
April
1.89
1.16
.09
.1
(w/o cover)
May
3.84
1.64
2.20
3.1
June
5.31
1.81
3.50
5.0
July
5.90
2.00
3.91
5.6
August
2.28
1.31
.97
1.4
Se
ason Totals
19.49 I/
8.07
10.67
T57I
Apples
3/20
9/15
March
.27
.17
April
1.93
1.18
.11
.2
May
3.91
1.64
2.27
3.2
June
5.42
1.82
3.60
5.1
July
6.02
2.01
4.01
5.7
August
4.81
1.71
3.11
4.4
September
1.22
.75
.47
.7
Se
ason Totals
23.59
9.27
13.57
1974
Strawberries
3/20
5/19
March
.42
.26
April
3.58
1.60
1.39
2.0
May
2.68
1.03
1.64
2.3
Se
ason Totals
6.67
2.89
3.04
4.3
Cotton
4/20
9/20
April
.26
.16
May
1.62
.99
June
4.45
1.72
2.70
3.9
July
7.15
2.14
5.01
7.2
August
5.63
1.79
3.84
5.5
September
1.99
1.06
.93
1.3
Season Totals
21.09
7785
TO9
TO"
]_/ Use 0.14 inches per day after maturity through September,
4-11
Table 4-2, Consumptive Use and Irrigation Water Requirements
Climatic Zone 2
- Inches
__
rop F
Date
lant j Maturity
Month
onsurnp-
ive Use
Effec-
tive
Rainfall
Irriga
Require
Net
tion
nents
Gross
orn, Grain
3/20 7/8
March
.44
.27
April
2.63
1,26
.79
1.1
May
5.99
1.77
4.22
6.0
June
6.98
2.24
4.73
6.8
July
1.77
.63
1.14
1.6
S a
son Totals
T77M
67T8
10.88
T53
Corn, Silage ' 3/20 | 7/8
March
.42
.26
April
2.40
1.24
.58
.8
May
5.64
1.74
3,90
5.6
June
7.39
2.30
5.09
7.3
July
1.96
.66
1.30
1.9
Se
ason Totals
17.80
6.19
10.87
15.5
Corn, Sweet
3/20 6/18
March
.45
,27
April
2.99
1.30
1.11
1.6
May
6.23
1.80
4.43
6.3
j
June
4.34
1.37
2.98
4.3
1 Season Total
TOT
O?
8.52
12.2
Soybeans
5/1 9/20
May
June
1.59
3.35
.97
1.83
1.39
2.0
Only
6.63
2,42
4.21
6.0
August
7.46
2.34
5.12
7.3
Seotembe
2.91
1.11
1.80
2.6
] Season Totals
21.93
OF
12.53
17.9
Soybeans
6/10 10/28
June
July
1.31
3.53
.80
1.96
1.33
1.9
August
5.92
2.14
3.78
5.4
September
6.46
1.87
4.59
6.6
2f\
1
October
3.02
.96
2.06
.9
Season Totals
20.24
7773
TOT
Ten
Small
2/20
4/21
February
.22
.14
r- 1
7
Vegetables
March
Anrll
2.79
2.66
1.62
.96
.51
1.70
./
2.4
T '
Season Totals
5.67
2.71
2.21
3.2
Small
3/20
5/19
March
.45
.27
2F
Vegetables
April
Mav
3.71
2,74
1.36
1.00
1.78
1.74
.5
2.5
S
9 1 WJf
eason Totals
6750
2.63
3.52
5.0
4-12
Table 4-2. Consumptive Use and Irrigation Water Requirements - Inches
Climatic Zone 2
Crop
Da
Plant
tp
Maturity
Month
Consump-
tive Use
Effec-
tive
Rainfall
Irriga
Require
Net
tion
ments
Gross
Small
4/20
6/19
April
.55
.33
Vegetables
May
4.61
1.64
2.44
3.5
June
2.97
1.25
1.72
2.4
Se
ason Totals
8.14
3.22
4.17
6.0
Small
4/20
7/19
April
.47
.28
Vegetables
May
3.84
1.57
1.71
2.4
June
5.65
2.08
3.57
5.1
July
2.75
1.31
1.43
2.0
Se
ason Totals
12,71
5.25
6.71
9.6
Small
8/1
10/15
August
3.97
1.87
1.34
1.9
Vegetables
September
4.53
1.68
2.85
4.1
October
1.01
.48
.54
.8
Se
ason Totals
"or
4.03
4773
6.8
Tomatoes
4/20
8/18
April
.55
.33
May
2.69
1.41
.75
1.1
June
5.59
2.08
3.51
5.0
July
6.80
2.44
4.36
6.2
August
2.94
1.19
1.76
2.5
Se
ason Totals
TOT
7.44
10.38
14.8
Peanuts
4/20
9/7
April
.10
.06
May
1.95
1.19
.05
.1
June
5.46
2.06
3,40
4.9
July
7.88
2.59
5.29
7.6
August
2.69
1.62
1.07
1.5
September
.14
.09
.06
.1
Se
ason Totals
18723"
7761
9.86
14.1
Grapes
3/15
8/31
March
--
->
n
4-2. Consumptive Use and Irrigation Water Requirements - Inches
Climatic Zone 2
1
p
Date
lant M
aturity
(
Month i
I
Consump-
tive Use
-ffec-
;i ve
Rainfall
Irrigat
Requireir
Net
ion
ents
Gross
S
4/10
6/9
April
1.32
.78
May
4.54
1.63
2.69
3.8
,
June
1.91
.65
1.26
1.8
Sea
son Totals
7.76
3.07
3.94
5.6
5/15
9/15
May
1.01
.61
June
4.82
1.99
2.47
3.5
July
7.71
2.57
5.14
7.3
August
5.58
2.10
3.48
5.0
S <
September
ison Totals
1.58
.78
.81
1.2
I7JO
20.70
8.05
11.90
3/15
9/15
March
April
.96
3.28
.58
1.33
1.58
2.3
May
4.99
1.68
3.31
4.7
June
6.13
2,14
4.00
5.7
July
6.83
2.44
4.39
6.3
August
6.22
2.18
4.04
5.8
In
September
2.27
1.30
. 97
.4
rT/-' " 1
Season Totals
11,65
18 ' 29
26.1
1
3/1
8/31
March
April
1.91
3.47
1.16
1.34
2.13
3.0
t
May
5,49
1.73
3.77
5.4
June
6.87
2.23
4,64
6.6
7*
July
7.51
2.54
4.97
.1
S<
August
sason Totals
6.66
"3T790
2.23
TT723
4.43
TO2"
6.3
28.5
3/20
9/30
March
April
May
.19
1.50
3.44
.12
.90
1.54
1.83
2.6
June
5.54
2.07
3.47
5.0
I
S
July
August
Septembe
eason Total
6.62
5.43
3.25
25797
2.42
2.08
1.56
TO8
4,20
3.35
1.69
14.54
6.0
4.8
2.4
20.8
3/1C
3 6/5
March
April
Mav
.76
2.73
5.44
.46
1.27
1.72
1.00
3.72
1.4
5.3
' 'Wj
June
1.22
0.74
0.48.
0.7
<
Season Total
H5TT51/
4.20
"B"^
7.4
3/1
7/5
March
April
May
.63
2.28
4.64
.38
1.22
1.63
.55
2.90
.8
4.1
i t ** j
June
6.13
2.14
3.99
5.7
July
1.09
0.67
0.43
0.6
U U J J
Season Total*
3 14.67V 6.04 7.88 11.2
4-14
Table 4-2. Consumptive Use and Irrigation Water Requirements
Climatic-Zone 2
Inches
Crop
Da
Plant
te
Maturity
Month
Consump-
tive Use
Effec-
tive
Rainfall
Irriga
Require
Net
tion
ments
Grc
Deciduous
Orchards
(w/o cover)
Strawberries
Cotton
Watermelons
3/10
3/10
4/20
3/25
8/5
Se
5/10
$
9/20
Se
7/12
Se
March
April
May
June
July
August
ason Totals
March
April
May
ason Totals
April
May
June
July
August
September
ason Totals
March
Apri 1
May
June
July
ason Totals
.58
2.08
4.14
5.60
6.19
0.79
.35
1.20
1.60
2.08
2.36
0.48
.36
2.55
3.52
3.83
0.31
i,
t
r
C
n
i
i
i
19.39V
1.21
4.10
1.13
8.06
.74
1.39
.46
10". 57
2.43
.68
rrr
.02
2.58
4.75
3.58
1.02
TO5"
.38
2.91
3.25
1.21
6.44
.27
1.70
4.54
7.26
5.69
2.04
2.58
.17
1.03
1.96
2.50
2.11
1.03
21.50
.23
2.26
4.54
5.30
2.90
8.80
.14
1.22
1.63
2.04
.87
i
T
14.41
5.91
7.75
V Use 0.14 inches per day after maturity through September,
4-15
e 4-2. Consumptive Use and Irrigation Water Requirements - Inches
Climatic Zone 3
Da
Plant
^e
Maturity
Month
Consump-
tive Use
TFTec-
tive
Rainfall
Irriga
Require
Net ,
tion
ments
Gross
ain
3/10
6/29
March
,94
.58
April
3.28
1.16
1.74
2.5
May
6.36
1.89
4.47
6.4
June
6.56
2.28
4.28
6.1
July
56
ason Totals
T77T5
1T3T
J * J J-
TO. 49
15.0
lage
3/10
6/29
March
.90
.55
April
2.93
1.14
1.39
2.0
May
6.22
1.87
4.34
6,2
June
7.10
2.36
4.75
6.8
Se
ason Totals
T77IB"
"OT
10748"
T570
Jeet
3/10
6/8
March
1.00
.61
April
3.79
1.19
2.24
3.2
May
6.47
1.90
4.57
6.5
June
1.97
.65
1.32
1,9
Se
ason Totals
T3723
4735"
F7TJ
IT76
5/15
9/15
April
1.00
.61
May
4.79
2.11
2.32
3.3
June
7.64
2.83
4.81
6.9
July
5.68
2.40
3.17
4.5
August
1.61
.88
,73
1.0
Se
ason Totals
20.62
1^3
11.03
15.8
s
5/1
9/20
May
1.58
.96
June
3.32
1.89
1.29
1.8
July
6.57
2.66
3.90
5.6
August
7.44
2.66
4.77
6.8
September
2.95
1.26
1.69
2.4
Se
ason Totals
21785
9.44
11.66
TeTT
s,
6/10
10/28
June
1.29
.79
July
3.47
2.06
1.17
1.7
August
5.86
2,44
3.42
4.9
September
6,51
2.12
4.39
6.3
October
3.12
1.05
2.06
2.9
Se
ason Totals
20,25
8.46
11.05
15.8
9/1
11/15
September
3.52
1.75
1.03
1.5
les
October
3.58
1.17
2.40
3.4
November
.77
.38
,39
.6
Season Totals
7.88 1 3.30
3.82
5.5
4-16
Table 4-2. Consumptive Use and Irrigation Water Requirements - Inches
Climatic -Zone 3
Crop
Da
Plant
te
Maturity
Month
Consump-
tive Use
Effec-
tive
Rainfall
Irriga
Require
Net
tion
ments
Gross
Small
2/15
4/16
February
.47
.28
Vegetables
March
3.10
1.66
.87
1.2
April
1.94
.63
1.31
l.S
Se
ason Totals
or
73ff
"OF
n
Small
2/15
5/16
February
.36
.22
Vegetables
March
2.48
1.43
.44
.(
April
4.22
1.22
3.00
4.;
May
2.15
.86
1.29
i.i
Se
ason Totals
9.22
3.73
4.74
6.f
Small
2/15
6/15
February
.31
.19
Vegetables
March
1,98
1.21
.14
, ]
April
3.90
1.20
2.70
3.'
May
5.22
1.77
3.44
4.'
June
2.06
1.02
1.05
I. 1
Se
ason Totals
T3T46
5.38
7733
10.
Small
3/1
4/30
March
2.18
1.29
.14
Vegetables
April
3.88
1.20
2.68
3.'
Se
ason Totals
6.05
2.48
2.82
4.
Small
3/1
5/30
March
1.65
1.01
Vegetables
April
3.99
1.20
2.67
3.
May
4.43
1.65
2.78
4.
Se
ason Totals
TO6
3TM
5.45
77
Small
3/1
6/29
March
1.33
.81
C
Vegetables
April
3.42
1.17
2.02
2.
May
5.29
1.78
3.51
5.
June
4.48
2.03
2.45
o
Se
ason Totals
TO2
5.79
7799
Small
8/1
10/15
August
Vegetables
September
October
Se
ason Totals
Tomatoes
3/1
6/29
March
April
May
June
Se
ason Totals
4-:
Table 4-2. Consumptive Use and Irrigation Water Requirements - Inches
Climatic Zone 3
Crop
Dat
Plan!
e
Maturity
Month
Consump-
tive Use
Effec-
tive
Rainfall
Irriga
Require
Net
tion
nents
Gross
Tomatoes
4/20
8/18
April
.55
.31
May
2.69
1.45
.73
1.0
June
5.55
2.20
3.35
4.8
July
6.75
2.69
4.06
5.8
August
2.94
1.36
1.59
2.3
Se
ason Totals
18.48
~or
9.72
TO
Peanuts
4/20
9/7
Apri 1
.10
.06
May
1.95
1.19
.05
.1
June
5.43
2.19
3,24
4.6
July
7.83
2.86
4.97
7.1
August
2.69
1.64
1,05
1.5
September
.15
.09
.06
.1
Se
ason Totals
18.15
8.03
9.37
13.4
Grapes
3/15
8/31
March
.35
.22
April
1.57
.88
.08
.1
May
3.21
1.58
1.63
2.3
June
4.41
2.07
2.34
3.3
July
4.94
2,43
2.51
3.6
August
4.35
2,24
2.11
3,0
Se
ason Totals
T8J33
9.42
8.67
12.4
Winter Wheat
11/1
5/31
November
1.98
.86
.36
.5
December
3.03
1.25
1.77
2.5
January
2.50
1.28
1.22
1.7
February
2.80
1.37
1.43
2.0
March
4.58
1.81
2.77
4.0
April
4.78
1.26
3.52
5.0
May
1.93
1.18
.75
1.1
St
sason Totals
21.59
9.02
11.83
16.9
Snap Beans
4/1
5/31
April
2.21
1.06
.40
.6
May
5.19
1.77
3.42
4.9
s<
sason Totals
7.40
2.83
3.82
5.5
Pasture
3/15
9/15
March
.98
.60
Grasses
April
3.27
1.16
1.74
2.5
May
4,97
1.75
3.23
4.6
June
6.09
2.27
3.82
5.5
July
6.77
2,69
4.08
5.8
August
6,20
2.49
3.71
5.3
September
2.31
1.38
.93
1.3
Season Totals
30.60 | 12.34
17.51
25.0
4-18
Table 4-2. Consumptive Use and Irrigation Water Requirements - Inches
Climatic Zone 3
Crop
Da
Plant
te
Maturity
Month
Consump-
tive Use
Effec-
tive
Rainfall
Irriga
Require
Net
tion
ments
Gross
Cotton
Pecans and
Walnuts
Deciduous
Orchards
(w/o cover)
Strawberries
Watermelons
4/20
3/10
3/1
3/1
3/1
3/25
9/20
Se
9/30
Se
5/30
Se
6/30
Se
4/30
Se
7/12
Se
March
April
May
June
July
August
ason Totals
March
April
May
June
July
August
September
ason Totals
March
April
May
ason Totals
March
April
May
June
ason Totals
March
April
ason Totals
March
April
May
June
July
ason Totals
.27
1.69
4.50
7.19
5.68
2.08
.17
1.03
2.08
2.76
2.42
1.17
.02
2.42
4.44
3.27
.91
.08
1.92
3.43
4.05
3.17
1.62
,03
3.5
6.3
4.7
1.3
TBT8
.1
2.7
4.9
5.8
4.5
2.3
21.43
.38
1.54
3.53
5.65
6.74
5.57
3.39
9.62
.23
.86
1.61
2.22
2.69
2.40
1.78
26.80
1.23
3.02
5.82
11.79
.75
1.14
1.83
14.26
1.60
3.99
20.4
2.3
5.7
10.06
.98
2.42
4.81
6.46
3.72
.60
1.10
1.73
2.32
5.59
.94
3.08
4.15
8.17
.14
2.68
8.0
1.3
4.4
5.9
14.67
2.18
3.88
5.75
1.29
1.20
11.7
.2
3.8
6.05
.24
2.25
4.53
5.26
2.07
2.48
.14
1.09
1.70
2.17
.96
2.82
14.35
]_/ Use 0.14 inches per day after maturity through September.
4-19
Pae
Open Ditch System - 5-25
Description --- 5-25
Determining Water Table Levels - 5-26
Underground Conduit - 5-28
Description - 5-28
Advantages and Disadvantages 5-28
Other Uses of Irrigation 5-28
Chemigation _-_-_--, 5.28
Application of Fertilizers 5-29
Application of Herbicides- ,- 5,33
Application of Insecticides & Fungicides 5-35
Waste Disposal--- 5_35
Frost Protection-- - , . 5.35
figures
Figure 5-1 Typical Types of Sprinkler Irrigation Systems- 5-2
Figure 5-2 Typical Emitters for a Trickle
Irrigation System ...... - ....... - ......... _-- 5^2
figure 5-3 Typical Subirrigation Systems ----- ............ 5,3
Figure 5-4 Layout for a Traveling Sprinkler System ....... 5-8
Figure 5-5 Typical Trickle Irrigation System ............. 5-ig
Figure 5-6 Typical Performance Curve for Trickle Emitter- 5-17
Mgure 5-7 Comparison of Idealized Wetting Patterns in
a Homogenous Fine Sandy Soil under a Drip
and a Spray Emitter ...................... c 17
Figure 5-8 Typical Subirrigation Layouts ......... - ....... 5
Tables
Table 5-1 Factors Affecting the Selection of a Water -
Application Method- ....... _ ........ r r
rable 5-2 Factors Affecting the Selection of Sprinkler""
Irrigation Systems ................ _ , ,.
Table 5-3 Estimated Wetted Areas for Different Soil ......
Textures, Rooting or Soil Depths, and
Dryness of Soil Stratification from a 1
gph Drip Emitter Under Normal Field
Operation .................
Table 5-4 Factors Affecting the Selection'oTl^'le .....
T.M. c K - Irn 9ati on Systems ............... _ , 99
table 5-5 Common Sources of Fertilizers
For Use With Irrigated Systems ............... 5 _ 31
SOUTH CAROLINA IRRIGATION GUIDE
CHAPTER 5. IRRIGATION METHOD SELECTION
GENERAL
Selecting the irrigation system for a site is not always straighforward but
is dependent upon many factors. Often times the case is that some sites
are adaptable to several methods of irrigation with the final selection
being based on factors such as initial cost, operating costs, adaptability
to farming operation, adaptability for other uses and personal preference.
Methods of irrigation used in South Carolina have advantages and disadvan-
tages that are discussed in this chapter. This chapter will also discuss
the various factors to consider in debermining method suitability and pro-
vide general guidance in irrigation method selection.
METHODS OF APPLYING WATER
There are four basic methods of applying water: (1) sprinkler, (2)
trickle, (3) subirrigation, and (4) surface.
SPRINKLER IRRIGATION
Sprinkler irrigation is a system in which the irrigation water is distri-
buted to the field through pipelines and applied to the soil by spraying
with sprinkler nozzles or perforations operated under pressure. Types of
sprinkler systems include: permanent solid-set, hand move, tractor move,
wheel or skid mounted, side move or side wheel-roll power move, hand or
power moved single sprinkler (volume gun), power moved boom sprinkler and
self propelled lateral move or center-pivot. The majority of sprinkler
systems used in South Carolina are power moved volume gun (traveling gun)
and center pivot. See Figure 5-1 showing the types of sprinkler irrigation
systems.
TRICKLE IRRIGATION
Trickle irrigation is a system for efficient, slow application of water for
irrigation directly to the crop root zone area. The water is applied on or
below the soil surface through emitters or applicators placed along small
diameter laterals operated under pressure. Common types of emitters
include orifices, micro tubes, sprayers, porous or perforated tubing and
bubblers. See Figure 5-2 showing typical emitters,
SUBIRRIGATIQN
Subirrigation is a system where the water is supplied to the root zone of
the crop by controlling the water table (natural or artificial). The basic
types of subirrigation are open ditch and under-ground conduit.
5-1
HAND OR TRACTOR-MOVED
TRIPOD MOUNTED
%*
WHEEL MOUNTED
SELF-PROPELLED
HAND-MOVED
SELF-PROPELLED
SELF-POWERED
AND PROPELLED
T SEMI PORTABLE
TRACTOR-MOVED
S NGLE-SPRINKLER
TRACTOR-MOVED
SELF-PROPELLED
OR WINCH
WHEEL MOUNTED
SELF-MOVED
SIDE WHEEL ROLL
MULTI-SPRINKLER
BOOM-SPR NKLER
TYPICAL SPRINKLER IRRIGATION SYSTEMS
FIGURE 5-1
POINT-SOURCE
EMITTER
MULTI-OUTLET
EMITTER
LINE-SOURCE
EMITTER
TYPICAL TRICKLE EMITTERS
FIGURE 5-2
,,OPEN
I -LATERAL
DITCHES
CHECK
DAM
JJN.5.ANP/QR. DITCH.
IRRIGATED
WATER TABLE
SOIL
SATURATED
NORMAL WATER TABLE
UNDERGROUND
PIPE
IRRIGATED
WATER TABLE
SOIL
SATURATED
LATERAL
PIPELINES
.(UNDERGROUND)
UNDERGROUND
HEADPIPE
NORMAL WATER TABLE
TYPICAL SUBIRRIGATION SYSTEMS
FIGURE 5-3
5-3
The water table is usually controlled by the use of check dams. See Figure
5-3 showing typical subirrigation systems.
SURFACE IRRIGATION
Surface irrigation is a system where the irrigation water is distributed
and applied by gravity flood flow over the area to be irrigated. Surface
flood methods include furrow, level and graded border, contour levee and
contour ditch. There are few if any true surface irrigation systems in
South Carolina.
FACTORS AFFECTING THE IRRIGATION METHOD SELECTION
TOPOGRAPHY
If the topography of the land is level or can be made level without too
much expense, then it will have little affect on the irrigation method. If
the land is sloping, it may be limited to only the sprinkler or trickle
irrigation system. With the sprinkler method, water can be applied slowly
enough to prevent runoff and possible erosion. With the trickle irrigation
systems, the emitter discharge rates can be matched to soil intake rates
and uniform pressure distribution can be obtained through pressure regula-
tion and lateral arrangement. Surface irrigation methods are applicable to
level or nearly level land; however, very little, if any, surface irriga-
tion is used in South Carolina.
WATER INTAKE RATE
The water intake rate of the soil affects the method of irrigation
selected. The sprinkler and trickle irrigation systems can be used on low
intake rates (0.5 inches per hour or less), or high intake rates (3.0
inches per hour or greater). The actual soil intake rate will dictate the
type of sprinkler system used since some sprinkler systems have application
rates higher than the soil intake rate. The intake rate for trickle irri-
gation systems will dictate the maximum application rate and number of
emitters for a particular system. For subirrigation systems, the soil
WIND ACTION
Wind action can affect the water application efficiency of the sprinkler
method. Strong winds will increase the direct evaporation losses to the
atmosphere. These losses are greater as temperature and wind velocities
increase and as humidity, drop size, and application rates decrease.
Table 5-1 summarizes the factors affecting the irrigation method selection
Table 5-1. Factors Affecting the Selection -of a Water-Application Method
Water Application
Method
Sprinkler
Trickle
Subirrigation
Surface
Irrigation
Factors Affecting Selection
Topography
Water Intake Rate
of the Soil
Wind Action
Adaptable to both
level and sloping
ground surfaces.
Adaptable to al 1
land slopes.
Land should be
level or contoured
Adaptable to nearly
level land where land
leveling can be pro-
vided at a reasonable
price and soil depth
is sufficeint to not
expose unproductive
soil .
Some sprinkler
systems limited
by intake rate.
However, any
intake rate can
be sprinkler
irrigated.
Adaptable to al 1
intake rates.
Adaptable to
intake rates of
0.5"/hour or
greater. Adaptable
only to those soils
which have an im-
pervious layer below
the root zone or a
high controllable
water table.
Permeabili ty should
be 2 in/hr or greater
for best results.
Soils with high
intake rates are
not suitable for
surface irrigation.
Wind may
affect
application
efficiency.
No effect
No effect
Very little
effect.
Once the method of water application has been selected (sprinkler,
trickle, or subirrigation), it is desirable to select the specific type of
system that is best suited to the farming operation, soil and crop
requirements, and desires of the farmer.
5-5
SPRINKLER IRRIGATION
PERMANENT/SQLID-5ET
Description
A solid-set system is an aluminum pipe system that is placed in the
field or fields to be irrigated prior to the start of the growing
season and left in place throughout the growing season. A permanent
solid-set system is defined as a pipe system placed underground with
only a portion of the risers and sprinklers above ground. Almost all
the permanent systems being installed today use pressure rated polyvi-
nyl chloride (PVC) plastic pipe.
Permanent and solid-set systems are normally designed for spacings of
40 ft x 40 ft, 40 ft x 60 ft, and 60 ft x 60 ft. When these systems
are used in orchards, the spacings may be somewhat different to con-
form to tree spacing. The actual spacings are based on a percent of
the sprinkler wetted diameter that is compatible with the farming
operation.
The sprinklers are either single or dual nozzle design with operating
pressures usually in the range of 30 to 60 pounds per square inch and
a wetted diameter up to about 125 feet.
Risers are located out of the way of equipment and constructed to a
height compatible with the height of the crop to be irrigated. The
risers, when permanent, are supported in concrete anchor blocks.
The field application efficiency used in design ranges from 70 percent
for daytime operation to 80 percent for nightime operation.
Advantages and Disadvantages
The advantages of solid-set and permanent systems are that they can be
adapted to irregularly shaped fields, low labor requirement, adaptable
for frost and freeze protection, and chemigation. The disadvantages
are high initial cost and moderate energy use.
TRAVELING GUN
ion
guns are of two general types and are referred to as cable-
lers and hose-pull travelers. The cable-tow traveler can be
I as a gun sprinkler mounted on a wheeled chassis to which a
connected and the machine winds up a steel cable anchored at
?nd of the field. Power to propel the cable winch is supplied
ciliary engine, water motor, water piston, or water turbine.
cases, the auxiliary engine may drive the unit directly or
hydraulic pump which drives a hydraulic motor to propel the
5-6
The hose for the cable-tow is a woven synthetic fabric tube covered
inside and out by either rubber or polyvinyl chloride. Hoses are
available in sizes from 2-inch to 5-inch and in lengths from 330 feet
to 1320 feet.
The hose-pull traveler is a system composed of a large hose reel
mounted on a four wheel cart to which is attached a polyethylene hose
that pulls a single gun sprinkler through the field and also supplies
water to the sprinkler. The trailer mounted hose reel is stationary
at the end of the field while irrigation is being applied. The hose
reel is driven by a turbine, bellows, water piston, or auxiliary
engine and as the reel turns the hose is wound around the reel.
Hoses for the hose-pull are available in sizes from 2-inch to 4s-inch
inside diameter. Hose length will vary from 620 feet to 1250 feet.
The hose is made of polyethylene with a wall thickness of 3/16 to
9/16-inch depending upon the diameter.
The sprinkler is a high capacity nozzle ranging from 50 to 1000 gpm.
Normally, the sprinkler pressure will be 70 to 100 psi . To satisfac-
torily operate, a large capacity cable-tow traveler will require a
minimum pump discharge pressure of 125 psi on reasonably flat terrian
to as much as 180 psi on steep terrain. In comparison a similar hose-
pull system will require a minimum pump discharge pressure of 145 psi
on reasonably flat terrain to as much as 200 psi on steep terrain.
The field application efficiency used in design is 70 percent. Under
certain conditions higher efficiencies can be obtained.
Operation of Cable-Tow and Hose-Pull Systems
Cable-Tow Systems
To obtain maximum performance from the traveler, the system should be
laid out to irrigate in the most economical manner. With a 660-foot
hose a field up to 1400 feet long can be irrigated with the supply
line across the middle of the field. The machine is moved into posi-
tion in the first alley 60 to 120 feet from the edge of the field
depending upon the size sprinkler. This will adequately water the
outside edge and some water will be thrown out of the field. The
cable will be uncoiled with a tractor and attached to an anchor which
may be an earth anchor, tractor, truck or tree. The operator should
be sure the anchor will withstand the pull exerted by the machine.
The pull will depend upon the size of the machine. For a 4i-inch, 660
foot hose this could be more than 6000 pounds. The hose is unrolled
and connected to a hydrant. There should be about 30 feet of hose
behind the machine.
The machine will be positioned some 60 to 120 feet from the end of the
field. The pump should be started and the sprinkler operated for
about 30-45 minutes before the machine is placed in gear. Speed should
be set to give the correct application of water. The anchor on the far
end should be some 60 to 120 feet from the end of the field. When the
5-7
machine reaches the end it will stop traveling, but the sprinkler will
continue to operate until the pump is shut down. A run time of 30 to
45 minutes on the end should adequately water the end. Figure 5-4
shows a typical layout for the cable-tow traveler.
ANCHOR
CABLE
SELF-PROPELLED
SPRINKLER OR
ROTARY BOOM
FLEXIBLE
LATERAL
IRRIGATED
Figure 5-4. Layout for a traveling sprinkling system.
The normal spacing between alleys is approximately 70 percent of the
sprinkler wetted diameter. Spacing will need to be reduced as wind
speed increases.
When irrigation from an alley is completed, disconnect the hose from
the hydrant, purge the hose of water, reel the hose onto the reel, and
move the traveler to the next alley. Repeat the process of laying the
cable and anchoring it and laying out the hose and connecting to the
supply line. Once the pump is shut down, it will require from 45 to
60 minutes of time to move and set up the equipment for the next irri-
gation. A tractor will be needed to move the machine.
There are several items that should be considered in the maintenance
of cable-tow systems. All of the pull of the traveler is against the
cable. Check, occasionally for frayed or worn cable and replace or
repair before a break occurs. Check the hose for small cuts or nicks
and repair before major damage occurs. The hoses can be repaired
either with a metal hose mender or with a repair kit by a commercial
company. When storing the hosej roll several coils of the hose
loosely on the reel. This prevents stretching the end of the hose.
Store hose away from grease, rodents , and sunlight. Do not try to
reel the hose with water in it. Keep obstacles away from the hose. A
hose that is handled carefully should last 10 years or more. Check
the mechanical components of the machine. This includes the drive
mechanism, sprinkler and hose reel, When the machine is operating,
check the travel speed to ensure that it is operating at the desired
speed and that it maintains the speed. Check the speed near the
5-8
beginning, middle and near the end of the run. Use the travel tables
furnished by the manufacturer to set the speed to give the desired
application, but check to see if the machine is performing as spe-
cified.
The cable-tow traveler is a versatile machine that can be used to
apply animal wastes. The water drive units will be less satisfactory
than some of the engine drive units. On the water drive units (water
piston, water turbine and water motor) solids may tend to clog the
drive mechanism. Check with a dealer on recommendations on using the
machine for land application of wastewater. Generally, swine
wastewater from a lagoon can be satisfactorily handled with any
machine; swine pit wastewater, poultry, beef and dairy waste will
have enough large and fibrous solids to possibly cause problems on
some machines.
Hose-Pull Systems
The hose-pull traveler is fairly easy to operate. On low growing
crops that a tractor can straddle, an alley is not needed. A tractor
or other prime mover is used to unwind the hose and move the sprinkler
cart and hose from the hose reel to the far end of the field.
Depending upon the size of the sprinkler, the first alley will be 90
to 125 feet from the edge of the field. Some water will be wasted
outside the field, but it is necessary to do this to adequately irri-
gate the edge of the field. It should be allowed to operate for 30 to
45 minutes before the hose reel is placed in gear. The sprinkler cart
is then pulled through the field at speed to give the correct applica-
tion of water. The sprinkler may be stopped 90 to 120 feet from the
near end of the field and allowed to operate for 30 to 45 minutes to
irrigate that end. The sprinkler may be operated in a full or part
circle mode. Some growers will leave a pie-shaped section in front of
the sprinkler unirrigated so that the sprinkler cart is operating on
dry ground.
The hose and sprinkler cart travels best in a straight line, but due
to the thick wall and heavy weight of the hose when it is full of
water, it will follow some contour. Ridges will also aid in allowing
the hose to follow a contour. Experience with operation of the
machine will dictate the amount of contour that can be handled.
Spacing of alleys or travel lanes through the field will depend upon
the particular sprinkler being used, i.e., diameter of coverage.
Normal distance between travel lanes is 70 percent of the sprinkler
wetted diameter. Wi th prevailing winds, this may need to be adjusted.
With different machines available, lane spacing will probably be from
220 to 330 feet.
Moving the hose-pull traveler is relatively easy. Once the sprinkler
cart has reached the end of a row, the pump is shut down, the supply
line is disconnected, and the hose reel is moved to the next lane with
a tractor. Then the supply line is reconnected, and the sprinkler
cart is moved to the far end of the next lane. The pump is then
restarted. One man should be able to make the move in 30 to 45 minu-
tes. All of the hose-pull travelers use stabilizers on the hose reel.
5-9
These are dropped to the ground when the machine is operating so that
the hose reel will not tip over. On some of the machines, the hose reel
is mounted on a turntable. With these models, an area on both sides of
a center alley or road can be irrigated without moving the reel. With
other machines, it will be necessary to turn the machine 180 to irri-
gate on both sides of a center alley.
Comparison of Cable-Tow and Hose-Pull Systems
In comparing the cable-tow traveler to the hose-pull traveler, one comes
to the following conclusions:
1. The hose-pull traveler can be moved in a shorter length of time
because there is no hose to reel in and no cable to unwind.
2. The hose-pull traveler will require more pressure to operate at com-
parable gallonage because the friction loss through the hose and
drive mechanism is usually greater.
3. The initial cost of the hose-pull traveler //ill usually be greater
than the cable-tow traveler.
4. Speed control, that is, uniform speed throughout the run may be more
difficult to obtain with the hose-pull traveler. However, this will
depend on the drive mechanism and the adjustment by the individual
operator. Several companies now offer a speed compensation device
as standard equipment or as an optional feature.
5. The hose-pull machines with auxiliary engine drive are being used
for land application of wastewater. On these machines, only the
sprinkler cart is subjected to the wastewater, whereas on the cable-
tow traveler the entire machine is subjected to the waste water.
6. On the hose-pull traveler, only the amount of hose that is needed
must be wound off the reel, whereas on the cable-tow traveler all
the hose must be wound off the reel and the hose stretched out to
allow water to flow through the hose.
7. The hose-pull traveler does not require a separate anchor; the
cable-tow traveler requires an anchor, such as a tree, tractor, or
h anchor to which the cable is attached.
on the hose-pull machine is pulled in a relatively straight
m the cable-tow machine, the hose is pulled in a loop. In
th obstructions, this could result in more hose damage on
e-tow machine,
1 lane is not required for the hose to travel for the hose-
chine. Except in low growing crops, a travel lane is
d for the cable-tow machine.
5-10
10. With the hose-pull machine, it is not necessary to walk to the
middle of the field to connect or disconnect the hose to the
supply line as is necessary with the cable-tow machine.
Advantages and Disadvantages of Travelers
The advantages of travelers are: (1) adaptable to many field sizes and
shapes, (2) adaptable to topography from level to rolling, and (3) can
be moved easily to irrigate several fields. The disadvantages of trave-
lers are (1) they require alleyways for row crops, (2) water distribu-
tion is seriously affected by wind, (3) high application rates, and (4)
high energy requirements for operation.
CENTER PIVOT
Description
A center pivot system consists of a single sprinkler lateral with one
end anchored to a fixed pivot structure and the other end continuously
moving around the pivot while applying water. The water is supplied
from the source to the lateral through the pivot. The lateral pipe with
sprinklers is supported on drive units and suspended by cables or by
trusses between the drive units. The drive units are mounted on wheels,
tracks or skids that are located 80 to 250 feet apart along the length
of the lateral pipe, which may vary from 200 to 2600 feet.
Each drive unit has a power device mounted on it that drives the wheels,
tracks, or skids on which the unit moves. The rate at which the drive
unit and lateral pipe advance around the pivot is determined by the
speed of the outermost drive unit. Alignment devices detect any drive
units that become misaligned. Either the units are speeded up or
slowed, as needed. Thus, the advance by the outermost drive unit sets
off a chain reaction of advances, beginning with the second drive unit
from the outer end and progressing along the lateral to the pivot.
Should the alignment system fail and any drive unit become too far out
of alignment, a safety device stops the whole system automatically
before the lateral can be damaged.
There are four methods of powering a center pivot sprinkler system:
hydraulic water drive, which utilizes pistons, rotary sprinklers, or
turbines; electric motor drive; hydraulic oil drive, using pistons,
rotary motors, or piston-cables; and air-pressure piston drive.
Hydraulic water-driven center pivot systems are powered by water from
the sprinkler lateral pipe with pressures from about 60 to 120 psi at
the pivot. Water used to drive the systems is discharged to the field.
On the piston-drive systems, each piston-drive unit activates a set of
5-11
trojan bars. The trojan bars engage wheel lugs to turn the drive unit
wheels. The rotary sprinkler and turbine drive systems transmit power
to the wheels of each drive unit through a gear box. Other systems use
a chain and sprocket mechanism connecting the gear box and the drive
wheels.
The electric-drive center pivot systems have motors of 1/2, 3/4, 1 or li
hp mounted on each drive unit. Most systems operate with 440-volt or
480-volt, 3-phase 60-cycle electric power. Electric power is supplied
by an engine-driven generator located at the pivot, or through
underground cables which convey electric power to wiring on the moving
lateral .
In oil-powered systems, the soil-supply and return-flow pipelines extend
from the oil pressure pump and oil reservoir to the piston or rotary
motors located on each drive unit. The oil pump is powered by an
electric motor or internal combustion engine and maintains 600 to 2000
psi oil pressure in the oil lines.
The cable-drive system has one oil-pressure powered hydraulic cylinder
at the pivot point. As the cylinder reciprocates, propelling power is
transmitted to each drive unit through a steel cable that extends from
the hydraulic piston to the outer drive unit.
Water is applied to the soil along a center pivot lateral at a low rate
near the pivot to progressively higher rates toward the outer end. The
application rate varies along the lateral because the length of time
water is applied to the field decreases from the pivot to the outer end
due to the increasing travel speed of the lateral.
The type of sprinklers, their spacing along the lateral, and the
diameter of area covered from an individual sprinkler affect the appli-
cation rates along a center-pivot lateral. There are three common
variations in sprinkler types and arrangements along the lateral* all of
which can produce uniform water distribution.
The small to large sprinkler arrangement uses some of the smallest agri-
cultural sprinklers near the pivot, gradually increasing sprinkler size
to large sprinklers at the outer end of the lateral, with 35 to 40
sprinklers used on a 1300 ft. lateral. Recommended pivot operating
pressure using this nozzling concept varies from 60 to 100 psi.
There is a sprinkler arrangement using the same medium-sized sprinklers
with variations in nozzle size and sprinkler spacing along the lateral.
The widest spacing of sprinklers is near the pivot and the closest
spacing at the outer end of the lateral. These laterals have 80 to 100
sprinklers normally operated with a pivot pressure of 45 to 75 psi.
The third sprinkler arrangement has fixed sprinklers with spray-type
nozzles. Low pivot pressures from 20 to 40 psi are suitable for spray
nozzle operations.
5-12
The spray-type center pivot lateral has the smallest drops, but the
highest peak application and the shortest duration of application.
Rates vary from 6 to 12 in./hr at the end of a 1300 ft. lateral. The
medium-sized sprinkler type lateral has the next highest application
rates with a peak varying from 2 to 3 in./hr. The variable sized
sprinkler-type lateral gives the largest drops, but the lowest peak
application rates, from 1.0 to 1.5 in./hr.
The application rates are determined by the nozzle size, nozzle
pressure, sprinkler spacing, length of lateral and sprinkler types
used. Once these items are fixed by the manufacturer, the application
rate for that point along the lateral is fixed and will not be changed
by varying the speed of lateral rotation. Changing the lateral speed
only changes the depth of water applied.
when water application rates exceed soil intake rates, surface runoff
can occur. Runoff results in poor water distribution, lower water
application efficiency, and potential erosion. This problem is
inherent in the design of all center-pivot irrigation systems but is
more serious with low-pressure systems due to the very high peak
application rates associated with this design. Crop production prac-
tices can be managed to significantly reduce the runoff potential.
Advantages and Disadvantages
The advantages of a center pivot system are the low labor reqirement,
its adaptability to circular or square blocks with an addition of an
end gun, its suitability to chemigation. The disadvantages are that
it requires a field with no obstructions, application rates are
usually high, especially at the outer end of the pivot, resulting in
excess runoff on low intake soils, and there is a tendancy for wheels
to cut deep ruts in some soils. The center pivot system ranges in
energy use from low to medium.
Table 5-2 lists the factors affecting the selection of sprinkler irri-
gation systems.
5-13
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5-14
TRICKLE IRRIGATION
DESCRIPTION
Trickle irrigation is the efficient application of water to the soil at low
rates, 0.5 to 50 gallons per hour (gph), through emitters operating at low
pressures, 5 to 30 psi. Emitters may be orifices, porous tubing or per-
forated tubing and may be placed on or underground. The objective is to
continuously supply each plant with enough m&isture to meet evapo-
transpiration needs without excessive water loss, erosion, or damage to
plants by poor water quality. This method of irrigation is suited to
orchard and row crops, nurseries, greenhouse operations, and urban
landscaping. Field application efficiency is the highest of any irrigation
method. For design purposes, the application efficiency can be as high as
90 percent.
SYSTEM COMPONENTS
Figure 5-5 shows a typical trickle irrigation system. The various com-
ponents are discussed below.
Emitters
The system and its performance are based on a specific discharge for each
emitter at a design pressure. Therefore, companies providing emitters need
to furnish performance curves that show gph flow rates vs. pressure for
each size of emitter to be used. Permissible flow rate is usually +!$%* of
the average flow rate, therefore, these performance curves are needed to
determine the permissible pressure variation. See Figure 5-6 for a typical
performance curve for a trickle emitter. Using Figure 5-6, the permissible
variation in flow rate for a 1.0 gph flow rate is from 0.9 gph to 1.1 gph.
The pressure corresponding to 0.9 gph and 1.1 gph is 12.5 psi and 17.3 psi.
The maximum pressure loss between the first and last emitter would then be
4.8 psi (17.3 psi - 12.5 psi).
Emitters generally fall under two categories - those that apply water by the
drip process at flow rates of 4 to 2 gph and those that anniv water hv
Pump
Plan View
Acid Injector
Pressure Pressure Fertilizer Pressure Above
Chlorinator xRelief TGauge /"injector f Gauge /^"Ground
f Valve f f _ f f.
g "..nil ;. O
Nonvibratoryx (^Check
Coupling Valve
( Combination VTototizing ^Filters
^ Air Vacuum Flowmeter
Release Valve
Underground-
Pressure Relief
Valve
Pressure Gauga
ft-
-0
Flushing Line
Combination
Air Vacuum
'Rease Valve
/2" Polyethylene Feeder Line3
^ Qboye Gf0und ^ 5 ., o /o 31ocK
so Emitters wont Move
Tree B
Riser
Trfte
Pressure Regulator set
in PVC Buried Line
End Cop so Line
can be Flushed
Valve
Riser with
Pressure Regulator
Figure 5-5. Typical Trickle Irrigation System
5-16
OL
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10 12.5 is
PRESSURE IN P.S.I.
Maximum Al lowable
Pressure
Figure 5-6. Typical Performance Curve for Trickle Emitter
Saturated
Radius
A w = 25 ft
<- Moisture
^^ Contour
= 150 ft'
Bottom of
RootTlone"
Deep Percolation-
Figure 5-7. Comparison of idealized wetting patterns in a
homogeneous fine sandy soil under a drip and a
spray emitter.
5-17
Table 5-3. Estimated wetted areas for different soil textures, rooting or
soil depths, and degrees of soil stratification from a 1.0 gph
trickle emitter under normal field operation.
Soil or Root
Depth and
Soil Texture*
Degree of Soil Stratification 2
Homogeneous
Stratified
Layered^
Equivalent Wetted Soil Area^
e ^ w
ft x ft
S e x S w
ft x ft
Sg x o\fj
ft x ft
Depth 2.5 ft
1.2 x 1.5
2.4 x 3.0
2.8 x 3.5
2.0 x 2.5
3.2 x 4.0
4.0 x 5.0
2.8 x 3.5
4.0 x 5.0
4.8 x 6.0
Coarse
Medium
Fine
Depth 5 ft
2.0 x 2.5
3.2 x 4.0
4.0 x 5.0
3.6 x 4.5
5.6 x 7.0
5.2 x 6.5
4.8 x 6.0
7.2 x 9.0
6.4 x 8.0
Coarse
Medium
Fine
1 Coarse includes coarse to medium sands, medium includes loamy sands to
loams, fine includes sandy clay loam to clays (if clays are cracked, treat
like coarse to medium soils).
2 Most all soils are stratified or layered. Stratified refers to relatively
uniform texture but with some particle orientation and/or some compaction
layering which gives higher horizontal than vertical permeability. Layered
refers to changes in texture with depth as well as particle orientation
and moderate compaction.
3 For soils with extreme layering and compaction which causes extensive
stratification, the S e and S w may be as much as twice as large.
4 The equivalent wetted rectangular area dimensions, S e and S w , are 0.8
times the wetted diameter and the wetted diameter, respectively.
5-18
Lateral Lines
Lateral lines normally are designed so that when operating at the design
pressure, the discharge rate of any emitter served by the lateral will
not exceed a variation of +1Q percent of the design discharge rate.
[SCS max. is +15 percent (Std. 441).]
Lateral lines supply water to the emitters. Polyethylene or similar
material is used for the lateral lines. The most common sizes used are
the inch, 3/4 inch, 1 inch, and H inch. Normally, this material is
installed above ground; therefore, it is important that it be purchased
from a reputable dealer that recommends it for this use. Below ground
installation should be considered where feasible. This will extend the
life of the material and protect it from damage.
Slack is left in the lateral line so that temperature variations will
not pull the emitters away from their initial position. When computing
friction loss in lateral lines, it is important to use the correct
tables for the inside diameter of pipe being installed. Inside diame-
ters vary, depending on the manufacturer and materials used.
Lateral lines are connected to buried main lines and sub-main lines
through risers, flexible PVC, or other acceptable means. Pressure
regulators may be installed on each riser where extreme elevation
variations exist, and the allowable pressure variation must be
controlled in the lateral lines. Use of pressure regulators increases
costs and maintenance and should not be installed where there is not a
real need.
Lateral lines are capped on the outlet end by means of a screw cap or
other device. This is removed periodically so the line can be flushed
to remove sediment and other debris.
Main and Sub-main Lines
Main and sub-mains are permanent pipelines normally constructed of ther-
moplastic materials that deliver water to the lateral lines. They are
buried below ground and installed in accordance wi^h -^ ~^n/^'
Fertili zer Injectors
Fertilizer should be injected upstream of the filters so unfiltered fer-
tilizer will not plug the lateral lines and emitters.
Chemical Injectors
Chlorinators are optional, depending on the quality of water used.
Guidelines for application of liquid chlorine to inhibit iron and slime
clogging should be obtained either from manufacturers, Appendix E of this
Guide, or other reputable sources.
Tensiometers or Other Soil Moisture Checks
Tensiometers,, neutron probes, and soil moisture locks have been used to
check the soil moisture condition. Normally, a check is made at a depth
where the main root concentration is found. A second soil moisture check is
made below the main root zone. When water is reaching this area, the irri-
gation should be stopped. For tree crops, tensiometers could be placed at
an 18" and 36" depth and about 15 to 16 inches from point of application of
drip emitters.
Valves
Gate valves, check valves, air valves, pressure release valves, flush out
valves, etc., are to be installed as needed.
Filters
A filtration system shall be provided at the system inlet. The type of
filter needed depends on the emitter selected and the quality of the water
supply. It is best to use the emitter manufacturer's recommendations in
selecting a filtration system. Three types of filters are used and are
sometimes used in combinations. For instance, a sand separator may be used
in very dirty water backed up by a screen filter. Sometimes a screen filter
is used downstream from a sand filter in case of failure of the sand filter.
Pressure loss of 5 to 15 psi can be expected across the filters.
ators - sometimes used to remove sand partricles where excep-
-irty water suply is used. The operation of a sand separator is
irinciple of centrifugal matter as small as 74 microns (200
Lh at this material is heavier than water. This is a rela-
e filtration system.
2. Screen filters - 20 mesh to 200 mesh screens are used to remove sediment
and other foreign material. The industry is in the process of making
automatic cleaning devices available. The filters will remove sand,
debris, organic material, some minerals, and some silt.
3. Sand filter - looks much like a swimming pool sand filter. Normal design
provides 1 sq. ft. of filter area to 20 gpm system capacity. For dirty
water, this may go to 1 sq. ft. to 15 gpm. Sand filters can be automated
to operate when there is a 5 to 10 psi differential across the filter
5-20
ADVANTAGES AND DISADVANTAGES
The advantages of trickle systems are:
1. Costs are Tower since smaller pumps, motors, and pipelines are
installed.
2. Water application is more efficient because irrigation water is applied
directly to the soil. This results in lower water use and energy
demands because of lower presssures. Low pumping rates make it
possible to use shallow wells, ponds and canals as a water source.
3. Labor requirements are reduced when adequate filters and water treatment
are used.
4. Damage to crops is reduced in areas of poor water quality.
5. Optimum moisture conditions can be maintained and drying cycles reduced.
6. In orchard crops, weed growth between rows is reduced since water is
normally applied to the canopy area.
7. There is better scheduling of irrigation for more effective use of
rainfall .
8. Smaller pumps and motors may use single phase electricity in areas
where three phase electricity is not available.
9. These systems have the capability of applying fertilizers and other
agents, hence reducing operations.
10. These systems may be used on sites with steep slopes and erosive
soils where runoff and pollution are a problem.
11. Water conservation due to travel lanes and other spaces between plants
that are not irrigated.
The disadvantages of trickle systems are:
1. Moisture distribution is limited in sandy soils rem
emitters per tree canopy.
2. Clogging can result from sand, organic growths, or
cal precipitations.
3. Life expectancy of systems is low.
4. Salt build-up in soils may result in areas of pool
5. Requires a high degree of management skills.
Table 5-4 lists factors affecting the selection of tri<
systems.
5-21
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5-22
SUBIRRIGATION
GENERAL
Subirrigation involves the application of water on level to gently
sloping slightly wet to wet soils to create an artificial or perched
water table over some natural barrier that restricts deep percolation.
Moisture reaches the plants through capillary movement. The basic prin-
ciple of this method of irrigation is the control of the water table to
supply moisture to plants from a subsurface zone saturated with free
water.
Irrigation water can be introduced by either open ditches or underground
conduits. The water table is maintained at some predetermined depth
below the ground surface, usually 24 to 36 inches, depending on the
rooting characteristics of the crop grown. The water table can be regu-
lated by controlling the drainage scheme as it applies to subsurface
water. Instead of removing subsurface water to make deeper rooting
possible, drainage is curtailed and water is added to keep the water
table high enough to provide adequate moisture to the root zone through
capillary action within the soil. However, the drainage system is still
responsible for removing excess surface water and maintaining control of
subsurface water so that the water table does not remain in the root
zone for a long enough period to cause crop damage.
The plan for drainage becomes more critical when the drainage facilities
will be used for subirrigation. A planner must be assured of a number
of items, as fol lows;
1. Ample water supply during dry season.
2. Naturally high water table, or a very slowly permeable soil layer
below the root zone on which an artificially elevated water table
can be maintained without excessive losses through deep percolation.
3. Rapidly permeable layer immediately below the topsoil that will
allow comparatively free lateral movement of water.
4. Uniform and nearly level topography permitting complete and even
distribution of water.
5. A well planned system of mains, laterals and structures which will
permit orderly movement of water to all parts of the area.
6. Adequate outlet for drainage of the system.
SITE INVESTIGATION
It is important that the site be thoroughly investigated. Major items
to be investigated are:
5-23
! Soils. Normally, the soils used for sub-irrigation systems are
classified as poorly drained or very- poorly drained. The following
soil characteristics are of major importance.
a. Effective depth. The depth of soil material favorable for root
growth should be at least 20 inches for most crops.
b. Thickness of the first significant layer below topsoil. This
may be the water-conducting layer. Thickness should be at
least 12 inches. It should not exceed 36 inches where suc-
cess of the irrigation system depends upon a very slowly per-
meable zone below.
c. The hydraulic conductivity of the topsoil should be medium (5
in./hr) to high (20 in./hr), otherwise laterals will need to be
closely spaced for good crop response.
d. Natural wetness. Presence of a naturally high water table is
indicated by wetness class. Should be slightly wet to very wet.
Moderately wet is optimum,
e. Permeability rate of first significant layer below topsoil
should be at least 5 inches per hour if it is a major water con-
ducting layer.
f . Permeability of second significant layer below topsoil should
not exceed 0.05 inch per hour. The importance of this layer
depends largely upon depth. Ideally, artificial saturation of
the soil should be based upon a naturally high water table and
not upon a relatively impermeable layer, even though the natural
water table itself may be "perched" in this manner. Since this
layer is often only moderately deep, the permeability value may
not provide key information.
g. Underlying material. The nature of the material underlying the
soil may be especially important. In communities underlain by
porous limestone or marl cut by ditches and canals, maintaining
a high water table may be difficult or impractical.
2 ' Topography. Normally, the land slope should not exceed one percent.
When slopes are greater than one percent, the water table is dif-
ficult to build and maintain, the number of structures become
excessive, and drainage water velocities may become erosive. Many
times it is feasible to level the land prior to installing the
system.
3. Drainage Outlet. The outlet must be investigated and must be eval-
uated as to its adequacy to provide the necessary drainage or
steps taken to make it adequate. Many broad areas in the State
do not have an adequate natural outlet. In such cases, the selected
field area is ditched and diked around the perimeter to keep out water
from other drainage areas. Pumps are then installed for drainage
5-24
outlet control. Water storage areas may have to be installed for
the pumped system so that increased runoff will not cause offsite
damages .
4- W_a_ter _bU.Vy. There must be adequate water for irrigation. A
supply rate of eight gallons per minute per acre is usually ade-
quate for most crops .
ADVANTAGES AND DISADVANTAGES
The major disadvantage of some subirrigation systems is that generally
more water may be used because of distribution losses and other inef-
ficiencies. Estimated irrigation efficiency of these systems may be
as low as 50 to 60 percent. With proper management, the irrigation
efficiency could be increased significantly. Another disadvantage of
the open ditch subirrigation system is the loss of crop land due to
the ditches. The advantages of subirrigation systems are the low ini-
tial installation costs, low operating costs, utilization of ground
water for crop production, and their capability for providing drainage
where needed,
OPEN DITCH SYSTEM
Description
The open ditch system consists of water being supplied to the main
supply ditch at the high point of the field. Irrigation water is con-
veyed by gravity through the entire field area with lateral ditches.
Laterals are located to run from the main ditch on the contour or with
less than about 1.0 foot vertical variation from end to end.
Structures are used to restage the water at about 1.0 foot intervals
or less so that water will back into the laterals and move laterally
to raise the water table. See Figure 5-8.
Main ditches usually require control structures at or near 0.5 ft.
vertical intervals, except on the steeper slopes where a structure is
required at each lateral. The variation in depth to water table can
then be controlled by one structure to stay within the 0,5 ft. per-
missible variation. A greater variation than this will usually result
in part of the area being under-irrigated and part being too wet for
shallow rooted crops.
Structures in ditches should be designed with removable gates so that
designed drainage will not be impeded and the water levels still
controlled for irrigation. A properly designed subirrigation system
will prove to be equally valuable as a drainage system during the
rainy season if properly managed.
Laterals should be on nearly flat gradients with a variation of not
more than 0.5 ft. from end to end. The length of lateral to be
supplied from one end should not be more than 1200 feet except in
extreme cases. Laterals will, in most cases, be spaced from 60 to 200
feet, depending on the characteristics of the soil that govern the
5-25
lateral movement of water through It and the degree of water table
management desired. Due to drainage requirements, a spacing greater
than 200 feet is not desirable. With a spacing of 60 feet or less, 10
percent or more of the field may be in ditches, and thus spacing beco-
mes critical .
Main and secondary distribution ditches will be designed (Manning's
Formula) to carry necessary discharges. On a large system, dimensions
of a channel in its lower reaches might be determined by requirements
for drainage. Dikes for transporting water against grade to higher
elevation for distribution should be designed according to sound and
accepted principles.
Determining Water Table Levels
In order to know when to start irrigating and when to stop applying
water, it is important to determine the depth to the water table below
the ground surface. This determination can be made by using a simple
gauge made from pipe U-inches in diameter and approximately 48 inches
long, perforated with 1/8-inch holes. A gauge should be placed near
the center of each 40 acres, spaced equidistant from laterals, and set
upright in the ground with approximately 6 inches above the ground
surface. The desired depth to the water table will vary with'the crop
stage and the rooting characteristics of the crop grown. Experience
in the area will generally reveal the desired depth of the water table
for the crop to be grown.
CONDUIT
DESCRIPTION
The function of underground conduits for irrigation is basically the
same as the open ditch method. Lateral ditches are replaced by
lateral pipelines which are usually perforated corrugated plastic
tubing (drain tubing). Water is supplied through the drain tubing -
regulating the water table. The water table is usually held just
below the root zone where capillary movement of water due to tractive
force of soil particles draw water up into the root zone.
As in the open ditch method of subirrigation, structures are needed to
control the water table at its desired elevation. Structures, whether
in an open ditch main or in a conduit main line, are designed to be
adjustable so water can be released during excessive rainfall and
water can be contained at the desired elevation during irriqation
pumping. See Figure 5-8. y y
ADVANTAGES AND
The advantages of the underground conduit are that it does not take up
surface area, can be installed closer and deeper than ditches low
till s Klnhpr V n i 1Uen ?l by cropping pattern. The disadvan-
in 9 ^nSu *A ?c i lal Cost than open d1t che&, requires mesh filter
rnn LI ^V** l*^* ^ * ] des1 9 n in S0 ? ls h1 9* '" SO uble
refeV to thP ^Jh^v " S n f 1lter requirements for various so s
reier to the bouth Carolina Drainage Guide.
5-26
Small irrigation system wiffo
we/I af high porn'. Entire
system acts as drainage and
irrigation system.
Morn for
Irrigation
and
Drainage
NOTE:
1 . Water is controlled
of ,5' interval.
2. Field laterals are stopped
a distance from edge of
field equal fo half the
lateral spacing*.
Large Irrigation System. Wafer
supply is pumped from c/eep
ditch thaf connects with river,
Where soil permits, an alternate
system is fo locate pump near
river and c/ilte centra/ supp'y
ditch to the high ground distri-
bution point.
LEGEND
Lateral
^i Water Control Structure
Pump
NS^Contour Line
o Well
*>|t-nOO'->H*]000'-M'
lateral movement of water through it and the degree of water table
management desired. Due to drainage requirements, a spacing greater
than 200 feet is not desirable. With a spacing of 60 feet or less, 10
percent or more of the field may be in ditches, and thus spacing beco-
mes critical .
Main and secondary distribution ditches will be designed (Manning's
Formula) to carry necessary discharges. On a large system, dimensions
of a channel in its lower reaches might be determined by requirements
for drainage. Dikes for transporting water against grade to higher
elevation for distribution should be designed according to sound and
accepted principles.
Determining Water Table Levels
In order to know when to start irrigating and when to stop applying
water, it is important to determine the depth to the water table below
the ground surface. This determination can be made by using a simple
gauge made from pipe U-inches in diameter and approximately 48 inches
long, perforated with 1/8-inch holes. A gauge should be placed near
the center of each 40 acres, spaced equidistant from laterals, and set
upright in the ground with approximately 6 inches above the ground
surface. The desired depth to the water table will vary with^the crop
stage and the rooting characteristics of the crop grown. Experience
in the area will generally reveal the desired depth of the water table
for the crop to be grown.
CONDUTT
DESCRIPTION
The function of underground conduits for irrigation is basically the
same as the open ditch method. Lateral ditches are replaced by
lateral pipelines which are usually perforated corrugated plastic
tubing (drain tubing). Water is supplied through the drain tubing -
regulating the water table. The water table is usually held just
below the root zone where capillary movement of water due to tractive
force of soil particles draw water up into the root zone.
As in the open ditch method of subirrigation, structures are needed to
control the water table at its desired elevation. Structures, whether
in an open ditch main or in a conduit main line, are designed to be
adjustable so water can be released during excessive rainfall and
water can be contained at the desired elevation during irrigation
pumping. See Figure 5-8. yanuii
f J he . under ^ound conduit are that it does not take up
area, car. be installed closer and deeper than ditches, low
C ft , 3 - P fluenced b * cropping pattern. The disadvan-
tages are h gher initial cost than open ditches, requires mesh filter
n sandy soils and may require special design in soils high n so uble
1
refer tSuJ^rTi- 011 n" f1Uer r T 1Ments for varios o ,
rerer no the South Carolina Drainage Guide.
5-26
Small irrigation sysfem with
well at high point. Entire
system acfs as drainage and
irrigation system.
Main for
Drainog^
NOTE;
1, Wafer is controlled
at .5' interval.
2. Field laterals are stopped
a distance from edge of
field equal to half the
lateral spocings.
Large Irrigation System. Wafer
supply is pumped from Jeep
ditch that connects with river,
Where soil permits, an alternate
system is fo locate pump near
river and dike central supply
ditch to the high ground distri-
bution point.
LEGEND
Lateral
r Water Control Structure
no Pump
NS^Contour Line
o Well
NOT5;
in each of the above illustrations, th>
of the edges of the irrigated field one
at least one-half fhe lateral spacing,
area wifh heavy equipment without cr
Figure 5-8. Typical Subirrigi
5-27
OTHER USES OF IRRIGATION
CHEMIGATIQN
Chemlgation can be defined as the application of a chemical
(fertilizer , herbicide, insecticide, fungicide, nematicide, etc.) via
an irrigation system by injecting the chemical into water flowing
through the system. Although the term chemigation is relatively
new, the concept of applying fertilizer in the form of animal manures
in the irrigation water likely began soon after the use of irrigation.
Advances in irrigation systems and injection equipment design have
stimulated research which has resulted in the chemigation application
of herbicides (herbigation) , fungicides (fungigation), nematicides
(nemagation), and insecticides (insectigation) . Chemigation is used
for both soil and foliar applied chemicals; however, several factors
should be considered before attempting to use chemigation as a means
of applying chemicals.
Application of chemicals by chemigation occurs only where the irrigation
water is applied; therefore, surface and trickle/drip type irrigation
systems have only been successful for soil applied chemicals.
Application of both soil and foliar applied chemicals have been success-
ful with sprinkler irrigation systems.
Uniformity of chemical distribution is an essential element of success-
ful chemigation and is proportional to the uniformity of water distribu-
tion by the irrigation system. The uniformity of application of water
or chemicals by an irrigation system or sprayer is often expressed as
the coefficient of uniformity (CU). The CU of properly calibrated
ground based sprayers ranges from 50 to 92%, while aircraft normally
obtain a CU of about 70%. Most types of sprinkler irrigation systems
can be designed and operated to achieve CU's of 85% or greater;
however, many solid set and portable pipe systems achieve CU factors of
only 70-75%. Traveling gun type systems normally achieve a CU of 80% or
less under optimum conditions, and most farmers achieve CU's of less
than 70%. A continuously moving lateral system, such as a center pivot,
normally achieves a CU of 90% when properly nozzled and operated. As
with, aircraft or ground based sprayers, the CU's of sprinkler irrigation
systems decrease with increased wind velocity. Competent management is
necessary to fully utilize the capabilities of chemigation.
The high CU's of center pivot and linear move systems make them ideally
suited for total chemigation. The operator must determine whether the
lower uniformity of other types of sprinkler irrigation systems is
acceptable for cheiTiigation. The minimum level of acceptable uniformity
will vary, depending on the chemical applied. A lower CU value will be
acceptable with chemicals which have a greater range of effective appli-
cation rates.
When chemicals are injected into irrigation systems, there is a possibll-
ity of contamination of the water supply if the injection system is not
carefully designed and maintained. The irrigator is responsible for
installing an appropriate anti-syphon device to protect the water
supply, See Chapter 6 for discussion on safety components necessary for
chemigation.
5-28
Application of Fertilizers
Applying fertilizer through chemigation permits nutrients to be applied
to the crop as they are needed. Several applications can be made during
the growing season with little if any additional cost of application.
Nitrogen, especially, can be applied during periods when the crop has a
heavy demand for both nitrogen and water. Corn, for example, uses
nitrogen and water most rapidly during the three weeks before tasseling.
About 60% of the nitrogen needs of corn must be met by silking time.
Generally, it is recommended that nearly al> the nitrogen for the crop
should be applied by the time it is pollinating, even though appreciable
uptake occurs after this time. Fertilization through irrigation can be
a convenient and timely method of supplying part of the plant nutrient
needs. Nitrogen is ideally suited to chemigation and is the element
most often applied to corn by this method. The ideal fertilization
program would be one that provides nitrogen and moisture to plant roots
as they are needed so there is never a deficiency or an appreciable
surplus.
The fertilizer solutions most commonly used with irrigation applications
contain both the ammonium and nitrate forms of nitrogen and have 28 to
32 percent nitrogen. Considerably more care is required if anhydrous
ammonia is used. Because the per-unit cost for ammonia has been less
than for solution forms of nitrogen, producers have shown an interest in
applying ammonia in sprinkler water. Also, relative to solution forms
of nitrogen, ammonia offers advantages in terms of economics and energy
requirements for production and transportation.
Application of ammonia in sprinkler water, though attractive in terms of
fertilizer costs, presents definite potential hazards unless special
precautions are taken. Nitrogen can be lost to the atmosphere as ammo-
nia gas and precipitation deposits can form which reduce the carrying
capacity of irrigation pipes and may clog sprinklers.
A potential solution to precipitation and ammonia volatilization
problems is acidification (adding sulfuric acid) of irrigation water
prior to injection of ammonia. In the past, application of sulfuric acid
with ammonia in water has not been economically feasible. If the price
of sulfuric acid comes down, this approach may have real value. Ammonia
use would become feasible. Although the ammonia form will be held a
little more tightly in the soil than the nitrate form, the ammonium form
will be rapidly changed to nitrate when the moisture, temperature, and
aeration conditions in soils favor root growth. The fertilizer solution
is injected into the irrigation delivery pipe usually near the water
pump. Safety devices must be installed to prevent the nitrogen solution
from moving back into the water source if there is an interruption in
pumping.
Almost any fraction of the total nitrogen application can be made suc-
cessfully by chemigation. It is suggested that, under most conditions,
not more than about one-third of the total intended nitrogen be applied
in this manner.
Single applications of 20 to 30 pounds of actual nitrogen per acre are
the most practical. There is probably little reason to apply nitrogen
after silking, unless there are still symptoms of a deficiency of this
element.
5-29
Although some phosphorus and potassium fertilizers may be applied by
chemigation, they probably are applied more satisfactorily ahead of
planting. Then, they are available to the crop as soon as root explora-
tion of the soil begins. Phosphorus, especially, does not move down
through the soil readily so, therefore, does not become available for
benefiting early growth. On sandy soils where the need for potash may
be high, it might be applied with nitrogen to coincide with the
rapidly increasing amount needed for the period of rapid vegetative
development. Where both potash and nitrogen may be needed later in
the growth of a crop, it would be possible to add a liquid mixed fer-
tilizer such as a 7-0-7 or similar grade. Adjustments would simply
have to be made with the injection pump to ensure that an adequate
amount of nutrient is applied.
Some phosphorus-containing fertilizers are corrosive, especially to
brass or copper fittings. Some phosphate materials do not have suf-
ficient solubility to be used satisfactorily in chemigation. If the
irrigation water contains appreciable amounts of calcium, calcium
phosphate may precipitate and clog nozzles, or screens, or both. Some
solutions may also cause leaf burning if applied in too great a con-
centration.
Sulfur may become deficient on some sandy soils. This nutrient could
be added by irrigation using nitrogen solutions containing sulfur.
Several major nitrogren and 2 to 5 percent sulfur. Probably this
should be done if there has been no other sulfur applied earlier in
the year with conventional mixed fertilizer.
Micronutrients can be applied through irrigation systems. If a defi-
ciency is positively identified in a growing crop, this may be the
most satisfactory method of correction for that crop. However, the
best ways to correct such deficiencies for successive crops probably
are to apply micronutrient materials to the soil before planting or to
the plants by foliar application as soon as the deficiency is
recognized. Foliar applications of micro-nutrients seem to be most
effective if they are not washed off the leaves by irrigation water or
rain.
In order to capitalize on the convenience of applying nutrients, her-
bicides, or other agricultural chemicals through an overhead irrigation
system, accurate amounts evenly distributed over the field must be
accomplished. In the material which follows, equations are presented
that will be useful in calculating the rate of material that must be
added using either a center pivot or self-propelled gun traveler to
apply selected sources of nitrogen. Application of other nutrients
either as clear liquid mixed fertilizers, single nutrients, such as
potash dissolved in water, or micronutrients dissolved in water, can
also be applied using the same equation.
Fertilizer sources suitable for fertigation must be completely water
soluble. Table 5-5 lists possible source of fertilizers for
fertigation.
5-30
TABLE 5-5. COMMON SOURCES OF FERTILIZERS
FOR USE WITH IRRIGATED SYSTEMS
Nutrient Source
Nitrogen Urea ammonia nitrate solutions are best. Soluble
dry fertilizers can be dissolved under special
circumstances. Aqua and anhydrous ammonia are not
recommended due to problems with corrosion and
volitilization.
Phosphorus This is not recommended. Phosphorus is immobile in
soils and is best applied with ground equipment. If
used in irrigation systems, phosphorus compounds will
have corrosion and precipation problems.
Potassium Pure (white in color) source of potassium chloride
is best. This is not commonly used because most
potassium sources are not completely water soluble.
Sulfur Sulf ur-sulfate source is the best.
Micronutrients Several sources are possible depending on crop needs.
The Cooperative Extension Service offices maintain
information on the suitability of the materials for
use in irrigation systems.
Several cautions are needed when planning to apply fertilizer with
irrigation water.
1. This is not foliar feeding. Soil application rates of nutrients
should be based on current soil and plant testing.
2. Crops can be burned by improper application techniques.
3. Scheduling may be a problem during adverse weather conditions.
4. Nonuniform applications are a problem. Poor irrigation patterns
are commonly on the ends of center pivot systems.
5. Fertilizers should be injected into the system with the firstwater
flow. Fertilizers injected into a system already in operation may
take considerable time to reach the perimeter.
6. This does not replace a basic fertility program. Lime, immobile
nutrients, preplant or starter fertilizers still require conven-
tional application practices.
Using Center Pivot to Apply Fertilizer
6PH = 100 AN
P H W
GPH = Liquid fertilizer to inject in gallons per hour
A = Total area actually irrigated in acres per revolution
N = Actual nitrogen (or other nutrients) to be applied,
Ibs/acre
5-31
H = Hours per revolution of system
p Percent N (or other nutrients) In fertilizer
W = Weight of one gallon of liquid fertilizer, in Ibs,
Example: 160-acre system, 80 hours/revolution, appy 50 Ibs. of
actual N, using 30 percent N liquid solution.
