Maximum peak flows for selected return periods for watersheds west of the Continental Divide in Idaho and Montana

Historic, archived document

Do not assume content reflects current
scientific knowledge, policies, or practices.

MAXIMUM PEAK FLOWS FOR
SELECTED RETURN PERIODS

FOR WATERSHEDS WEST OF
THE CONTINENTAL DIVIDE
IN IDAHO AND MONTANA

Nedavia Bethlahmy

a
2
ce
co
—
ies

om

gquo2se
bi

USDA Forest Service Research Paper INT-113
INTERMOUNTAIN FOREST AND RANGE
EXPERIMENT STATION
Ogden, Utah 84401

+ ¥ =f
- oer
1 ‘
“
¥)
i
are i ia
fi
aL
Da
; 1;
4
d t
he F ‘
hs
' Ny fi
y ee | LARS
i ay o¢

USDA Forest Service
Research Paper INT-113
December 1971

MAXIMUM PEAK FLOWS FOR

SELECTED RETURN PERIODS

FOR WATERSHEDS WEST OF
THE CONTINENTAL DIVIDE
IN IDAHO AND MONTANA

Nedavia Bethlahmy

INTERMOUNTAIN FOREST AND RANGE EXPERIMENT STATION
Forest Service
U.S. Department of Agriculture
Ogden, Utah 84401
Robert W. Harris, Director

THE AUTHOR

NEDAVIA BETHLAHMY is Principal Forest Hydrologist for
the Streamflow Regulation research work unit of the Intermountain
Forest and Range Experiment Station in Moscow, Idaho. He began
his career with the Forest Service in California in 1940, and since
that time has worked and conducted experiments in watershed man-
agement research in the Northeastern, Southwestern, Pacific North-
west and Intermountain Regions. During the years 1966-1968, he
was assigned to the Food and Agriculture Organization of the United
Nations to help the Republic of China solve the watershed manage-
ment problems of Taiwan. He is a Graduate Forester from Penn
State, and holds M.F. and Ph.D. degrees from Yale and Cornell
Universities.

CONTENTS

NLR OD UC AION Gmconicu omicl | cicureptciivei enleli oti inewel oie toil il eine
EXAMPLES FOR FIELD APPLICATION ...........
DISCUSSION oo GoeGo oboe oo oo Sb OOOO oOo bo

Tai CATHONS Weiss)! "=! 6) ce) eo re SOo00 00 GD OOo On
REFERENCES......... ‘ . 6. OO Goo 6 0O1e
AN PIV ASPDIDC IU o.d Oo O16 0 0 dig 06 GN Io oe kel isiiie’) olen ehte 0

APPENDIX TI .

ABSTRACT

The long-term average water yield of a watershed appears
to be a good index to the magnitude of its expected peak flow. On
the basis of this relation, tables are presented showing expected
peak flows that are applicable to watersheds in Idaho and Mon-
tana west of the Continental Divide. Tabulated peak flows are
for four different return periods: mean annual; 5; 10; and 20
years. Three examples are given to illustrate the tables’ field
application.

What is the 20-year flood potential of this watershed?

INTRODUCTION

Foresters and other land managers have long considered water an important product
of forest lands. This product yields great benefits when its flow is orderly, timely,
and is confined within the banks of a stream. On the other hand, water appearing as a
flood is a potentially destructive force that land managers should consider when plan-
ning future forest operations.

The effects of clearcutting operations on the hydrologic regime of a watershed are
complex, and the magnitude of these effects is highly variable. Nevertheless, we do
know that a clearcut watershed yields more water (Hibbert 1967), and that the pattern
of runoff distribution is changed, including an increase in base flow and peak flow
(Bethlahmy 1971). Thus, foresters and other land managers who contemplate clearcutting
operations should consider the associated problem of future changes in the hydrologic
regime.

