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- UNITED STATES DEPARTMENT OF AGRICULTURE

Washington, D. C.

STRUCTURES USED IN DRAINING
AGRICULTURAL LAND

L. T. JESSUP, Associate Drainage Engineer
Bureau of Public Roads

CONTENTS

Wntronuchone: ovatc cere ase recs sete ane Structures for Open Ditches—continued
‘ Structures for Use with Underdrains .... 2 Surface-Water Inlets ......... 14
‘ai Wiamhibles (ais matic bat al's ce alee. sacs, st 2 Shot Garde. 320 i ocd eek eee: wae ae t)
| | Surface-Water Inlets ......... 4 Sluiceways and Tide Gates ...... 15
Py PAMIDMOIGS 2 fo oe a ra ke let SOM wpe Ta 6 Ocean Qutletsis) 33. S05" were eae - 18
By: CAGES ides ona Silvia i fo! Lats hin) 0. 7 Bridges and Culverts .......- at) shine
& Angle Boxes .....-.-- Bay ASR | Flumes and Inverted Siphons ..... 25
7 Lateral Connections .. ...@.- =.=. 8 | Miscellaneous Structures ......... 27
Pe MDT RCo nak Chee erie ot odie isk Gaay Os 8 Pamp Houses })o3)2) 33: 3:02. SS aetet eee
: f Crossings Under Railroadsand Canals. . 9 Connections for Flushing Drains .... 29
: 4 Lumber Box Drains .........-. 10 Relief Well Connections ........ 380
a Structures for Open Ditches ........ 11 Connections for Diverting Water... . 31
3 Dropsand Checks .......... Il Watering Places for Livestock . .... 31
4 Timber Linings in Open Ditches . . . . 12 Transifions':)<\ 0x8 ce) ae! eke eeliphaltehe Oem
WASHINGTON

GOVERNMENT PRINTING OFFICE
1926

: Washington, D. C. June, 1926

STRUCTURES USED IN DRAINING AGRICULTURAL LAND

By L. T. JESSUP
Associate Drainage Engineer, Bureau of Public Roads

CONTENTS
Page Page
PATEEO CUCETO TA. ceed. ENB eke Piatt hs i Structures for open ditches—Contd.
Structures for use with underdrains_ 2 Surface-water inlets__________ 14
aT OT ES ee eee er ee 2 Stockp cuardS2 2 = seo eee 15
Surface-water inlets _____--___ 4 Sluiceways and tide gates_____ 15
amp an Ole Spiess sae ee a es oe 6 Ccean Hough ts= as ses et 18
Cradles 242s Se as Be PE eg TE. Bridges and culverts__________ 19
Angl@n bOk€S 23s 5 es ei ee € Flumes and inverted siphons__ 25
Lateral connections___________ 8 | Miscellaneous structures_______-____ 27
Outlets#2 2 wow ee eae a 8 Um piehOuses ese Ss ae ee were 27
Crossings under railroads and Connections for flushing drains 29
Canals. Stes Sea Se Mary wa ee 9 Relief well connections_____-__ 30
umber: boxdnains=— = oe 10 Connections for diverting water 31
Structures for open ditches_______~_ 11 Watering places for livestock__ 31
Drops and -checks#.2 233 23st 11 SPAM STG ONS ee ee Be els 32
Timber linings in open ditches_ 12
INTRODUCTION a

A system for the drainage of agricultural lands requires a variety
of structures in addition to the tile or ditches. To permit cleaning
underdrains, manholes are used at connections with laterals and at
changes in alignment. Lamp holes may be installed to facilitate
inspection. In soft ground and at crossings under railroads and
canals, cradles and other foundations are used. Open drains sub-
ject to erosion require checks, drops, and bank protection.

In the installation of such structures care should be taken to select
suitable material, to prepare standard plans and specifications, to
obtain proper locations, and to coordinate the structures with the
rest of the system. Improper design and location of structures
introduce defects in drainage systems which decrease their effec-
tiveness.

A wide variation exists in the design and cost of structures serv-
ing identical purposes. This bulletin describes the principles of
design indicated by practice and experiment to be the most satis-
factory in reduction of cost and of maintenance expenses and in
increase in the efficiency of drainage systems.

83435°—26——1 1

2 BULLETIN 1408, U. S. DEPARTMENT OF AGRICULTURE

STRUCTURES FOR USE WITH UNDERDRAINS

MANHOLES

On some tile drains more sand or silt finds its way into the drain
than the water can carry. If the drain is to be kept open, it is
necessary that this material be intercepted at suitable intervals and
later removed. This can be done by building a manhole of suitable
size. It should be so proportioned that there will be an appreciable
loss of velocity as the water passes through it and consequent deposi-
tion of the sand or other material that the water has in suspension.
Manholes are not required on all drainage systems; and, unless it is
clear that their use is necessary, they should not be installed as they
increase the cost of the drainage and there is always danger that
débris may get into the manholes and obstruct the drains.

When their use is necessary they should be located at points where
a reduction in gradient occurs, at sharp angles, at connections with
main laterals, and at special crossings. Usually it is not best to
construct them at frequent intervals on tangents. The cost of
installing them near enough to each other for efficient use of sewer
rods is prohibitive, and they are of but little use except in the special
circumstances mentioned.

The depth of the silt basin below the bottom of the outlet tile
should be not less than 18 inches; 2 feet is preferable. For farm
drains not over 8 inches in diameter, in firm ground, a 30-inch man-
hole with a depth of 2 feet for the silt basin should be the minimum
size. Where the size of the drain is the only governing factor, the
diameter of the manhole should be not less than 18 inches plus
the diameter of the outlet, and 36 inches should be the minimum
diameter for district systems. High velocities, existence of a long
tile line above the manhole, junctions with laterals, and the proba-
bility of infrequent cleaning, require larger sizes.

Loss of head occurs at manholes, and for this reason a dro
should always be provided between the inlet and outlet. Ordi-
narily a drop equal to the velocity head in the pipe will be enough,
but the loss may amount to 50 per cent more than this in manholes at
sharp angle points. The minimum drop should be 1 inch. Surface
inlets should not be connected with manholes, as the falling water
may prevent the deposition of silt and defeat the purpose of the
manhole.

Where the lower part of the manhole is located in gravel, hard-
pan, or stiff clay formation, a floor is not necessary; otherwise timber
or concrete must be used. In soft ground provision against settle-
ment must be made by the use of gravel or piling. In fine silty
materia} the joints in the lower part of the structure must be made
tight.

Elevation of the top depends upon the kind of material used in
the cover and the location of the manhole. When it is located on a
fence line the elevation makes little difference, but if in a field the
top must be strong enough to support farm machinery and stock or
the structure must rise above ground. The latter is sometimes
objectionable to the farmer. A cast-iron top and frame similar to
but hghter than that used in sewer practice is an excellent type
(fig. 1). Heavy reinforced concrete covers are satisfactory, pro-

STRUCTURES USED IN DRAINING AGRICULTURAL LAND

vided the diameter of the top of the manhole is not over 24 inches
and it is not located in a road. Locks on covers prevent unauthor-
ized persons from opening them but are a source of trouble where

the top is flush with the
ground surface, especially in
freezing weather. Probably
it is better to make the cov-
ers very heavy or otherwise
hard to lift.

Manholes are made in
various shapes and of dif-
ferent materials. A jug-
shaped structure is the most
desirable, but some mate-
rials can not be made into
this shape. Wooden man-
holes have the lowest first
cost, but their life is short.
Figure 2 shows a wooden
manhole so designed that
earth pressure will hold it
in place after the failure of
the nails.

A very good type of man-
hole for small drains can be
made from clay or concrete
pipe. Large sizes are heavy
and very difficult to trans-
port and handle. Plate
I, A, shows a_ concrete-
pipe manhole made up of
1-foot sections 36 inches in
diameter, reinforced with
heavy wire mesh. When
used on large tile lines the
lower part of the structure
is made of brick.

Galvanized corrugated
pipe has been used to some
extent. It is hght in weight
and very easy to install.
Customarily the top ex-
tends above ground and has
a cone-shaped cover of the
same material. (See pl. 1,
B.) The metal should not
be lighter than 14 gauge.

Excellent manholes’ are
made of concrete with 6-inch

walls. They are usually rectangular in form. Concrete blocks have
not been found very satisfactory. Figure 1 shows a brick manhole
with cast-iron top. This type is considered good. It is easier to

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MANHOLE COVER
Partial Plan

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Fic. 1.— Brick manhole withi cast-iron cover

construct than the monolithic concrete manhole.

4 BULLETIN 1408, U. §. DEPARTMENT OF AGRICULTURE

Drops, sometimes called “well holes,” may be needed in under-
drains. These should be built like a manhole. Small ones may be
made of heavy pipe, but concrete should always be used in large
structures and the walls should have a greater thickness than
that necessary in manholes. Plenty of depth below the outlet tile
must be provided to form
a cushion for the falling
water.