GPH = 100 x 16Q x 50 = 31.3 gal/hr
30 x 80 x 10.65
or 31.3 = ,52 gal min
60
Using Self-propelled Gun Traveler to apply Fertilizer
GPH = 100 SIN
43,560 P W
GPH = Liquid fertilizer to inject, gallons per hour
S ~ Rate of sprinkler travel, feet per hour
L = Distance between sprinkler lanes, feet
N = Actual nitrogen (or other nutrients) to be applied,
Ibs/acre
P = Percent N (or other nutrients) of liquid fertilizer
W ~ Weight of one gallon of "liquid fertilizer in Ibs.
Example: Travel speed of 90 feet/hour, 300 feet between lanes,
50 Ibs. of actual N, using 30 percent liquid nitrogen
fertilizer
GPH = 100 x 90 x 300 x 50 = 9,7 gal/hr
43,560 x 30 x 10,65
or iiZ = - 162 galAiin
60
Application of Herbicides
of herbicides is advantageous from the standpoint that time
The effectiveness of some herbicides is increased by applica-
irrigation water. Several herbicides are registered for
;o corn through the irrigation system. Eradicane, Sutan,
azine, Lasso and Lasso and Atrazine are currently
be used in this manner. Tests at the University of
hown that these herbicides have performed well when
both water and electric drive center pivot systems,
ts in Nebraska have shown that with some herbicides, the
5-32
rate may be reduced when application is made by the sprinkler water.
It is very likely that certain other preplant and pre-emergence her-
bicides could be applied through a center pivot system with good
results. A careful examination of the label will determine if the
herbicide can be applied in irrigation water. The current
Agricultural Chemical Handbook provides information on approved herbi-
cides for South Carolina crops.
Generally, preplant and pre-emergence herbicides must be distributed
in the surface two inches of soil to be effective against germinating
weed seeds. As a rule of thumb, the herbicide should be applied with
about 0.5 inch of water on sandy soils and 0.75 inch of water in fine
textured soils. Large amounts of water may move highly soluble her-
bicides too deep, especially on sandy soils. Less water may not move
certain herbicides deep enough.
To ensure good performance, apply the herbicide very soon after
planting. Usually the field is tilled just prior to planting, but by
the time the field is finally tilled and planted, it may take four to
five days. It may take the sprinkler system one or two days to
complete the application. Some weed seeds may have started to ger-
minate before the herbicide is applied. It is important that the her-
bicide be applied within about five days of the final tillage
operation. A good procedure is to till and plant one-half the circle,
then start the system and herbigate while tilling and planting the
rest of the circle.
Problems could arise if highly volatile herbicides such as Eradicare
and Sutan are applied in the irrigation water to soils that are
already wet. For best results, apply volatile herbicides to dry soil.
Also, inject the herbicides all the time while irrigating or at the
beginning of the set. Don't apply herbicides at the end of a set
after the soil has been wetted. Where plenty of rainfall has occurred,
the irrigator may be foreced to irrigate to apply the herbicide even
though soil moisture is adequate if he has no other means of applying
the chemical .
If at all possible, applying herbicides through a sprinkler system
should be avoided when wind speeds exceed 10 mph. Strong winds can
contribute to uneven application of water and herb1 r ^ A"Kn, drift
the area may become sterilized. If an overdose of herbicide is
applied at any particular point, quite a large number of acres will be
affected.
Application of Insecticides and Fungicides
Use of insecticides and fungicides through irrigation systems has been
successful in research. No compounds are registered for use in South
Carolina with irrigation systems as research continues to look for the
best formulations and rates to use. Insecticides and fungicides that
are effective in irrigation systems are foliar applied, requiring a
low pressure injection pump. Foliar applied chemicals need small
amounts of water during application. Application rates of 0.1" to
0.3" will allow good leaf coverage without washing the chemical off
the leaf surface. High speed drive motors will allow application of
low amounts of water. This should be planned before the system is
installed to avoid unnecessary expense.
Waste Disposal
Disposing of waste on land is not a new concept. Crops have been
grown for centuries on land used for spreading manure and sewage.
These materials were regarded as fertilizers, not wastes. Many kinds
of grasses, vegetables, legumes, and woody plants have been subjected
to waste disposal. Grass seems to be the most effective vegetation
for this purpose. Many species of grass possess a high water use fac-
tor combined with abundant root production. The roots and sod retard
runoff and enhance infiltration. The plant leaves pump water back
into the atmosphere. Wastes become pollutants when they are intro-
duced into the air, water, or soil in excessive amounts or otherwise
become offensive in the environment.
The interaction of soils, plants, and water must be thoroughly con-
sidered before a sprinkler disposal system is installed and expected
to operate successfully.
Generally, an existing irrigation system can be utilized to apply
effluent to the land. The sprinkler nozzle will need to be large
enough to pass the solids that are in the effluent. One of the major
nrnh" 1 ------- - ii , -. , . . . ...
The total depth of effluent application per season can be determined
when the total concentration of plant nutrients and/or metals is
known. Technical Guide Standard 633 - Waste Utilization, provides
guidance in this area.
Application rates must be selected to not exceed the intake rate of
the soil. See Table 2-6 (Chapter 2) of this guide for guidance in
determining maximum sprinkler application rates.
When effluent disposal is planned, especially on the heavier soils,
extreme care must be exercised to plan drainage systems that will
dispose of excess runoff without causing erosion or pollution.
Examples of this might be to divert water from the disposal area
through a grass buffer or filter zone before access to surface water-
ways is reached.
Some of the critical considerations of sprinkler application of
effluent follow;
1. Excessive rate or volume of application may result in runoff
and pollution of surface water,
2. Excessive application depths may result in pollution of ground
water especially on highly permeable soils.
3. Effluent may contain toxic or detrimental materials to soil or
plants.
4. Odors from sprinkling may be obnoxious.
5. Effluent is highly corrosive and may shorten the useful life of
equipment.
6. Solids from the effluent may coat plant leaves and reduce photo-
synthesis.
The system should be operated with clear water for at least the last
15 minutes to wash the system as well as remove solids from the
plants.
SOUTH CAROLINA IRRIGATION GUIDE
CHAPTER 6. IRRIGATION SYSTEM COMPONENTS
Contents
Page
lonoval ______________________ __ ______ ____ _ ___ _ _ ____ 1
Jd ic t u i i -. _ _ _ _ _ .. _ ____________________________*,_ u *" j.
'urnoi no Plant --------- -----__-.---__---.__ _.._____.._____,._ fi-l
Selection of the Pumping Plant ............. -------- ........ 6-1
_..-*---___--.,---- --__---_-.-__ ____-..-> _-.-,-,_*_-_ -* __. .. _. ____-.__ (\ 1
_-..-. -. MH - . WP --.-----.-*->.- l ,--...-*_<,.*__...- V .-.._l..._t__.-ti_ i ...._.-_*->*_,,_l U J,
-,-,---,--.-----,,.-_---.,_---.,__ ___.*-., _.,.-.,* MM ~-.-.-._*---~--. __._.____ K_*9
_ .-. _._.____ __----- _____---._.-._-.*--__--_-_---_ -_-__.q____--.. H _-___._- vn U (_.
Centrifugal Pumps -- ..... ---- ......... ------------------ 6-2
Turbine PUDIDS -_---_-_---_----_--__..--_--.-_ 6-2
Flnw Pnmn^ __________________ _ ____________________ fi_^
I Jl/Tf 1 UMJU^7 .i_-.^, ____-_______-^____ *.^_ .v^^^.**... ^*^ v _^ L/(J
Flnw Piimn'; ____-,-_____-_____-____-.-.__________-.__ fi_R
I JL'Tt I Mlilpo ___ _ __*___ _".____ _ ______ __ UtJ
Pump Characteristic Curves ---------------------- ......... 6-8
Total Dynamic Head Versus Discharge ---------- ....... 6-8
Efficiency Versus Discharge ---- ............ -- .......... 6-11
Input Power Versus Discharge ----------------- ........ -- 6 LI
Net Positive Suction Head Versus Discharge ----- ........ 6-12
Pnwftr Unite ___________________ - _____ _. ___________ - ________ A-1'3
IWTT^I wll^v-J -.-- ------- ,_--____----i -._-_--. ___-__._i----____-_i-- __ \JJLO
Pumping Plant Head ....................................... 6-15
Jistribution Pipelines -------- ...... - ...... ------------------ 6-18
jc IwUU IU*I *" --_----* _- _._.-.*.*-< , _>, _i>M-.- HW - V rt. _. h -. M ^ -HH-.P* ,_ -.-.M-^-^i-iw* 0*"XO
Design Considerations ------------ ...... ----------- ........ - 6-18
Water Hammer --------- ..... -------------- ....... ---------- 6-18
Pressure Reducing Valve ............ - ................... 6-20
Anti-Syphon or Backflow Prevention Units ....... - ....... 6-22
Drain Valuer _. _ _______________ . _____ - _____ - ___________ _ __ fi_99
U I Ctlll VtAlVC-J _ _____ ->___->______^___-._ ______________ t/Lt.
Pressure Regulating Valves ............................. 6-22
Pressure Release Valves ----------- ..... - .......... ----- 6-23
Air Valwo<: _ ___-... ___.,.._________________..______ _______ (>_ 9^
/111 VulVC^ - -^ ^_ < ^ ^ _^^^^__ ^^ ^ -^--^^^ pp^-^^-^-^ \j L-\J
General .............................................. 6-23
Air-Release Valves ................................... 6-23
Operation of Air-ReTease Valves ...................... 6-24
Air-and-Vacuum Valves ................................ 6-25
Operation of Air-and-Vacuum Valves ................... 6-25
Combination Air Valves ............................... 6-26
I it I U -> U D I UC- IN -i (-__ *^**---*--p-tw-ti-* _-p-4P^ --._I.~P*-----*-* a*-* -**.*-*.*-----**..*- D**_l/
roQQnvi OQ --.-,-_._,^_-_-_.^-_-_._.--._.---_.-_._.-.-_._.^*,-_.---^--, &~07
- ^ c .> -j \j i w*> ---* *-- -- Pta-H-B '* _._H M -^_._H-M -- p*^_*--_-*^-<i_ii_.i_._-^- Ut-/
Booster Pumps .......................................... 6-27
Pressure Tanks ......................................... 6-27
Pressure Gauges ........................................ 6-30
nnw MptorQ -. -_- _ _____ - ___ - ____ -____--_ ___ _____-__ fi-.^0
Un iicuci j __ _ _ - u jw
Chemical Injectors ..................................... 6-30
Chlorine Injection -. _ __--_ 5^33
Filters -------- .-...._.._.._.. . _- .,.._.-..- 6-33
Sand Filters - __ 5.33
Screen Filters -.---__--_ _^^ 5_35
Automation - --.,-.-..-- _ , _ ___.. 5.35
Automatic Valves and Controllers 6-36
Automatic System with a Master Valve 6-40
Wells ~- .-,.--.. 6-40
Figures
Figure 6-1 Horizontal Centrifugal Pump 6-3
Figure 6-2 Deep Well Turbine Pump 6-5
Figure 6-3 Submersible Pump - - 6-6
Figure 6-4 Propeller Pumps - - --- 6-7
Figure 6-5 Typical Pump Performance Curve 6-10
Figure 6-6 Schematic for NPSHA Versus Atmospheric Pressure,
Suction Lift, Friction and Vapor Pressure 6-12
Figure 6-7 Elements of a Pumping Plant and The Corresponding
Elements of "Total Dynamic Head" Used in
Calculating Pump and Power Requirements 6-17
Figure 6-8 Illustration of Valve Location - 6-21
Figure 6-9 Typical System Using a Deep Well Pump with a
Pneumatic Pressure Tank 6-29
Figure 6-10 Chemigation Safety Equipment for an Internal
Combustian Engine Irrigation Pumping Plant 6-32
Figure 6-11 Chemigation Safety Equipment for an Electic Motor
Irrigation Pumping Plant 6-32
Tables
Table 6-1 Advantages and Disadvantages of Commonly
Used Pumps 6-9
Table 6-2 Advantages and Disadvantages of Various
Power Units _ 6-1
u
SOUTH CAROLINA IRRIGATION GUIDE
CHAPTER 6. IRRIGATION SYSTEM COMPONENTS
GENERAL
In order to have an irrigation system operate as designed and function
effectively, consideration of many irrigation components is necessary.
This chapter will attempt to identify some of the components and
briefly discuss them.
It is important to consider in the design, components that affect
pressure losses and also those that affect control of operations. The
characteristics and operation requirements of components may vary
depending on the designs of different manufacturers. It is very
important that the designer has the necessary data for all system com-
ponents utilized in an irrigation system. This information needs to
be secured from literature available from the manufacturer. Each
designer should collect this information for all irrigation system
components utilized in his area. Additional data on components is
also available from technical manuals, publications on irrigation, and
from National Engineering Handbook, Section 15 - Irrigation.
Conveyance components for surface systems are discussed in NEH,
Section 15.
The SCS Technical Guide provides minimum standards and specifications
for many of the components to be discussed in this chapter.
PUMPING PLANT
SELECTION OF THE PUMPING PLANT
General
The pumping plant selected must be capable of delivering the required
capacity at the designed operating pressure. Economy of operation is
also a primary consideration. More detailed discussion of pumping
plants is contained discussion of pumping plants is contained in
Chapter 8 of the SCS National Engineering Handbook, Section 15 -
Irrigation. It may be necessary to contact manufacturer's represen-
tatives to assure that the pumping plant selected can perform in
accordance with the system requirements.
The function of an irrigation system pumping plant is to perform the
work of moving water at the rate needed and at the pressure required
to meet the requirements of the irrigation system. A pump operates
best at the specific head and at the specific pump speed for which it
was designed. The operating conditions should therefore be determined
as accurately as possible. If there is a variation in operating head,
both the maximum and the minimum should be determined and furnished to
the manufacturer to permit selection of the most satisfactory pump.
With the use of accurate data, the system planner can make proper
selection of pumping equipment and assure the user a satisfactory per-
formance of his system.
6-1
Centrifugal, turbine, and propeller pumps are commonly used for irri-
gation pumping. Each type of pump is adapted to a certain set of con-
ditions under which it will give efficient service.
Centrifugal Pumps
Centrifugal pumps are built in two types--the horizontal centrifugal
and the vertical centrifugal. The horizontal type has a vertical
impeller connected to a horizontal shaft. The vertical centrifugal
pump has a horizontal impeller connected to a vertical shaft.
Both types of centrifugal pumps draw water into their impellers, so
they must be set only a relatively few feet above the water surface.
In this respect the vertical type has an advantage in that it can be
lowered to the depth required to pump water and the vertical shaft
extended to the surface where power is applied. The centrifugal pump
is limited to pumping from reservoirs, lakes, streams, and shallow
wells where the total suction lift is not more than approximately 20
feet,
The horizontal centrifugal (Figure 6-1) is the one most commonly used
in irrigation. It costs less, is easier to install, and is more
accessible for inspection and maintenance; however, it requires more
space than the vertical type. To keep the suction lift within
operating limits, the horizontal type can be installed in a pit, but
it usually is not feasible to construct watertight pits more than
about 10 to 15 feet deep. Electrically driven pumps are best for use
in pits because they require the least cross-sectional area.
The vertical centrifugal pump may be submerged or exposed. The
exposed pump is set in a watertight sump at an elevation that will
accommodate the suction lift. The submerged pump is set so the
impeller and suction entrance are under water at all times. Thus, it
does not require priming, but maintenance costs may be high as it is
not possible to give the shaft bearings the best attention. Pumps of
this kind usually are restricted to pumping heads of about 50 feet.
Turbine Pumps
^1 turbine pump is adapted for use in cased wells or where
urface is below the practical limits of a centrifugal pump.
he proper selection of a turbine pump the following must be
ipth of well
iside diameter of casing
spth of static water level
rawdown/yield relationship curve
epth of screen section
uoip capacity requirements
6-2
DISCHARGE PIPE
ELECTRIC MOTOR
SUCTION PIPE
B AS E
DIRECT CONNECTED HORIZONTAL CENTRIFUGAL PUMP
INTERNAL. COMBUSTION OB ELECTRIC MOTOR MAY BE USED
DISCHARGE PIPE
PRIMING PLUG
I M p E i_ i_ e R
ENCLOSED TVPf
SUCTION PIPE
SHAFT
CROSS SECTION OF MODERN HORIZONTAL CENTRIFUGAL PUMP
SINOUE SUCTION ENCLOSED IMPELLER
Figure 6-1. Horizontal Centrifugal Pump
6-3
All this is essential in selecting a pump that will fit inside the well,
deliver the required amount of water at the desired pressure, and to assure
that the bowls are submerged during operation.
Turbine pumps are equipped with Impellers that are fitted inside a bowl-
appearing case. Each of these units is known as a stage. Stages are added
to develop additional head. You can determine the number of stages needed
for a pump installation by the amount of water required and the pressure at
which it is to be delivered.
Turbine pumps may be either oil-lubricated or water-lubricated. The oil-
lubricated pump has an enclosed shaft that oil drips into, thus lubricating
the bearings. The water-lubricated pump has an open shaft. The bearings
are lubricated by the pumped water. If there is any fine sand being
pumped, select the oil-lubricated pump because it will keep the sand out of
the bearings. If the water is for domestic use, it must be free of oil.
So you should use the water-lubricated pump.
Turbine pumps are available with either semi-open or enclosed impellers.
The semi-open impeller will tolerate more sand than the enclosed impeller
and it can be adjusted. The enclosed impeller claims to retain high effi-
ciency without adjustment. Figure 6-2 shows a typical deep-well turbine
pump.
The submersible pump is simply a turbine pump close-coupled to a submer-
sible electric motor attached to the lower side of the turbine. Both pump
and motor are suspended in the water, thereby eliminating the long-line
shaft and bearing retainers that are normally required for a conventional
deep-well turbine pump. Operating characteristics are the same as for
deep-well turbine pumps. Figure 6-3 shows a typical submersible pump.
Propeller Pumps
Propeller pumps are chiefly used for low-lift, high-gallonage conditions.
There are two types of propeller pumps, the axial-flow or screw type, and
the mixed-flow. The major difference between the axial-flow and the mixed-
flow propeller pumps is in the type of impeller (Figure 6-4).
The principal parts of a propeller pump are similar to the deep-well tur-
bine pump in .that they have a head, an impeller, and a discharge column. A
shaft extends from the head down the center of the column to drive the
impeller. Some manufacturers design their pumps for multi-stage operation
by adding additional impellers where requirements demand higher heads than
obtainable with single-stage pumps.
Where propeller pumps are adapted, they have the advantage of low first
cost and the capacity to deliver more water than the centrifugal pump for a
given si*e impeller. Also, for a given change in pumping lift, the pro-
peller pump will provide a more nearly constant flow than a centrifugal
pump. Their disadvantage is that they are limited to pumping against low
heads.
6-4
BEARING
IMPELLER
SHAFT
ELECTRIC
MOTOR
DISCHARGE:
DISCHARGE
COLUMN
BOWL
IMPELLER
Figure 6-2, Deep-well Turbine Pump
6-5
WC1-U CASING
OlSCHAflGE PIPE
CUCCTHIC MOTOR
Figure 6-3, Submersible Pump
6-6
ELECTRIC MOTOR DRIVE
BASE PLATE
DISCHARGE
DISCHARGE ELBOW
DISCHARGE COLUMN
SHAFT ENCLOSING TUBE
AXIAL FLOW
IMPELLER
PUMP ABOVE THIS POINT
SAME AS AXIAL FLOW PUMP
LINE SHAFT BEARING
STRAINER
MIXED FLOW
IMPELLER
DETAIL OF SINGLE STAGE
AXIALFLOW M1XEDFLOW
Figure 6-4. Propeller Pumps
6-7
Pumps
single stage propeller pumps are limited to pumping
')>;t, h-;<i-Js of around 10 feet. By adding additional stages, heads
j'i t-j !j reet are obtainable. These pumps are available in sizes
;ir.'j rrr,n hi to 43 inches. The impeller has several blades like a
p'onsl1er. The blades are set on the shaft at angles determined
r.jiny no the head and speed. Some manufacturers have several pro-
'- i r J *"or the same size of pump, thereby providing for different
KitiM-s and heads. The water is moved up by the lift of the pro-
Mt 1 bUrie<; and the direction of flow does not change as in a
rif-jqal puTip. A spiral motion of the water results from the screw
jn, hut fay be corrected by diffusion vanes.
J-
OW propeller pump is designed especially for large capaci-
*uh n<;.ierate heads. The smaller size single-stage pump will
it- "rriMoritly at low heads of from 6 to 26 feet. The multiple
imi l,iry K -,\M pumps will handle heads up to approximately 125
lfl ^ 3r " generally built in sizes ranging from 10 to 30 inches
.' <N~Mo pump uses an open vane curved blade impeller which com-
. th --crow and centrifugal principles in building up the pressure
'^^^c a capacity range of from 1 S 000 gpm to approximately
'H' Bending on size, stages, and heads. The mixed-flow pump
' C1 y agalnSt hfgher heads than the ^al-flS
advanUges and disadvantages of commonly used
^^"^ f Pumping effl ciency cannot be over emphasized
^^ " S6eing the P-P curvestfore
ost co^on appro cho use qr^Th'r^ 5 / 56 tables ' but
llustrated in Figure 6-5. 9 P he four ty ^ s of cur ves are
nco od head
curves will dip downward to th HnSt t ^ u dlschar 9e. Generally these
which ni have multiple humps T h 9 mn" f h U9h there are some P^P
P-PS have a shape similar tS'the Sn e ^n Flg^'s^ 8 '^ ^**"
-^''
6-6
Table 6-1 Advantages and Disadvantages of Commonly Used Irrigation Pumps
___ HORIZONTAL CENTRIFUGAL PUMPS
Advantaq^ Disadvantages
High efficiency is obtainable. Suction lift is limited, should be
within 20 feet of water surface.
Efficiency remains high over a range
of operating conditions. Requires priming.
Adaptable to a range of operating Loss of prime can damage pump,
conditions.
May overload if head Is decreased.
Simple and economical .
Available head per stage is limited.
Easy to install .
Does not overload with increased head.
Produces a smooth even flow.
VERTICAL CENTRIFUGAL PUMPS
A*Jyantaae_s__ Dj_s_a_d_v ant ages
May be exposed or submerged Maintenance costs may be high to the
shaft and bearings.
Submerged pump does not require
priming. Usually restricted to pumping heads
of no more than 50 feet.
May overload if head is decreased,
More expensive than horizontal
centrifugal .
TURBINE PUMPS
D i s advantages
Adapted for use uT wells. Higher initial cost than centrifugal.
Adapted for use where water surface Requires closer setting than cen-
fluctuates. trifugal pumps.
:an be adapted for high heads and large Efficient over narrower range of
discharges. operating conditions than centrifugal
pumps.
Small chance of losing prime.
Not adaptable to change in speed.
Requires additional stages for larger
heads,
Difficult to install and repair.
PROPELLER PUMPS
_____ _
Dfsaciv ant ages
limple construction. Not suitable for suction lift.
adaptable to high flow against low heads Requires proper clearances between
(0-25 feet for axial-flow pump) walls and bottom of pump,
(6-45 feet for mixed-flow pump)
fficient at variable speeds.
an pump some sand with water.
eeds no priming. _ ___ _ _____
fi-o
Figure 6-5. Typical Pump Performance Curve
~p r-rnt: JDH
8^ T- Efficiency^
C'irves
80 '
..... . _.^. .-. .
--.^. (.--.. i . " f **~\ I ' "I'-'T It 1 - - - . -. > T*^-; ^_^
me 11 OFF BOTTOM
SHUT Orf HEAD *MUT OFF B M f
II 123.0 FT. 28 5 B. HP.
1 1 5.6 FT, i5.9B.HP
104.7 FT. it 6B.HP.
(7) 96.4 FT. 20 OB HP
-: -ir . r^:!rx,'rv' -:
::1 L -;;t...40Q ./.,. 600 .'. 90O . 1 100Q_... L
14LD
US GALLONS PER MINUTE
Curve No. 4805999 Impeller No. 2634705 1760 RPM
6-10
If a pump is operated against a closed valve, the head generated is
referred to as the shut-off head. Shut-off head is shown in Figure
6-5. Note that the efficiency of the pump at this point is zero
because the pump still requires energy to drive it. For turbine or
centrifugal pumps it is necessary to know the shut-off head. The pipe
on the discharge side must be capable of withstanding the shut-off
head in case a valve is accidently closed on the discharge side.
For a turbine pump the manufacturer's reported efficiency is for a
specific number of stages. If, for a specific application, the number
of stages differs, then it is necessary to adjust the reported effi-
ciencies upward or downward depending on the number of stages. Figure
6-5 indicates that efficiency values as graphed must be lowered 1.8
percentage points for only a single stage pump, lowered 1.2 percentage
points for a two-stage pump, lowered 0.6 percentage point for a
three-stage pump, and would remain unchanged for more than three
stages.
Efficiency Versus Discharge
The efficiency discharge relationship is drawn as a series of envelope
curves upon the TDH-Q curve in Figure 6-5. There is generally only
one peak efficiency which is related to a specific discharge. If the
pump can be operated at this discharge then for a given amount of
energy input to the pump, the output work will be maximized.
Efficiencies vary between types of pumps, manufacturers and models,
Generally, the larger pumps have higher efficiencies. The efficiency
also is related to types of materials used in construction, the finish
on the castings or machining, and the type and number of bearings
used. For example, enameled impellers, which are smoother than bronze
or steel, will result in a higher efficiency.
Efficiency is defined as the output work divided by the input work.
See Chapter 8 for discussions on pumping plant efficiency.
Input Power Versus Discharge
The input power if referred to as the brake horsepower required to
drive the pump. The curve is commonly called bhp-Q curve. It should
be noted that even at zero discharge when the pump is operating
against the shut-off head, an input of energy is needed.
The shape of the bhp-Q curve can take several different forms. The
most common form for irrigation pumps is similar to the curve of
Figure 6-5. In other instances the bhp-Q curve will have the highest
horsepower demand at the lowest discharge rate and the required input
power will continue to decline as Q increases. The shape of the bhp-Q
curve is a function of the TDH-Q and Eff-Q curves.
6-11
Net Positive Suction Head Versus Discharge
The fourth characteristic curve is the net positive suction head
required, NPSHR, versus discharge relation. The NPSHR is the amount
of energy required to move the water into the eye of the impeller and
is a function of the pump design. This characteristic also varies for
different types of pumps, manufacturers and models. Its value is
determined by the manufacturer from laboratory tests. The NPSHR is a
function of pump speed, impeller shape, liquid properties, and the
discharge rate. If sufficient energy is not present in the liquid on
the intake side of the pump to move the fluid into the eye of the
impeller, then the liquid will vaporize and pump cavitation will
occur.
Theoretically s if a pump could be designed to produce a perfect vacuun
at its center and it was being operated at sea level, the atmospheric
pressure of about 14.7 psi acting downward on the surface would force
water up the suction line to the pump a distance of 34 feet (14.7 psi
x 2.31 ft/psi). In practice this is impossible first because a per-
fect vaccum cannot be created at the center of the impeller and seconc
because there are losses due to friction created by the flow through
the suction line and losses due to turbulence at the entrance to the
suction line and at the entrance to the impeller.
To assure that the required energy is available, an analysis must be
made to determine the net positive suction head available, NPSHA. Th<
available head is a function of the system in which the system opera-
tes and can be calculated for all installations. If the NPSHA does
not exceed the NPSHR then the pump will cavitate. The equation for
computing NPSHA is as follows:
NPSHA = 144 Pa - Pv
- h + z
f
where Pa = pressure, psia, on a free water surface, atmospheric
Pv = vapor pressure, psia, of the water at its pumping temperat'
hf = friction loss in the suction line, ft of water
z = elevation difference, ft (suction lift) between pump cente
line and water surface. If the suction water surface is
below the pump centerline, z is negative.
w = unit weight of water, Ib/ft3
VI 11
fii
NPSHA
Vapor pressure
Frfction loss
Suction lift
Absolute Zero Pressure
Figure 6-6 Schematic for NPSHA Versus Atmospheric Pressure,
Suction Lift, Friction and Vapor Pressure
6-12
A person should keep in mind that there are many pump manufacturers and
many pump models. If the first pump investigated does not fit the needs,
then the designer should investigate other pumps. There should be pumps
available to meet the particular situation. Also, do not expect a pump to
maintain its peak efficiency over the years. Select a pump capable of
filling the demands at a little less than its peak design efficiency.
Power Units
The power required to pump depends on (1) the quantity of water, (2) the
total head or pressure against which it is pumped, and (3) the efficiency
of the pump. See Chapter 8 for computing horsepower requirements of power
units.
Many types of power units can be used for operating pumps. An old automo-
bile engine belted to the pump may do the job at low initial cost, but
operating cost is likely to be high and service unreliable. Money is
often wasted by investing in old inefficient engines not suited to the
job.
It must be remembered that a farm tractor used to furnish power will not
be available for other farming operations and may require modification of
the cooling system. Farm tractors are not built for continuous operation
such as is needed to power an irrigation pump. If a tractor is used, it
should be large enough so that it is not necessary to operate the engine
at full throttle. Also, the motor should be equipped with safety devices.
Where available at reasonable rates, electricity is usually the most
satisfactory source of power for irrigation pumping. Electric motors
offer high efficiency, reliability, compactness, and low maintenance cost;
which makes them especially desirable for operating pumping plants.
Internal combustion engines are most widely used where electric power is
not available or where it is too expensive. These include gasoline and
diesel engines. The former type may be adapted to burn natural gas, kero-
sene, or distill ages. Proper cooling is very important when internal com-
bustion engines are used for irrigation pumping.
Gasoline engines cost less initially than diesel engines and are better
adapted to smaller loads and shorter operating hours. Diesel engines are
best for heavy duty and generally give longer service. The choice of an
internal combustion engine for a given job depends on the size of load,
length of operating-periods, and the required life of the engine.
Table 6-2 lists some of the advantages and disadvantages of various types
of power units.
6-13
u-t. mivdNtayea diiu u i bduvdntctyeb u" vdr loub rower units
DIESEL
Advantages
Variable speed allows variation
of pumping rate and horsepower.
Moderate depreciation rate.
Can be moved from site to site.
Fuel costs are usually lower than
gasoline or UP.
Disadvantages
Service may be a problem.
High initial cost.
GASOLINE
Advantage?
Variable speed allows variation of
pumping rate and horsepower.
Parts and service are usually
available locally on short notice.
Can be moved from site to site.
Disadvantages
High depreciation rate.
High maintenance cost.
Fuel costs may be high.
Fuel pilferage may be a problem.
NATURAL GAS
Advantages
Variable speed allows variation of
pumping rate and horsepower.
Moderate depreciation rate.
Low energy costs if gas is avail-
able at favorable rates.
Disadvantages
Requires natural gas pipeline.
Not easily moved from site to site.
LP GAS
Advantages'
Variable speed allows variation of
pumping rate and horsepower.
Parts and service are usually
available locally on short notice.
Moderate depreciation rate.
Disadvantages
Special fuel storage must be provided
Fuel costs may be high.
ELECTRIC MOTOR
Advantages
Long life, low depreciation.
Low maintenance.
Easily adapted to automatic
controls.
High operating efficiency.
Easy to operate.
Requires no fuel storage.
Disadvantages
Constant speed, pumping rate can be re-
duced only by increasing head on system.
Requires three-phase power or phase
converter.
Not easily moved from site to site because
of the necessary electric service.
Electrical storms may disrupt service,
sometimes many miles from the site.
6-14
Irrigation pumping plants often operate for long periods without attention.
For this reason, power units should be equipped with safety devices to shut
them off when changes in operating conditions occur that might cause
damage. Such changes include when: (1) oil pressure drops, (2) coolant
temperature becomes excessive, (3) pump loses its prime, (4) the
discharge pressure head drops, or (5) oil level drops.
Pumping Plant Head
For proper pump and power unit selection the total dynamic head (TDK) must
be computed. A knowledge of certain terms is necessary to compute the TDH
and in discussing pumping plant head requirements.
Pressure-Pressures are usually measured with a gauge. When water in a con-
tainer is at rest, the pressure at any point consists of the weight of
water above the point (i.e., water weighs 62.4 pounds per cubic foot or
0.433 pounds per square inch (psi). The column of water is referred to as
head and is expressed in feet. Head can be converted directly to pressure
in evaluating systems by multiplying head by 0.433. Conversely, pressure
can be converted to head by multiplying pressure by 2.31.
Dynamic Head - An operating sprinkler system has water flowing through the
pipes. Thus, the head under which the system is operating is dynamic.
Dynamic head is made up of several components as follows:
1. Static Head - Static head is a vertical distance. It is the
distance through which the pump must raise the water.
Where the water source is below the pump centerline, the distance
from the water surface to the pump centerline is called the static
suction lift or head. For centrifugal pumps, friction losses in
the suction pipe and fittings should be included.
The elevation difference between the centerline of the pump and
the point of discharge is referred to as the static discharge
head.
Total static head is the summation of the static suction lift or
head and the static discharge head.
2. Pressure Head - Sprinkler operating pressure converted to head
is termed pressure head. The sprinkler converts pressure head
to velocity head which carries the water out into its trajectory.
3. Friction Head - The friction caused by water flowing through a
pipe decreases pressure in the pipe. The pump must overcome
this loss which is termed friction head which is a function of
size, type, condition and length of the pipe and water velocity
in the pipe. Similar losses are incurred by water flowing
through pipe fittings. Losses through specific fittings can be
stated as an equivalent length of pipe of the same diameter and
can be taken from Appendix C.
6-15
Losses in fittings and valves can also be computed by the formula:
h = Kv2
f 29
Where: h = friction head loss in feet
f
K = resistance coefficient for the fitting or valve
v2 - velocity head in feet for a given discharge
2g and diameter
Values of the resistance coefficient K may be taken from Appendix C.
4. Velocity Head - Flowing water represents energy and work must
be done by the pump to impart motion to the water. The
resistance to movement by the water is similar to friction.
Velocity head is computed by squaring the velocity and dividing
by two times acceleration due to gravity or
H = v2
v 2 g
Velocity is measured in feet per second and can be computed from:
V = 0.408 x gpm
2
Where gpm is discharge in gallons per minute and is inside diameter
of the pipe. Hv values are small and usually negligible unless large
volumes are pumped through small diameter pipes.
Total Dynamic (TDK) - As mentioned, this is a very important factor in
selecting the pumping unit. An accurate estimate is necessary to
assure a satisfactory pump performance. First calculate the com-
ponents discussed in the preceding paragraphs and add them together:
Total dynamic head = total static head + pressure head + friction head
See Figure 6-7 for a sketch showing the above terms, NEH Section 15,
Chapter 8, Figures 8-19, 8-20> and 8-21 give examples of computing TDH
for centrifugal pumps, turbine pumps, and propeller pumps,'
respectively,
6-16
Sprinkler head
Frlclion head
Pressure head-
TDK - total static head + pressure head + friction head
Where
1. Total static head static discharge head + static suction
head or lift
a. Static discharge head is the difference is elevation
between the centerline of the pump and the elevation of
the sprinkler orifice or other point of use.
b. Static suction lift is the difference in elevation
between the water surface elevation being pumped and the
centerline of the pump.
2. Pressure head is the average operating pressure for the
lateral.
3. Friction head is pressure loss due to friction in the main,
lateral suction pipe, and fittings and valves.
Figure 6-7 Elements of A Pumping Plant and the Corresponding
Elements of Total Dynamic Head Used In Calculating
Pump and Power Requirements
6-17
DISTRIBUTION PIPELINES
SELECTION
When selecting the distribution pipelines, both the annual installa-
tion cost and the annual operating cost should be considered. The
installation cost of smaller diameter pipelines is less, but the
operating cost (pumping po^er cost to overcome pipeline friction) will
be more than for larger diameter pipelines. The most economical size
would be the one with the smallest sum of annual installation and
operating costs. This requires the comparison of the sum of installa-
tion and operating costs of the various pipeline sizes being
considered.
The annual installation cost is computed by multiplying the initial
installed cost by the appropriate amortization factor. The amor-
tization factor can be found from Chapter 9, Table 9-1. Use the same
life expectancy and interest rate that will be used in the economic
evaluation.
The annual operating cost of a pipeline essentially consists of only
the pumping power fuel cost to overcome pipeline head loss (friction)
since the total static head and pressure (operating) head remains
constant when comparing pipeline sizes, only the friction and velocity
head change. The annual fuel cost can be found by using the following
formulas.
Fuel cost per yr = bhp x hr/yr x cost/unit of fuel
bhp-hr/unit of fuel _!/
Where bhp = TDH x Q
3690 x pump eff. x drive eff.
bhp = brake (dynamometer) horsepower
TDH = total dynamic head, feet
Q = capacity in gpm
I/ bhp-hr/unit of fuel is shown in Chapter 8, Table 8-1
stored in the fluid due to its mass and velocity. When a value is quickly
closed, the velocity is suddenly stopped. Since liquids are nearly
Incompressible, this energy cannot be absorbed, and the momentum of the
fluid causes a shock called "water hammer." This may represent excessively
high momentary pressures. The shutting down of a pump and then restarting
it before the system comes to rest is also a cause of excessive surge
pressure. Four factors that greatly influence the magnitude of water
hammer (surge pressure) are:
1. Length of pipeline (the longer the line, the greater the shock)
2. Velocity
3. Closing time of valves
4. Diameter of pipe
Minimum valve closing times, pressure relief valves, and thrust blocks are
utilized to help minimized and/or control surge pressures. Since velocity
is the primary factor contributing to excessive surge pressure, the velocity
of pipelines generally should be limited to five feet per second. Also,
irrigators should be advised against quick closing of valves and restarting
pumps before the system returns to static rest. Another factor that
influences surge is the instantaneous stopping of electric motors whereby a
backlash condition is created and higher than normal pressures occur.
When pipeline working pressures and velocities exceed the limits generally
recommended in the SCS technical guide standards, special considerations
should be given to protect the pipeline for flow conditions and the total
pressure generated during a surge condition. Measures utilized may include
pressure-relief valves with control of valve opening and closure times. The
total pressure subjected to the mainline pipe during a surge condition is
equal to:
P Total = Po + Ps
where P Total = total system pressure during a surge (psi)
Po = the operating pressure at the time of the surge(psi)
Ps = the surge pressure: an increase in pressure over
and above the existing operating pressure at the
time of the surge(psi)
The approximate magnitude of the surge pressure (Ps) for gradual closure
conditions may be calculated by the following formula (reference - Rainbird
Design Guide For Turf and Ornamental Irrigation Systems 1976, p. 54)
Ps = V x L x .07
where V = original velocity of flow at time of surge (ft/sec)
L = the length of the straight mainline pipe which extends
between the water source and the point in the mainline
(valve or pump location) where the flow was stopped (feet).
t = the approximate time required to stop the flow of water
(i.e. time to close the valve - seconds)
6-19
Closure is considered instantaneous whenever t is less than 2 L/U where
U is the velocity (fps) of a pressure wave in the pipe as follows:
0.5 0.5 I
U = (E/R) (l/(l+ED/EpT))
6
where E = modulus of elasticity of water, 43.2 xlO psf
2 4
R = density of water, 1.94 Ib sec per ft
D = diameter of pipe, ft
6
Ep = modulus of elasticity of pipe material, 57.6 x 10 psf for
Type 1, Grade 1 or 2 PVC pipe
T = thickness of pipe wall, ft
For instantaneous closure the maximum surge pressure may be calculated
as follows:
Ps = RUV |
where Ps, R, U s and V are as defined above.
1[ Reference - Standard Hbk. for Civil Eng. by F.S, Merritt McGraw-Hill,
Inc. Page 21-33.
If it is not practical to keep the total pressure during a surge equal
to or less than the working pressure rating of the pipe, the total
system pressure during the surge should be less than 75 percent of the
burst pressure rating of plastic pipe. The burst pressure rating of
plastic (PVC) pipe is approximately 3.0 times the nominal working
pressure rating (PVC 1120, 1220, & 2120, see ASTM D 2241)
Safety Devices
Figure 6-8 illustrates many of the devices that enhance the water deli-
very process and protect the pipeline investment. The relative location
of each of these devices is important and alteration of their location
should be reviewed carefully.
Manual Valves
valves are principally used to isolate sections of a system for
ion, for purpose of repair and for manual drain valves. The
"hould be gate valves rather than globe valves to keep friction
minimum. Generally, cross handles are preferred as the access
ves is through valve sleeves. A sprinkler control valve key
open them. Non-rising stems are often required.
y a gate valve is used as a flow control, but its use is
hydraulically simple systems.
6-20
Check Valves
into the ground water formation when chemical injectxon xs used.
Check valves can be of the swing-check variety (which depends on it. own
pressed into the upstream opening by backflowj.
sr.'sss ss-r-sr. rrr;:,
rapid buildup of line pressures during pump start-up.
Pump "
Pressure Release
Valve
Combination
Air Valve
Air-release
Valve
Pressure
Reducing Valve
and Rate of
Flow Controller
Vacuum
Release
Valve
Chemical
Injection
Thrust
Blocking
Figure 6-8. Illustration of Valve I
6-21
nti "Syphon or Backflow Prevention Units
outh Carolina passed legislation June 6, 1986 CSC Code of Laws, Section
6-1-140) requiring installation of an anti-syphon or backflow preven-
ion device on any irrigation system designed or used for the applica-
ion of fertilizers, pesticides or other chemicals. Effective June 6,
388, all irrigation systems must be in compliance with this new law.
i anti-syphon device could consist of the following components:
Functional Check Valve. Such valve shall be equipped with re-
placeable disc and shall be serviceable with conventional tools.
This valve shall be located in the irrigation supply line between
the irrigation pump and the point injection of fertilizer,
pesticide or chemical. This valve, when installed, shall be on a
horizontal plane and level.
Low Pressure Drain. Such drain shall be at least three-fourths
inch in diameter. It shall be located on the bottom of the hori-
zontal pipe between the functional check valve and the irrigation
pump. It must be level and must not extend beyond the inside sur-
face of the bottom of the pipe. The outside opening of the drain
shall be at least two (2) inches above grade.
) Vacuum Relief Valve. The low pressure drain shall include a
vacuum relief valve as a component part, or shall be complemented
with a separate vacuum relief valve. The separate vacuum relief
valve shall be at least three fourths inch in diameter and shall
be located on the top of the same horizontal pipe section in which
the low-pressure drain is located.
ai n Valves
iln valves can be either manual or automatic and are used to drain the
;er from pipe lines. Manual drain valves are usually used on distri-
-ion lines which are continually under pressure. When the system is
iterized, the valve is opened and the water is drained out of the
es. Often pressurized air is also introduced at other points of the
tern to clear out any pockets of water caused by low pipe lines.
ual drain valves are normally located at lower pints of the system and
uld be an angle valve which incorporates a flexible and replaceable
U
omatic drain valves are usually a spring and ball combination and are
d in lateral lines which are under pressure only when the sprinklers
operating. When the water pressure in the pipe reduces, the spring
relieved of the pressure contracting it, it expands, pushing the ball
the seat to allow water to flow through it to the atmosphere.
ssure Regulating Valves
isure regulating valves have an automatic internal throttling action
Deduce high upstream pressures to a constant downstream pressure.
lin limits, a pressure regulator can throttle a wide range of higher
.sures to deliver the constant downstream pressure. There is always
nherent loss through the regulator itself due to friction, in
6-22
addition to the throttling action. They cannot increase pressure A
given pressure regulator can deliver a constant downstream pressure at
several flow rates. If a pressure regulator is placed upstream of a
gate valve, the flow rate through the combination can be varied by
opening or closing the gate valve. However, at all flow rates the maxi-
mum discharge pressure of the regulator will be the same. A pressure
regulator only creates a constant, desired pressure immediately
downstream of itself. Further downstream the pressure will be
different.
Pressure-Release Valves
Pressure-release valves are attached to a pipeline and exhaust water from
the pipeline into the atmosphere when the pressure in the pipeline
exceeds a set value. They are located where high pressures will occur,
such as at the bottoms of hills. They are also located immediately
upstream of valves which could create sudden pressure buildups if closed
quickly. Pressure relief valves do not prevent pressure fluctuations;
they do prevent water pressures in the line from exceeding set valves.
Air Valves
General
There has been confusion in the industry as to the difference between an
air-release valve, air-and-vacuum valve and a combination air valve.
First it must be stated that these valves are for liquid systems and
not for air or gas systems. To clarify the difference between these
valves, the following will describe the specific purpose, function and
operation of each valve.
Air-Release Valves
An air-release valve can be described as a device which will automati-
cally release accumulated small pockets of air from high points in a
system while that system is in operation and under pressure.
If we stop to consider some of the problems associated with air in a
system, we can better understand how air-release valves can be utilized
to eliminate those problems.
First of all, as a function of nature, some of the air entrained in a
system will settle out of the liquid being pumped and collect at high
points within that system. If no provision is made to remove this air
from the high points, a small pocket of air will grow in size as addi-
tional pockets of air accumulate. This action will progressively reduce
the effective area available to the flow of liquid and create a
throttling effect as would a partially closed valve. The degree to
which the flow is reduced and some of the ensuing problems are described
in the following paragraphs.
6-23
In many instances, the liquid flow velocity will be sufficient to par-
tially break up an enlarging pocket of air and flow a portion of it
downstream to lodge at yet another high point. This ability of the flow
velocity to trim back the size of an air pocket, as it grows larger, may
prevent the flow rate from being drastically reduced. However, as a
result of the throttling effect caused by the presence of this remaining
air, the flow rate will always be less than intended and power consump-
tion wil 1 be increased.
This type of problem is difficult to detect and if allowed to go
uncorrected, constitutes a constant drain on system efficiency and will
thereby increase operating costs.
In more extreme instances, it is actually possible for an enlarging
pocket of air collecting at a high point or a series of high points
within a system, to create a restriction to such a degree that the flow
of liquid is virtually stopped or at the least greatly reduced. In a
severe situation such as this, the problem is more easily identified and
the installation of air release valves at high points in the system
should be taken as a corrective measure to remove the restrictive
pockets of air, thereby restoring system efficiency.
Of a more serious nature is the factor that sudden movements of these
air pockets can result in a rapid change in the velocity of the liquid
being pumped. The dyanmics involved in this change of velocity can be
substantial and can lead to high pressure surges and other destructive
phenomenon. As we can see, the problems associated with air in a system
can range from mild but costly to severe and potentially destructive.
The ideal situation is of course to anticipate those problems as
outlined earlier and prevent the accumulation of air through the
installation of air-release valves at all high points within a system,
thereby avoiding the negative consequences described.
Operation of Air-Release Valves
First of all, consider the valve installed at a high point within the
system, filled with liquid and under system pressure.
Now, during system operation, as small amounts of air enter the valve
from the system, they will displace the liquid within the valve and
lower its level relative to the float. When the liquid level has been
lowered to the point where the float is no longer buoyant, the float
will drop. This action opens the valve orifice and allows the air which
has accumulated in the upper portion of the valve body to be released to
the atmosphere. As this air is released, the liquid level within the
valve once again rises, lifting the float and closing the valve orifice
This cycle automatically repeats itself as often as necessary. The abil
lifcy of the valve to open and release accumulated air under pressure is
achieved through the use of a leverage mechanism. When the float is no
longer buoyant, this mechanism produces a greater force to open the
valve than the system pressure produces against the valve orifice, which
attempts to hold the valve closed. Accordingly, for a given air-release
6-24
valve, the higher the system pressure, the smaller the orifice diameter
must be allow the valve to open and release accumulated air.
Conversely, in the same valve, the lower the system pressure, the
larger the orifice diameter that can be used to release accumulated air.
It should be noted, an air-release valve is intended to release pockets
of air as they accumulate at high points during system operation. It
will not provide vacuum protection nor will it vent large quantities of
air quickly on pipeline fill, air-and-vacuum valves are designed and
used for the purpose.
Air-release valves should always be installed on the discharge side of
the pump having a suction lift and should be as close to the pump check
valve as possible.
Air-and-Vacuum Valves
An air-and-vacuum valve (also referred to as air-vacuum-release and air-
vent-and-vacuum release) can be described as a float operated device,
having a large discharge orifice equal in size to its inlet port, which
will automatically allow a great volume of air to be exhausted from or
admitted into a system as circumstances dictate.
If we consider its use on pipeline service, we would find the following
condi tions prevail :
Prior to filling, a pipeline is thought to be empty. But this is far
from true, for in reality it is filled with air and the presence of this
air must be taken into consideration when filling the pipeline. It must
be exhausted in a smooth and uniform manner to prevent pressure surges
and other destructive phenomenon from taking place.
In addition, air must be allowed to re-enter the pipeline in response to
a negative pressure in order to prevent a potentially destructive vacuum
from forming. It should also be noted that even in those instances
where vacuum protection is not a primary concern, some air re-entry is
still necessary to properly drain a pipeline.
To perform those functions as outlined above, air-and-vacuum valves are
installed whereever there is a high point or a change in grade.
Operation of Air-and Vacuum Valves
As the line is filled, the air present in the pipeline Is exhausted to
atmosphere through air vacuum valves mounted at high points in the
system. After all the air has been exhausted, water from the pipeline
will enter the valve, lift the float and close the valve orifice. The
rate at which air is exhausted is a function of a pressure differential
which develops across the valve discharge orifice. This pressure dif-
ferential develops as water filling the pipeline compresses the air suf-
ficiently to give it an escape velocity equal to that of the incoming
6-25
fluid. Since the size of the valve controls the pressure differential
at which the air is exhausted, valve size selection is a very important
consideration.
At some time during system operation, should the interal pressure of the
pipeline approach a negative valve due to column separation, draining of
the pipeline, power outage, pipeline break, etc., the float will imme-
diately drop away from the orifice, and allow a flow of air to re-enter
the pipeline. This action will minimize the potential vacuum and pro-
tect the pipeline against collapse or other related damage. The size of
the valve will dictate the degree to which the vacuum is minimized,
therefore, valve size selection is once again a very important
consideration.
The valve, having open to admit air into the pipeline in response to a
negative pressure, is now ready to exhaust air as the need arises. This
cycle will automatically be repeated as often as necessary.
One additional point must be made. While the system is in operation and
under pressure, small amounts of air may enter the valve from the pipe-
line and displace the fluid. Even though the entire valve may even-
tually fill with air, the air-and-vacuum valve will not open. The
system pressure will continue to hold the float against the valve ori-
fice and keep the valve closed. To reiterate, an air--and vacuum valve
is intended to exhaust air during pipeline fill and to admit air during
pipeline drain. It will not open and vent air as it accumulates at high
points during system operation, air-release valves are designed and used
for that purpose,
Combination Air Valves
As the name implies, this valve combines the operating features of an
air-and vacuum valve and air-release valve.
It is utilized at high points within a system where it has been deter-
mined that the functions of air-and-vacuum and air-release valves are
needed to properly vent and protect a pipeline.
The valve is available in two body styles, the single housing com-
bination and the custom built combination.
The single housing combination air valve is utilized when compactness is
preferred or when the potential for tampering exists due to accessibi-
lity of the installation. This style is most popular in the 1", 2" and
3 JI sizes with the 4" and 6" sizes used to a lesser degree.
The custom built combination air valve is a standard air-release valve
piped with a shut off valve to a standard air-and-vacuum valve. It has
greater^versatility than the single housing style because many different
model air-release valves with a wide range of orifice sizes can be uti-
lized. This style is most commonly used in sizes 4" through 16".
6-26
When there is doubt as to whether an air-and- vacuum valve or a com-
bination air valve is needed at a particular location, it is recommended
that the combination air valve is selected to provide maximum
protection.
Thrust Blocks
Thrust blocks are important components of irrigation water conveyance
systems. They are required at abrupt changes in pipeline grade or
alignment or changes in size to protect certain type pipelines from
failure due to axial thrust of the pipeline. The thrust block should be
designed in accordance with instructions contained in the appropriate
Technical Guide for Irrigation Water Conveyance, Code 430.
Accessories
Booster Pumps
The booster pump can be used in a large irrigation system where compen-
sations are necessary for pressure losses due to elevation. Booster
pumps usually are of the centrifugal type which produce pressure by
forcing movement of water. A booster does as its name implies, boosts
the pressure. If the pressure at a certain point in a system is 30 psi
at 20 gpm and the system requires 50 psi at 20 gpm at that point, a
booster pump rated at 20 psi aL 20 gpm can be installed in the line.
Pneumatic pressure tanks are often used where a wide variance of gallo-
nage requirements exists. The pressure tank will relieve the pump from
kicking on for a short period of time when a low gallonage demand is
made. "The tank acts as a pressurized reservoir of water with expanding
air forcing water out of the tank to fulfill low and infrequent water
demands. Often times a small "jockey" pump is used to replenish the
tank if low demands exist for a period longer than that for which the
tank can provide.
An example for the above case would be to have the "jockey" pump acti-
vate, by way of a pressure switch, at 120 psi. It would continue to run
until pressure tank is replenished to 140 psi. If the demand was
greater than the jockey pump, the pressure would continue to decrease
until it reached the low limit of the pressure switch of the main supply
pump. At that point the main pump would activate. If more than one main
pump is used, they would be activated in turn as the pressure continued
to drop. See the sketch on the following page.
If the pressure tank is too small for low gallonage demands, it will
cause frequent and repetitive start-up of the pumps. This can also hap-
pen it the tank becomes waterlogged (the air is absorbed in the water
causing a loss of the volume of air.)
6-37
CUT OFF PRESSURES CUT ON PRESSURES
140 P.SI.
JOCKEY PUMP
MAIN PUMP*
MAIN PUMP #2
130 PS.I.
130 P.SI.
no P.SI
iOOPSt
90 P.SI.
80 P.S.I.
JOCKEY PUMP (RUNS UNTIL PUMPING PRESSURE
BUIUDS TO 14O P.S.U
MAIN PUMP #1 (RUNS UNTIL PUMPING PRESSURE
BUILDS TO 130 PSU
MAIN PUMP # 2 (RUNS UNTIL PUMPING PRESSURE
BUILDS TO 115 PSI)
An alternative for a pressure tank in a system where the demand varies
widely is recirculation using a "dump" valve. Recirculation means to
take the water supplied by the pump in excess of the water demanded of
the system and dump it back into the supply. The dumping should be back
into the reservoir as just repiping it back to the inlet can cause
severe heating of the water when the demand is small, making the recir-
culated water volume large. A pressure relief valve is used to control
the amount of water to be recirculated. Pressure tanks and the related
equipment necessary for proper operation can become a maintenance
headache -so should be designed by an expert in the field of pumps and
tanks.
Figure 6-9 is a typical system using a deep well pump with a pneumatic
pressure tank. This system has an automatic air replenishing feature
which can't normally be used when pumping from a reservoir using hori-
zontal centrifugal pumps.
6-28
TO SYSTEM.
TANK SADDLES
COMBINATION STARTER
DEEP WELL PUMP
4- RUBBER HOSE CONNECTION
5- FLO AT VENT VALVE
FILTER
7-WATER GAUGE
8- AUTOMATIC DUAL PRESSURE AND
9- PRESSURE GAUGE
10-PRESSURE RELIEF VALVE
((-PRESSURE TANK
1 2- SOLENOID VALVE
The water in the pump column (3) drains back into the well after each
pumping cycle, replaced by air entering through the float vent valve
(5). When the pump is started again, some of the air is forced into the
tank, replenishing the air supply there. Excess air is vented to
atomaphere by the float operated level control valve (8) opening the
solenoid valve (12). The float in the control valve (8) will close the
solenoid valve when the level is proper, readying the system for the
next pumping cycle.
Figure 6-9. Typical System Using A Deep Well Pump
With A Pneumatic Pressure Tank
6-29
Pressure Gauges
Pressure gauges are desirable to have In a system so that the operator
can operate the system in accordance with the system design. The
system efficiency is often dependent upon operating pressures.
Flow Meters
Information from flow meters should decide the duration of pumping for
many systems. A flow meter is indispensable in order to have effi-
cient and economical irrigation operations. It will often reflect
water supply problems from wells or other sources and provide data
that will indicate repairs and maintenance needs in water supply
equipment.
Chemical Injectors
A chemical injector is a device which injects a rnetered amount of
liquid chemical (fertilizer, herbicides, pesticides, etc.) into the
irrigation system. Three principal methods used in the injection of
fertilizers and chemicals into irrigation systems are pressure dif-
ferential, venturi vacuum, and metering pumps. Injectors are
available to match most system needs and should be installed in the
system ahead of the filter so that any undissolved chemicals will be
filtered out before they enter the lines. If the injector is a pump
which pumps chemicals from a tank into the system, it will not contri-
bute any system pressure losses; however, when considering an injector,
it is necessary to size it so that it will inject at a higher pressure
than the main pump.
When chemicals are injected into irrigation systems there is a possi-
bility of contamination of the water supply if the injection system is
not carefully designed and safely managed. In many cases, the irriga-
tion water supply is also a drinking water supply. The irrigator has
the responsibility of protecting water quality. Water contaminated by
chemicals could affect the health of other users of the water supply.
If not properly used, chemigation exposes an irrigator to possible
liability. Safety equipment exists which will protect both the water
supply and the chemical purity in the storage tank. The possible
dangers in chemigation include backflow of chemicals into the water
source and water backflow into the chemical storage tank. Backflow to
the water source will contaminate it. Backflow to the storage tank
can rupture the tank or cause overflow, contaminating the area around
the tank, and perhaps indirectly contaminating the water source. Once
these problems are solved, the risk of liability in chemigation is not
substantially greater than the liability which arises from the field
use of agricultural chemicals utilizing other modes of application.
For technical reasons such as reduced wind drift, rapid movement into
the soil* and high dilution rates, chemigation could result in less
risk of liability than the traditional methods of chemical application
if proper backflow preventers are used.
6-30
Safety features recommended for internal combustion and electric irri-
gation pumping plants are shown in Figures 6-10 and 6-11. The safety
equipment package consists of the following items which should be in
good operating order before chemigation of any type.
1. A check valve must be installed between the pump and the chemical
injection point on the irrigation pipe. This will prevent, water
from flowing from a higher elevation in the irrigation system back
into the well or surface water supply. Thus water contaminated
with chemicals will not flow back into the water source.
2. A vacuum breaker must be installed on the irrigation pipe between
the pump and the check valve. This will allow air to enter the
pipe when pumping stops so that water flowing back to the pump
will not create a suction, pulling additional water and chemicals
with it.
3. A low pressure drain should be provided to allow the irrigation
pipe to empty without flowing back into the water source.
4. If chemical injector pumps are used, power supplies must be inter-
connected so that the injector pump cannot operate unless the
irrigation pump is also operating. If the injector pump is
mechanically driven, such as by a bell from the drive shaft of
an internal combustion engine (Figure 6-10), this is not a
problem. In this case, the power supplies are interconnected and,
when the internal combustion engine stops, the injector pump
will also slop. If, however, the chemical injector pump is
electrically driven (figure 6-11), then its electrical circuit
must be interconnected with the irrigation pump circuit to assure
that it stops when the irrigation pump stops. This precaution
will assure that the chemical injector pump does not continue
to inject into an empty irrigation pipeline, or worse., backwards
into the water supply.
5. If chemical injector pumps are used, a check valve on the chemical
injection line must be used to prevent water flow backwards from
the irrigation system through the chemical injector pump and into
the chemical storage tank. This will prevent dilution of the
chemical by the irrigation water. It will also prevent possible
rupture or overflow of the chemical storage tank and pollution
of the surrounding area.
Chemical injection line check valves are typically spring-loaded
and require a large pressure to allow fluid to flow through them.
These valves thus permit flow only when that flow is a result of
the high pressure generated by a chemical injector pump. When
the injector pump is not operating, chemicals will not leak due
to the small static pressures created by the chemical level in
the storage tank.
6. A valve must be provided for positive shutoff of ,the Chemical
supply when the injection system is not in use. This may be a
6-31
Anti-siphon Device
Vacuum
Breaker
Check
Valve
Check Valve
Pressure Switch
Discharge Line
Irrigation Pipe Line
rrigation
Suction Line
Strainer
Chemica
Tank
Figure 6-10. Chemigation safety equipment for internal combustion
engine irrigation pumping plant.
Vacuum
Breaker
Electric Motor
and Pump
Anti-siphon Device
Check
Valve
^Electrically
/Interlocked
/ Control
-^' Panels
Dram
Point
Motor
Check Valve
Pressure Switch
Discharge Line
Solenoid
Valve
Suction
Line
Strainer
Chemical
Tank
^^
Figure 6-11. Cheraigation safety equipment for electric motor
irrigation pumping plant.
6-32
manual gate valve, ball valve, or a "normally off" solenoid
valve. This valve must be installed near the bulk chemical
storage tank. It must be open only when the injector pump is
operating. It must be constructed of materials resistant to
chemical corrosion. A disadvantage of the solenoid valve is
that corrosive chemicals may cause the valve to fail to
operate after only a short period of time. A PVC ball valve
will be less affected by corrosion. However, it will require
manual operation.
7. Chemical storage tanks must be located remote from the well
site or surface water supply. Tanks should be located at a
site sufficiently remote and sloped so that contamination of
the water supply will not occur if the tank ruptures or it a
spill occurs while it is being filled.
Chlorine Injection
Chlorine injection into trickle systems is the most effective and inex-
pensive treatment for bacterial slimes. The chlorine can be introduced
at low concentration, 1 ppm, or as slug treatments at intervals as
necessary at concentrations of 10 to 20 ppm for only a ""ew minutes at a
time. Slug treatments are generally favored. Sodium hyperchlori te or
chlorine gas may be used. Sodium hyperchlorite is usually more economi-
cal and safer to use.
Filters
Filters are a necessary component of irrigation systems when the water
source is not clean enough to allow for proper operation of the system.
Filters are usually needed for pumping for channel or reservoirs and for
trickle systems.
When water is supplied from a reservoirs, ditch or lake, a series of box
screens should surround the intake of the water line to prevent debris,
plants and even fish from ending up in the irrigation system. Slotted
PVC pipe can often be used as a pump intake screen. The type filter cho-
sen for system design needs to provide the needed capacity and provide
for head loss through the filtering process. Manufacturer's information
is vital in this design aspect. Pressure gauges installed prior to
filtering and following filtering are vital to determine pressure losses
and when back washing is needed. Refer to the manufacturer's
recommendations.
Sand Filters
Sand filters are classified in many ways, but in general, have the
following features:
1. Enclosure - to house the filtration media(s) and store
the raw water until it is passed through the filtration
media(s).
6-33
2. Raw water distributor - spread raw water over filtration
media.
3. Filtration media - material used to trap the particulate
material in the raw water.
4. Underdrain - to collect filtered water and regain, ii^lt rat ion
media in the enclosure.
5. Clean out port - removal of filtration medial from the
enclosure .
Water
Gravel
Pack
B.W Valve
Ft } tered
Water
Sand
S.S.
Underdrain
Water Being Fi Itered
Sand
TTT $ ,S . Underdra
Cross Section
;-S- Gravel
Filtration Operation - Raw water enters filter through the backwash
valve, over the water distributor, through the sand bed, deposition of
the particulate material, and the filtered water is collected through the
stainless steel underdrain and discharged out the bottom.
6-34
Backwash Operation - The backwash is initiated by screwing the backwash
handle forward. This shuts off the incoming raw water and opens the
backwash port to a near atmospheric condition. The pressurized filtered
water from the adjacent filter(s) is forced through the stainless steel
underdrain, upward through the gravel pack, expanding the sand bed and
forcing the lighter particulate material out the backwash port and down
the backwash line. Screwing the backwash handle in the reverse direction
puts the sand filter back into the filtration operation.
Screen Filters
Screen filters have many different configurations but are basically
classified as;
1. Flow from insi.le out - Raw water enters interior of screen
cartridge and filtered water exits along housing body. the
support structure for the screen material is the inside of
some type cylinder or the cylinder itself is the screen.
6-35
2.
Flow from outside in - Raw water enters along housing body
and through exterior of screen cartridge. Filtered water
exits through interior of screen and out the bottom of the
housing. The support structure for the screen material is
the outside of some type cylinder or the cylinder itself
is the screen.
SUPPORT
AUTOMATION
Automation is a term applied to processes which reduce or eliminate human
labor. A fully automated irrigation system would be one that would senstl
the crops need for irrigation, turn on and operate the system and turn
off the system after the proper amount of water has been applied. Few
systems are fully automated, but solid-set and self propelled big gun,
boom, lateral move and center pivot sprinkler systems and trickle irriga-
tion systems have reduced human labor requirements for irrigation. Most
are manually turned on and operated. Mechanical or electronic
controllers can be used to activate automatic valves for automatic opera-
tion of the system. The controllers are usually programmed by the irri-
gator. Moisture sensing equipment that will signal controllers to start
and stop irrigation is still in the developmental state.
AUTOMATIC VALVES AND CONTROLLERS
This type system provides advantages for many irrigation systems and
greatly facilitates proper system management.
The system's operational sequences are programmed into the controller.
The controller directs the opening and closing of automatic valves as
needed to accomplish the operational sequences. The controller can be
mechanical or electrical. The possibility of failure from weather, etc.,
makes it necessary to have manual operable arrangement as well as having
means for quick repairs. Valves are hydraulically or electrically
operated.
The following sketches explain in greater detail the automatic valve
operation.
6-36
1. Normally Open Hydraulic - If, with a normally open valve, pressurized
water is introduced at the inlet of the valve, the water will pass
through the valve when there are no external connections to the valve
mechanism. Pressure has to be applied to the inside of the diaphragm
or piston of the valve to close it.
Pressure applied to top of diaphragm
from control tubing causes closure
of valve. ,
Pressure on top^ of diaphragm is
relieved through control tubing
allowing valve to open.
2.
Normally Closed Hydraulic - If, with a normally closed
pressurized water is introduced at the inlet of the valve, the
water cannot pass through the valve when there are no external
connections to the valve mechanism. Pressure has to be applied to
the diaphragm or piston to open the valve.
OUT
OUT
IN
Pressure applied to top side of
diaphragm through stem causing
closure of valve.
Pressure applied to lower side of dia-
phragm through control tubing causing
water on top side to be displaced
through valve and allowing valve to open.
6-37
3. Electric - Electric valves are controlled by electric current from the
controller, whereas the previously mentioned types are hydraulically
controlled by the control mechanism. Electric valves are generally of
the normally closed types with current supplied to open the valve.
Most electric valves are actually hydraulic valves electrically operat-
ed. The current energizes a solenoid which clears a passage for water
to flow to or from the diaphragm or piston allowing the valve to open.
Pressure applied to top of diaphragm Pressure on top of diaphragm is
through screened inlet causes closure relieved through solenoid assembly
of the valve. to downstream side of valve allow-
ing valve to open,
Desirable features on controllers include:
1, Infinite time adjustments on each station, (For precise
control of watering time.)
2. No time lag between stations. (To eliminate wasted watering
time. )
ant locking cabinet. (To prevent weather and
>r up to 14 days is desirable. (To allow the
gramming flexibility.)
and hour programming. (To allow the maximum in
be made quickly and simple.)
6-38
6. Sufficient stations on the controller for the area being covered.
(Usually a minimum of 11 stations to avoid the requirement of too
many controllers. }
7. Pump Circuit. (To enable a controller to kick on the pump starter
circuit when the controller begins its watering cycle.)
8. Readability of controls. (To enable the manager to understand and
decipher what he needs to know.)
9. Freeze resistance in hydraulic controllers. (To prevent damage
due to freezing in areas where the controller mst remain function-
al even though nighttime temperatures drop below freezing.)
10. U.L. listing. (To qualify for specification on federal, state,
and municipal projects.)
11. Manual override switch. (To allow checking of system without
disturbing watering program.)
12. Off master switch. (To manually cancel the automatic watering
program without disturbing program settings.)
13. Fuse protection of the timing mechanism, electric controllers, the
transformer. (To protect against damage to the timing mechanism
and transformer in the event of a circuit short.)
14. Easily removable timing mechanism. (So non-field repairs can
be made on controller.)
15. Manual operating capability if timing mechanism is removed. (To
have continuous operations if timing mechanism is removed for
repair. )
16. Filtered supply line on hydraulic controllers. (To protect the
pilot valve from plugging.)
Desirable features on valves include:
1. Low friction loss. (To allow pressure to be used in the pipes
and sprinklers. )
2. Smooth opening. (To avoid hydraulic ram conditions.)
3. Smooth closing. (To avoid water hammer conditions.)
4. High pressure rating. (To avoid equipment failure at high
pressures. )
6-39
SOUTH CAROLINA IRRIGATION GUIDE
CHAPTER 7. CONSERVATION IRRIGATION PLANNING
ontents
General ------ ..... - .......... 7-1
Definition of Conservation Irrigation Planning- - - 7-1
Plan Requirement- ----------------- 7-1
Irrigation System Plan- ------------- 7-1
Irrigation Water Management Plan- - - - - - - - - 7-2
Planning Steps- ------------------ 7-3
Preliminary Considerations- ----,------ 7-3
Collecting Basic Data -------------- 7-4
Planning the System ------- ........ 7-5
SOUTH CAROLINA IRRIGATION GUIDE
CHAPTER 7. CONSERVATION IRRIGATION PLANNING
GENERAL
The material in this section of the Irrigation Guide is intended to
help planners assist landowners in planning their irrigation
system(s). For more specific information, planners should refer to:
SCS - National Engineering Handbook - Section 15
Chapter 1 - Soi 1-Plant-Water Relationships
Chapter 3 - Planning Farm Irrigation Systems
DEFINITION OF CONSERVATION IRRIGATION
The use of irrigated soils and irrigation water in a way that insures
high production without casting either water or soil. To an irrigator
conservation irrigation can mean saving water, controlling erosion,
better crop yields, lower production costs, and continued productivity
of his irrigated land.
A conservation irrigation system is the completed arrangement of the
delivery and application facilities needed to distribute irrigation
water efficiently for all land served by the system.
PLAN REQUIREMENT
An irrigation plan can be divided into two parts;
1. An irrigation system plan which provides for a system of delivery,
application and disposal of the water that is consistent with the
soil and relief of the land being irrigated and the crops to be
grown. The system should apply irrigation water efficiently.
2. An irrigation water management plan which provides for the proper
use of water delivered. The document should provide only that
data that can be used by the landowner based on his management
ability and degree of expertise in irrigation.
IRRIGATION SYSTEM PLAN
The irrigation system plan should provide for the following:
1. The amount and kinds of the crops to be grown, the irrigation re-
quirements of the crops and the expected costs and returns of the
system.
2. A water supply that is adequate to meet the requirements of the
plan. The supply must be balanced with the irrigation require-
ments as well as other uses (frost protection, etc.). This may
require a water budget.
7-1
The si?e and layout of the distribution system needed to supply
me Ht-M' as well as the needed components.
The pn.npinq plant requirements to supply the system at the
specified rate and pressure.
5. The selacleu irrigation iiiethod LapabM of applying irrigation
water consistent with the soil characteristics and crop require-
ments.
a. Subsurface irrigation systems must he capable of moving water
to the root zone of the crop at a rate sufficient to supply
the plant requirements during peak use periods. Also, it must
be capable of draining excess water from the soil profile
during periods of high rainfall at a rate sufficient to pre-
vent crop damage due to poor aeration.
b. In sprinkler irrigation, the sprinkler spacing, nozzle sizes
and operating pressure that will most nearly meet the planned
application rate and distribution will be used. The main
lines, lateral lines, hoses, etc., must be able to supply the
water to the sprinklers at the rate and pressure required,
c. In trickle irrigation the emitters must be capable of provid-
ing the peak consumptive use of the crop on a daily basis with
a wetted area that will provide good distribution to the root
zone. The main lines, submains and lateral lines must be
capable of supplying the water to the emitters.
6. Tailwater recovery system when needed for efficient use of water v
7. The necessary practices to remove runoff and excess subsurface
water without excessive erosion or other problems,
8. A flow meter or other type of measuring devise that measures the
rate of flow and total water use, so the irrigation efficiency
and proper water use can be determined quickly.
9. Access to all areas for easy operation of the irrigation system,
normal fanning operations and removal of crops. This may involve
access roads, culverts in ditches, etc.