Our research has shown that on a unit area basis the long-term average water yield
of a watershed is a good index to the magnitude of its expected peak flow. The greater
the average yield per unit area, the greater the expected peak flow for period of record.
This relation is readily perceived from table 1 that shows data for 11 rivers in Idaho
which have good or excellent streamflow records (U.S. Department of Interior 1964).
Notice the regular decrease in values of both average annual flow and associated peak
flow. Although peak flow per unit area is related to unit drainage yield, any discus-
sion of peak flow should include the element of chance. A record of many years of data
will probably include. greater peak flow values than a short record. Hence, a comparison
of peak flows for different areas should be based not only on the watershed's average
yields but also on the element of time; how long is the record, and how often can one
expect a peak flow of a given magnitude? Such considerations are especially important
to engineers and economists who are concerned with investments in structures having an
economic life expectancy.

Table 1.--Relation of peak flow to average annual flow for some Idaho rivers with good
or excellent stream records

Average : : :
: annual : Peak : Elevation :; Length : Watershed
River : flow : flow! : of gage : of record : area
“Chipfo@ollle “CoipoSolilh VRAGE Years Sq.mt.
Cub 4.24 36.86 55520 Pil 19.4
Boundary 1.98 SSO a0, 34 97
Mission eval! 22.96 2,800 6 23
Clearwater (Kamiah) 1.68 oa! 1,162 54 4,850
Moyie (Eastport) ey25 18.60 2,620 $5 570
Yaak 1.20 15.80 1,850 8 766
Moyie (Eileen) 1.16 14.57 2,124 39 755
Big Lost River (Wild Horse) . 86 Hail gala! 6,820 20 114
Robie 550) ORS 2 4,960 14 15.8
Thomas Fork 44 7.69 6,280 15 PIS

Bannock . 36 Sow 5,240 16 5.75

1Peak flow for period of record.
Cubic feet per second per square mile.
3Above mean sea level.

Peak flows which can be expected in Idaho and Montana, in watersheds west of the
Continental Divide, are listed in tables 2 and 3 for four different return periods. The
selected return periods are: 2.33 years (usually termed the mean annual return period) ;
5; 10; and 20 years. In these tables, peak flow is a function of average water yield
and an expected return period, and is expressed in units of cubic feet per second per
square mile (c.f.s.m.). In table 2, average water yield (the independent variable)
increases by selected increments in inches, and in table 3 by selected increments in
c.f.s.m. These tables were constructed in accordance with the methods described in
Appendix 1, and are based on sources of data listed in Appendix 2.

Table 2.--Maximum peak flows (¢c.f.s.m.) for selected return pertods for watersheds west
of the Continental Divide tn Idaho and Montana