Bolt 1 2x6" 33:

SURFACE-WATER INLETS

Often where tile drains
are used provision must be
made for rapid removal of
surface water caused by
heavy rains or the accumu-
lation of waste water from
irrigation on low areas.
Such accumulations pass
slowly into dense soils, de-
laying cultivation or even
destroying crops. If the
soil is porous this water
may break into and damage
the drain. Sometimes a
separate system of shallow
ditches is constructed to
care for this water, but
often it is more satisfactory
and economical to admit
the water directly into the
drains. Surface water in-
lets have not been used ex-
tensively in the drainage of
irrigated lands except in
Yakima Valley, Wash., and
a few other places, but they

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(ZZIKXSYZ7 will be found advantageous
Fay eae cae ik properly installed and
maintained.

Where the drains are shallow: the cheapest method of admitting
small quantities of surface water is to fill a short section of the
trench with gravel or other coarse material. The sides of the trench
should be sloped. ‘Trench inlets should be located along fence lines,
if possible, or so protected that cultivation and trampling of stock
will not affect their usefulness.

Trench inlets are not desirable for deep drains. Three other
types are shown in Figure 3. Figure 3, C illustrates a type useful
where the grades throughout the system are good; but care should
be taken in using it on a line that is dry part of the time, since earth
and débris falling in during such dry periods may choke the drain.
The connecting pipe may be brought up vertically instead of on a
slope as illustrated. In this case precautions should be taken to
prevent settlement which might break the tile at the point of con-
nection. This type will also serve as a lamp hole. The riser pipe

STRUCTURES USED IN DRAINING AGRICULTURAL LAND 5

may be made of any size, but the top opening should never be less
than 12 inches in diameter. For very large inlets the upper section
of the vertical riser pipe is sometimes of larger diameter than the
lower sections and is connected with a concrete ring. Where the
soil freezes to considerable depth, a more substantial riser pipe may
be made by placing a large pipe around a smaller one and filling the

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Fic. 3.—Types of surface water inlets for closed drains

intervening space with concrete. The entrance may be protected
by a cast-iron grate of the type illustrated in Figure 3, C, or one
made in the form of the frustrum of a cone may be substituted.
The latter type is more expensive but will provide greater area of
opening. The grate should be secured against removal.

A type of inlet which will prevent débris from dropping into the
tile line is shown in Figure 3, B, but the entrance of water at the

6 BULLETIN 1408, U. S. DEPARTMENT OF AGRICULTURE

top stirs up the silt and much of it passes through the connection.
The silt traps, of 18 or 24-inch sewer pipe, have a concrete cover
provided with openings (pl. 1, A). :

A type more expensive but better adapted to exclude silt consists
of a concrete box which permits the water to enter on grade with
the outlet (fig. 8, A). This is an important part of the design, since
the disturbance of the water in the box must be reduced to a
minimum. |

Inlets with openings at the top have sometimes washed out. This
is usually caused by swirling water. To prevent this motion, the

openings in the grate must be of good

pele, size and ribs must be provided either
(QA We on the grate or the concrete rim sur-

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rounding it, as shown in Figure 3.

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WS zy vs & #“% located at one side of the drain and not
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sy YAS be made with sewer pipe and the
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3, A, shows this pipe leading hori-
zontally to a point over the drain and
then straight down, an arrangement
often necessary at connections with
drains constructed in soft ground
where sheeting is employed; otherwise
the better method is to slope the pipe
directly to the drain. Connection with
the drain should be made with a
BY DSPUSSNS T-junction and the tile at this point
toxins «surrounded with gravel or concrete.
For those types shown in Figures 3, A,
and 38, B, the covers should not be
eee, | OCKeU ON, SO thal (ie Ihe Canecuam
AKEMMAIIZ/-awW/E,_~—«tthe traps, and the outlet pipe should
Fic. 4—Lamp hole for observation Not be put lower than necessary to
' have it out of the way of cultivation.
A concrete bottom should be provided in silt traps, and in every case
the earth should be well puddled around the entire structure.

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LAMP HOLES

For observation purposes on underdrains, lamp holes are some-
times installed at angle points or curves where manholes are not
constructed or at intervals on long tangents (fig. 4). The same
objections apply to their use as to manholes but in a lesser degree.
The connection with the drain is best made with a T-junction, but
may be made by cutting a hole in the top of the tile and extending
a 6-inch pipe from this to a point about 1 foot above ground. The
earth around the riser should be puddled and a bank thrown up
around that part above ground. If possible they should be out of
the way of farm machinery. If necessarily installed in fields a
protecting post should be set by each.

A lock-fastened lid is likely to be unsatisfactory, but a wire screen
across the first joint below the top will keep out rubbish and small

Listens

oF ol

STRUCTURES USED IN DRAINING AGRICULTURAL LAND vf

animals. Heavy galvanized wire with meshes of one-third or one-
fourth inch will exclude everything but fine débris, and the tile
line can be inspected readily by reflecting hght toward the bottom

with a mirror.
CRADLES

In soft ground some means must be provided for holding the tile
in alignment. The best method consists of excavating the trench
below grade and tamping in gravel until a firm foundation is made.
Boards may be laid under small drains where the bottom of the
trench is not too soft. They should be fastened together at each
joint by short strips underneath.

In very soft ground cradles on piling may be required. For
small drains they can be made of two parallel 2 by 4 inch stringers
held together by 1-inch cross boards. The upper inside corners
of the stringers should be beveled, and they should be so spaced
that the tile will bed firmly on them. The cross strips should be
arranged so that overlapping will occur at each joint. At the up-
stream end of each set of stringers the crosspiece should extend .
at least 6 inches beyond the stringers, with the grain parallel to
the stringer, but the other two crosspieces should be nailed on with
the grain at right angles to the stringers (pl. 1 C). The sections
should be nailed together at the joints and to the piles, on which
the crosspieces must rest. This work often has to be done under
several inches of thin mud; but the nails or spikes may be easily
driven if inserted in a short section of small pipe, by striking the
nail head with a rod that fits snugly in the pipe.

Tor tile larger than 8 inches the stringers must be made of 4 by 4
inch timbers fastened together with planks as shown in Figure 5.
The upper inside corners should be beveled, and they should be
spaced so that the tile will be supported as nearly as possible at its
quarter points. When pipe with bell ends is used, notches must
be cut in the timbers. Joints of the stringers should be staggered
and cross sills at joints should be 2 by 6 inch planks. Usually it
is difficult to cut off the tops of piles in the bottom of a trench,
but sometimes piles of the same or a gradually changing length
may be used where conditions can be anticipated closely. The driv-
ing may then be stopped at the proper point to support the cradle.

In difficult construction it is not expedient to open a long line
of trench ahead of the tile. For this reason and because of the
many braces in the trench, cradles made up in short sections must
be used. Their length should have some relation to the length of
the sets used in sheeting the trench.

ANGLE BOXES

At angle points on main drains, not sharp enough to call for a man-
hole, an angle box should be made of a pipe somewhat larger than
the diameter of the tile, extending from a point a few inches below
the bottom of the tile to the ground surface; and a small drop should
be provided between the inlet and outlet. A corrugated iron pipe
is desirable for this purpose. Angle boxes are sometimes made of
large sewer pipe at the bottom, above which is placed a reducer and
then a stack of 8 or 12-inch pipe extending to the top, which can

8 BULLETIN 1408, U. S. DEPARTMENT OF AGRICULTURE

be made as for a lamp hole or like the top of the surface water
inlet shown in Figure 3, C. Elimination of the expensive reducer
may be accomplished by use of a concrete ring placed in the bell and
having its inside diameter the same as the interior of the small pipe
used above. (See pl. 1, A.) For large lines, manholes had best
be used.

LATERAL CONNECTIONS

Main lateral connections should be made with manholes, but for
small connections angle boxes will serve the purpose. On a system
having a great many closely-spaced farm laterals, it probably will
be necessary to eliminate these structures and simply make a hole
in the upper part of the main lateral to receive the end of the small
farm lateral. This joint should be well surrounded with pieces of

DIMENSION TABLE

4x4" Stringers rough

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Berrie ers)
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Mer eer ae |

Fie. 5.—Cradle for supporting large tile in soft ground

broken tile and gravel or concrete. The elevation of the top of
the small lateral should be near that of the top of the line to which
it is connected. If possible, branch hnes should be provided where
numerous small farm laterals are needed, as it is not advisable to
connect these with main trunk drains.