2. The estimated application rate, irrigation time required and
irrigation interval .
3. A method or methods to measure the soil moisture content.
4. A method or methods to determine when to irrigate (irrigation
scheduling procedure).
5. A procedure of how to compute the amount of water to apply each
irrigation.
6. The soil moisture level when irrigation is needed and priority
water needs of crops to be grown.
7. A method of evaluating the uniformity and adequacy of irrigations
and suggestions for improvement.
PLANNING STEPS
The planning aspects of irrigation system cannot be over emphasized. A
quality irrigation system plan and water management plan does not
happen accidentally but comes about through quality planning.
Planning can be divided into three phases consisting of (1) prelimi-
nary considerations, (2) collecting basic data, and (3) planning the
system.
PRELIMINARY CONSIDERATIONS
The major items requiring preliminary considerations are discussed
below:
1. Consider the capability of the soil to be irrigated. Irrigation
should be confined to land that is capable of sustaining yields
high enough for the land user to get a profit from irrigation
without soil deterioration.
2. Consider the entire farm unit even if the landowner is interested
in only one field. This will make sure that pipelines will be of
an adequate size and elevations to service the rest of the land
unit. Implementation of the plan will usually begin with one
field or one pipeline and normally will continue over a period of
time. Revisions will normally be necessary before the entire
system is installed.
3. Landowners preference - Each landowner has a preference as to the
kind of farm enterprise he wishes, which may dictate the kind of
irrigation system and application method. He may have some strong
feelings about one system over another. He will operate it much
more effectively if he hasn't been pressured into a system. The
planner needs to layout the pros and cons including the labor
requirements and economic considerations of the "best fit" system.
4. Quantity and Quality of Water - An adequate source of good quality
irrigation water must be available or there must be the possibility
7-3
of developing an adequate source. If the quantity of water is inade-
quate during the growing season, there could be crop loss even with an
irrigation system. The landowner should be presented with an esti-
mated seasonal water demand and peak use rate of the crop to be grown.
5. Wildlife wetland - locate on map all wildlife wetland in area
planned for irrigation, prepare an Environmental Evaluation, and
explain SCS policy concerning drainage and alteration of wetlands
to land user.
6. Consider that erosion control practices may need to be installed
or strengthened to protect the land from more intense use. The
erosion control system may need to be modified to prevent inter-
ference with the irrigation system.
COLLECTING BASIC DATA
After the preliminary meeting with the landowner and considerations are
given to the items discussed above, basic data should be collected.
Listed below are basic data that should be obtained.
1. List the following soil and cropping system data;
a. Soil types and area of each soil type.
b. Amount and kind of crops to be grown.
c. Water holding capacity to the depth of root zone of the
crops grown.
d. Intake rate of the soils under the cropping conditions that
may occur during irrigation.
e. Production costs before and after irrigation for crops to
be grown.
2. The water supply quantity, quality and location should be
determined.
3. Physical features that will affect the system design and location
should be placed on the layout map. This includes such items as
roads, utility lines, buildings, etc.
4. A complete topographic map may be required but in some areas the
following topographic information may be all that is needed:
a. Expected Low elevation of water supply.
b. Ground elevation of pump location.
7-4
c. Ground elevation of low and high points, along the supply
system and the irrigation system.
d. Intake rate of the soils under the cropping conditions that
may occur during irrigation.
e. Production costs before and after irrigation for crops to be
grown.
5. Locate on map all existing surface and subsurface drainage
features such as terraces, waterways, tile drains, ditches,
washes, etc., so the irrigation system can be properly planned
and cost of making the needed changes to these features can be
estimated.
6. Locate on map the needed surface and subsurface drainage
practices, such as terraces, waterways, ditches, subsurface
drains, etc. This information should be in enough detail to
estimate the cost for each needed practice.
7. The location and sizes of the existing system should be checked,
It should be determined if it is adequate in part or in whole and
how it will fit with the proposed system. The best kind of trans-
ition from the present system to the future system should be
determined.
PLANNING THE SYSTEM
The actual irrigation system can be p-lanned once the basic data has
been collected. Listed below are some steps to follow in planning the
system:
1. Decide on the type(s) of systems that will be used. Sprinkler,
trickle, subirrigation, etc. Develop alternatives for each
practical system.
Develop and plan field arrangement, consider:
a. Method of irrigation,
b. Workability, shape and access to field. Make the field as
big and as square as possible.
c. Direction of irrigation. Would changing the direction of
irrigation have any benefits?
2. Prepare the irrigation system plan:
a. Sprinkler irrigation:
(1) Determine type of sprinkler system to use: center pivot,
single sprinkler, volume gun (manual move or self move),
portable or permanent solid set.
7-5
(2) Spacing of sprinkler heads on lateral.
(3) Spacing of laterals or lane spacing.
(4) Discharge (gpm) per sprinkler head.
(5) Sprinkler discharge pressure.
(6) Lateral and mainline pressure.
(7) Application rate.
b. Trickle irrigation:
CD Determine type of trickle irrigation: drip, spray, etc.
(2) Spacing of emitters along lateral
(3) Lateral spacing
(4) Percent of design area covered by emitters
(5) Lateral and mainline pressure
(6) Discharge rate of emitter
c. Subsurface irrigation:
(1) Determine type of subsurface irrigation: open ditches,
underground pipes, or combination,
(2) Spacing of ditches and/or pipes.
(3) Number and location of water control structures.
(4) Tail water recovery or disposal.
(5) Number and location of water table measuring structures
Plan the Water Distribution System:
a. Ditch or Pipeline:
(1) Cost of each.
(2) Convenience in farming over pipeline.
(3) Value of land displaced by surface ditch. How much
income would be generated if it was in production?
7-6
b. Type of turnout to field:
(1) Gated concrete turnout, port, or siphon for ditch.
(2) Alfalfa valve turnout for pipeline can be automated.
c. Measurement of water:
(1) Parshall flume, propeller meter, etc.
(2) Consider totalizer as well as flow meter when possible
so total quantity is known.
4. Plan water disposal and/or tailwater resuse system:
a. Tailwater pit size (volume of storage).
b. Pineline if pump back system.
c. Gravity flow to downslope field.
d. Pump size needed - head and capacity.
e. Location of tailwater pump and other structures.
5. Plan farm road system:
a. Access to all parts of the irrigation distribution system for
maintenance and operational ease.
b. Access to all fields for planting, tillage, and harvesting
operations.
c. All season roads needed? In whole or in part?
d. Don't use bottom of Grass Waterway for road.
6. Plan subsurface drainage system:
a. Size- of drains.
b. Depth of drains.
c. Filter material required.
d. Outlet necessary - gravity or pump.
7. Plan erosion control measures - may need
mulch left on ground, etc.
a. Erosion control measures should be c
irrigation system.
b. Consider use of Water and Sediment C
ground outlets when possible.
7-7
8. Develop a maintenance program for the following (minimum):
a. Ditches - maintenance of berms, removal of vegetation when
necessary, cleanout of debris and soil from ditch.
b. Erosion control practices such as terraces, grass waterways,
and field boders,
c. Pipelines and components valves working properly, any leaks?
d. Turnout structures and measuring devices in proper working
order?
e. Sprinklers - check for wear.
f. Pumps and motors - Maintenance not performed will cost money
because of shutdowns at critical times, lowered efficiency
so more fuel use, etc.
g. Trickle irrigation - check for clogging, make schedule for
flushing system out and operating system off-season to re-
duce emitters clogging.
h. Schedule a time to perform maintenance. Off-season if
possible, preparation for winter, etc.
9. Develop cost guidelines:
a. Cost per unit and total cost for all alternatives considered.
b. Cost of energy, i.e., hours system in operation times cost
of fuel used per hour.
10. Prepare a development schedule:
a. Least costly segments with greatest returns first.
b. How will the new pieces fit in with the existing system,
i .e., dirt ditch to pipeline?
11. Consider automation - more automation means more water efficiency
and less labor,
12. Prepare a water management plan - specify operating criteria for
application of water under varying conditions.
SOUTH CAROLINA IRRIGATION GUIDE
CHAPTER 8. IRRIGATION _ENERGY JJ_SE
.(LONTENTi
General 3-1
Pumping Plant Efficiency 8-1
Pumping Plant Energy Requirements 8-3
Energy Facts 8-5
Pumping Plant Performance 3-5
Calculating Pumping Plant Efficiency 3-5
Causes of Substandard Pump Performance -- 8-7
Energy Costs - a -a
Methods of Reducing Energy Requirements 8-ii
Increasing Pumping Plant Efficiency --- B~8
Reducing operating Pressure 8-3
Sizing of Irrigation Pipeline 8-11
Scheduling Water Applications 8-14
Increasing Application Efficiency 8-14
Figures
Figure 8-1 Performance Curves of a Deep-Well Turbine
of the Mixed Flow Type 8-2
Figure 8-2 Typical Engine Performance Curve 8-4
Figure 8-3 Fuel Cost Comparison 8-10
Table 8-i Nebraska Performance Standards for Irrigation
jh Pumping Plants - - - 8-5
Table 8-2 Irrigation Power and Fuel Cost Comparison
Thrift __._--__-.-- --___ fi Q
\J \ tU * I* ^ ^ ~ ^ p- ^ ^^.-^^^ ^ip **,-, ij J
SOUTH CAROLINA IRRIGATION GUIDE
CHAPTER 8. IRRIGATION ENERGY USE
GENERAL
With the high costs of energy, it is important that the irrigator exam-
ine every aspect of the irrigation system and seek ways to optimize
energy use. It is possible to combine energy conservation techniques
and good irrigation management practices to conserve both water and
energy.
PUMPING PLANT EFFICIENCY
The pumping plant should be designed to deliver the water as econom-
ically as possible and is one area of the irrigation system where
needed improvements in operating efficiency can be made relatively
easy. Proper repair of a formerly efficient component, or proper
selection of a replacement for an inefficient component, can bring
efficiency up to the desired level.
A pumping plant consists of three components - a pump, a power unit
and a drive assembly. Drive assemblies will be discussed first.
Direct drive assemblies - hollow-shaft motors, flexible couplings and
tabular drive shafts - are 100 percent efficient in transmitting
power. Nothing can be done to improve their power transmission effi-
ciency. Belt drives are not 100 percent efficient. Pulley diameter,
distance between pulley centers and belt tension, all affect belt life
and power transmission efficiency. Properly designed, installed and
maintained V-belt drives are capable of 95-97 percent efficiency while
flat belt drives are capable of transmitting 80-90 percent of the
power from the drive to the driven unit. Ninety (90) degree gear
drives are 95 percent efficient.
Pump assemblies is one area where proper design and selection can
really pay. One factor must be kept in mind. Each particular
model/size of pump has its own operating characteristics. See Figure
8-1 showing a typical operating curve. The operating efficiency of a
pump depends upon the combination of gallons per minute, discharge
pressure and purnp speed. A properly selected pump will have a high
operating efficiency while delivering the desired combination of gpm
and pressure. The most efficient combination of discharge and
pressure varies with changes in pump speed. Changes in either pumping
lift, discharge pressure or well yield also affect pumping efficiency.
The power unit is easier to maintain in top efficiency than the pump
since it is readily visible and available to repair. Electric motors,
especially three-phase units, are inherently quite efficient in con-
verting electrical energy into mechanical motion. Internal combustion
engines vary considerably in their ability to convert petroleum fuel
into mechanical motion. Proper maintenance does much toward keeping
the engine operating efficiently. Many irrigation engines have been
selected on the basis of low initial cost. This has frequently
resulted in a smaller engine being operated at its upper limits
of revolutions per minute which not only shortens engine life but
8-1
Figure 8-1
PERFORMANCE CURVES OF A DEEP- WELL
TURBINE OF THE MIXED-FLOW TYPE,
SPEED 1,750 r.p.m.
80
75
70
65
60
59
50
45
UJ
o
01
IU
CL
O
UJ
u.
u.
UJ
O)
7
A
\
30
as
20
o:
ui
o
CL
UJ
20 OT
a:
o
15 x
UJ
L
7
\
BRAKE HDRSEPOW
10
a:
en
200 400 600 800 1000 1200
CAPACITY PER MINUTE (GALLONS)
1400 J600
WATER HORSEPOWER Q( *' H(ft) -
BRAKE HORSEPOWER
Q(9pm)-H(ft)
3960 efficiency
UP EFFICIENCY - ^^1
X 100%
frequently increases the amount of fuel consumed per horsepower-hour
of output. Manufacturers provide performance data on their engines
which includes a curve showing the "amount of fuel per horsepower-
hour" output by the engine at various speeds. See Figure 8-2 showing
typical performance curves. Considering fuel consumption per
horsepower-hour as well as initial price can be profitable.
PUMPING PLANT ENERGY REQUIREMENTS
There are three factors that determine the power and energy require-
ments of an irrigation pumping plant. They are:
1. The quantity of water being pumped expressed as gallons per minute
(gpm).
2. The total dynamic head (TDH) expressed in feet.
3. The efficiency of the pump expressed as a decimal.
The useful work done by a pump or the water horsepower (whp) required
is expressed by the formula:
gpm x TDH
whp * 3960
The water horsepower represents the power that would be required to
operate the pump if the pump and drive were 100-percent efficient.
The brake horsepower (bhp) required to operate a pump is determined by
the formula:
bhp = whp
pump efficiency x drive efficiency
The horsepower requirement of the power unit is expressed by the
following formula:
Size of engine or motor = bhp
efficiency of power unit
Inefficient irrigation pumping systems waste fuel and increase the
cost per unit of water delivered. As fuel and electrical power costs
increase, the cost of operating an inefficient pump increases even
more.
Efficiency of a pumping system is defined as a ratio of the work being
done by the system to the power or energy being supplied to it. Pump
efficiency can be expressed as:
output whp
input = bhp
8-3
Curva
144"
Unl.
rVd At Maximum performance.
rva fi; Maximum porminibU for inlertnittant i*rvic.
rv C: Maximum ptirmiuible for conllnuaui trvlc.
jipmont Includtd: 4-btadi fan, oil-bath air eloanar,
ffl*r and generator.
:e 8-2. Typical Engine Performance Curve
8-4
ENERGY FACTS
Table 8-1 presents performance standards for both power units and
pumping plants. Power unit performance standards are given in terms
of power produced (in horsepower-hours, hp-hr) per unit of fuel con-
sumed (in gallons, gal or kilowatt-hours, kwh). These figures repre-
sent the efficiency of a typical power unit in converting fuel or
electrical power to mechanical. Note the efficiency of a power unit
(pumping plant) in this situation is a percent of the standard rather
than a ratio of energy in (fuel) to energy out (whp). Pumping plant
performance standards are given in water horsepower-hours (whp-hr) per
gal or kwh. They include allowances for normal pump efficiencies,
drive losses, and friction losses in the discharge column and discharge
head. Pumping system performance standards are expressed in terms of
units of fuel consumed because they can be easily measured, whereas
mechanical power input to a pump can be measured only with specialized
instrumentation.
Table 8-1
Nebraska Performa nee Standards for Irrigation Pumping Plants
"Power Unit " Pumping Plant*
Performance Performance
Fuel Standards Standards
Diesel
Gasoline
14
11
.58
.30
hp-hr/gal
hp-hr/gal
10
8
.94
.48
whp-hr/gal
whp-hr/gal
Propane
(LP-gas;
i 9
,20
hp-hr/gal
6
.89
whp-hr/gal
Natural
Gas
88
.93
hp-hr/1000 cu ft
66
.70
whp-hr/1000
cu ft
Electricity
1
.18
hp-hr/kwh
0.
885
whp-hr/kwh
*Based on 75% pump efficiency. Figures do not include drive assembly losses
From Table 8-1, it is readily seen that diesel fuel Ts the most
cient of the liquid fuels. However, the initial cost of a diesel power
unit is usually considerably greater than that of other internal com-
bustion engines.
PUMPING PLANT PERFORMANCE
A pumping performance test requires that the physical properties that
determine pumping plant efficiency be measured. Pumping rate, pumping
lift, pressure at the discharge outlet, and the amount of fuel consumed
over a period of time must be measured while the pump is operating at
its normal load. The engine and pump speed should also be measured to
ensure that the manufacturer's recommendations are being followed.
CALCULATING PUMPING PLANT EFFICIENCY
An example set of field data is presented to illustrate the procedure
for calculation of pumping plant efficiency:
Pump Discharge Rate, Q - 600 gpm
Pumping Lift, Le = 70 ft
Discharge Pressure, P = 60 psi
Pump Speed = 1750 rpm
Fuel Consumed (Diesel) = 4.0 gal
Pump Test Duration = 1.0 hr
1. Check Pump Speed:
Pump should be measured with a portable tachometer to assure that
the pump is being operated according to its specifications. The
design pump operating speed should be stamped on a plate attached
to the pump discharge head.
In this example, the measured pump speed (1750 rpm) was found to
be very nearly the required pump operating speed (1760 rpm). If
it were not, speed must be adjusted before continuing.
2. Calculate Total Dynamic Head (TDH):
TDH = Pumping Lift (ft) + Discharge Pressure (ft)
TDH = 70 ft + (60 psi x 2.31 ft/psi)
TDH = 70 ft + 139 ft - ?09 ft
3. Calculate Water (Output) Horsepower, whp:
whp = Q x H
3960
whp = 600 gpm x 209 ft
3960
whp = 31.7 hp
4. Calculate Pumping Plant Performance:
Performance (whp - hr/gal) * whp x Test Duration (hr)
Fuel Consumed (gal )
Performance = 31.7 hp x 1.0 hr
4.0 gal
Performance =7.9 whp - hr/gal
5. Calculate Pumping Plant Efficiency, Eff
Eff = Pumping Plant Performance x 100%
Performance Standard
Etf = 7.9 whp - hr/gal x 100%
10.94 whp - hr/gal
Eff = 72.2%
8-6
6. Calculate Fuel Wasted per Hour:
Fuel Wasted/Hour - Current Fuel Consumption Rate x (1-Eff)
Fuel Wasted/Hour = 4.0 gal/hr x (1-0.722)
Fuel Wasted/Hour = 1.1 gal/hr
In this example, the actual pumping plant performance of 7.9
whp-hr/gal is only 72.2 percent of the performance standard for
diesel powered pumping plants. For the size of unit described, 1.1
gal/hr of diesel fuel is wasted because the pumping plant is not
operating efficiently in its current condition. Whether or not this
loss in efficiency is significant enough to justify having the pumping
unit repaired depends upon the expected repair cost and the number of
hours of pump operation per year. In general, if the repair cost can
be regained by savings in operating costs over a 2-3 year period of
time, then it will be economically feasible to have the repairs made.
The actual repayment time can only be calculated using a detailed eco-
nomic analysis including the expected efficiency increases, fuel cost,
and the repair costs amortized over the period of time.
CAUSES FOR SUBSTANDARD PUMP PERFORMANCE
Substandard performance in the pump can be caused by several factors.
The pump could be mismatched for present conditions. The pump may not
have been properly selected or the operarting conditions may have
changed. The water table could have dropped or a new pipeline could
have changed the pumping head requirement. The power source may not
be operating at the specified speed (rpm) for maximum efficiency.
The impellers could be out of adjustment. Qualified repair-merit can
adjust the impeller clearance with the bowl for the greatest effi-
ciency. If the impeller is badly worn or corroded, adjustment will
not help. Cavitation occurs in pumps that attempt to operate at flow
rates greater than the well can supply. This pits the impellers and
ruins them.
Poorly designed pumping systems would result in low efficiency
ratings. This could be caused by such factors as an undersized suc-
tion pipe, restrictions in the Intake strainer, or improperly sized
discharge column. Misalignment of the drive shaft also decreases
efficiency. Excessive wear is a sign of this.
ENERGY COSTS
Table 8-2 shows the cost per hour pumping for various fuels, fuel
costs and horsepower loads. These will serve as valuable information
in planning irrigation systems.
Figure 8-3 compares the cost of diesel, propane, and gasoline to the
cost of electrici ty.
METHODS OF REDUCING ENERGY REQUIREMENTS
Proper selection, operation, maintenance and management of an irriga-
tion system to fit the soil type and cropping system can save much
energy. In the selection of an irrigation system, the system's energy
costs should be considered as well as its initial costs. Sprinkler
irrigation systems vary in the energy requirements. Single sprinkler
volume guns are high energy users, permanent/solid-set systems are
medium energy users and center pivot systems range from medium to low
energy users. Subirrigation systems using furrows, ditches or pipes
are relatively low energy users as well as trickle irrigation systems.
Ways to save energy are discussed below.
INCREASING PUMPING PLANT EFFICIENCY
As was shown in the example on page 8-7, much energy can be saved by
increasing the efficiency of the pumping plant. An irrigation pumping
plant efficiency testing program was recently initiated in Georgia.
Measured efficiencies have ranged from 12 percent to 119 percent and
averaged 63 percent. This represents an average monetary loss of 37
cents per dollar of fuel cost and a potential energy savings of up to
9 million gallons of diesel fuel annually in Georgia if system effi-
ciencies were increased to optimum levels.
REDUCING OPERATING PRESSURE
Table 8-2. IRRIGATION POWER AND FUEL COST COMPARISON CHART
A - ELECTRICITY - Cost/hour of pumping (Based on 1,18 hp-hr/KWH*)
Pump Rates per kilowatt-hour
Load
HP 4c 5c 6C 7c 8c
10
?0.34
$0.42
$0.51 $0.59
$0.68
$0.76
20
0.68
0.85
1.02 1.19
1.36
1.53
30
1.02
1.27
1.53 1.78
2.03
2.29
40
1.36
1.69
2.03 2.37
2.71
3.05
50
1.69
2.12
2.54 2.97
3.39
3.81
75
2.54
3.18
3.81 4.45
s.oa
5.72
100
3.39
4.24
5.08 5.93
6.78
7.63
B - DIESEL -
Cost/hour of
pumping (Baaed on
14.58 hp~hr/gal*)
Pump
Fuel cost per
gallon
Load
HP
1.00
$1.10
$1.20 $1.30
$1.4U
$1.50
10
$0.69
$0.75
$0.82 $0.89
$0.96
$1.03
20
1.37
1.51
1.65 1.78
1.92
2.06
JO
2.06
2.26
2.47 2.67
2. 88
3.09
40
2.74
3.02
3.29 3.57
3.84
4.12
50
3.43
3.77
4.12 4,46
4.80
5.14
75
5.14
5.66
6.17 6.69
7.20
7.72
100
6.86
7.54
8.23 8.92
9.60
10.29
C - GASOLINE
- Cobt/hour of pumping (Based on 11.30 hp-hr/gal*)
Pump
Fuel coat per
gallon
Load
HP
$1.00
$1.10
$1.20 ?1.30
$1.40
$1.50
10
$0.88
$0.97
$1.06 $1.15
$1.24
$1.33
20
1.77
1,95
2.12 2.30
2.48
2.65
30
2.65
2,92
3.19 3.45
3.72
3.98
40
3.54
3,89
4.25 4.60
4.96
5.31
50
4.42
4,87
5.31 5.75
6.19
6,64
75
6.64
7.30
7.96 8.63
9.29
9.96
100
8.U5
9.73
10.62 11.50
12.39
13.27
D - PROPANE
- Cost/hour of
pumping (Based on
9.2 hp-hr/gal*)
Pump
Fuel cost per
gallon
Load
HP
$0.80
$0.90
$1.00 $1.10
$1.20
$1.30
10
$0.87
$0,98
$1.09 $1.20
$1.30
$1.41
20
1.74
1.96
2.17 2.39
2,61
2.83
30
2.61
2.93
3.26 3.59
3.91
4.24
40
3.48
3.91
4.35 4.78
5.22
5.65
50
4.35
4.89
5.43 5.98
6.52
7.07
75
6.52
7.34
8.15 8.97
9.78
10.60
100
8,70
9,78
10.87 11.96
13.04
14.13
*Nebraska Standards for Engine Performance considered attainable in practice. Of 376
pumping plants tested in Nebraska 1956-62, only 33 or 8.8% exceeded the standard, 59% met
or exceeded 75X of the standard. Efficiency of internal combustion engines can be
expected to drop in normal use. Electric motor efficiency should change very little.
NOTE: All costs per hour are rounded to the nearest cent. Costs are for Fuel or
power only, no lubrication, repairs, etc.
to get actual cost/hour.
8-9
Must divide by pump and drive efficiency
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8-10
30 psi system, whp = (800 gpm) (30 psi x 2.31 ft/psi) = 14.0
3960
The savings of using the 30 psi system over the 80 psi system would be
23.3 whp (37,3 whp - 14.0 whp).
From Table 8-1, for a diesel unit the fuel savings would be:
23.3 whp - 10.94 whp - hr/gal = 2.1 gal/hr
Using a diesel price of $1.15/gal, then the savings would be:
2.1 gal/hr x $1.15 gal = $2.42/hr
If the system is operated 500 hours per year, then the annual fuel
savings would be:
500 hrs x $2.42/hr = $1,210
or
2.1 gal/hr x 500 hrs = 1050 gal of fuel
Some farmers are converting from high pressure systems to low pressure
systems. It should be understood that converting to low pressure
systems will reduce pumping costs only if the pumping plant is
designed for low pressure. Most pumps are set to deliver a given gpm
at a given head to get the maximum efficiency of the pumping plant.
When this head is reduced, the gpm will increase. This usually
results in a lower efficiency for the pumping plant, with the con-
sequent higher energy use for pumping an acre inch of water.
Converting high pressure center pivot to low pressure center pivot
reduces the wetted diameter of the sprinklers on the order of j;100
feet to 40 to 60 feet. So the same amount of water would be put on a
strip about half as wide with low pressure center pivots. Therefore,
the application rate of water Is about twice as much in inches per
hour, this can cause serious runoff on the heavier soils especially
where there are sloping areas. This should be given consideration
when deciding on converting center pivot systems from high pressure to
low pressure.
SIZING OF IRRIGATION PIPELINE
The friction loss in a pipeline increases, approximately, in propor-
tion to the square of the water velocity in the pipeline.
8-11
Mater Velocity
ft/sec Square
1 1
2 4
3 9
4 16
5 25
Consider friction loss to be comparable to energy use. The higher the
friction loss the more energy that is required to pump water through a
pipeline.
Compare the three foot per second velocity to the four foot per second
velocity in the table above. This compares three squared which equals
nine to four squared which equals sixteen. Sixteen divided by nine
equals 1.78. Friction loss at a velocity of four feet per second is
approximately 1.78 times the friction loss at three feet per second,
It is considered advantageous to keep pipeline velocities between
three and four per second considering initial cost of the material,
installation costs and operating costs.
Obviously, on very short pipelines or irrigation systems using gravity
flow it may not be- advantageous to keep the velocities low because
there would be very little savings in operational costs. In this
case, five feet per second velocities are considered a maximum to pre-
vent problems connected with surge, water hammer and air entrapment.
On very long pipelines, H may be advantageous to reduce the pipeline
velocity to as little as two feet per second thus reducing energy use.
Initial material and installation costs should be studied and compared
to operating costs to determine the most economical pipe size to be
installed. The biggest cost in installing larger pipes is the
increased cost of material. Trenching, backfilling, and labor costs
,
increase very ittle when a pipe diameter is increased one
Velocities should not be dropped below two feet per second
unless special studies are made of potential sediment problems.
Example of sizing a pipeline based on energy use and annual pipe cost.
Reference: Appendix C, Friction loss characteristics P.V.C. qass 125
s, SDR 32.5
per minute
3000 feet
8-12
operating time = 1000 hours per year
electricity cost = 5 cents per kw-hr/hr
diesel fuel cost = $1.10 per gallon
total dynamic head = 100 feet + friction loss in pipeline
Pipeline Friction Loss
Pipe Size Velocity Friction Loss Friction Loss in
(Dia) (ft/sec) psi/100 ft ft head/100 ft 30QQ feet
8 in 6.22 0.58 1.34 40 ft
10 in 4.00 0.20 0.46 14 ft
12 in 2.84 0.09 , 0.21 6 ft
It should be noted to begin with that the 8 inch diameter pipeline should
not be used because of velocities exceeding 5 ft/sec. This could cause
water hammer, surge, or air entrapment problems. The 8 inch size is being
shown in the example to illustrate the extra cost associated with higher
velocities.
Cost of Electricity
Pipe Si ^e
(Dia)
Total Head
Loss
whp
35
whp-hr
per kwh
kw-hr
per hr
Cost/hr Cost per
@$0.05/kwh 1000 hrs
8 in
140
0.885
40
$2.00
$2000
10 in
114
29
0.885
33
1.65
1650
12 in
106
27
0.885
30
1.50
1500
Pipe Size
(Dia)
Total Head
Loss
Cost
of Diesel
gal
per hr
Cost/hr
0$0.80/gal.
Cost per
1000 hrs
whp
35
whp-hr
per gal
8 in
140
10.94
3.2
$2.56
$2560
10 in
114
29
10.94
2.7
2.16
2160
12 in
106
27
10.94
2.5
2.00
2000
8-13
The annual amortized pipe cost using the following conditions are:
,-,1 i -1 -f n TnfpPP^t.
PIDP Size Initial Lite intere^
(Dia!) r " ct fYrs) Rate
R in 12% $1484.
10 in sOO 25 1W S2104.
12 in $22,050 25 12% ^ yil -
The most economical pipe size would be the one that has the lowest
total cost considering both the annual amortized cost and the energy
cost as follows:
Pine Size Annual Annual Total
(p ia .) Amortized Co_sl Energy Cost _CS_t
Electric
8 $1484. $2000 $3484
10 2104. 1650 3754
12 2811. 1500 4311
Diesel
8 $1484 $2560 $4044
10 2104 2160 4264
12 2811 2000 4811
The most economical pipe would be the eight inch size with the ten
inch being the next choice. Due to possible water hammer and surge
problems with the eight inch size, the ten inch pipe would be the
recommended size.
SCHEDULING HATER APPLICATIONS
Probably the one place where energy savings can be affected the
quickest is to use management practices which obtain the optimum
fuel saved = 100 acres x 1 ac-ln x 27,154 gal x 1 min x 1 hr x 2.1 gal
ac ac-in 800 gal 60 min hr
= 118.8 gal jf diesel fuel
INCREASING APPLICATION EFFICIENCY
Increasing the application efficiency of the irrigation system will
directly save water and energy. This can be done by selecting a
system of known high efficiency, designing and laying out the par-
ticular system to obtain the most efficiency application possible or
irrigate at times when the efficiency would be greater. The example
below will illustrate how increasing the application efficiency will
save energy.
Assume the system previously discussed with 70 percent application
efficiency and an 80 percent application efficiency. If the next
irrigation requirement is 1 inch then the gross irrigation requirement
for the two efficiencies are:
70 percent = 1.00 inch 7 0.70 = 1.43 inches gross application
BO percent = 1.00 inch -i 0.80 = 1.25 inches gross application
fuel used at 70% eff. of application
= 100 acres x 1.43 ac-in x 27,154 gal x 1 min x 1 hr x 2.1 gal
ac ac-in 800 gal 60 min hr
= 169.9 gal
fuel used at 80% eft 7 , of application
= 100 acres x 1.25 ac-in x 27,154 gal x 1 min x 1 hr x 2.1 gal
ac ac-in 800 gaT 60 mm hr
= 148,5 gal
The fuel saved per 1-inch net applications is 21.4 gal (169.9 gal - 148.5
gal). If six 1-inch net applications are required in one season, then 128.4
gallons of fuel could be saved.
SOUTH CAROLINA IRRIGATION GUIDE
CHAPTER 9. IRRIGATION ECONOMIC EVALUATION
Contents
Paqe
ftonoral --._....___ _____ .. _______ .____=.__ ___________ Q 1
U *! H d I Q I -*_ ___J-__*-'- n ^*._q<_ p________l____*H^. HW __ w _ ^7 " J.
Determining Irrigation Cost and Return on Investment 9-1
Compiling Information Needed 9-2
Initial PrKt -. . Q-3
X 1 1 I l 1 Q 1 \j\J J if -**-- i- ____,._._ -, -H -. -^ W ^,^ UK4VD . U ^__^_ -__,__-* .7 O
Determining Annual Ownership Cost 9-3
Determining the Annual Operation and Maintenance Cost 9-5
Determining Return on Investment 9-8
Tables
Table 9-1 Amortization Factors 9-5
Table 9-2 Annual Fuel Consumption 9-6
Table 9-3 Annual Oil Consumption -- - 9-8
Table 9-4 Annual Cost of Repair and Maintenance 9-8
Exhibits-Cost and Return
Exhibit 9-1 General Information - 9-2
Exhibit 9-2 Initial and Annual Ownership Cost - 9-4
Exhibit 9-3 Annual Operation and Maintenance Cost 9-6
Exhibit 9-4 Return on Investment 9-9
SOUTH CAROLINA IRRIGATION GUIDE
CHAPTER 9. IRRIGATION ECONOMIC EVALUATION
GENERAL
The proper use of economic tools and procedures will provide cost and
return information for alternative courses of action. With adequate
economic data, an individual can make a reasonable decision as to the
resource management system that best fits his requirements.
In advising farmers on the merits of one irrigation system versus
another, or on the question of whether or not to invest in irrigation
equipment, it must be remembered that in 'many instances, factors enter
into the decision-making process that cannot be explained in a simple
cost-return analysis. In some cases, such considerations as invest-
ment tax credit or other tax incentives may strongly influence the
decision. If the farmer is financially secure, personal preference
may guide his thinking. Another example is a situation where the
grower considers an irrigation system to be justifiable in order to
protect against the complete loss of a crop during an extremely dry
season or for freeze protection but where the average annual benefit
may not justify the purchase of a system.
If the farmstead is located in a remote area, an available irrigation
system could be used to suppply water for fire suppression. Just the
availability of a large, dependable supply of water could provide a
sense of security for the farm family.
The above-mentioned reasons for, or advantages of, owning an irriga-
tion system may at least complement the primary purpose for investing
in the system which is to increase farm net income. Procedures
outlined in this chapter should be useful in analyzing not only
whether or not to irrigate, but which system would be most profitable.
DETERMINING IRRIGATION COST AND RETURN ON INVESTMENT
This chapter provides information and methods for determing how
much an irrigation system will cost and how to estimate the return on
investment. In the final analysis, comparison is made of the average
annual cost of irrigating to the value of the estimated annual
increase in production. This return on investment may be the deciding
factor as to whether to invest in an irrigation system.
As an aid in better understanding the mechanics of calculating irriga-
tion costs and returns, an example is presented and the steps are given
for developing cost and return data for a typical irrigation system.
9-1
COMPILING INFORMATION NEEDED
To develope cost and return data for an Irrigation system, certain infor-
mation has to be obtained. Exhibit 9-1, General Information, can be used
to compile information. The information entered in Exhibit 9-1 will be
used as the example in the following sections.
General Information
Item
Information
Needed
1. CropCs) to be irrigated
2. Expected increase in yield per acre from irrigation
3. Value of crop per unit (pounds, bushels, tons, etc.)
4. Maximum soil water- intake-rate
5. Seasonal consumptive use of the crop
6. Peak-use rate of the crop
7. Number of hours to operate per day
8. Minimum days required for each irrigation
9. Number of irrigations expected per season
10. Number of hours operation per year
11. Shape and dimensions of field
12. Number of acres in field
13. Type of system
14. Number of acres to be irrigated
15. Pumping rate needed in gpm
16. Source of water
17. Total height water is to be lifted
18. Total operating head
19. Size of power unit needed
20. Type of power unit
21. Interest rate
22. Stand-by charges for electricity
23. Hours labor per acre per irrigation
Corn
75 bu
$3.00/bu
2.6 in/hr
21 in
0.33 in/day
22
2.7
486 .
2640' x 2640'
160
Center-Pivot
126
1200
Well
55 '
170'
100 bhp
Diesel
15%
Not Applicable
0.05
Exhibit 9-1 General Information
9-2
INITIAL COST
When purchasing an irrigation system,, one of the first things needed in
determining cost and return of an irrigation investment is an estimate of
the initial cost. This information is needed to: (1) help decide whether
to pay cash for the system or finance it, and, (2) determine the annual
ownership cosl 9 which is a part of the total cost of owning, operating, and
mai ntaining a system,
Just because an irrigation system would be profitable for a particular farm
doo r i not mean that, the buyer can affcr'd to finance it. An irrigation
system may "last J5 to 20 years, but many lending agencies require that they
be pdid for in 6 to 10 years. If this is the situation, the landowner may
Tind himself with an annual payment that is more than the value of the
expected increase in yield per year as a result of installing the irriga-
tion system. For example, if $25,000 is borrowed to buy a system, at 15%
interest for 10 years, then the annual loan payment would be $4,981
($25,000 x 0.19925). If the expected value of the increased yield is
$3,500, then the loan payments must be supplemented with additional money
other than that expected from irrigating.
DETERMINING THE ANNUAL OWNERSHIP COST
The annual ownership cost is determined from the: (1) initial cost minus
trade-in value of the system, (2) interest, (3) taxes and insurance, (4)
fixed charges, (5) loss of income from land taken out of production for
water development and (6) life expectancy of the system. Exhibit 9-2
should be completed as shown below to obtain the annual ownership cost for
the system.
1 Enter in Column 2 the initial cost of the items applicable to the
* system and their trade-in value in Column 3. Enter in Column 4
the initial cost minus the trade-in value (Column 2 - Column 3).
2. Find the appropriate amortization factors from Table 9-1 for
applicable items and enter in Column 6.
3 Compute the annual ownership cost for each item by
the initial cost minus trade-in value by the appropri
zation factor (Column 4 x Column 6) and entering in Column 7.
4. Estimate annual cost of taxes and Insurance and enter it in space
provided. This is estimated to be 1% of the initial COST:.
,
being used, stand-by charges can be obtained from the power
supplier.
9-3
Initial and Annual Owhershi
p Cost
Initial Cost
Initial Trade-in Minus Trade-
Hem Cost Value in Value
(1) (2) (3) (4)
Expected Amorti-1/
Years of nation
Life Factor
(5) (6)
Ow,
WELL CASING
Plastic 12,000 12,000
25+ .15470
ii:
RESERVOIR
PUMPS
Line Shaft Pro-
peller
10
n
Turbine 8,500 8,500
15 ~7I7TG2~
Centri fugal
12
POWER UNIT
Electric
25
T:
Gasoline
Diesel 8,000 2,UOO 6,000
12 .13448
Natural Gas,
LPG, OR Propane
10
L.
LANU DRAINAGE " "
20
LAND LhVtUNG " ...
15
WATER PIPE
Underground Pipe
Plastic 9,000 9,000
25+ .15470
Aboveground Pipe
Aluminum
15
liaiv. Steel
PIPE TRAILER
10
SPKiNKLtR SYSTEMS
Hand-Moved
15
51
center-Pivot 60,000 15,000 45,000
10 .19925
big bun
12
Permanent
(Solid-Set)
20
Ditches
25
Pipe 1 i nes
20
Structures
I'll JLLLLrtHCUUi
s
-
Total Initial Cost 97,500
Taxes and Insurance (Total Cost x .01) = $97,500 x
.01 * 975.00
Stand-By (Fixed Charges) for Electricity =
Loss of Income Due to Acreage out of Production ($ -
Total Annual Ownership Cost(Column 7) = $15,750.50
_/Acre x __ - Acres)
. . . _
. .
!/ 15* Interest Rate Used (Factors from Table 9-1)
Exhibit 9-2. Initial and Annual Ownership Cost
9-4
Fxpecled
No. of
Years of
Li_fe_
2
4
6
8
10
12
15
20
Determine a value for the loss of production from r.he
land taken out of produc-tion. For this example, no loss
is involved since a well supplies the water and uses a
negligible amount of land. If a pond, lake, or reservoir
is the water source, the value of any loss of production
from the former use of the land should be considered.
Find the total annual ownership cost by adding the
figures in Column 7 and enter in space provided.
I/
9-1. Amortization Factors
_io?L
.57619
.31547
,22961
.18744
.16275
.14676
.13147
.11746
.11017
11%
13%
14%
15%
16%
1 7^
Lfia
.58393
.59170
.59948
.60729
.61512
.62296
.63083
.32233
.32923
.33619
.34320
.35027
.35738
.36453
.23638
.24323
.25015
.25716
.26424
.27139
.27861
.19432
.20130
.20839
.21557
.22285
.23022
.23769
.16980
.17698
.18429
.19171
.19925
.20690
.21466
.15403
.16144
.16899
.17667
.18448
.19241
.20047
.13907
.14682
.15474
.16281
.17102
.17936
.18782
,12558
.13388
.14235
.15099
.15976
.16867
.17769
.11874
.12750
.13643
.14550
.15470
.16401
.17342
"Aniortfzation ~~ Used" to convert installation costs into equal annual paymervts
DETERMINING THE ANNUAL OPERATION AND MAINTENANCE COST
The annual operation and maintenance cost is determined from the annual
expense of operating the system. This includes (1) fuel, (2) oil, (3)
repair and maintenance of equipment, (4) reservoir and field maintenance
(b) additional seed, fertilizer, pesticides, and harvesting cost for the
increase in yield, and (6) labor.
Annual Operation and Maintenance Costs shown in Exhibit 9-3 may be com-
pleted as shown below to obtain the annual operation and maintenance cos
1. Find the total annual cost of fuel. Table 9-2 gives the brake
horsepower hours per unit of fuel. Record the values needed fr
Exhibit 9-1 and Table 9-2 and follow the mathematical
instructions given for Item 1. Using $1.20 per gallon for
diesel fuel, the total fuel cost is $4,000.00.
9-5
jVnnujQ_OperatlQn and Maintenance _._Cost
Horse Number Cost Per bhp Hours
Item power of Hours Unit of Per Unit Total
Requi red Operated Fuel
1.
2.
3.
4.
5.
Fuel
Oil-Engine
Oil-Gear Drive
or Electric Motor
Repair and Maintenance
(power unit)
Repair and Maintenance
100
X
X
X
X
X
ini
486
X $ 1,20 - 14.58
$4,000.
00
100
486
X $ 4.00 ~ 900
S 216.
00
X $ - -
$
X $ -
$
100
486
X $0.002 per bhp
X .005
$ 97.
20
$97,500
tial cost
$ 487.
50
6. Reservoir and Field
Maintenance $ : initial cost X .005 $_
7. I/Additional Seed, $_2L-35 anticipated additional expense
Fertilizer, Chemicals, " per acre X 126_ (number acres) $<
and Harvesting Cost
(estimate)
8. Labor O.OS hours per acre per irrigation
X _9 No. of irrigations X 126
acres X $4_JOO per hour $_ .226^80
9. Total Annual Operation and Maintenance Cost -- $j
T7~Tim value fsThe amount you expect to spendTn add it Ton to "that which "you
would spend if you did not irrigate. It varies with the crop. For some
crops, you may not have any additional expense.
Exhibit 9-3 Annual Operation and Maintenance Cost
_____ Table 9-2 Annual Fuel Consumption
Fuel or Power blip-Hours per Unit of Fuel
Electric 1.18 per Kilowatthour
Gasoline 11.30 per gallon
Diesel 14.58 per gallon
Propane 9.20 per gallon
Natural Gas 88.93 per 1000 cubic feet
9-6
2. Find the total annual cost of oil. Table 9-3 gives the brake
horsepower hours per gallon of oil. Record the values needed
from Exhibit 9-1 and Table 9-3 and follow the mathematical
instructions given for Item 2. Using $4.00 per gallon for oil,
the total cost of oil is $216.00.
3. Find the total cost of gear oil. No cost was figured for gear
oil in this example.
If this cost is to be added, record the values needed from
Exhibit 9-1 and Table 9-3 and follow the mathematical instructions
given for Item 3.
4. Find the total annual cost of maintenance of the power unit.
Table 9-4 gives the estimated cost of power unit repair and
maintenance per brake horsepower per hour. Record the values
needed from Exhibit 9-1 and Table 9-4 and follow the mathematical
instructions given for Item 4. Total for this example is $97.20.
5. Find the total annual cost of repair and maintenance of the
irrigation equipment. The cost used for repair maintenance of
the irrigation equipment /jas estimated at 0.5% of the initial
cost. The initial cost of the equipment is obtained from Exhibit
9-2. The total for this example is 0.005 x $97,500 = $487.50.
6. Find the total annual cost of reservoir and field maintenance.
For this example, no cost was figured for reservoir and field
mai ntenance.
If reservoir or field maintenance is required for your irrigation
system, obtain the initial cost of the equipment from Exhibit
9-2 and follow the mathematical instructions given for Item 6.
7. Estimate the total annual cost for the additional yield from
irrigation by following the mathematical instructions for Item
7. If the fanner is expected to spend more for seed, fertilizer,
pesticides, labor, handling or storage than he would without
irrigating, estimate the cost. This will depend on his crop and
the manner in which he has been farming, A figure of $21.35 per
acre was used for this example.
8. Find the total annual cost of labor. Record the values needed
from Exhibit 9-1 and follow the mathematical instructions given
for item 8. In this example using $4.00 per hour for labor,
the total cost is $226.80.
9. Find the total annual operation and maintenance cost. This is
obtained by adding all items in the "Total" column. The total
for this example is $7,717.60.
9-7
Table 9-3. Annual Oil Consumption (1982)
bhp - Hours
Type of Engine and Drive Per Gallon of Oil
TTlHTTc ~~ 9000
Gasoline 90
Diesel 900
Propane 100
Natural Gas 1000
Right Angle Gear Drive 5000
Table 9-4. Annual Cost of Repair and Maintenance (1982)
Type of Power Unit Cost Per blip Per Hour
Electric motor and controls $
Gasoline $ .0017
Diesel $ .0020
Propane $ .0013
Natural Gas $ .0013
DETERMINING THE RETURN ON INVESTMENT
The primary purpose for estimating the total annual cost of an irriga-
tion system is to have a figure with which to compare the value of the
expected increase in production from using that system. To obtain the
return on investment, Exhibit 9-4 "Return on Investment 11 should be
completed as shown below.
1. Determine the value of the expected increase from irrigation
per acre. Record the expected yield increase and value from
Exhibit 9-1 and follow the mathematical instructions on
Exhibit 9-4. In this example the total value of the increase
in yield is $225.00 per acre.
2. Find the total annual cost per acre for irrigating. Add the
total annual ownership cost from Exhibit 9-2 to the total
annual operation and maintenance cost from Exhibit 9-3 and
divide by the number of acres. The total in this example is
$186.25 per acre.
3. Find the expected return on investment per acre from
""gating with this system. This is obtained by subtracting
the total annual cost of irrigating from the value of the
expected increase. The total expected return on investment
per acre for this example is $38.75 '"vestment
9-8
Return on Investment
1. Value per acre of expected increase from irrigation:
75 bu yield/acre (Exhibit 9-1) x $3.QQ/bu (Exhibit 9-1) = $225.00
2. Total annual cost per acre of irrigation:
$15,750.50 (annual depreciation cost - Exhibit 9-2)
+ $ 7,717.60 (annual operating cost - Exhibit 9-3)
Total = $23^68.^10 - 126 number of acres {Exhibit 9-1) - $186.25
3. Expected Return per acre on Investment = JI225_.OU - 1JM:_25. = $38.75
Exhibit 9-4. Return on Investment
Using the assumptions and data contained in the above example, the
following analysis can be made as to the price and yield required to
"break-even" ([he point where the additional income due to irrigation
equals the cost of irrigation):
Break-even Price for 75 bu increase = $2.4B/bu
($136.25 Increase in Cost - 75 bu)
Break-even Yield for $3.00/bu corn = 62 bu/ac
($186. 2b Increase in Cost - $3.00/bu)
Break-even Yield for 2.00/bu corn = 93 bu/ac
($186.25 Increase in Cost - 2.00)
NOTE: Source of format used for this section: Planning for an Irrigation
System. This publication was developed by the American Association
Tor Vocational Instructional Materials in cooperation with the Soil
Conservation Service. Data in this section has been updated to
approximately the 1982 to 1985 period.
9-9
SOUTH CAROLINA IRRIGATION GUIDE
CHAPTER 10. IRRIGATION METHOD DESIGN
Contents
Chapter 10-A. Permanent/Solid- Set Sprinkler Irrigation System ------- 10-A--1
General ------------..------.--. ----.---- ---- 10-A-l
Design Criteria ----------- ---- --- --_ --_ 10-A-l
Example Problem -------- ---- - --. ._ -__ 10-A-l
Layout Considerations ---. ------- ---- - ---- .--- 10-A-9
Construction Requirements - -..--..-_--_ ---- 10-A-10
Chapter 10-15. Traveling Gun Sprinkler Irrigation System --- ---- -- ---- 10-B-l
fipnpral ____ .-- ___ ,_-.-__- ___ . = ____ - _____ __ _______ ... ___ in_R-1
IJ^IIt-l U 1 m -, _ , _ -i. ^^* --. v .t*" Mn .* A ... m ..* n -_ HUM ,_.* a w **-i J.kJ-'LJJ.
Design Criteria -- --- ----- - --------- ------ 10-B-l
Example Problem ------- ----- ------- ..... -- - ----- -- 10-B-l
Layout Considerations ---------- .-. - _ ...- 10-B-6
Construction Requirements -------- ----- -------- --....- 1Q-B-6
Chapter 10-C. Center Pivot Irrigation Systems - ........ ------ - ---- - 10-C-l
General --------- ~ - ----- ...... - ----- _ ---- - ------ 1Q-C-1
Formula Used in Design and Evaluating Center
Pivot Irrigation Systems - -------- - ------ - ----- -- 10-C-l
Example Problem --- ----------- ........... ---- ..... 10-C-2
Construction Requirements ---------- - ----------- -- 10-C-6
Layout Considerations ------------ ..... ----------- 10-C-6
Procedure for Determining Gross Application
of Center Pivot Sprinkler -- ........... ---- ..... 10-C-7
Chapter 10-D. Trickle Irrigation System ----------------------------- 10-D-l
General ______ - - _________ - _____ - ________ -- __ -~~ __ ~- 10-D-l
Design Criteria ---------------------------------- 10-D-l
Example Problem ................. --------- ....... - 10-D-l
Material and Construction Requirements ----------- 10-D-4
Tables
Page
Table 10-A-l Typical Sprinkler Manufacturer's Data 10-A-9
Table 10-B-l Recommended Towpath Spacings For
Traveling Sprinklers 10-B-7
Table 10-B-2 Guide for Flexible Irrigation Hose
n -.-._._-_____.__ __ -___-._ __-.___ __ _.___.. lri_R 7
IP ^ ^p^ *- *- -'- * '-**- - . ^U U /
Exhibits
Exhibit 10-A-l Irrigation Data Sheet - Permanent/Solid-Set
Sprinkler Irrigation System (Example
Q VT* K T j^ni i __ __ _ __- . _. _ M _ -.___.._ M -^-*-^--^~ ^-"^ -*. ^_ _ ^_ 1 f^ A IT
r I UU ] cUI ^ -- -* ----* ^,~-- -. -,,,. 1U"A\-J.1
Exhibit 10-B-l Irrigation Data Sheet - Traveling Gun
Irrigation System (Example Problem) -- 10-B-8
Exhibit 10-C-l Irrigation Data Sheet - Center Pivot
Irrigation System (Example Problem) 10-C-lO
Exhibit 10-D-l Irrigation Data Sheet Drip Irrigation
System (Example Problem) -- 10-D-5
SOUTH CAROLINA IRRIGATION GUIDE
CHAPTER 10-A. PERMANENT/SOLID-SET SPRINKLER IRRIGATION SYSTEM
GENERAL
The example problem in this chapter is intended to illustrate the proce-
dure to follow in the design of permanent and solid-set irrigation
systems. It is understood that one example cannot illustrate all design
situations or alternatives to consider when designing a permanent or a
solid-set irrigation system.
DESIGN CRITERIA
Design criteria for permanent and solid-set irrigation systems is con-
tained in the Technical Guide, Irrigation System, Sprinkler, Code 442, for
South Carolina. All sprinkler irrigation systems must be designed in
accordance with the criteria contained in Code 442.
EXAMPLE PROBLEM
The following example problem is intended to cover the basic design steps
to follow in the design of permanent/solid-set sprinkler irrigation
systems. A standard form (Exhibit 10-A-l) is used which is a useful tool
in designing and recording data.
Given
1. Location: Aiken, South Carolina.
2. Field Shape: 1320 feet east to west by 660 feet north to south (20 acres)
3. Soil: Dothan loamy sand on to 5 percent slopes.
4. Crop: Small vegetables - Recommended design use rate of 0.18 in. /day,
5. Row direction and spacing: Rows run north to south 30 inches aoart
6. Plant spacing along row: Varies.
7. Well information: 12-inch well without
electric, 3 phase. Static water level
At a 400 GPM pumping rate, water level
centerline is at 140 feet.
8. Owner would like to operate system abou
shut off valves.
9. All pipe to be buried a minumum of 30 i
10-A-l
So1utj_on_:
The item numbers mentioned in the step by step solution refer to the items on
the "Irrigation Data Sheet" in Exhibit 10-A-l.
Step 1. Complete Items 1-4. These items provide an inventory of pertinent
data at the site.
Step 2, Complete Item 5. Make a drawing to scale of the field locating
buildings, trees, well and other features.
Step 3. Complete Item 6, except for acreage to be grown which will be discussed
later. Guidance in selecting the moisture extraction root depths (soils
moisture control zone) and the design peak use rate are to be taken
from this guide, Tables 3-1 and 4-1 respectively. The weighted AWC is
computed using data from item 1.
Step 4. Complete the following parts of Item 7.
a. Available water capacity (AWC) within the water control (root)
zone is the product of the root zone moisture extraction depth
(12 in.) times the weighted moisture holding capacity of the
soil (0.08 in. /in.). AWC = (12 in.)(0.08 in. /in.) * 0.96 in.
b. The percent depletion recommended prior to irrigation is 40%
for truck crops as set forth in the Chapter 11 of this guide.
c. The maximum net water allowed per irrigation (in.) is the
product of the percent depletion allowed prior to irrigation
times the water available within the root zone. The maximum
net water allowed per irrigation in this example is = (0.40)
(0.96 in.) = 0.38" in.
d. The net water to be applied must be less than or equal to
the maximum allowed. Use the maximum for this example - 0.38".
e. Maximum application rate from table 2-6 for loamy sand, 0.38"
water applied, and 4 percent predominate maximum slope =
(No limit).
f. The system efficiency is assumed to be 70 percent,
g. The gross water applied per irrigation (in.) is found by
dividing the net water applied per irrigation by the system
efficiency. Gross water applied = 0.38 in, 4- 0.70 = 0.54 in.
h. The peak irrigation interval (days) is determined by dividing
the net water applied per irrigation by the crop peak
consumptive use rate. Peak irrigation interval = 0.38 in.
-t- 0.18 in. /day = 2.1 days.
i. Normally, the irrigation period in days to be used in the
formula for determining QR Is the irrigation interval (2.1
days) determined above. However, in this example the field
was broken up into four irrigation units of 5 acres each
which resulted in two units being irrigated each day (lOac/
day). Therefore, one (1) day was entered in each column
for the irrigation period and 5 acres per irrigation unit in
Item 6. The advantages of dividing the field into four units
is that a smaller pump can be used and a small well capacity
is required.
h. Four hours operating per day per plot was requested by the
owner; however, do not enter this value yet.
Step 5. Tentatively determine the quantity of water required QR for each
irrigation unit. Use the formula:
QR = 453 Ad
pfl
Where QR = minimum required discharge capacity in gallons per minute
A ~ acreage of the design area
d = gross depth of application in inches
F = number of days allowed for completion of one irrigation
H = number of actual operating hours per day
QR = 453 x 5 acres x 0.54 In. gross application
4 hrs operating per day x 1 day per irrigation
QR = 306 gpm
Note that the QR should not exceed the well capacity. In situations
where the well capacity is exceeded then the irrigation unit acreage
would need to be decreased or the operating hours per day' increased
or a well of higher capacity would have to be installed.
Step 6, Select a sprinkler spacing that is compatible with farming operations.
Some alternatives would be 40 ft by 60 ft or 60 ft by 60 ft, The 40
ft by 60 ft in a rectangular pattern was tentatively selected.
10-A-3
i,i* cnaMnn retirement in the Technical Guide
Step 7. Check the spnn spa 9 equ e^e^ g ^ condn1ons
n "!c tL m hr The sprinkler spacing should be no greater
6 a "5 % fitted dialer and the lateral spacmg shouid
be no greater than 65% of the wetted chaneter.
r , v , vinHav Thprp are two requirements for which the
' p fn leV n lllo bS Cased: (1) the wetted diameter.
spnmaer seiecj u computed by dividing the
: , "
is used to determine the gpm/spk:
App. rate (in./hr) =
A L
Where S = Spacing of sprinklers along lateral
L = Spacing between laterals In feet
For a tentative application rate, divide the gross application
of 54 inches by the hours operating per day (4 hrs) which
results in 0.135 inches per hour. Now solve the formula for
gpm/spk:
gpm/spk = QJjSjjK/hjix 40 ft x 60 ft
96.3
gpm/spk - 3.36 gpm
With the two sprinkler requirements of 3.36 gpm and 92,3 feet
wetted diameter, refer to the sprinkler manufacturer's charts,
Table 10-A-l shows a typical manufacturer's sprinkler data and
was used to select the sprinkler. The sprinkler selected has
a capability of 3.84 gpm @ 45 psi with a wetted diameter of 92
feet which meets the criteria. The nozzle size Is 9/64 inches.
This data was entered in Item 9.
Step 9. Complete Item 8.
a. Application rate is recomputed using the formula:
Application rate (In./hr) = gpm/spk x 96,3. 3.84 x 96. .3 a 0.15
S x L ~W~T65
b. Time per lateral or unit set in hours is computed by
dividing the gross application of 0,54 in. by the
application rate of 0,15 in./hr. Time per lateral set =
0.54 in. 4- 0.15 in./hr = 3.6 hr,
c. Determine the number of sprinklers per unit, Divide the
field using the drawing prepared in Step 2 into 4 as nearly
10-A-4
equal units as possible. Place the sprinklers, pipe layout
and valves on the plan. Label each unit and place it on
the drawing. Count the number of sprinklers per unit and
enter in Item 8. Units have 88 sprinklers.
d. Determine the actual gpm/unit, Q/\ per unit. Multiply the
number of sprinklers per unit times the gpro/spk to determine
gpm/unit.
Units: 88 spk x 3.84 gpm/spk = 338 gpm
Step 10. Complete the last entry of Item 7. Enter the actual hours
operating per day of 3.6 hours as calculated in Step 9.b.
The Q is obtained by the following formula:
QR = 453 x 5 acres x 0.54 in. gross application = 340 gprn
3.6 hrs operating per day x 1 day per irrigation
Note that as a check, the Q A should be approximately equal to Q R
Step 11. Determine Total Dynamic Head. Refer to Item 10, as each of
the following points are discussed:
a. Size the lateral and submain to determine its head loss.
Usually the longest lateral and submain is used to
determine the head loss within the irrigation unit.
However, ground elevation changes may sometimes cause the
maximum head loss to occur elsewhere. This will be dis-
cussed a little later in this step. Sheets 4 and E> of
Exhibit 10-A-l Pipe Sizing Data Sheet were used for this
purpose. First, the gpm for the lateral and submain was
listed in a cumulative manner beginning with the last
sprinkler. The length of pipe carrying the corresponding
gpm was then listed. Then using Appendix C, the pipe was
sized and corresponding friction head loss (HLf) in
ft/100 ft, listed on the data sheet. The pipe is sized so
that the velocity of water flow through the pipe is less
than or equal to 5 fps. The total friction head loss is
determined by multiplying the HLf (ft/100 ft) x the pipe
length (ft) and suming the results. The elevation
differences are then totaled and added to the total
friction head loss to obtain the total head loss in the
lateral. The summation of 6.38 ft was used in the design,
Elevation difference of natural ground between the risers
and within an irrigation unit must be evaluated for each
design as it can affect the layout of the irrigation unit
and the pipe sizing. It affects the layout because the
nozzle pressure must be maintained within certain limits
in each irrigation unit. These limits are discussed in Step
13.
The effect that elevation difference has on pipe sizing can
best be explained using an example. For instance, if
10-A-5
a lateral is to be installed downhill from the mainline,
a smaller pipe with higher friction head loss may be used.
The elevation difference is downhill (increase in pressure)
which offsets the decrease in pressure due to friction head
loss. An increasing elevation plays a reverse role often
resulting in a larger diameter pipe.
b. The head loss for the irrigation unit is then modified so
that the theoretical mid-system sprinkler is operating at
the design nozzle pressure. This provides for a more
balanced system in that the sprinkler closer to the pump
operates at a pressure a little higher than the design
nozzle pressure and the farthest sprinkler a little lower
in pressure. The head loss can be modified by multiplying
the summation of 6.38 ft x 0.5 = 3.19 ft. (The factor 0.75
would be used if this was a single pipe size lateral
because approximately 7b percent of the pressure loss in
a single pipe size lateral with uniformly decreasing
discharge has already occurred at the midpoint of the
lateral.) Assume the sprinklers within an irrigation unit
are desired to operate at a pressure within + 10% of the
design operating pressure. Technical Guide Code 442 allows
maximum variation of _+ 20 percent. In this case, with the
design operating pressure at 45 psi , the allowable
variation in sprinkler operating pressure is + .10 x 45
psi = +_ 4.5 psi. Therefore, 45 psi + 4.5 psi~= 40,5 psi
and 49.5 psi for the minimum and maximum sprinkler
operating pressure.
c. Size the mainline and determine the head loss. Item 10
could have been used For sizing and determining the mainline
head loss since no elevation changes were involved but the
pipe sizing data sheet was used for the mainline also. The
6 in. main with 338 gpm has a friction head loss of 0.69
ft/100 ft. Total head loss is equal to 0.69 ft/100 ft x
495 ft = 3.43 ft. The 3.43 ft is equal to 1.48 psi.
d. Determine the recommended maximum working pressure. This
is_the class of pipe (160 psi) multiplied by 0.72 - 115
psi since it is assumed special surge and water hammer
control is not to be provided. Do not compute actual
working pressure until later in the design.
e. Design sprinkler nozzle pressure. The 45 psi sprinkler
operating pressure was determined in Item 9. Remember
that this is the operating pressure of the theoretical
mid-sprinkler of the irrigation unit.
f. Miscellaneous and fitting friction losses. This can be
computed using the formula h = (Kv2/2g) where values of
fn d h! , 1 " J?P endlx c - However, this is usually estimated
to be within a range of 1.3 psi to 3.5 psi depending on
the complexity of the system. This example was estimated
to have about 1.3 psi head loss for miscellaneous and
ncttng losses.
10-A-6
Riser height. The height required to get the sprinkler
above the vegetation to prevent distortion of the water.
In this case, 3 feet is required.
Pump discharge pressure (at the entrance to the main pipe
line). This is the pressure the pump must produce so that
the theoretical mid-sprinkler of the irrigation unit is
operating at its design operating pressure of 45 psi .
To obtain the pump discharge pressure the preceding items
were totaled as follows:
Lateral & sub-main friction losses - 1,38 psi
Mainline friction losses - 1.48 psi
Nozzle pressure - 45.00 psi
Miscellaneous & fittings friction
losses - 1.30 psi
Riser height - 1.30 psi
Pump discharge pressure 50.5 psi
Maximum pipe working pressure in main. This is the same as
the pump discharge pressure just determined (50.5 psi).
From step 11-d, maximum recommended working pressure for the
6" class 160 pipe is 115 psi, thus the pipe strength is
adequate throughout.
Pumping lift. This is discussed in Chapter 6. It is the
vertical distance the pump must lift the water in the
well to reach the ground level (main inlet) or in the case
of a centrifugal pump the vertical distance plus losses
(suction lift) from the water elevation at maximum
drawdown to the pump discharge. The pump-drawdown
is considered in determining the pumping lift. This
example has the static water level at 75 feet with 50
feet of drawdown when pumping. Therefore the pumping
lift is 75 ft + 50 ft - 125 ft which is equal to 54.1 psi.
Total dynamic head (TDH). This is the total head loss
that the pump must operate against in order for it to
perform the required work. The pump discharge pressure
(50.5) psi + pumping lift (54.1 psi) = 104.6 psi TDH.
This is usually expressed in feet which would be 241.6 ft
TDH. (use 242 ft.)
Net positive suction head available (NPSHA). This
represents the energy available to move the fluid(water)
into the eye of the impeller.
10-A-7
NPSHA = 144 (Pa - Pv)/w - hf + z
where the minimum probable value for the term 144
(Pa - Pv)/w @ 70F @ sea level * 144 (13.57 - 0.37)/
62.3 = 30.49, use 31 ft. This value (31 ft)
may be used throughout the piedmont (up to 1000 ft
about sea level) and lower lying areas of S.C. for
acceptable accuracy. For higher lying areas (up to
about 4000 ft above sea level) the value should be reduced
about one ft for each 1000 ft rise in elevation.
hf = head loss (ft) due to friction in inlet line and at
the impeller entrance (use 3 ft as average value
in most situtations).
z = elevation difference between pump centerline and the water
surface (assume 20' for this example). If the suction water
surface is below the pump centerline, z is negative. There-
fore, NPSHA = 31 - 3.0 + 20. * 48 ft.
Step I?. Complete Item 11, Pump Requirement. This is the maximum gpm
the pump must produce at a given TOH and minimum not positive
suction head. From Item 8, the maximum Q/\ for an irrigation
unit is 338 gpm. The TDH from the preceding section is 242
feet. The NPSH required must be less than 48 ft. Therefore,
the pump requirement would be expressed as 338 gpm at 242 feet
TDH with NPSH less than 48 ft.
Step 13. Complete Item 12, Power Unit Requirement. This is the brake
horsepower needed at the output from the power unit to supply
power to the pump. The pump efficiency would be obtained
from the characteristics curve for the particular pump to be
used. A value of 0.70 would be a reasonable value for some
pumps, use 0.7. The drive efficiency for a direct connected
electric motor is approx. 100 percent, use 1.00. Therefore,
compute BHP using gpm and TDH from the preceeding step.
BMP > 338 gpm x 242 ft TDH = 29.5
3960 x 0.7 x 1.0
Step 14. Complete Item 13. Check the sprinkler pressure variation
within the system (Irrigation Units) against the allowable.
This was discussed earlier under Item 11. b. The actual is
found by using sheet 4 of 5 of Exhibit 10-A-l. The actual
nozzle pressure of the closer sprinkler is the pump
discharge pressure (50.5 psi) - the mainline losses (1.48
psi) - miscellaneous and fitting friction losses (1.30 psi)
- the riser height loss (1.30 psi) = 46.4 psi. The actual
nozzle pressure of the farthest nozzle is the pump discharge
pressure (50.5 psi) - the mainline loss (1,48 psi) -
miscellaneous and fitting friction losses
10-A-8
(1.30 psi) - the riser height loss (1.30 psi) - actual total lateral
and sub-main losses (2.8 psi) = 43.6 psi.
The allowable nozzle pressure as taken from section 11. b. is 40.5 psi
(minimum) and 49.5 psi (maximum). The actual nozzle pressure of 43.6
psi and 46.4 psi is within this range.
Table 10-A-l. Typical Sprinkler Manufacturer's Data
Highest point of stream is 7' above nozzle.*
Nozzle
Nozzle
+ Nozzle
Nozzle
Nozzle
psi@
7/64"
1/8"
9/64"
5/32"
11/64"
Nozzle
diam
3E! n ._.
di
am gpm
di
am
ap m
di
am CJPJT
di
am gpm
25
78
1.73
82
2.25
85
2
.90
88
3.52
90
4.24
30
79
1.89
84
2.47
87
3
.16
90
3.85
92
4.64
35
80
2.05
85
2.68
89
3
.40
92
4.16
94
5.02
40
81
2.?0
86
2.87
91
3
.63
94
4.45
96
5.37
45
82
2.32
87
3.05
92
3
.84
96
4.72
98
5.70
50
83
2.44
88
3.22
93
4
.04
98
4.98
100
6.01
55
84
2.56
89
3.39
94
4
,22
100
5.22
102
6.30
60
85
2.69
90
3.b5
95
4
.20
101
5.54
103
6.56
H-Standard Nozzle.
*Shown for standard nozzle at normal operating pressure. Area below
dotted line in chart is the recommended working pressure for best
distribution.
LAYOUT CONSIDERATIONS
Items that must be considered in the layout of a permanent and solid-
set irrigation system area as follows:
a. Soil limitations which may affect the ease of installation such as
cut banks caving, depth to rocks and wetness.
b. Plant spacing and row direction so that riser can be properly
located.
c. Maximum height of plants for determing riser height.
d. Location of obstacles such as ponds, fences, overhead power lines
and buried electrical and gas lines which are safety hazards.
e. Topography which may affect the layout of the system and valving
arrangement so that each irrigation unit can be operated within
the allowable pressure variation.
10-A-9
CONSTRUCTION REQUIREMENTS
Construction Items that must be checked to be assured of a quality
installation are as follows:
a. The depth of cover over the buried main line must be adequate for
protection from vehicular traffic and the farming operation.
b. Thrust block dimensions, location and alignment to prevent pipe
joint separation.
c. Location and size of air vents and pressure relief valve. Risers
function as air vents but others may be required if a pipeline has
a sumrni t with no riser.
d. Riser material, diameter, height and spacing.
e. Sprinkler model and size nozzle. Location of part circle
sprinklers if planned.
f. Location and size of valves which serve each irrigation unit.
g. Depth of cover over the buried pipe.
h. Verify the pipe requirements such as SDR number, pressure rating,
ASTM designation, PVC material, pipe diameter and if PIP or IPS
pipe. '
i. Check valve installed at pump discharge.
j. Verify purnp s motor and well size. Then check the nozzle pressure
and variation within each irrigation unit using a pressure gauge
with a pitot tube.
10-A-10
EXHIBIT 10-A-l
Sheet 1 of 5
IRRIGATION DATA SHEET
System type (circle): Center Pivot, Traveling Gun,
CONSERVATION DISTRICT
COOPERATOR
At
IDENTIFICATION NO.
^
H9< J-
FIELD OFFICE
LOCATION ~
FIELD NO.
Co.
1. Design area
2,0
acres (Area actually irrigated)
Soil series *?t>*&xn
Design
t/^<=
Soil Series: -^
?nyA& >7
Predominate maximum
Average
slope 4 %
Soil Depth
Texture
AWC
(in.)
o-t/
(USDA)
^S.
(in. /in
*&$
.)
//- 31
^,A.
.t*
'- 0~/3
L S
,0%
Crops:
Crop
Total
Planting Date Maturity Date
- -N
Water supply:
Source of supply ; ( stream, (we Ijj reservoir, etc.)
Stream: Measured flow (season of peak use) gpm
Reservoir: Storage _ ~__ ac. ft. Available for irrigation
Stream or Reservoir: Maximum drawdown available -
ac. ft.
_ -^__ ft.; Maximum
elevation lift on intake side of pump ft.
Well: Static Water
M-easured Capacity
gpm @
ft drawdown
Design Pumping Lift
Pump Impeller Level
ft (to ground level - main pipeline inlet)
ft
Distance supply source (main pipeline inlet) to field
Quality ofc water (evidence of suitability):
4. Other Data:
Type of power unit and pump to be used;
* ~ 3
10- A- 11
PERM. /SOLID-SET SPRINKLER IRRIG. SYSTEM Sheet -2 : of JL.
Cooperator: ToKn Poo. Designed by : Tom Uones Checked by: A. Engineer
5. Map of design area - Scale 1" = _OQ ft
Sketch map on grid or attach photo or overlay.
O
r*-
- /3iO'
>.
i
i
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;
i y
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1
< J
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Sketch map should show:
J. Source of water
b.
c.
d. sprinkler system
e> pi an of
"
g. North arrow
lies,
10-A-12
PERM. /SOLID-SET SPRINKLER IRRIG. SYSTEM
Sheet 3 of 5
6.