Average
annual : Return period (years)
yield g DSSS : 5.0 : 10 : 20
Inches = ----+------------- C.f.S.m---------- - - - - =
5.0 2.6105 3.2904 4.1589 52,959
6.0 2.9845 3.7810 4.7295 5.9284
750 3.3984 4.3267 SS 57 6.6899
8.0 3.8526 4.9282 6.0433 7.5180
9.0 4.3465 5.5856 6.7854 8.4111
10.0 4.8791 6.2975 7.5818 9.3661
11.0 5.4484 7.0619 8.4294 10.3791
12.0 6.0520 7.8755 9.3240 11.4450
SIO) 6.6866 8.7343 10.2609 12.5578
14.0 7.3487 9.6336 TS 234'5 13.7109
15.0 8.0341 10.5679 12.2388 14.8972
16.0 8.3787 11.5314 13.2676 16.1092
17.0 9.4580 12.5180 14.3145 17.3395
18.0 10.1875 13.5216 15.3730 18.5808
19.0 10.9229 14.5361 16.4370 19.8258
20.0 11.6600 15.5554 17.5005 21.0677
21.0 12.3948 16.5741 18.5581 22.3004
22.0 13.1236 17.5867 19.6047 23.5181
23.0 13.8431 18.5885 20.6356 24.7157
24.0 14.5503 19.5751 21.6467 25.8885
25.0 15.2426 20.5426 22.6346 27.0356
26.0 15.9176 21.4877 23.5963 28.1450
27.0 16.5736 22.4075 24.5291 29.2226
28.0 17.2089 23.2997 25.4313 30.2636
29.0 17.8224 24.1624 26.3011 31.2663
30.0 18.4131 24.9941 ZT OUSTS 32.2294
31.0 18.9804 25.7938 27.9398 33.1524
32.0 19.5239 26.5609 28.7075 34.0348
33.0 20.0434 27.2948 29.4406 34.8767
34.0 20.5390 27.9956 30.1391 35.6784
35.0 21.0108 28.6634 30.8036 36.4404
36.0 21.4592 29.2985 31.4345 3751635
37.0 21.8846 29.9016 32.0326 37.8485
38.0 22.2876 30.4734 32.5988 38.4967
39.0 22.6689 31.0146 33.1341 39.1092
40.0 23.0291 31.5263 33.6394 39.6871
41.0 23.3690 32.0094 34.1159 40.2318
42.0 23.6893 32.4649 34.5648 40.7447
43.0 23.9910 32.8941 34.9873 41.2272
44.0 24.2747 33.2979 35.3845 41.6807
45.0 24.5413 33.6776 SST SIS 42.1065
46.0 24.7917 34.0343 SOmlO77 42.5061
47.0 25.0266 34.3690 36.4361 42.8807
48.0 25.2469 34.6830 36.7440 AS R254
49.0 25.4532 34.9774 S17 A0S235 43.5605
50.0 25.6465 35.2530 37.3022 43.8681

Table 3.--Maximun peak flows (c.f.s.m.) for selected return pertods for watersheds west
of the Continental Divide in Idaho and Montana

Average
annual 3 Return period (years)
yield : BEES : 5.0 : 10 : 20

a SSP 8 = = Cafes. — ==) =) = 2) |
O82 1.8989 2.3648 3.0639 3.8924
OS 2.2982 2.8829 3.6801 4.6489
0.4 2.7664 3.4946 4.3972 5.5242
OSS 3.3070 4.2059 5.2192 6.5222
0.6 3.9216 5.0199 6.1472 7.6432
Os 4.6092 5.9363 7.1786 8.8830
0.8 5.3663 6.9514 8.3073 10.2335
0.9 6.1871 8.0581 9.5239 11.6827
1.0 7.0638 9.2462 10.8160 3), 215i
LF 7.9868 10.5032 12.1695 14.8154
eZ, 8.9455 11.8146 13.5689 16.4635
1S 9.9289 13.1654 14.9980 18.1414
1.4 10.9259 14.5402 16.4414 19.8309
eS 11.9261 15.9241 17.8839 21.5148
1.6 12.9196 17.3031 19.3120 23.1778
The7/ 13.8976 18.6645 20.7135 24.8062
1.8 14.8526 19.9974 22.0783 26.3886
139 15.7782 21.2924 23.3978 27,5955
230 16.6694 22.5419 24.6652 29.3798
Ze WeES222 23.7401 25.8756 30.7759
Bez 18.3339 24.8825 27.0254 32.1004
DiS 19.1026 25.9662 28.1124 33.3509
D4 19.8273 26.9894 29.1358 34.5267
255 20.5079 27.9516 30.0954 35.6282
216 21.1447 28.8530 30.9921 36.6565
2, 21.7386 29.6946 31.8274 37.6136
258 22.2908 30.4779 32.6033 38.5018
2.9 22.8030 31.2051 5525222 39.3244
3.0 23.2768 31.8783 33.9867 40.0841
Sal 23.7143 32.5004 34.5997 40.7846
32 24.1173 33.0739 35.1642 41.4292
Sa5 24.4881 33.6018 35.6830 42.0215
3.4 24.8286 34.0868 36.1592 42.5649
S55) 25.1407 34.5317 36.5957 43.0626
3.6 25.4267 34.9395 36.9952 43.5182
Shih 25.6882 555126 37.3605 43.9346
3.8 25.9273 35.6537 37.6942 44,3148
359 26.1454 35.9652 37.9987 44.6617
4.0 26.3445 36.2494 38.2765 44.9781
4.1 26.5259 36.5086 38.5295 45.2662
4.2 26.6911 36.7446 38.7599 45.5285
4.3 26.8415 36.9595 38.9696 45.7672
4.4 26.9784 Sy US SZ 39.1604 45.9842
4.5 27.1028 37.3330 39.3338 46.1816
4.6 27-«2159 37.4947 39.4913 46.3608
4.7 27.3186 37.6416 39.6344 46.5236