OUTLETS

Structures are usually necessary at outlets of underdrains to prevent
injury from frost and to afford protection of adjacent banks. For
drains with diameter of 16 inches or less a continuous section of
wood box or corrugated pipe will be satisfactory (pl. 1, D). This
should be from 14 to 20 feet long, depending upon the slope of the
bank and nature of the material. A tight box made of 2 or 3-inch
lumber will prove economical. However, boxes are likely to be

PLATE I

A, Concrete pipe manhole and surface-water inlet. B, Sections of corru-
gated metal manhole. C, Cradle for small tile in soft ground, Palisade
drainage district, Mesa County, Colo. D, Corrugated pipe outlet for
closed drain. #, Outlet structure and surface-water inlet, subdistrict
No. 7 of drainage district No. 3, Yakima County, Wash. F, Automatic
gate outlet. G, Drop, Millard County, drainage district No. 3, Utah.
H, Timber lining and drop (looking downstream), Sulphur Creek wastec-
way, United States Bureau of Reclamation, Yakima project, Wash.
I, Surface-water inlet near Brownsville, Tex. J, Surface-water inlets
and irrigation flume, Ada County, drainage district No. 2, Idaho

STRUCTURES USED IN DRAINING AGRICULTURAL LAND 9

destroyed where weeds on the banks of the main drain are burned,
and in such places heavy corrugated pipe must be used. The outlet
end of such conduits should protrude a short distance from the bank
so that the water in the channel will make a cushion for the outflow
of the drain.

For large drains, concrete bulkheads, wing walls, and an apron for
the falling water should be provided (fig. 6). Modification of the
wing walls is required where the drain enters the channel at a
sharp angle. Reinforcing must be used for large structures, and
for all structures if in very soft soils. The main considerations
should be stability and prevention of undermining or cutting around
walls. To prevent damage from floods in the main channel, the
structure should be set well into the bank. Failures may be caused
by surface water flowing over or around the outlet, to prevent which
surface-water inlets should be provided with the lower end of the
pipe passing through the head
wall of the concrete outlet struc-
ture at one side of or just above the a” Bohs fi SRS
drain, as shown in Plate 1,E. This &* holding gate 715! coment joints
type is particularly desirable where pean ith F2| for distance
the outlet is just below a road. If
frequent heavy floods are antici-
pated the structure must be de-
signed as a check or drop similar ——
to that shown in Plate 1, G, with Sa ei
the underdrain outlet in the lower cnet es
part of the breast wall.

SP ERET SBE

Grea meen A Bho SiS
5

Concrete 8” thick up to D=24”
10" 24"to36”

Where outlets of underdrains are 4
at times completely submerged, it We
is advisable to provide fiap gates
to prevent water from backing up ce
the drain. ‘These valves may be a
made of lumber, but under many |
conditions an automatic iron gate ae
will prove very satisfactory, as PLAN

shown in Plate 1, F. For small se. ¢—outiet structure for closed drains
drains they may be attached to

the end of a corrugated iron pipe, and for large drains they should
be installed on the head wall of the concrete outlet structure. Drains
not submerged may require a flap gate made of rods to keep out
small animals,

CROSSINGS UNDER RAILROADS AND CANALS

Where underdrains cross under railways and canals, pipe with
bell-and-socket joints should be used and the joints made tight
with mortar. Pipe of extra strength should be used immediately un-
der the fill or canal. A concrete foundation usually envelops the
lower half as shown in Figure 7, and the pipe is laid before this con-
crete has set. This foundation should extend not less than 6 inches
below the bottom of the pipe and its total width should exceed
the outside diameter of the pipe by not less than 8 inches. In
trenches with exceptionally soft bottoms, gravel should be tamped
in before the concrete is placed.

83435 °—26——_2

10 BULLETIN 1408, U. S. DEPARTMENT OF AGRICULTURE

For canal crossings three cut-off walls should be constructed as
shown in Figure 7. "The minimum height and width of these should
be 4 feet. Under some canals it may be desirable to use, on the
lower side, only one cut-off wall extending to the top of the embank-
ment instead of two small ones as shown. Should the top of the
pipe coincide closely with the bottom of the canal, the whole sec-
tion between the two upper cut-off walls should be cased in concrete.

Railway crossings are similar to canal crossings except that cut-
off walls are omitted.

LUMBER BOX DRAINS

Box drains are chiefly used where cost of transportation prohibits
use of tile. The life of a wooden structure is reasonably long if it
is always wet; but failure, especially of the top, may occur in a few
years where alternate wetting and drying take place. The boxes

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should be built to retain their form after failure of the nails, which
will happen soon if alkali is present. Shoulders milled in the lum-
ber effect this; they are cut cheaply by passing each end of the top
and bottom boards over a circular saw set to cut a rabbet as deep
as the thickness of the saw and as wide as the thickness of the side
planks (fig. 8).

The ih pe shown in Figure 8, A may be used for small sizes where
cheapness is desirable. The lumber runs with the box and long
sections may be made. The bottom is held from the sides by short
pieces of lath separated to admit the water. The widest boards
should not exceed 8 inches for 1-inch lumber and 12 inches for
2-inch lumber. Lumber for the top and bottom of larger drains
should run crosswise, with the ends milled to provide shoulders
(fig. 8, B). Decay is likely to be the most rapid at the top, which

STRUCTURES USED IN DRAINING AGRICULTURAL LAND 11

should be 2-inch material. One-inch lumber will do for bottoms
except in fluid soils where an upward pressure is exerted. The top
pieces should fit tightly together, but the bottom pieces should be

separated from one-fourth to one-half inch to admit water. Such.

boxes should not be over 24 inches in width nor over 14 inches in
height. In larger sizes 3-inch lumber should be used for the top,
with the sides made up of short pieces and arranged so that the
joints interlock as shown in Figure 8, C. The larger sizes should
be built in short sections and arranged so that joints can be fastened
together.

Trenching covers a large percentage of the total cost of deep
drainage, and it will usually prove better economy in the long run to
use durable material even at a greater first cost.

STRUCTURES FOR OPEN DITCHES
DROPS AND CHECKS

To prevent injury to canals from excessive velocities, drops are
installed to concentrate the excess fall at one or more points. Plate
1, G shows a type used for small discharges. In design, drainage

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drops are not different from those used in irrigation practice with the
exception that in most cases they should be able to withstand the
destructive action of discharges considerably in excess of the normal
flow of the canal.

The primary purpose of many open drainage systems is to carry
seepage water, and to provide drainage this flow may occupy only
a small part of the cross-sectional area of the channel, which may
have steep grades without danger of erosion. However, floods or
breaks in irrigation systems may produce high velocities and con-
sequent damage. This may be overcome by (1) reducing the grade
and installing drops; (2) using checks to retard flood flows but
also permitting the passage of the normal fiow without checking; or
(3) a combination of these two methods. Figure 9 and Plate 1, H
show a combination check and drop which may be made to serve
equally well for any one of the three methods by the varia-
tion of certain dimensions. The breast-wall or overflow weir should
be made as long as possible and the opening for normal flow as large
as conditions will permit.

Factors to be considered in the design of such a system are: (1)
Quantity of normal flow, its depth, and minimum velocity permis-
sible; (2) the volume and maximum allowable velocity of the flood

aera

BULLETIN 1408, U. S. DEPARTMENT OF AGRICULTURE

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STRUCTURES USED IN DRAINING AGRICULTURAL LAND 13.

linings are employed to prevent sloughing in of soft material. These
are usually constructed without a bottom. They should be designed
as simply as possible. . Usually they are regarded as temporary
structures which will not require replacement after the water table
has been lowered and the slope of the banks has become stable.
Unless a bottom is needed they should be made as wide and low as
possible, so that after they have decayed little or no smoothing of the
banks will be required. Careful placing is necessary to insure that
such structures will remain in alignment, both vertical and hori-
zontal. Although sometimes necessary, cross braces on the top

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PARTIAL PLAN
Fie. 10.—Types of cunettes

usually are objectionable, particularly where large weeds are apt
to blow in. If such braces are used, they should be placed well above
the surface of the normal flow.

Three types are shown in Figure 10. (See also pl. 1, H.) The
type shown in Figure 10, B does not require piles and may be used
where the bottom is firm and there is no difficulty in maintaining
horizontal alignment. The design in Figure 10, A calls for piles
at intervals of 5 or 6 feet. In case these can not be driven into
firm material, a top cross brace or a side brace as shown in Figure
10, B will be required. The loading boards on the outside help to

14 BULLETIN 1408, U. S. DEPARTMENT OF AGRICULTURE

keep out the soft material and to prevent the structure from
floating.

In exceptionally soft ground a bottom may be needed, or at least
one or two planks on each side, to prevent material from being forced
up into the ditch. When a bottom is planned, either the piles should
be very firm or extra width should be given the loading boards to
prevent lifting. Figure 10, C shows a design by which bottom plank-
ing may be avoided. It consists of sheet piling driven deep enough
to prevent pressure of the banks from forcing the material up into
the ditch.