>erator: _Jt>hn Da<^ , Designed by: ^^27 , /r>r.7 Checked by: /q Mt
Crop Information
ff
IRRIGATION UNIT NUMBER
1
2
3
4
Kind of crop
V
Acreage to be irrigated (acres) Lf
#$-
Depth of soil water control zone (in.)
tn
Peak use rate (in. /day)
0* 11
Weighted AWC for water control zone(in, /in)
_ f\ 9
O.Q <a
7. Design Procedure
AWC within water control zone (in.)
0,7(0
Depletion allowed prior to irrigation (%)
^6
Maximum net water allowed per irrig. (in.)
#,38
Net water applied per irrigation (in.)
0.3%
Max. recommended_a_pplication rate (in./hr.)
tfo /imtT
System efficiency (%)
70
Gross application per irrigation (in.) ^
0,3-^
Peak irrigation interval (days)
J,/
Irrigation Period (days per irrig.)
J
Hours operating per day
+
QR = Quantity of water required (gpm) L f
3*0
8. Irrigation Unit Design
Application Rate (in./hr)^/
frt^
Actual Time per lateral or unit set
gross application
3.6
(tira n application rate )
Number of sprinklers per unit
n
QA ' *" Quantity of water actual (gpm/unit)
No. of sprinklers/unit x gpm/spk.)
33$
9. Sprinkler' Specifications:
a. sprinkler spacin
b. nozzle size
c. capacity ^ % gpm @
ft, lateral spacing
wetted diameter
6 ft
or
/of-
t:
acres x
in . gross application =
nrs P r * P er
days per irrigation
I/ Application rate (in./hr)
gpm/spk x 96.3 MUST BE < MAXIMUM RECOMMENDED RA
S x L
Where S = Spacing of sprinklers along lateral in feet.
L = Spacing between laterals in feet.
maximum unit gpm: Must be approximately equal to
10-A-13
PERM. /SOLID-SET SPRINKLER IRRIG. SYSTEM
y
_ _ _^f**\
Cooperaton ^y 0/4/7 '2/O&. Designed by:
10. Determining Total Dynamic Head zf
ones' Checked
Sheet 4j> f 5
: -_A^
(J
11.
Kind of Pipe
Design
Capa-
city
(gpm)
IPS
PIP
Other
Lengtt
(ft)
Friction
Head
Loss 5J
(ft/lOOft)
Total
Head
Loss
HL
(ft)
Total Head
Loss, HL
Working
Pressure
(ft)
(psi)
Recom-
mendet
Max 6/
(psij
Act
Max
(pa
Main
Sub-
Main
Lateral
Diameter
(in.)
XXXX
y
/
(jrcc. O
"fac/iety &,
oe, c.o.
'<x^*j)
6.3f
XXXX
xxxx
xxxx
* '
XXXX
xxxx
xxxx
XXXX
xxxx
xxxx
XXXX
xxxx
xxxx
XXXX
xxxx
V W \
AA A. JT
xxxx"
XXXX
XXXX
XXXX
XXXX
XXXX
(s>3l
J,I1 7 /
_/.3ff
y
xxxx
xxxx
xxxx
3,13
/.f
//i( -
-j
1
xxxx
xxxx
xxxx
xxxx
xxxx
xxxx
xxxx
xxxx
xxxx
xxxx
xxxx
xxxx
Design Sprinkler Nozzle Pressure
10 4,
fy&o
Miscellaneous and Fitting Losses (usually 3 psi +)
3,0
A3
Riser Height
/, 3
Pump Discharge Pressure (at main pipeline inlet)
II&.6
Pumping Lift (including losses)
!3.S~.
f\l
Total Dynamic Head, TDH
zt!>6>
jo^6
Estimated Net Positive Suction Head Available, NPSHA
48
Pump Requirements: 33% gpm @ /Q^-,6, psi or ^V-?ft of head and NPSH less
12. Power Unit Requirement:
3960 x
ft TDH
' 7
drive eff.
13. Check pressure variation within system (irrigation unit).
Allowable = +_ JQ % of nozzle operating pressure = +
Allowable - VA^" psi to
8_/ Actual = 43,6, psi to
psi
4/ Use pipe sizing data sheets where elevation differences are present and/or
additional data lines needed.
_5/ Keep velocity <^ 5 fps unless means to control surge and water hammer are other-
wise adequate.
J6/ For plastic pipe, pressure rating divided by 0.72 unless means to control
surge and water hammer are otherwise adequate.
If Sets^optimum nozzle pressure at a theoretical raid-system sprinkler.
8/ Consider elevations and location, Adjust ]_/ if possible to stay within
_ allowed variation. If not, the system must be redesigned.
Design approved by: 7^ ^ ^7o/?<2<y Date:
10-A-14
10-A-15
SOUTH CAROLINA IRRIGATION GUIDE
CHAPTER 1Q-B. TRAVELING GUN SPRINKLER IRRlGATIlDNJYSTgH
GENERAL
The example problem in this chapter is intended to illustrate the pro-
cedure to follow in the design of traveling gun irrigation systems.
It is understood that one example cannot explain all design situations
or alternatives to consider when designing traveling gun sprinkler
irrigation systems.
DESIGN CRITERIA
Design criteria for traveling gun sprinkler irrigation system is con-
tained in Technical Guide, Irrigation System, Sprinkler, Code 442, for
South Carolina. All traveling gun sprinkler irrigation system must be
designed in accordance with the criteria contained in Code 442.
Guidelines for line spacings may be obtained from this chapter.
EXAMPLE PROBLEM
The following example problem is intended to cover the basic design
steps to follow in the design of traveling gun sprinkler irrigation
systems. A standard form (Exhibit 10-B-l) is used which is a useful
tool in designing and recording data.
Given:
1. Existing Nelson 200 gun, 27 trajectory, 1 3/4" Ring Nozzle, 270
angle of operation.
2. Crop & Acres: 40 acres soybeans
28 acres peanuts
3. Soil: Fuquay Sand
4. Location: Qrangeburg, South Carolina
5. Slope: Maximum 656
6. PU.P capability (existing): 500 gpm % 320 ft TDH; 600 gpm
350 ft TDH; 700 gpm 400 ft TDH
7. Crop Rows: North and South
Solution:
S.,p !.
pertinent data of the site
10-B-l
Step 2. Complete Item 5. Make a drawing to scale of the field locat-
ing trees, buildings, well and other features.
Step 3. Complete Item 6. Guidance in selecting the moisture extrac-
tion root depths (soil water control zone) and the design
peak use rate are to be taken from this guide, Tables 3-1
and 4-1 respectively. The weighted AWC is computed using
data from item 1.
Step 4. Complete the following parts of Item 7 (the figures used in
the following steps will be specifically oriented to the
soybeans, the crop with the larger peak consumptive use).
a. Available water capacity (AWC) within the water control
(root) zone is the product of the root zone moisture
extraction depth (24 inches) times the moisture holding
capacity of the soil (0.05 in. /in.) AWC = (24 in.)(0.05
in. /in.) = 1.20 in.
b. The percent depletion allowed prior to irrigation is
selected to be 50%.
c. The maximum net water applied per irrigation (in.) is
the product of the percent depletion allowed prior to
irrigation (50*) times the water available within the
root zone. The maximum net water applied per irrigation
is * (0.50)(1.2 in.) = 0.60 in.
d. The net water to be applied should be less than or
equal to the maximum allowed. Use the maximum for
this example - 0.6 inches.
e. Maximum application rate from table 2-6. Use 0.8" oer
hour or less.
f. The water application efficiency is selected to be 70%
(average for day and night irrigation).
g. The gross water applied per irrigation (in.) is the net
water applied (0 60 in ) divided by the system efficiency
(70%). Gross water applied = 0.60 in. 4- 0.7 = 0.86 in.
fifrpc-- 1s the net
.60 nches) divided by the design peak use rate
(0.30 in./day). Peak irrigation interval = 0.60 in,
u.ou = {,() days.
The irrigation period to be used in the formula for
detemng the Q R 1s the irrigation interval 2*0 days
10-B-2
j. The hours operating per day were discussed with the owner
who advised that he irrigated continuously until
completed. Therefore, the 20 hours were agreed upon
providing another 4 hours for moving the equipment.
k. Now determine the quantity of water required (gpm) using
the formula as follows:
QR * 453 Ad (See page 10-A-3 for explanation of formula.)
~TH
QR = 453 x 68 acres x 0.86 inches gross application
20 hrs~opr\ per cfay x 2,'CTdays per irrigation
Qft = 662 gpnn
Step 6. Complete Item 8, Irrigation Unit Design.
a. Keeping in mind the capability of the pump (see sheet
10-B-l) and the minimum Q required of 662 gpm, determine
the nozzle size, sprinkler gpm, and nozzle pressure. Using the
Volume Gun Performance Tables (Table C-27) with a ring
nozzle size of 1 7/8 inches, a capacity of 675 gpm at 80
psi and a wetted diameter of 470 feet was selected,
b. Determine the lane spacing using approximately 60-65% of
the wetted diameter of the sprinkler assuming a wind speed
of 5 to 10 mph (see Table 10-B-l, p. 10-B-7). The total
length of the field is 1,660 feet. The spacing of
290 ft between risers was tentatively selected which is
62% of the wetted diameter. Now, in order to properly
irrigate the ends of the field, the riser needs to be
approximately 75% of the wetted radius away from the
field boundary (i.e., .76 x 235 ft) or 176 feet. Now
determine the distance actually available by dividing
the distance 1,800 ft. by 290 ft. = 6.21 spaces. Take
1.Z1 spaces x 290 ft/space = 350 ft. and place half of
this (175 ft) distance at each end of the field between
the riser and field boundary. The 175 feet is adequate.
c. The application rate is computed using the following
formula:
Q x 360
s 13630 X q
270.
Application rate - jfff^SJ ' ' K
10-B-3
d. The travel speed is computed by the following formula:
Travel Speed (ft/mi n)
- 1.605 x sprinkler gpm
lane spacing (ft) x gross water applied (in.f
= 1*605 x 675 * 4.34 ft/min for soybeans
290 x 0.86
e. Time per 660 ft. run (hrs) = 660 ft x 1 hr
4.34 ft/min 60 mm
= 2.53 hours
Step 7. Complete Item 9, Sprinkler Specification.
Step 8. Make a scaled plan layout of the system. Pipe sizes etc.,
will be added later.
Step 9. Complete Item 10. Size the mainline and determine the Total
Dynamic Head required for the pump:
a. Use a 8-inch diameter PVC, SDR 26, class 160 IPS pipe. A
length of 1725 ft was determined from the layout. The
friction head loss is 0,69 ft/100 ft and is taken from
Appendix C. The total head loss for the 8-inch PVC is
0.69 ft/100 ft x 1725 ft = 11.9 ft. The recommended maxi-
mum working pressure in the pipe is 0.72 x 160(class
rating) = 115 psi since it is assumed special means to
control surge and water hammer will not be provided. Do
not enter the actual working pressure yet.
b. Using 660 ft of 5 inch flexible hose, the friction loss
taken from Exhibit C-l is 2.0 psi/100 ft or 4.62 ft/100
ft. Total head loss for the hose is 660 ft x 4.62 ft/100
ft - 30.5 ft. Table 10-B-2 is a guide for flexible hose
selection.
c. Enter the sprinkler pressure at the nozzle* miscellaneous
losses and elevation differences between the main pipe-
line inlet and the nozzle when located on the high point
in the field.
10-B-4
d. The sum of a, b, and c gives a pump discharge pressure
at the main pipeline inlet required of 249.1 feet of head
or 107.84 psi. Enter this value also as the actual
maximum working pressure 1 in the main.
e. The pumping lift (suction lift in this example) is the
sum of the static suction lift and friction losses in
suction pipe and miscellaneous inlet fittings. The
static suction lift is 15 ft. from item 3. The friction
loss in 6 inch inflow line (30 linear ft, 5" PVC SDR-26)
is 5.9 ft/100 ft x 30 ft = 1.77 ft. The losses in the
inlet fittings may bs calculated using appropriate head
loss coef . k from Table C-18. Usually these losses are
_< 2 feet, use 2 ft. The total pumping lift is approxi-
mately 15.0 + 1,77 + 2.0 = 18.77 (use 19 ft),
f. The total dynamic head is the pumping lift plus the
pump discharge pressure, 19.0 ft + 249.1 ft = 268.1 ft =
116.06 psi .
g. The minimum net positive suction head available (NPSHA)
is approximately equal to 31.0 - suction lift = 31.0 -
19.0 = 12.0 ft (see example in section 10-A and Chapter 6
of this guide for more information).
Complete item 11. The pump requirement of 675 gpm at 268
feet of head (TDH) is within the capability of the pump.
Although not given for this pump, the NPSH required must
be less than about 12.0 ft or cavitation is likely.
Step 11. Complete item 12, Power Unit Requirement. This is the brake
horsepower needed at the output from the power unit to supply
power to the pump. The pump efficiency would be obtained
from the characteristics curve for the particular pump to be
used. A valve of 0.70 would be a reasonable value for some
pumps, use 0.7. The drive efficiency for a direct connected
electric motor is approximately 100 percent, use 1.00.
Therefore, compute BMP using gpm and TDH from the preceeding
step.
BHP > 675 gpm x 268 ft TDH = 6 5.3
3960 x 0.7 x 1.0
Step 10,
10-B-5
Step 12, Complete the plans. The specifications, location of the
pipe, check valve, air vents, pressure relief valve, risers,
thrust blocks, etc., should be shown on the plans. See
sheet 2 of 5 of Exhibit 10-B-l.
LAYOUT CONS1DERSATIQNS
Items that must be considered are as follows:
a. Plant spacing and/or row direction so that travel lanes can be
located properly.
b. Location of obstacles and safety hazards.
c Whenever possible, place the risers a full hose length away from
the edge of the field. This greatly facilitates laying out the
hose and reeling it back up.
d. Soil limitations such as surface texture may necessitate a part
circle volume gun so that the area is not irrigated in front of
the gun as it moves, providing a dry footing.
e. Topography may dictate the lane direction to prevent misalignment
of the traveler while in operation.
CONSTRUCTION REQUIREMENTS
The following is a list of construction items that should be checked
to be assured of a quality installation;
a. The depth of cover over the buried mainline must be adequate for
protection from vehicular traffic and the farming operation.
b. Thrust block dimensions and location to prevent pipe joint
separation*
c. Location and size of air vents and pressure relief valve.
d. Size and proper direction of installed check valve.
e. Riser material, size, number and location,
f . Verify the pipe requirements such as SDR number, pressure rating,
ASTM designation, PVC material, pipe diameter and if PIP of IPS
size,
9. Verify pump, motor and well size. Check nozzle pressure.
10-8-6
50
55
Percent of Wetted Diameter
60
Spri nkler
Wetted
Oi ameter
ft
200
300
3bO
400
450
500
bbO
6UO
Wind over
10 mph
ft
100
150
175
200
22b
2bO
27b
300
ft
ft
65
Wind up to
10 mph
ft
110
120
137
150
165
180
192
210
220
240
248
270
275
300
302
330
330
360
130
162
195
227
260
292
325
358
390
70
Wind up to
5 mph
ft
140
175
210
245
280
315
350
385
420
ft
150
187
225
262
300
338
375
412
80
No
Wind
ft
160
200
240
280
320
360
400
440
Table lG-fl-4.
Recommended towpath spacings for traveling sprinklers
with ring (lower) and tapered (higher percentages)
nozzles
FLOW RANGE (gpm)
50
150
200
250
400
500
Table 10-B-2.
150
250
300
600
750
1000
HOSE DIAMETER (Inches 1
3.0
3.5
4.0
4.5
5.0
Guide for Flexible Irrigation Hose Selection
(See Exhibit C-l, p. C-16 for friction loss table)
10-B-7
IRRIGATION DATA SHEET
System type (circle): Center Pivot, (Traveling
CONSERVATION DISTRICT
COQPERATQR
IDENTIFICATION NO.
\, Design area
-
FIELD OFFICE
LOCATION '
FIELD NO.
EXHIBIT 10-B-l
Sheet 1 of 4
(Other, list)
/)r~Cf/iej c0uSj
tfjj <r~c^:
3
acres (Area actually irrigated)
Soi
1
series
/
f
/
Design
Soil
Soil
Ser ies :
jiQty Predominate maximum
slope //
Depth
^T
^
Texture
Average
AWC
(in
.)
(USDA)
(in.
/in
.)
Q-0*
Crops:
Crop
Total
Acres
PlaiUin^Dajj
t//
Ma tu r it y Da t e
2/2
Water supply :
Source of supply; (stream, well, reservoir, etc.)
Stream: Measured Elow (season o peak use) IQQO
Reservoir: Storage - ac. t. Available for irrigation
Stream or Reservoir: Maximum drawdown available
ac . t'l .
ft.; Maximum
elevation lift on intake side of pump
Well; Static Water Level_
Measured Capacity _
Design Pumping Lift
Pump Impeller Level
gpm
ft drawdown
_ft (to ground level - main pipeline inluO
Distance supply source (main pipeline inlet) to field /poo ft
Quality of water (evidence of suitability): ^ POC ^
Other Data:
Type of power unit and pump to be used;, "Z?/e.Je./
10-B-8
IgAVELtNG GUN IRRIGATION SYSTEM
Designed by vVkx\-\er Sone-bChecked by:
5, Map of design area ~ Scale V * . __3OQ ft
Sheet >f
Cnoperator:
. __
Sketch map on grid or attach photo or overlay,
T
no 1
Sketch map should show:
a Source of water
Si Major elevation differences
c. Row direction
d. Sprinkler system layout
e Plan of operation
f Field obstructions
' trees, buildings, etc.)
. North arrow
10 -B -9
Sheet 3 of
TRAVELING GUN IRRIGATION SYSTEM
Cooperator:
Designed by: t/ J.
Checked by: j;
6. Crop Information
IRRIGATION UNIT NUMBER
1
2
3
4
Kind of crop
l/&w/)J&
joyptian*
So/^-r
Acreage to be irrigated (acres) -^
JL%
*fo
6f
Depth of soil water control zone (in.)
/t
JS/S
&*
Peak use rate (in. /day)
,1>
, 3&
Weighted AWC for water control zone(in./in)
.o5"
.05"
.OS"
7. Design Procedure
AWC within water control zone (in.)
0-1
/.z
I.Z
Depletion allowed prior to irrigation (%)
3~o
5^>
$>
Maximum net water allowed per irrig. (in.)
o.tf
\j* to
0-fp
Net water applied per irrigation (in.)
Q.tf'
\f * t
O.&
Max* recommended application rate (in./hr.)
OL?
0.8
o.<&
System efficiency (%)
7b
7>
70
Gross application per irrigation (in.) ^J
Oi& f
an
Peak irrigation interval (days)
i, I
JJ.D
I*
Irrigation Period (days per irrig.)
L A*
2,t>
Z.b
Hours operating per day
JZ^>
ZO
QR - Quantity of water required (gpm) -L/
z&S'
JQQ
8. Irrigation Unit Design
Q/W - Quantity of water actual (apm)
6>7^
Application rate (in./hr)-^
O. (Z->
Lane Spacing ^'Jfift
4 1 , 3*/
Travel Speed(f t/min)^/ h Lane Spacing, ft
Lane Spacing .j&iflf t
jt.5-3
lime per <^Qrun (hrs) Lane Spacing, ft
i
Sprinkler Specifications:
a. Lane Spacing Z?Q ft
b. Nozzle Size
Capacity
/ W m.^lor taper (circle); Wetted Diam. ^7^ ft;
@ g o psi; Trajectory Angle ^7 degrees;
__
Degrees of coverage
c. No. of sprinklers operating simultaneously
d. Total design capacity all sprinklers &&
g pm
"II
R ~
ac ^es x
must be
S&> in. gross application
hrs opr. per day x %, days per irrigation
3/ Application rate 13630 X sprinter ap m
(radius of wetted circle)*
coverage)
4/ Travel Speed =
1-605 x sprinkler gpm
Lane Spacing, ft, x gross water applied, in.
10-B-10
Sheet 4 of
Designed by:
^operator:
10, Determing Total Dynamic Head:
TRAVELING GUN IRRIGATION SYSTEM
Checked by:
(Total main line length
Kind of
Pipe &
SDR, Sch,
Class ,etc
Pipe
Size
(in.)
Design
Capacity
(gpm)
IPS:
PIPE
>/ PIP:
SIZING
HOS15 SIZING^-/
Total
Head Loss
Working
Pressur
Lengtl-
(ft)
i- riccion
Head Los si/
(ft/100 ft)
Lengtli
(ft)
p t ic cion
Head Loss
(ft/100ft)
(ft)
(psi)
Ke com-
mended
max-Z-t (psi
AC
Ma
(P
fVC, JPtfU
c./qjs /6>&
t
475"
iTZf
A*?
_ .
//.9
z-7, tr
IIS.
/<
f*ay F/at-
Hoje^
.<
67S"
b(*0
^;s<
3&-5~
/y.&o
~
-
'}toJULMll*JL^^ ,
'Sprinkler Pressure at Nozzle*, (circle which)
/?+%
$0,0
Misc. & Fitting Losses (usually 3 psi +)-
&**?
&#
Elevation Dif ferencel^/
/s-.o
&.&
_j ,
Pump Discharge Pressure (<J (Main Pipeline Inlet)
#?/
it>7*W
Pump Lift (Including losses)
ft
f.&3
Total Dynamic Head, TDH
2,H
//&
Estimated Net Positive Suction Head Available, NPSHA
/Z.&
_^
11. Pump Requirements:
Capacity ttftT gpm @ //& psi or
and NPSH less than /^ fl
%
ft of head
12, Power Unit Requirement:
BHP > 6,7^ gpm x
ft TDH
3960 x
pump eff. x
drive ef.
5/ Keep velocity 5 fps unless means to limit surging and water hammer
are otherwide adequate.
6/ Omit this section if required hose inlet pressure is known and is used
in TDH calculations.
ll For plastic pipe 72 percent of the pressure rating unless means to
limit surge and water hammer are otherwise adequate*
8/ Mfg, recommended pressure plus one-half the elevation difference
(plus or minus) from hose inlet to highest point in the field along
the lanes.
/ Traveler turbine losses (approx. 10 psi) would need to be added as
applicable,
1Q/ Difference in elevation either from well or pump discharge and the
elevation of the highest hose inlet or nozzle (plus or minus) in
the field along the lanes.
Design Approved By:
Date
IQ-B-II
SOUTH CAROLINA IRRIGATION GUIDE
CHAPTER 10-C. CENTER PIVOT IRRIGATION SYSTEMS
GENERAL
The example problems in this chapter are -intended to illustrate the
procedure used in the design of center pivot irrigation systems. It
is understood that these two examoles cannot show all design
situations or all alternatives to consider when designing a center
pivot irrigation system. Most often center pivot irrigation systems
are designed by the manufacturer and evaluated by the engineer.
DESIGN CRITERIA
Design criteria for center pivot irrigation systems are contained in
the Technical Guide, Irrigation System, Sprinkler, Code 442, for South
Carolina. All center pivot systems must be designed in accordance
with applicable requirements contained in Code 442.
FORMULA USED IN DESIGN AND EVALUATING CENTER PIVOT IRRIGATION SYSTEMS
The following formulas are used in the design and evaluation of center
pivot irrigation systems:
a. Total capacity requirements based on known application depth, area
and time of application.
Q - 453 Ad
FH
Where; Q = Total system discharge capacity in gpm
A = Acreage of the design area to be sprinkler irrigated
in acres,
d = Gross depth of application in inches.
F = Number of days allowed for completion of one
irrigation.
H = Number of actual operating hours per day
b. Application rate from center pivot systems.
I = 96.3 Qs
SB D
Where: I Average application rate in inches per hour
Qs= Discharge from individual sprinkler in gpm
D = Wetted diameter of sprinkler nozzle in feet
SB= Spacing of nozzles along the boom in feet
96.3= Units conversion constant = (12 In/ft) (60 min/hr)
-t- (7.48 gal/cu.ft.)
10-C-l
Gross application depth in inches from individual sprinklers on a
center pivot.
d = Qs
0.62 SB v
Where : d = Application depth in inches (gross)
v = Velocity of rotational speed of individual sprinkler
around the pivot point in feet per minute
0.62 = Units conversion constant = 7.48 gal/ft3 divided by
12 in. /ft.
Equations b. and c. can be combined to relate terms into a re-
lationship sometimes useful.
v * D I
60 d
End gun discharge, q g (gpm)
q - Q <1
Where: L = the length of the lateral pipe (ft)
R = L plus 90 percent of the radius wetted by the end
gun (ft)
Q = total system capacity (gpm)
EXAMPLE PROBLEM
The following example illustrates a typical problem. Since center
pivots are designed by the manufacturer using computers, this example
could apply to many situations in which SCS merely would be providing
soils and other data or either could be evaluating a system design.
SCS could provide data sheets partially completed to the landowner. The
landowner then could have an irrigation company provide pertinent
design data on the forms and return them to SCS. An SCS employee then
s ^uld complete the data sheets as a permanent record for future
and provide copy to the landowner.
acres corn.
, South Carolina
jsel.
10-C-2
7 ^Innp- fl~fi#
r * sJIUJJC. J U /o
8. End gun will not be used for this system.
SpJuVkjn;
The Hem numbers mentioned in the step by step solution refer to the
Herns on the standard form "Irrigation Data Sheet" in ExhiDit 10-':-l.
Step 1. Complete Items 1-4. These items provide pertinent data of
the site.
Step ?, Complete Item 5. Make a drawing to scale of the field locat-
ing trees, buildings, well and other features.
Stop 3. Complete Item 6. Guidance in selecting the moisture extrac-
tion rooting depths (soil moisture control zone) and the
design peak use rate are to be taken from Tables 3-1
and 4-1 respectively. The weighted AVJC is computed using
data from Item 1.
Slop 4. Complete the following parts of Item No. 7,
cu Available water capacity (AWC) within the water control
(root) zone is the product of the root zone moisture
extraction depth (24 in.) times the AVJC of the soil
(O.Ob in. /in.)
AWC = 24 in. x 0.05 in. /in. - 1.20 in.
b. The percent depletion allowed prior to irrigation is
selected to be 50%.
c The maximum net water allowed per irrigation is the product of
percent depletion allowed prior to irrigation (bO%)
times the available water within the root zone (1.20 in .).
The maxfmum net *ater allowed * 0.50 x 1.20 in. = 0.60 in.
d The net water to be applied should be less than or equal
iS the maxlmlim allowed. Use the maximum for this example
- Q.6 inches.
e
Maximum application rate from Table 2-6 for sand 0.6"
water applied, & 5* predominate maximum slope - (No
limit).
f The system efficiency is assumed to be 70%.
M
water appli
Vi, The peak
. , , j
day)= 2.6 days
10-C-3
j. The hours operating per day is 22 hours.
k. The quantity of water required (gpm) is computed using
the formula:
QR = 453 x ___ acres x inches gross application
___ hours operating per day x __ days per irrigation
_ . _____
22 hrs/cTay x 27(1 cfays/irrigatfon
QR = 1,284 gpm
The manufacturer used 1,300 gpin for the design of the system.
Step 5. The manufacturer provides the data for Item No. 8. This must
meet the criteria previously discussed.
a. Pivot length = 1,360 ft(outside tower = 1330 fb); pivot
inlet pressure = 65 psi .
b. Impact sprinklers.
c. Gross application per revolution is 0.86 in. per 44 hours.
d. Nozzle gpm and pressure along last 100 ft of span is 10.1
gpm at 45 psi on spacing of 6.4 ft.
e. Nozzle wetted diameter is 102 feet.
f . Gun coverage = __ ___/t; ____ gpm @ ____ psi (Not
applicable to this problem)
Step 6. Check the maximum application rate, Item 9.
a. Time per revolution to apply gross application = 44 hrs
(from manufacturer) .
b. Velocity of outside tower:
v, ft/hr =
hours per revolution
_
44 hours
* 190 ft/hr
c. Determine time of application (i.e., time it takes the
sprinkler to move past one point), average, and maximum
application rates using the formulas provided in item 9,
10-C-4
Step 7. Complete Item 10. for sizing the mainline, determining total
dynamic head and the net positive suction head required
for the pump.
a. The mainline is 30 feet of 10-inch diameter PVC
pipe (SDR 21). The friction head loss is 0.88 ft/100 ft and
is taken from Appendix C. The total head loss in the mainlin
is 0.88 ft/100 ft x 30 ft = 0.3 ft. The recommended maximum
working pressure in the pipe is 0.72 x 200 (class rating)=
144 psi since it is assumed special means to control surge
and water hammer will not be provided. The actual working
pressure will be computed later in the problem.
b. The pressure at the pivot was given by the manufacturer
and is 65 psi. The elev. increase from pivot inlet to
highest sprinkler at high point along the lateral = 15 ft.
or 6.5 psi. Therefore, the recommended pressure at pivot
inlet - 65 + 6.5/2 = 68.2 psi.
c. The miscellaneous and fitting losses were estimated to be
3.0 psi.
d~ The elevation difference from well to the pivot inlet was
measured to be 12.0 feet.
e. The sum of a., b., c. and d. gives a pump discharge
pressure at the main inlet pipe required of 176.7 ft or 76.5
psi. Enter this value also as the actual maximum working
pressure in the main. The working pressure is less than the
recommended maximum thus the pipe should be adequate.
f. The elevation pumping lift (from item 3) is 150 ft. Total
lift including pump column and other losses would be slightly
more. Use* 150 ft as approximation for lift plus losses.
g. The total dynamic head is the pumping lift plus the pump
discharge pressure, 150.0 ft * 176.7 ft = 326.7 ft or 141.4
psi .
h. The minimum net positive suction head available (NPSHA) is
approximately equal to 31.0 - hf + z. (see example in
section 10-A for definition of values and Chapter 6 of this
guide) .
hf = (use 3 ft for loss at impeller and in the well pipe)
z = 180-150 = 30 ft.
Therefore, NPSHA = 31,0-3.0 + 30. = 58.0 ft
Step 8. Complete item 11, Pump Requirement. This is the maximum gpm the
pump must produce at a given TDH. From Item 7, the actual Q for
the irrigation unit is 1300 gpm. The TDH from the preceeding
section is 141 psi or 327 ft. The NPSH required must be less
than 58.0 ft (usually this value is most critical for centri-
fugal pumps).
Step 9. Complete item 12, Power Requirement, using formula given,
10-C-5
Step 10. Complete the plans. The specifications, location of the pipe,
check valve, air vents, pressure relief valves, etc., should
be shown on the plans.
CONSTRUCTION REQUIREMENTS
Once a system is designed it must be installed as planned in order for
n to function property. The following is a list of key points that should
be checked during construction to be assured of a quality installation:
a. Depth of cover over the buried mainline is important for protection
from vehicular traffic and farming operation.
b. Thrust block dimension and location to prevent pipe joint separation.
c. Location and size of air vents and pressure relief valve.
d. Size and proper direction of installed check valve.
e. Riser material and dimension as well as location for pivots.
f. Length and quality of pipe, diameter, location, appropriate
ASTM designation, size, pressure rating and SDR as measured
or found written on the pipe,
g. Determine if IPS or PIP pipe is used which will have an
effect on the total head loss of the system.
h. Verify length of the center pivot lateral and if spray or
impact type sprinklers.
LAYOUT CONSIDERATIONS
During planning and layout of a center pivot there are many things to be
considered. Items to be considered are the soil limitations, obstacles
such as fences, ponds, ditches and trees, topography of the field, the
farming operation and safety hazards such as electrical and buried gas
lines.
The soil limitations might affect the pivot's ability to traverse the field
and/or the runoff erosion potential from high application rates.
Obstacles, if not considered, could result in severe damage to the pivot.
Bridges or culvert crossings may be needed to cross wet areas or ditches.
Electrical lines and buried cable or gas lines must be located prior to
burying the pipe or locating the pivot, not only to facilitate installa-
tion, but to prevent a real safety hazard.
Topography must be considered because center pivots are limited as to the
slope on which they can function properly.
The greater the land slope the greater the erosion potential, Therefore,
the application rate must be compatible with the slope to prevent erosion
from center pivot systems.
10-C-6
Procedure
For
Determining Gross Application of Center-Pivot Sprinkler
Objective
To develop a table that relates the dial setting of the center-pivot
timer to the gross water (in inches) applied. The table may be used
by the irrigator to adjust the system speed to obtain a desired gross
application. The procedure described applies to electric system
timers which read from to 100 percent. However, the procedure can
be adapted to other timers.
Procedure
1. Determine Speed of End Tower
Select a reference mark on a wheel on the end tower. Set a stake
by this mark. Start timing when the wheel starts moving forward.
Continue timing until the wheel has moved 20 to 30 feet or until
after the can catch is made. Mark distance traveled by placing a
second stake by reference mark on wheel ans stop timing just as
the wheel starts to move forward. Read time and measure distance
between the two stakes.
Speed of end tower, ft per hr = Distance traveled, ft x 60
Time, min
2. Determine Time Per Revolution
Once speed is determined, compute time of travel for one re-
volution at the % setting on the timer.
Time per revolution, hrs = Distance traveled by end tower, ft
(At % setting on timer) Speed of end tower, ft per hr
Distance traveled by end tower, ft =
2 x 3.14 x Distance from pivot to end tower, ft
3. Determine Hours Per Revolution For 100% Dial Setting
Hours per revolution (at 100%) =
(Hours per revolution)(Dia1 Setting)
100
Note: Use the dial setting on the control panel at the time the
speed was determined and hours per revolution corresponding to
this setting.
4. Determine Hours Per Revolution For Each Dial Setting
Hours per revolution at W = (Hours per revolution at 100%) 10Q
X*
10-C-7
5. Determine Gross Application For Each Dial Setting
Gross application, in. =
jjjours_per revolutlgnjgrjjlal setting) (GPM)
(153) (Acres irrigated)
Note; For acres irrigated, use design acres. If not available,
use the effective wetted area.
Example
The center-pivot timer was set on 35% and end tower traveled 60.2
feet in 19 minutes. Distance from pivot to end tower is 1330
feet. System applies 1300 gpm on 145 acres.
End tower speed = (60.2)(60). = 190 ft per hr
19
Time per revolution at 35% = (2X3.14 )(1330) = 44 hrs
190
Hours per revolution at 100% = (44) (35%) = 15.4 hrs
~
Hours per revolution for each of the other dial settings
For 90% = 05.4X100} * 17.1 hrs
0"
For 80% = 05,4)000) = 19.2 hrs
m
For 70% * 05.4X100) s 22 A hrs
70
For 60% = 05.4)OOO) = 2 5.7 hrs
60
For 50% = .OS>4)QOO) =30.8 hrs
50
For 40% = O5. 4) UW = 33.5 hrs
40
For 30% = 05.4)0001 51.3 hrs
30
For 20% - OMK100! .
20
10-C-8
For 10% - (15. 4) (100) = 154.0 hrs
10
Gross application for each dial setting:
For 100% = (15.4H130Q) , o.30 in.
453 (145)
For 90% = (17.1H1300) = 0.34 in.
453 (145)
For 80% = (19.2)(1300) = 0.38 in.
453 (145)
For 70% * (22.0)(1300) = Q.44 in.
453 (145)
For 60% * (25.7H130Q) = p. 51 in.
453 (145)
For 50% * (30.8)(1300). B . 6 1 in.
453 (145)
For 40% = (38.5)(1300). ^ Q.76 in.
453 (145)
For 30% * (51.3)(1300) a l.Qg In.
453 (145)
For 20% = (77.0)(1300) = 1,52 in.
453 (145)
For 10% => (154.00(1300) = 3 .05 in
453 (145)
Summary
Dial Setting Hour/ Revolution
100 15.4
90 17.1
80 19.2
70 22.0
60 25.7
50 30.8
40 38.5
30 51.3
20 77,0
10 154.0
10-C-fi
System type (circle):
CONSERVATION DISTRICT
COOPERATOR
IRRIGATION DATA SHEET
EXHIBIT 10-C-l
Sheet 1 of
(Other, list)
QrcincydtiKf FIELD OFFICE^ >r<g/ffi
(f "" LOCATION
IDENTIFICATION NO.
1 . Design area
Soil series
2.
FIELD NO.
acres (Area actually irrigated)
Design Soil Series:
Soil Depth
(in.)
Texture
(USDA)
Predominate maximum slope
Average AWC
(in. /in. )
2. Crops:
Crop
C&rn
Total
Acres
Planting Date Maturity Date
jfa , 7/f 1
3. Water supply: ^___
Source of supply: (stream, CweJJV reservoir, etc.)
M.
Stream; Measured flow (season of peak use) gpm
Reservoir: Storage ac. ft. Available for irrigation
Stream or Reservoir: Maximum drawdown available
ac. ft
ft.; Maximum
elevation lift on intake side of pump ft.
Well; Static Water Level
Measured Capacity
@
JQ
ft drawdown
_
Design Pumping Lift /$~Q f t (to ground level - main pipeline inlel
Pump Impeller Level
Distance supply source (main pipeline inlet) to field Q ft
Quality of water (evidence of suitability); ^
Other Data:
Type of power unit and pump to be used :
10-C-lO
CENTER PIVOT IRRIGATION SYSTEM
Sheet 2 of 4
Cooperator: Rill
Designed by:
Sff\'Ah Checked by: ^77 :
5. Map of design area - Scale 1" = 5~QO
Sketch map on grid or attach photo or overlay.
ft
2.640'
Sketch map should show:
a. Source of water
b. Major elevation differences
c. Row direction
d. Sprinkler system layout
e. Plan of operation
f. Field obstructions (gulliesi
trees, buildings, etc.)
g. North arrow
10-C-ll
CENTER PIVOT IRRIGATION SYSTEM
Sheet 3 of 4
Cooperator: <0,(l ^TonQS Designed by: <$%, S'm'i-f-n Chec
- ked ^'-^I^^23&
6.
Crop and Soil Information
CROP NUMBER
1
2
3
4
Kind of crop
C^n
Acreage to be irrigated (acres)
t*f<*r
Depth of Soil Water Control Zone
AW
EEEj
Design peak use rate (in, /day)
>30
~ i
Weighted AWC for water control zone(in./in)
. A5*
7, Design Procedure
AWC within water control zone (in.)
L^
Depletion allowed prior to irrigation (%)
5~o
Max. net water allowed per irrigation (in.
>,&
Net water applied per irrigation (in.)
O,6
Max. recommended application rate (in../h r /
A/o /i'tY>i1~
System efficiency () ,
-TO
Gross application per irrigation (in.)
>#6
Peak irrigation interval (days)
J..Q
Irrigation period (days per irrig.) -i/
2.6
Hours operating per day'
AZ
* 1
Qft = Quantity of water required (gpm) Jj
tzzt
Q A = Quantity of water actual (gpm) j/
/3o
8. Pivot Specifications:
a. Pivot Ungth^/^ftCoutside bower /^30tt)\ Pivot \Uet Pressure
- 0-b _ P S1 (Nominal pressure assuming level topoftraJnv)
b. Spray_ or Sprinkler^,/ v y
c. Gross application per revolution Q.8& in. per ^4- hours
d. HoU gpm along last 100' of span ^^gp m j
J. NozzU wetted dimeter _^^ftj trajectory-low, or
f. End gun wetted diam. f t; g pm . psi;
_ _
Q rh - Per Ccircle) i Trajectory-low, medium or high (ci
9. Checking Maximum Application Rate; A
a. Time (hrsj per revolution to apply gross application
b. Vel.(V) of end of line = outside circum. ^ 7T I33& ^ /9/l
- - -~ . ----- _~_^ - -_ , / ' ^_
y-y' lira/revolution
Time of application (hrs) =
V, ft/hr
Average application rate, in./hr Hlg_!P_Hcat:ion. in.
time of applic,, hrs
hr
, .
~~
- 1.3*
gro^_aprUation , J^j^ g ^
opr. per day x _2,day s per irrig,
Q A must be >
A V R
Final specifications to be provided by manufacturer
10-C-12
bneec *+ or
Cooperator: -#,//
CENTER PIVOT IRRIGATION SYSTEM
# / 5Wm Checked by: ,77 .
Designed by:
10. Determining Total Dynamic Head:
Total main line length $0 t
Kind of
Pipe and
SDR, Sen,
Class, etc
Pipe
Size
(in.)
Design
Capacity
(gpm)
IPS:_j/ PIP:
PIPE SIZING
Total
Head Loss
Working Pressure
LengtV
(ft)
Friction^
Head Loss
(ft/100 ft)
(ft)
(psi)
Recommend-
ed Max. 5/
(psi)
Actual
Max.
(psi)
fvc. t SOR-M
C/SU&&&&
JO..
,, 130Q
_^
0.2$
0.3
O,/
/*#
r^r
Needed at Pivot Inlet jj./
fttf
^y.2.
Misc. & fitting losses (usually 3 psi +)
6.?
&*>
Elevation Difference Z/
(Z.O
s.z>
Pump Discharge Pressure (main pipeline inlet)
f767
faf
Pumping lift (including losses)
ISO.
(,*.<?
Total Dynamic Head, TDK
&*3
Mp
Estimated Net Positive Suction Head
Available, NPSHA
ss
11. Pump Requirements:
Capacity
gpm @
12.
NPSH less than 3-$ ft.
Power Requirements:
3960
317 ft.
pump eff. x
pai or
TDlr
ft of head and
Sheet 3 of 4
CENTER PIVOT IRRIGATION SYSTEM
Cooperator:
<ff,/f
Designed by:
I sv;
Checked by : ^77
6. Crop and Soil Information
CROP NUMBER
1
2
3
4
Kind of crop
(_^&f~fl
Acreage to be irrigated (acres)
itf
Depth of Soil Water Control Zone
Zty
Design peak use rate (in. /day)
,30
Weighted AWC for water control zone(in./in)
7 . Design Procedure
AWC within water control zone (in.)
iiZ
Depletion allowed prior to irrigation (%)
5"o
Max. net water allowed per irrigation (in.)
Oik
Net water applied per irrigation (in.)
0.6
Max. recommended application rate (in./hr.)
/l/o 1 1 ft" t
System efficiency (%) ,/
70
Gross application per irrigation (in.)
Peak irrigation interval (days)
3., to
Irrigation period (days per irrig.) Lf
3,6
Hours operating per day'
3.A
QR - Quantity of water required (gpm) _L/
/2% 1 /'
Q = Quantity of water actual (gpm) 2J
/JOO
Pivot Specifications: '
a. Pivot Length /36Q f t(outside tower /33Q ft) ; Pivot ' f ilet Pressure
/> S" psi (Nominal pressure assuming level topogra^ny)
b. Spray or Sprinkler
c. Gross application per revolution ___<?. %&> in. per *^^__ hours.
d. Nozzle gpm along last 100' of span /./ gpm @ V^psi on spacing of ^,
e. Nozzle wetted diameter
f* End gun wetted diam.
ft; trajectory-low, (u), or high (circli
ft; gpm; J psi; Nozzle size inch-
ring or taper (circle); Trajectory-low, medium or high (circle) degree!
Checking Maximum Application Rate:
a. Time (hrs) per revolution to apply gross application = V-f^ hrs
b. Vel.(V) of end of line = outside circum. ^ TT 133$ t = j<}0 ft/hr
hrs/revolution
c. Time of application (hrs) = wetted dia. ft = JQ& =
V, ft/hr
hr
d. Average application rate, in./hr = gross application, in. = ,
time of applic., hrs
in / h]
e. Max, application rate = 1.3 x av. applic. rate = 1.3x /*6 in./hr =
t
= 453 x /fiacres
inches gross application
gpm
2/
hrs opr, per day x _ - L days per irrig.
~ Q A must be ,> Q
o /
_' Final specifications to be provided by manufacturer
IO-C-12
btieec + or
CENTER PIVOT IRRIGATION SYSTEM
Cooperator: *&,//
Designed by:
*wm
Checked by: J77
10, Determining Total Dynamic Head:
Total main line length ^O ft
Kind of
Pipe and
SDR, Sch,
Class, etc
Pipe
Size
(in.)
Design
Capacity
(gpm)
IPS:j/ PIP:
PIPE SIZING
Total '
Head Loss
Working Pressure
Length
(ft)
Friction^
Head Loss
(ft/100 ft)
(ft)
(pai)
Recommend-
ed Max. 5/
(psi)
Actual
Max.
(psi)
/Vc /t tttf2y
C/Q3S ZOO
If)
1300
_J
o.
0.3
OJ
/f^
r^.r"
Needed at Pivot Inlet &/
(57^
^2.
Misc. & fitting losses (usually 3 psi +)
(*3
Z*
Elevation Difference Z/
{2.0
S,Z>
Pump Discharge Pressure (main pipeline inlet)
I7&<7
76.S*
Pumping lift (including losses)
ISO.
1*4.1
Total Dynamic Head, TDK
326*7
Mp
Estimated Net Positive Suction Head
Available, NPSHA
ft
11. Pump Requirements:
Capacity
NPSH less than
12. Power Requirements:
BHP _> I3O&
gpm @
ft.
psi or
x 327 ft. TDH
head and
/S3
3960 x
pump eff. x /, e
SOUTH CAROLINA IRRIGATION GUIDE
CHAPTER 1Q-D. TRICKLE IRRIGATION SYSTEM
GENERAL
The example problem in this chapter is intended to illustrate the pro-
cedure to follow in the design of trickle irrigation systems. It is
understood that one example cannot illustrate all design situations,
site conditions or alternatives to consider when designing a trickle
irri cjation system.
DESIGN CRITERIA
Design criteria for trickle irrigation systems are contained in the
Technical Guide, Irrigation System, Drip, Standard 441. All trickle
irrigation systems must be designed in accordance with the criteria
contained in Standard 441. Detailed guidelines for design of trickle
irrigation system are given in NEH 15, Chapter 7.
EXAMPLE PROBLEM
The following example problem is intended to cover the basic design
steps to follow in the design of trickle irrigation systems. A stan-
dard form (Exhibit 10-A-l) is used and is a useful tool in designing
and in recording data.
Given:
1. Location: Aiken County.
2. Field Shape: 2,640 feet north to south and 1,320 feet east to
west (80 acres) .
3. Soil: Faceville S.L.
4. Crop: Pecans.
5. Row direction and spacing: north and south.
6. Tree spacing: 50 ft. x 50 ft.
7. Well information: existing 6 in. diameter.
8. Owner would like to operate half the system at one time. Emitter
discharge rate preferred is 2 gph.
Sol ution:
The item numbers mentioned in the step by step solution refer to the
items on the standard form "Irrigation Data Sheet" in Exhibit 10-D-l.
10-D-l
Step 1. Complete Items 1-4. These items provide pertinent data of
the site.
Step 2. Complete Item 5. Make a drawing to scale of the Mold
locating trees, well, and other features.
Step 3. Complete Item 6. The moisture extraction depth (soil water
control zone) for the soil is 24 inches (Table 3-1). The
design peak use rate 0.13 inches/day is taken from Chapter 4
Table 4-1 and is denoted by F n . Note that F n varies dopond intj
upon the value F (see step 5-C following) for orchards.
Step 4. Complete Item 7. The weighted AWC can be computed from item
1 and the permeability rate can be obtained from section II
of the Technical Guide or from the county soil survey.
Step 5. Design procedure. Complete the following parts of Hum H.
a. Determine the field area "A" (ft? served by "N" emit-
ters). This is determined by the troo spacing which
is 50 feet x 50 feet which equals 2,bOO ft?.
b. Determine the design area of the crop for "N" emitters
The design area may be less than 100 percent of 1 ' tho
field area but not less than the mature crop root jono
area. The mature crop root zone area for tho pecans in
this example was determined to be .70 x 2500 17bO ft?.
c. The value "F" which is the percent of "A" USGC! for tho
design area, was determined to be 0.70.
nf th f em1tters for the
of thumb is wet a minimum of 25% of tho root
In Wt example > the 1 nlmunf wetted oa
would be 0.25 x 1,750 ft2 = 8 ft-' The
jetted area from one emitter is estimated to be about
un, r f d m ?t er S L a H Ut " 3 Sq ft " Thus th '""
TQ ThI ^t ters b ased upon area wetted = 438/113 =
fo r'lz or l^ "^ f emitters based "Pon capacity
K R n a f . PP ln 9 = 2471/0.9) -^ [(2x12) x 17 41-
f emi e S r SoSW,'" 9 ? '" 3ll W "' d' "
(4 emitter! per lateral )!"" S6rV1 ' nQ ^ ^ f trees
f. ^preferred discharge rate of emitters, Q, was given as
9. Determine the hours of operation per day, T.
T -
"
10-D-2
h. Determine the system capacity. There are 676 trees to be
irrigated at one time with eight 2 gph emitters per tree.
Therefore, the system capacity is:
676 trees x 8 emitters x 2 gph emitters = 180 gpm
60 min/hr
Step 6. Complete Item 9. Select an emitter that will provide a flow
rate of 2.0 gph. When selecting an emitter, a flow chart for
the emitter should be obtained. Lateral lines normally are so
designed that when operating at design pressure the
discharge rate of any emitter served by the lateral
will not exceed a variation of +_ 10 percent of the design
discharge rate (Technical Guide Standard 441-minimum
variation = 15%).
The flow chart for the emitter selected in this example (2
gph @ 15 psi) has flow rate variations and corresponding
pressure variations as follows (see similar flow chart for
a 1.0 gph emitter in Chapter 5, Figure 5-6):
2.0 gph -i- 103S = 2.2 gph @ 17.5 psi
2.0 gph - 10% = 1.8 gph @ 12.5 psi
This allowable variation can be entered in the appropriate part
of Item 11.
Step 7. Complete Item 10. The procedure for determining total dynamic
head and net positive suction head available is similar
to that described for sprinkler irrigation in Chapter 10-A.
The pipe sizing data sheet was used to compute the friction
loss in this example. Friction loss tables are included
in Appendix C. The topography was gently sloping so
elevation differences were included in the calculations.
The design emitter pressure was determined in Step 6.
The filter selected should be based on water quality and
manufacturer's recommendations. The pressure loss in this
example was based on manufacturer's literature.
The NPSHA = 31.0 - hf + z = 31.0 - 3 + 20 = 48.0'
23.1 psi - 1.0 psi (misc. loss) - 5.0 psi (filter loss ) - 3.3
psi (submain loss) - 0.8 psi (lateral loss) = 13.0 psi. This
is greater than the minimum allowable of 12.5 psi.
Step 11. Complete the plans. Include as needed: a chlorinator, check
valves, pressure regulators, pressure relief valves, combination
air vacuum valves, flow meters, gate valves, etc.
MATERIAL AND CONSTRUCTION REQUIREMENTS
Construction shall be done to the lines and grades determined by the
design and the equipment and materials shall be of type, size and quan-
tities specified in the plans. The installing contractor will be respon-
sible for the proper installation of the system.
Emitters shall be installed as recommended by the manufacturer. Trenches
excavated for pipe placement shall have a straight alignment. The width
of the trench at any point below the top of the pipe shall be no wider-
than is necessary to lay, join, and backfill the pipe and in no event IM
more than 18 inches wider than the diameter of pipe. The buried pipe
shall have a settled minimum cover as specified in the appropriate tech-
nical guides. All joints and connections involved in the installation ol
the pipe shall be made in accordance with the pipe manufacturer's recom-
mendations and shall be constructed to withstand the maximum design
working pressure for the pipelines without leakage. The quality of the
pipe placed underground shall equal or exceed the quality requirements
specified in the appropriate Technical Guides. Pipe placed above ground
shall be as recommended by the manufacturer.
The filter system shall be of such that flushing, cleaning or replacement
can be performed as required without introducing contaminants or foreign
particles into the system. All injectors, such as fertilizer injectors,
shall be installed upstream of the filter system, except for injectors
equipped with separate filters.
Pumps, power units and filters shall be set on a firm base and be placod
in proper alignment. All pertinent safety codes and manufacturer's
recommendations shall be met.
Once completed, the system shall be tested for operating pressures,
strength, leakage and satisfactory operation. During the initial start
up, the lateral lines shall be flushed to remove any sediment or foreign
materials before placement of end plugs.
The installing contractor or material supplier shall furnish the owner
with written certification that pipe installed below ground will comply
with the applicable standards referred to in the Technical Guides. The
owner shall also be furnished a written guarantee by the contractor pro-
tecting the owner against defective materials and workmanship over a
period of not less than one year after completion of all work covered
under the contract.
10-D-4
EXHIBIT lU-u-i
Sheet 1 of 5
IRRIGATION DATA SHEET
System type (circle): Center Pivot, Traveling Gun,
(Other, list)
CONSERVATION DISTRICT
COOPERATOR
IDENTIFICATION NO. tfaifc d
\ . Design area
Soil series
FIELD OFFICE
LOCATION ~
FIELD NO.
_acrea (Area actually irrigated)
Design Soil Series:
Soil Depth
(in.)
-73-
Texture
(USDA)
Predominate maximum slope
Average AWC
(in. /in.)
.5",
S.
0.
Crops
Cro
Total
Ac re s
Planting Pate Maturity Date
Water supply:
Source of supply: (stream, well, reservoir, etc.)
gpm
Stream: Measured flow (season of peak use)
Reservoir: Storage _ ac, ft. Available for irrigation
Stream or Reservoir: Maximum drawdown available
ac. ft
ft. ; Maximum
elevation lift on intake side o
TRICKLE IRRIGATION SYSTEM
Cooperator: Robert" ..S*ru4h Designed by: T
5. Map of design area - Scale 1" = 400 _ ft
Sketch map on grid or attach photo or overlay.
Sheet _2 of_JT
Checked by: J~, ^A**
132.0'
o
Sketch map should show:
a. Source of water
fa. Major elevation differences
c. Row direction
<* Sprinkler system layout
-, , ,
T.
Plan of operation
Field obstructions (gullies,
trees, buildings, etc.)
North arrow
10-D-6
Sheet 3 of 5
TRICKLE IRRIGATION SYSTEM
Cooperator:
*
Designed by: JyT
Checked by:
6.
Crop Information
IRRIGATION UNIT NUMBER
1
2
3
4
Kind of crop '
/ccan
&ca
Acreage to be grown (acres) 1 /
*0
*{&
Soil Water Control Zone (in.)
zty
2~y-
Peak use rate (in. /day), il n
./3
i/3
7. Soil Information
Weighted AWC
for rooting
depth
( in. /in. )
QJ3
0./3
Permeability
(in./hr)
o.o -2.0
&*t>~z-&
8. Design Procedure
"A" field area served by N emitters <ft^)
JJVO
Z5-t>G
Design area of crop for N emitters (ft z )
17 SO
)7S&
"F"-% of "A" used for design area(decimal)
0,70
f><70
"E"- water application efficiency (decimal)
o.i
0.1
"N"- number of emitters for design area
X
r
"0"- discharge rate of emitter (gph)
&
2s
"T"- hours of operation per day(18 hrs max) '*-!
1*1
9.2
System capacity - " N " P er irrigation unit X "Q"
ISO
/Z0
(gpm) 60
9* System Specifications
a. Emitter spacing &
b. Emitter capacity
ft) lateral spacing
gph @
ft (duo/
c. Max. length lateral
f t , size
in. , Number of emitters
d. Total number laterals
\ Number operating simultaneously
Total number of emitters
J For orchards^ list tree spacing and canopy area.
Tree spacing J5*O ft by ^Q ft
Canopy area
[assumed to be the root (design) area]
U Use the following formula:
T = F n AF
1.604
10-0-7
Sheet 4 of
TRICKLE IRRIGATION SYSTEM
Designed
Checked by: *-/ 3V<
"
10. Determining Total Dynamic Head _
Kind of Pipe
Design
Capa-
city
. .... , . . ' "
IPS
PIP
Other
Diameter
(in.)
I -*
Length
(ft)
^ "-
Friction
Head
Loss 4/
(ft/lOOft)
Total
Head
Loss
HL
(ft)
Total Head
Loss, HL
Workir
Presax
(ft)
(psi)
Recom-
mendec
Max y
(psi)
.?*&...
_J /aJ t
Sub-
Lateral
^
^
jT" 07
^ '
XXXX
XXXX
XXXjj
AA._V-
W V
_ Mi"*r *-
H ' -f '
i. .1- ...i . ..--
- 1--.- - i - " '
^ ,-, ' i -
, i .- -
xxxx
xxxx
xxxx
XXXX
xxxx
xxxx
xxxx
~xxxx
,1, HaBjM "
xxxx
XXXX~
_ ^ . , .^- _ ^-j
XXXX
W^,
xxxx
xxxx
*./
xxxi
xxxxl
xxxx
xxxx
xxxx
xxxx
XXXX
o
xxxx
_ ^- "
XXXXj
-
xxxx
xxxx
xxxx
xxxx
xxxx
xxxx
xxxx
xxxx
xxxx
Des
en Em]
itter Prt
^^.4_
jS>0
Friction T," ^n filter Svstem _
//.&
&6
Miscellaneous Losses
^^^^^^^m^==g= 1.11. jii_i^ . j T.'-jji ~
Pump Discharge Pressure
^2,3
.UL
,,J **** 6 ^^0,'nj
&*
*v.l
Pumping Lift (including losses)
/%>
^-/?
Total Dynamic Head, TDH
I-72' 1 /
7 ff.l>
Estimated Net Positive Suction Head Available, NPSHA
W
1. Pump Requirements: /go gpm @
than <f$ ft,
.2. Power Unit Requirement:
BHP > /$O gpm x
If 3 ft TDH
3960 x 0,7 pump eff. x
1,0
drive eff.
L3. Check allowable pressure variation that will provide a +_ 10% flow rate
Allowable == /^?,>rpsi to /^psi (Taken from manufacturer's curve)
?/ Actual = /J.d psi to y^o psi
14. Remarks__ _ _ __
j3/ Use pipe sizing data sheets where elevatTon d^ifTererices are T present and/or
additional data lines needed.
4/ Keep velocity 5fps unless means to control surge and water hammer are other-
wise adequate.
57 For plastic pipe, pressure rating divided by 0.72 unless means to control
surge and water hammer are otherwise adequate.
2.' Sets optimum nozzle pressure at a theoretical mid-system sprinkler.
2/ Consider elevations and location. Adjust / if possible to stay within
allowed variation. If not) the system must be redesigned.
Design approved by;
Date;
JLO-D-8.
o
I
ti
t
ft)
M-
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H
SOUTH CAROLINA IRRIGATION GUIDE
CHAPTER 11. IRRIGATION WATER MANAGEMENT
CONTENTS
Page
General ----- - - -.,--.,-_ ---- ~ ------ - ----- - - --- .,- _--_ n_i
Irrigation Evaluation ------ - ------- -- ------- --- ---- . .. ----- 11.3
inn- ---------- - ~ __ --...,- --_.-.-_.._ _-__---_ 1 1 _ ^
Mi 1 "^"~"'^" 11 '"" "'^ "* *""^""* * ****- .L j. j
Soil Moisture Measurements -------- --------- -- ------ - ---------- 11-3
Sampling Procedures ---- - ------ - ..... ------------------ - ----- 11-4
Selection of Moisture Measuring Station-- ------------------- 11-4
Measuring Soil Moisture ----- - ------- --------- - ---------------- 11-6
Feel and Appearance Method --------- - ---- - ------------------- 11-6
Gravimeterlc Method ---- ..... - ------------------- - ----- 11-6
Tensiometers ------ - - -- ---------------------------------- 11-6
Electrical Resistance Blocks --------------------------------- 11-7
Soil Moisture Computations-Determining When and How Much
tn Annlv---. ________________________________________ -- ________ 11-R
lw ripjjij' p* -. . -i - - - .* .- i J. U
firmvnl _____ ________ __ ___ _____ ___________ __ - ____ 11-R
ijd 1C I U I _ -,____ ~ _ _ - -. -- J.J.U
Root Zone Water Balance ..... --------------------------------- 11-8
Moisture Accounting Method of Scheduling ------- - ------------ 11-10
Tensiometer Method of Scheduling ---------------------------- 11-12
Pan Evaporation Method of Scheduling ------------------------ 11-10
Irrigation Water Management Plan ------------------------- ..... 11-13
ft on oval - _______ __ ______________ __ __ _____ _____ __________ 11-13
UCMCt Q I "*- " -* * - . -. *, -*. , >^ ** J.J. AU
Pritpri a ___ - _________ ____ __________ , _____ __- ___ -_- ____ _-.__^_ __ ,-_ 11 -11
Vjl PUCI IQ * * '- * " " - -" *^ -^ ,L J. Jl bl
Example Irrigation W?ter Management Plan ---------------------- 11-13
Figures
Figure 11-1 Average Daily Consumptive Use Curve for Corn, Climatic
9 ___ ~-- ___________________________________ - 11-Q
<- -- __ -~ _ _ XJ.""3
Figure 11-2 Moisture Balance Sheet for Scheduling Irrigation-- 11-10
Exhibits
Exhibit 11-1 Irrigation Water Management Plan (Example) -------- 11-17
SOUTH CAROLINA IRRIGATION GUIDE
CHAPTER 11. IRRIGATION WATER MANAGEMENT AND EVALUATION PROCEDURES
GENERAL
Irrigation water management is the act of timing and regulating irri-
gation water applications in a way that will satisfy the water
requirement of the crop without the waste of water, soil, or plant
nutrients. It means applying water according to crop needs, in
amounts that can be held in the soil and available to crops, and at
rates consistent with the intake characteristics of the soil and the
erosion hazard of the site.
Management is a prime factor in the success of an irrigation program.
The system may be of the best possible design with equipment that is
up-to-date and efficient, but success is still not insured.
Labor requirements for a hand-moved irrigation system are large.
Often the equipment has to be operated at the same time other labor
demands are at their peak. Solid-set and mechanically-moved systems
require very little labor. The irrigator must carefully consider how
the operation of his type of irrigation system will fit into the total
farming enterprise. He must be sure that he has the manpower
available for his choice of irrigation system. Good planning and uti-
lization of labor are essential.
Large quantities of water are required for irrigation. Therefore,
efficient use of water should be the goal of an adequate program of
irrigation system management. Benefits from investments in the irri-
gation system, labor and irrigation water, are derived from improved
quality, yield and marketing advantages that can be achieved from
irrigated crops. To obtain these benefits with efficient water use,
the irrigator must answer three very pertinent questions: When should
I irrigate, how much water should I apply, and is the irrigation
system functioning properly?
Man irrigators tend to delay irrigation in hope that rain will come.
A cardinal rule of the irrigator must be that he keeps his eyes on the
soil and plants and not on the sky. If drainage is adequate, no
serious problems should develop ahnuld rainfall occur after the
completion of proper irrigation.
The question "When should I irrigate?" cannot always be answered pre-
cisely. No set rule applies to all situations. Several factors must
be considered in each individual case, such as the particular crop,
stage of crop growth, minimum practical amount of water to apply,
available water supply, irrigation system capacity, and other farm
operations schedules.
Most crops should be irrigated by the time that half of the available
moisture in the crop root zone has been used. Some crops, however,
are thought to do better at higher or lower moisture levels at time of
11-1
irrigation than other crops (see Chapter 3, Irrigation Needs of
Particular Crops Section). An irrigation may be needed before half of
the available moisture has been used. The need for irrigation could
be doubtful for any crop until the soil moisture deficit approaches
one-third of the available moisture holding capacity of the crop root
zone. With these considerations in mind, unless otherwise noted, a
good general rule is to commence irrigation for row crops when the
soil moisture deficit reaches about the forty percent level for fine
to medium textured soils and about fifty percent for moderately coarse
to coarse textured soils. Some special purpose irrigations, such as
for seed germination, are exceptions to this general rule. Also vege-
table crops normally should be irrigated at least by the time 40% of
the available moisture is depleted.
It is not always practical and probably not desirable to maintain the
same soil moisture level throughout the growing season. Aside from
moisture needs to ensure a stand, most crops have critical periods
during the growing season when good soil moisture levels must be main-
tained to obtain high quality yields. The critical period for most
crops occurs during the part of the growing season of pod, fruit,
tuber, or ear formation and development. Chapter 3, Table 3-2, lists
the critical growth periods for a number of important crops.
If sufficient growing season exists for the desired development of the
crop, short periods of low moisture during the early part of the
growing season may not be harmful except for leaf or forage crops.
However over-stimulation of vegetative growth from a combination of
high soil fertility and available soil moisture can also be objec-
tionable. This may delay time of harvest enough to miss the period of
highest fresh market demand, affect the grade for processing, or cause
losses in late maturing crops from frost damage. If irrigation water
supplies are limited, the best use of the irrigation water supply
would be during the critical growth period of the crop.
Irrigation must begin in time so that the irrigated area can be
covered before the available moisture level in the last portion of the
field to be irrigated reaches a point to cause unfavorable moisture
stress of the crop.
Irrigation schedules often can be varied somewhat to fit other opera-
tion schedules. Many times the irrigation system is utilized on a
diversity of crops which are at different stages of growth. When the
available soil moisture level for each crop area is known, the timing
of irrigations can be varied. For example, irrigations of a par-
ticular crop may be moved ahead a day or two to facilitate application
of insecticides or herbicides.
In determining the need for irrigation one must not overlook the fact
that some portions of the field may be drier than others. Poor water
distribution during a previous irrigation may cause the soil moisture
deficiency in one portion of the field to be considerably greater than
in other parts of the field; also, the soil in one part of the field
may have less available moisture holding capacity than the soils in
11-2
another part. The moisture in this soil might be depleted to the 50
percent level long before the other soils approach that level. If
these kinds of critical areas are of significant size, the decision as
to when to irrigate should be based on the available moisture in the
drier areas.
IRRIGATION EVALUATION
The effectiveness of a farmer's irrigation water management practices
can be determined by making field observations and evaluations. These
observations and evalations should also be used to determine if the
values and assumptions that were used in the planning and design of
the systems conform to the actual field conditions. The results of
these observations and evaluations are used to help the irrigator
improve his water management techniques and/or upgrade his irrigation
system. Procedures for evaluating irrigation systems are not
addressed in this chapter but are covered in detail in Appendix B.
IRRIGATION SCHEDULING
The amount of crop evapotranspiration or water requirement varies
according to climatic conditions and crop growth stage. The rate of
evapotranspiration is much less during the winter season than in the
summer. Likewise, the rate Is much less when a crop just begins to
grow than it is as the crop reaches maturity.
The determination of when and how much to apply requires a knowledge
of the available water capacity (AWC) of the soil, the crop rooting
depth, the management allowed deficit (MAD) or plant stress level for
the specified crop, the crop consumptive use, and the critical periods
in the growing season when the crop should not be stressed.
SOIL MOISTURE MEASUREMENTS
The amount of moisture remaining for crop use in found by making soil
moisture measurements. The moisture level can be estimated by the
feel and appearance method, as well as by various soil moisture
measuring devices. Moisture measurements can be used alone for sche-
duling irrigations, but usually are used in combination with consumptive
use prediction methods to reduce the number of moisture measurement needed
11-3
Also, one or more days lead time may be needed by the irrigator to plan
farming operations or make other management decisions prior to irrigating.
He may not be able to wait until a moisture measurement reveals it is time
to irrigate.
The consumptive use information in Chapter 4 can be used for reasonable
estimates of the rate the crop is using moisture. If the rate of crop
moisture use and the amount of soil moisture remaining are known, the date
irrigation is needed can be predicted.
Soil moisture measurements should be made from the part of the soil from
which plant roots extract their moisture and according to the moisture-
extraction pattern of the particular crop. Regardless of the moisture
measurement method used, the sampling procedures and selection of the
moisture measuring stations are important.
Sampling Procedures
The sampling procedure should be as follows:
1. In uniformly textured soils, one measurement should be made at
the midpoint in each quarter of the root zone. For shallow
rooted crops it is probably desirable to take three measurements
As an example, in a 24-inch zone, measurements may be taken fronr
the 6-, 12-, and 18-inch depth.
2. In stratified soils, one measurement should be taken from each
textural strata. It may not be necessary to take a measurement
in very thin layers when this thin layer can be lumped with
another layer from estimating soil moisture. Where the strata
is thick a sample should be taken in 1-foot increments as a
minimum. Thickness of the strata should be noted.
3. The crop root depth for annual crops changes through the early
part of the growing season. Measurements should be made in
the soil profile according to the current depth of the majority
of the crop roots.
Selection of Moisture Measuring Station
The selection of soil moisture measurement stations is important. The
stations should be located so that average soil moisture conditions in
the root zone of the crop are measured. Excess water from leaks in pipe
joints, low spots in a field, etc., should not be allowed to come in con
tact with the measurement station. High spots with excessive water
runoff should not be chosen because the soil profile in this area will
not represent average root zone conditions. Average soil and slope con-
ditions in the field should be represented in station locations.
Measurements should be made at other locations as indicated by any
critical condition in the soil, such as an area that dries out first. It
is yoocl practice to have at least two measurement stations in each criti-
cal area and two or three stations in areas that are typical of the
field. This information provides direction for adjusting the amount and
frequency of irrigation for different parts of the field or for different
periods in the growing season.
1. Location in relation to plants.
a. Row crops - locate in the crop row as near the plants
as possible.
b. Mature trees - located 8 to 10 feet from the trunk for
pecans and 4 to 6 feet from the trunk for peaches and
apples but inside the tree drip line; and
c. Crops with complete cover such as alfalfa and grains -
locate in representative soil and slope areas of the
field.
2. Location in relation to irrigation systems.
a. Lateral move sprinklers such as side roll or hand move
aluminum pipe - locate measurement stations halfway
between adjacent sprinkler heads and 10 to 15 feet from
the lateral .
b. Center pivot sprinklers - locate measurement stations
at about two-thirds of the total lateral distance from
the pivot.
c. Traveling gun sprinklers - locate measurement stations
midway between towpaths.
d. Solid set sprinklers - locate measurement stations where
the diagonals from four adjacent sprinkler heads cross.
e. Trickle systems - locate in the wetted ball in the root
zone.
3. Location in field for sprinkler or trickle irrigation systems.
Sprinkler and trickle irrigation systems generally lose pressure
down the lateral due to friction loss throughout the lateral
so sprinkler heads farthest from the main lines put out the
least irrigation water. To check adequacy of irrigations,
locate measurement stations as follows:
a. 50 to 100 feet downstream from the beginning of the
lateral .
b. 50 to 100 feet upstream from the distant end of the
lateral .
11-5
MEASURING SOIL MOISTURE
Irrigation water management requires that soil moisture measurements be
made to determine the amount of soil moisture available to the plants.
Numerous techniques have been developed to obtain this information. A
brief discussion of the more common methods follows. More detailed
information can be found in Appendix A.
Feel and Appearance Method
With experience, and irrigator can achieve adequate accuracy by using the
simple feel and appearance method to judge soil water content. Soil
augers or probes are used to obtain soil samples down through the root
zone of the crop. The percent of available moisture remaining is esti-
mated by observing the feel and appearance while manipulating the sample
according to a guide table (see Appendix A). The equipment required is
simple and easily obtained, but requires time and effort to obtain
reliable results. An added benefit of this method is that the irrigator
actually observes his spoil profile and gains a better knowledge of the
soil-plant-water relationship.
Gravimetric Method
The gravimetric method or oven dry method is the most accurate, but
requires much time and effort to obtain the data. Soil samples are
collected in the field and then oven dried in a lab. Moisture proof
sample containers, a beam balance, drying oven (microwave can be used and
reduce time needed to dry soil) and core samples are necessary equipment.
This method gives the percent of total moisture in the soil, which must
be converted to plant available moisture. It is used primarily for eva-
luation and research data and for calibrating other devices.
Tensiometers
Tensiometers measure soil moisture suction. They are a closed tube with
a hollow ceramic tip at the soil contact end and a vacuum gage on the
above ground end. It is filled with water and installed in the soil. As
the soil dries, it pulls water through the ceramic tip, creating a vacuum
inside the tensiometer. As the soil is wetted again from irrigation or
rain, water is pulled back into the tensiometer, thus lowering the
reading on the vacuum gage.