*SsoTqe}
oy} JO osn [eoTJOVId oY} o4eAISNI[I SeTdwexe oolyL *saeak 07
pue ‘OT ‘cg ‘[enuue uve :spotsod UAnjor JUOAOFJIP INOJ OJ ore pus
‘ples 1oyem Tenuue UveW JO UOTJOUNJ ve Se SMOTJ Yeod MOYS SoaTqey
eUL “eprlaAiIg [eyUeUTJUOD oy} JO JSoM LUO] pue OYepP] UT spoys
-10}eM 0} o_qeoT{dde o1v yey} poyuosord o1e SoTqe} MOT} yeod

‘Snipes O° CD
-LNI ‘ded “soy “Atog jso10q VaSn ‘eueyuoy, pue
OYep] UI SprIAIq [eJUSUTJUOD oY} JO JSOM SpoyssojeEM
IO} SpOTiod uinjor pojo9eTos TOF SMOTJ Yeod WNUWIXeL “TL6T

VIAVGHN ‘ANHVIHLGd

*solqey
ey} JO osn yeoTjOVId oy} o3eAJsNI[I SoTdwiexe sey, ‘“sareVdk QZ
pue ‘OT ‘cg ‘jenuue ueoW ‘spolied urnjot JUOLOFJIP ANOJ OJ ore pue
‘plerh 1oyem [enuUe UeOUI JO UOTIOUNJ B Se SMOTJ Yeod MoYsS seTqe}
eyUL “eplAiqd [eJWSUyUOD oY} Jo JSOM vULIUOJ, puv OYepP] UI spoys
-1eyem 07 oTqeoydde o1z yey} poyuosord o1e satqe} MOTI yeod

SSO Ue Cree
-—LNI “*deq ‘soy “Ades ysot0q YaSn ‘euezyoy pue
OYBP] UI OplAIq [eySUTJUOD oY} JO JSOM SpoyszojeM
IO} Spotted uinjord pojoojos LOJ SMOTJ Yeod WNUWUIXeL “TL6T

VIAVGAN ‘ANHVIHLGd

*soTqey
ay} JO osn [eotjoeid oy} oJeIXsNI[I soyduiexe soryL “savek OZ
pue ‘OT ‘g ‘yenuue uvow ‘:spotied uinjor JUOLOJJIP INOJ TOF ore pue
‘plots 10ye8M TeNuUUL UvSU Jo UOTIOUNJ we Se SMOTJ Yeod MoOYsS soTqe}
oUL ‘ePIAIG [eyWouTWOD oy} Jo jsom vULIOW pue OYEp] UT speys
-1oyeM 0} o[qeoTdde ore yey} poyuoseid oie Sotqe} MOT] yeed

*snqqt ‘°d ZT ‘ert
-LNI ‘ded ‘soy ‘Ares ysorOoq Vasn ‘eueyoy, pue
OYyep] UI SpIAId [eJUSUTJUOD oY} JO ISOM SpoyssojVM
IO} SpOlzod UANjoI pojooTVsS OJ SMOTJ Yeod WNWITXRIN “TLET

VIAVGHN ‘ANHVIHLAG

Ya

iE Be a

A mountain stream at flood stage.