These structures are expensive and are to be avoided whenever
possible. In some districts drainage ditches in soft material have
been dug in successive stages; in other instances excavation has been
carried as far as possible and the ditches sluiced to completion by use
of large heads of water. Using a flat side slope is sometimes cheaper
than the methods described above, and often the trampling in of
brush and weeds will prove effective. Russian thistles have been used
successfully for this purpose.

ML IIID

LAA
S

END VIEW

SECTION

Fie. 11.—Surface water inlet for open drains

SURFACE-WATER INLETS

Surface inlets are installed on open drains to permit entrance of
water wasting from irrigation and run-off from heavy rains, without
injury to the banks. For irrigation waste the most common and
cheapest form consists of a short wooden flume secured at the upper
end with a cut-off wall and extending out over the bank of the
canal, so that the inflow will discharge upon the water passing down
the drain. (See fig. 11; pl. 1, J; and pl. 2, H.) These are some-
times destroyed by fire. A more permanent type consists of a cor-
rugated metal pipe and a concrete cut-off wall, the length depending
on the slope of the bank and the nature of the ground. In loose-
grained soils, easily eroded, the cut-off wall should be located further
from the edge of the bank than shown in Figure 11. Where main-
tenance may require the use of heavy machines operating from the
bank of the canal, the upper end of the pipe or flume and cut-off
wall should not extend above the surface of the ground. Where
banks are not subject to erosion by water in the main canal, and
cobblestones are handy, satisfactory inlets have been constructed by
excavating small chutes and lining them with cobblestones in cement
mortar.

Plate 1, I shows a type used to admit the run-off collected by shal-
low road or farm ditches in sections having heavy rainfall. In the

STRUCTURES USED IN DRAINING AGRICULTURAL LAND 15

case shown, where the inlets are located opposite each other on a
narrow canal, a concrete apron extends across the entire bottom.
For single inlets the outlet structure should be similar to that shown
in Figure 6. A pipe is connected with a concrete cut-off wall or
other form of intake structure at the upper end. Where concrete
culverts or bridges with concrete abutments and wing walls or other
structures are near such inlets, the lower end of the pipe should pass
through these walls to obviate the necessity for a special structure
at the pipe’s lower end. If the pipe is to be made up of short sec-
tions, usually it should be incased with concrete.

STOCK GUARDS

Where fence lines cross open drains subject to wide variations in
discharge, stock guards should be so constructed as to offer but little
restriction to flow at high stages. Such a guard can be made in the
form of a wooden gate pivoted at each side of the channel, so that
the bottom will swing downstream about a horizontal axis.

SLUICEWAYS AND TIDE GATES

Lands affected to some extent by tides or subject to occasional
overflow from rivers are protected by levees or dikes. After periods
of flood the interior water or part of it may*be discharged by
gravity through sluiceways of various materials, such as wood,
concrete, and iron pipe. Reinforced concrete usually is best for
large outlets, which are similar in design to large culverts in soft
formations. They are usually located: near the outlets of large
sloughs which have been cleaned out and used to storé and convey
the interior water to the sluiceway. The structure should generally
be located on the bank at one side of the slough where a sump
may be excavated by a dredge, obviating in many cases the neces-
sity for cofferdams and also affording better foundation material.
After the structure is completed channels for inlet and outlet may
be excavated.

Gates hinged at the top and placed at the discharge end of the
sluiceway are better adapted to ordinary practice. In this arrange-
ment each sluice should be not more than 5 feet in height by 6 or 7
feet in width, and often smaller dimensions are preferable. To pro-
vide sufficient waterway several conduits or boxes may be built to-
gether, and except for small farm installations there should never be
less than two openings. :

The length of the sluiceways will depend upon the width of the
embankment at its location. For greatest efficiency the elevation of
the sluiceways should be such that the gates will be submerged at all
stages of the water. Substantial head and wing walls must be pro-
vided at each end and the outlet end protected against erosion,
drift, or ice. Grooves or guides should be provided for emergency
gates to cut off the water and permit the sluiceway to be drained
by pumping, inspected, and repaired, and for use in case of damage
to the tide gate. A trash screen should guard the interior end.

It has been necessary to support many of these structures with
piling. Frequently, however, the material under the sluiceways set-
tles under the weight of the adjoining levee, and when piling is

16 BULLETIN 1408, U. S. DEPARTMENT OF AGRICULTURE

used an opening is left under the floor through which water is very
likely to pass even though good cut-off walls have been installed.
Some engineers build these structures without foundations with the
expectation that they will settle somewhat. The sluiceways are
designed to withstand the strain of such movement, and an effort
is made to weight them so that the settlement will be uniform. This
method appears to be satisfactory. |

Cut-off walls are an important part of all such structures. Not
less than two lines should extend crosswise under the bottom, up
the sides and well out along the line of levee. Where piles are not
employed care should be used that portions of the cut-off walls do
not reach into firmer material and prevent uneven settlement; it
may be necessary to depend upon a greater number of lines of short-
length sheet piling. Head walls and cut-off walls are equally nec-
essary where pipe is used for conduits.

Iron tide gates, machined to provide close seating, in many cases
have been highly satisfactory. Where chemicals in the water may
corrode iron, bronze or wooden gates should be installed. Wood
gates have had wide use and where properly constructed and con-
tinuously submerged have given excellent service. Figure 12 shows
a wooden flap valve made up of a double thickness of 2-inch mate-
rial cross lapped and well bolted together, with an angle iron frame
on the outside. Three-inch material embedded in concrete forms
the seat. This particular gate is suspended from two trolley rails,
which readily permit it to move outward. This gate will operate
under very low heads and was designed especially for districts in
the vicinity of Portland, Oreg.

Many types of hinges have been designed to meet particular con-
ditions. A short single-pin hinge is not desirable; better balance
and action will be obtained from a double-pin hinge connected with
a long link or hanger bar and fastened to the gate about one-third
the distance from the top. The lower part of the gate should be
arranged so that weights can be attached or removed readily, and
adjustments made after the gate is in place so that it will operate
under a very low head. ‘The seat should incline from the vertical
slightly, but not more than 18°, so that the gate will seat tightly at
low water. Careful and accurate construction should insure this.

Plate 2, A shows the land end of a reinforced concrete sluiceway.
This particular structure has a superimposed culvert and a platform
on the interior end to provide for the installation of an electrically
driven chain-lift pump the use of which may be required occasionally
when the gravity discharge is not sufficient.

Where tidal range permits and much water is to be passed, sluice-
ways with wide gates hinged at.the side are used. These gates are
the so-called “ barn-door ” type which has had successful use in cer-
tain sections of the Southeast. The bearings supporting the gate
should be bronze or some other noncorrosive material. The frame
should be wood, which best absorbs the shock occurring when the
gates close against each other. The gate panels may be steel as in
Plate 2, B. When closed the gates should be at an angle of from 18°
to 28° with a line connecting their points of support. The bottom
of each gate fits against an offset on the concrete floor of the
structure.

PLATE II

Ar Sluiceways for tide gates, Wahkiakum County, Wash. 8B, Sluice and
tide gates combined with highway bridge, near Savannah, Ga. OC, High-
way bridge over drain, United States Bureau of Reclamation, Rio Grande
project, N. Mex. D, Concrete-arch culvert, Ada County, drainage district
No. 2, Idaho. £, Ocean outlet, Oxnard drainage district, Ventura
County, Calif. F, Flood gates, diking district No. 2, Pend Oreille County,
Wash. G, Relief well connection, Livermore Valley, Alameda County,
Calif. H, Concrete culvert and small flume, Ada County, drainage
district No. 2, Idaho. J, Flume and farm crossing, United States Bureau
of Reclamation, Rio Grande project, N. Mex. J, Culvert and connec-
tion for flushing open drain, drainage district No. 2, Yakima County,
Wash. For plans see Figure 5. K, Concrete fiume and structure for
diverting water from drain for irrigation, United States Indian Irriga-
tion Service, Yakima project, Wash. JL, Concrete flume with waste gate
for flushing drain, Boise Valley, Idaho

ma 5 ‘

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STRUCTURES USED IN DRAINING AGRICULTURAL LAND
Where occasional floods pass from high lands down the main
drains, water must be prevented from backing up in laterals across
nary sluice gate hinged at the top, except that the gate is placed

flat bottom land. The type of structure used is similar to an ordi-

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The structure

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Plate 2, F shows
location of these

at the inner instead of the outer end and a manhole i
of the interior

gate to permit of easy inspection and for makin

18 BULLETIN 1408, U. 8S. DEPARTMENT OF AGRICULTURE

railway embankment near the outlet of a stream draining the back
area. The gates are made of heavy timber, but the structure itself
consists of two concrete sluiceways each 7.5 feet wide, 10 feet high,
and 85 feet long, these large openings being necessary to permit pas-
sage of logs. This sluiceway is supported with piling.