Most tensiometer gages read from to 100 in centibars. One hundred cen-
tibars equal one bar, which is about the same as one atmosphere. A ten-
siometer can operate on the range of to 80 centibars. A reading of
indicates a saturated soil. Different soil textures release water at
uliu p S i- raois * ur t ? n ? ions and > therefore, different tensiometer
mn cff,: Read 9 s of a^ 10 and 25 represent field capacity and ideal
mn c,
of n ^n 1 Condlt1o j s respectively for sandy soils. Readings
ot about 30 to 60 represent corresponding conditions in clay soils
3ther soil texture combinations would utilize tensiometer values
somewhere between these values for sand and clay soils. The wilting
3oint occurs in the 1000 to 2000 centibar range which is well beyond the
)perating range of tensiometers .
)f the total water released by a soil between field capacity and the
jilting point, the percentage released within the tensiometer measuring
-ange may be as high as 90 percent for a sandy soil and as low as 30 per-
;ent for a clay soil. Tensiometers are best suited for soils that
-elease 50 percent or more of their available water in the tensiometer
'ange, to 80 centibars.
fensiometer readings tell when to irrigate, but do not tell how much- to
ipply. Calibration curves are needed to relate soil tension to available
noisture percentage (see Chapter 3, Irrigation and- Crop Production
section, for general relationship and Appendix A).
lectrical Resistance Blocks
This method is based on the changes of electrical resistance of the
>locks due to change in moisture contents. The blocks are buried in the
ioil, a change in the soil moisture makes a corresponding change in the
noisture of the blocks. The electrodes in the blocks are connected by
irires to the surface that can be connected to a portable resistance
neter. Any change in the resistance of the blocks is an indirect
neasurement of the change of soil moisture tension. The reading can be
calibrated in terms of percent moisture, but must be calibrated for spe-
:ific soils. Resistance blocks are less sensitive than tensiometers in
che range of to 80 centibar range, but can operate in the range of
: ield capacity to wilting point.
\ special electrical resistance block is available that is as sensitive
is a tensiometer, but will not have the high maintenance characteristics
in the high tension region above 80 centibar.
11-7
SOIL MOISTURE COMPUTATIONS-DETERMINING WHEN AND HOW MUCH TO APPLY
General
Regardless of the mehtod used to measure soi moisture, it should either
provide the answer on percent of plant available mositure remaining or
have curves to convert to percent of available moisture. Appendix A
shows the method used to convert the soil moisture measurement to percent
of available moisture remaining for each of the soil moisture measurement
methods discussed above.
Root Zone Water Balance
The minimum root zone moisture balance to be maintained is dependent upon
the current rooting depth, AWC of the soil and the MAD (based on the
crop's characteristics). For example, with an AWC of 2.2 in. for the
rooting depth and a MAP of 40#, the minimum root zone balance to be main-
tained is 1.32 in. (2.2 in. x 0.60).
Computer programs are in use that estimate crop water usage from actual
climatological data and maintain a current root zone water balance. They
also predict crop water requirements, date of irrigation, and compute net
irrigation requirements. The water balance computations are normally
begun from initial soil moisture measurements. Subsequent measurements
are also needed to verify predicted deficits. As discrepancies develop s
the necessary corrections are made. These services may be available from
commercial management firms that provide the irrigator weekly printouts
containing scheduling information.
Farmers can also keep their own root zone water balance records. They
will need to make soil moisture measurements to determine the initial
soil moisture content and balance, as well as occasional measurements
during the growing season to verify the computations, A rain gage will
be needed to record the rainfall. Estimated crop water use the needs are
provided by various means. It may be provided on a current basis
through the local news media by a public agency or irrigation group using
actual climatological data on a computer program. Seasonal data may also
be available using normal climatological data from a local weather sta-
tion. The consumptive use data in Chapter 4 of this guide can also be
used.
Figure 11-1 illustrates one method that can be used to obtain estimated
crop water use for scheduling irrigations. This method uses the consump-
tive use data contained in Chapter 4, Table 4-2, and is a plot of average
daily consumptive use versus time. The curve is constructed by taking
the monthly consumptive use and dividing by the number of days within the
month (or part of month) and plotting this point at the midpoint of the
month (or midpoint of the part month). This is done for each month of
data. The point for the peak use period may be approximated by using the
recommended design peak from table 4-1 of Chapter 4. When all the points
are plotted a smooth curve is drawn connecting the points. In Figure
11-1 the monthly consumptive use curve was plotted for corn grown in cli-
miatic zone 2. From Table 4-2, the consumptive use for May is 5". 99
inches or 0.19 in. /day (5.99 inches -r 31 days) average. This was plotted
11-8
MARCH
5 10 13 2O 23
APRIL
10 13 20 35
MAY
1O IS 2O 23
JUNE
a 10 is 20 23
JULY
g 10 is 20 as
3 10 15 20 25 S 10 IS 2O 23
MARCH APRIL
9 tO 15 2O 25
MAY
1O 13 2O 23
JL/NE
3 10 13 20 23
JULY
on the graph at the middle of May. For June, the consumptive use is 6.98
inches or 0.23 in. /day (6.98 inches -r 30 days) average. Since this is
the peak use month, the peak value can be estimated by using the design
peak from Chapter 4 of this Guide (0.3 in. /day). This was plotted
on the graph at the middle of June. Points were plotted for each month
and the curve drawn connecting the points. The average daily consumptive
use can be taken from the graph by projecting vertically from the day of
the month in question until intersecting the curve and then projecting
horizontally to read the consumptive use. For example, on May 5 the
estimated consumptive use is 0.15 in. /day,
Moisture Accounting Method of Scheduling
Once the consumptive use data and actual rainfall is obtained, the irri-
gator can schedule irrigations using the moisture accounting method. Figure
11-2 illustrates the accounting method for corn grown in climatic zone 2
for one month of the crop's growing season. Similar sheets would need be
prepared for each month of the growing season. At the beginning of the
season, moisture measurements should be taken and the moisture content
determined. Moisture measurements should also be taken periodically
during the growing season to verify soil moisture content or make adjust-
ments as necessary. The example in Figure 11-2 shows that the AWC of the
soil is 1.66 inches. With a MAD of 40%, irrigation is needed when the
root zone moisture balance is l.UO in. [(1.66 in. - (0.40H1.66 in.)].
The example shows a balance from the previous month of 1.50 inches.
Knowing the balance, it is a matter of subtracting the estimated consump-
tive use and adding any effective rainfall and/or irrigation. The
account is kept on a daily basis. The estimated consumptive use in this
example is taken from Figure 11-1. The rainfall can be measured using
rain gages. It must be remembered that all rainfall is not effective.
The rainfall may exceed the amount needed to fill the root zone to field
capacity resulting in some of it lost to deep percolation or runoff. For
example, referring td Figure 11-2, on May 8 a 1.5 inch rain occurred but
the amount needed to refill the root zone was only 0.63 inches (1,66 in.
- 1.03 in. 3. Therefore, .87 inches was not effective (1.50 in. - 0.63
in.).
11-10
Figure 11-2. Moisture Balance Sheet for
Scheduling Irrigation
Farm
County g>rtt
Field No. J,
Crop
Climatic Zone
Month Ho Year
Soil
Moisture Holding Capacity in Root Zone
Net Moistuie to Apply at Each Irrigation
inches
inches
Irrigate when balance is /,O
inches
Estimated
Daily
Net
Daily
Consumptive
Rainfall
Irrigation
Balance
Date
Use, inches
inches
inches
Inches
Remarks /\
Balance brought forward
TOTAL
11-11
Tenslonmeter Method of Scheduling
Detailed information concerning use of tensionmeters for scheduling irrigatic
is given in Appendix A. Tensionmeters are suited for use in medium and coar:
textured soils in the active root zone. Tensionmeters placed at shallow and
deep depths as per Table A-2 (Appendix A) may be used to indicate when to
begin and end irrigation respectively.
Pan Evaporation Method of Scheduling \j
Evaporation from an open or screen-covered pan can be used to schedule irrigc
tion in either of two methods. The daily plan evaporation value can be used
to estimate potential evapotranspiration (ETp) in a water balance procedure.
Based upon research results at Florence, South Carolina, evaporation from a
screen-covered pan is approximately 0.87 open pan evaporation and can be user
to directly estimate ET p , If open-pan evaporation is used, the values must L
adjusted to estimate ETn. The second method for using an evaporation pan to
schedule irrigation is to modify the pan so that it can be used to physical Ij
simulate ETn on a daily basis. Due to the combined simplicity and reliabilit
of this method, it has much potential for on-farm use and is described below.
Modifications include the installation of an overflow device to remove excess
water and a rustproof (stainless steel, brass, etc.) measuring scale to
measure water level in a standard National Weather Service Class A evaporatic
pan. The overflow should be set so that the pan will fill to within 1-2
inches of the top edge of the pan before excess water is removed. The
measuring scale should be mounted securely in the vertical position (e.g., tc
the side of the pan using a clamping device) so that it can be adjusted to
place the scale reference point at the water surface when the pan is full
(overflowing).
The amount of water that can be depleted from the soil profile before irriga-
tion is initiated is dependent upon several factors, all determined by the
specific site. Also, three assumptions required when using this method to
schedule irrigation are that (1) pan evaporation is equal to RP D , (2) all
rainfall and irrigation infiltrates the soil, and (3) water from rainfall and
irrigation in excess of soil storage is lost either as runoff of deep per-
colation. Rooting depth, irrigation system efficiency, water storage capacit
of the soil, and the fraction of water stored in the soil profile that can be
depleted before irrigation is initiated (allowable depletion) must be known
before the scale-setting calculation can be made. Details of the calculation
of this value can best be explained through the use of an example.
Assume a center pivot system with an application efficiency of 80% is used to
irrigate corn in an area which includes three soil types in the proportion
indicated: Raines, 10*; Norfolk, 40%; and Wagram, 50%. Assume the moisture
control zone for corn is estimated to be 24 inches, and irrigation is to be
applied when 40% of the available water in the rooting zone is depleted.
Available water capacity for the soil may be calculated using published SCS
OA LJ th ^ indlvldu al soils. Assume the available water stored in the
24-inch rooting zone for the Norfolk, Wagram, and Raines soils is 2.3, 1.8,
S ' r ? s P e ' tlvel y- This information can be used in several dif-
,
ways to estimate a representative value for available water stored
11-12
!/ By C. R. Camp and C^W. Doty with modi ficat tons by SCS,
in the soil profile under this center pivot system. Simple or weighted
means of the three values are two obvious methods, A more conservative
approach would be to use the value for the Wagram soil since it has the
lowest storage value and comprises 50% of the area. One potential danger
in this approach is that the other soils might become too wet if signifi-
cant rainfall immediately follows irrigation, but the maximum difference
in storage among these soils at the 50% level is only 0.45 inches, which is
only a 1- or 2- day difference in irrigation timing. Available water
stored in the soil profile may be calculated several times during the
growing season, if desired, to reflect the changing rooting depth.
The amount of water to be applied at each irrigation is determined by the
relationship, I = (AW)(AD)/E where I is the amount of irrigation water to
be applied, AW is the volume of available water in the rooting zone, AD is
the allowable depletion (fraction of available water to be used by the crop
before irrigation is applied), and E is the irrigation system efficiency
expressed as a fraction. For this case, I = (1 .8) (0.5)/0.8 = 1.12 inches.
The amount of pan evaporation required before irrigation is initiated is
determined by the equation, PE = (AW)(AD)/C, where PE is pan evaporation
required before irrigation is initiated, C is a crop coefficient relating
ET to Efp, and other variables are as defined earlier. Recommended values
of C are given below. For this example, using a C value of 1, PE -
1.8(Q.S)/1.0 - 0.9 inches
Crop Coefficient (C)
Corn Emergence to 20 inch height .
20 inch height to maturity l.Oi/
Cotton 1st bloom to boll maturity 1.0
Soybeans Emergence to canopy closure
canopy closure to maturity
Peanuts 1st bloom to nut maturity 0.8
Snap beans to 20 days from emergence
21 to 30 days from emergence
^1 t-n if! Hav<; Frnr
example, if the scale was installed with zero at the original water
surface), irrigation should be initiated. If the total amount of depleted
water is not replaced by irrigation (partial or reduced irrigation), the
depth of irrigation water actually applied (measured, if possible) is then
added to the pan. If the total amount of depleted water is replaced by
irrigation, water can be added to the pan until it overflows. For
sprinkler irrigation systems, the pan may be placed under the irrigation
system where it will receive the irrigation applied, if this is not
possible, water must be added to the pan after each irrigation. When rain-
fall occurs, water level in the pan will rise proportionally, reflecting
the increase in available water. Rainfall in excess of storage will be
lost from the pan via the overflow. The evaporation pan simulator will
operate in a similar manner for the entire season.
The pans used in research are stainless steel like those used by the
National Weather Service and may cost several hundred dollars. Irrigators
may make their own from a barrel or large galvanized tub. The pan, tube,
or barrel should be about 2 feet or more in diameter and deep enough to
hold at least a foot of water. This volume is needed to keep the water
from heating up too much. Chicken wire should be secured over the top to
keep wildlife out and will reduce evaporation by about 12 percent.
Household bleach may be added to the container to help keep water free of
scum or algae.
I/ Doty, C.W., C.R. Camp, and G. D. Christenbury. 1982. Scheduling
irrigation in the Southeast with a screened evaporation pan. Proc.
Speciality Conf. on Environmentally South Water and Soil Management,
Am. Soc. Civil Engr., Orlando, FL> July 20-23.
21 Smittle and Stansel - Scheduling Snap Bean Irr. From Pan Evaporation
Data, Tifton Ga., approx. 1981.
3/ Campbell, R. B. and C. J. Phene. 1976. Estimating potential evaporation
from screened pan evaporation. Agric. Meteorol. 16:343-352
IRRIGATION WATER MANAGEMENT PLAN
GENERAL
An irrigation water management plan is an essential part of the conser-
vation irrigation plan. See Chapter 7 for explanation and contents of an
irrigation water management plan. Irrigation water management plans shoulc
be tailored to the individual site and the management expertise and desire*
of the irrigator.
11-14
CRITERIA
General requirements for an Irrigation water management plan are contained
in the SCS Technical Guide, Irrigation Water Management, Std. 449,
EXAMPLE IRRIGATION WATER MANAGEMENT PLAN
The following example is intended to cover the basic steps to follow in the
development of an irrigation water management plan. An example irrigation
water management plan is shown in Exhibit 11-1.
Given:
Develop an irrigation water management plan for the center pivot system in
Chapter 10-C of this guide.
Solution:
Step 1. Provide the irrigates basic data such as: acres to be irrigated
of each crop, water supply, irrigation flow rates, water quality,
soil type, AWC, MAO, peak consumptive use rate, intake rate,
irrigation efficiency, and rooting depth (water control zone).
This data is contained in the irrigation data sheets as shown in
Chapter 10-C. In this example, information would be provided to
the irrigator by giving him a copy of the Irrigation Data
Sheets 1-5.
Step 2. The various methods available to monitor or determine soil moisture
should be discussed with the irrigator in such detail that he
can select a method to use. Once he chooses a method, then work
with him until he understands how to use the method. The
irrigator in this example selected the feel and appearance method
of determining soil moisture content along with tensiometers. The
irrigator should be able to convert the soil moisture measurement
to inches of water available to the crop. A form for converting
soil moisture measurement to AWC was included in the irrigation
water management plan Exhibit 11-1, sheet 1 of 6.
Appendix A shows how to convert the soil moisture measurement to
AWC in inches for the major soil moisture measurement methods.
Step 3. Provide the irrigator with information on the crop water require-
ments - daily, monthly, and seasonal. These can be approximated
by using computed values from Chapter 4 of this guide with the
planting and harvest dates shown that are close to the actual
dates. This example is for grain corn in climatic zone 2. This
data would be given to the irrigator and is shown on Exhibit 11-1,
sheet 2 of 6. The irrigator should have an understanding that
this information is estimated. Also he should have an under-
standing of effective rainfall (i.e., that all rainfall is not
available for the crop).
11-15
Step 4. The irrigator should have a method to determine when to irrigate
(i.e., an Irrigation scheduling procedure). The different methods
should be explained to the irrigator in such detail that he can
select a method. Once the irrigator has selected a method to use
in scheduling irrigations, he should be taught how to use it. In
this example, the irrigator selected to use the tensionmeter
method. Needed information would be prepared for the irrigator
and included in the irrigation water management plan, Exhibit
11-1, sheet 3 of 6.
Step 5. The critical stages of growth where sufficient moisture is
necessary for crop production should be provided to the
irrirjator, The information can be obtained from Chapter 3, lab In
3-2j of this <juide. The critical periods for corn were included
in Ihe irrigation water mananoment plan, Exhibit li-1, sheet 4 ol (>
Step G- The irrirjator should Know how much to apply. The not amount 1,0
apply for 1 this example was determined by the feel and appearance
method of osLimatinq the AWC and MAD and will vary at different,
rooting depths (i.e., crop growth stages}. The yross amount to
apply is the net amount divided by the irrigation system
efficiency. Hie irrigate* 1 should understand that the irr iyat ion
system is not 100% efficient in delivering water to the field an<l
that he should divide the net amount by the irrigation efficiency
lo obtain the rjrosc amount to apply, irrigation eificiency VM I ,
yiven on the irrigation data sheets as 70 percent.
The irrigator should know the application rate of his irrigation
system (in./hr) in order to determine the time needed to apply
the required water, in the case of self -propel led irrigation
equipment, operating adjustments should be made to apply I ha
necessary irrigation amount. For center pivot systems a tablo
should be developed to relate the dial setting to the gross wal.ir'
applied. Chapter 10-C of this guide gives a procedure for
determining gross application of center pivot systems. The dial
setting for this system was computed and included in the
irrigation water management plan, Exhibit 11-1, sheet 4 of 6, '-.ho-
ing the gross amount and net amount applied.
Step 7. The Irrigator should be taught how to recognize erosion caused by
irrigation and excess runoff of irrigation water and should bo
provided ways to make adjustments to prevent runoff. The infor-
mation provided will vary with each situation due to the variance
in erosion potential of soils, land slope, soil intake rate, etc.
A statement was made for this example and included in the irri"
gation water management plan, Exhibit 11-1, sheet 4 of 6.
Step 8. The irrigator should be provided a method of evaluating the per-
formance of his irrigation applications. This would consist of
explaining the reasons to evaluate the system and forms that
would be helpful in evaluating the system. It may be necessary
to work with the landowner on the first evaluation to teach him
how to gather and interpret the data. In this example, forms
were included in the irrigation water management plan, Exhibit
11-1, sheets 5 of 6 and 6 of 6. Plans were made to assist the
irrigator in evaluating his irrigation system. Appendix B gives
information on how to evaluate irrigation systems.
11 1C
Cooperator:
Location:
Exhibit 11-1
IRRIGATION WATER MANAGEMENT PLAN
Field No. 3
Sheet
ur-j
<]
C&,
1. Format for figuring the net amount of water needed for an irrigation
using the feel and appearance method of soil moisture measurements.
(1)
(2)
(3)
(4) (5)
(6)
Depth
(feet)
Soil Series
Avai lable
water
capacity
(inches)
Soil water content
before irrigation
(percent) (inches)
Soil water
deficiency
(inches)
(texture)
0-(>5-
bQ<y/ny SvfW
O.JO
.**? *W
o.*~
o-z.o
,/ //
/,zo
.52> O.&o
Q'&O
Column 1, the depth increment sampled.
Column 2, the soil texture of the sample.
Column 3, the available water capacity based on the texture of the sample.
AWC (inches) = depth (inches) x AWC (in. /in.)
Column 4, the percent of soil water content (remaining).
0-25% AWC - Dry, loose, flows through fingers.
25-50% AWG - Looks dry, will not form ball with pressure,
50-75% AWC - Will form loose ball under pressure, will not
hold together even with easy handling.
75-100%AWC - Forms weak ball, breaks easily, will not "slick."
Column 5, Column 3 x Column 4, the soil-moisture balance, inches.
Column 6, Column 3 - Column 5, soil-moisture deficiency or net irrigation
requirement.
2. Alternate format for figuring the net amount of water needed for an
irrigation using soil water tension versus water content (average
values obtained from table 2-1 for coastal plain soils).
Estimated soil moisture content @ Ot/& bar tensiometer reading ~ t j3 in. /in.
Estimated soil moisture content @ 4*30 bar tensiometer reading == ,Jv in. /in.
For early to mid-season corn, net amt. to irrigate =
For raid to late season, corn, net amt. to irrigate
depth x t 03 - 0/7%
11-17
Exhibit 11-1
Sheet 2 of 6
Crop - Corn, Grain
Moisture Allowed Deficiency (MAD)
Approx. Planting Date - March 20
Approx. Maturity Date - July 8
Estimated
Month Consumptive
Use - Inches
March 0.4
April 2.6
May 6.0
June 7.0
July 1.8
= 50%
Estimated
Accumulated Consumptive
Use - inches
0.4
3.0
9,0
16.0
17.8
11-18
Sheet 3 of 6
Exhibit ll-l
IRRIGATION SCHEDULING INFORMATION
Crop - Corn Soil - Fuquay Loamy Sand
Method - Tensiometers
Number of Tensiometers - 2 each at three locations as shown on Plan Map
(place in the crop rows).
Tensiometers should be placed as follows:
Estimated
Depth of
Recommended depths
Time of Season
Early to mid-
season (corn
generally less
than 3' high)
Mid-to Tate season
Water Con- of setting Tensiometers
trol Zone Shallow Deep
10"
24"
12"
12"
18"
Estimated
net water
to apply
Initially*/
0.45
0.6
Begin irrigation when shallow tensiometer reads 30 centibars (.3 bars).
After the initial application, vary the application amount as needed so
that the deep tensionmeter reading drops to about 10 centibars (.10 bars)
wi th In 1 to 12 hours afterwards. ___
Value given for net water to apply is for estimating purposes only based
upon the feel and appearance method of estimating soil moisture as given
on p. 1 of 6. Install tensiometers and service at regular intervals as
recommended by mfg.
11-19
Sheet 4 of 6
Exhibit 11-1
IRRIGATION WATER MANAGEMENT PLAN
CRITICAL GRQVJTH STAGE
Demand for water is especially high and important during the tasseling and
grain filling period. The grain filling period is the 3 weeks following
tasseling.
Corn should never be allowed to wilt appreciably. If limited irrigation is
necessary, the critical period for irrigation is from the tassel stage
through grain filling.
IRRIGATION APPLICATION
Irrigation to be Applied, Inches Time Required per Dail Setting
Revolution-Hours
15.4 100
17.1 90
19.2 80
22.0 70
25.7 60
30.8 50
38.5 40
51.3 30
77.0 20
2.14 3.05 154.0 10
EROSION OR EXCESS IRRIGATION RUNOFF
Soil intake rate can change. The intake rate will usually decrease the
longer the irrigation time (i.e., during the lower dial settings), Visual
observations should be made to determine if erosion or excess runoff OCCUT
Appropriate adjustments in the irrigation system operation or other conset
vation practices should be applied to reduce erosion and runoff as needed
Net
Gross
(@ 70X efficiency)
.21
0.30
.24
.34
.27
.38
.31
.44
.35
.51
.43
.61
.53
.76
.71
1.02
1.06
1.52
11-20
Sheet 5 of 6
Exhibit 11-1
IRRIGATION WATER MANAGEMENT PLAN
CENTER PIVOT SPRINKLE IRRIGATION EVALUATION
1. Location , Observer , Date & Time
2. Equipment: make , Ien 9 tn __ ft* pip fi diameter in
3. Drive: type speed setting %> water distributed?
4. Irrigated area = 3.14 (wetted radius ft)? = acres
43,560
5. N wind *Mark position of lateral direction
of travel, elevation differences,
wet or dry spots and wind direction.
Wind mph, Temperature
oc
Pressure: at pivot psl
at nozzle end psi
Diameter of largest nozzle in
Comments:
6. Crop: condition __ , root depth _ ft
7. Soil: texture _ , tilth _ _ , avail, moisture _ in. /ft.
8. SMD: near pivot _ _ in, at 3/4 point __ _ in, at end _ in.
9. Surface runoff conditions at 3/4 point _ , and at end _
10. Speed of outer drive unit _ ft per _ min = _ ft/mi n
11. Time per revolution = (outer drive unit radius ft) = _ hr-
9.55 (speed ft/mTn
12. Outer end: water pattern width _ ft, watering time _ min
13. Discharge from end drive motor _ gal per _ min= gpm
14. System flow meter _ gallons per _ min = _ gpm
15. Average weighted catches:
System = (sum all weighted catches _ I - m i = i n
(sum all used position numbers _ )
Low 1/4 - ( UITI 1ow ^/^ weighted catches _ )_ = m i = -j n
(sum low 1/4 position numbers _ )
16. Minimum daily (average daily weighted low 1/4) catch;
( hrs operation/day) X (low 1/4 catch _ in) = in/day
( _ hrs/revolution)
11-21
Sheet 6 of
17.
Exhibit 11-1
IRRIGATION WATER MANAGEMENT PLAN
CENTER PIVOT SPRINKLE IRRIGATION EVALUATION (Cont.)
Container catch data in units of , Volume/depth ml/ in
Span length __ ft , Container spacing ft
ml ml
Evaporation: initial
final
loss
ml
ml
ml, ave ml =
in
Span
Container 1 Span
Container j
no.
Position ra _ h _ Weighted No.
,, . AUdLCn , n
Number Cacch ||
Position Y _ . _ Weighted 1
., , A oaccn _ . . i
Xunber Catch ]
1
^
3
37
38
39
4
5
6
40
41
42
7
8
9
43
44
45
10
11
12
46
47
48
13
14
15
49
50
51
16
17
18
1
52
53
54
19
20
21
55
56
57
22
23
24
58
59
60
25
26
27
61
62
63
28
29
30
64
65
66
31
32
33
1
67
68
69
34
35
36
1
70
71
72
Sura all; used position numbers
Sum low 1/4: position nur.ib^rs
, weighted catches
, weighted catches
11-22
IRRIGATION GUIDE
Contents
General
Methods of Measuring Small Irrigation Streams _______ ....... 1? ?
Volumetric -- ............ ______________________ \~~_~
Submerged Orifice Plates - ..... ____________________ "" ....... 12 2
Washington State College (WSC) Flume ......... __________ 19%
Siphon Tubes ------- ..... - ....... _ ............ ____________ ~_ 12-4
Methods of Measuring Pipe Flow ----------------- ..... \? 4
Pipe Orifices ---------------------- ...... ____________________ 12 4
Venturi Meters -- ............ ------------ ....... ______________ 12 _ 5
Irrigation Flow Meter ------------------------ ..... ___________ 12-6
Coordl nate Method ------------- ........ _______ ..... ___ ...... __ i ? _ 7
Methods of Measuring Channel Flow ---- ....... ---- ..... __ ..... ___ i 2 -8
Float Method -- ...... --------------- ..... _____________________ 12-8
Submerged Orifice ------------------------------------------- 12 IQ
Gates ~ ...... ..... ----------- ...... --------- ..... ---------- 12-11
Weirs - _________ ____ _______________________ ,. i o 11
Flumes ...... - ..... ------- ...... ---------- ......... ___ ..... ___ 12-12
Current Meters ----------------- ...... ------------------------ 12-12
Culvert Method ---- .......... - ..... ------- ...... ______ ..... _._ 12-13
Figures
Figure 12-1 Submerged Orifice Plate
Figure 12-2 WSC Flume
Figure 12-3 Pipe Orifice
Figure 12-4 Venturi Meter -- .......
Figure 12-5 Irrigation Flow Meter -
Figure 12-6 Coordinate Method .....
Figure 12-7 Typical Cross Section [
Figure 12-8 Computing Channel Flow
Figure 12-9 Weir Notch ..... - ......
Figure 12-10 Parshall Flume ---------
SOUTH CAROLINA IRRIGATION GUIDE -
CHAPTER 12. IRRIGATION WATER MEASUREMENT
GENERAL
Reasonably accurate water measurement is necessary for proper design and
evaluation of an irrigation system. The units of flow measurement com-
monly used for water are cubic feet per second (cfs) and gallons per'
minute (gpm).
The following equivalents may be found useful:
1 gallon (gal) = 231.02 cubic inches = 0.1337 cubic feet
1 gallon of water weighs 8.33 pounds
1 million gallons = 3.0689 acre-feet
1 cubic foot (cu ft) = 1,728 cubic inches
= 7.48 gallons
1 cubic foot of water weighs 62.4 pounds
1 acre-foot (ac-ft) = amount required to cover one acre
one Foot deep
= 43,560 cubic feet
= 325,828.8 gallons
= 12 acre inches
1 gallon per minute (gpm) = 0.00223 cubic feet per second
= 1,440 gallons per day (24 hrs)
1 million gallons per day (mgd) = 1.547 cfs
= 694.44 gpm
1 cubic foot per second (cfs) = 7.48 gallons per second
= 448.8 gpm
= 646,272 gpd
= 0.992 acre
= 1,983 acre
12-1
It is common practice In planning to round off certain conversion factors
such as:
1 cfs = 450 gpffl
= 1.0 acre-inch per hour
=2.0 acre-feet per day
Many methods of water measurement have been used in different situations
for different purposes. The methods herein discussed will be as follows:
(1) methods of measuring small irrigation streams, (2) methods of
measuring pipe flow, and (3) methods of measuring channel flow.
METHODS OF MEASURING SMALL IRRIGATION STREAMS
VOLUMETRIC
Volumetric flow measurements are made by measuring the time required to
fill a container of known volume.
Q (gpm) - Volume of water (gal) x 60
Time required to fill container (seconcf?
Refer to NEH 15, pages 9-3 to 9-5,
SUBMERGED ORIFICE PLATES
The submerged orifice plate is placed across the furrow and the head "
through the orifice is measured under submerged conditions. See Fiqui
12-1.
Orifice plates consist of small sheet iron, steel, or aluminum plates
that contain accurately machined circular openings or orifices usual 1
ranging from 1 to 3i inches in diameter,
In use, an orifice size is selected so as to produce a head differen
within the 0.50 to 2,5 inch range, and the plate is placed in and ar
the furrow with its top as nearly as level as possible. Flow throuf
the orifice must be submerged.
Flow through the orifice is calculated by the standard orifice forrr
Q = CA 2 gH, (cfs) which for gallons per minute can be wr j
Q = 7.22 Ca h
Where Q = gpro
C coefficient of discharge (use 0.60 for approximate
h = head differential in inches
a = area in square inches
See NEH 15, pages 9-5 to 9-7 for more information,
12-2
Figure 12-1. Submerged Orifice Plate
WASHINGTON STATE COLLEGE (WSC) FLUME
The WSC measuring flume, developed at the Washington State College,
adapts the Venturi principle to the measurement of flow in small
channels. This flume consists of four principle sections: An entrance
section upstream, a converging or contracting section leading to a
constricted section or throat, and a diverging of expanding section
downstream (Figure 12-2). The bottom of the flume is placed level, both
longitudinally and transversely, at a height equal to or slightly higher
than the channel bottom. Only one reading on the slanting scale is
required. This reading is readily converted to gallons per minute by
the use of tables. See NEU Section 15, Chapter 9, pages 9-10 - 9-12 for
more information,
Figure 12-2. WSC Flume
12-3
SIPHON TUBES
Siphon tubes, used to remove water from a h?ao ditch and distribute it
over a field through furrows, corrugations, or borders, are also used to
measure the rate of flow into these distribution systems.
These tubes, made of aluminum, plastic, or rubber, are usually preformed
to fit a half cross section of the head ditch. The normal diameter range
is from 1 to 6 inches, although both smaller and larger sizes are
available. The smaller sizes are used with furrows and corrugations and
the larger sizes with borders. Various lengths are available.
See NEH 15, Chapter 9, pages 9-10 to 9-14 for more information.
METHODS OF MEASURING PIPE FLOW
PIPE ORIFICES
Pipe orifices are usually circular orifice plates placed within or at the
end of a circular pipe (see Figure 32-3). The head on the orifice is
measured with a manometer. A manometer is a device that measures the
pressure differential in feet of water or inches of mercury. The orifice
is often used for well discharge measurement from wells in a range of 50
to 2000 gpm. Discharge through the orifice is computed by the formula:
Q = CA 2 gh
where Q = Discharge in gpm
C = Coefficient of discharge (See Fig. 9-8,
Section 15, Chapter 9, NEH)
a = cross sectional area of the orifice in square
inches
g = Acceleration due to gravity = 32.2 ft/sec 2
h = head on the orifice in inches measured above the
center for free flow.
For discharge tables refer to NEH 15, Chapter 9, Table 9-5,
12-4
RULER
(GAGE)
ORIFICE
PLATE
Figure 12-3. Pipe Orifice
VENTURI MKTIiRS
The Venturi meter measures ttic flow in a pipe under pressure. It
utilizes the Venturi principle in that 1'low passing through a
constricted section of pipe is accelerated and its pressure head
lowered. With the relative cross sectional ureas Icnown the flow is
measured by measuring the drop in pressure. For further information,
refer to pages 9-17 to 9-20, Section 15, Chapter 9, N1SH (see Figure
12-4).
Figure 12-4. Venturi Meter
12-5
IRRIGATION FLOW. METER
Meters of this type are generally of the velocity type. They
essentially consist of a conical propeller connected to a registering
head by a gear train (see Figure 12-5). They are operated by the
kinetic energy of the flowing water. Three basic types are mainly used;
(1) low-pressure line meters, (2) open-flow meters, and (3)
vertical-flow or hydrant-type meters. Flow tables and charts are
available from each company making the device.
FLOW
METER
PIPE
WATER FLOW
Figure 12-5. Irrigation Flow Meter
COORDINATE METHOD
In a coordinate method, coordinates of the jet issuing from the end of a
pipe are measured (see Figure 12-6). The flow from the pipe can be
measured whether the pipe is discharging horizontally or vertically.
They should be used only where facilities for more accurate measurement
are not available, and where an error o up to L0% is permissible.
Refer to pages 9-24 through 9-28 of Section 15, Chapter 9, of the NEH of
procedures and tables.
FULL PIPE.
D
Figure 12-6. Coordinate Method
12-7
METHODS OF MEASURING CHANNEL FLOW
FLOAT METHOD
The flow rate can be estimated by timing the passage of a small Moat
through a measured length of channel. The procedure for estimating rate
of flow by the float method is as follows:
1. Select a straight section of ditch with fairly uniform cross
sections. The length of the section will depend on the current,
but one hundred feet usually will be adequate. A shorter length
may be satisfactory for slow flowing ditches.
2. Make several measurements of depth and width within the trial
section, to arrive at the average cross section area. The area
should be expressed in terms of square feet (see Figure 12-7).
3. Place a small float in the ditch a known distance upstream from the
upper end of the trial section. Determine the number of seconds it
takes for the float to travel from the upper end of the trial
section to the lower end. Make several trials to get the average
time and travel. The best floats are small rounded objects which
float nearly submerged. They are less apt to be affected by
wind or to be slowed by striking the side of the channel. Among
small objects which make good floats are a long necked bottle partly
filled with water and capped, a rounded block of wood, or an orange.
A wooden sphere, like a croquet ball, is excellent.
4. Determine the velocity (or speed) of the float in units of feet per
second by dividing the length of the section (in feet) by the time
(in seconds) required for the float to travel that distance.
5. Determine the average velocity of the stream. Since the velocity
of the float on the surface of the water will be greater than the
average velocity of the stream, the float velocity must be
multiplied by a correction coefficient to obtain a good estimate of
the true average stream velocity. The correction factor varies with
the type of float used with the shape and uniformity of the channel.
With floats that sink only an inch or two below the water surface, a
coefficient of about 0.80 should be used for most unlined farm
ditches. A coefficient of 0.85 is appropriate for smooth uniform
lined ditches. With floats that extend two-thirds or more of their
depth below the surface, the coefficients should be about 0.85 for
unlined ditches and 0.90 for lined ditches (see Figure 12-8).
12-8
Station 0+00
Distance from left water edge (ft.) 0.0 1.5 3.6 5.0
Water depth (ft.) 0.00 1.10 1.15 0.00
Area = 1.10 x 1.5 + (1.10 + 1.15) 2.1 + 1.15 x 1.4
= 0.82 + 2.36+0.81 = 3.99
Station Q+40
Distance from left water edge (ft.) 0.0 1.3 3.8 5.2
Water depth (ft.) 0.00 0.85 1.05 0.00
Area = 0.85 x 1.3 + (0,85+1.05)2.5 + 1.05 x 1.4
22 2
= 0.55 + ?.37 + 0.73 = 3,65
Station 0+90
Distance from left water edge (ft.) 0.0 0.9 1.9 3.3 4.8
Water depth (ft.) 0.00 0.80 1.15 1.15 0.00
Area = 0.80x0.9 + (0.80+1.15) + 1,15x1.4 + 1.15x1.5
6. Compute the rate of flow. The rate of flow is obtained by
multiplying the average cross sectional area (Item 2) by the
average stream velocity (Item 5) (see Figure 12-8). The accuracy
of these estimates of flow rates is dependent upon the precisenesi
with which average cross sectional areas and float velocities havi
been determined and upon the selection of the proper correction
coefficient.
DETERMINE THE SPEED OF THE STREAM FLOW
NUMBER OF METERS 30... _ u 3 METERS PER M , NUTE
NUMBER OF MINUTES 2.1 14 ' 3 METERS PER MINUTE
30M (100ft)
Figure 12-8, Computing Channel Flow
SUBMERGED ORIFICE
A submerged orifice is a hole in a bulkhead through which water flows
under submerged conditions. The opening of a standard submerged orif
is sharp edged and usually rectangular with a width 2 to 6 times the
height. They can be used in channels having grades which may be too
flat for weir operation. The forumla used is the same as for pipe
orifice:
= ca
3.61 for orifices with complete contraction.
Keter to pages 9-63 to 9-65, Section 15, Chapter 9, NEH for installat
procedures and flow tables.
12-10
GATES
Gates can be arranged and calibrated to operate as a type of submerged
orifice. The same pipe orifice formula applies:
Q = ca V 2gh
The c value here will be a variable depending on the nature of the
specific gate opening. When the discharge is free, the head (h) is the
difference in elevation beLweun Lhu upjjLruaiu water surface and the
center of the gate. Figure 9-33, Section 15, Chapter 9, NE1I gives an
illustration and flow chart for a commercial meter gate.
WEIRS
A weir notch IB one of the simpler water measuring devices to use and
construct (see Figure 12-9). There are three general types depending on
the shap of the notch: (1) rectangular, (2) trapezoidal of Chipolletli,
and (3) 90 triangular. They require considerable loss of head, often
not available in ditches on flat grades. Triangular weirs give the most
accurate readings on flows of less than 1 cfs. Rectangular and
trapezoidal flumes are uaed to measure discharges up to 75 cfs or more.
Refer to NKIl, Section 15, Chapter 9.
DEPTH OF WATER TO
THE BOTTOM OF
THE NOTCH
NOTCH
M-
Figure 12-9.
FLUMES
There are three major types of flumes used to measure irrigation water:
(1) Parshall (see Figure 12-10), (2) trapezoidal, and (3) cutthroat: .
They all operate similarly and require less operating head than weirs.
They all have a converging or contracting section, a constricted sectioi
or throat, and a diverging or expanding section. The ARS cast-in-placc,
2-foot concrete trapezoidal flume was designed for use in trapezoidal
irrigation canals flowing up to 50 cfs.
The cutthroat flume was developed as a portable flume, although it: c.&\\
be permanently installed, for flows up to 10 cfs. The Parshall is
generally a permanently installed flume and used to measure flows up Co
100 cfs or more. Refer to NEH, Section 15, Chapter 9, for Parshall
flume. Refer to USDA-ARS Technical Bulletin No. 1566 for the
cast-in-place trapezoidal flume and for the cutthroat flume.
GAGES
Figure 12-10. ParshnH Flume
CURRENT METERS
The current meter is .ImiUr to the flow muter in that it measure the
Y ^^ f r cll KM of the propeller IH
and using a stop watch. They are either
'
12-12
Culvert Method
If a culvert is near the area where a flow measurement is needed the
velocity can be determined by the float method discussed on page 12-8
using the appropriate coefficients for lined ditches.
The flow is determined by use of the following chart:
HYDRAULIC PROPERTIES OF CULVERTS FLOWING PARTIALLY FULL
d 1
a 1
d l
a 1
(Depth
factor)
(Area of
Flow Factor)
(Depth
factor)
(Area of
Flow Factor)
Full 1.0
0.7854
Half 0.5
0.3927
0.95
0.7708
0.4
0.2934
0.9
0.7445
0.3
0.1981
0.8
0.6735
0.25
0.1536
0.7
0.5874
0.2
0.1118
0.6
0.4920
0.1
0.0408
Empty 0.0
0.0
Adapted From Handbook of Culvert and Drainage Practice 1947
Depth factor (d 1 ) is expressed as depth of flow in culvert divided by culvert
diameter (D). d 1 (in table) = Depth of flow
Diameter (D)
Measure depth of flow at both ends and use average depth in calculations.
Multiplying area of flow factor (a 1 ) by the pipe diameter squared (D) 2 for the
corresponding depth of flow.
Multiply this area by the velocity in feet per second to obtain flow in CFS.
Example Problem - Determine culvert flow.
Given: Average velocity in a 2.0 foot diameter culvert is estimated to
be 2.0 ft/sec.
Average measured depth of flow in the culvert = 1.5 ft.
Solution: d 1 = Depth of flow = 1.5 = 0.75
1 " D ~T~
Interpolating from chart: a 1 = .6735 + .5874 = 0.63
2
Area of flow = a'D 2 = 0.63(2) 2 2.52 sq. ft.
Culvert Flow = 2.52(V) = 2.52(2) = 5.0 cfs
12-13
Appendix A - Measuring Soil Water Content
Contents
Feel and Appearance Method A-l
Tenaiometers A-l
Electrical Resistance Blocks A-8
Figures
Figure A~l Soil Suction Versus Soil Water Content and Soil
Water Deficiency
Figure A-2 Water Retention Curves
Figure A-3 Calibration Curve for Delmhorst Gypsum Blocks
A-5
A-6
A-9
Tables
Table A-l Guide for Judging how much Moisture is Available
for Crops
Table A-2 Recommending Depth of Setting Tensiometers
Table A-3 Interpretation of Tensiometer Readings
A-2
A-3
A-7
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r
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l-l
>ry, loose, sing]
grained, flows
zhrough fingers.
3 (0 1
W
u a a
p.
J LLJ ^
4J .TJ rH
*J JJ
J H H
PtrH rH M
P.-H fO p
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h ft i* 3
rt w
(0 rH H CO
P<H H Q)
Q< -H nj M
< I* rQ &
lends to stick
together slightly
soaetimes fonns
a very weak ball
under pressure.
upon squeezing, n
free water appear
on soil but vet
outline of ball
is left on hand,
s formed by scuee:
H
^ H
*J rH
W
JJ
n)
rt
41 (tt
01
S
u
U
W
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y
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A-2
''Vn i' i ' I P" ;, m i ', !i| ' r th Ml ;,! 1 ,, i } i \ ,[
1 ' OPI-, Hue .,!,,! u-u ',](< Id IMJ M. , ( . . h,.
-Hid ill- ol her u, >,u flic !,,>,,! -ud u ilojr i (MI- fit,! - i ; i ., i,,^. iM , UJ1 ,,U' ( !
111 llL '' J : ' w '"' ' r ' f h* 1 -io i 1 i: in t: I OIK ; 'f,u y ._ ,, uiti i e pri-riijal 'it i -Ji jo i 1 ;;
01 ijlopi"i in Liu- Jjckl. Wln-n i-lacuij', u-n'si uui te r-j , tlie follo'-ins
tjiij^ff ;-! t ions shou Id be kept in mind
(1) "in row crop;.,, the Lens i orne ter s should be placed in the crop
row. Stations should be at points where the plant population
is re pro sen ta (rive of the field.
(2) for orchards, the tens iome ter -3 should be located within the
drip Hne and 3 tn d feet from I he tree trunk and on the
sunny s iclp .
O) Measuring stations shuujd be in representative soil areas
oi the Held. Tuiisumiet en; should nor be placed in low
..'i i 11 tin 1 tit; Id
(4) Toa.si omo i <u a should hi? pi ticc-d after the last fieeae in the
cprLiij; and should be i-omovud beiore the first freeze in the
Tal 1 .
Ufpth ol I (Misiomet ur i nsl t \ I I ati mi i :; del cum nerl by tho active
root i.niu 1 of I IIP crop. This .ulivu i out zone depends upon the
f f'op , 'il a;',o dl growth, and dcplh oi" so-i I , Recommended depths
' 01 sdlLii); I ciij, Loinel ot s aii 1 KW-'n in '1'aii 1 o A -2, Tensiometer s
'ihnuld ui)l In- ut.-.tallpfl iu a line leitlurod soil at the shallow
tool tUijith bpr.une HOI'] MK'tirm wi I L eiceeed IGt) centibars before
I Ijc iiit-n.igtMiipnL allowud defiriency is reached.
Table A- 2
RKCOMMliNDKl) l)Fl>TH OF SETTING TENSIOMETERS
Trvigation Depth of
Active Root Zone
Inches
12
18
24
36
48 or more (deep)
Sh
Te
I/ Only one tensiometer is recommended fo
A-3
g. The tensiometer may be Installed in an auger hole several
times larger than the diameter of the tensiometer. The cup
should be pushed into the soil at the bottom of the hole, if
it is soft enough. If the soil is too hard, it may be
softened by water or a small hole can be made to receive the
cup. The hole should.be refilled in layers and compacted
around the tensiometer tube. A special tool supplied by the
manufacturer may be used to install the tensiometer. It is
important to get good soil contact.
h. The above-ground parts of the tensioraeter should be shielded
from the sun to avoid a "thermometer" effect,
i. Readings should be examined carefully to detect the effect of
a leak. A leaky tensiometer can give misleading results. The
tensiometer should be kept filled with deaired (boiled) water
or serviced regularly with deairing equipment.
j. Tensiometer readings should be correlated with the total soil
water content in the soil profile at each station. This can
be done by using the gravimetric method in Paragraph 6.
Gravimetric measurements should be made for several different
tensioraeter readings and plotted on a graph. Figure A-l shows
an example of tensiometer readings versus soil water content
in the root zone.
k. To schedule irrigation it is necessary to know which
tensiometers should be used at a given site. The greatest
soil suction will occur near the soil surface where the roots
are most active. This may cause the activity of the soil
water to decrease so rapidly that the range of operation of
the tensioraeter will be exceeded. This will cause air to
enter the instrument.
(1) In sandy soila, tensiometers in the active root zone
should be used to schedule irrigation.
(2) For clayey soils, the soil auction will usually exceed
the operating range of the Instrument before it is
necessary to irrigate. The graph in Figure A-2 shows
that it takes about 2.0 bars (200 centibars) of suction
to reach a 50 percent water depletion level for a clay.
At 0.8 bar or 80 centibars the water depletion level
would be about 25 percent. This makes it necessary to
use the lower tensiometers in the root zone to schedule
irrigation.
(3) Soil suction values that indicate need for irrigation
will differ for the different soils. A guide for
interpreting tensiometer readings is given in Table A-3,
A-4
r-* - .1 -a*
Suction {cervtibofy _ A- 5
"igure
AVAILABU WATER DEPLETION . Prcon(
100
Water ictention curves tot
soili plotted in tcrmi of par-
cent available water removed, re-
drawn with chanse in *cle torn
Richwdi and Manh (1&61) and
Taylor (IQftS),
A-6
Table A- 3 .
INTERPRETATION OF TENSIOMETER READINGS
* Dial Read ing
Inches of
Mercury
Centi-
bars
Interpretation
Nearyly
Saturated
10
Near saturated soil often occurs for a
day or two following irrigation. Danger
of water-logged soils, a high water table,
poor soil aeration, or the tensiometer may
have broken tension, if readings persist.
Field
Field capacity. Irrigations discontinued
Capacity
6
9
11 in this range to prevent waste by deep
percolation and leaching of nutrients
20 below the root zone. Sandy soils will
be at field capacity in the lower range,
30 clayey soils will be at field capacity in
the upper range.
Irrigation
Usual range for starting irrigations.
Range
Soil aeration is assured in this range.
12
15
18
40
50
60
In general, irrigations start at readings
of 30-40 in sandy textured soils (loamy
sands and sandy loams) . Irrigations
usually start from 40-50 on loamy soils,
(very fine sandy loams and silt loams).
On clay soils (silty clay loams, silty
clays, etc. ) irrigations usually start
from 50-60. Starting irrigations in
this range insures maintaining readily
available soil moisture at all times.
21
24
70
80
This is the stress range. However, crop
is not necessarily damaged or yield reduced,
Some soil moisture Is readily available
to the plant but is getting dangerously
low for maximum production.
Top range of accuracy of tensiometer,
readings above this are possible but the
tensiometer will break tension between
80 to 85 centibars.
Indicative of soil conditions where the tensiometer is located.
Judgment should be used to correlate these readings to general crop
conditions in the field.
A-7
3. Electrical resistance blocks
a. Electrical resistivity can be used to measure a change in soil
water content. The equipment used to measure changes in soil
water content consists of a portable resistance meter and
electrodes inbedded in small blocks.
b. The blocks consist of permanently embedded electrodes in
materials such as nylon, fiberglass, or gypsum. The
electrodes are attached to lead wires which are plugged
into a meter. When the blocks are placed in contact with
Che soil, the moisture content of the block tends to
equal the moisture content of the soil. Because the
electrical resistance of the electrodes in the block
varies with the moisture content, a measurement of
electrical resistance by the meter is a good indication
of the soil moisture content. The drier the soil, the
greater the electrical resistance, and vice versa. This
method will work satisfactorily in any soil that does not
exhibit saline or alkaline problems.
c. The location and depth of Installation of these blocks is the
same as for tensiometers. The gypsum blocks should be placed
in the soil, in the rooting zone of the crop as early in the
season as is practical and left in the soil throughout the
growing season. The following procedure is suggested for
installing the blocks.
(1) The electrical resistance blocks should be thoroughly
soaked in a pail of water before installing (follow
manufacturer's recommendations for soaking time).
Soaking removes air from the blocks and Insures accurate
readings of the soil moisture,
(2) A soil probe or auger can be used to bore a hole in the
row slightly larger than the electrical resistance block.
In row crops, the hole should be angled toward the
furrow.
(3) The last 3 inches of soil removed from the hole should be
crumbled and put back into the hole. About ^ cup of
water should be poured into the hole so a slurry of mud
is formed in the bottom,
(4) The blocks should be pushed into the hole with the soil
probe, or 4 inch diameter electrical conduit, setting
them solidly in the bottom with a firm push of the probe.
Firm contact between the blocks and surrounding soil must
be made.
A-8
(5) The hole should then be filled with soil, 3 or 4 inches
at a time , tamping the soil firmly as the hole is filled,
(6) The wire leads from the blocks should be brought to be a
single station, midway be tween the holes and tied to a
s take with the wires separated. The wires should be
color coded with colored plastic tubing or other means of
identation.
d. Irrigations should be scheduled when the meter readings from the
water control zone reach the desired level of soil water depletion
using the calibration curve developed for a given site.
(1) Meter readings that indicate the need for irrigation will
be different for various textured soils and MAD.
(2) There will be differences in electrical resistance readings
due to the frequency of the A.C. resistance meters. Each
company selling these meters for measuring soil water content
has instructions which are provided with the meters. Because
of these problems, it is desirable to develop site specific
calibration curves. Curves for three different soils are as
follows.
CD
2
Q
<
UJ
or
200
160
120
ft
UJ 80
UJ
s
COARSE SANDY LOAM
(0 20 30 40 50 GO 70 60 90 K
PERCENT AVAILABLE WATER
IN SOIL
Figure A-3 Calibration curve for Delmhorst
gypsum blocks for 3 different
soil types.
A-9
APPENDIX B - IRRIGATION EVALUATION PROCEDURES
Contents
General B_l
Sprinkler Irrigation Field Evaluation Procedure B-2
Center Pivot B-2
Periodic Hove and Fixed System B~12
Traveling Sprinkler B-22
Trickle Irrigation Field Evaluation Procedure B-35
Figures
Figure B-l Center Pivot Sprinkle Irrigation Evaluation B-4
Figure B~2 Profile of Container Catch from Center Pivot
Evaluation Test B-9
Figure B--3 Sprinkler-Lateral Irrigation Evaluation B-13
Figure B-4 Combined Catch Pattern Between Sprinklers
5 and 6 for a 50-foot Lateral Spacing B-15
Figure B-5 Loss of Presbure Duo to Friction Along a
Lateral Having Only One Size of Pipe B-16
Figure B-G Layout of Catch Containers for Testing the
Uniformity of Distribution AJong a Sprinkler
T -i t" r~* T" :n 1 T T TIA*-,^* *~.^- ,_H-_ n ^_ n _ n n _____._* uu _ u . . _ , _^_^. 13 _ 1 D
jjct UU.LCIA j-jj m-* ^-^ ^^- -H-^"^^ ~-^ ^ -<^-.*-H ^^, ^-^.^- i . _. _ _ j^'-'j_o
Figure B-7 Traveling Sprinkler Irrigation Evaluation B-24
Figure B-8 Typical Layout for Traveling Sprinklers B-27
Figure B-9 Profile from Overlapped Container
Catch Data from Traveling Sprinkler Evaluation B-30
Figure B-1Q Trickle Irrigation Evaluation B-36
APPENDIX R - IRRIGATION EVALUATION PROCEDURES
1. General
a. The effectiveness of a farmer's irrigation water management
practices can be determined by making field observations and evaluations.
The results of these observations and evaluations are used to help the
irrigaLor improve his water management techniques and/or upgrade his
irrigation system. These improvements shoul d save money by conserving
water and energy, reducing nutrient losses, and improving crop yields.
The following principles apply to all irrigation methods,
(1) Irrigation should be made in a timely manner so as to
maintain a favorable soil water content for good crop growth. An excep-
tion may be made where the water supply is limited. In this situation,
water should be applied in a manner that will maximize net income,
(2) The amount, of water applied should be sufficient to
bring the root zone profile up to field capacity. Center pivots may
have difficulty meeting this requirement. In these cases, more frequent
irr igati cms with a small or application amount is practical . Recent
research in the southeastern United States has revealed that shallow
frequent applications may be more efficient and effective than attempting
to bring Che root zone profile up to field capacity. In cases of shallow
control r.ones maintained at low-soil-water suctions on sandy soil,
frequent small applications may be required to adequately meet crop water
requirements without* risking excessive leaching.
(3) The water should be applied at a rate that will not cause
waste, erosion, or pollution.
b. An examination of a farmer's irrigation water management
practices, then, should attempt to answer the following questions.
(J) Are Irrigations being applied in a timely manner?
(2) What is the soil moisture deficiency?
(3) How much water is being applied?
Is the irrigation causing excessive erosion?
(5) How uniformly is the applied water spread over the
field?
(6) How much of the water is infiltrated into the soil?
(7) Is there excessive deep percolation and/or runoff?
(8) If so, how much deep percolation and/or runoff?
(9) Is there a pollution problem being caused by irrigation?
(10) What is the application efficiency and the uniformity of
application?
(11) On a sprinkler irrigated field, is there translocation or
surface runoff?
B-l
c. To answer some of the above questions, use should be made of the
Irrigation Water Management sections on Irrigation Timing, Measuring Soil
Water Content, and Procedures for Measuring Intake* and Application Rates.
2. Sprinkler Irrigation Field Evaluation Procedure.
a. Center Pivot. It is good practice to occasionally test the
performance of a center-pivot system to check on the uniformity of
application and flow characteristics.
(1) Information required. Center pivot systems are propelled
by using some of the water or by such independent power sources as
electricity, oil hydraulics, or compressed air. Where water is used, it
must be included as part of the total applied water; this somewhat
lowers computed values of water use efficiency. When the water discharging
from the pistons or turbines is distributed as an integral part of the
irrigation pattern, its effectiveness should be included in the uniformity
of application or the Distribution Uniformity (DU) ; otherwise, it should
be ignored in the DU computations but should be included in computing
the Application Efficiency of the Low Quarter (E ).
The following information is required for evaluating center pivot irrigation
systems .
(a) Rate of flow from the total system,
(b) Rate of flow required to propel the system if water
driven.
containers .
(c) Depth of water caught in a radial row of catch
(d) Travel speed of end drive unit.
(e) Lateral length to end drive unit and radius of the
portion of the field irrigated by the center pivot.
(f) Width of the wetted strip at end drive unit.
(g) Operating pressure and diameter of largest sprinkler
nozzles at the end of the lateral.
(h) Approximate differences in elevation between the
pivot and the high aad/or low points in the field and along the lateral
at the test position radius (taken to within plus or minus 5 ft).
(i) Additional data indicated on Fig, B-l.
Accurate measurement of the flow rate into the system is needed for
determining the E of the system; however, if no accurate flow metering
device is at the inlet, the E can only be estimated.
(2) Equipment, needed. The equipment needed is essentially
the same as for the full evaluation of sprinkler-lateral systems.
B-2
(a) A pressure gauge (0-100 psi) with pilot attachment.
(b) A stopwatch or watch with an easily visible second
hand.
(c) From 60 to 100 (depending on the lateral length)
catch containers such as 1-quart oil cans or plastic freezer cartons.
(d) A 250-ml graduated cylinder to measure volume of
water caught in the containers.
(e) A tape for measuring distances in laying out the
container row and evStimating the machine's speed.
(f) A soil probe or auger.
(g) A hand level and level rod to check differences in
elevation.
(h) A shovel for smoothing areas to set catch containers
and for checking profiles of soil, root, and water penetration.
(i) Fig. B-l for recording data.
(j) Manufacturer's nozzle specifications giving discharge
and pressure and the instructions for setting machine's speed.
(k) For water-driven machines which do not incorporate
the drive water into the sprinkler patterns, a 2- to 5-gallon bucket and
possibly a short section of flexible hoze to facilitate measuring the
drive water discharge.
(3) Field procedure. Fill in the data blanks of Fig. B-l
while conducting the field procedure. In a field having a low-growing
crop or no crop, test the system when the lateral is in a position where
differences in elevation are least. In tall-growing crops, such as
corn, test the system where the lateral crosses the access road to the
nivot nnint.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10
12
13
14
15
16
Figure B-l. CENTER PIVOT SPRINKLE IRRIGATION EVALUATION
Location Field F202 , Observer JK , Dace & Time 8-18-71 p.m.
Equipment: make HG 200 _ , length 3375 E, pipe diameter g 5/6 in
Drive: type htoter speed setting %, water distributed? t^es
2
(wetted radius 14SO ft) ,_._
- = J52 acres
Irrigated area =
eroded wneel
tracks .
*Mark position of lateraL direction
f 2(7 /t of. travel, elevation, differences,
wet or dry spots and wind direction.
Wind mph, Temperature 90 $
f
j t
Pressure: at pivot
86
at nozzle end
DSJ
Diameter of largest nozzle 1/2 in
Conuaen t s : Sprinklers operating
OK but end part circle sprinklers out of adjustment
Crop: condition corn., good except north edge, root depth 4 ft
Soil: texture sandy loam , tilth poor , avail. moistureJ.i? in/ft
SKD: near pivot 0,5 in, at 3/4 point 0- 5 in, at end 3.0 ' in
Surface runoff conditions at 3/4 point s Hgh t , and at end moderate
Speed of outer drive unit 4S ft per 10 min ^.5 ft /min
. _ ,
11. Time per revolution =
*
(outer drive unit radius I35c? ft)
- - ~~ - ~ ~~ - =
j
9.55 (speed
C 7 ~~\
. 6 f t/minj
Outer end: water pattern width 16 ft, watering time 39 min
Discharge from end drive motor 5.0 gal per 0- <$? min - J3. 5 gptn
Systen flow meter 115000 gallons per ^ min =
1150
gpm
Average weighted catches:
, (sum all weighted catches 257,708
System = -/ - ^ - 5 - ^T^ - -
(sum all used position numbers
T , , .
LOW 1/4 -
low I/A weighted catches 5? 3 974 )
- - - - - - \
)
-. ^ r
(sum low 1/4 posxtion numbers
Minimum daily (average daily weighted low 1/4) catch:
( 24 hrs operation/day) X (low 1/4 catch 0.45 in)
- '
B-4
17.
Figure B-l
CENTER PIVOT SPRINKLE IRRIGATION EVALUATION (Cont.)
Container catch data in units of ml , Volume/depth 250 ml/in
ft
Span length
90
Evaporation: initial ISO ml
final -147 ml
loss 3 ml
_ft_, Container spacing
150 ml
-245 ml
22.5
5 ml , ave 4 ml = 0.016j n
Span,
no.
Container
Span
No.
Container
Position v C t h - We ^B nCed
Number Catch
Position v fc . Weighted
.. - X Catch =
Number Catch
1
1
7
1
2 i
. 3 si
atari numbering at
)ivot end of inner
)an. Do not wait
ir completion of
^rigation at first
ID containers.
10
10
10
37
38
39
118
127
115
4366
4816
4485
1
2
2
4 ^
5 i:
6 *
10
ii
11
40
41
42
147
127
122
5880
5207
5124 '
2
2
3
7
a
9
141
1269
11
11
12
43
44
45
118
144
112
5074
6336
5040
3
3
3
10
11
12
160
122
130
1600
1342
1560
12
12
12
46
47
48
124
126
151
5704
5922
709?
4
4
4
13
14
15
143
ISO
134
1859
2100
2010
13
13
13
49
50
51
120
122
115
5880
6100
536$
4
5
5
15
17
18
123
144
138
1963
2448
2484
13
14
14
52
53
54
143
124
114
7436
6572
7776
5
5
6
19
20
21
135
207
722
1565
4140
2562
14
14
IS
55
56
57
115
160
120
6325
8960
88-40
6
6
6
22
23
24
114
115
138
2508
2645
3312
15
15
IS
58
59
60
110
109
11?
6380
6431
7020
7
7
7
25
26
27
109
113
114
2725
2335
30? 8
16
16'
16
61
62
63
85
194
148
5185
12023
9324
7
8
8
28
29
30
126
116
107
3584
3364
3210
End
64
<;
82
5248
8
8
,9
31
32
33
122
140
n?
3782
4480
3861
5
9
34
35
36
105
111
125
3570
3885
4428
Sura all: used pobiticn nur.bcrs 2Q44 .
Sum low l/: position numbers 5/g > weij
1-5
As an example, a typical layout between wheel tracks for 90-foot spans
and any type of drive can be accomplished by;
o Placing the first container position 5 ft downstream from the
o Setting container positions 2, 3, and 4 at 22.5-foot intervals.
fourth container position is now 17.5 ft from the wheel track of the
pivot.
The
first span.
o Kepeat the above procedure to the end of the actual wetted
circle placing a catch container at each container position along the
w.iy.
Howuver, to save time it is most convenient to leave out the first few
containers adjacent to the pivut since the watering cycle is so long in
this area. Typically, the containers under the first one or two spans
die omitted with little adverse effect on the evaluation. A number
should be assigned to each container position with a sequential numbering
system beginning with 1 at the container position nearest the pivot
point. Even the locations not having containers under the first spans
should be numbered.
(b) Fill in the blanks (Fig.B-1) in parts 1 through 9,
dealing with climatic conditions, machine and test specifications,
topography, general system, soil moisture, and crop performance. Determine
the irrigated area, part 4, in acres by first estimating the wetted
radius of the irrigated circle.
(c) Determine the length of time required for the system
to make a revolution by dividing the circumference of the outer wheel
track by the speed of the end drive unit. (See parts 10 and 11 in which
the conversion constant is 60/(2 x 3.14) = 9.55.)
o Stake out a known length along the outer wheel track and
determine the time required for a point on the drive unit to travel
between the stakes. The speed of travel will be the distance divided by
the number of minutes. An alternative method is to determine the distance
traveled in a given time.
n,,h s -h 81 *" m St machines have uniform span lengths except for
trackman I lllu T^ ?* ? adiUB between the * ivot and the oute ' "heel
number of spans * dete ined b * multiplying the span length by the
to the lateralnd "'V^ "^ f the Wetted P attern (P^pendicular
near th * * iv u U Th ^ - tim f. wat " is received b V ^"containers
^ p-tlera vid^d^ed ^% ^l^^^^^ *
B-6
(e) On water-driven systems, number each drive unit
(span) beginning with the one next to the pivot. Time how long it takes
to fill a container of known volume with the discharge from the water
motor in the outer drive unit and record on line 13. The exact method
for doing this depends on the water motor construction, and it may
require using a short length of hose.
(f) If the system is equipped with a flow meter, measure
and record the rate of flow into the system on line 14 of Fig. B-l.
Most standard flow meters indicate only the total volume of water that
has passed. To determine the flow rate read the meter at the beginning
and end of a 10-min period >and calculate the rate per minute. To convert
from cubic feet per second (or acre-inches per hour) to gpm, multiply by
450,
(g) At the time the leading edge of the wetted patterns
reaches the test area, set aside two containers with the anticipated
catch to check the volume of evaporation losses. Measure and record on
line 17 the depth of water in all the containers as soon as possible and
observe whether they are still upright; note abnormally low or high
catches. The best accuracy can be achieved by using a graduated cylinder
to obtain volumetric measurements. These can be converted to depths if
the area of the container opening is known. For 1-quart oil cans, 200
ml corresponds to a depth of 1.0 in. Measure the catch of one of the
evaporation check containers about midway during the catch reading
period and the other one at the end.
Sample Calculation: Utilization of center pivot field test
data .
Given:
o The field data presented in Fig. B-l
Find:
o Use the field data to evaluate the system.
Calculation:
o The volumes caught in the containers must be weighted, since
the catch points represent progressively larger areas as the distance
from the pivot increases. To weight the catches according to their
distance from the pivot, each catch value must be multiplied by a factor
related to the distance from the pivot. This weighting operation is
simplified by using the container layout procedure described earlier and
Fig. B-l, part 17.
B-7
o The average weighted system catch is found by dividing the sum
of the weighted catches by the sum of the catch positions numbers where
containers were placed. Space for this computation is provided in parts
15 and 17.
o For the average minimum weighted catch, an unknown number of
containers that represents the low 1/4 of the irrigated area must be
used. The low I/A is selected by picking progressively larger (unweighted)
catches and keeping a running total of the associated position numbers
until the subtotal approximates I/A of the sum of all the catch numbers.
The average weighted low 1/4 of the weighted catches by the sum of the
associated catch position numbers. Space for this computation is also
provided in parts 15 and 17.
o In order to determine whether the system is operating at
acceptable efficiency, the losses to deep percolation and DU should be
evaluated by:
nil - average weighted low quarter catch 10Q
average weighted system catch
which for the example problem (Fig. a-1, part 15) is:
x 100 = 90 percent
This is a reasonable value and is independent of the speed of revolution.
o It is useful to plot the volume of catch against distance from
the pivot (Fig.B-2). Such a plot is useful for spotting problem areas
and locating improperly nozzled or malfunctioning sprinklers. Usually
there is excess water near each water-driven drive unit where the water
is distributed as part of the pattern.
o If the system is operating on an undulating or sloping field
and is not equipped with pressure or flow regulators, DU will vary with
the lateral position. The DU will remain nearly constant if the
differences in elevation (in feet) multiplied by G.43 (to convert to an
equivalent psi) do not exceed 20 percent of the pressure at the end
sprinkler. Thus, for the example test the line position would have
minimal effect on the DU since the pressure at the end sprinkler was 60
psi and the maximum elevation differences were only 25 ft, equivalent to
11 psi which is only 18 percent of 60 psi,
The E can be determined if the pivot point is equipped with an accurate
flow measuring device. For the average low quarter rate caught use the
average weighted low one-quarter of the catches expressed as a depth per
revolution. The average jigpth of water applied per revolution is calculated
by the formula: Q = ^ where Q = system discharge capacity, gpm
220
20O
180
160
I4O
120
100
80
60
40
IO 2O 30 4O SO 60
Container catch position number
0.75
O.50
5
7O
Figure B-2.
Profile of container catch from center pivot sprinkler
evaluation test. Pivo-t is loca-VetA cxt "O* position.
B-9
A = design area, acres
d = gross depth of application, in
F = time allowed for completion of one irrigation, days
H = actual operating time, hr/day
and from data computed on Fig.B-1, in parts 11, 14, and 4, the depth
applied per irrigation (revolution) is:
x 1,150 s .
x 152
IT - rm average weighted system catch
q ~ UU x d
- 90 x j^|2 = 85 percent
The small difference between DU of 89 percent and E of 85 percent
indicates that evaporation losses are quite small arid within the limits
of accuracy of measurement.
The system flow rate and E can be estimated without a flow meter at the
inlet. This is done by first estimating the gross application by adding
the average depth caught and the estimated evaporation, which for the
data recorded in Fig. B-l,parts 15 and 17, is 0.50 -f .02 = 0,52 in per
revolution. The flow in gpm; which was distributed through the sprinkler,
can be estimated by;
ru.*. -u 4- ^ n _ 453 x 152 x 0.52 _ , , 00
Distributed flow = - ^ r - = 1,.133 gpm
If water from the drive motor was not distributed, it must be added to
the distributed flow to obtain the total system flow. The E is then
computed as before by using the computed system flow. For tfie recorded
data the drive water was included in the distributed flow and need not
be computed. However, if it had not been included in the distributed
flow, it should be estimated by;
sum of drive unit numbers X gpm
Drive flow = - - - low from end _ w ^ter motor_
Number of drive units
for the 15 drive motors and a flow rate of 13.5 gpro from the end water
drive motor:
B-10
Drive flow = * 20 13 ' 5 = 108 gpm
15
- Runoff. The computation of E is meaningful only if
there is little or no runoff. Runoff and/or^ponding may occur near the
moving end of the system (Fig.B-'2). Increasing the system's speed
will reduce the depth per application and often prevent runoff. However,
on some clay type soils, decreasing the system's speed and allowing the
surface to become drier between irrigations will improve the soil
infiltration characteristics and reduce runoff even though the depth per
application is increased. Therefore, both increasing and decreasing the
speed should be considered. Other methods for reducing runoff include:
(a) Using an implement called a pitter, which scrapes
indentations in the furrows followed by small dikes every 2 or 3 ft.
(b) Reducing the total depth of water applied per week
by turning the system off for a period after each revolution. (Automatic
stop devices are available for many systems.) This allows the surface
soil to become drier between irrigations and thus have a higher infiltration
capacity. Careful planning is required in order to avoid extensive
underirrigation which may reduce crop yields.
(c) Decreasing sprinkler nozzle diameters to decrease
the system capacity and application rate. All the nozzles must be
changed to maintain uniformity.
(d) Increasing system pressure and reducing nozzle sizes
throughout the system to maintain the same system flow rate. This
decreases the average drop size and thereby drop impact which reduces
the surface sealing that restricts infiltration.
(e) Using special nozzles with pins to break up the jets
and reduce drop sizes.
B-ll
b. Periodic Hove and Fixed System
Successful operation of sprinkle irrigation systems requires that the
frequency and quantity of water application be accurately scheduled.
Field application efficiency must be known to manage the quantity of
application. Since system performance changes with time, periodic field
checks are recommended. Data from the field evaluation of a periodic
move sprinkle system is presented in Figure B-3. The procedure for
collecting the data follows.
(1) Information required. The desired information includes;
(a) Duration of normal irrigations.
(b) Spacing of sprinklers along lateral lines.
(c) Spacing of lateral lines along the main lines.
(d) Measured depths of water caught in catch containers
at a test location.
(e) Duration of the test,
(f) Water pressures at the sprinkler nozzles at the Lest
location and along laterals throughout the system.
(g) Rate of flow from the tested sprinklers.
(h) Additional data specified on Figure B-3.