EXAMPLES FOR FIELD APPLICATION

Three examples are given to show how the tables can be used for field application.
EXAMPLE 1

Problem: A road will be built across the outlet of a 1.5-sq.-mi. drainage having
an expected annual water yield of 40 inches. What is the maximum
rate of flow the culvert should accommodate:

(a) if designed for a 20-year flood?
(b) if designed for a 50-year flood?

Solutton:

(a) For an annual yield of 40 inches, table 2, col. 5, shows a peak flow of 39.69
c.f.s.m. Since the drainage area is 1.5 sq. mi., we can expect a 20-year flood of 59.53
Crees (5 9/.091X) 1h. Si)iz

(b) The tables do not show peak flows for return periods exceeding 20 years.
Extrapolation is required, but this procedure is fraught with great uncertainty. In
table 2, opposite an average 40-inch annual yield, we find the expected peak flows for
the 10- and 20-year floods to be 33.64 and 39.69 c.f.s.m., respectively. Plot the
paired values (year versus flow) on log-log paper, connect them with a straight line,
and extend the line to the 50-year flood. The peak flow is 49.3 c.f.s.m. Inasmuch as
the area is 1.5 sq. mi., the expected SO-year flood is 74 c.f.s. (49.3 X 1.5 = 74).

It must be understood that such extrapolation results in only approximate values.

EXAMPLE 2

Problem: A road crosses the outlet of a 40-acre watershed over a 12-inch corrugated
metal culvert whose top is 1 foot below the road surface. Plans call
for clearcutting the watershed that has an annual yield of 35 inches.
After cutting we expect annual water yield to increase by 15 percent.
Assuming a 20-year-design flood, will the presently located culvert
accommodate the increased flow?

Solutton:

The expected annual flow is 40.25 inches (35 inches X 1.15). In table 2, col. 5,
interpolating for peak values between 40 and 41 inches, we obtain an expected peak flow
of 39.82 c.f.s.m. Since the area involved is 40 acres, the expected peak flow is 2.49

40 : A
Co LS 19282 0x $40) Using culvert discharge tables (e.g., Hendrickson 1957), we find

that the presently installed culvert (use 1,0 percent slope and 0.025 roughness coeffi-
cient) will accommodate only 2.4 c.f.s. Because there is a present capacity of only
2.4 c.f.s., and the expected need is for 2.49 c.f.s., it appears that the road will
probably be damaged by overflowing unless a larger culvert is installed or the surface
of the road is raised to allow for ponding.

EXAMPLE 3

Problem: The annual water yield from a 5.0-sq.-mi. drainage is 40 inches.
Plans call for clearcutting a 40-acre subwatershed. What are the
present and expected peak flows at the outlet of the main drainage for
a 10-year flood if the annual water yield of the clearcut area is ex-
pected to increase by 15 percent?

Solutton:

Under present conditions (before cutting) the expected 10-year flood for the en-
tire drainage is 168.20 c.f.s. In table 2, col. 4, opposite 40 inches, read 33.64
c.f.s.m. and multiply by 5.0 sq. mi., and for the 40-acre subwatershed it is 2.10 c.f.s.

40

(33.64 X 640)

After cutting, the average yield from the clearcut 40-acre subwatershed will be
46.0 inches (40 X 1.15). In table 2, col. 4, we read a peak flow value of 36.11 c.f.s.m.
Since the subwatershed is 40 acres, the peak flow is 2.26 c.f.s. 40

(36.11 X =).
640

On the clearcut area, the peak flow will increase by 0.16 c.f.s. (2.26 - 2.10).

Add this value to the precutting peak flow for the entire drainage:

168320 F410 216) = 1G 8) SOC. t.S:.

It is apparent that clearcutting the 40-acre subwatershed will not alter the peak flow
of the main watershed in any significant way.

ag * he Pa oes - nip, fs.
OO nl ot Mea llc te Stn 9
A raging mountain stream overflows a bridge.