OCEAN OUTLETS

Some drainage districts are so situated that their outlets must
discharge directly into the ocean (pl. 2, E). Such structures are
continually subject to wave action intensified at times by storms.
The profile in Figure 13 shows the conditions existing at the outlet
of the Oxnard drainage district, Ventura County, Calif.

Tide records and the tide tables of the United States Coast and
Geodetic Survey should be studied in planning ocean outlets. The
mean rise and fall of spring tide varies from 5.1 feet at San Diego,
Calif., to 7.7 feet at Astoria, Oreg., with extreme variation several
feet more than this. The elevation of mean lower low water is 2.9
feet below mean sea level at San Diego and increases to 4.6 feet at
Astoria. The elevation of the invert of outlet end of sluices will de-
pend upon the elevation of land to be protected, tidal range, and
difficulties of construction, but it should usually be below mean
lower low water. The elevation of the Oxnard outlet is 4 feet be-
low mean lower low water or 6.9 feet below mean sea level, United
States Coast and Geodetic Survey datum. The extreme low tides of
the year go below this, but usually the full ebb does not.

All possible information should be obtained regarding the per-
manence of the shore line and the soil through which the outlet pipe
will pass. After the installation of the Oxnard outlet the loose for-
mation at the outer end was shifted by wave action, with the result
that the piling and outer end of the pipe were washed away.

The end of the pipe should be carried out until the invert is about
2 or 2.5 feet above the ground surface. If it is carried out too far
the difficulty of holding the structure in place will be increased,
whereas too short a distance will permit sand to be washed in.

Because of ease of installation and flexibility, corrugated-iron cul-
vert pipe, heavily galvanized, is well adapted to construction of the
outer end; hght cast iron has longer life. The sand-covered part
of the conduit may be any strong, durable type. Besides the difficulty
of holding the outer end in place some trouble may be experienced
in making the pipe joints air tight, or as nearly so as is possible.
Wave action may cause air and water to flow through weak joints,
sucking sand into the pipe or completely uncovering it so that the
entire structure may be endangered at high tide. Where corrugated
pipe is used the joints at the outer end should be secured with a band
not less than five corrugations wide equipped with pull lugs to
insure adequate clamping. The safest method of protecting those
joints entirely covered with sand is to surround them with concrete.

Figure 13 shows a good design for the supporting structure.
Square reinforced concrete piles are used. This form is easily made
and offers greater clamping surface for the caps. The wooden caps
should be creosoted and the pipe must be slung from the caps. Never
less than two pipe lines should be installed, so that if one is dam-
aged the other may operate while repairs are being made. Two

STRUCTURES USED IN DRAINING AGRICULTURAL LAND 19

lines make possible a supporting structure of greater stability. Pro-
vision for breaking the force of waves against the outer end
should be made as shown in the illustration.

The gates must of necessity be at the land end. The gate cham-
ber should be reinforced concrete supported with piling and should
be divided into as many sections as there are outlet pipes. Grooves
adjacent to the outlet pipes are desirable to accommodate flash
boards for an emergency gate. Figure 13 shows self-acting iron
tide gates, but lumber gates properly balanced might serve very
well. The design shown is similar to the Oxnard outlet in that two
gates for each outlet pipe are used. Where the outlet pipes are

Air Vents. 6” Pipe—~ Soin

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less than 20' at

Penetration not
outlet end.

SECTION A-A

Fic. 13.—Outlet structure into ocean

less than 5 feet in diameter one gate for each, of proper size, will
be sufficient. Cut-off walls of sheet piling should extend out a con-
siderable distance beyond the ends of the wing walls, and a trash
rack must be provided.

BRIDGES AND CULVERTS

Bridges and culverts are among the most expensive structures used
for open drains.

Permanent structures of steel, concrete, or treated timber are re-
quired for railway or primary road crossings and must conform to the
requirements of the railway or highway system on which they are
built. The bed and banks of ditches are subject to considerable

20 BULLETIN 1408, U. S. DEPARTMENT OF AGRICULTURE

erosive action, the extent of which can not be foreseen with any cer-
tainty. ‘Location of substructure should allow sufficient unobstructed
waterway at time of greatest flow and abutments should be so lo-
cated as to prevent water seeping behind them after possible erosion
of adjacent banks. Foundations should extend below the anticipated
erosive effect of the current and never less than 3 feet below the
bed of the ditch in. material other than rock, hardpan, or clay.
Piers or bents should not be placed in the watercourse.

Since they perform the same service, these bridges should afford
the same security as those elsewhere on the railroad or highway and
should be designed and constructed according to the same principles
of permanence as well as economy.

The permanent crossing types are reinforced-concrete box and arch
culverts, slab and T-beam spans, steel girders, low trusses, and
treated-timber trestles. Where the passage of floating equipment is
necessary, spans which can be lifted to one side should be provided.

Most open-drain crossings, however, are for secondary or farm
roads where permanent structures are not justified. Extreme flood
conditions are seldom provided for in designing bridges of this type.
They are generally simple beam spans or timber trestles. |

The former are satisfactory for narrow ditches, banks of which
suffer little erosion and give firm support to the mud sills or blocks.
Short, longitudinal mud blocks give greater and more uniform bear-
ing area than sills placed directly on the ground. The life of sills
and blocks may be increased by embedding them in gravel or
broken stone, to drain off the water.

Decay of the stringers at the ends of trestles may result from their
contact with the ground. A clearance of at least 12 inches should be
provided to prevent this.

Timber trestles (fig. 14) should consist of a channel span over
the center of the ditch and approach spans long enough to place the
ends of the trestle out of range of ordinary erosion. (See pl. 2, C
and pl. 2, 1). This arrangement is better than two-span trestles
with a bent at or near the center of the ditch, because of the ob-
struction to flow offered by the central bent. Single-span trestles
with timber back walls higher than 2 feet are not desirable because
the timber in the back walls is subject to rapid decay, and earth
pressure against a back wall on a timber bent tends to push the
bent out of place. Longitudinal bracing to prevent this obstructs
the waterway.

A timber trestle may be supported on either pile or frame bents.
Pile bents should consist of three or more piles and be braced. with
double diagonal sway bracing. The cap should be drift bolted to
each pile and the bracing should be bolted or spiked to the cap and
each pile. Under some conditions pile bents are not economical for
small jobs, because they can not be driven to good bearing by hand
and the cost of pile-driving equipment is not justified for the few
piles needed.

Frame bents consist of three or more posts and a cap and sill,
which may be placed directly on the ground on mud blocks or on
concrete piers or pedestals. They should have double diagonal brac-
ing bolted at the ends to the cap and sill and at intermediate points
to the posts. The caps and sills should be dapped to receive the ends

STRUCTURES USED IN DRAINING AGRICULTURAL LAND

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22 BULLETIN 1408, U. S. DEPARTMENT OF AGRICULTURE

of the posts, to which they should be securely drift bolted. The
sills should be anchored to concrete piers or pedestals by bolts in the
masonry and extending into the sill. The provisions to be made
against undermining of the foundations by erosion are explained on
page 20. Concrete foundations should be high enough to keep the
timber sills above the ordinary water level, with such bearing area
at the bottom as will prevent settlement.

Spacing between stringers should be not more than 27 inches cen-
ter to center, preferably between 18 and 24 inches. Inside stringers
should have full bearing on the caps, and should be separated at the
laps to avoid retention of moisture between them. The outside string-
ers may be placed end to end over the center line of the cap. Double
2 by 4 inch bridging should be used when the width of stringer is
less than one-third of the depth. The number of lines used should
depend upon the span, as follows: Spans under 15 feet, 1 line; spans
from 15 to 20 feet, 2 lines; spans above 20 feet, 3 lines. Tables 1 and
2 show sizes and number of stringers for various spans, allowable
unit stresses, and widths of roadway.

Floor planks, spiked to each stringer, should be not less than 3
inches thick for public highway crossings and 2 inches for private
crossings, but preferably 3 inches for a 5-ton loading.