It is useful to know what wetting patterns the operation produces at
different pressures and also operating pressures at the pump and alone
the mainline and laterals. General study of data obtained in Uho field
enables determination of system DU and E Further study enah^es
em an urter study enah^es
determination of the uniformity and econSmics of the spacings and/or
T* th H C r mlC ? f SiZ6S f Pi ' es Used f .afns a
.t.sK y .2 thn^r ? p :^: ng pressures
(2)
The equipment the evaluate? needs is:
(a) A pressure gauge (0-100 psi) with pi tot attachment,
(b) A stopwatch or watch with an easily visible second
lion or larger VlargTsS^ ^ V lume clea ^ ****** (1
preciably larger than'th^r^ $ flexlblc h 2e havin * diameter
y rger tnan the outside diameter of nozzles.
B-12
Figure B-3. SPRINKLER-LATERAL IRRIGATION CVALUATION
Location Field C-22 , Observer Jltf , Dace 9-30-75
t
i. t
3.
4.
5.
6.
7.
Crop Tomatoep Rootl zone depth 4.0 ft, MAD SO %,
MAD 4.4 in
Soil: texture clay loam, available moisture 2.2 in/ft T SMD
4.4 in
Sprinkler: make .Rain Bird , model
298 , nozzles 5/32
by in
Sprinkler spacing 30 by 50 ft,
Irrigation duration
23.5 hrs
Rated sprinkler discharge 4.4 gpm
at 40 psi giving
0.28 in/hr
Lateral: diameter 2 in, slope 1
h %, Riser height
18 in
8. Actual sprinkler pressure and discharge rates:
Sprinkler location number on test
1 4 S 8 10
lateral
^5 end
9.
10.
Initial pressure (psi) 45 40
40 40 39
40
Final pressure (psi) 45
40 39
40
Catch volume (gal) 1,0 1.0
1.0 1.0
1.0
Catch time (min or sec) 0. SI 0.22
0.22 0.22
0.22
Discharge (gpm) 4.8 4.6
4.6 4,6
4.6 .
5
Wind: direction relative to .
Part 10: initial \
2 -f
Speed (mph) ; initial
_, during / , final
, during , final
Container grid test data in units of
Container grid spacing 10 by 10
"d , Volume/depth
*W ml/in
fc
* 1.68 hr
Test: start 2;S5 p/n, stop 4:30 pm, duration 1 hr 35 min
32 68 77 90
j) 73' 66 9
ml
.10 .21 .24 .28
35 66 84 100
.U .21 .03
100 52 3
iph
.11 .21 .16 .31
32 50 60 104
99 48 12
.10 .16 .11 .32
31 ?4 88 104
^..31 .15 .04
& 86 56 11
.10 .23 .27 .*?
27 64 dO
_ 9-7 17 tit
.08 .20 .25
20 49 S9
11.
12.
13.
.06 .16 .19
Evaporation container: initial _
Sprinkler pressures: max 45 ps i
Comments Test duration was too s
1000 ml graduated cylinder. Win
B-l
(e) From 50 to 100 (or more depending on sprinkler size)
catch containers such as 1-quart oil cans or plastic freezer cartons.
(f) A measuring stick (or ruler) to measure depth, or a
500-ml graduated cylinder to measure volume of water caught in containers.
(g) A soil probe or auger.
(h) A 50- or 100-foot tape for measuring distances in
laying out catch container grid.
(i) A shovel for smoothing spots to set containers and
for checking soil, root, and water penetration profiles.
(j) Figure B-3 for recording data.
(k) Manufacturers' sprinkler performance charts showing
the relationship between discharge, pressure, and wetted diameter plus
recommended operating pressure ranges.
(1) A set of drill bits ranging in size from 3/64- to
1/4-inch in diameter in increments of l/64~inch makes a handy set of
feeler gauges to check nozzle wear.
Field procedure. The information obtain from the following
field procedure should be entered in a data sheet similar to B-3.
(a) Choose a location along a lateral for the test. It
may be either a single location at which the pressure is typical (or
average) for the entire system, or two locations near the ends of a
Dr^nr I H ^i Stud ^ f effects ^ differences in pressure. Loss of
such that ? , r ^ tl0 c n J n a lateral that has onl V one Bize of pipe is
of the L a 5 aU f ,n he PreSSUre loss occurs ^ the fi ' st 20 percent
first h^f g .f S d ? V6r 8 , percent of the P^sure loss occurs in the
the most reSr * l ;. Cral " length ' (See Fi ' B ~ 5 ' ) On a "at field
about * percent of the
B-14
Figure B-4. Combind Catch Pattern (iph) Between Sprinklers
5 and 6 for a 50-foot Lateral Spacing
Literal set
Laftfot stt
A
B
-
5C feef
o
*
c:
S 6 1
)
(
3 S fi ~H
/
H
O.I O
O.2 t
0.2 4
0.2 6
' d
/
O.23
O.2 1
O.O 3
/
0.23
0.3 I
O.24
Q.24
o. 2 e
(0.03)
(O.O 5)
(0.02)
(O.O 2)
(0.02)
O.I 1
O.2 I
0.2 6
0.3 t
<ih
0.3 t
O. t 6
O.QI
_ _
_ - -
O.3 t
0-27
0.22
0.26
O. 3t
t
(0.05)
(O.O/)
(0-04)
(0.0 0)
(0.05)
*\
O.I O
O. 16
0,2 2
O.32
fc
0-31
.t 5
O*04
\
0.3 /
0.25
O.2O
0.2 2
O.32
(0-05)
(0.0 1)
fO-06)
(0.04)
(0.06)
^
t
<
S 5 **
( ) Oe vialion from
avcrogt
B-15
100
Average pressure-head fine
20 40 60 30
Length of lateral % of total _
100
Figure B-5.
Loss of pressure due to friction along a lateral
having only one size of pipe.
B-16
(b) Set out at least 24 catch containers (see pattern in
Fig. B-6 ) on a grid having a spacing not to exceed 10- by 10-foot for
testing along a single lateral line. The catch containers' pattern
should be laid out to cover two adjacent areas between three sprinklers
since sprinklers may not apply water at precisely uniform rates. Each
catch container is assumed to give the representative depth of catch
over the square having the same dimensions as the can spacing in which
it is centered. (See dotted grid lines in Fig. B-6.)
For solid set or block move systems where several adjacent laterals
operate simultaneously, the catch containers should be placed in the
area between two adjacent laterals. Caution should be exercised to
allow for any water that could enter the test container area from adjacent
blocks. These tests cannot be used to study other lateral spacings.
Each container should be located within a foot of its correct grid
position and set carefully in an upright position with its top parallel
to the ground; any surrounding vegetation that would interfere with a
container should be removed. When it is windy, it may be necessary to
fasten containers to short stakes with rubber bands, and weight them
with a known depth of water or a stone (which is later subtracted from
the total depth shown after the catch); or they may be set in shallow
holes. The most accurate means for measuring the catch can be achieved
volumetrically by using a graduated cylinder. These measurements can be
converted to depths if the area of the container opening is known. For
1-quart oil cans, 200 ml corresponds to 1.00 in depth. Other suitable
catch containers may be square or cylindrical plastic freezer containers
with sides tapered slightly for nesting or any similar container.
Determine and record the container grid spacing and the ratio of volume
to depth of catch. Also indicate the position of the lateral and record
the location and position numbers of the sprinklers on the lateral,
(c) Determine the soil texture profile and management
allowed deficit, MAD, then estimate the available soil moisture capacity
in the root zone (see Measuring Soil Water Content section of Irrigation
Guide) and check the soil moisture deficit, SMD, in the catch area on
the side of the lateral that was not irrigated during the previous set.
These values should be recorded as shown on lines 2 and 3 of Fig. B-3.
(d) Check and record the make and model of the sprinkler
and the diameter of the nozzles.
(e) Obtain the normal sprinkler spacing, duration, and
frequency of irrigation from the operator and record them. The standard
way of expressing the sprinkler grid spacing is - by -foot; this
indicates the sprinkler spacing on the lateral and the spacing between
laterals in that order.
(f) Read ^nd record the rated sprinkler discharge,
pressure, the computed average design application rate from the system
design data and manufacturer's sprinkler catalogs.
B-17
Figure B-6. Layout of Catch Containers for Testing the Uniformity
of Distribution Along a Sprinkler Lateral Line
l
\
/ v
t N. "* C
"" N /
o
' O O *^,^O Q *"
"o o \o/
Q
j x - .
\/
\ /
A
o
\ <y o o o
o o /o\
o
V
/ 1
o
/ o o o o-
> 1
o
Lot era/ line
\
\*~-Quter edge of
Sprinkler N v /
X
N
o i <y o o
o / <? o o
; \
; x v^'
i /
\ /
V
/ \
/ \
t x
\
\0/
o i o |/o\ o
4- -/- \
1 o J o
o
container
\
/
B-18
(g) Check and record the size and slope of the lateral
pipe and the height and erectness of the risers.
(h) Before starting the test, stop the rotation of the
sprinklers at the test site to prevent water from entering the containers,
A short piece of wire or stick wedged behind the swinging arm facilitates
this.
Turn on the water to fill the lateral lines. When the test lateral is
full, turn the pressure up slowly to observe the trajectory, breakup of
drops, and effect of wind at different pressures. Then set the pressure
at the value desired for the test.
Measure and record the pressure at the sprinklers to he tested at several
places along the line and at both ends to observe the differences in
pressure. Pressures should be checked at both the beginning and end of
the test period and recorded on line 8. When measuring srinkler pressures,
the pitot tube must be centered in the jet, which must impinge directly
onto its tip. The tip may be rocked slightly. Record the highest
pressure reading shown while the pitot tube is being held about l/8~inch
from the sprinkler nozzle.
Also on line 8, record how long it takes each sprinkler in this test
area to fill the large container of known volume. Do this by slipping
the short length of hoze over the sprinkler nozzle and collecting the
flow in the container. To improve accuracy, measure the nozzle output
several times and compute the average. (If the sprinkler has two nozzles,
each can be measured separately with one hose.) Often the measured
sprinkler discharge rate is greater than what the manufacturer specified
at the given pressure. This occurs because sprinkler nozzles often
erode during use and become enlarged, or because the hose fits too tightly
and creates a syphoning action. You can check nozzle erosion with a
feeler gauge such as a drill bit that has the diameter specified for the
nozzle.
(i) Note the wind speed and direction and record the
wind direction in part 9 by drawing an arrow relative to the direction
of water flow in the lateral.
(j) Empty all catch containers before starting the test;
start the test by releasing all sprinklers surrounding the test site so
they are free to rotate and note the starting time on line 10.
(k) Set outside the catchment area a container holding
the anticipated amount of catch to approximately check the volume of
water lost by evaporation. (See Fig. u-3, line 11.)
(1) While the test is in progress, check sprinkler
pressures at 20 to 40 systematically selected locations throughout the
system (for example, at the two ends and quarter points along each
lateral) and record the maximum, minimum, and average pressures encountered
in part 12.
B-19
(m) Terminate tlte test by either .stopping the sprinklers
the test site in a position such that the jets do not fall
hf Lont.iinersj or by deflecting the jets to the ground. NoU* the
chock ami record the pressure, and turn off the water. It is most
Irsir.ible for duration of the test to be equal to the duration of an
inig.ition to get the full effect of wind and evaporation. Ideally
niiurflum duration tests sould apply an average of about 0.5 in of water
in the. 1 containers.
the depth of water in all the containers and observe whether
.still upright; note any abnormally low or high catches. As
wi in p,irt 10, caught depths or volumes are recorded above thf line
rhr proper gride point, which is located relative to the sprinkler
'iiiortiou of flow U the pipe line. For long runs, where maximum
th-; exceed 2.0 in, a measuring stick provides suitable accuracy up to
in
. utilization of the <Uu
<Usc.ussed in connection with the test data presented in Fig. ]j-4.
general procedure for utilizing the data is:
(a) Convert the depths or volumes of water caught in thr
ampis to rates and record them (iph) below the line on the data
t jurt tO. Assuming that the test is representative and that tho
'..a would give identical results, the ri^ht-lund side of the rnldi
'iu may as if it were a subsequent bet, be overlapped for
nrnpo.ed) on the left-hand side to s iulat e different.' lateral spacin
l spacings that are whole units of the container apacinJ I h
ot the catches of the two set, represents a coplotc rri^i on
1--4 illustrates overlapping.) For very close lateral snacin.
may overlap from as many as four lateral positions The K
of overlapping is not suggested whore wind* are
.cceptable ecicerSn^^
O is based on rh^ ,!! , should be ovalualed. The
o? h ,,?au ( a e "tt infllLraled JU -
l to ] J - ly ^ enl nn 3t " 01 " to d <= ep wou ld ba
system DU. (A simUac celationahip exists
"ould be detdo a.??^" 1011 eff V, E and
the Wrfter .upp? y and what t^? ?? effective ly tho Sy.tem
of Mtet a f -- s -y be. The
c ^ei can be estimated
B-20
The E and E. values are always a little lower than the DU aad CU of a
sprinRle irrigation system because the average water applied is greater
than the average water caught. The difference between the average water
applied and the water caught or received is an approximation of losses
due to evaporation and drift plus loss of water due to some of the
area's being ungauged and some evaporation from the gauge cans. The
system E and E, indicate how well the tested sprinklers are able to
operate Sf they are run the correct length of time to satisfy the SMD or
MAD. It is, therefore, a measure of the best management can do and
should be thought of as the potential of the system within the limit
that the test represents the whole field.
The effective portion of applied water, R , can be determined from the
field data by:
p - Average catch rate (or depth)
e "" application rate (or depth)
average catch rate
~ 96.3 q/(S 1 x S m )
where
q = average sprinkler discharge rate, gpm
S, = sprinkler spacing on the lateral, ft
S = lateral spacing along the main, ft
B-21
c.
Traveling Sprinkler
The following procedures are designed mainly to check the uniformity and
efficiency of irrigation across the travel paths. However, the nature
of the operation and the large size of the sprinklers tend to reduce the
quality of irrigation around field boundaries. It is particularly
difficult to obtain high quality irrigation at the ends of the towpaths
unless special control systems are used on the sprinkler, and on small
fields this is an appreciable areaas much as 200 feet on each end.
If the traveling unit is powered by a water piston, the expelled water
should not be included in evaluating the DU but should be included in
computing the AELQ and PELQ.
DU - "Distribution Uniformity" indicates the uniformity of infiltration
(or application in the case of sprinkle or trickle irrigation) throughout
the field and is expressed as a percent relating the average depth
infiltrated in the lowest one-quarter of the area to the average depth
of water infiltrated.
AELQ - "Application Efficiency of Low Quarter" indicates the actual
efficiency being achieved with a given system and is expressed as a
percent relating the average low quarter depth of water stored in the
root zone to the average depth of water applied.
PELQ - "Potential Application Efficiency of Low Quarter" is the measure
of how well a system can perform under reasonably good management when
the desired irrigation is being applied and is expressed as a percent
relating the average low quarter depth infiltrated when equal to MAD to
the average depth of water applied.
(1) Information required. The following information is
required for evaluating traveling sprinkler irrigation sytems:
(a) Frequency of normal irrigauions.
(b) MAD and SMD.
(c) Nozzle diameter and type for estimating system's
flow rate.
(d) Pressure at the nozzle.
(e) Depth of water caught in catch containers.
(f) Travel speed when the unit is at the test location
and extreme ends of the towpaths.
(g) Spacing between towpaths.
B-22
(h) Rate of discharge from water piston (jf applicable),
(i) Additional data indicated on Fig. 11-7.
An accurate estimate for the flow rate from the nozzle is necessary for
calculating the PELQ and AELQ of the system. A good way to estimate
this flow is to use the sprinkler performance chart provided by the
manufacturer. A typical performance chart gives the rate of sprinkler
discharge and diameter of coverage for various nozzle sizes at different
pressures .
(2) Equipment needed. The equipment the evaluator needs is:
(a) A pressure gauge (0-150 psi) with pitot tube attachment
(b) A stopwatch or watch with an easily visible second
hand.
(c) Approximately 60 catch containers such as 1-quart
oil cans or plastic freezer cartons.
(d) A 500-ml graduated cylinder to measure volume of
water caught in the containers.
(e) A 50- or 100-foot tape for measuring distances in
laying out the lines of containers and estimating machine's speed.
(f) A soil probe or auger.
(g) Manufacturer's sprinkler performance chart giving
the relationship between discharge, pressure, and wetted diameter plus
recommended operating pressure range. Also speed specifications and
setting instructions for the traveling vehicle.
(h) A shovel for smoothing areas to set catch containers
and for checking profiles of soil, root, and water penetration,
(i) A hand level to check differences in elevation,
(j) Fig- B-7 for recording data.
(k) For travelers powered by a water piston, a 2- to
5-gallon bucket and possibly a short length of flexible hoze to facilitate
measuring the piston discharge.
(3) Field procedure. Fill in the data blanks of Fig. B-7
the field procedure progresses. Choose a test location about midway
along the towpath where the traveler operates. The location should be
far enough ahead of the sprinkler so no water reaches the test area
before the catch containers are set up. It should be far enough from
the outer end of the path so that the back (or trailing) edge of the
B-23
Figure B-7. TRAVELING SPRINKLER IRRIGATION EVALUATION
1. Location Field 200 , Observer JK , Date ?/S/?4
2. Crop Corn _ , Root zone depth 4.0 ft, MAD 35 _ %, MAD 2. 1 in
3. Soil: texture fine sandy loam , available moisture 1.5 in/ft
4. SHD: near tow path 2. 1 ln > at 1/4-point 2. 2 in, at mid-point 3. ?in
5. Sprinkler /Traveler makes and models Nelson 202 / tieinzman 6645
6. Nozzle; size ? . 5 in , type ^Mg, pressure 200 psi, discharge 500 gpm
7. Hose: length 660 ft, diameter _j* _ in, type lay-flat _
inlet pressure 237 psi, outlet pressure -HO
8. Drive: type tttrbins , discharge (if piston) gal/ min -min
9. Towpath: spacing 330 ft, length 3320 ft, sloped _ %
10. Evaporation loss: ( 2QQ ml catch 1.0 in)
cup //I initial - final volume 500 - 4?0 3Q ml
cup ff2 initial - final volume * 500 - 452 IB ml
average evaporation loss _ 24 _ ml = 0.1 _ in
11. Traveler speed check at:
beginning 9.5 ft/ 10 min 0.9S ft/min
at test site ?Q. Q_ ft/ 30 min = 3.0 ft/min
terminal end 30.2 ft/ 30 rojrx " ^-02 ft/min
12. Total: discharge 500 _ gpm, pressure loss 37 psi
13. Average application rate:
96.3 X (sprinkler discharge 500 gpm) X 360 B g ^ gin / nr
(towpath spacing 330 ft) X (wet sector _345 )
14. Average depth applied:
96 .3 (sprinkler plus piston discharge 500 gpm) _ .
60 * (path spacing 330 ft) X (travel 3.0 ft/min) " -^^ - ^~
*"erage overlapped catches:
(sum all catch totals 74. 8? in) n .
tern = - T - r - .. . , - rrr - * 2. 2 7 in
(number of totals 33) -
. ,, (sum of low 1/4 catch totals 22.93 in)
Low 1/4 - 1 - 7 - ~ 7 r - =-TJ - ; - z\ - 1.
(number of low 1/4 totals 5) ij
16. Comments (wind drift, runoff etc.): no evidence of serious wind
drift or runoff; crop Mas stunted midway between paths _
B-24
Figure li-7.
17. Container cest data in units of
Wind: speed 5- 10 mph
direction -L/
Note part circle operation
and the dry wedge si?,e in
degrees
TRAVELING SPRINKLER IRRIGATION EVALUATION (Cont.)
, Volume/depth 200 ml/in
Left Right
Towpath and
travel
direction
Container
catch row
Path
Spacing
feet
Container Catch Volume
Right plus Left
Left side of path
Rip.ht side of path
Side Catch Totals
Catch No.
Catch
Catch No.
Catch
ml
inches
330
320
310
1
g 2
?
o 6
50
540
510
33
32
31
560
540
510
2. 80
2.70
2.55
300
290
230
n 4
a s
.0 5
6
490
505
475
30
29
28
490
505
475
2.45
2.53
2.38
270
260
250
?
"S 8
9
480
460
430
3 27
n 26
S 25
480
4GO
430
2.40
2.30
2.15
240
230
220
% 10
3 n
a 22
410
370
325
1 24
* 23
"S 22
410
370
325
2.05
1.85
1.63
210
200
190
13
"5 24
^ 1C
a IS
305
345
335
22
e 20
3 19
305
345
335
1.53
2.73
2,68
180
170
160
o 1C
17
18
310
305
290
8 18
1?
16
35
310
305
325
2.55
2.53
1.62
150
140
130
19
* 20
* 21
250
230
215
o 15
14
5 ; 3
75
120
215
325
350
430
2.62
2,75
2.15
120
110
100
8. 22
o 23
-i 24
1G5
95
65
12
" 11
i~-i
JO
365
410
515
530
505
580
2.65
2.52
2.90
90
80
70
25
.0 25
G
^
25
o 9
% 8
S 7
540
525
500
565
525
500
2.82
2.62
2.50
60 '
50
40
30
20
10
-C
)-j
TH
5
f B
U
-H 5
"* 4
490
470
490
490
470
490
2.45
2.35
2.45
u
In
n)
tj
VI
^ 3
ft
2
U~l
540
60S
625
5'W
605
625
2.~7ff~
3.02
3.12
Sum of all catch totals
Sum of low I/A catch totals
B-25
74.8?
sprinkler pattern passes completely over it before the sprinkler reaches
the end of the towpath. A good location for the test area is along the
main line where an access road is usually provided. In tall growing
crops such as corn, an access road is the only practical location for
the test.
(a) Set out a row of catch containers 10 feet apart
across the towpath (see Fig. B-8 ); the containers that are adjacent to
the towpath should be set on both sides of the towpath about 5 feet from
the center of the patch. The outer containers should be at the edges of
the wetted strip. It is good practice to provide at least two extra
containers on both ends of the container row to allow for changes in
wind direction or speed.
(b) Fill in the data blanks about the crop and soil
(parts 2 and 3 of Fig. B-7).
(c) Check the SMD at the following locations: 10 feet
from the towpath; one-fourth of the distance to the next towpath; and
midway between the towpath in use and the one to be used next. Enter
these SMD data in part 4.
(d) Note the make and model of the traveler, the sprinkler,
type of nozzle (orifice ring or taper bore), and nozzle diameter. (It
is also good practice to measure the nozzle size after the system is
turned off. This is done to check for nozzle erosion so the estimated
flow rate can be adjusted if necessary.) Enter this information in
parts 5 and 6.
(e) Check the hose length and diameter, also the inlet
and outlet pressures of the hose, if feasible. Record in part 7.
(f) Check and record in part 8 the type of drive used in
the traveler. In evaluating water-piston powered travelers to estimate
the drive flow, determine how long it takes the discharge from the piston
to fill the bucket (or jug) of known volume.
(g) Measure and record the spacing between towpaths and
the towpath length and general slope in part 9.
(h) Set out two containers with the anticipated catch to
check the volume of evaporation losses. The first container should be
set out when the wetted pattern first reaches the catch row and the
second container when the sprinkler vehicle reaches the row. Record
these catches in part 10 which is set up to record these data.
(i) Determine the travel speed of the unit (ft/min) as
it passes over the row of containers. This speed should also be checked
at the extreme ends (beginning and terminal on Fig. B-7 ) of the towpath
and recorded in part 11. To do this, stake out a known length, say 10
B-26
Figure B-8. Typical Layout for Traveling Sprinklers Showing Location
of Catch Container Line for Evaluating the Distribution Uniformity
Extent of planted orsa
Towpafhs
13
I
Buried mom
Pumping
_ .
Connections
/o main
Ho SB
Cofch container
row
1-27
f t .M, ami determine the time required for a point on the vehicle to
travel between the stakes. An alternate method is to determine the
distance traveled in a given time, say 10 minutes.
(j) Check and record in part 6 the pressure at the
sprinkler nozzle when it is about directly over the catch row and estimate
the sprinkler discharge from the manufacturer's performance chart.
(k) Estimate and record in part 12 the total discharge
from the traveler by adding the sprinkler nozzle and piston discharges.
Also estimate and record the total pressure loss through the hose and
sprinkler.
11) Note in part 17 the general test conditions including:
wind speed and direction, angle degrees of the dry wedge of part-circle
sprinkler operation, wet or dry spots, and runoff problems.
(m) Measure and record in part 17 the depth of water in
all the containers as soon as possible and observe whether they are
still upright; note any abnormally low or high catches. Then measure
and record in part 10 the catch in the two evaporation check containers
after the last container in the row has been recorded.
(n) Note any special comments such as runoff, test
problems, and crop water stresses in part 16.
(o) Do the computational work required in parts 17 and
13 through 15 of Fig. B-7.
Part 17 of Fig. B-7 1S designed to simplify the procedure of overlapping
the catches to simulate a complete irrigation between adjacent towpaths,
s,
with 1 5 ^ r !; nu "* e M; he Containers from the towpath outward beginning
''
d irtinn''r i r e "5^ ^ t0 the left Io kin 8 opposite to
o lows fn r 'f^r ^ 6 C0ntainer *ers "*d catch volumes as
h actual tLn^h' ? lde , d ta start numbering with container 1 opposite
ff ?? ? P u Spacing (whlch for the exa Ple field evaluation is
330 feet) and number downward; and for the right side data start the
da ' ah
n
system in a orfId (Fig H l )" evaluatlon f - traveling sprinkler
the
B-28
of DU, PE;LQ, and AKLQ that follow, it is assumed that this depth profile
represents the distribution throughout the field. In other words, the
assumption is that iho depth profile across the strip between towpaths
is the same along the entire strip. This is obviously subject to question
because of discontinuities at the path ends, changes in travel speeds,
variations in pressure due to elevation, and changes in wind speed and
direction.
(5) Distribution uniformity. In order to determine whether
the system is operating at an acceptable and economical efficiency, the
DU should be evaluated. For the sample test using the average and low
one-quarter catch data from part 15 of Fig. u-7 is:
DU = ~~ x 100 - 71 percent
This is a fair value for a traveler system with widely spaced towpaths
and is generally independent of the speed of travel.
It is useful to plot the depth of catch along the distance between
towpaths (see Fig. B-9 ) as a means for spotting problem areas. Note
that the plotted points represent the depth of catch at the midpoint of
each 10-foot interval between adjacent towpaths. Fig. B-9 shows that
either the towpaths are too far apart, which results in a shallow wetted
depth midway between towpaths, or that the angle of the part circle is
set too narrow. The effect of narrowing the spacing between towpaths
can be measured by using a blank copy of Fig. B-7 , part 17, and repeating
the above procedure with the same catch data and the new spacing.
Widening this angle of the dry wedge would reduce the depth of water
applied near the paths and would increase the depth of water applied
midway between towpaths; but to measure the effect of widening the angle
requires another catch test run.
The check of travel speed shows that the unit moves faster toward the
terminal end of the towpath run. (See sample Fig. B-7, part 11.)
This change in speed is caused by the interaction of the buildup of
cable on the winch reel and the increased drag exerted by the hose as
the unit moves from the beginning to the terminal end of the towpath.
Fortunately, these two factors somewhat offset each other, and in the
operation reported here the unit was traveling only 2 percent faster at
the terminal end than in the test area and 5 percent slower at the
beginning end, (See Fig. B-8.) These changes of speed would lower
the DU over the entire strip by about three-eights of the total percent
speed change, i.e., 3/8 x (2 + 5) or less than 2 percent.
Since the nozzle pressure is normally near 100 psi, differences in
elevation are usually not great enough to affect DU appreciably. Only
differences in elevation along the towpaths are of concern because
valves can adjust hose inlet pressures. However, even with a difference
of 40 to 50 feet in elevation along the towpath, the DU decreases by
only about 4 percent,
B-29
Profile of Overlapped Container Catch UaLa From
Traveling Sprinkler Evaluation
7CO
Average of low 1/4 catch
50 (00 150 2OO
Container position to the right of path
250
B-30
Changes in wind speed and/or direction can greatly affect DU, especially
if the wind direction changes appreciably during the operation in adjacent
towpaths (blows from the left in Fig. B-8 one day and from the right
the next day). However, if the system is managed to operate approximately
24 hours in each towpath, as in the example test, wind problems are
minimized. The traveler is in about the same relative position along
adjacent towpaihs at ,1 given time of day, when wind speed and direction
are most likely to be similar.
(6) Potential application efficiency (PELQ) should be determined
in order to evaluate how effectively the system can utilize the wa&e*
supply and what the water losses may be, then the total amount of water
required to irrigate the field can be estimated. PELQ is calculated
from the ratio of the average low-quarter depth caught in the containers
to the average depth applied (rather than rates as used in othet sprinkler
system evaluations).
The average depth applied, D (in inches), is calculated from a constant
times the total traveler discharge (the sprinkler discharge plus the
piston discharge, if the traveler is driven by water piston) divided by
the towpath spacing and the sprinkler's travel speed.
_ 96.3 sprinkler plus piston discharge (gpm)
60 x path spacing (feet) x travel (feet/min)
From the sample data given in parts 9, 10, and 11, and computed in part
14 on Fig. B-7, the average depth applied is 2. A3 inches. The PELQ
with a low one-quarter depth of 1.61 inches is:
PELQ = ~~ x 100 = 66 percent
This is a reasonable value for the central portion of a traveler irrigated
field with such wide towpath spacings; however, the PELQ around the
boundaries will be much lower.
(7) Application efficiency. Effectiveness of the use of the
traveler system can be estimated by how much of the applied water is
stored in the soil and available for consumptive use and by comparing
the AELQ and the PELQ.
The fine sandy loam soils in the area tested hold about 1.5 inches pe*
foot available moisture. Depth of the rooL zone of the corn was 4.0
i'cet at that time, and a 35 percent MAD was considered ideal. This
gives an MAD of 2.1 inches. The field checks showed that SMD near the
lowpath nnd at the 1/4 point where 2.1 inches and 2,2 inches, respectively,
while in the middle of the strip it was 3.7 inches.
The minimum depth of 1.6 inches was applied in the middle of the strip
where the SMD was 3.7 inches (Fig. B-8 and B-9 ). Thus, the system
did not apply a full irrigation; no water was lost to deep percolation
in the low-quarter application area; and AELQ = PELQ = 66 percent.
B-31
Apparently much of the area had been receiving adequate irrigation
because the SMD and MAD over much of the strip were less than or equal
to the depth of application. However, underirrigation had created a
cumulative deficit in the middle areas between towpaths. This deficit
was beginning to affect the corn growth as evidenced by stunted plants
midway between paths.
(8) Application rate. The gun sprinklers normally used on
travelers produce a rather flat pattern of distribution. That is, if
the traveler vehicle were standing still, the application depth or
application rate over most of the wetted area would be fairly uniform.
An estimate of the average application rate, R, in inches per hour can
be obtained from a conversion constant times the flow (in gpm) from the
sprinkler divided by the wetted area. The wetted area depends on the
angle of the wet sector (for part-circle sprinklers).
R - 96.3 x sprinkler discharge (gpm) x 360
2
towpath spacing (feet) x wet sector (degrees)
For the sample evaluation (Fig. B-7, , parts 6 and 9), the sprinkler
discharges 500 gpm and the towpath spacing is 330 feet with the part-circle
sprinklers set for a 15 dry sector, i.e., 345 wet. The estimated
average application rate computed in part 13 of Fig. B-7 is R = 0-46
in/hr. This is a fairly high application rate for the fine sandy loam
soils which could cause infiltration and runoff problems in steeper
areas or where the soil is in poor condition (tilth).
(9) Analysis and recommendations. Many of the observations
and some recommendations that can be made from the additional data on
Fig. B-7, plus the DU and PELQ computations have already been referred
to here and in other sections about sprinkle evaluation.
() Operational checks. The pressure of 100 psi at the
nozzle is ideal for good breakup of drops. The total recorded losses of
37 psi (10 psi in the drive turbine and 27 psi in the 4-inch by 660-foot
flexible hose) are reasonable. (See Fig. B-7, parts 6, 7, and 12.)
0>) Runoff. Infiltration did not appear to be a problem.
The fine sandy loam soils could receive the light application at 0.46
iph with no runoff, and the towpath remained relatively dry.
(c) Underi rrlgation. After reviewing the full value of
the operation, it was concluded that the amount of underirrigation was
reasonable. The area receives considerable summer rain which may offset
the cumulative SMD along the center of the strips; furthermore, the
large area of the field and the restricted supply of water made it
impractical to increase the average depth of application very much.
Only improvements in DU and possibly slightly higher flow rates would be
practical.
(d) Improvements. The only major improvement necessary
would be to increase the DU. However, it is not reasonable to narrow
the towpath spacing during the growing season. If this spacing were
reduced, the numbers of towpaths and consequently the number of days
between irrigations would need to be increased.
Several practical possibilities for improving the DU might be tried in
the following order:
o
Increase the angle of the dry area up to between 90 and 120 {
o Try a taper bore nozzle, which would have a greater range for
the same discharge and pressure.
o Increase the nozzle size to the next larger sized ring nozzle.
(e) Edftft effects. The outside towpaths of the present
system are placed 150 feet inside the field boundaries. The field was
laid out similarly to what appears in Fig. B-8. There were 8 towpaths
across the 2, 610-foot width of the field--2,640 feet less a 30-foot road
right-of-way. Data on Fig. u-7, i part 17, indicate this layout should
give a reasonable application (1.7 inches) on the downwind side but a
very light (0.4 inch) watering along the upwind side.
The traveler started at one edge of the field and stopped at the opposite
edge. This resulted in considerable overthrow but watered the ends of
tin; field (Fig. B-8) fairly well. The full length of the 660-foot
hose was needed because it had to be dragged through the 1,320-foot
length of the towpaths.
The PELQ of 66 percent computed earlier was for the central portion of
the field; however, because of poor uniformity along the boundaries
where there is insufficient overlap, plus water that is thrown outside
of the planted area (ser Fig. B-8) the overall field efficiency is
considerably lower. For the SO-acrc field evaluated, the overall field
PELQ was only estimated to be 52 percent. Much of this reduction in
efficiency is due to poor uniformity along the edge of the field where
. . -, _, _....,.,i _j ^u ,! where it stops ' c " Vl " "-" "*
Apparently much of the area had been receiving adequate irrigation
because the SMD and MAD over much of the strip were less than or equal
to the depth of application. However, underirngation had created a
cumulative deficit in the middle areas between towpaths. This deficit
was beginning to affect the corn growth as evidenced by stunted plants
midway between paths.
(8) Application rate. The gun sprinklers normally used on
travelers produce a rather flat pattern of distribution. That is, if
the traveler vehicle were standing still, the application depth or
application rate over most of the wetted area would be fairly uniform.
An estimate of the average application rate, R, in inches per hour can
be obtained from a conversion constant times the flow (in gpm) from the
sprinkler divided by the wetted area. The wetted area depends on the
angle of the wet sector (for part-circle sprinklers).
R - 96,3 x sprinkler discharge (gpm) x 36Q
2
towpath spacing (feet) x wet sector (degrees)
For the sample evaluation (Fig. B-7, , parts 6 and 9), the sprinkler
discharges 500 gpm and the towpath spacing is 330 feet with the part-circle
sprinklers set for a 15 dry sector, i.e., 345 wet. The estimated
average application rate computed in part 13 of Fig. H-7 is R = 0-46
in/hr. This is a fairly high application rate for the fine sandy loam
soils which could cause infiltration and runoff problems in steeper
areas or where the soil is in poor condition (tilth).
(9) Analysis and recommendations. Many of the observations
and some recommendations that can be made from the additional data on
Fig. ii-7, plus the DU and PF.LQ computations have already been referred
to here and in other sections about sprinkle evaluation.
( a ) Operational checks. The pressure of 100 psi at the
nozzle is ideal for good breakup of drops. The total recorded losses of
37 psi (10 psi in the drive turbine and 27 psi in the 4-inch by 660-foot
flexible hose) are reasonable. (See Fig, 0-7, parts 6, 7, and 12.)
(k) Runoff. Infiltration did not appear to be a problem.
The fine sandy loam soils could receive the light application at 0.46
iph with no runoff, and the towpath remained relatively dry.
(c) Undenrrigation. After reviewing the full value of
the operation, it was concluded that the amount of underirrigation was
reasonable. The area receives considerable summer rain which may offset
the cumulative SMD along the center of the strips; furthermore, the
large area of the field and the restricted supply of water made it
impractical to increase the average depth of application very much.
Only improvements in DU and possibly slightly higher flow rates would be
practical .
B-32
(d) Improvements. The only major improvement necessary
would be Lo increase the DU . However, it is not reasonable to narrow
the towpath spacing during the growing season. If this spacing were
reduced, the numbers of towpaths and consequently the number of days
between irrigations would need to be increased.
Several practical possibilities for improving the DU might be tried in
the following order;
o Increase the angle of the dry area up to between 90 and 120.
o Try a taper bore nozzle, which would have a greater range for
the same discharge and pressure.
o Increase the nozzle size to the next larger sized ring nozzle.
(e) Edge effects. The outside towpaths of the present
system are placed 150 feet inside the field boundaries. The field was
laid out similarly to what appears in Fig. -fj-8. There were 8 towpaths
across the 2, 610-foot width of the field--2,640 feet less a 30-foot road
right-of-way. Data on Fig. 11-7, , part 17, indicate this layout should
give a reasonable application (1.7 inches) on the downwind side but a
very light (0.4 inch) watering along the upwind side.
The traveler started at one edge of the field and stopped at the opposite
edge. This resulted in considerable overthrow hut watered the ends of
the field (Fig. IJ-8) fairly well. The full length of the 660-foot
hose was needed because it bad to be dragged through the 1,320-foot
length of the towpaths.
The PELQ of 66 percent computed earlier was for the central portion of
the field; however, because of poor uniformity along the boundaries
where there is insufficient overlap, plus water that is thrown outside
of the planted area (see Fig. B-8) the overall field efficiency is
considerably lower. For the 80-acre field evaluated, the overall field
PELQ was only estimated to be 52 percent. Much of this reduction in
efficiency is due to poor uniformity along the edge o Lhe field where
t id*-! ML lh" futlporuons of the strips between towpaths. Changing
vi" .1 UK- >!ty ,wa of the sprinkler or the type or size of the sprinkler
V [t- n iy iTipi'tvp the UU.
i.ii ''^nff^l -jysiems which essentially eliminate the reduction in
l'j . i'j;,t'I by the poor uniformity along towpath ends are in the pilot
*'!;): i"ii -r.^ p These control systems change the angle of the part
t-l- -prLiskU-r and the speed of travel upon leaving and approaching
* t .wp.ith ends. For the 80-acre field evaluated, such a control
. ft n njuM increase the overall field PELQ by about 10 percent or up
ijpjft'jxi^.jtcly 62 percent.
8-34
3- Trickle Irrigation Field Evaluation Procedure
Successful operation of trickle irrigation requires that the frequency
and quantity of water application be accurately scheduled. The field
emission uniformity, EU 1 , must be known in order to manage the quantity
of application. Unfortunately, EU' often changes with time; therefore,
periodic field checks of system performance are necessary.
The data needed for fully evaluating a trickle irrigation system are
available by determining:
1. Duration, frequency, and sequence of operation of normal
irrigation cycle.
2. The S , and M , in the wetted volume where
md ad
S . - Soil moisture deficit is the difference between field
capacity and the actual soil moisture in the root zone soil at any given
time. It is the amount of water required to bring the soil in the root
zone to field capacity.
M , - Management allowed deficit is the desired soil moisture
deficit at the time of irrigation. It is expressed as a percent of the
available water capacity (W^) or the corresponding soil moisture deficit
(S .) related to the desired soil moisture stress for the
crbp-soil-water-climate system. Sprinkle and surface irrigation is
usually scheduled when S , equals M, , but trickle irrigation is often
Scheduled with a much lower S .. However, in humid areas supplemental
irrigation depths are often applied to only partly replace S , in order
to leave some root zone capacity for storage of anticipated rainfall.
3. Rate of discharge at the emission points and the pressure near
several emitters spaced throughout the system.
4. Changes in rate of discharge from emitters after cleaning or
other repair.
5. The percent of soil volume wetted.
6. Spacing and size of trees or other plants being irrigated.
7. Location of emission points relative to trees, vines, or other
plants and uniformity of spacing of emmision points.
8. Losses of pressure at the filters.
9. General topography.
10. Additional data indicated on Fig. B-10,
B-35
1.
2.
3.
4,
5,
6,
7,
8
10
11
12
13
Figure B-10.
Location
TRICKLE IRRIGATION EVALUATION
, Observer , Date
Crop: type
years, spacing -by
root depth
Soil: texture
Irrig: duration
a se _
ft, percent area covered or shaded
, available moisture _
J> M ad
-feet
in/ft
Filter pressure: inlet
Emitter: make
hrs, frequency
psi, outlet
i type
I.
psi, loss
in
psi
Rated discharge per emission point
Emission points per plant , giving
Lateral: dia. in, material
, point spacing ft
_ gph at psi
gallon per plant per day
ft, spacin ft
9. System layout, general topography, and test locations;
System discharge
No. of manifolds
and blocks
Average test manifold emission point discharges at
w .- ,, (sum of all averages gph) m
Manifold ~. r * ^~ ^^
(number of averages ) ~
psi
Low 1/4
(sum of low 1/4 averages
(number of low 1/4 averages
Adjusted average emission point discharges at
System - (DCF ) (manifold average
Low 1/4 - (DCF ) (manifold low 1/4
Comments:
psi
Figure B-10. TRICKLE IRRIGATION EVALUATION (Cone.)
14. Discharge test volume collected In mln. (1.0 gph 63 ml/min)
Location
on Lateral
Lateral Location on the Manifold
inlet end
1/3 down
2/3 down
far end
ml
gph
ml
gph
ml
gph
ml
gph
inlet
end
A
B
Ave
1/3
down
A
B
Ave
2/3
down
A
B
Ave
far
end
A
B
Ave
15 . Lateral inlet
closed end
16, Wetted area
per plant
psl
psi
ft'
psl
psi
ft'
pBJ
psi
psi
psi
17. Estimated average Smd in wetted
Equipment needed
The equipment needed for collecting the necessary field data is:
1. Pressure gauge [0-50 psi range) with "T" adapters for
temporary installation at either end of the lateral hoses.
2. A stopwatch or watch with an easily visible second hand.
3. Graduated cylinder with 250 ml capacity.
4. Measuring tape 10 to 20 ft long.
5. Funnel with 3- to 6-in diameter.
6. Shovel and soil auger or probe.
7. Manufacturer's emitter performance charts showing the
relationships between discharge and pressure plus recommended operating
pressures and filter requirements.
8. Sheet metal or plastic trough 3 ft long for measuring the
discharge from several outlets in a perforated hose simultaneously or
the discharge from a 3-ft length of porous tubing. (A piece of 1- or
2-in PVC pipe cut in half lengthwise makes a good trough.)
9. Copies of Figure B-10 for recording data.
Field Procedure
The following field procedure is suitable for evaluating systems with
individually manufactured emitters (or sprayers) and systems that use
perforated or porous lateral hose. Fill in the data blanks of Form
7-11.1 while conducting field procedure.
1. Fill in parts 1, 2, and 3 of Figure B-10 concerning the general
soil and crop characteristics throughout the field.
2. Determine from the operator the duration and frequency of
irrigation and his concept of the M , to complete part A.
3. Check and note in part 5 the pressures at the inlet and outltt
of the filter and, if practical, inspect the screens for breaks and any
other possibility for. contaminants to bypass the screens,
4. Fill in parts 6, 7, and 8 which deal with the emitter and
eral hose characteristics. (When testing perforated or porous tubing
discharge may be rated by the manufacturer in flow per unit, length.)
Locate four emitter laterals along an operating manifold (See
11 ) ; one should be near the inlet and two near the "third"
he fourth near the outer end. Try to select a manifold
B-38
Block
H)
Block
Manifold
Block
*
^
Mainline
n
Water Supply
and
Control Head
Block
Y
Laterals
With
Emitters
m
QT
Control Valves
IV
Figure B-H. Typical two station split flow layout for trickle
irrigation system with Block T and III, or II and IV
operating simultaneously.
B-39
which appears to have the greatest head differential for evaluation.
Sketch the system layout and note in part 9 the general topography,
manifold in operation and manifold where the discharge test will be
conducted.
6. Record the system discharge rate (if the system is provided
with a water meter) and the numbers of manifolds and blocks (or stations)
in Part 10. The number of blocks is the total number of manifolds
divided by the number of manifolds in operation at any one time,
7. For laterals having individual emitters, measure the discharge
at two adjacent emission points (denoted as A and B in part 14) at each
of four different tree or plant locations on each of the four selected
test laterals. Collect the flow for a number of
full minutes (1, 2, and 3, etc.) to obtain a volume between 100 and 250
ml for each emission point tested. Convert each reading to ml per
minute before entering the data in part 14 on Figure B-10. To convert
ml per minute to gallons per hour (gph) , divide by 63.
These steps will produce eight pressure readings and 32 discharge volumes
at 16 different plant locations for individual emission points used in
wide-spaced crops with two or more emission points per plant.
For perforated hose or porous tubing, use the 3-ft trough and collect a
discharge reading at each of the 16 locations described above. Since
these are already averages from 2 or more outlets, only one reading is
needed at each location.
For relatively wide-spaced crops such as grapes where one single outlet
emitter may serve one or more plants, collect a discharge reading at
each of the 16 locations described above. Since the plants are only
served by a single emission point, only one reading should be made at
each location.
8. Measure and record in part 15 the water pressures at the inlet
* downstream ends of each lateral tested in part 14 under normal
"tion. On the inlet end, this may require disconnecting the lateral
'Calling the pressure gauge, and reconnecting the hose before
^ pressure. Some systems are equipped with tire valve stems
~~"* and pressure can be read with the use of portable
wnstream end, the pressure can be read after connecting
;e the simplest way possible.
-centage of the soil that is wetted at one of the
test lateral and record in part 16. It is best
lifferent relative location on each lateral. Use
or shovel--whichever seems to work best-~for
the wetted zone in a horizontal plane about 6 to
il surface around each tree. Determine the
ividing the wetted area by the total surface area
e.
B-40
10. If an interval of several days between irrigations is being
used, check the soil moisture deficit, S , in the wetted volume near a
few representative trees in the next blocfi to be irrigated and record it
in part 17. This is difficult and requires averaging samples taken from
several positions around each tree.
11. Determine the minimum lateral inlet pressure, MLIP, along each
of the operating manifolds and record in part 18. For level or uphill
manifolds, the MLIP will be at the far end of the manifold. For downhill
manifolds it is often about two-thirds down the manifold. For manifolds
on undulating terrain it is usually on a knoll or high point. When
evaluating a system with two or more operating stations, the MLIP on
each manifold should be determined. This will require cycling the
system.
12. Determine the discharge correction factor, DCF , to adjust the
average emission point discharges for the tested manifold. This adjustment
is needed if the tested manifold happened to be operating with a higher
or lower MLIP than the system average MLIP. If the emitter discharge
exponent, x, is known, use the second formula presented in part 19.
13. Determine the average and adjusted average emission point
discharges according to the equations in parts 11 and 12 of FLfturc H-10,
Utilization of field data
In trickle irrigation all the system flow is delivered Lo individual
trees, vines, shrubs, or other plants. Essentially, there is no opportunity
for loss of water except at the tree or plant locations. Therefore,
uniformity of emission is of primary concern, assuming the crop is
uniform. Locations of individual emission points , or the tree locations
when several emitters are closely spaced, can be thought of in much the
same manner as the container positions in tests of sprinkler performance.
Average application depth. The average J '
the wetted area, D , is useful for es'
r 'aw'
from:
1.604 e q' T
_ lo a
aw
in which
D 1 is the average depth applied pei
B-43
q 1 is the adjusted average emission point discharge of the system for
part 12 Ft*. B-10 (gph)
e is the number of emission points per tree
T g is the application time per irrigation (tirs)
2
A is area wetted per tree or plant from part }6 (ft )
W
The average depth applied per irrigation to the total cropped area can
be found by substituting the plant spacing, S x S , for the wetted
area, A , in eq. B-l. Therefore: p r
D' -.
l p * S r
(eq. B-2)
in which
D' is the average depth applied per irrigation to the total cropped
area (in)
S and S are plant and row spacing, ft.
d ay . The average volume of water applied per day for each
tree or plant is:
e <ll T.
ri _ a
G - . B-3)
in which
G' is the average volume of water applied per plant per day (gal/day)
F. is the irrigation interval (days)
Emission Uniformity. The actual field emission uniformity, EU 1 , is
needed to determine the system operating efficiency and for estimating
gross water application requirements. The EU' is a function of the
emission uniformity in the tested area and the pressure variations
throughout the entire system. Where the emitter discharge test data is
from the area served by a single manifold:
EU' = 100 q'/q 1
(eq. B-4)
in which
EU' m is the field emission uniformity of the manifold area tested (percent)
q' n and q 1 ^ are the system low quarter and overall average emitter
discharges, taken from Figure B-10, part 12 (gph).
Some trickle irrigation systems are fitted with pressure compensating
emitters or have pressure or flow) regulation at the inlet to each
lateral. Some systems are only provided with a means for pressure
control or regulation at the inlets to the manifolds, others are provided
with regulators at each lateral. If the manifold inlet pressures vary
more than a few percent (due to design and/or management), the overall
EU 1 (of the system) will be lower than EU r (of the tested manifold).
An estimate of this efficiency reduction factor (ERF) can be computed
from the minimum lateral inlet pressure along each manifold throughout
the system by:
FRF - ( 1<5 ,
ERF " 2?5 (average KLIP) ^ < e <l
in which
ERF is the efficiency reduction factor
MLIP is the minimum lateral inlet pressure along a manifold (psi)
Average MLIP is the average of the individual MLIP along each manifold
(psi)
Minimum MLIP is the lowest lateral inlet pressure in the system (psi)
A more precise method for estimating the ERF can be made by:
ERF =
minimum KLIP
average
B-5b)
x is the emitter discharge exponent
In cases where there are relatively small pressure variations and x =
0.5, the two methods for computing ERF give essentially equal results;
B-43
however, for pressure variations greater than 0.2 h or x values higher
than 0.6 or lower than 0.4, the differences could be significant.
Note - h is the average emitter pressure head.
3
The value of x can be estimated from field data as follows:
Step 1 Determine the average discharge and pressure of a group of at
least 6 emitters along a lateral where the operating pressure is uniform,
Step 2 Reduce the operating pressure by adjusting the lateral inlet
valve and again determine the average discharge and pressure of the same
group of emitters.
Step 3 Determine x by Equation B-6 using the average discharge and
pressure head values found in Steps 1 and 2.
log q
x = \2L
log /hi \ (eq. B-6)
1 K
Where
x = Emitter discharge exponent
q_ = Average discharge of a group of emitters at pressure, lu
q = Average discharge of the same group of emitters at pressure, h
t
Step A Repeat steps 1, 2, and 3 at two other locations and average the
x values for the three tests.
The EKF is approximately equal to the ratio between the average emission
point discharge in the area served by the manifold with the minimum MLIP
and the average emission point discharge for the system. Therefore, the
system EU 1 can be approximated by:
B-7)
General criteria for EU 1 values for systems which have been in operation
for one or more seasons are; greater than 90% excellent; between 80%
and 90%, good; 70 to 80% fair; and less than 70% poor.
application required. Since trickle irrigation wets only a small
the soil volume, the S . must be replaced frequently. It is
icult to estimate S , Because some regions of the wetted
iot zone often remain near field capacity even when the
irrigation is several days. For this reason, S , must
a weather data or information derived from evaporation
stimates are subject to error and since there is no
B-44
practical way to check for slight underirrigation, some margin for
safety should be allowed. As a general rule, the minimum gross depth of
application, I should be equal to (or slightly greater than) the
values obtained by eq. B-8.
A bulbous tipped probe can be used to determine the area of the wetted
bulb. If the wetted bulb increases over a series of irrigations, too
much water is being applied. If the wetted bulb is decreasing in size,
then there is underirrigation.
The gross depth per irrigation, I , should include sufficient water to
compensate for the system uniformity and allow for unavoidable losses of
the required leaching water. (Unavoidable losses can be used to satisfy
leaching requirements or vice versa) To minimize the gross depth, systems
should be well designed, accurately scheduled and carefully maintained.
Where the unavoidable water losses are greater than the leaching water
required, T r > 1/(1,0 - LR t ) or LR t < 0.1:
\
(eq, B-8)
and where T r > l/(1.0~LR t ) and LRt < 0.1:
in which
however, for pressure variations greater than 0.2 h or x values higher
than 0*6 or lower than 0.4, the differences could be significant.
Note - h is the average emitter pressure head.
The value of x can be estimated from field data as follows:
Step 1 Determine the average discharge and pressure of a group of at
least 6 emitters along a lateral where the operating pressure is uniform,
Step 2. Reduce the operating pressure by adjusting the lateral inlet
valve and again determine the average discharge and pressure of the same
group of emitters.
Step 3 Determine x by Equation B-6 using the average discharge and
pressure head values found in Steps 1 and 2.
log
X =
log/ hi ^ (eq. B-6)
1 K
Where
x = Emitter discharge exponent
q = Average discharge of a group of emitters at pressure, h
q- - Average discharge of the same group of emitters at pressure, h ?
Z> i+
Step 4 Repeat steps 1, 2, and 3 at two other locations and average the
x values for the three tests.
The ERF is approximately equal to the ratio between the average emission
point discharge in the area served by the manifold with the minimum MLIP
and the average emission point discharge for the system. Therefore, the
system EU' can be approximated by;
EU 1 = (ERE (EU '") (eq. R ~ 7 )
General criteria for EU 1 values for systems which have been in operation
for one or more seasons are: greater than 90% excellent; between 80%
and 90%, good; 70 to B0% fair; and less than 70% poor.
Gross application required. Since trickle irrigation wets only a small
portion of the soil volume, the S , must be replaced frequently. It is
always difficult to estimate S , Because some regions of the wetted
portion of the root zone often remain, near field capacity even when the
interval between irrigation is several days. For this reason, S , must
be estimated from weather data or information derived from evaporation
devices. Such estimates are subject to error and since there is no
B-44
practical way to check for slight underirrigation, some margin for
safety should be allowed. As a general rule, the minimum gross depth of
application, I , should be equal to (or slightly greater than) the
values obtainea by eq. B-8.
A bulbous tipped probe can be used to determine the area of the wetted
bulb. If the wetted bulb increases over a series of irrigations, too
much water is being applied. If the wetted bulb is decreasing in size,
then there is underirrigation.
The gross depth per irrigation, I , should include sufficient water to
compensate for the system uniformity and allow for unavoidable losses of
the required leaching water. (Unavoidable losses can be used to satisfy
leaching requirements or vice versa) To minimize the gross depth, systems
should be well designed, accurately scheduled and carefully maintained.
Where the unavoidable water losses are greater than the leaching water
required, T > 1/(1.0 - LR C ) or LR t < 0.1:
T r
S -- EU/100
and where T c > l/(1.0-LR t ) and LRc < 0.1:
in which
I is the gross depth per irrigation, inches
o
T is the peak use period transpiration ratio
EU is the emission uniformity, percentage
LR is the leaching requirment under trickle irrigation, ratio - for
I is the net depth to be applied per irrigation, in
The T is the ratio of the depth of water applied to the area where T,
is exactly satisfied to the depth of water transpired. It represents
the extra water which must be applied, even during peak use period, to
offset unavoidable deep percolation losses. These losses are due to
excess vertical water movement below the active root zone which is
unavoidable in porous and shallow soils when sufficient lateral wetting
is achieved. With efficient irrigation scheduling and for design purposes
use the following peak use period T values:
B-45-
i) T = 1,00 for deep (greater than 5 ft) rooted crops on al] soils
except very porous gravely soils; medium (2.5 to 5 ft) rooted crops on
fine and medium textured soils; and shallow rooted (less than 2.5 ft) on
fine textured soils.
ii) T = 1.05 for deep rooted crops on gravely soils; medium rooted
crops on coarse textured (sandy) soils; and shallow rooted crops on
medium textured soils.
iii) T = 1.10 for medium rooted ciops on gravely soils; or shallow
rooted crops on coarse textured soils.
T, in the above discussion is the peak month average daily transpiration
rate of a crop under trickle irrigation, in/day.
When estimating Ig by eq. B-8 for managing (scheduling) irrigations
let EU be the field EU 1 and estimate the net depth or irrigation to
apply; I , as follows:
i) First estimate the depth of water which could have been consumed
by a full canopy crop since the previous irrigation, 1 ' . This can be
done using standard techniques based on weather data or pan evaporation
data.
ii) Next, subtract the depth of effective rainfall since the last
irrigation, R '
iii) Then calculate I by:
n
I n = (I n ' - VHlM + 0.15 (1.0 - -jfljy)] ( eq . B-9)
P is the ground area shaded by the crop canopies at midday as a percent
of the total area, percentage
Using I (computed by eq. B _g ) , the average daily gross volume of
water required per plant per day, G, can be computed by eq, B-10. The
average volumn of water actually being applied each day is computed by
eq. B-3. If G G' the field is being overirrigated and if G> G 1 , it
is underirrigated. This can be verified with the use of a neutron probe
or similar equipment. The gross volume of water required per plant per
day, G, is useful for selecting the design emitter flow rate:
G = 0,623 Sp S r I /FJ (eq. B-10)
r L g x
in which G is the gross water required per plant per day, gal/day.
B-46
S and S are the plant and row spacings , ft
I is the gross depth per irrigation, in
6
F. is the irrigation interval (frequency), days
Application Efficiencies
A concept called potential application efficiency (of the low quarter) >
PE , is useful for estimating how well a system can perform. It is a
function of the peak use transpiration ratio, T , the leaching requirement,
LR and EU 1 . When the unavoidable water losses are greater than the
leaching water requirements., T >!/(!. - LR.):
JL L-
and where T r <1/(1.0 - LR fc ) :
PE, = EU 1 Ceq. B-llb)
The values for T are given in conjunction with eq. B-8 anc i LR by eq. B-12
Leaching requirement, LR . In arid regions where salinity is a major
importance, most of the natural precipitation is accounted for in R
e
W , nonbeneficial consumptive use, and/or runoff. There is usually very
a
little additional natural precipitation, D , that can add to deep
percolation and consequently help satisfy tne leaching requirements.
Furthermore, since only a portion of the soil area is wetted and needs
leaching under trickle irrigation, the effective additional precipitation
is reduced to (P /100) D ; therefore, it can almost always be neglected.
P is the average horizontal area wetted in the top part (6 to 12 in) of
tne crop root zone as a percentage of the total crop area.
Calculating the leaching requirement for trickle irrigation, LR is
greatly simplified by neglecting (P /100)D and
W t Vr
LR = i". = LN EC W
~
.
t T T Trr> .
I and I N are the net per irrigation application and net annual irrigation
depths to meet consumptive use requirements, respectively in,EC w is the
electrical conductivity of the irrigation water, romhos/cm EC, is the
electrical conductivity of the drainage (deep percolation) water, mmhos/cm
Equation B-12 is based on a steady state salt balance condition, or in
popular terminology, "what goes in, must come out and nothing comes from
in between." It is important to understand the meaning of the number
calculated for LR . It represents the minimum amount of water (in terms
of a fraction of applied water) that must pass through the root zone to
control salt buildup. The actual LR , however, is that amount of leaching
water necessary to control salts in the root zone and this can only be
determined by monitoring the soil salinity which is then related to
field water management.
In a trickle irrigation system, there are no field boundary effects or
pressure variations along the manifold tested which are not taken into
account in the field estimate of EU' . Therefore, the estimated PE. is
an overall value for the field except for possible minor water losses
due to leaks, draining of lines, and flushing (unless leaks are excessive),
with the system EU' (see eq. 5-7) ,
The system PEL may be low because the manifold inlet pressures are not
properly set arid ERF (see eq. B-5) is low. In such cases, the
manifold inlet pressures should be adjusted to increase the pressure
uniformity and consequently ERF. When there is overirrigation, the
actual application efficiency of the low quarter, E- will be less than
PE. . In such cases the E- can be estimated by: ^
Iq lq y
B-i3)
when there is underirrigation and G' G then E will approach the
system EU 1 . In such cases the
This may cause excessive salt b
a reduced volume of wetted soil.
system EU 1 . In such cases the LR and/or the T^ will not be satisfied.
This may cause excessive salt buildup in the least interest areas and/or
APPENDIX C - DESIGN AIDS
Contents
Table C-l Conversion Factors C-l
Table C-2 Friction Head Loss in Plastic Irrigation
Pipelines of PVC or ABS Compounds
miR f )~\ TPQ Pi no P_9
<-JLJl\ v- -L- , J- L O i4.pt- -~ i _ ~__~.~_____-~. .___ _ _ ._ ~_ \ vJ 1 ^^.
Table C-3 Friction Head Loss in Plastic Irrigation
Pipelines of PVC or ABS Compounds
SDR 21 PIP Pino C 5
Table C-4 Friction Loss Characteristics PVC Class
315 IPS Plastic Pipe, Sizes V-3V 1 C-7
Table C-5 Friction Loss Characteristics PVC Schedule
40 IPS Plastic Pipe, Sizes ^"-3 l ," C-8
Table C-6 Friction Loss Characteristics PVC Schedule
40 IPS Plastic Pipe, Sizes 4"-12" (1 gpm~60G gpm) C-9
Table C-7 Friction Loss Characteristics PVC Schedule
40 IPS Plastic Pipe, Sizes 4"~12" (650 gpm-5,000 gpm) - C-10
'I able C-8 Friction Loss Characteristics PVC Schedule
80 IPS Plastic Pipe, Sizes V-3V' C-ll
Table C-9 Friction Loss Characteristics PVC Schedule
80 IPS Plastic Pipe, Sizes 4"-12" (1 gpm-600 gpm) C-12
Table C-10 Friction Loss Characteristics PVC Schedule
80 IPS PlastJc Pipe, Sizes 4 lf -12" (650 gpm-5,000 gpm) - C-13
Table C-ll Friction Loss in Feet Per 100 Feet in
Asbestos Cement Pressure Pipe C-14
Table 1 C-12 Pressure (Friction) Loss, in Feet Per
100 Feet, for Portable Aluminum
irrigation Pipe with Couplings C-15
Exhibit C-J Flexible Irrigation Hose Pressure Loss
Per 100 Feet of Length C-16
Table C-13 Friction Loss Characteristics Polyethylene (PE)
SDK-Pressure Rated Tube, Sazes V'-6 rt C-17
Exhibit C-2 Friction Loss in Polyethylene Pipe C-18
Table C-14 Feeder Line Friction Loss C-19
Exhibit C~3 Friction Head Loss as a Function of
Flow Kate for Lateral Tubing Manufactured
in English Units C-20
Exhibit C-4 Friction Head Loss as a Function of
F.low Rate for Lateral Tubing Manufactured
in Metric Dimensions C-21
Table C-15 Friction Head Loss in 0.580" and
0.622" ID Plastic Hose C-22
Table C-16 Pressure Loss in Center Pivot System, psi C-27
Table C-17 Factors (F) for Computing Friction Head
Loss in a Line with Multiple Outlets C-28
Table C-18 Head Loss Coefficients for Fitting
and Special Corrections where
H = K ^2 C-29
2g
Table C-19 Friction Losses through Pipe Fittings
in Terms of Equivalent Lengths of
Standard Pipe -- C-30
Exhibit C-5 Horsepower Required to Pump Water C-31
Exhibit C-6 Capacity Requirements for Irrigation
^v/c h o m L. ,________,.,- . _ _ _ ..._ ^-____-___ --__ -- f* T ?
J j D i* c 1 1 1 j **-_^. ^-j..,-^-,,.-..- -, .* -,-*^.^_^^-.** -^ ^ -* ,* . _ ^ vJ f .,
Table C-2Q Application Rate for Planning
Irrigation Systems C-33
Table C-21 Center Pivot Systems Time Required
to, Apply 1" Gross Application
(nrs/in.) and Gross Capacity (in. /day) C-34
exhibit C-7 Center Pivot Water Supply
Nomograph C-3S
Table C-22 Standard Pipe Dimensions Rigid PVC
Plastic Pipe -- C-36
Table C-23 Standard Pipe Dimensions
Flexible Polyethylene Tube (PE) C-36
Table C-24 Standard Pipe Dimension
Asbestos-Cement Irrigation Pipe C-36
Table C-25 Friction Head Loss in Plastic Irrigation Pipelines
Manufactured of PVC or ABS Compounds
Standard Dimension Ratio-SDR = 26 (For IPS Pipe) -- C-37
Table C-26 Friction Head Loss in .Plastic Irrigation Pipelines
Manufactured of PVC or ABS Compounds
Standard Dimension Ratio-SDR = 32.5, (For IPS Pipe)- C-40
Table C-27 Gun Sprinklers Performance Tables ~- 1 ~- ' C-43
Table C-l . Conversion Factors
Length
1 millimeter
1 centimeter
1 meter
1 kilometer
0.03937 inch
0.3937 inch
39. 37 inches
3.2980 feet
3,280.8 feet
1 acre
1 hectare
Area
1 mile
1 rod
1 chain
1 link
5,280 feet
1.60935 kilometers
16.5 feet
100 links or 66 feet
7.92 inches
43,560 square feet
2.471 acres
Vol umc
1 acre-inch
1 acre-foot
1 U.S. gallon -
27,152.4 gallons
325,828.8 gallons
43,560 cubic feet
12 acre-inches
231.0 cubic inches
0.1337 cubic foot
3. 7853 litres
cubic foot =
1 litre
1 cubic meter
7.48 U.S. gallons
1728 cubic inches
28.316 litres
0.2642 U.S. gallons
264.0 U.S. gallons
Rate of Flow
1 cfm
1 acre-inch/hr
1 cfs
1 p.jim
VJoij?,htji
1 U.S. gallon
cubic foot of water
Degrees C
Degrees F
Tempera Cure
Pressure
1 atmosphere
] foot of water =
] psi
1 inch of Mercury (Hg) =
7.48 gpm
452.57 gpm
448.83 ppm
7.48 gallons per second
0.0023 cubic foot per second
1440 gallons per day
8 . 326 pounds
62.428 pounds
5/9 (F
9/5 C -
32)
32
0.433 psi
0.883 inches of Mercury (Hg)
2 , 31 feet of water
1.133 feet of water
Mechanical and Electrical
1 horsepower
1 kilowatt
745.7 watts
33)000 foot pounds per minute
1 ,000 watts
1 , 341 horsepower
C-l
Q
Gallons
per min,
FRICTION HEAD LOSS IN PLASTIC IRRIGATION PIPELINES
MANUFACTURED OF PVC OR ABS COMPOUNDS
STANDARD DIKENSION RATIO - SDR = 21 I/
For IPS Pipe
1-inch li;-inch Ifc-inch 2-inch 2i,-Inch 3-inch 3^-inch Q
Gallons
1.189 ID 1.502 ID 1.720 ID 2.149 ID 2.601 ID 3.166 ID 3.620 ID per min,
Friction Head JLos^ j.n Feet .per ;_. Hundred Feet
2
.15 .04 .02
2
4
.54 .17 .09 .03
.01
4
6
1.15 .37 .19 .06
.02
6
8
1.97 .63 .32 .11
.04
.01
8
10
2.98 .95 .49 .16
.06
.02
.01
10
15
6.J2 2.03 1.04 .35
.14
.05
.02
15
20
10.79 3.46 1.78 .60
.23
.09
.04
20
25
16,30 _5.:J2_ 2.70 .91
.36
.13
.07
25
30
22.86 7.32 3.78 1.27
.50
.19
.10
30
35
9.75 Ji.J?:J 1.70
.67
.25
.13
35
40
12.46 6.46 2.18
.86
.32
.17
40
45
15.51 8.02 2.71
1.07
.40
.21
45
50
18.87 9.75 3.30
1.30
.49
.25
50
55
22.48 11.64 __3.91_
1.54
.59
.30
55
60
13.64 4 62
1,81
.69
.36
60
65
15.85 5.36
2.10
.80
.41
65
70
18.19 6.14
2,42
.92
.47
70
75
20.65 6.99
2,75
1.06
.55
75
80
23.28 7.86
3UO
1,19
.62
80
85
8.81
3.47
1.33
.69
85
90
9.79
3.85
1.48
.77
90
95
10.82
4.25
1.64
.85
95
100
11.89
4,69
1.80
.93
100
110
14.21
5.59
2.14
1.11
110
120
16,69
6.56
2.52
1.31
120
130
19.35
7.63
2.92
1.53
130
140
22.21
8.73
3.36
1.75
140
150
9.94
3.82
1.99
150
160
11.20
4.29
_2.,_24_
160
170
12.51
4,80
2.50
170
180
13.90
5.35
2.79
180
190
Table based on Hazen-Will tarns
15.39
5.92
3.08
190
200
equation - Cj. = 150
16.91
6.50
3.38
200
220
20.19
7.77
4.04
220
240
23.73
9.12
4.76
240
260
i/ To find friction head loss in PVG
10.57
5.51
260
280
or ABS pipe having a standard dimension
12.11
6.32
280
300
ratio other than 21, the values in the
13.78
7.18
300
320
table should be multiplied by the ap-
15.52
8.10
320
340
propriate conversion factor shown
17.37
9.07
340
360
below:
19.27
10.08
360
380
21.33
11.13
380
400
Conversion
23.45
12.22
400
SDR No. Factor
420
13.5 1.35
13.40
420
440
17 1.13
14.59
440
460
21 1,00
15.86
460
480
26 .91
17.15
480
500
32.5 .84
18.50
500
41 .785
51 .75
*6HiCULiuBE, soil. eonsenvATioif stimcc. ran WORTH. TCMS
Velocity of va'lues below dotted c-2
line exceed 5 fps
Rev. B-67 4-L-3062I
of 3
Table C-2
FRICTION HEAD LOSS IN PLASTIC IRRIGATION PIPELINES
MANUFACTURED OF PVC OR ABS COMPOUNDS
STANDARD DIMENSION RATIO - SDR = 21 I/
For IPS Pipe
Q
Gallons
per min.
4-inch
4.072 ID
I
5-inch
5.033 ID
friction Head
6-inch
5.993 ID
Loss in
8-inch 10-inch
7.805 ID 9.728 ID
Feet per Hundred Feet
12-inch
11.538 ID
Q
Gallons
per min
15
.01
15
20
.02
20
25
.04
.01
SDR No.
Factor
25
30
.05
.02
13.5
1.35
30
35
.07
.02
.01
17
1.13
35
40
.09
.03
.01
21
1.00
40
45
.12
.04
.01
26
.91
45
50
.14
.05
.02
32.5
.84
50
41
.785
55
.17
.06
.02
51
.75
55
60
.20
.07
.03
60
65
.23
,08
.03
.01
65
70
.27
.09
.04
.01
70
75
.31
.11
.04
.01
75
80
.35
.12
.05
.01
80
85
.39
.14
.05
.01
85
90
.43
.15
.06
.01
90
95
.48
,17
.07
.02
95
100
.52
.19
.07
.02
100
110
.63
.22
.09
.02
110
120
.74
.26
.10
.03
.01
120
130
.85
.30
.12
.03
.01
130
140
.98
.35
.14
.04
.01
140
150
1.11
.40
.16
.05
.01
150
160
1.26
.44
.19
.05
.01
160
170
1.41
.49
.21
.06
.02
170
180
1.57
.55
.24
.07
.02
.01
180
190
1.73
.61
.26
.07
.02
.01
190
200
J.-JP-
.67
.29
.03
.02
.01
200
220
2.28
.81
.34
.09
.03
.01
220
240
2.67
.95
.40
.10
.03
.01
240
260
3. 10
1.10
.46
.12
.04
.02
260
280
3.56
1.26
.54
.14
.05
.02
oon
300
4.04
_1.43__
.61
.17
.05
.02
320
4.56
1.62
.69
.19
.06
340
5.10
1.82
.77
.21
.07
360
5.67
2.02
86
.24
,08
380
6.26
2.22
.95
.26
.09
400
6.90
2,45
1.04
.28
.10
420
7.55
2.69
1.14
.31
.10
440
8.23
2.92
_jj_25_
.34
.11
460
8.94
3.18
1.35
.37
.12
480
9.67
3.44
1.46
.41
.14
500
10.42
3.70
1.58
.43
.15
550
12.44
4.42
1.89
.52
.18
600
14.61
5.21
2.22
.61
.21
C-3
Table C-2
FRICTION HEAD LOSS IN PLASTIC IRRIGATION PIPELINES
MANUFACTURED OF PVC OR ABS COMPOUNDS
STANDARD DIMENSION RATIO - SDR 21 !'