DISCUSSION

The three examples illustrate how the tables may be used, and the practical signifi-
cance of the effects of clearcutting operations. We once again remind the reader that

the tabulated values are expressed in yield per unit area, and hence may be applied to
watersheds of any size or at any elevation.

In illustrating the use of the tables, we used a potential water yield increase of
15 percent. Some readers may consider this figure as too conservative, because it is
considerably smaller than figures reported in the literature. At Fraser, Colorado,
for example, where 75 percent of the annual precipitation occurs as snow, a 40-percent
commercial clearcut in strips yielded a first-year increase of 30 percent in annual
streamflow (Goodell 1958). We used the figure 15 percent as an example, and not as a

universal recommendation. In using the tables, the reader should consider the special
circumstances applying to his case.

The tables may also be used to solve problems relating to channel stability, bank
cutting, and stream level. However, because the characteristics of stream channels
vary considerably from one segment to another, it is apparent that a particular problem
May not have a unique solution. Nevertheless, the land manager may sometimes be
particularly concerned with certain segments of a stream channel because they appear
vulnerable to changes in the hydrologic regime. In such cases, it may be worthwhile to
make the assumptions needed to perform the calculations and to determine the magnitude
of changes that can be expected.

Limitations

Flood peaks reflect the complex interaction of many variables, and many formulas
have been devised to account for the effects of these variables. In most cases, how-
ever, the land manager has only limited information about the magnitude of the important
variables. For example, Rosa (1968) published water yield maps for Idaho, but maps of
this sort are not available for even such basic variables as rainfall intensity or
soils grouped according to their hydrologic properties.

The user of these tables is cautioned that the tabulated values are far from being
definitive; they are only an approximation to give the land manager an idea of what may
be expected. Mr. C. A. Thomas has observed! that the tabulated values may be too high
for streams with a high base flow and are probably too low for streams with flashy run-
off and low base flows.

The user should bear in mind that the tables will probably be applied to areas
considerably smaller than those from which the tables were derived. Furthermore, flow
data for the very small drainages cover only a brief span of time.

1Personal communication, on file at Intermountain Forest and Range Experiment
Station, Forestry Sciences Laboratory, Moscow, Idaho.

REFERENCES

Bethlahmy, Nedavia
1971. Effects of forest clearfelling on the storm hydrograph--a reanalysis.
Amer. Geophys. Union Trans. 52(4): 204.

Bodhaine, G. L., and D. M. Thomas
1964. Magnitude and frequency of floods in the United States. Part 12. Pacific
Slope Basins in Washington and Upper Columbia River Basin. Geol. Surv.
Water-Supply Pap. 1687.

Goodell, B. C.
1958. A preliminary report on the first year's effects of timber harvesting on
water yields from a Colorado watershed. USDA Forest Serv., Rocky Mountain
Forest Exp. Sta. Res. Pap. 36, 12 p.

Hendrickson, John G., Jr.
1957. Hydraulics of culverts. Chicago, I11.: Amer. Concrete Pipe Assoc.

Hibbert, Alden R.
1967. Forest treatment effects on water yield. P. 527-543, tm: William E.
Sopper, and Howard Lull (eds.), Forest Hydrology. Pergamon Press.

Rosa, J. Marvin
1968. Water yield maps for Idaho. USDA Agr. Res. Serv. 41-141.

Thomas, C. A., H. C. Broom, and J. E. Cummans
1963. Magnitude and frequency of floods in the United States. Part 13. Snake
River Basin. Geol. Surv. Water-Supply Pap. 1688.

U.S. Department of Interior
1964. Surface water records of Idaho. USDI Geol. Surv., 281 p.

APPENDIX |

The published tables are based on the finding that peak flow is a function of mean
water yield. The equation is:

In (P/A) = atb [1.5708 - arc tan (sinh F/A)] (Gis)

in which P, A, and F are, respectively, peak flow (c.f.s.), area (square miles), and
mean flow (c.f.s.). The constant 1.5708 is the angle 90° expressed in radians.