TABLE 1.—Size and number of stringers for timber trestles using Western larch,
Pacific post oak, bur oak, bald cypress, mountain region Douglas fir, or red-
wood for which a fiber stress of 1,200 pounds per square inch is assumed

[Truck load 80 per cent on rear axle, axles spaced 12 feet, wheels spaced 6 feet impact 30 per cent]

16-foot roadway 14-foot roadway
10-ton truck 5-ton truck 3-ton truck
Span
Lumber Lumber Lumber
in string- in string- in string-
Stringers required| ers per | Stringers required} ers per | Stringers required| ers per
lineal foot lineal foot lineal foot
of bridge of bridge of bridge
Feet Number| Inches | Feetb.m.|Number| Inches | Feetb.m.|Number| Inches | Feetb.m.
Qs Se ee 12 4x12 48. 0 Vill 3 x 10 27.5 10 2x10 16. 7
9 4x14 42.0 8 3 x12 24. 0 Zi 3x 10 Wit
LQ ae le Wesel aie 11 4x14 51.3 13 3x10 S25 12 2x10 20. 0
9 4x 16 48. 0 9 3 xo? 27.0 8 3x 10 20. 0
1, Hie o> Se ice 4 Let 13 4x14 60. 7 11 Oo Xl 33. 0 10 3x 10 25. 0
10 4x 16 53.3 8 4x12 32. 0 7 Boke le 21.0
9 6x 14 63.0) | sso en Sek ee 2 ee ee eee
Ge es Peer a it 4x 16 58. 7 12 3} >. 36. 0 11 3x10 2155
10 6x 14 70.0 10 4x12 40.0 8 yey 24. 0
aS ee ee 13 4x16 69. 3 13 Exel2, 39. 0 13 3x10 32. 5
11 6x 14 77.0 11 4x12 44.0 9 3 xX pl2 27.0
9 6 x 16 72.0 8 4x14 37.3 7 4x12 28. 0
20 ee ba ee 13 6x14 91.0 12 4x12 48.0 10 3x12 30. 0
10 6 x 16 80. 0 9 4x14 42.0 8 4x12 32. 0
Set | eye rae | ye ee b 4x16 Ole. |- ak Gass) 2 ba SS ees
Dad Mes 25 Ea Ro cai 14 6x 14 98. 0 13 4x12 52. 0 12 3 x2 36. 0
11 6x 16 88. 0 10 4x14 46. 7 9 4x12 36. 0
8 6x18 20 8 4x16 4D. || = se Se ee See ee
DAR enna eat Sak 12 6 x 16 96. 0 11 4x14 51.3 13 3x12 39.0
10 6x18 90. 0 9 4x16 48, 0 10 4x12 40.0
ie 3 ee | Set eee ee ee 8 6 x 14 56. 0 8 4x14 37.3
26%)_2 ee See 14 6x 16 112.0 13 4x14 60. 7 12 4x12 48.0
11 6x18 99. 0 10 4x16 58% 3° 9 4x14 42.0
8 8x18 96. 0 9 6x14 63.0 |) .t3. eRe eee
D8 2 te 3s at Se 12 6x18 108. 0 13 4x14 60. 7 13 4x12 52. 0
12 8x 16 128. 0 11 4x16 53. 3 10 4x14 46.7

STRUCTURES USED IN DRAINING AGRICULTURAL LAND 23

TABLE 2.—Size and number of stringers for timber trestles using tanbark oak,
white oak, Cuban pine, longleaf pine, coast region Douglas fir, and shortleaf
pine (treated) for which a stress of 1,600 pounds per square inch is assumed

[Truck load 80 per cent on rear axle, axles spaced 12 feet, wheels spaced 6 feet, impact
30 per cent]

16-foot roadway 14-foot roadway
| 10-ton truck 5-ton truck 3-ton truck
Span |

| Lumber Lumber Lumber

in string- in string- in string-

| Stringers required) ers per | Stringers required} ers per | Stringersrequired| ers per
lineal foot! lineal foot lineal foot

of bridge of bridge of bridge

Feet Number| Inches | Feetb.m.|Number| Inches | Feet b.m.|Number| Inches | Feet b. Me
1] erie. on IZ] * 3x12 36. 0 12 2x10 20. 0 8 2x10 13.3
9 4x12 36. 0 8 3x10 PAG OF ia Woes |S ae Ce |e ee
| 7 teens ee ee 11 4x12 44.0 10 3x10 25. 0 9 2x10 15.0
9 4x14 42.0 i 3x12 21.0 ,.|2e oe 3 aed ee
Ase 2 2 17) eorars 13 4x12 52. 0 11 3x10 225 1] 2x10 18.3
10 4x14 46. 7 8 | 3x12 24.0 7 | 3x10 Wats
8 4x16 ART Aer es Es eileen | nano HORI 17 Se Sin ao SE
1G PATE Res Sy 11 4x14 51.3 13 | 3x10 32. 5 12 2x10 20. 0
9 4x16 48.0 10 | Bi. Pe 30. 0 9 3x10 22.5
Ls ati Les aes Bara. Pee 8 4x12 BAN eee ee | (pe eee a (eee
ik eS eee, © ee 13 4x14 60. 7 11 3x12 33. 0 10 3x10 25. 0
| 9 6x14 63.0 8 4x12 32.0 7 3x12 21.0
10 4x16 HSU )s | eat ln eee Se PEPER Es | (tM sD cee ler aie ge 8) Cot eee
Fe Re 2 By eso 10 6x14 70.0 12 | 3x12 36. 0 11 3x10 he
14 4x14 65.3 9| 4x12 36. 0 8 3x12 24.0
11 4x16 58. 7 7/ 4x14 VON fet Re eee | Snel ie Sey (er ee
DD ON. AE re 12 4x16 64.0 13 3x12 39.0 | 12 3x10 30. 0
1i 6x14 77.0 10 4x12 40.0 9 3x12 27.0
8 6x14 64.0 8 4x14 Si3s = See ee ee Raee as
DAs ee ee 13 4x16 69.3 11 4x12 44.0 14 3x10 35. 0
11 6x14 77.0 9 4x14 42.0 10 3x12 30. 0
9 6x16 CTSNet (DA oe Fe ia Sat 8 4x12 32.0
DG Bn ee 13 6x14 91.0 13 4x12 52. 0 yal 3x12 33. 0
10 6x16 80. 0 10 4x14 46. 7 9 4x12 36. 0
8 6x18 72.0 8 4x16 C. OG Wiel Se Sea, (GEE Se eae ean See
ee Me ea ee 14 6x14 98. 0 11 4x14 51.3 De 3x12 36. 0
11 6x16 88. 0 8 4x16 42.7 10 4x12 40. 0
9 6x18 81.0 Zi 6x14 AGS Ou | Saas ee eae
9 8x16 96. 0 lepo= lop oes sailca erat Gas eS a re

Handrails should be secured to the outside stringers by at least
two bolts, spaced as far apart as the depth of the stringe> permits.
The usual type of handrail has one rail spiked to the top of posts
and two side rails, one at the top of the post, the other midway be-
tween the floor and the top of posts. A wheel guard should be on
each side of the roadway and be wide enough to prevent contact be-
tween vehicles and handrails.

For small drains, or large ones where the discharge is not exces-
sive or subject to considerable increase, a culvert is more economical
than a bridge; but in deciding between them it must be remembered
that a culvert must be capable of passing more than the normal flow,
otherwise weeds and debris may clog the intake. Pipe culverts
should never be less than 15 inches in diameter. Except for very
shallow fills, two parallel lines are not recommended, because of
their cost and the greater possibility that the waterway may become
obstructed. On many drainage ditches, culverts can not be used
because of floods which occasionally greatly exceed the normal flow,
and in some districts because small motor boats are used in main-
tenance work.

24 BULLETIN 1408, U. S. DEPARTMENT OF AGRICULTURE

Corrugated-metal pipe is easily installed and on farm crossings
it may be used without end walls. Very good small culverts can be
made of concrete or vitrified clay pipe. They require good founda-
tions. For corrugated-metal pipe, the coefficient of roughness, n
in the Kutter formula, ranges from 0.019 for the 12-inch size to
0.023 for the 80-inch size. For the same sizes of vitrified clay pipe,
n ranges from 0.010 to 0.018. For large sizes the reinforced box
will be more nearly permanent (pl. 2, H) or where good natural
foundations exist arch culverts of plain concrete may be used (pl.
2, D).

ne end walls should be used on most types of culverts except
wood. (See pl. 2, D, and pl. 2, J.) Figure 15 gives designs for two

W:-4 D ana
WY \888
Ort HON

: kB» SECTION R-R
Front Elevation KBr Front Elevation *T'* Find Elevation

Concrete /:3:6

CONCRETE END WALL

CONCRETE END WALLN
(Straight ) -

D (With Wings )

STRAIGHT |

| B | F {Cu Yas [oi [Fake | en] aS leis

0
2
3
4
6
8
fe)
0

Fic. 15.—Concrete end walls for culverts

types, with dimensions and estimated quantities for various sizes of
pipe culverts. These may also be used for box culverts. The U type
is not recommended, since it requires approximately the same quan-
tity of concrete as the type having wings set at an angle and is less
efficient in reducing entrance loss than either of the two types shown.
To reduce entrance losses, rounding the entrance to the pipe is
more important than the type of structure used, as it will increase
the capacity of a pipe culvert from 10 to 18 per cent. For this rea-
son the bell end of clay or concrete pipe should be placed upstream.
In soft soils the bottom of the canal should be paved with riprap for
a short distance below the structure outlet.