Q
Gallons
per min,
-inch
5 -inch
For IPS Pipe
6 -inch 8-inch
10-inch
4.072 ID 5.033 ID 5.993 ID 7.805 ID 9.728 ID
Fr ic t_ 1 o n Hea d Loss i n Fe e t pe T Hundr e d Feet
12-inch
11,538 ID
Q
Gallons
per min.
600 14761
5.21
2.22
.61
.21
.09
600
650 16.94
6.04
2.58
.71
.24
.10
650
700 19.45
6.92
2,96
.81
.28
.12
700
750 22.08
7.87
3.36
.93
.32
.14
750
800
8.88
3.78
1.04
.36
.16
800
850
9.93
4.24
1.17
.40
.17
850
900
11.05
4.71
1.30
.44
.19
900
950
12.18
5.21
1.44
.49
.21
950
1000
13.40
5.73
1.58
.54
.23
1000
1050
14.67
6.27
1.73
.59
.26
1050
1100
16.00
6.83
1.88
.65
.28
1100
1150
17.39
7.41
2.05
.70
.30
1150
1200
18.80
8.02
2.21
.76
.33
1200
1250
20.27
8.66
2.39
.82
.35
1250
1300
21.78
9.32
2.57
.88
.37
1300
1350
9.99
2.76
.95
.40
1350
1400
10.66
2.95
1. 01
.43
L400
1450
11.40
3.16
1.08
.47
1450
1500
12.13
3.35
1.15
.50
1500
1600
13.68
3.78
1.30
.56
1600
1700
15.29
4.23
1.45
.62
1700
1800
16.99
4.70
1.62
.70
1800
1900
18,81
5.20
1.79
.77
1900
2000
20.66
5.72
1.97
.84
2000
2100
22.61
6.26
2.15
.93
2100
2200
24.67
6.83
2.34
1.01
2200
2300
7.42
2.55
1.10
2300
2400
8.02
2.76
1.19
2400
2500
8.67
2,97
1.29
2500
2600 SDR No.
Factor
9.31
3.20
1.39
2600
2700 13.5
1,35
9.98
3.43
1.49
2700
2800 17
1,13
10.67
3.67
1.59
2800
2900 21
1.00
11.39
3.92
1.69
2900
3000 26
.91
12.10
4.17
1.81
3000
3100 32.5
.84
12.89
4.43
1.92
3100
3200 41
.785
13,66
4.71
2.04
3200
3300 51
.75
14.46
4.97
2.15
3300
3400
15,29
5.27
2.28
3400
3500
16,11
5.56
2.41
3500
3600
16.99
5.85
2.53
3600
3700
17.89
6.17
2.67
3700
3800
18.76
6.47
2.80
3800
3900
19.69
6.79
2.94
3900
4000
20.67
7.11
3.08
4000
C-4
3 of 3
Table C-3
FRICTION HEAD LOSS IN PLASTIC IRRIGATION PIPELINES
MANUFACTURED OF PVG OR ABS COMPOUNDS
STANDARD DIMENSION RATIO - SDR = 21 I/
For PIP Pipe
Q 4 -inch 6 -inch 8-inch 10-inch 12-inch Q
Gallons Gallons
per min. 3.736 ID 5.556 ID 7.382 ID 9.228 ID 11.074 ID per min.
Friction He^ad Loss in Feet per Hundjr^d Feet
15 .02 Table based on Hazen-Williams equation - C^ = 150. 15
20 .04 20
25 .06 y To find friction head loss in PVC 25
30 .09 .01 or ABS pipe having a standard 30
35 .12 .02 dimension ratio other than 21, the 35
40 .15 .02 values in the table should be mul- 40
45 .18 .03 tiplied by the appropriate conver- 45
50 .22 .03 sion factor shown below: 50
55 .27 .04 Conversion 55
60 .31 .05 SDR No. Factor 60
65 .36 .05 .01 65
70 .42 .06 .02 13.5 1.34 70
75 .47 .07 .02 17 1.13 75
80 .53 .08 .02 21 1.00 80
85 .60 .09 .02 26 .91 85
90 .66 .10 .02 32.5 .84 90
95 .73 .11 .03 41 .785 95
100 .80 .12 .03 51 .75 100
110 .96 .14 .03 110
120 1.13 .16 .04 .01 120
130 1.31 .19 .05 .02 130
140 1.50 .22 .05 .02 HO
150 1.70 .25 .06 .02 150
160 1.92 ,28 .07 .02 160
1-70 _2J5^. .31 .08 .03 170
180 2,39 .35 .09 .03 180
190 2.64 .38 .10 .03 190
200 2.90 .42 .11 .04 .01 200
220 3.46 .50 .13 .04 .02 220
240 4.07 .59 .15 .05 .02 240
260 4.72 .68 .17 .06 .02 260
280 5.41 .78 .20 .07 .03 280
300 6.15 .89 .22 .08 .03
320 6.93 1.00 .25 .08 ,03
340 7.76 1.12 .28 .09 .04
360 8.62 _Ii25_ .31 .11 .04
380 9.53 1.38 .35 .12 .05
400 10.48 1.52 .38 .13 .05
420 11.47 1.66 .42 ,14 ,06
440 12.50 1.81 .45 .15 ,06
460 13.58 1.96 .49 .17 .07
480 14.69 2,13 .53 .18 ,07
500 15.84 2.29 .57 .19 .08
550 18.90 2.74 .69 .23 .10
600 22.21 3.21 .81 .27 .11
Velocity of values below dotted
line exceed 5 fps
Table C-3
FRICTION HEAD LOSS IN PLASTIC IRRIGATION PIPELINES
MANUFACTURED OF PVC OR ABS COMPOUNDS
STANDARD DIMENSION RATIO - SDR = 21 i'
For PIP Pipe
Q
4-inch 6-inch
8-inch
10-Inch
12-inch
Q
Gillons
Gallons
j-i.r rin.
3.736 ID 5.556 ID
7.382 ID
9.228 ID
11,074 ID
per mtn.
Friction Head 1
.nss in Feet
: per Hundred 1
?eet
650
1773"
.93
,31
.13
650
Kl.i
4.28
1.07
.36
.15
700
750
4.66
1.22
41
.17
750
SCO
5,47
1.37
,46
.19
800
650
6.13
1.53
52
.21
850
VOO
6.81
1.71
.58
.24
900
f oo
7 53
1 89
64
.26
950
1000
8.28
2.07
_,OP__
.29
1000
1050
0.06
2.27
.77
.31
1050
11 DO
9 87
2.47
.83
,34
1100
115Q
10 72
2.6y
.91
.37
1150
1200
1 1 . 60
7.91
.98
.40
1200
1250
12.51
3.13
!.06
.43
1250
1300
13 45
3,37
1.14
.47
1300
1350
14 43
3 61
1.22
.50
1350
UCQ
15.43
3.87
1.30
.54
1400
1450
16 4?
4 13
1.39
.57
1450
150Q
17.54
4 39
1.48
.fcj_
1500
16CO
19.70
4 . 95
1.67
.69
1600
1700
22 11
5.54
1.87
.77
1700
1800
24 58
6.16
2.08
.85
1800
1'JOO
6.81
2.29
.94
1900
20uO
7.49
2.52
1.04
2000
2100
8.19
2.76
1.14
2100
2200
8.93
3.01
1.24
2200
2300
9.70
3.27
1.35
2300
2400
10 49
3.54
1,46
2400
2500
11 .32
3.82
1.57
2500
SDR No. Factor
2600
12 17
4.10
1.69
2600
2700
13.5 1.34
U.05
4.40
1.81
2700
2BGQ
17 1.13
13.96
4,71
1.94
2800
2*00
21 I. 00
14.90
5.02
2.07
2900
in no
26 .VI
15.86
5.35
2,20
3000
3
32 5 .64
16.85
5.68
2.34
3100
41 .785
17.88
6.03
2.48
3200
51 .75
18.92
6.38
2.62
3300
20.00
6,74
2.77
3400
21.10
7,11
2.93
3500
22.23
7.50
3.08
3600
23.39
7,89
3.24
37OO
24.57
8.28
3.41
3800
8.69
3,58
3900
9.U
3.75
4000
C-6
2 of
Table. C-4
FRICTION LOSS CHARACTERISTICS
PVC CLASS 315 IPS PLASTIC PIPE
(1 120, 1220) SDR 13.5 C - 150
PSI LOSS PER 100 FEET OF PIPE (PSI/100 FT)
Sizes //" thru 3V4"
Flow GPM t thru 600
SIZE
050
075
1.00
1.25
1.50
2.00
2.50
3.00
3.50
SIZE
OD
0.840
t 050
1.315
t 1 .660
1.900
2.375
2. a? 5
3.500
4.000
OD
ID
0716
0894
1.121
1.414
1.618
2.023
2.449
2982
3.408
ID
WALL
0.062
079
0-097
0.123
0.141
0.176
0.213
0259
0296
WALL
THK
THK
U. CD
E 0-'
> LU
vt
, J f>
w a
a_ _i
> u,'
a.' I
a> ^-.
> U.
nJ i
> uJ
W a
a." i
> u,"
a,' _i
01 Q-
> U.
a.' ~i
s-
> uJ
i
ex. i
> LU
', tfl
V*
a. _J
3 oJ
> LL.
eu -J
o &-
iZ to"
1
2
3
4
5
0.79
1 59
2 38
3.18
3 97
22
78
1 65
2.82
4 26
0.51
1.02
1.53
2.04
2.55
07
27
0.56
0.96
1.45
0.32
0.64
0.97
1.29
1.62
02
09
19
0.32
48
20
0.40
0.61
O.81
1 02
01
0,03
06
O 1O
O 16
0.15
31
46
0.62
77
00
O1
O3
05
OS
0.19
0.29
0.39
49
0,00
01
002
003
0.20
0.27
34
0.00
01
01
022
000
1
2
3
4
5
6
7
e
9
1O
-AJ.1
5.57
636
7.16
7.95
5 97
~7.9S
10 18
12 66
15 38
3.06
3.57
4.08
4 59
5.l6~
2.03
2.70
3.45
4.30
" 5 22
1 94
2,27
2,59
2 92
3.24
0.67
0.90
1.15
1.43
1 74
1 22
1.42
1.63
1 83
2 04
O 22
0.29
37
46
56
0.93
1.O9
1.24
1 40
1 55
0.1 1
0.15
0.19
0,24
29
59
69
0.79
89
099
04
05
0.06
08
O 10
0.40
0.47
0.54
0.61
G8
02
02
03
0.03
004
027
0.32
0.36
0,41
45
0,01
0.0 1
0.01
01
0.01
O 24
O28
31
O35
00
01
0,01
0.01
6
7
8
9
to
1 t
12
14
16
IB
8.75
9 55
11 14
12.73
14,32
18.35
21 56
2S.&9
36.74
45 69
5.61
6.12
7.14
(J.16
9.18
6.23
7 32
3.74
12.47
IS 51
3 57
3 89
4,54
S.1<f
5.84
2 07
2.43
3 24
4 15
5 16
2 24
2 44
2.85
3 26
3 67
67
0,79
1 OS
1 34
1 67
1,71
1.8?
2.18
2 49
2 BO
35
0.41
Q 54
70
0.87
1,09
1 19
1 39
1.59
1.79
O.12
0.14
18
023
29
74
0.81
0.95
1.08
1.22
0,05
0.05
O 07
0.09
0.12
0.50
0.55
0.64
0.73
82
0.02
002
0.03
0.04
004
0,38
042
0.49
0.56
0.63
0.01
01
01
0.02
002
1 1
12
14
16
18
20
22
24
2G
28
15.91
17,50
19.10
55 54
66 26
77.84
10.20
11.23
12.25
13 27
14.29
18.86
22.50
26 43
30 65
35.16
6.49
7.79
B 44
9 09
6 27
7 18
8 79
1O 39
11 C9
4 Ofl
4 48
4_B9_
5 30~
5 71
2 03
2 42
2 84
~3 29
3 7B
3.11
3.42
3 74
4.05
4 36
1.05
1,25
1,47
1.71
1 96
1 99
2,19
2 39
2 50
2 79
35
042
50
58
66
1.36
1.49
1 53
1 76
1 9O
14
0.17
O20
023
026
91
1.00
1.10
t.19
1.28
005
06
ooa
09
10
0.70
077
84
91
98
03
0.03
04
05
O.OS
20
22
24
26
28
3O
35
40
45
5O
15 31
17 86
39.95
53.15
9.74
11.36
12.90
14 61
16.23
13 29
17.68
22 64
28 IS
34 2?
6 12
7.14
8 16
9 1fl
10,20
<t 29
3 71
7 31
9 10
1 1 OG
f 4 - CV
5745"
6.23
7.01
7.79
2.23
" 2 96
3.80
4.72
5.74
2 99
3 40
393
4,48
_-L90.
75
1 DO
1 28
I 59
2 04
2 38
2 72
3,06
3.40
O30
039
O51
O63
0.76
1.37
1.6O
t.83
2.06
2 29
0.11
0.15
0.19
0.24
0.29
.OS
22
.40
58
.75
OG
08
10
0.13
15
3O
35
40
45
50
55
65
70
75
17.85
19.40
4O 83
47 97
11 22
12.24
13 26
14.28
JJ5 30
13 19
IS 50
17.97
20.G2
23 43
8.57
9.35
10.13
10.90
J_l 63
6.85
8.O4
9 33
10.70
12.16
5.48
5 90
648
6 97
7 47
2 31
2.71
3.15
3 61
,_ 4,10
3.74
4 08
4 42
4,76.
S 10
O91
1 07
1 24
1 42
~ 1 62
2 52
2.75
2.98
3.21
3 44
0.35
041
0.48
0.55
0.62
1 93
2.10
2 28
2.45
2 63
Q.1D
021
025
029
032
55
60
65
70
75
80
85
90
95
100
16 32
17 34
18.36
19 38
26.40
29 54
32 84
36.30
12.46
13 24
1-1 02
14 80
15.58
13.71
16.33
17.05
18.84
20,72
7 97
8 47
8.97
9 47
9 96
4 t>2
5.17
5.75
6 35
6 99
E 44
5.78
6 12
G.4Q
6 80
1 82
2.04
2 27
2 5J
2 76
3 67
3.89
4.12
4.35
-4*58.
Q.70
0.7 B
OC7
0.96
_jjifi
2.81
2.98
3.16
3 33
3 51
037
041
045
50
0.55
80
85
90
95
1OO
1 10
120
130
140
150
17.14
18.70
24.72
29.O4
10 96
t 1.96
12 96
13 95
14 95
8 34
9,79
1 1 36
13 03
14 81
7.48
8,16
8 84
9,52
1070
3 29
3 83
4 48
5 14
5.84
5.04
5.50
5.96
6.42
6 88
1.26
1.48
1.72
1 97
2 24
3 86
4 21
4,56
-A2L
5 26~
66
077
090
1.03
" 1 17
110
120
130
140
150
160
170
180
190
200
15 95
16.94
17.94
18 94
19 93
16.69
18,67
20.75
22 94
25.23
1088
11 56
12 24
12.92
13 60
6 59
7 37
8 19
9 O5
9 95
7.34
7.79
8.25
8.71
9.17
2 53
283
3.14
3.47
3 82
5.62
5.97
6.32
6.G7
7.02
1 32
1.48
1.64
1 99
160
170
180
t9Q
200
225
250
275
300
325
15 30
17 00
18.70
12 'J8
15.O5
17.95
1O.32
1 1.47
12.01
-1 75
5.77
6.89
7.90
8.7B
9.66
2 49
3,01
360
225
250
275
350
375
4OO
425
450
470
5OQ
550
600
Velocity below dotted 1
C-7
SIZE
OD
10
WALL
THK
0.50
0.8-10
0.622
0.109
0.75
1.050
0.824
0.113
Table C-5
FRICTION LOSS CHARACTERISTICS
PVC SCHEDULE 40 IPS PLASTIC PIPE
(1120, 12201 C = 150
PSI LOSS PER 3 00 FEET OF TUBE (PSI/100FT)
Sues '/" thru 3'/i"
Flow GPM 1 thru 600
1.00 J.25 1.50 2.00 250
1.315 1.660 1.900 2.375 2.875
1.049 1.380 1.610 2,067 2469
0.133 0.140 0.145 0,154 0.203
3.00
3.500
3.068
0.216
3.50
4.000
3.548
0.226
SIZE
00
lt>
WALL
TKK
>s
IX
ul ej
'i"
"5 &-.
> u.
l/i 3
0. _J
&
s
S Q-.
> u.
3
a. -J
&
i
"B Q-.
> u.
3
0. _J
>
1
"a 0-,
> u-
; vt
"I a
a. I
2r
3">
5 a-.
> u.
:8
a. -J
84
-5*-.
> u-
vt
3
a. -J
r
si
"oJ -,
> U.
w o
a. -i
&
3">
"5 -.
> u.
(/) S
&.' -i
5-
'I"i
~aj ~.
> u-
S
o. _J
3 2
O tL-
U, C3
i
2
3
4
5
0.93
1 86
2.79
3.72
*A&&
0.32
1,14
2.42
4.13
-&?i
60
1.20
1.80
2.40
3 00
11
0.39
034
1.42
2 15
0.37
0.74
1.11
1.4S
1.85
0.03
0.12
0.26
0.44
0.66
21
0.42
0.64
085
1,07
0.01
0.03
0.07
0,12
0.18
15
0.31
0.47
0.62
0.78
0.00
0,02
003
05
OS
0.19
028
0,38
047
00
01
02
02
020
0.26
33
00
0.01
01
021
00
t
2
3
4
!i
6
7
8
g
10
5,58
6.51
7.44
8.37
9.30
8.75
11,64
14.90
T8.54
22.53
3,60
4.20
4 ao
5,40
6.00
3.02
4.01
5 14
~6.39~
7.77
2.22
3.59
2.96
3,33
3.70
0.93
1.24
1.59
1.97
2 40
1.2S
1.49
1.71
1.92
2.14
0.25
0,33
0.42
0,52
63
94
1.10
1.25
1.41
1.57
12
0.15
0.20
025
0.30
0.57
0.66
0.76
0.85
095
03
0.05
06
07
09
040
0.46
0.53
060
66
01
0.02
02
0.03
0.04
0.26
30
0.34
0.39
0.43
01
001
01
0.01
01
025
0.29
0.32
00
0.01
001
G
7
Q
9
10
1 1
12
11
16
18
10.24
11.17
13,03
14.89
16.75
2.6.88
31 58
42.01
53.80
6692
6,60
7.21
8. 41
9.61
10.B1
9.27
10.89
14.48
18.55
23.07
4.07
4.44
~5.19~
5.93
667
2 86
3.36
4.47
3.73
7.13
2.35
2.57
2.99
3.42
3.85
0.75
0,89
1 18
1,51
1 88
1.73
1.88
2.20
2.51
2,83
0,36
0.42
0.56
71
039
1.05
1.14
1.33
1.52
1.71
0.11
0.12
0.17
021
26
073
080
093
1 07
1 20
004
005
07
0.09
11
0.47
0.52
0.60
0.69
0,78
002
02
02
03
OO4
035
0.38
045
0.51
058
0.01
0.01
0.01
0.02
0.02
1 1
13
14
1C
IS
20
22
24
26
28
18.61
81.34
12.01
13.21
14.42
15 62
16 S2
28,04
33.45
39.30
45 SB
52 28
7.41
8.15
8.39
9.64
10 38
8.G6
33
2.14
4 08
<j 15
4.28
4.71
5.14"
5.57
Ej 99
2.28
2_72
3 2O
3.17
4,25
3,14
3,46
3.77
4 09
4.40
1 08
1 29
1 51
1.7b
2 01
1.90
2.10
2.29
2.48
2.67
032
38
045
52
60
1.33
1,47
1.60
1 74
1 87
0.13
0.16
0.19
072
25
0.86
0.95
1.04
1 12
1 21
0.05
0.06
0.07
08
09
064
0.71
0.77
0.84
090
0.02
003
0.03
04
04
2O
22
24
26
2B
30
35
40
45
BO
18.02
59.41
1 1.12
12.97
14.83
16.68
18.53
8. 35
24.42
31.27
38.89
47 27
6.42
7.49
S,56
9.G4
0.71
4 S3
6 43
8.23
0.24
2.4S
_4_72
sTBo
6.29
7.08
7 87
2_?8
3.01
3.89
4,84
5.88
2.86
3.34
3.81
4.29
-4*11
68
090
1.15
1 43
.JUZ4.
2 00
2.34
2.67
3.01
3.34
029
38
49
0.60
73
1 30
1.51
1.73
1.95
2.16
10
0.13
17
0.21
26
097
1.13
1.29
1.45
1 62
0,0!3
00
0.00
o to
0.1-1
ao
35
4O
45
5O
55
60
65
70
75
1.78
3.85
3.92
4.99
6 06
4.85
7.45
20.23
23.21
26,37
8,65
9.44
10.23
11.01
11.80
7.01
8.24
9.56
10,96
12.46
5.25
5.72
6.20
6.68
7.16
2.08
2,44
2.83
3.25
3.69
3.68
4 01
4 35
_4.6_.
5.0?
0.88
1.03
1,19
_ LPZ.
~ 1.56
2 38
2.60
2 81
3 03
3.25
30
0.36
41
0.48
54
1.78
1.94
2.10
2.26
2,43
0,15
0.13
0.20
23
27
55
GO
C5
7O
75
80
85
90
95
100
7.13
18.21
19.28
29.72
3326
36.97
12 59
13.37
14.16
14,95
15.74
14.04
1571
17 46
19.30
21 11
7 63
8.11
8.59
9.07
9 54
4.15
4 66
5.18
5.72
6 29
5 35
5,68
6.02
6 35
6 6Q
1.75
1,96
2 18
2.41
2 65
3.46
3.68
390
4.11
4 33
0,61
063
76
084
092
2.59
2.75
2.91
3.07
3 24
0.30
34
0.3?
0.41
45
SG
85
HO
as
1OO
17,31
18.88
25.32
29.75
10 SO
11.45
12.41
13.36
14 32
7.51
8 82
10.23
11 74
13 33
7 36
8 03
8.70
9.37
1O 03
3 16
3 72
4,31
4.94
5 62
4.76
s"3o
5 63
6.06
6 50
1 10.
' 1,29
1.50
1.72
1 95
3.56
3.8S
421
4.53
h^*L5.
O.S4
0,04
74V
Q,BS
^QjSiL,
1 10
120
I3O
MO
ISO
15.27
16 23
17.18
18 14
19 09
15 03
1681
18 69
20 6S
22.72_
10.70
11.37
12.04
12 71
13 3S
6 33
7 08
7 87
8 70
9 r i7
6 93
7 36
7 80
8 23
H 66
2 20
2 46
2 74
3.02
3 33
5.18
5.50
5.83
6 15
6.48
1.0&
1 21
1.35
1.40
1 64
160
170
130
190
2OO
15 OS
Ib73
18 40
1 1 90
14 4/
17 26
9 75
1083
1 1 92
13 00
14 08
4.14
f i 03
6 00
7 05
8.17
7 29
8.10
8.91
9.72
10 53
2.04
2.4B
2 96
3.-17
-1.03
725
750
275
300
3? 5
15 17
16 25
17,33
18,42
19.50
9.38
10 65
12.01
13.43
14 93
1 1.34
12.15
1296
1377
14 58
4.62
5 23
592
6.62
7 36
350
375
4QO
12$
4 SO
15.39
16 20
17.82
19,44
8,14
3,95
10.67
12.54
4J5
500
550
600
ocity below dotted line exceeds 5 fps
C-8 "
Table C~6
FRICTION LOSS CHARACTERISTICS
PVC SCHEDULE 40 IPS PLASTIC PIPE
(1120, 1220) C = 150
PSI LOSS PER 100 FEET OF TUBE IPSI/IOOFT)
Sizes A" thru 12"
Flow GPM 1 thru 600
SIZE A 00 5.00 6.00 8.OO 10.00 12.00 SIZE
OD 4.500 5 563 6 625 8.625 10.750 12,750 OO
ID 4.026 5.047 6.065 7.981 10.020 11.814 ID
WALL 0237 0.258 0.280 0.322 0.365 0.406 WALL
THK THK
*s
O O-
U. U
r
':
3 Q-.
> u-
W g
0. 1
r
'ii
s *-.
> u_
58
a. i
r
S
"S> -.
>u-
Xfl
f 3
a. i
&
"I"?
"53 &
> u.
fl
i
W
0. _J
e-
'g?
"3 &-.
> u.
H. tf,
in g
a. J
-*
'gn
T5 H
> u.
la
Crt o
0- -J
15
U. C2
1
2
3
4
5
1
2
3
4
5
6
7
8
9
10
6
7
8
9
10
11
12
14
16
18
0.30
35
4O
045
000
01
001
001
1 1
12
14
16
18
20
22
24
26
28
5O
0.55
0.60
0.65
070
0.01
001
02
002
002
0.35
D 38
O.41
0.44
000
001
0,01
01
20
22
24
26
28
30
35
40
45
50
0.75
0.88
1.0O
1.13
1.25
0.03
0.04
04
006
07
0.48
O 56
0.64
0.72
080
01
01
01
002
02
38
44
049
55
00
01
0.01
01
30
35
40
45
50
&5
60
65
70
75
1.38
1 51
1.63
1.76
1 88
0.08
10
0.11
0.13
14
O.B8
O.96
1.04
1 12
1.2O
0.03
03
004
0.04
05
061
66
0.72
0.77
033
O.O1
O1
02
O.O2
O2
0.44
0.48
O.OO
O1
55
60
65
70
75
80
85
90
95
100
2.01
2,13
2 26
2.39
2 51
10
18
020
022
025
1.28
1.36
1.44
1 52
1.6O
05
0,06
007
007
08
0,38
0.94
0.99
1.05
1 10
O.O2
0,O2
03
03
0.03
0.51
0.54
0.57
0.60
64
O1
OO1
O.O1
0.01
O.O1
80
85
90
95
100
110
120
130
140
150
2.76
3 02
3.27
3.52
377
029
034
040
46
52
1.76
1.92
2.08
2.24
2 40
1O
1 1
13
15
17
1 22
1 33
1 44
1 55
1 6G
O.&fl
005
O5
06
007
070
0.76
0.83
0.89
096
O1
01
01
O2
02
0.52
0.56
O.6O
0.00
01
01
110
120
130
140
150
160
170
ISO
19O
200
4.02
4.27
4 53
4 78
-5 03
59
56
0.73
081
" 089
2.56
2,72
2.88
3.O4
3.2O
0.20
22
24
O 27
30
1.77
1.88
1 99
2,10
2 21
008
OD
10
1 1
12
1.02
1.O9
1.15
1.21
1.28
02
02
03
03
03
0.65
O.69
O.73
0.77
0.01
01
0.01
01
01
01
O.5S
00
160
170
1BO
190
2OO
225
250
275
300
325
5.66
6.29
692
7.55
B 18
1 10
1 34
1 60
1.88
2.18
3.GO
4 OO
4 40
4. SO
""351
37
4!)
0.53
0.63
" 0.7T 1
2.49
2.77
3.05
3,32
3 60
15
18
22
26
30
1.44
1.60
1.76
1.92
2 OS
O.O4
05
0.06
O7
08
0.91
1.01
1.11
1.21
.32
01
02
02
02
03
O.65
0.73
0.80
0.87
0.95
0.01
O.O1
0.01
0.01
01
225
250
275
300
325
350
375
400
425
450
8 81
9.43
10.06
10.69
11 3?
2.50
284
3 20
3.58
3.18
5.6O
6.00
G 40
6.80
7 2O
0.83
095
1 07
1 19
1 33
3.88
4.15
4,43
4.71
-i*aa
0.34
39
0,44
40
-JliM
2.24
2.40
2.56
2.72
2 S3
O.O9
10
0.11
0.13
14
.42
,52
.62
.72
,82
0,03
0.03
O 04
04
05
1.02
1.09
1.16
1.24
1.3T
0.01
O.02
02
O.02
0.02
350
375
400
425
450
475
500
550
60O
11.95
12. 5&
13.84
IB. 10
4,40
4 8d
5.77
6,78
7.6O
8.0O
8.80
9 61
1 46
1.61
1.93
2 26
5,26
5.54
6,10
6.65
O.GO
66
79
0.92
3 04
3 20
3 52
3 84
1G
0.17
21
24
.93
2 03
2.23
2.43
0,05
06
07
08
1.38
1.46
1.60
1.7S
O.02
0.03
0.03
O.O4
475
5OO
S50
600
Velocity below dotted line exceeds 5 fps
C-9
Table C-7
SIZE
OD
ID
WALL
THK
4.00
4,500
4026
0237
FRICTION LOSS CHARACTERISTICS
PVC SCHEDULE 40 IPS PLASTIC PIPE
11120, 1220) C= 150
PSI LOSS PER 100 FEET OF TUBE (PSI/1QOFT)
Sim 4" thru 12"
Flow GPM 650 Ihru 5000
500 600 800 10.00
5563 6625 8625 10750
5047 60G5 7981 10020
258 2SO 322 365
1200
12750
11 814
0406
SIZE
00
ID
WALL
THK
>-
-J
>
>.
>
>.
5?
'I
i
- in
1 t/i .
isi
|w
i
_J
I.
~ v-i
5 5 '
tt;
~Z o-
vt 3
M -
W>
"ai <*-. *
"i a
-S Q-
in S
3 o-.
(A a
"3 o.
to S
oa.
U- 13
> u-
a. ~i > LL,
a 1
> u. (
X. -J
> U.
D, 1
> U.
, _J
> u.
a.' -*
U. (j
650
TFJRT"
V5iTTTcr<iT "
~2T2"
"7^20""
ToT
4 1G
28
2 64
09
1 90
04
650
700
17,62
9 02 11.21
3 00
7,76
1 23
-1 48
32
2 84
1 1
2 04
05
700
750
18 87
25 12.01
3 41
8 31
1 dQ
_4_ao
37_
3 04
12
2 19
O 05
750
800
2.81
3 S5
8 87
1 57
5.12
41
3 25
14
2 33
06
800
850
3 61
4 30
9 42
1 7G
5 44
046
3 45
15
2 48
007
850
900
4 41
4 78
9 ya
1 96
5 70
51
3 65
17"
2 63"
08
300
950
5 21
5 29
1O 53
16
G.08
57
3 86
19
2.77
03
950
1000
6 O1
5 81
11 O9
38
6 40
OG3
4 06
21
2 92
09
1000
1050
16 &1
G 3G
1 1 64
60
6.72
0.68
4 26
23
3 06
10
1050
1 1OO
17 61
6 94
12.20
84
7 CM
075
4 47
25
321
1 1
1100
1 150
1S.42
7 53
12,75
OS
7 36
81
4 67
27
3 36
12
1150
1200
1.3.22
8.15
13.31
3,1
7 68
088
4 87
29
3 GO
0,13
12OO
1250
1
13.06
60
a oo
095
5 07
31
3 65
14
1250
1300
14.41
8/
a 32
1.02
5 28
0.34
3 80
15
1300
1350
M.97
1C
8 G4
1 09
5 48
36
3 94
16
1350
140O
15.52
44
a.96
1 17
5 68
39
4 09
17
1400
1150
16. oa
73
9 28
1 24
5 89
41
4 23
18
1450
1GOO
16 G3
04
9 60
1 33
6 O9
44
4.38
20
1500
1550
17 19
36
9 92
1 41
G 29
47
4 53
21
1550
1SOO
17 74
r>n
21
I 49
6 50
49
4 67
22
1600
1650
IS 30
01
56
i ba
6 70
0,52
4 82
a 23
1650
1700)
IB 85
jj
oaa
1 67
6 90
5fa
5 96
0~25
1700
1750
19 41
70
I 20
1 76
7.11
SB
5 11
26
1750
1800
TO 96
Oil
1 52
1 86
7,31
61
5 26
0.28
1800
1850
1 R4
1 95
7 51
65
5 40
029
1850
1900
2 17
2.05
7 72
GS
5 55
30
1900
1950
12.49
2.15
7 92
71
5 70
32
1950
2000
12 81
2 26
a 12
75
5 84
33
2000
21 DO
13 45
2 47
8 53
02
G 13
037
2100
22001
14 09
|_2 69
8 94
89
6 43
40
2200
2300
14 73
2 92
3 34
0.97
6.72
43
2300
240O
15 37
3.1G
9.75
1 05
7.01
047
2400
2SOQ
16
3 <1
10 15
1.13
7.30
051
2500
2600
16 C
3 57
10.56
1 21
7 GO
54
260O
2700
17 2
394
10 97
1.30
7 39
53
2700
2800
17 9
4 2
1 1.37
1 39
a, 18
062
2800
2000
IB 5
4 43
1 I 78
t 49
8.47
67
2900
3DOQ
19 2
4 73
12.19
1 58
8.76
0.71
3000
3100 |
19 8
508
12.59
1 68
9 06
75
3100
32OQ
13 00
1 78
9.35
080
3200
3300
13.4
1 89
9.64
085
3300
3400
13.8
1 99
9 93
89
3400
3500
14 2
2.10
1023
094
3500
3600
14,6
2 22
10.52
0.99
3600
37 OO
15
2 3
10 81
1 05
3700
3800
15 4
2 4
1 1.10
1.10
3800
3900
15 8
2 5
11 40
1,15
3900
4000
16.2
2.6
11.69
1.2
4OOO
4100
16.6
2 8
11.98
1 27
4100
4200
17.0
2.9
12 27
1,32
4200
4300
17.4
30
12.56
1.33
4300
44OO
17.8
3.2
12.86
1 44
4400
4500
18.2
3 3
13.15
1.5
4500
46OO
18.6
3.4
13.44
1.57
4600
4700
19.09
3.6
13.73
1 G
4700
4aoo
19,5
3.7
14 03
1.6
4800
4900
199
3.9
14.32
1.7
4900
5000 I
14.61
1.8
5000
Ibcity below dotted line exceeds 5 fps
C-10 , ,
Table C-8
SIZE
050
075
1 00
OD
0840
1 050
1.315
ID
0.54 G
0742
0957
WALL
THK
0147
0.154
179
FRICTION LOSS CHARACTERISTICS
PVC SCHEDULE 80 IPS PLASTIC PIPE
(1120, 12201 C = 150
PSI LOSS PER 100 FEET OF TUBE (PSl/100 FT)
Sires Vi" thru 3%"
Flow GPM 1 thfu GOO
1 25 1 50 2 00 2.5Q
1 660 1 9OQ 2375 2.075
1 278 I 500 1 939 2.323
191 200 218 027G
3.00
3.500
2.900
0.300
3.50
4.000
3361
0318
WAL
TH
a-
e-
r
."
fr
-
-
fr
5 **
W
V
o w *
*** \f,
^
' u.
o ^
*' .-
'a ^
S to
_.
'u ^
to
'5 in
^ s
0-
S a.
"5 fc-
W a
*S D-'
to S
~S> a-"
X* ""
V) o
"3 aJ
c/j
"3 -L
[/) O
"3 **T
to o
"eJ ^
t/3 S
"3 -
. j *fl
to o
_o a
u_ O
> u.
a.' ~J
> u.
D. -J
> U-'
1
> u."
0, _J
> U."
al -i
> 11-
a. i
> u.
a.' J
> U-
Cu 1
"> u-
a. -J
u- c:
I 36
OB
74
18
O 44
05
024
01
O 18
01
Q.5O
o.oo
i
A
2 73
2 92
1.48
66
O 89
O 19
49
05
O 36
02
0.21
0.01
15
00
I
4 10
6 19
2 22
1 39
1.33
40
74
D 1O
54
O O5
32
0.01
"022
0.01
4
5.4 T
"10 54
2 96
2 37
1 78
69
99
17
0,72
00
43
02
30
0.01
t
684
1593
3,70
3 5EI
2 22
1 04
1 24
2G
9O
12
0.54
0.03
37
01
24
00
6
8 21
22 33
4 44
5 02
2 67
1 46
1 49
36
1 OS
1G
0.65
0.05
15
D2
29
01
l
7
9 58
29 71
" 5.1S'
G 6l7
3 11
1 94
1,74
47
1 2G
22
75
06
52
O3
33
001
0.25
OO
8
1094
38 05
5,02
8 5G
3 56
2 4E
1.99
G1
1 45
2fi
86
03
GO
O3
0.30
001
0.28
01
1
9
12 31
47 33
6 66
10 64
4.00
3 0-J
2 24
7G
1,63.
35
97
10
G8
O4
0.43
01
32
01
10
13 68
57 52
7,41
12 93
4 45
L _3_7JS
? 49
92
1 81
42
1 O3
12
75
O5
4B
0?
0.36
Ol
1i
11
15 05
68 G3
8 15
15 43
4 90
4 47
2 74
1 10
1,99
5O
1 19
14
083
D 06
53
O 02
0.39
01
1
12
16 42
RO 63
B 89
18 13
5 34"
~ "b 26
2 99
1 20
2.17
59
1 30
17
O90
O7
0.5Q
0,02
0.43
Ol
1
14
10 37
24.12
6 23
6 99
3 49
1 71
2 53
70
1.51
23
1 05
O9
0.67
03
050
OO2
1
16
1 1.85
30 88
7.12
8 95
3 99
2 19
2 90
01
1 73
29
1 2O
1 12
077
Q 04
0.57
O 02
1
18
13 33
33 41
B 01
11 \A
4 49
273
3 26
1 25
1 95
3G
1 36
O 15
87
05
64
02
1
20
14 B2
46 69
S 90
13 54
4 39
3 31
3 62;
1.52
2 17
44
1 51
O IB
97
06
72
O 03
2
22
16 30
55 70
9 80
16 15
5 49
3~95
3 9EJ
1 81
2 38
52
1.6G
O 2?
1 O6
0.07
79
0.04
2
24
17 78
65 44
1O 69
18 97
5 99
4.64
4 35
2 13
2.60
61
1.81
O 25
1.16
09
86
04
2
26
19.26
75 9O
11 Sfl
22 Ol
6 49
5 39
4.71
2 47
2 B2
71
1.96
O 29
1 26
0.10
93
05
2
28
12 47
2524
699
G 18
5.07"
283
3 03
81
2 11
O 34
1 35
0.11
1 00
06
2
30
13, 3G
28 09
7.40
7 O?
5.41
3 22
3 25
92
2 25
0.3S
1 45
13
1 OB
06
3
35
15 59
33 16
8 74
9 34
6 34
4 29
3 79
1 23
2.64
0.51
1 69
17
1 26
ooa
3
40
17 81
40 07
9 99
11 90
7 25
fa 49
4 34
1 57
3.02
G5
1 94
022
1 44
11
4
45
11 24
14 as
8.16
6 P3
4 BS
1 90
3.40
O 81
2.18
0.2 B
1 62
13
4
50
12 49
18 09
9 O6
6 30
5 42~
~ 2 JJET
1 78
O 99
2 42
34
1 80
16
tt
55
13.73
21.55
9.97
9 90
9G
2 84
4.15
ma
2,66
0.40
1 98
19
c.
60
14 98
25 35
10.87
11 63
6 51
3 3J
4.53
1.3B
2 91
47
2.16
0.23
t
65
16 23
20 40
11.78
13 40
7 05
3 87
4.91
1.61
3 15
55
2 34
27
e
70
17 48
33 72
12. GO
IS 47
7 59
4 44
5.29*
1.84
3 39
63
2 52
0.30
-,
75
IB 73
38 32
13 50
17,59
8.13
5 04
5.67
2.O9
3.63
071
2.7O
35
-
80
1998
43 19
14 50
19 81
S.Gfi
5.G8
6 O4
2.36
3.88
80
2 BB
39
t
85
15.41
22.16
D.22
6.3G
6.42
2.63
. 12
090
3.06
44
f
90
16 32
24 64
9.76
7.07
6.80
2.93
4.36
1 00
3.24
O 48
<
95
17 22
27 23
10.3O
7 01
7,10
3 24
4.60
1.10
342
OS4
i
100
18 13
29 95
10 85
8 59
7.56
3 57
4 fl 1 )
_JL2J_
360
59
1i
1 10
19 94
35 73
11 93
10 25
8 31
4.25
5 33
1.45
3 96
0.7O
1
120
13 O2
12. 04
3 07
5 OO
5.82
1.70
4.32
0,62
I 1
130
14 10
13 9G
9 82
5 GO
6.30
1.97
4 6d
96
1
140
15 19
16 02
10.5B
6 G5
6 79
2.27
~5"O4~
~ 1.1O
1
150
16 27
IS 70
1 1.34,
7 56
7 27
2 57
5 40
1.25
160
17 36
20 51
12.09
8 51
7 7G
2 89
5 76
1.41
1
170
10 44
22 95
12.85
9 53
8 24
3.24
6 13
1.57
1
180
19 53
25 51
13.6O
IO 59
8.73
3.60
6,48
1.75
1
190
14.36
1 1.71
9 21
39B
G SB
1.93
1
200
15.12
12.87
9 7O
4 37
7 21
2 12
225
17.01
16.01
10 91
5 44
8,1 1
2.64
2
250
18.90
19.4G
12.12
6 G)
9.01
3.21
2
275
13,34
7 89
9 91
3 83
2
300
14.55
9 27
1081
4.5O
3
325
1 15.76
10 75
5 22
350
16 97
12 33
12.61
5 99
;
375
18.19
14 01
13.52
6,8,1
;
400
19.40
15 79
14 42
7 57
I
425
15.32
a 58
t
450
16.22
9.54
i
475
17.12
1O.54
l
500
18.02
11.51
l
550
19.82
13,83
i
6OO
(
Velocity below dotted line exceeds 5 fps
C-11
Table C-9
FRICTION LOSS CHARACTERISTICS
PVC SCHEDULE 80 IPS PLASTIC PIPE
(1120, 1220) C - 150
PSE LOSS PER 100 FEET OF TUBE (PSI/100 FT)
Sues 4" thru 12"
Flow GPM 1 thru 600
SIZE 4 CO 5 00 6 00 8 00 10.00 12.00 SIZE
OD 4500 5563 6625 8.625 10.750 12.750 OD
[D 3,826 4813 5.761 7.625 9 564 11 .376 ID
WALL 337 0,375 0.432 500 593 687 WALL
THK THK
j3
U. C3
> uJ c
n a
1- 1
3 a! t
> u_ e
^ o
L -i :
-
1 ^.
> U-
'o
s
OO O 01
oJ -i >
-.
u. c
V>
fl n
I.' -1
j
E -,
a u.
CL. ~1
3 o-!
> u.
x -J
ll
1
2
3
4
5
'
1
2
3
4
5
6
7
B
9
10
0.27
00
6
7
8
9
ID
11
12
14
16
18
0.30
0.33
0.39
0.44
0.50
0.01
0.0 U
001
Oil
001 0.31
OO
11
12
14
16
18
20
22
24
76
28
55
&1
66
O 72
78
HI 02 O 35
O.O2 38
O,02 042
03 0.45
03 0.49
001
01
01
01
OQ1
1!
20
22
24
26
28
30
35
40
45
50
O 83
0.97
1.11
1.25
1.39
03 1 0,52
O.Ob 0.61
0.06 0.70
007 0.79
009 088
Gl
001
OO2
002
O3
0361 OOOl
0.43 001
O.49 001
055 001
0.61 001
30
35
40
45
50
5&
60
65
70
75
1.53
1.67
1,81
1 95
2.09
0.10 096
0,12 1.05
0,14 1.14
0.16 1 23
018 1 32
O.O3
O.Q4
0.05
05
06
0.67 001
0.73 002
O.79 O2
0.861 002
092 003
0.45
4
5
000
001
01
55
60
65
70
75
80
85
90
95
too
2.22
2,36
2.50
2.64
2 78
021 1.40
0.23 1 40
026 1.58
0,29 1.67
031 1.76
0.07
008
0.08
0.09
0.10
0.98 O.O3
1.04 003
1.10 004
1,16 004
1.22 004
0.5
OS
06
0.6
0.7
0.01
0.01
001
001
001
80
85
90
95
100
110) 3 O6
120 3.34
130 362
140 390
150 4 18
0.30 1 93
0.44 2.11
051 2.28
59 2.46
0.67 2 64
0.12
0.14
0,17
IS
o 2:
1 35 0.05
1.47 O.OG
1.59 007
1.72 O.OB
1 84 0.09
7
0.8
0.9
9
1
01
02
02
02
02
4
0,5
0.5
062
0.66
0.00
001
01
01
01
110
120
130
140
150
160 4.45
170|_4.73
180|~~5.01
19O 5.29
20O1 6.51
0.75I 2.81
^ 0_8jlj 2.99
"O.ail 3.1]
"1.031 3.3^
1 14J 35'
2
2E
3
0.3
3
1 96 10
2.08 Oil
2.21 013
1 2.33 0.14
? 245 0,16
1.1
1.1
1 2
1 3
1.4
Of
o^;
00.
00-
00'
071
0,75
o.ac
0.84
0,8$
001
01
01
01
0.56
0.59
0.63
00
0.0
160
170
180
190
200
225 G.2]
250 6.9E
275 7 6(
300 8 3
375 9.0
1.41 3.9
> 1,72J 4 4
> 2.05L 4.8
i 2.4ir52
5 2.79 S.7
0.46 2 761 0.191
56 3.O7 023
.Q.GTl 3 3S| 023
O.TOI 3 &8 Q 33
o.gil 3991 nnal
1.55
1.7E
1.9'
2.1
2 2
e-o
00
) 01
1 0.1
,QC
.1
.2:
.3
3 4
) 0.02
02
o o;
) o.o:
> n.o:
0.70
0,78
0.86
0.94
1,02
0,0
0.0
225
250
275
300
325
350 1 9.7
375|1Q.4
400n 1.1
425 1 l.B
450 1 12.5
5 3.20 6.1
6 36.1 6.6
4 4.10| 7.O
4 4.59 7.4
* 5 1 Q| 7 9
1.0
1,1
1.3.
1 &
1,6
5 4.301 044'
9 4.60 0.50
4 4 91 1 56
of"5~2"2T 0.63
7 5.531 n.?n
2 4
2.6
2,8
2.9
3 1
S 0,1
3 1
3 1
3 1
5 O.t
1 .5
3 .6
4 ,7
5 8
3 20
i 0.0-
? o <y
3
3 00
3 00
.10
.18
> .26
> .33
3 41
0.0
0.0
0.0
350
375
400
425
450
47SJ13.2
500 13.9
550 15.3
6OOU6.7
3 5
3 6
2 7
2 9
641 8.3
20 8,8
4Q| 9.6
.691 10 E
i a
2 r
2 4
2 S
5 5,
3 6.
2 6.
4 7.
831 077
14 035
7G 1 01
37l 1.19
3 3
3 5
38
4 7
3 02
02
5 02
1 3
2.1
2 22
6 2.4
2.6
1 00
3 00
5 O<
7 1
r .49
J ,57
3 .73
3 89
0.0
0"
475
500
550
60O
Velocity below dotted line exceeds 5 fps
'C-12'
Table C-10
SIZE
OD
ID
WALL
THK
FRICTION LOSS CHARACTERISTICS
PVC SCHEDULE BO IPS PLASTIC PIPE
(1120, 1220) C - 150
PSI LOSS PER 100 FEET OF TUBE (PSI/100 FT)
Sizes 4" thru 12"
Flow GPM 650 thru 5000
4,00 5.00 6 00 S 00
4,500 5.563 6625 8625
3.826 4813 5761 7.625
0337 0375 0-132 0500
1000
12,00
SIZE
10750
12.750
OD
95G4
11.376
ID
0.593
O.G87
WALL
THK
IS
U- CD
s*i
E o-
> u.
:
n- -i
fr
'">:
"3 0;
> u.
^ 8
a, _J
r
S
~Z ~i
> u.
u\ o
D 1
S"
3 o-
> uu
:S
ex. i
fr
i
3 n-.
> U-
S
0. _I
r
'i
"5 o-.
> u.
S g
e 1
s?
o a.
U. IS
650
700
750
800
850
Te-ir
19.51
Tooa"
11.56
(n^
12 32
13 20
14.09
14 97
hrso"
3.78
4.30
4 85
S 42
-7^9"
6.60
9.21
9 83
10 44
~T5r
1 58
1 79
2.02
2 26
4.56
4.91
5.26
5 61
5 96
35
4O
"6". 4 6
52
58
2.89
3,12
3 34
3.56
3.79
12
0,13
0,15
0.17
0.1D
2.O4
2.20
2.36
2.52
2 67
05
0&
O,07
07
08
660
7OO
750
BOO
850
900
950
1000
1050
1100
1585
16.73
17.61
18 49
19 37
G.03
6 66
7.33
8 02
8 74
1 1 06
11 57
12 29
12 90
13 52
2 51
2,78
3,05
3 34
3 6-1
6 31
6.G6
7.O1
7.36
7 71
0,64
0.71
078
085
93
4.01
4.23
4.46
4.68
-4&U.
21
24
2G
0.28
IL3J.
0.34
3G
39
42
O 45
2 83
2,99
3.15
3 31
3 46
O 09
O 1O
11
13
O 13
900
950
1000
1050
1 100
1150
1200
1250
1300
1350
14 13
1475
15,36
15.98
16 59
3 96
4 28
4 62
4.97
5 33
8 Q7
8 42
8 77
9.12
9 47
1 01
1 O9
1.18
1.27
1 3G
5.12
5.35
5.67
6.79
6-O2
3 62
3.78
3.94
4,09
4 25
O,14
16
17
o.ia
0.19
1150
1200
1250
1300
13SO
1400
1450
1500
1550
1600
17.21
17.82
18.43
19.05
19.66
5 70
e. cm
6.47
6 B8
7.29
9 02
10 17
1O 52
10.87
11 22
1 46
1.55
1 65
1 76
1 06
6,24
6.46
6.69
6 91
7.13
0.48
62
55
O.5B
0.62
4.41
457
4.72
4.B8
B.O4~
0.21
0.23
0.24
0.25
~0.2 7
1400
1450
15OO
1550
160O
1650
1700
1750
isoo
1050
11.57
11 92
12 28
12.63
12.98
1.97
2.O9
2. 2O
2.32
2 44
7.35
7 58
7 BO
a 02
B 25
0.56
0.69
0.73
0.77
81
5.20
5.35
5 51
5.57
5 33
0.28
0.30
O.31
0.33
0.35
165O
1700
175O
1800
1850
1900
1950
2000
2100
2200
13 33
13 68
14.03
14.73
15 43
2 56
2.69
2.82
3 OS
3.36
8 47
8.69
8.92
9.36
9.81
0.8S
0.89
0.94
1.O2
1.12
5.99
6.14
6 3O
6 62
6 93
0.37
038
40
44
48
1900
1950
2000
2100
220O
2300
2400
2500
2600
2700
16 14
16.84
17.54
1B.24
18 94
3.65
3 95
4. 26
4.G8
4.91
10.25
10 70
11.15
11.59
12 O4
1.21
1.31
1.42
1.52
1.63
7.25
7.56
7. 88
8.19
8.51
0.52
S6
0.61
0.65
O 7O
2300
2400
2500
2 GOO
27OO
2800
2900
3000
3100
3200
19.64
6,26
12.48
12 93
13 38
13 82
14 27
1.75
1 86
1 98
2.11
2.24
8.82
9.14
9.45
S.77
10.08
O 75
0.80
0.85
91
O 96
28OO
2900
3000
3100
3200
3300
3400
3500
3600
3700
14 71
15.16
15.61
16.05
16.50
2.37
2.50
2.64
2.78
2 93
10.40
10 71
11,03
1 1.34
11.66
1.02
1.03
1.13
1.20
1.26
3300
3400
3500
360O
3700
3SOO
3900
4000
4100
4200
1G.94
17.39
17.84
18.28
18.73
3.07
3 22
3 38
3,54
3.70
11 98
12.29
12,61
12.92
13.24
1.32
1.39
1.45
1.52
1,50
3800
3900
4ODO
4100
4200
4000
4400
4500
4600
4700
19.17
19.62
3.86
4.03
13.55
13.87
14.18
14,50
14,31
1 G6
1.73
1.G1
1 88
1.96
430O
4400
4500
4 600
4700
4800
4900
5000
15 13
15,44
16,76
2.04
2.12
2.30
48OO
49OO
5OOO
Velocity below dotted line exceeds 5 fps
C-13
Table C-11. Friction loss in feet per 100 feet in asbestos cement
pressure pipe
Flow
(gallons _
per
minute)
Nominal pipe diameter in inches--
4
6
8
10
12
I.D. = 3.95 ]
[.D. = 5.85 I
.D. = 7.85 ]
[.D. = 10.00
I.D. = 12.00
100
0.677
From Scobey
's formula
120
.954
trl. 9
140
1.28
H f -
v v
"R -1 '
160
1.65
~ u
180
2.06
200
2.53
0.372
wnere Hf = head loss in 1000 feet
220
3.03
.447
of pipe
240
3.56
.525
K s ~ roughness coefficient ^
260
4.16
.611
0.32
280
4.77
.705
300
5.44-
.803
V = velocity in feet per
320
6.16
.910
second
340
6.91
1.02
D = inside pipe diameter
360
7.70
1.14
in feet
380
8.54
1.26
400
9.4O
1.39
0.324
420
10.3
1.52
.355
440
11,3
1.66
.389
460
12.3
1.81
.423
430
13.3
1.96
.458
500
14.4
2.12
.495
550
17.2
2.55
.594
600
20.3
2.99
.701
0.214
650
23.7
3.49
.818
.249
700
27.3
4.02
.935
.287
750
31.1
4.57 1 1.07
.328
800
5.18 (" 1-21
.370
0.152
850
5.81
1.36
.415
.170
900
6.46
1.51
.464
.190
950
7.17
1.68
.511
.210
1000
7.91
1.85
.564
.232
1100
9.45
2.21
.675
.278
1200
11.2
2.62
.800
.328
1300
13.0
3,04
.932
.384
1400
15.0
3.50
1.07
.438
1500
17.1
3.99
1.22
.502
1600
19.3
4,52
1.38
.566
1700
5.06
1.55
.637
1800
5.67
1.73
.710
1900
6.26
1.91
.787
2000
6.90
2.11
.864
2200
8.27
2.53
1.04
24OO
9.75
2.98
1.23
2600
11.4
3.47
1.43
2800
13.1
4,00
1.64
3000
14.9
4.56
1.87
Velocity of values below dotted line exceed 5 fps
C-14
TABLE C -12.
PRESSURE (FRICTION) LOSS, IN FEET PER 100 FEET, FOR PORTABLE
ALUMINUM IRRIGATION PIPE WITH COUPLINGS. (BASED ON SCOBEY'S
FORMULA K S = 0.40, AND 30-FT. PIPE LENGTHS.)!/
Gallons
Per
Minute
Pipe Dianie tiers
3-in. OD
2.914 ID
4-in. OD
3.906 ID
5-in. OD
4.896 ID
6-in. OD
5.884 ID
7-in. OD
6.872 ID
8-in. OD
7.856 ID
10-in. 01
9.818 ID
40
50
.658
1.006
.157
.239
60
1.423
.339
70
1.906
.449
.150
ao
2.457
.584
.193
90
J . 7 3
.731
.242
100
3.754
. 89 3
. 295
.120
120
5.307
1.2GJ
.417
.170
140
7 . U 3
1 . 69 i
.560
. 2?7
]60
9 . Id 9
2.182
. 721
.293
'80
11.47
2. 12 9
.967
.366
200
U.01
3 ."333
1.102
.468
.209
2?0
16.79
3. ( )96
1 . 321
.537
.251
240
19.81
4 . / 1. i
1.5 Mi
.633
.296
200
23.06
5.4JU1
1 .814
.737
.344
2 80
25.55
6.316
2.0 By
.849
.397
300
30. '2 I
/.203
2.381
.967
.452
.235
320
14. 22
8.142
2.692
1.094
.511
.265
340
38.39
9,1 37
3.0?0
J .227
.573
.298
3 60
42.80
10.18
3.366
1.368
.639
.332
380
4 / . 4 3
1 1. , 29
3. / n
J .516
.708
.368
400
!i2.28
12.44
4.113
1.671
.781
.399
.136
420
13.65
4.513
J .833
.857
.445-
.149
440
14,57
4.930
1.988
.936
.486
.163
460
16.23
5.364
2. J 79
1.019
.529
.177
.
480
17.59
5.815
2.363
1 . 104
.573 I .192
500
19.01
6.284
2,554
1.193
.620 .208
550
22.79
7.532
3.060
1-430
.742 .249
600
26.88
8.886
3.611
1.687
.876 .2-94
650
31.30
10.35
4 . 204
1.965
1.020 .342
700
36.03
11.91
4.839
2.262
1.174 .394
750
41.08
13.58
5.517
2.520
1.339 _| -449
800
15. 35
6.237
2.915
1.513
,507
850
17.22
6.999
3.271
1.698
.569
900
19.20
7.80L
3.646
1.893
.635
950
21.28
8.645
4,041
2.097
.703
1000
23.45
9.530
4.454
2.312
.775
1100
28,11
11.42
5.338
2.771
.929
1200
31.75
13.53
6.298
3.269
~I7096
1300
15.69
7.333
3.806
1.277
1400
18.06
8.441
4.382
1.470
1500
20.59
9.264
4.996
1.675
1600
23.28
10.88
5.648
1.894
170Q
26.12
12,21
6.337
2.125
1800
13.61
7.064
2.369
1900
15.08
7.829
2.625
2000
16.62
8.630
2 . 894
V For ZO-ft pipe lengths, increase values
" lengths, decrease values by 3,0 percent
exceed 5 fps. - *-
in the table by 7
Velocity of val
.0 percent
ues below
For 40-ft
dotted line
Exhibit C-l
FLEXIBLE IRRIGATION HOSE
PRESSURE LOSS PER 100 FEET OF LENGTH
g
o 4
t-t
01
Cu
CO
(U
6.0
5.0
3-0
2.0
0,0
500
400 600
Gallons per Minute
300
1000
C-16
Table C-13
FRICTION LOSS CHARACTERISTICS
POLYETHYLENE (PE) SDR-PRESSURE RATED TUBE
(230S, 3206. 3306) SDR 7, 9. 11 5, 15 C = 140
PSI LOSS PER 100 FEET OF TUBE IPSI/100 FT)
Sizes 1/2" thru 6"
Flow GPM 1 iluu 1800
SIZE
050
075
1 00
1 25
1 50
2OO
2 50
3.00
400
600
OD
0000
0000
0000
0000
0000
0000
0000
O.OOO
0000
0000
ID
0622
0824
1 049
1 380
1 610
2067
2469
3 0GB
4.026
60G5
WALL
0000
0000
0000
0000
0000
0000
0000
0000
000
0000
THK
3^
> 0.
U, (J
>-
1 w
>
!
*-
"3^
>.
4--
S^
>
|w
>.
!
>
!
>
Sw
>-
<~"
"s
s-
S w
"S ^
> u.
ts\
a 1
a> -.
> U.
w
Q. _J
"3 -
> u.
W o
0. -1
~. <*-,
> u.
f> 3
o_ i
"3 o.
> u_
c/i a
0,' 1
**-.
> u.
s
0. _J
3 ^
> u.
v\ o
Cl 1
3 &-
> u.
V> o
a." J
0"
> Li.
ui a
Q. J
15 <*-.
> u.
^ S
Q- J
1
2
3
A
5
1 05
2 10
3 IB
1 21
5 27
49
1 76
3 73
6 35
9 60
60
1 20
1 80
2 40
3 00
12
45
95
1 62
2 4.1
37
74
1 1 1
1 48
1 S5
04
14
79
50
75
21
42
64
85
1 07
01
04
08
13
2Q
15
31
47
62
78
00
02
04
o oe.
09
09
19
2B
38
47
00
01
01
02
03
a so
02G
33
O 00
01
o 01
2 1
O 00
6
7
a
9
10
6 32
7 38
B 43
9 49
1054
13 46
17 91
22 93
28 52
34 67
3 GO
4 20
4 80
~5~40~
6 00
3 43
4 5G
5 84
7 26
8 82
2 22
2 59
2 96
3 33
3 70
1 OG
1 41
I 80
2 24
2 73
1 28
1 49
1 71
1 92
2 14
028
37
<17
059
72
94
1 10
1 25
1 41
1 57
13
18
22
O 28
O .14
57
GG
75
085
095
04
05
07
ooa
10
4O
046
053
GO
66
O 0?
02
03
03
O 04
26
Q 30
Q 34
39
43
01
01
001
01
001
1 1
12
14
16
18
1 1 60
12 65
14 76
16 87
1898
41 36
48 60
04 65
82 79
0297
6 00
7 21
8 41
9 61
10 81
10 5J
12 37
16 46
21 07
2G21
4 O7
4 44
5,19~
5 93
6 67
3 25
3 82
5.08
6 51
8.10
2,35
2 57
2 99
3 42
3 85
OBG
1 01
1 14
1 71
iZOi
1 73
1 08
2 20
2.51
2 83
o .10
48
G3
O 81
1 01
1 OS
1 14
1 33
1 b?
1 71
12
M
19
24
30
073
000
093
1 07
1 20
O 05
O 06
o aa
O 10
O 13
47
Q i32
Q GO
69
Q 78
002
002
OO3
04
04
27
O 30
3b
O 40
O 45
OO
Ql
01
01
01
20
22
24
26
28
12 01
13 21
14 42
15 62
16 82
31 86
38 01
44 65
41 /9
59 41
7 41
8 15
8 89
9 64
10 38
9 84
1 1 74
1J /9
16 00
13 35
A 28
4 71
5 14*
S.57
S 99
2 59
3 09
~ 3 63
421
1 R3
3 14
3.46
3 77
4.09
4 40
1 22
1 4G
1 72
1 99
2 2B
1 90
2 10
2 29
2 40
2 67
36
43
51
L.9
OR
1 33
1 47
J CO
1 74
1 87
15
IS
O 21
25
Q 29
06
95
1 04
1 12
I 21
005
006
07
oay
10
O 5O
O 55
GO
65
7O
01
02
02
02
03
30
35
40
45
50
10 02
67 50
1 1 12
12 97
14 83
16 6fl
18 53
20 85
27.74
35 53
44 19
-S3J_L
5 42
7.49
B. 56
9.64
JJL7JL
1 1 78
12.85
13,92
14 99
16 OG
5 49
/ 31
9.36
1 1 64
J444-
16 R7
10 82
22 99
2G 'J7
-zaaz.
33 7 f
37 /9
42 01
4 72
~5~50
6 29
/ 08
7 87
2- L>9
3 45
4 42
5 50
6.G8
2 8G
J 34
3 81
1 29
~diIZ,
77
1 02
1 31
1 tiJ
-JU2B.
2 00
2 34
2 67
3 01
3 34
32
43
55
69
81
1 30
1 51
1 73
1 95
2 1G
1 1
Q 15
o ig
^4
?0
75
88
1 00
1 1 3
25
03
04
05
OG
OB
33
0.38
44
0.49
55
a o
00
55
60
65
8 G5
9 44
10 23
1 1 01
1 1 (10
7 97
9 3G
10 86
12 46
1<) 16
5 25
5 72
6 20
6 68
7 If.
2 3,6
2.V8
3 22
3.S9
4 ?0
3 GO
4 Ol
4,35
4 68
5 Q1~
00
17
3G
5G
77
J 38
2 GO
3 81
3 OJ
3 25
035
41
47
54
fil
33
51
63
76
80
09
1 1
13
14
a ir>
U,Q 1
0.66
72
077
0.83
00
o o
00
flow GPM 650 (hru 1800
SIZE 400 600
OD 0000 0000
ID -1 026 6 065
WALL 0000 0000
H-IK
17 13
10 21
19 20
12 59
13 37
14.16
14.95
15 7rt
15 95
17 85
19 84
21 93
24 12
7 G3
8 1 1
B 59
9 07
9 "34
4 73
5 29
5 BO
6 50
7.15
5.35
5 68
6 02
6.35
6 69
1 99
i. 71
2. 48
274
3 01
3 4G
3 58
3 90
4 1 1
4 33
O.G-9
o n
(Jfi
005
1 O'j
2 01
2 13
2 26
2 39
2 '31
o is
21
23
025
28
83
94
9<i
1 05
1 10
o a
0,0
OG
C
G'oO
700
750
800
850
16 36
17 G2
18 87
8 94
10 2G
I 1 65
7 20
7 7B
8 31
a 87
9 42
1 22
1 40
1 59
1 79
2 00
17 31
IB 88
28 77
33 8O
10 50
11.45
12 41
13.36
14 32
8 53
10 02
11 62
13 33
15 15
7 3(i
8.03
8.7O
9.37
10.O3
3 59
4.22
4 90
S 62
6 30
4 76
S,20~
S G3
G 06
6 50
1 25
~ T4T
1 70
1 95
2 22
2 76
3 02
3 27
3 52
3 77
33
39
045
52
59
1 22
1 3)3
1 44
1.55
1 66
C
oc
o.c
o,c
C
900
950
1000
1050
1 100
9 93
10 53
1 1 09
1 1.64
12 20
2 22
2 46
2 70
2 96
3,22
15.27
16-23
17 18
10.14
19 O9
17 Ofl
19 11
21 24
23, 4U
25 81
10.70
11.37
12 04
12 71
13.38
7 19
8 05
8,95
939
1O87
6 93
7 36
7.08
B.23
8 66
2 50
2 80
3 11
044
3 78
4 02
4 27
4 53
4 78
5 03
067
75
003
OQ2
1.01
1 77
1 88
1 99
2. 10
2.21
t
1
1
1
1 150
1200
1250
1300
1350
12 75
13 31
13 86
14 41
14 97
3 50
3,79
4 09
4 39
4.71
15.05
16,73
18 40
1352
1G 44
1061
9.75
10 83
1 1 92
13 00
14 08
4 10
5 7 1
C>82
B 01
9 29
5.66
G.29
692
7 55
8 18
1.25
1 52
1 82
2.13
2 48
2 49
2 77
3.05
3.32
3.60
1
o
IdOQ
1450
1500
1550
1600
15 52
16 08
16 63
1 / 19
17 74
5 04
5 38
5 73
6 09
6 45
15 17
16.25
17.33
18 42
19 50
10 65
12.10
13 G4
15 26
16 97
0,8 t
9.43
10 06
1O 69
11.32
2 84
3 23
3 64
4 07
4 52
3 88
4,15
4.43
4 71
l 33
t
'
'
-&J
1650
1700
1750
1800
18 30
is as
19 41
19 96
683
7 22
7 62
B.03
1 I 95
12 58
13B4
15 10
5.OO
S SO
6.56
7 7O
5 26
5.54
6.10
6.65
o.
o.
o.
1.
C-17
Exhibit C-2. FRICTION LOSS IN POLYETHYLENE PIPE
1000-
BOQ-
600-
400-
30D--
200-
too.
80-
EO
40-
30
HEAD Loss Vs FLOW RATE
FDR WATER AT 60" F
NATIONAL POLYETHYLENE PIPE
20"
10- -
A
A
y\
\
XI
\
\
A
S
A
- 418
03 Dfi
D3 * OS
O
I .04-
A
y
\
-\
.03
CRITICAL
\
.OZ
FLOW
.ot
.DOB
.006
.tXM
.003
S
Si
LAMINAR
V
FLOW
L
\
A
ZONE
N
.002-
.001.
V
J . 3 jj
< 5 6 7 8 ,IQ IS ZO
FLOW RATE IN GALLONS PER MINUTE
C-18
30
SO
Table C-14
FEEDER LINE FRICTION LOSS {PER 100 FEET)
34 i BOO 101
13 1 580 ID)
JB i 3)5 ID'
Flow in
GPH
CPM
Fuel ion
Lou
mm.
Wlncuv
fin
Sc
Flo.sm
GPH
Flo i .n
GPM
Fuclion
lou
in Pll
VHociiv
F.ti
Sic
Flowut
GPH
flow in
GPM
Fnclicm
Loit
in |iii
Vlldritv
fl.l
SKC
30
OEO
005
o 3a
'B
030
00'
037
CP
001
0001
no3
J?
070
007
15
4
10
OH
OJP
\ P
001
DPP-
OOP
JB
QUO
008
Obi
m
P5P
PI'
Pl'l
30
OC&
f -
P '6
W
00
10
M
i'
Ou(l
p;3
07J
I'P
10
T
(i -n
GO
00
o n
(11.4
-
70
Pll
ff-'
i?P
0?l*
o:~
P''S
CO
'0
IS
o :o
J8
I'SO
P4p
Pl>
IPO
Oil)
054
OS7
7!
>o
n ve
77
4
"n
050
IP
r-io
HJO
O'V
1 li>
78
JO
0?1
R1
I'd
on
POP
?:
300
050
1 3"
i -i;>
84
40
0?4
Ofin
l<
"p
P'?
34
3C-0
CPU
1 "5
i "i
$0
'.0
0?7
01G
!?
n o
OP&
JC
4TP
70
?!'0
r c,i
JIG
liO
0.10
0?
'c
30
ppa
5S
ipfl
CBO
333
r :
to?
1 70
OJ4
0"
81
IP
1 1?
?0
b*P
0"Q
-l M
r 11"
iflfl
1 HO
03?
15
10
5P
I:Q
32
BOO
1 OCl
so:
:v
111
1 HO
11
?l
If.
*>0
i Jj
95
EGO
1 ID
a 39
j i' 1
i;o
?OD
OJ5
:a
IQ:
70
i PI
307
7?0
130
7D5
343
12G
2 ID
050
14
108
BO
1 7f
1 10
760
1 30
a n
3 ;;
133
3:0
064
-10
in
510
118
331
BJO
1 41)
930
J Pii
US
230
050
17
wo
?0
3 17
3-14
DOO
ISO
IOC5
A 15
144
?40
OC4
53
i?a
? 10
23Q
JEG
OGO
1 GO
1?00
4FJ
ISO
J 50
Of"
on
132
1 X
2EO
JOB
10?
1 70
13-13
1 D3
ISO
3 BO
JJ
130
138
?3n
2 a?
3 HO
IOBO
1 CO
IJ PI
5 32
10:
370
71
72
114
3 10
305
?13
U4
ISO
16 ![>
&Q1
1GS
780
85
71
ISO
350
3 3d
104
1300
300
IB 13
&30
174
? 90
OPR
H5
l EG
3 GO
353
1 16
mo
TOO
01U
01
1Q3
3 70
370
338
mo
1 10
0?
1 OB
IPit
3 no
UID
341
19;
370
OH
704
174
3 10
433
3 S3
19B
130
15
? 11
iflO
300
4 CO
1G5
304
140
21
? 17
inn
.1 10
4(10
a?7
3io
310
2B
223
n?
3 30
5 10
JBO
310
3 CO
Tj
330
mn
330
541
403
323
370
W
330
IDA
J40
D1!Q
4 13
KB
3 HO
.11
?42
310
3 r iO
13
-1?E
234
300
IG
3 fin
JIG
3 TO
G-15
.137
J4Q
400
G4
355
?32
370
G 7fi
440
?4G
4 10
71
2G3
??ii
3 no
7 13
OI
20?
430
7il
?G8
?34
300
74B
473
358
1 30
B7
374
?IO
4 00
7&1
4H5
2fi4
4-40
%
2fll
270
450
?04
287
?7G
460
? 13
304
?B?
4 JO
331
3 CO
2BB
4 HO
??(!
ao<i
2H4
4 HO
?38
3 13
300
600
3-17
3 10
30fl
& 10
357
335
31?