Drainage crossings under large canals also require culverts. The
material should be more permanent than wood. Where pipe made

STRUCTURES USED IN DRAINING AGRICULTURAL LAND 25

up of short sections is used, a good foundation must be provided and
the joints surrounded with mortar. (See fig. 16 and fig. 7.) End
walls should be similar to those shown in Figure 15. Water must
be prevented from finding its way along the sides and bottom of the
structure, and cut-off walls must be provided as shown in Figure 7.
In some soils it will be necessary to pave the section of the canal
passing over the culvert with concrete.

FLUMES AND INVERTED SIPHONS

Drains frequently cross irrigation or other canals, necessitating
the construction of flumes. These are commonly used in irrigation
to carry water across natural depressions. but because the cross sec-

= SECTION B-B

10 10"

SECTION ON CENTER LINE

Fic. 16.—Culvert under canal and connection for flushing open drain, drainage dis-
trict No. 2, Yakima County, Wash.

tion of a drainage ditch is very apt to change, greater care is neces-
sary in the design of substructure, and intake, and outlet structures
than is common for irrigation requirements. A design for small
metal flumes is shown in Figure 17 and Plate 2, H and I. Intakes
and outlets can usually be made similar in form. Figure 17 shows
a design suitable for sizes to and including No. 72. If desirable the
wing or transition walls for large flumes may be warped. The slope
of the intake and outlet floors will depend upon available slope and
change in cross section of the ditch. Usually the fall available in
such cases is not great and fiumes with large cross section will be
required. For small flumes such structures should be made as sim-
ple as is consistent with correct hydraulic design. Many failures
are caused by washing and undermining due to seepage. To provide
against this and erosion in very loose sandy soils, it may be necessary

26 BULLETIN 1408, U. S. DEPARTMENT OF AGRICULTURE
to line the canal for a short distance beyond the structures. For
size No. 24 and smaller in good soils a straight wall may do, but
the end of the flume should extend back farther than for other types.
Figure 17 shows connection between metal flume and end struc-
tures. The end of the metal sheet should not be turned into the
concrete. The flume, when filled with water, sags at bottom and the
opening in the head wall must be shaped approximately to cor-
respond to this form. The bars across the top may be omitted from
small sizes of some types. This is desirable where large weeds may
SussTRucTure DIMENSIONS 16” SPAN

of semi-circle in inches | Flume Posts | Braces | Braces |Spreader

oe [p= 2
ae 24-42 Hid"
ie 48-72 | 3%8"| 4x6" | 3%6 | 2k6"| 2*3"|

Rites: {4p Adel a ce aie Wires
er eae S| SSO

Q 2'x/2" Foot plank

No. of flume= perimeter

PLAN

2’ Minimum
sree = OSS SI IS ETE =

Sway Brace
Fiber Cement . Yy
ON B-B y
k--Variable —~

rae ae
| g K

im
| &3 &
aes §
ye aS
ELEVATION OF BENT -G

Fic. 17.—EHnd connections and substructure for metal flumes

ea overflow. In all cases a liberal free board should be pro-
vided.

Creosoted wood-stave flumes are coming into favor and it is
believed that their cost of maintenance will be low. The substruc-
ture required is in some respects similar to that for metal flumes.

Where the bottom of the drain is very soft or the structure may
be endangered by floods, trusses similar to those in Plate 1, J, are
recommended for small flumes. Corrugated pipe, requiring no sup-
port, is a convenient means of carrying small laterals across narrow
ditches. Reinforced concrete is desirable for large flumes. (See
pl. 2, K, and pl. 2, L.)

ot eksabl

STRUCTURES USED IN DRAINING AGRICULTURAL LAND yar

As a general rule it is economy to make the drain deep enough to
obviate necessity for inverted siphons. When this is impossible the
inverted siphon should be used on the canal carrying least water,
and possibility of flood discharges must be considered. A screen
should be provided at the inlet structure to keep out weeds and
_trash. This screen should be inspected and cleaned frequently,
otherwise it may become so badly clogged with trash that it will
obstruct the flow and endanger the canal bank.

MISCELLANEOUS STRUCTURES

PUMP HOUSES

Pumping from wells is being resorted to in some localities to
drain lands damaged by irrigation seepage. Figure 18 shows a
type of pump house used in Salt River Valley, Ariz., which is a
suitable shelter for electrically-driven, direct-connected plants. The
lower part of the derrick, which is essential in pulling the pump for
repairs, forms a part of the framework of the building. At the
top is a removable hatch, and a section of the roof and wall over the
door is also removable. A weir is desirable, but for small plants
a cheaper arrangement brings the discharge pipe above the floor
and carries it out to a less elaborate stilling pool and weir in the
ditch. A concrete floor is provided, drop siding is used on the
walls, and the top is covered with asbestos roofing. Belt-driven
pumps will need longer housing, and where engines are used gal-
vanized corrugated iron is recommended for covering walls and
roof.

On levee districts where gravity outlets are not available the loca-
tion of the pumping plant is often determined by topographic con-
ditions; but it should be such that pumped water will be conveyed
as short a distance as possible. Stable foundation material should
be present, and transportation of heavy machinery and fuel or power
should be handled easily.

The most common form of pumping plant consists of a structure
supported on piling, with discharge pipes passing through or over
the levee and suction pipes leading to a sump in the rear of the
building. This requires long pipes with attendant friction losses,
to overcome which sumps may be placed under the pump house and
the structure located in the levee where the foundation alone or both
the foundation and wall must serve asa dam. This requires careful
design but permits economical operation and sometimes also in-
volves cheaper construction than other arrangements, except per-
haps for small plants with low lifts.

Borings and a very careful examination of the formations at the
proposed site must precede the design. Settlement under the floor is
an important and difficult problem to handle. In some soils, where
the pump is located some distance back of the levee, subsidence due
to drainage may occur, and where located in the levee, settlement
due to weight of adjacent fill must be anticipated, making it essential
to construct carefully designed cut-off walls.

Often where the lift is low the pump-house floor may be placed
at an elevation such that flooding the motors or engines is not likely
in case of accidents or forced suspension of pumping. The suction

EBLE SE’ bolt
Crown block
SEN SQ" bolts

ad ee
\
Ty
«
Mart!

h
teh Removable yi)
Roof

_— - — -—— -——. 3 3+-¢"- pe
ae)

\
us
7 TI

F Removable Wall?

Po
Tal

Lesy
4

‘i0'+ - —4"/0"—~

NM
*
A
pA
[*

LONGITUDINAL SECTION

| ee Pier
FRONT ELEVATION Rear: Half

-— -F9—- + PB —2-34

Stilling box Ter

Lapeer aig |
> jad ia 4" i

+
al PLAN OF WEIR BOX

== - ——- — = — 444" — - — -—

o> = 4g -

PLAN

: wy
Grout in above S
this line after =k
pump and motor |
are Set

pac
heed

Bee

ae ES Sire SE Rec ee

“8 Well casing SECTION ON CENTER LINE

Iig. 18.—Pump house for drainage wells, Salt River Valley,
Ariz.

BULLETIN 1408, U. S. DEPARTMENT OF AGRICULTURE

hit should be kept as
low as possible, how-
ever, this often requir-
ing the walls of the
structure to be de-
signed to prevent the
entrance of water. A
plant in operation on
the Sacramento River
was designed to
withstand a head of
water 20 feet above
the floor, with walls
and floor several feet
thick to prevent float-
ing.

The suction bay
must have a greater
depth than the main
canal and a sufficient
area to permit move-
ment of the water to
the intake pipes at low
velocities. A screen
must be provided to
protect the intake. If
the suction bay is not
an integral part of
the concrete house or
foundation, its sides
must be well protect-
ed with sheet piling;
and in case sand boils
develop, the sides and
bottom must be made
of reinforced concrete
designed to withstand
upward pressure. In
fixing the elevation of
the floor, allowance
should be made for
subsidence where
muck or peat soils
exist.

Where the discharge
pipe passes through
the levee, extreme
care must be taken
to prevent seepage by
construction of cut-
off walls. The dis-
charge bay, made of

reinforced concrete, should be substantially protected against wash-
ing and undermining, with elevation such that the outlet pipes will

STRUCTURES USED IN DRAINING AGRICULTURAL LAND 29

be submerged. For some types of pump installations, gates must
be provided at the discharge structure. Discharge and suction pipes
usually are steel, but sometimes they are reinforced concrete. The
diameter should be sufficient to produce a velocity of not more than
approximately 5 feet per second, and the intake and discharge ends
must be enlarged to reduce losses.

The house should be durable and fire proof. Galvanized cor-
rugated metal is desirable for small plants, but excellent houses have
been made of brick. Reinforced concrete is well adapted to large
structures and must be used on all plants where there is danger of
flooding the machinery. The building should be well ventilated.
Reinforced-concrete columns or pilasters must be carried up on the
inside of the walls to support rails for a crane, which is an essential
part of all except very small plants.

Figure 12 shows the design of a pumping plant installed in Mult-
nomah County drainage district No. 1, Oreg. This reinforced-con-
crete structure has unusual features in that the wail of the plant is
designed to withstand a high head of water, and the entire structure
rests on a silty formation without rigid support. It was thought that
the earth would settle and thus leave an opening beneath the floor if
the structure were otherwise supported, which would be very hazard-
ous particularly during the high-water period which sometimes lasts
for several weeks. Five rows of sheet piling were placed beneath
the floor. These are only 8 feet in length so that none of them would
reach into what appeared to be a hard layer of sand beneath the silt
and thus tend to prevent uneven settlement. The entire structure
has settled about 3 inches since installation.

The floor was designed against upward pressure, and an effort was
made to reduce the pressure to some extent by filling with porous
concrete five boxes each 1.5 feet square placed in the down-stream side
of thesump. The structure is also provided with five sluiceways hav-
ing openings 5 feet square for gravity discharge. Automatic gates
are used. Emergency dams can be installed easily in case repairs
must be made to gates or pipes.

CONNECTIONS FOR FLUSHING DRAINS

Often it is desirable to connect open drains and underdrains with
irrigation or other canals for periodic flushing. This is the cheapest
form of maintenance work that can be done. Figure 16 and Plate
2, J, show connection to an open drain which passes through a cul-
vert under an irrigation canal. The canal is lined with concrete, and
riprap at the lower end of the outlet pipe and culvert prevents ero-
sion of the embankment. The connection is made by an ordinary
turnout gate. Use of this connection for sluicing has reduced main-
tenance cost to a minimum, and has lowered the grade line of the
main canal approximately 2 feet for several miles.

Where a concrete box culvert is used, the connection should consist
of a small concrete tower with a gate at one side of the upper canal,
through which the flushing water may be discharged directly into the
culvert instead of at its lower end as in the example shown. At
flume crossings a gate may be provided, as shown in Plate 2, L. Un-
stable soils below such a discharge will require a short paving of con-
crete or riprap to prevent erosion.

30 BULLETIN 1408. U. 8. DEPARTMENT OF AGRICULTURE

Connections between canals and intersecting underdrains resemble —
in some respects that shown in Figure 16, but the discharge pipe will —
be much smaller and its lower end will discharge into a manhole. —
Usually it will be unnecessary to pave the canal. As a rule special
eates and elaborate connections are not needed on underdrains since
most properly built mains and laterals have flushing structures at
the upper end. Water may be conducted to the tile line from small
laterals as shown in Figure 19, the connection being made either with
a T-junction or an elbow, depending on whether the line is to be ex-
tended. The riser may be tile of the same size as the drain, but
usually it does not need to be larger than 6 or 8 inches. In case
surface run-off is to be admitted a regular surface-water inlet should
be used. Ordinary drain tile may be used for tile ends on farm
laterals, but on more important lines bell-end tile to prevent dis-
placement will be preferable. Gravel should be placed around the
tile at the connection and the earth should be well tamped or puddled
in around the riser. Wherever possible tile ends should be located
out of the way of farm machinery, but where such location is im-
possible the top should be about 16 inches below the ground and cov-
ered with gravel. Vitrified clay or concrete stoppers may be used
for the cover.

RELIEF-WELL CONNECTIONS

Relief wells of various types are used to conduct ground water
under pressure to closed drains or open ditches. Often a large
number of small wells are sunk with augur or drill to drain land
underlain with water-bearing shale formation. If the tile line
reaches into the shale, casing is usually unnecessary; otherwise the
well should be cased from the top of the shale to the tile line. This
upper part may be cased with tile from 4 to 8 inches in diameter if
the adjacent material can be excluded from the joints; otherwise an
iron-pipe or wooden-box casing must be used.

Many relief wells flow only at certain seasons, hence they must
be located at one side of the drain to keep them free from silt. In |
shale the small wells should be drilled close to the drain line, to _
which they should be connected by a hole in the side several inches _ |
above the bottom of the tile. The well and the hole should be
covered with a large piece of tile, surrounded by small pieces of tile
and gravel.

Some drainage systems include deep relief wells of large diameter,
cased with iron pipe, as in artesian well practice. Here it is neces-
sary to perforate the lengths extending into the formation under
artesian head, the size, shape, and number of these openings depend-
ing upon the nature of the formation. Casings should extend above
ground and the covers should be secured against removal. T-junc-
tions should be used at connections and the bottom of the outlet
opening in the well casing should be several inches above the grade
of the tile line into which it discharges. If manholes are near, wells
should be connected with them. Gravel pockets which will discharge
large quantities of water when tapped are occasionally found below
the grade of the tile line. These may be connected to the drain by a
structure similar to a small manhole, located at one side of the line.

STRUCTURES USED IN DRAINING AGRICULTURAL LAND 31

Relief wells discharging into open ditches must be located and
lined in the manner described above. The elevation of the T-junc-
tion discharging into the ditch should be that of ordinary high
water in the line of the drain (pl. 2, G).

CONNECTIONS FOR DIVERTING WATER

Drainage water is valuable for irrigation if the percentage of
alkali is not too high. When water is diverted by gravity from an
open drain the required structures will be similar to those used in
irrigation practice, consisting of a turnout gate located just above
a check as shown in Plate 2, K. The elevation of the water is con-
trolled by flashboards. The gate should be large and low enough
to permit diversion with a checked
head of only a few inches; otherwise
the purpose of the drain will be
defeated.

When good fall exists on an under-
drain, water may be diverted from it
through a pipe having a flatter grade. S
This pipe must have tight joints and ie
the connection should be made at a 2

S
S

me
NSass SV
~ a
.

A
woos ;
< . >
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Yay
NAN A
.

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. ‘es

manhole and at an elevation slightly
less than that of the outlet drain.
A slide gate should be fitted on the
diversion pipe and a similar gate may
be installed on the outlet drain pipe;
but the latter should be so constructed
that it can not be completely closed

WAAAAAAAA
—
«

AARRS

WS
yy S/
WI 1

SN
S\
V7

Vitrified Clay Stopper
VK

SSOP

unless the diversion pipe has a capac- EAM Ft
ity equal to that of the drain. Sy

As a general rule, any considerable ANOB t
checking of the normal flow of drains W Cr re

is to be avoided. This is particularly /
true for underdrains and for any type ’
when alkali is present, except perhaps

in peat soils where it is necessary to

practice subirrigation. In such sys-

tems the level of the waterin thesmall we. 19 —Tite end to permit flushing
open drains is controlled by wooden

check gates. If underdrains are used checking may be accomplished
by means of slide gates at frequent intervals; these have a stem
reaching to the ground surface through a pipe similar to an observa-
tion well.

Pumps on closed drains should be located at manholes with deep
sumps, and for small plants on open drains a suitable sump should
be provided at one side of the main channel in such a manner as to
offer no obstruction to the flow.

WATERING PLACES FOR LIVESTOCK

In some localities special watering places for livestock must be pro-
vided on underdrains and on open systems where stock are not per-
mitted to graze on the banks. On open drains the channel bottom
should be widened at one side, a flatter side slope excavated for

32 BULLETIN 1408, U. S. DEPARTMENT OF AGRICULTURE

entrance, and a fence so located as to prevent the forming of a bar
in the main channel by the trampling of stock. In very soft ground
a plank floor will be needed at the lower end of the approach.

Watering places on underdrains should be provided by the in-
stallation of a by-pass consisting of a trough situated several feet
from and parallel to the main line and connected to it at each end
with Y-branches. A coarse screen must be placed at the lower end
of the trough, which is located in a sump with sloping sides to per-
mit access by stock. The earth excavated should be spread entirely
around the sump so as to exclude surface water.

TRANSITIONS"

Occasionally it is necessary for an open drain to discharge into a
pipe line of considerable length. Elaborate structures with warped
transitions are usually unnecessary. In a general way they should
resemble the intake structure of a culvert and have ample cut-off
walls. A sloping screen or trash rack should be provided. The
joints of the pipe should be cemented for a distance of 20 to 30 feet
below the structure. :

ADDITIONAL COPIES
OF THIS PUBLICATION MAY BE PROCURED FROM
THE SUPERINTENDENT OF DOCUMENTS
GOVERNMENT PRINTING OFFICE
WASHINGTON, D. €.
AT
10 CENTS PER COPY

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