530
3 GO
133
31B
630
J7G
338
331
640
3BS
145
330
550
305
151
338
r j GO
305
157
343
5 70
3 15
304
i4a
580
a 30
370
3!i4
500
T3fi
,170
3GO
GOO
341
38J
3GG
10
3&B
,180
372
030
3r.a
J96
178
010
1)9
10?
JB4
40
311
10H
300
r>5G
10?
1 10
3DG
060
1 14
431
40?
C 70
4?5
I3B
408
060
437
434
4U
GOO
440
140
4?Q
TOO
>U1I
443
476
7 10
1 H
153
432
120
4 Hli
4"i7
43B
30
4 UK
IG(>
44-)
740
611
.1 U
4t,0
700
5?4
1 71
ISC
;co
5 1'
185
4S3
1 70
5M1
101
4G8
78(1
51.1
108
474
7(10
57'
504
480
800
500
{. 10
C-19
o
o
r
-H
4-
t/l
O
o
ro
Of
O.I
0.2
0.3 0.4 a5 1.0
Flow Rate, Q, gpm
3.0 4.0 5.0
10
Exhibit C-3. Friction head loss as a function of flow rate for lateral tubing
manufactured 1n English dimensions.
020
O.I
0.2 0.3 0.4 0.5 0.7 I.O 2.0 3,0 4,0 5.O 70
Flow Rate , Q, gpm
10
Exhibit C-4. Friction head loss as a function of flow rate for lateral tubing
manufactured in metric dimensions.
C-21
FRICTION HEAD LOSS AND VELOCITY IN u.ouu <mu u.u*.*. ,. ..
(For Drip Irrigation Laterals)
Hf In PSI Per 100 Feet; V in Feet Per Second
Accumulated Head Loss Based on 1-GPH Emitters Spaced 5 Feet On Line
Table Cased on Hazen-Williams Equation - C * 130
Q
GPH
I.D. - 0.580"
I.D. - 0.622"
Line
Length
Ft
GPM
Hf
V
Accum.
H f
Hf
V
Accum.
Hf
1
,017
.0004
.02
.0003
.02
5
2
.033
.0015
,04
.0001
.001
.03
10
3
.050
.003
.06
:0002
.002
.05
.00015
15
4
.067
.005
.08
.0005
.004
.07
.0004
20
5
.083
.008
.10
.0009
.006
.09
.0007
25
6
.100
,011
.12
.0015
.008
,11
.0011
30
7
.117
.015
.14
.002
.011
.12
.0015
35
8
.133
.019
.16
.003
.013
,14
.002
40
9
.150
.024
.18
.004
.017
.16
.003
45
10
,167
.029
.20
.006
,020
,18
.004
50
11
.183
.034
.22
.007
.024
.19
.005
55
12
.200
.040
.24
.009
.028
.21
.007
60
13
.217
.047
.26
.012
.033
.23
.008
65
14
.233
.053
.28
.014
.038
.25
.010
70
15
.250
.060
.30
.017
.043
.26
.012
75
16
.267
.068
.32
.021
,049
.28
.015
80
17
.283
,076
.34
,025
.054
.30
.017
85
18
.300
.085
.36
.029
.060
.32
.020
90
19
.317
,094
.38
.034
.067
.33
.024
95
20
.333
.10
.40
,038
.073
.35
.027
100
21
.350
.11
..42
.04
.080
.37
.03
105
22
.367
.12
.45
.05
.088
.39
.04
no
23
.383
,13
.46
.06
.095
.40
,04
115
24
.400
.14
.49
.06
.10
.42
.04
120
25
.417
.16
.51
.07
.11
.44
,05
r~125
26
.433
.17
.53
.08
.12
.46
,06
130
27
.450
.18
.55
.09
.13
,47
.06
135
28
.467
.19
.57
.10
,14
.49
.07
140
29
.483
.20
.59
.11
.15
.51
.08
145
30
.500
.22
.61
.12
.16
.53
.09
150
C-22
1 of 5
Table C-15 (con't)
FRICTION HEAD LOSS AND VELOCITY IN 0.580" and 0.622' 1 PLASTIC HOSE
(For Drip Irrigation Laterals)
Hf in PSI Per 100 Feet; V in Feet Per Second
Accumulated Head Loss Based on 1-GPH Emitters Spaced 5 Feet On Line
Table Based on Hazen-Williams Equation - C = 130
Q
GPH
Q
GPM
T.D. - 0.580"
I.D. - 0.622"
Line
Length
Ft
Hf
V
Accum.
Hf
Hf
V
Accum.
Hf
31
.517
.23
.63
.13
.17
.55
.09
155
32
.533
.25
.65
.14
.17
.56
.10
160
33
.550
.26
.67
.16
.19
.58
.11
165
34
.567
.28
.69
.17
.20
.60
.12
170
35
.583
.29
.71
.19
.21
.62
.13
175
36
.600
.31
.73
.20
.22
.63
.14
180
37
.617
.32
.75
.22
.23
.65
.16
185
38
.633
.34
.77
.23
.24
.67
.17
190
39
.650
.35
.79
.25
.25
.69
.18
195
40
.667
.37
.81
.27
.26
.70
.19
200
41
.683
.39
.83
.29
.28
.72
.21
205
42
-?nn
. / u^
/i i
. T I
OC
* U
01
. 1
on
~TA
* ~
00
1_ L,
210
43
.717
.43
.87
.33
.30
.76
.24
215
44
.733
.44
.89
.35
.31
.77
.25
220
45
.750
.46
.91
.38
.33
.79
.27
225
46
.767
.48
.93
.40
.34
.81
.29
230
47
.783
.50
.95
.43
.36
,83
.30
235
48
.800
.52
.97
.45
.37
.84
.32
240
49
.817
.54
.99
.48
.38
.86
.34
245
50
.833
.56
1.01
.51"
.40
.88
.36
250
51
.850
.58
1.03
.54
.41
.90
.38
255
52
.867
.60
1.05
.57
.43
.91
.40
260
53
.883
.62
1,07
.60
.44
.93
.43
265
54
.900
.65
1.09
.63
.46
.95
.45
270
55
.917
.67
1.11
.66
.48
.97
.47
275
56
.933
.69
1.13
.70
.49
.98
.50
200
57
.950
.71
1.15
.73
.51
1.00
.52
285
58
.967
.74
1.17
.77
.53
1,02
.55
290
59
.983
.76
1.19
,81
.54
1.04
.58
295
60
1.000
.79
1.21
.85
.56
1.06
.60
300
C-23
2 of 5
FRICTION HEAD LOSS AND VELOCITY IN 0.500" and 0.622" PLASTIC HOSE
(For Drip Irrigation Laterals)
Hf in PSI Per 100 Feet; V in Feet Per Second
cumulated Mead Loss Based on 1-GPH Emitters Spaced 5 Feet On Line
Table Based on Hazen-Williams Equation - C = 130
n
o
I.
0. - 0.58
0"
T.
D. - 0.62
2"
4
PH
GPM
Hf
V
Accum.
Hf
Hf
V
Accum.
Hf
Length
Ft
1
1.017
.81
1.23
.89
.58
1.07
.63
305
2
1.033
.83
1.25
.93
.59
1.09
.66
310
3
1.050
.86
1.27
.97
.61
1.11
.69
315
4
1.067
.89
1.29
1.02
.63
1.13
.72
320
5
1.083
.91
1.31
1.06
.65
1.14
.76
325
6
1.100
.94
1.33
1.11
.67
1.16
.79
330
7
1.117
.96
1.35
1.16
.69
1.18
.82
335
8
1.133
.99
1.37
1.21
.70
1.20
.86
340
.9
1.150
1.02
1.40
1.26
.72
1.21
.90
345
1.167
1.05
1.42
1.31
.74
1.23
.93
350
1
1.183
1.07
1.44
1.36
.76
1.25
.97
355
'2
1.200
1.10
1.46
1.42
.78
1.27
1.01
360
'3
1.217
1.13
1.48
1.47
.80
1.28
1.05
365
'4
1.233
1.16
1.50
1.53
.82
1.30
1.09
370
'5
1.250
1.19
1.52
1.59
.85
1.32
1.13
375
'6
1.267
1.22
1.54
1.65
.87
1.34
1.18
380
7
1.283
1.25
1.56
1.72
.89
1.35
1,22
385
'8
1.300
1.28
1.58
1.78
.91
1.37
1.27
390
'9
1.317
1.31
1.60
1.85
.93
1.39
1.31
395
JO
1.333
1.34
1.62
1.91
.95
1.41
1.36
400
1.350
1.37
1,64
1.98
.97
1.42
1.41
405
1 -}7
1 an
1.66
2.05
1.00
1.44
1.46
410
1.68
2.12
1.02
1.46
1.51
415
1.70
2.20
1.04
1.48
1.56
420
1.72
2.27
1.07
1.49
1.62
425
36
1.433
1.53
1.74
2.35
1.09
1.51
1.67
430
37
1.450
1.56
1.76
2.42
1.11
1.53
1.73
435
38
1 .467
1.60
1.78
2.50
1.14
1.55
1.78
440
89
1.483
1.63
1.80
2,59
1.16
1.56
1.84
445
Qfi
l Knn
i ^.n-,*-i.
1
1 . 3UU
I .00
.82
2.67
1.18
1.58
1.90
450
C-24
3 of 5
Table C-15 (con't)
FRICTION HEAD LOSS AND VELOCITY IN 0.580" and 0.622" PLASTIC HOSE
(For Drip Irrigation Laterals)
Hf ip PSI Per 100 Feet; V in Feet Per Second
Accumulated Head Loss Based on 1-GPH Emitters Spaced 5 Feet On Line
Table Based on Hazen-Williams Equation - C = 130
Q
Q
1.
D. - 0.58
0"
I.
D. - 0.6
22"
1
Line 1
GPH
GPM
Hf
V
Accum.
Hf
Hf
V
Accum.
H f
Length !
Ft. j
91
1.517
1.70
1.84
2.75
1.21
1.60
1,96
455 '
92
1.533
1.73
1.86
2.84
1.23
1.62
2.02
460
93
1.550
1.77
1.88
2.93
1.26
1.64
2.08
465 !
94
1.567
1.80
1.90
3.02
1.28
1.65
2.15
470
95
1.583
1.84
1.92
3.11
1.31
1.67
2.21
475
96
1.600
1.87
1.94
3.20
1.33
1.69
2.28
480 i
97
1.617
1.91
1.96
3.30
1.36
1.71
2.35
485 :
98
1.633
1.95
1.98
3.40
1.39
1.72
2.42
490
99
1.650
1.98
2.00
3.50
1.41
1.74
2.49
495 j
100
1.667
2.02
2.02
3.60
1.44
1.76
2.56
500 :
101
1.683
2.06
2.04
3.70
1.46
1.78
2.63
505 i
102
1.700
2.10
2.06
3.81
1.49
1.79
2.71
Sin !
103
1.717
2.14
2.08
3.91
1.52
1.81
2.78
515 ;
104
1.733
2.17
2.10
4.02
1.55
1.83
2.86
520
105
1.750
2.21
2.12
4.13
1.57
1.85
2.94
525
106
1.767
2.25
2.14
4.24
1.60
1.86
3.02
530
107
1.783
2.29
2.16
4.36
1.63
1.88
3.10
535
108
1.800
2.33
2.18
4.48
1.66
1.90
3.18
540
109
1.817
2.37
2.20
4.59
1.69
1.92
3.27
545
no
1.833
2.41
2.22
4.71
1,72
1.93
3.36
550
111
1.850
2.45
2.24
4.84
1.75
1.95
3.44
555
112
1.867
2.49
2.26
4.96
1.77
1.97
3,53
560
113
1.883
2.53
2.28
5.09
1.80
1,99
3.62
565 ;
114
1.900
2.58
2.30
5.22
1.83
2.00
3.71
570 i
115
1.917
2.62
2.33
5.35
1.86
2.02
3.81
575
116
1.933
2.66
2.35
5.48
1.89
2.04
3.90
580
117
1.950
2.70
2.37
5.62
1.92
2.06
4.00
585 i
118
1.967
2.75
2.39
5.75
1.95
2.08
4.09
590
119
1.983
2.79
2.41
5.89
1,98
2.09
4.19
595
120
2.000
_ i
2.83
2.43
6.03
2.02
2.11
4.29
600
C-25
4 of 5
FRICTION HEAD LOSS AND VELOCITY IN U.bUU" ana
(For Drip Irrigation Laterals)
H f in PSI Per 100 Feet; V in Feet Per Second
Accumulated Head Loss Based on 1-GPH Emitters Spaced 5 Feet On Line
Table Based on Hazen-Will iams Equation - C = 130
Q
GPH
Q
GPM
I.n. - 0.580"
I.D. - 0.622"
Hf
V
Accum.
H f
Hf
V
Accum.
H f
Lenath
Ft
121
2.017
2.88
2.45
6.18
2.05
2.13
4.40
605
122
2.033
2.92
2.47
6.32
2.08
2.14
4.50
610
123
2.050
2.97
2.49
6.47
2.11
2.16
4.61
615
124
2.067
3.01
2.51
6.62
2.14
2.18
4.71
620
125
2.083
3. OS
2.53
6.78
2.17
2.20
4.82
625
126
2.100
3.10
2,55
6.93
2.21
2.22
4.93
630
127
2.117
3.15
2.57
7.09
2.24
2.23
5.04
635
128
2.133
3.19
2.59
7.25
e.27
2.25
5.16
640
129
2.150
3.24
2.61
7.41
2.30
2.27
5.27
645
130
2.167
3.29
2.63
7.57
2.34
2,29
5.39
650
131
2.183
3.33
2.65
7.74
2.37
2.30
5.51
655
132
2.200
3.38
2.67
7.91
2,40
2.32
5.63
660
133
2.217
3.43
2.69
8.08
2.44
2.34
5.75
665
134
2.233
3.47
2,71
8.25
2.47
2.36
5.87
670
135
2.250
3.52
2.73
8.43
2.51
2.37
6.00
675
136
2.267
3.57
2.75
8.61
2.54
2.39
6.13
680
137
2.283
3.62
2.77
8.79
2.58
2.41
6.25
685
138
2.300
3.67
2.79
8.97
2.61
2.43
6.39
690
139
2.317
3.72
2.81
9.16
2.65
2.44
6.52
695
140
2.333
3.77
2.83
3.35
2.68
2.46
6.65
700
2.350
3.82
2.85
9.54
2.72
2.48
6.79
705
2,367
3.87
2.87
9.73
2.75
2.50
6.93
710
><->->
3.92
2.89
9.93
2.79
2.51
7.06
715
s ~7
2.91
10.13
2.82
2.53
7.21
720
2.93
10.33
2.86
2.55
7.35
725
10.53
2.90
2.57
7.49
730
0.74
2.93
2.58
7.64
735
0.95
2.97
2.60
7.79
740
'1.16
3.01
2.62
7,94
745
1.37
3.05
2.64
8.09
750
'-26 c f c
TABLE C-16
PRESSURE LOSS IN CENTER-PIVOT SYSTEM, psi
System
Length
Pipe
Size
"o
gpm at Pivot
300
400
500
600
700
800
900
1000
1100
1200
600
4"
5"
11
3.5
18
6
27
9
700
5"
6"
4.0
1.7
7
3
11
4.5
15
6
800
5"
6"
4.5
2.0
8
3.5
12
5
18
7
24
10
900
5"
6"
6V
5.0
2.3
9
4.0
14
6
20
8
27
11
7
34
14
10
1000
5"
6"
6V
5.5
2.6
10
4.5
16
6.5
23
9
30
12
8
38
15
11
19
14
1100
5"
6"
6V
6.0
3.0
11
5
17
7
25
10
6
33
13
9
42
17
12
21
15
26
18
1200
5"
6"
6V
12
5.5
3.5
19
7.5
5.0
27
11
7
36
15
10
19
13
23
16
28
19
35
23
1300
6"
fi 1 -"
0-2
7"
8
5.5
12
8
5
16
11
7
20
14
9
25
17
12
31
21
15
37
25
18
45
30
22
1400
6"
6V
7"
13
9
fi
17
12
a
22
15
10
27
19
13
33
23
16
40
27
19
48
32
23
1500
6"
6V
7"
18
13
q
23
16
11
29
20
14
35
24
17
42
28
20
51
34
24
1600
6"
6V
7"
25
17
12
31
21
15
37
26
18
45
30
21
54
3C
1700
6"
6V
7"
33
23
16
39
27
19
47
32
22
1800
6"
6V
7"
41
29
20
50
34
23
C-27
ACTORS CF) FOR COMPUTING FRICTION HEAD
LOSS IN A LINC WITH MULTIPLE OUTLETS
No
Outlets
F
Ho
Outlets
F
1
1.000
24
.372
2
.639
25
.371
3
.534
26
.370
4
.485
28
.369
5
.457
30
.368
6
.438
32
.367
7
.425
34
.366
8
.416
36
.365
9
.408
38
.364
10
.402
40
.363
11
.398
45
.362
12
.394
50
.361
13
.390
55
.360
14
.387
60
.359
15
.385
70
.358
16
.383
80
.357
17
,301
90
.356
18
.379
100
.356
19
.378
110
.355
20
.376
120
.355
21
.375
130
.355
22
.374
140
.355
23
.373
150
,355
C-28
Table C-18. Head Loss Coefficients for Fittings
and Special Conditions Where 11 = Ky
Nature of Resistance
Typical Value
K Remarks
Check Valve
3.0 - 10.0
Elbows
45
90
0.4
0.65
Entrance
Square
Projecting
Rounded
0.5
0.78
0.05
Gate Valve, Open
0.25
Globe Valve, Open
6.0
Sudden Contraction
0.4 v = velocity of smaller pipe
Sudden Enlargement
2
l- d l di & d? - diameter ol' small
2 and large pipe
2 respectively
Taper Reducer
0.25 v velocity oC smaller pipe
Taper Increaser
0.15 v velocity of smaller pipe
Tees or Crosses
Straight flow
Angle flow
0.10
1.50
Angle Valve
5.0
Foot Valve
0.8
Strainers - basket type
. yj
Table C-19
FRICTION LOSSES THROUGH PIPE FITTINGS IN TERMSOF
EQUIVALENT LENGTHS OF STANDARD PIPE
*
*
^
%
&
^
a
5
5
5
Size of Pipe
(Small Dia.)
(Inches)
Standard
Elbow
Medium
Radius
Elbow
Long
Radius
EJbow
45 Elbow
Tec
Return
Bend
Gate
Valve
Open
Globe
Valve
Open
Angle
Valve
Open
Length of Straight Pipe Giving Equivalent Resistance Flow ft
1/2
1.5
1 4
1 1
0.77
34
38
0.35
16
8.4
3/4
2.2
1 8
1.4
1
4.5
50
047
22
12.0
1
2.7
23
1.7
1.3
58
6,1
0.6
27
15.0
1-1/4
3.7
3.0
2.4
1.6
78
8.5
08
37
18,0
1-1/2
4.3
3.6
2.8
20
9.0
10,0
0.95
44
22.0
2
5.5
4.6
3.5
2.5
11.0
13.0
1.2
57
28.0
2-1/2
6.5
5.4
4 2
3.0
140
150
1.4
66
33.0
3
8.1
6,8
5 1
38
170
18.0
1.7
85
42.0
3-1/2
9.5
8.0
60
4.4
19.0
21.0
2.0
99
50.0
4
11.0
91
70
5.0
22.0
24.0
2.3
110
58.0
A 1/2
12.0
10.0
7,0
5.6
24.0
27.0
2.6
130
61.0
5
14.0
120
8.9
6.1
27.0
31
29
140
70.0
6
160
14.0
11.0
7.7
33.0
370
35
160
83.0
8
21,0
18.0
14.0
100
430
490
4.5
220
110.0
26.0
22.0
17,0
130
56.0
61.0
5.7
290
140
C-30
Exhibit C-5
HORSEPOWER REQUIRED TO PUMP WATER
u p 9pm x head
n r 3960 x eft
15
TO USE CHART: Start at value of How and move horizontal!/ lo line ol required pump head Fro*
vertically downward lo line of known or expected pump efficiency From ihis point move horizontal
read value Of required motor horsepower Next relef to Figure 20 and select standard molor size
than value obtained from Ihe chart
C-31
Number of days (F) X Hours per day (H)
0,5-
EXAMPLE:
Area irrigated = 40 acres
0.6 Depth of water to be applied = 2.5 inches
Area to be irrigated in 6 days of 15 hours
0.7-
each (6 XI5=90hours)
0.8
Then pumping capacity = 504 G P.M.
0.9-
400 nr
- 10
I.O
300
230-
200
1 5-
to
150
15-
UJ
x 123-
o
5
-100
45OO-T
4000-
-2.0 o ao-
o
-
~ 20
" n
-70 u
3000-
i S; 6 ^
5
2500-
2.3-
*. . *<
-50 5
25-
z "~~~t . -
y
2000-
N*"
nj 40-
, ._"-
cc
r^.o ^ 35-
oT" _1
_ 1500-
UJ
P30 D
o
- 3^
-30 ^
N"
13
; x.
3-5
I S 25-
-' I 35-
-1000
: a
UJ
-4.0 ^
Q-.
-20
N :
cc
- _ UJ
r40
t
: Q.
\
-800 5.
o
4.5
uJ
: a 15-
-5.0
\
i
in
-BOO *>
O
; a:
H ^
Ss
500^
X J
. vJ
-10
-6.0 9
400-
>^ u
~ aw>
6,5
-8
-350 \
-7,0 r
300-
V
-70
-6
-250 \
-8.0 5
^
-80
200-
X
-9.0
-4
-180 x
^90
160-
-too
-140
-IOO
120-
110-
-100
-120
130-
-140
150-
Rfernci;
Agricultural Enginflrmg, July 1951
Capacity Requirements For Irrigation Systems.
C-32
ffi
w
H
to
1
QJ H
M
P-i
H
H
O.
in
ooo
m
CX3
o
CO
rHHr-HiH
ca
tM -) rH *-\ rH rH
n eg
o
o
CN
(N H
rH r-H rH
o o
fN rH
r-I rH rH rH
r~~- o <) ro in m
(N i I i I i I rH rH
t-H rH
rH i-H
rH
O-HrH
CN
4-)
Wl IW
a> *-'
H 00
.-.; c
d -H.
..-I O
ui rj
a. c,
-T tO
-a- us CN o co m r-H
(N i-l i-H rH O rH rH
o
o o
COOOOmOOCOOOOOCOOOOOOOOOOOrH
cv!r^<r^^r-iro<run^^inv^a3u^^r^'jDr^aDr^co^coa-'rH x
XXWXXXXXXXXMXXXXKX^WXXXXXXO
oooooinoooooooooocoooocooooo
C-33
Table C-21
CENTER PIVOT SYSTEMS
TIME REQUIRED TO APPLY 1" GROSS APPLICATION (hrs/in.)
AND GROSS CAPACITY (in. /day)
'onal
Lateral
Length
Area *
Coverec
(acres)
Hours Per 1" Application (Col. 1)
Groaa Capacity in In, /day (Col. 2)
400 grrai
600 spm
800 .gura
1000 ?pm
12CO trrna
hrsT in./
In, day
hrs/ tn./
in. day
hrs/ in./
in. day
Hrs/ in./
in. day
hrs/ in./
in. dav
500
26
29.2 .82
19.5 1.23
14.6 1.6-5
11.7 2.06
9.3 2.44
550
30.5
34,4 .70
23.0 1.04
17.2 1.4
13.7 1.75
11.4 2.10
600
35.3
33.7 .62
26.4 .91
19.8 1.2
15.9 1.51
13.2 1.82
650
40.6
45.6 .52
30.4 .79
22.9 1.05
18.2 1.32
15.2 1.58
700
52.1
58.6 .41
39.0 .61
29.4 .82
23.4 1.02
19.5 1.23
800
53.4
66.1 .36
44.0 .54
32.8 .73
26.3 .91
21.9 1.09
850
65.0
73. .33
48.7 .49
36,6 .65
29.3 .82
24.3 .99
900
72.2
81.2 .29
54.2 .44
40,6 .59
32.5 .74
27.1 .89
950
79.5
89.2 .27
59.5 .40
44.8 ,53
35.8 ,67 4
29,3 .51
LCOQ
87.4
98.3 .24
65.5 .37
49.2 .49
39.4 .61
32.8 .73
1050
95.3
107 .22
71.5 ,33
53.6 .45
42.9 ,56
35.7 .67
1100
104,0
117 .20
78.0 .31
58.5 .41
46.8 .51
39.0 .61
1150
112.6
126 .19
84 ,29
63.4 .38
50.7 .47
42.2 .57
1200
121.9
137 ,17
91.5 .26
68.6 .35
54.9 .44
45,6 .52
1250
130.0
146 .16'
97.5 .25
73.1 .33
58.5 .41
48,7 .49
.15
106 .23
79.5 .30
63.6 .38
53.0 .45
L4
113 ,21
85.5 .28
68.3 .35
56.7 .42
13
122 .20
91.2 .26
73.0 ,33
60.7 .40
L2
130 .18
97.5 .25
78.0 .31
65.0 .37
11
138 ,17
104 .23
83.0 .29
69.2 .35
re circle.
C-34
Exhibit C-7
Center Pivot Water Supply Nomograph
WATER SUPPLY
{GALLONS PER MINUTE)
200
500
00
600 IOOO
J
l?00
1400 I6OO 1800
J 1 . I
1600
1500 1400 1300 I20O IIOO IOOO 9OO 300 TOO 60O
RADIUS OF WCTTEO CIRCLE FOR CIRCULAR SYSTEM
(FEET)
The nomograph above can be used to calculate water supply requirements for
self-propelled center pivot sprinkler systems. Its use is explained by the
following examples.
Example 1:
Given: Water supply, 800 gpm; plant water use rate, 0.28" per day; water
application efficiency, 6C$. What is the radius of -he circle that this
system will adequately irrigate?
Solution: Locate 0.23" on the "V/ater Use Rate" scale and 60 on the appli-
cation efficiency scale. Connect the two points by using a straightedge
and note the point of intersection on the solid diagonal line. Locate
800 gpra on the upper scale labeled ''Water Supply"; connect this point with
the point located* on the diagonal line and project this line to the lower
scale labeled "Radius of Wetted Circle." This point reads slightly ^iore
than 1,100' - the maximum radius of the wetted circle that 800 gpm will
properly irrigate.
Example 2:
Given: Desired radius of v/etted circle, 1,320'; Tracer use rate 0.20" per
day; application efficiency, 603. V/hat is the required .-rater supply?
Solution: Locate 1320 on the lower scale, then drvw a line from this
ooint through the intersection point on the diagonal and extend it on to
the upper scale labeled "Water Supply,' 1 The point on the upper scale is
between 1,100 and 1,150 gprr,. A 'water supply of 1,125 gpm is required to
adequately irrigate a circle this size under the given conditions. It is
obvious that an increase in 'rater application efficiency will reduce the
total water requirements.
C-35
Table C-22
STANDARD PIPE DIMENSIONS
ALL DIMENSIONS IN INCHES
RIGID PVC PLASTIC PIPE
Nominal Pips
Dtamslef-Jnch
Outside
Dia
CL 100 SDR 41
CL 125 SDR 32 5
CL 160 SDR 26
CL 200 SDR 21
CL 315 SDR 13.5
SCH <10 Plastic
SCH 00 Plastic
ID
WALL
ID
WALL
ID ]
WALL
ID
WALL
ID
WALL
ID
WALL
ID
WALL
1/2
840
716
OG2
.622
109
.546
.147
3/4
1 050
.930
060
.894
.078
.824
.113
.742
.154
1
1 315
1.195
.060
1 189
,063
1.121
.097
1.O49
.133
.957
.179
MM
1.660
1 532
.064
1,502
079
1 414
123
1 380
.140
1.278
.191
1-1/2
1,900
1.754
073
1,720
090
1.618
141
1.610
.145
1 500
.200
2
2 375
2.193
.091
2 149
113
2 023
.176
2.067
154
1.939
.218
2 1/2
2,875
2655
.110
2 601
.137
2. 449
213
2.469
.203
2.323
.276
3
3 500
3.284
.108
3 230
135
3 1G6
1G7
2 982
.259
3 068
216
2,900
.300
A
4.800
4 280
110
4 224
138
A 154
173
4.072
214
3.834
,333
4.026
.237
3.826
.337
6
6.625
6,301
,162
6.217
20-1
6.115
.255
5 993
,316
5 643
491
6.065
.280
5.761
.432
ft
S.625
8 205
210
8.095
265
7,961
.332
7,805
.410
10
10 750
10,226
.262
10.0D8
.331
9924
.413
9.728
511
12
12 750
12.12B
.311
11 966
,392
11.770
.490
11.538
606
Table C-23
STANDARD PIPE DIMENSIONS
FLEXIBLE POLYETHYLENE TUBE |PE)
Nominal Pipe
Size Inch
Inside Dia.
Inch
SDR 1G-80 PSI
SDR 11.5 100 PSI
SDR 9 125 PSI
SDR? 125 PSI
Wall Thickness
/Inch
Wall Thickness
Inch
Wall Thickness
Inch
Wall Thickness
Inch
1/2
0.622
O.OGO
0.06O
0.069
0.089
3/4
0,824
0,060
0.072
0.092
Q.11B
1
1,049
0.070
0.091
0,117
0.160
1-1/4
1.380
0.092
0.120
0.153
0.197
1-1/2
1,610
0.107
0.140
0.179
0.230
2
2.0G7
0.138
0.180
0.230
0.297
2-1/2
2 469
0.165
0215
3
3.068
0.205
0.267
4
4.026
0.268
0.350
6
6.065
0.404
0.527
Table C-24
STANDARD PIPE DIMENSION
ALL DIMENSIONS IN INCHES
ASBESTOS - CEMENT IRRIGATION PIPE
Nominal Pipe
Size Inches
Inside
Diameter
Typ25
Outside Dia.
Type 75
Outside Dia.
Type 125
Outside Dia.
Class 100
Outsido Dia.
Class 150
Outside Dia.
Claw 200
Outiida Dia.
3
3.00
4,00
4,00
4.O6
4,06
4.03
4,20
4
4.00
5.06
5.06
5.08
5.08
5.15
6.31
5
6,OO
5,92
5,92
6
6.00
6.90
6.90
7.17
7.17
7.13
7.3S
8
8.00
9.06
9.0B
9.38
9.33
9.45
9.69
10
10.00
11.15
11.15
11.40
11.45
11.85
H.B9
12
12.00
1325
13.25
13.58
13,70
14.12
M.I 2
14
14.00
15.31
16.31
15 35
15,36
16.40
16,44
15
15 00
16,45
1645
17.04
17.03
17,91
18.46
16
16.00
1749
17.49
17.48
17.50
18,65
18.75
18
18.00
19.61
19.61
20.29
20.45
21,21
20
20.00
21.66
21.66
22.50
22.50
23.55
21
21.00
22.75
22.75
23.72
24.00
24.94
24
24.00
26,01
26.01
26.67
27.18
28,21
C-36
Table C-25
FRICTION HEAD LOSS IN PLASTIC IRRIGATION PIPELINES
MANUFACTURED OF PVC OR ABS COMPOUNDS
STANDARD DIMENSION RATIO - SDR = 26
For IPS Pipe
Q
1-inch 1^-inch
1^-inch
2-inch
2^-inch
3-inch
3^-inch
Q
allons
Gallon:
2r min. 1.195 ID 1.540 ID
1.754 ID
2.193 ID
2.655 ID
3.230 ID
3.692 ID
per mil
Friction Head
Loss in
Feet per Hundred Feet
2
.14 .04
.02
2
4
.49 .15
.08
.03
.01
4
6
1.05 .34
.17
.05
.02
6
8
1.79 .57
.29
.10
.04
.01
8
10
2.71 .86
.45
.15
.05
.02
.01
10
15
5.75 1.85
.95
.32
.13
.05
.02
15
20
9.82 3.15
1.62
.55
.21
.08
.04
20
25
14.83 4.75
2.46
.83
.33
.12
.06
25
30
20.80 6.66
3.44
1.16
.46
.17
.09
30
35
8.87
4.58
1.55
.61
.23
.12
35
40
11.34
5.88
1.98
.78
.29
.15
40
45
14.11
7.30
2.47
.97
.36
.19
45
50
17.17
8.87
3.00
1,18
.45
.23
50
55
20.46
10.59
3.59
1.40
.54
.27
55
60
12.41
4.20
1.65
.63
.33
60
65
14.42
4.88
1.91
.73
.37
65
70
16.55
5.59
2.20
.84
.43
70
75
18.79
6.36
2.50
.96
.50
75
80
21.18
7.15
2.82
1.08
.56
80
85
8.02
3.16
1.21
.63
85
90
8.91
3.50
1.35
.70
90
95
9.85
3.87
1.49
.77
95
100
10.82
4.27
1.64
.85
100
lid)
12.93
5.09
1.95
1.01
110
120
15.19
5.97
2.29
1,19
120
130
17.61
6.94
2.66
1.39
130
140
20.21
7.94
3.06
1.59
140
150
9.05
3.48
1.81
150
L60
10.19
3.90
2.04
160
L70
11.38
4.37
2.28
170
L80
12.65
4.87
2,54
180
L90
Table based on Hazen-Williams
14.00
5.39
2.80
190
200
equation - C^ =150
15.39
5.92
3.08
200
220
18.38
7.07
3.68
220
240
Dashed line indicates
5 Ft/sec
. velocity.
21,59
8.30
4.33
240
260
9.62
r- f\ i
0M
280
11.02
300
12.54
320
14.12
340
15.18
360
17.54
380
19.41
400
21.34
420
440
460
480
500
C-37
(1 of 3)
Table C-25
FRICTION HEAD LOSS IN PLASTIC IRRIGATION PIPELINES
MANUFACTURED OF PVC OR ABS COMPOUNDS
STANDARD DIMENTION RATIO - SDR 26
For IPS pipe
Q 4-inch Scinch
Gallons
per min. 4.154 ID 5.135 ID
6-inch 8-iflch 10-inch 12-inch Q
Gallons
6.-115 ID 7,961 ID 9,924 ID 11,770 IJJ p'er min,
Fricfciori Head ^ossi iri.Fe'et. .p'er Hundred Feet
15
20
25
30
35
40
45
50
55
.01
.02
.04
.05
.06
.08
.11
.13
.15
.01
.02
,02
,03
.04
.05
.05
,01
.01
.01
.02
.02
15
20
25
30
35
40
45
50
55
60
.18
,06
,03
60
65
.21
.07
.03
.01
65
70
.25
.08
.04
.01
70
75
.28
.10
.04
.01
75
80
.32
.11
.05
.01
80
85
.36
,13
.05
.01
85
90
.39
,14
.06
,01
90
95
.44
.15
.06
.02
95
100
.47
.17
.06
,02
100
110
.57
.20
.08
.02
110
120
.68
.24
.09
.03
.01
120
130
.77
.27
.11
.03
.01
130
140
.89
i32
.13
.04
.01
140
150
1.01
= 36
<15
.05
*01
150
160
1.15
.40
.17
.05
.01
160
170
1.28
.45
,19
.05
.02
170
180
1.43
.50
j22
M
.02
,01
180
190
1.57
.56
.24
M
.02
,01
190
200
1.73
.61
.26
.07
.02
,01
200
220
2.07
.74
.31
)0 g
.03
,01
220
240
2.43
.86
.36
.09
.03
,01
240
260
2.82
1.00
.42
.11
.04
.02
260
1QO
3.24
1.15
.49
.13
.05
.02
280
1 HA
.56
.15
.05
<02
300
.63
-17
.05
.03
320
.70
.19
.06
.03
340
.78
,22
.07
,03
360
.86
.24
.08
.04
380
.95
.25
.09
.04
400
1.04
.28
.09
.05
420
1.14
,31
.10
.05
440
1.23
.34
.11
,05
460
1.33
.37
.13
.05
480
1.44
.39
.14
.05
500
1.72
.47
.16
.06
550
2.02
.56
.19
.08
600'
C-38 (2 of 3)
Table C-25
FRICTION HEAD LOSS IN PLASTIC IRRIGATION PIPELINES
MANUFACTURED OF PVC OR ABS COMPOUNDS
STANDARD DIMENTION RATIO - SRS =26
For IPS Pipe
Q 4-inch 5-inch 6-inch 8-inch 10-inch 12-inch Q
Gallons Gallons
per min. 4.154 ID 5.135 ID 6.115 ID 7.961 ID 9.924 ID 11.770 ID per min
Friction Head Loss in Feet p er Hundr e d Feet
600 13.30
4.74
2.02
.56
.19
.08
600
650 15.42
5.50
2.35
.65
.22
.09
650
700 17.70
6.30
2.69
.74
.25
.11
700
750 20.09
7.16
3.06
.85
.29
.13
750
800
8.08
3.44
.95
.33
.15
800
850
9.04
3.86
1.06
.36
.15
850
900
10.06
4.29
1.18
.40
.17
900
950
11.08
4.74
1.31
.45
.19
950
1000
12.19
5.23
1.44
.49
.21
1000
1050
13.35
5.71
1.57
.54
.24
1050
1100
14.56
6.22
1.71
.59
.25
1100
1150
15.82
6.74
1.87
.64
.27
1150
1200
17.11
7.30
2.01
.69
.30
1200
1250
18.45
7.88
2.17
.75
.32
1250
1300
19.82
8.48
2.34
,80
.34
1300
1350
9.09
2.51
.86
.36
1350
1400
9.70
2.68
.92
.39
1400
1450
10.37
2.88
.98
.43
1450
1500
11.04
O nc
1 f\ C
i f
1 C f\f\
1600
12.45
1700
13.91
1800
15.46
C-39 (3
FK1U11UW HfcAU UJbb IN fLASiiu iKKJ.unj.iun fire,
MANUFACTURED OF PVC OR ABS COMPOUNDS
STANDARD DIMENSION RATIO - SDR = 32.5
Q
Gallons
per min.
For IPS Pipe
Ik-inch 1^-inch 2-inch 2^-inch 3-inch 3^-inch Q
Gallons
1,540 ID 1.780 ID 2.255 ID 2,709 ID 3.184 ID 3.754 ID per min
Friction Head Loss in Feet per Hundred Feet
2
4
.03
.14
.02
.08
.03
.01
2
4
6
.31
.16
.05
.02
6
8
.53
.27
.09
,03
.01
8
10
.80
.41
.13
,05
.02
.01
10
15
1.71
.87
.29
.12
.04
,02
15
20
2.91
1.50
.50
.19
.08
.03
20
25
4.38
2.27
.76
.30
.11
.06
25
30
6.15
3.18
1.07
.42
.16
.08
30
35
87l9
4,23
1.43
.56
.21
.11
35
40
10.47
5,43
1.83
.72
.27
.14
40
45
13.03
"6,74
2.28
.90
.34
.18
45
50
15.85
8.19
2.79
1.09
.41
.21
50
55
18.88
9,78
3.31
1.29
.50
.25
55
60
11.46
3.88
1.52
.58
.30
60
65
13,31
4750
1.76
.67
.34
65
70
15.28
5.16
2.03
.77
.39
70
75
17.35
5.87
2. -31
.89
.46
75
80
19.56
6.60
2.60
1.00
.52
80
85
7.40
2.91
1.12
,58
85
90
8.22
3.23
1.24
.65
90
95
9,09
~3757
1.38
.71
95
100
9.99
3.94
1.51
.78
100
110
11.94
4.70
1.80
.93
110
120
14.02
5.51
2.12
1.10
120
130
16.25
6.41
2.45
1,29
130
140
18.66
7.33
2.82
1.47
140
150
8.35
3.21
1.67
150
160
9.41
3.60
1.88
160
170
10.51
4.03
2.10
170
180
11.68
4.49
2.34
180
190
Table based on Hazen-Williams
12.93
4.97
2.59
190
200
equation - Cj = 150.
14.20
5.46
2.84
200
220
Dashed line indicates
16.96
6.53
3.39
220
9An
e fc
'"- velocity
19.93
7.66
4.00
240
8.88
4.63
260
10.17
5.31
280
11.58
6.03
300
13.04
6.80
320
14.59
7.62
340
16.19
8.47
360
17.92
9.35
380
19.70
10.26
400
11.26
420
12.26
440
13.32
460
C-40 (1 of 3)
14.41
480
15.54
500
Table C-26
FRICTION HEAD LOSS IN PLASTIC IRRIGATION PIPELINES
MANUFACTURED OF PVC OR ABS COMPOUNDS
STANDARD DIMENSION RATIO - SDR = 32.5
For IPS Pipe
Q
Gallons
per min,
4-inch 5-inch 6-inch 8-inch 10-inch
4.224 ID 5.221 ID 6.217 ID 8.095 ID 10.088 ID
Friction Head Loss in Feet per Hundred Feet
12-inch
11.966 ID
15
20
25
30
35
40
45
50
55
.01
.02
.03
.04
.06
.08
.10
.12
.14
.01
.02
.02
.03
.03
.04
.05
.01
.01
.01
.02
.02
60
.17
.06
.03
65
.19
.07
.03
.01
70
.23
.08
.03
.01
75
.26
.09
.03
.01
80
.29
.10
.04
.01
85
.33
.12
.04
.01
90
.36
.13
.05
.01
95
.40
.14
.06
.02
100
.44
.16
.06
.02
110
.53
.18
.08
.02
120
.62
.22
.08
.03
.01
130
.71
.25
.10
.03
.01
140
.82
.29
.12
.03
.01
150
.93
.34
.13
.04
.01
160
1.06
.37
.16
.04
.01
170
1.18
.41
.18
.05
.02
180
1.32
.46
.20
.06
.02
.01
190
1,45
.51
.22
.06
.02
.01
200
1.60
.56
.24
.07
.02
.01
220
1.92
.68
.29
.08
.03
.01
240
2.24
.80
.34
.08
.03
.01
260
2.60
.92
.39
.10
.03
.02
280
2.99
1.06
.45
.12
.04
,02
300
3.39
1.20
.51
,14
.04
.02
320
3.83
1.36
.58
.16
.05
.03
340
4.28
1.53
.65
.18
.06
.03
360
4.76
1.70
.72
.20
.07
.03
380
5.26
1.86
.80
.22
,08
.03
400
5.80
2.06
.87
.24
.08
.03
420
6.34
2.26
.96
.26
.08
.04
440
6.91
2.45
1.05
460
7.51
2.67
1.13
480
8.12
2.89
1.23
500
8.75
3.11
1.33
550
10.45
3.71
1.59
600
12.27
4.38
1.86
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100
110
120
130
140
150
160
170
180
190
200
220
240
260
280
300
320
340
360
380
400
420
C-41 (2 of
Q 4-inch
Gallons
per min. 4 .224 ID
600
650
700
750
800
850
900
950
1000
1050
1100
1150
1200
1250
1300
1350
1400
1450
1500
1600
1700
1800
12.27
14.23
16.34
18.55
Table C-26
FRICTION HEAD LOSS IN PLASTIC IRRIGATION PIPELINES
MANUFACTURED OF PVC OR ABS COMPOUNDS
STANDARD DIMENSION RATIO - SDR =32.5
For IPS Pipe
5-inch 6-inch 8-inch 10-inch 12-inch Q
Gallons
5.221 ID 6.217 ID 8.095 ID 10.088 ID 11.966 ID per rnin
Friction Head Loss in Feet per Hundred Feet
4.38
1.86
.51
.18
.08
600
5.07
2.17
.60
.20
.08
650
5.81
2.49
.68
.24
.10
700
6.61
2.82
.78
.27
.12
750
7.46
3.18
.87
.30
.13
800
8.34
3.56
.98
.34
.14
850
9.28
3.96
1.09
.37
.16
900
10.23
4.38
1.21
.41
.18
950
11.26
4.83
1.33
.45
.19
1000
12.32
5.27
1.45
.50
.22
1050
13.44
5.74
1.58
.55
.24
1100
14.61
6.22
1.72
.59
.25
1150
15.79
6.74
1.86
.64
.28
1200
17.03
7.27
2.01
.69
.29
1250
18.20
7.83
2.16
.74
.31
1300
8.39
2.32
.80
.34
1350
8.95
2.48
.85
.36
1400
9.58
2.65
.91
.39
1450
10.19
2.81
.97
.42
1500
11.49
3.18
1.09
.47
1600
12.84
3.55
1.22
.52
1700
14.27
3.95
1.39
.59
1800
C-42 (3 of 3)
TABLE 027
GUN SPRINKLER PERFORMANCE TABLES (Courtesy Nelson Corp.)
MODELS F100T, P100T & PC100T
4 ' tralacioty ' ' Tap*' Bwe
No?jle
PSI
5
GPM
DIA
55
GPM DIA
6
GPM DIA
65-
GPM DIA
7
GPM DIA
75-
GPM DIA
B"
GPM DIA
85
UPM DIA
9
GPM DIA
Nfi'.lo
10
GPM DIA
it)
47
t9!
57 202
66 213
78 222
91 230
T03 240
18 250
134 256
152 26!
50
SO
205'
64 2 IS
74 225
B7 235
100 245
115 256
30 265
'50 273
IC.5 2dO
204 200
60
55
215
69 227
81 240
96 250'
110 260
126 270
43 230
164 2ifl
182 295
22- JIB
70
60
225'
75 233
88 250
03 263
1 20 273
IJ6 2B3
55 235
177 302
197 310
2 3JD
60
61
235'
79 248
94 260
10 273'
1 28 285'
1 295'
65 305
tB9 314
210 325
25fl 354
90
68
245'
83 2 58'
100 270'
17 233'
135 285'
1 55 306
75 315
201 326
223 335
274 362
100
72
55
87 26S
106 230'
23 293
1 43 306
163 316
65 325
212 336
235 315
2Ba in
110
76
65
92 276
111 290'
29 303'
ISO 31S'
171 324'
95 335
223 314
247 355
3D 4 3oO
JTFhariis
met BIO
llue
mapproiima
ely3%lessl
theai'lraje-
c lory analog
oioasloi IS'
'i'Noie 5' and 55'fapernz2iearaNab[eoniyviimPC1DDandF100
|jf" Tra
eclory" Ring
Nozzle
PSI
Ring 712
GPM DIA
Ring 768
GPM OIA
Ring 812
GPM DIA
Ring B57
GPM DIA
Hing B95
GPM OIA
Rmg 327
GPM DIA
GPM OIA
50
74 220
88 225
100 230'
115 240
129 250
160 255
167 26Q
60
81 235'
96 240
110 245
125 260'
141 270
164 275
183 280
70
88 245'
104 250
118 260
135 275
152 290
177 295'
19B 300
80
94 255'
111 265
127 275
145 285
163 300
169 305
211 315
90
99 265'
117 275
134 285-
154 295
173 310'
201 315
224 325
too
105 270'
124 280
142 295'
162 305
182 320
212 325
236 335
110
110 275'
130 290
149 305
170 315
191 325'
322 335
248 345
STtie diameter cllhicwls approximately 3% IBSS (oMhu 2r trajectory angle, 6% less forie'
JODELS F150T & I P156T
Ttajeclory" ' Taper Bore Ntafcla
PSI
Noille
7
GPM DIA
Noitle
6
GPM OIA
NOiile
9
GPM DIA
Nojile
1
GPM DIA
Non la
i i
GPM OIA
Nott lo
12
GPM DIA
Ho; JIB
13
GPM DIA
50
100 350
130 270'
185 290'
305 310'
255 330'
300 345'
350 360
60
110 265
143 285
182 305'
225 325
275 345'
330 365
385 360
70
120 280
155 300'
1S7 320
245 340'
295 360
355 380
415 395
BO
128 290
165 310
210 335'
360 355
31 S 375'
380 395'
445 410
SO
135 3DO
175 320'
223 345
275 365
335 390
405 410
475 425
100
143 310
185 330'
235 355'
290 375'
355 400'
425 420
500 440
110
150 320
195 340'
247 365'
305 385'
370 4 10'
445 430
525 450
120
157 330
204 350'
258 375'
320 395'
365 420
465 440
545 460
F150R A P150R
,
f i
$
l
rc ''''
PSI
> V ' -v
Rmg
OS
GPM DIA
. II
Ring
97
GPM DIA
Ring
ioa
GPM DIA
fling
1 IB'
GPM DIA
Ring
I2S
GPM DIA
fling
134
PPM DIA
B ,n fl [' !
141 li!,
GPM DIA {''
50
60
70
BD
90
100
110
120
100 245
110 260
120 270
128 280'
135 290
143 300'
150 310
157 315
130 265
143 280
155 290'
165 300
175 310'
185 320
195 330
204 335
165 285
182 300'
197 310
2 tO 320'
223 330
235 340'
247 350
258 360
205 300
225 315
245 330
260 340'
275 350
290 360
305 370
320 380'
255 320
275 335
295 350'
315 360
335 370'
355 380
370 390
385 400'
300 335'
330 350
355 365
380 380'
405 390
425 400'
445 410
465 420'
350 360 i
385 365 J *
415 380 j,-i,
445 395' *"!
475 405 'V '
500 415 f,;''J
525 425 ' r' '
545 435 l' '
j ' l
i
T* '-
PSI
Noillfl
105
GPM OIA
Nome
i i
GPM DIA
Naitle
12
GPM DIA
No j lie
13
GPM DIA
Noil la
14
GPM OIA
Nan la
15
GPM DIA
Home
16
GPM OIA
Hauls
175
GPM DIA
NoiHc
1 9
GPM DIA
60
250 345
285 355
330 375
385 390'
445 410'
515 430
585 445
695 470
825 495
m
70
270 360
310 3GO
355 395'
415 410'
480 430
555 450'
630. 465'
755 495
890 515
m
80
290 375
330 395
380 410'
445 430'
515 450
S90 470
675 465
805 515
950 535
m
90
310 390'
350 410
405 425'
475 445'
545 465'
625 485'
715 505
855 535
1005 555
IP
100
325 400
3/0 4SO'
425 440'
500 460'
575 480
660 SOD'
755 520
900 550
1060 575
B
110
340 410'
390 430
445 450
525 470'
605 495'
69S 515'
790 535'
945 565
1110 590
if
120
3SS 420
405 440
465 460'
545 460'
630 605'
725 530
825 550
985 5BO
1160 605
H
130
370 425
4J5 445
485 465'
565 465
6:55 515'
755 540
860 550
1025 59Q
1210 620
.
r iODELSF200Rft,P200R'
',',iTi I'rdiflcitfry 1
1 . Ring
11 29 acuiali
GPM OIA
1 Ring
II i16 actual)
GPM DIA
1 Ring
|l 56 aclt.,111
GPM DIA
'
1 Hint]
|l 6 acnull
Gi'M DIA
1 . Ring
<1 74 JLIU3II
GPM. DIA
1 Ring
(1 61 arlu.il>
HPM DIA
1 Mmg
(193 acl"J
dPH tllA
50
230 325
300 355
350 370
410 390
470 405
535 420
640 435
60
250 340
330 370
385 390
445 410
515 425
585 440
695 455
70
270 355
355 365
415 405
480 425
555 440
630 455
755 475
no
200 370
3BO 400
>14S 420
515 440
590 455
G75 470
805 490
90
310 380
405 415
475 435
545 455
62") 170
715 485
855 505
100
325 390
425 425
500 445
5/5 165
6fiO 480
FS'i Via
900 E"n
110
340 400
445 435
52B 455
605 1/5
695 490
79U bio 945 ti
120
355 410
465 445
545 4G5
630 4B5
725 500
BJ5 52L> 965 '. I' 1
130
370 415
485 450
565 470
655 490
7b5 505
HBO -i25
1025 >."
' ' ' '"'
BSBB'Tf?
C-43
APPENDIX D - GLOSSARY
Available Water Holding Capacity (AWC)
Available water holding capacity is the amount of water the soil will
hold between field capacity and the permanent wilting point.
Carryover Soil Moisture
Moisture stored in soils within root zone depths during the winter, at
times when the crop is dormant, or before the crop is planted. This
moisture is available to help meet the consumptive water needs of the
crop.
Consumptive Use
Consumptive use, often called evapo-transpiration, is the amount of water
used by the vegetation in transpiration and building of plant tissue and
that evaporated from adjacent soil or intercepted precipitation from plant
foliage. If the unit of time is small, consumptive use is usually expressed
as acre inches per acre or depth in inches, whereas, if the unit of time is
large, such as a growing season or a 12-month period, it is usually expressed
as acre feet per acre or depth in feet.
Consumptive Water Requirement
The amount of water potentially required to meet the evapo-transpiration
needs of vegetative areas so that plant production is not limited from lack
of water.
Crop Growth Stage Coefficient
A factor that modifies the Blaney-Criddle Formula which reflects the type
of plant and stage of growth on consumptive use.
Discharge Head (Dynamic)
The elevation (in feet) between the center line of the pump, if a horizontal
type, or the center line of discharge of a vertical turbine type, and the
point of free discharge, plus the friction head between these two points,
plus the residual pressure existing at the point of discharge (expressed
in feet), plus the velocity head.
jDrawdown.
The difference, in feet, between the pumping level and the static level of
the source.
Dynamic Head
me head condition that exists when water is flowing through a system of
pipes, etc.
D-l
Effective Rainfall
Precipitation falling during the growing period of the crop that is
available to meet the consumptive water requirements of crops. It
does not include such precipitation as is lost to deep percolation
below the root zone nor to surface runoff,
Field Capacity
The moisture percentage, on a dry weight basis, of a soil after rapid
drainage has taken place following an application of water, provided
there is no water table within capillary reach of the root zone. This
moisture percentage usually is reached within two to four days after
an irrigation, the time interval depending on the physical characteristics
of the soil and the effect of the growing crop.
Eviction Hea_d
Pressure loss (in feet) due to frictional resistance when water flows
through pipe, fittings, orifices, etc.
Gross Irrigation Requirement (Gross water application)
The net irrigation water requirement divided by the irrigation efficiency.
Head (H)
A term related to pressure but usually expressed in "feet" rather than
"psi." It is derived from the fact that a column of fluid exerts pressure
at a given point in relation to the height of the column above that point,
and the density (weight per unit volume) of the fluid. For example, a
column of water one foot high exerts a pressure of approximately 0.433 psi
on its base. Thus, 1 ft. head (water) = 0.433 psi. or 2.31 ft. head 1 psi,
Irrigation Depth
Is the soil depth used to determine irrigation water requirements for
design of systems. A high moisture level must be maintained in this
depth for top production of crops. It is not necessarily the maximum
root depth for any given plant.
Irrigation Efficiency
The percentage of applied irrigation water that is stored in the soil
and available for consumptive use by the crop. When the water is measured
at the farm headgate, it is called farm-irrigation efficiency; when measured
at the field, it is designated as field-irrigation efficiency; and when
measured at the point of diversion, it may be called project-efficiency.
D-2
Irrigation Frequency
Refers to the allowable numbers of days between irrigations. It depends on
the consumptive-use rate of a crop and on the amount of available moisture
in the root zone (moisture extraction depth) between field capacity and the
starting moisture level for irrigation. Irrigation period refers to the
number of days a system, of given capacity, takes to irrigate the design
area. Irrigation period should always be equal to, or less than, irriga-
tion frequency,
Maximum Application Rate
Is the maximum rate that water can be applied to a soil during the time
required for the soil to absorb the depth of application without runoff
for the conditions of soil, slope and cover.
Net Irrigation Requirement (Net water application)
The depth of irrigation water, exclusive of precipitation, stored soil
moisture, or ground water, that is required consumptively for crop
production and required for other related uses. Such related uses may
include water required for leaching, frost protection, etc.
Peak Period Consumptive Use
Peak period consumptive use is the average daily rate of use of a crop
occurring during a period between normal irrigations when such rate of use
is at a maximum.
Static Head
The difference in elevation (in feet) between the source of supply and
the point of free discharge, when there is no flow (sometimes called
elevation head) .
Suction Head
Velocity Head
The energy contained in a stream of water by reason ot its velocity. It
represents the force necessary to accelerate the water in the pipeline and
is equivalent to the distance in feet through which It would have to fall
in a vacuum to attain that velocity. This is a relatively small factor
and need not be considered in the design of the average irrigation system,
Wilting Point
The wilting point is the moisture percentage, on a dry weight basis,
at which plants can no longer obtain sufficient moisture to satisfy
moisture requirements and will wilt permanently unless moisture is added
to the soil profile.
APPENDIX E
CHEMICAL TREATMENT TO INHIBIT CLOGGING
OF
LOW PRESSURE IRRIGATION SYSTEMS
When using low-pressure irrigation systems, particularly if water supply con-
tains iron, sulfides, or high pH, there is a chance of emitters becoming
clogged. Sodium hypochlorite (liquid bleach) may be used to inhibit iron and
slime clogging. f
The key given in this appendix may be used to determine the amount of liquid
bleach or any equipment adjustment needed. The key was developed by Harry W.
Ford, horticulturist, Agricultural Research and Education Center, Lake Alfred,
Florida.
Before using the key or recommending the chemical, it is necessary that good
water quality data be obtained. Also, once treatment has been started, free
residual chlorine must be measured. People unfamiliar with water test kits
may want to contact the state wildlife and fish biologist or SCS biologist for
assistance .
The rate at which liquid bleach (5.25 percent sodium hypochlorite - 50,000 ppm
available chlorine) is injected into systems may be converted from ppm to
ounces/min. by use of the following formula:
Chlorine Injection Rate (oz./min.) K x Initial Rate (PPM) x Pumping Rate (GPM)
where the term K is a conversion constant =
128 oa. /gal. = 0.00256
1,000,000 x 0.05
EXAMPLE: Drip system has a flow rate of 45 gallons per minute and the initial
injection rate of 2 ppm of chlorine is desired. At what rate should the
liquid bleach be injected into the drip system?
Chlorine Injection Rate = .Ot)256 x 2 PPM x 45 GPM =
Conversion Factor: 1 ounce = 29.57 milliliters
E-l
Lake Alfred AREC Research Report-CS79-3
5/17/79-HWF-100
A Key for Determining tue Use of Sodium Uypochloritc (Liquid Chlorine) to Inhibit
Iron and Slime Clogging of Low Pressure Irrigation Systems in Florida
Harry W. Ford
Professor (Horticulturist)
Agricultural Research and Education Center
Lake Alfred. Florida 33850
Terminology
chloriue -tast jcit. A- required purchase to measure jrec residual chlozitie.
DO NOT use an orthocolodene swimming pool test kit vhlch measures only total chlorine.
Free rtisidtMl __chlprino. The excess chlarine available to kill bacteria. Excess
chlorine c-umoc be pre.sent until chtudcal reactions uith chlorine have been satisfied.
Injection .system. A good quality variable rale injectioa pump is suggested. Increase
the rate of injection until the correct chlorine froo >*cB_idu_nl la obtained.
j.n.1 e si i on t i me. A ^10 minute miainium injection of NaOCl should occur early enough in
the irrigation cycle to periait 3D miuunes of chlorine to reach the last emitter.
NaOCJU SE2: Sodium hypoclilorlte
Sodium hypocblorJr.c (KaOClt. Liquid bleach or swimming pool chlorine cither as
5.2iX or 10X.
Wat a r_cju n 1 j. c y me ri ^ u re- nic-n t ^ are essential in order to use thla hey. Throughout the
irrigation season, cn^uguj iu water quality will occur for iron, aulfides, and pH,
These should be checked dt intervals and appropriate modifications made in the chlorine
injection procedure.
Vlater holding tan'itii with uir spaces should not be uqcd ou lov; pressure systems. They
serve as chambers for bacterial slime growth particularly sulfur slime. The frequency
of ohlorinarion mist be increasocl. Cartrain precipitation reactions associated with
holding ranks have not been controlled in the range of pH 6.5-7.5.
E-2
A key for the use of sodium hypochlorite to inhibit slime clogging of low pressure irrigar*
systems.
1. Surface water go to _2^
1, Well walur to to 10
2. 0.2 to 2.0 ppm maximum of iron; lower than pH 6.5 go to 3
2. 0.2 to 2.0 ppm maximum of iron; higher than pH 6.5 E to _JL
2. to 0.1 ppui Ft^ lower than pll 7.0 go to 3
2. to 0,1 ppm FP; higher than pH 7.0 go to 8
3, Visible greenish algal clumps in water go to 4
3, Water visibly free of blologica.1 growths E to 6
A, Chlorine injected on vacuum intake line before filter go to _Jj_
4, Chlorine injected on pressure side after filter
filter will f-loE- from si Imcs. Unsatisfactory pro-
jccdur. Otherwise 8 to -A
5. Sand filtration go to _A
5. Screen filtration may have frequent bockflush problems.
Otherwise BO to _A
5. Slotted Cil (.ration will not remove alpae use only for
i. n IC.9 r _ Llinn 7.0 p.ph spray jet: nozzles. Keep daylight out
oC : the* w'hite PVC filter. Otherwise go to _A
6. Inject NaOCl (aodlum hypochlorite) on intake aide
of filter 8 to -1
6. Inject NuOCl on pressure side after fllterunsatls-
_f m:U)ry_; uthcrwists 8
7. Sum) filt-cr; more frequent bnckf lushing during algal blooms. go to J3
V. Jiprc'un LiUer; j^ckC.lubli..prQbji;mo durinf. alp,al blooms.
Otherwiuo " go to _A
7, iilottcul filter; will not trap alp t al blooms. Use only with
larc,r tlwm 7.0 p.uh micro KprJnklcrn. Keep out light.
Ou^rwiVe ' go to ^
fl. Trickle lonp, path emitters uoe only sand filtration.
VfiiinHoto mnygcear nfter 800 lire oven with
~ ' --- --- ' -- * - ~~ on CO A
E "
Micro sprinkler oystem; 7 fiph or e^cater each emitter.
.
Mny_or mnyjrioL. nrr^''J - ^^_j^jjj-_q. l . 1 '. t J-" d R G fQr block-
t^ji": "u'uu yandTiltrVtion. Otherwise 8
6. Micro sprJnkJer :.yatemj emitters lott*. than 7 gph. Ma^; o to A
have aludfi.Qj>lojskafla E
10. Wall wator contains iron but no aulfldua 8 to |i
10. Wall watur with no iron and also no aulfides B to ^
10. Wull water with no iron but contains sulfldea 8 " |i
10. Well wator contuining iron and also sulfideu S to ii
,. 11. pH lass than 6.5 | t
11. pH 6.5 to 7.5 J ^
11. pll 7.5 to 8.0 *
ihor than 8.0 Unsatisfactory for lov pressure irrigation*
.
11. pll hifihor than 8.0 Unsatisfactory for
12. Open well with drop type suction Inlet. Foot valve.
Contrlfucal pump. NaQCl injection point deep into well.
12. Submoracnblo pump. Covered top. Injection point: for NaOCl
no deep into well AS poaoiblo.
E-3
below turbine
U .".r PU.P - Pio. 8 u .ido
V.ar contains less than 3.5 P P* won
,ui e-mwic* uorti Chan 3.5 ppo iron. Unsatisfactory
,,
line
; Unk with air chamber.
if well is concaninatBd with Iron deposits and iron
ctmcfuLraticm is less Chan 2 ppm
If iron i'; c.ore than 2 ppm. Ui>satiHl^2DL
..IL-H: r of wLpcnded solids and/or or B anlc-iron
- . .
i-u.4t.ini, j,us,pndtfd solids and organic-iron completing
lev, clian I p'.ira iron. Mnv_clog from fa us P e .Q- d -gl
Otherwise
uclJ vUh centrifugal pump, S ubrae i gcd pumps with
Aiijucciun tor tMOCl. Iron iess than 2 p]jm. More
tan-.
t..nk.
_
injection for NdOCl. Wo holuing
than 1.0 pjim. More than 1 ppm is
cp injectAon for NaOCl. No hi/lditi
than 2 ypm. Note than 2 ppra is
E to i
BOW 15
to
b
go to J)
e to
J
to
2,
witii
j.njicc:cJ
Iron
i;, and
.ii tlian 2 ppm.
with
i ^ui 1 ;). /^ dtv[i HjOCJ injection as possible. Iron
thjn 2 ppm. _Sy_^CPiii_ will __cl op, _ j n 2/< , ji ours 1 f c h 1 o r_Jn^t -Lon
&, Otlierwisc
Water .ilt.wst free of suspended bolJds and/or organic
diucolor.icion
Water coutaint. buc t >cnded iolids and/or discoloraClon
wells apd/or other noana of wtill contflminni ion
Ko well conCaDlnaiion, IUY NOT WWD CHLOltTNATlaM. Otherwise
Sulfldtis ifb^ thjn /( pjim
Sulfides Lort! than ^ ppm JJ^J^^OAJC to_ jjl^nr rpocs
is not artuswn
No leaks in well casina or other points on vacuum
side. Check valvt. Positive artesian pressure during
irrigation season.
23. Any one of the followine: Possible leaks in well casing
or other points on vacuum side. Old gate valve on
\mra side- Pressure holding tank near pump. Artesian
-re may be negative during dry season.
on vacuum side of pump
^f purap. Pressure holding
Artesian pressure negaeive
go to
go Lo _Ji
go to _F
go LO _C
g to 33
go to 24*
go Co
go to
than 0.6 Ppm. Unsatifl factory
0Htnklers. Otherwise
go to ?.0
go to ^
go Lw ?
po tJ
*
eo to u
E
o to
E-4
No air leaks in system.
BO to
Chlorine Treatment
A -
P
A. pll 7-5-8.0: Use minimum 2.0 ppm (Mg/L) free re fi idual chlorine as measured at the lr
witter. (Start with 4.0 ppm free residual as measured near the WBD at th fii I
emitter). Inject for 40 .in. toimum) each 6 hours accumulated irrigation time?
B. P H 7.0: Use minimum of 1 ppm (Mg/L) free, residual chlorine as measured at
the last emitter (Start with 3 ppm free residual as measured near the pump
at the first emitter). Inject for 40 min (minimum) each 12 hours of
accumulative irrigation time,
B. pH 7-7.5: Use minimum 1.5 ppm (Mg/L) free residual chlorine as measured at the
last emitter. (Start with 3,5 PP m tree residual as measured near Che pump at
the first emitter). Injected for 40 min (Minimum) each 12 hours of accumulated
irrigation time.
B. pH 7.5-8: Use minimum 2.0 ppm (Mg/L) free residual chlorine as meacured at the
last emitter. (Start with 4.0 ppm free residual as measured near the pup ar
the first emitter). Inject for 40 min. (minimum) each 12 hours accumulated
irrigation lime.
C. pH lesa 'than 6.3: Use minimum of 1 ppm (Mg/L) free residual chlorine ae meaeured at
the last emitter (Start with 3 ppm free residual as measured near the pump at the
flrat emitter). Inject for 40 min (minimum) each 6 hours of accumulative Irrigation
time.
D. pH 6.3-7.5. Use minimum 1 ppm (Mg/L) free residual chlorine as measured at last
emitter (Start with 3 ppm free residual as measured near the pump at the fiiet
emitter). Inject NaOCl for minimum of 40 minutes each 2 hours of accumulated
irrigation time.
E. pH 7.0-7.5. Use minimum of 2 ppm (Mg/L) free residual chlorine as measured at the
last emitter. (Start with 4 ppm free residual as measured near the pump at the
flrot emitter). Inject NaOCl CONTINUOUSLY.
F. Select the treatment and pH range of the water as indicated.
pH 7.0: Use minimum of 1 ppm (Mg/L) free residual chlorine as measured at
the last emitter (Start with 3 ppm free residual as measured near the pump
at the first emitter). Inject for 40 min (minimum) each 12 hours of
accumulative irrigation time.
pH 7-7.5: Use minimum 1.5 ppm (Mg/L) free residual chlorine as measured at the
last emitter. (Start with 3.5 ppm free residual as measured near the pump at
the first emitter). Injected for 40 miu (Minimum) each 12 hours of accumulated
irrigation time.
pH 7,5-8: Use minimum 2.0 ppra (Mg/L) free residual chlorine as measured at the ^
last emitter. (Start with 4.0 ppm free residual as measured near the pump at
the first emitter). Inject for 40 min. (minimum) each 12 hours accumulated
irrigation time,
E-5
7.5 use NaOCl with minimum of 0.75 ppm (Mg/L) free, residual chlorine as
ed ac the end of line (2.5 ppm free rc-sidual near pump).
for a minimum of 40 minutes each 25 to 40 hours accumulative time.
carefully for any sulfur slime formation In the area of the last emitter
system.
-8.0 increase treatment by 1 ppm of NaOCl.
i 7.5 use NaOCl with minimum of 0.75 ppw (Mg/L) jreti residual chlorine
sured at end of line (2.5 ppm free residual near pump).
for a minimum of 40 minutes each 10 hours of accumulative time.
carefully for any sulfur slime formation in the area of the last emitter
1 system,
1-8.0 increase treatment by 1 ppm of NaOCl.
> 7.5 use NaOCl with minimum of 0.75 ppm (Mc/L) free* residual chlorine
mured at end oC line (2>5 ppm free residual near pump).
: fur a minimum o 40 .minutes each 10-20 hours accumulative time.
carefully for any sulfur slime formation in Lhu area of the last emitter
i system,
i-8.0 increase treatment by 1 ppm of NaOCl.
a 7,5 use NaOCl with minimum of 0.75 ppm (Mg/I,) free residual cliloiinc
asured at end of line (2.5 ppra free rc.sidual near pump).
t for a mininum of 40 minutes each 6-8 hours accumulative time.
carefully for any sulfur sllinc formation in the area of the; last emitter
e system.
5-8.0 increase treatment by 1 ppm of NaOCl.
E-6
APPENDIX P - TECHNICAL RELEASE 21
INPUT DATA FOR TABLE 4-2
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APPENDIX G - REFERENCES
i-NfilNU.HINO I'll;!!) MANUAL, Chapter 15, USDA-Soil Conservation Service
NAMONAI, KNGINU'.KING HANDBOOK, Section 15, USDA-Soil Conservation Service
PLANNING FOK AN IRRIGATION SVSTEM, Second Edition 1980, American
Assoddt.lon (or VocrtUonal Instructional Materials, Engineering Center,
Atliom*, GnwyKi
IKRIGAl'ION WAfKK REQUIREMENTS, Technical Release No. 21, Revised September
1M/0, UMJA-Soil Conservation" Service
GliOUtilA IHKIGAflON GUIDE, November 1984, USDA-Soil Conservation Service
PI-ANUf IKKIGATION IN GEORGIA, L.E. Samples, Cooperative Extension Service,
Circular firtb, Roprinto'd AprTl 1978
SUPPLKMLNIAL WAfEK EKFECTS ON PECAN TREES JJSJNG
f. fieortji'a Agr\ *Exp". Sta. R"es. BuTTT 289:13
WAH-K ftEUUIKliMENrS OF PECAN TREE_S, J.W. Daniel 1, Georgia Agr. Exp. Station
IRIUGAriON SCIIKUULING, (Pecans), 0. W. Daniell, Georgia Agr. Exp. Station
IRRIGATION DESIGN AMD MAINTENANCE, (Pecans), Oaniell and K. A. Harrison,
ffobrgia Agr. xp/ "fta'tTon YritlTdop. Extension Service, Univ. of Georgia,
respectively
IRRIGATION AS AN INTEGRAL MANAGEMENT TOOL IN PECANS, J. B. Aitken and C. R.
CamTWrnYoTW^ Station, and ARS, Florence, S. C,
respectively
WATER REQUIREMENTS IN PEACH ORCHARDS, Irrigation Fact Sheet, Jere Britton,
SCHEDULING IRRIGATION. WITH PAN EVAPORATION, C.R. Camp and C.W. Ooty.
AgrTcuTfufal "Research "lervTce, 'Florence^- s.C.
METHODS FOR MEASURING SOIL MOISTURE -- .
"e extenslonTervTceTfTiirson Universi ty
CHLORIHATIOH CAN PREVENT DRIP IRRIGATION CLOGGING^ Southeast Farm Press Page
5T^ Extension '
son University
- f r
Environmental Data Service.
6-1
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