Equation (1) is based on data found in Thomas, Broom, and Cummans (1963) and
Bodhaine and Thomas (1964). Only those rivers were analyzed whose records indicated
no diversions, impoundments, or poor data. The equation was derived as follows: For
each streamflow record, the annual peak flow data were arranged in a descending order
of magnitude. If W represents the baa Ris of items in the series, and M. is the
ordered position in the series (i.e. .V), then the probability of Gecumeence
(Py) (or percent chance) for a peak ae ee to or smaller than that in ordered
position M . is

(, - 0.5)
100 X ry

This probability was calculated for each ordered position, and defined the plotting
position of the associated peak flow on log-normal paper. A smooth line was drawn
through the plotted data, but was not extended beyond the range of the plotted data.
We then read the adjusted peak flows for the selected recurrence periods: 2.33; 5; 10;
and 20 years. (The recurrence period is 100 divided by the probability of occurrence;
Ouse ae P, = 20, r., = 5.)

Data drawn from the smooth curves formed four new sets of data, one for each
selected recurrence period. Each set of data was then analyzed to obtain the values
of a and b in equation (1). We have listed below these values, as well as the correla-
tion coefficient (Af) relating the dependent and independent variables.

Recurrence pertod a b R
(Years)
Zeros 3.3434 -1.9693 0.966
5 3.6653 -2.0440 -950
10 3.7141 -1.8908 .938
20 3.8733 -1.8324 902

Values for tables 1 and 2 were calculated for selected values of mean flow (F/A)
using the equation P
P atb[1.5708 - arc tan (sinh — )] (2)
7 wae A

where e is 2.71828, base for Naperian logarithms.

11

APPENDIX Il

Data for the following rivers were used to derive equation l.

River No. Length of
(USGS) River name and location record : Area
Years Sq.mt.
IDAHO

12-3055 Boulder Creek near Leonia Sif 53
12-3065 Moyie River at Eastport 36 570
12-3075 Moyie River at Eileen 40 755
12-4110 Coeur d'Alene River near Prichard 14 335
12-4130 Coeur d'Alene River at Enaville 26 895
13-3170 Salmon River at White Bird 53 13,550
13-3375 South Fork Clearwater River at Elk City 21 261
13-3390 Clearwater River at Kamiah 55 4,850
13-3405 North Fork Clearwater River at Bungalow

Ranger Station NS 996
13-1200 Big Lost River at Wildhorse, near Chilly 21 114
13-1625 East Fork Jarbridge River near

Three Creek 16 89
13-1850 Boise River near Twin Springs 54 830
13-1965 Bannock Creek near Idaho City 17 56

WYOMING
13-115 Pacific Creek near Moran 21 160
13-320 Bear Creek near Irwin 12 UU 6
MONTANA

3505 Kootenai Creek near Stevensville 1 28.
3560 Skyland Creek near Essex 6 8.
3585 Middle Fork Flathead River near West

Glacier 18 1,128
3590 South Fork Flathead River at Spotted Bear 10 958
3595 Spotted Bear River near Hungry Horse 8 184
3600 Twin Creek near Hungry Horse 8 47
3610 Sullivan Creek near Hungry Horse 9 ilies
3615 Graves Creek near Hungry Horse 9 aif

09

Mean

elevation

Feet

4,980
4,870
4,710
4,120
3,610
6,720
5,150
5,010

4,930
8,540

7,600
6, 350
5,240

8,160
7,130

6,670
5,920

5,800
6,130
5,960
5,300
5,510
5,430

¥ U.S. GOVERNMENT PRINTING OFFICE: 1971—780-410/56 REGION NO. 8

12

Headquarters for the Intermountain Forest and
Range Experiment Station are in Ogden, Utah.
Field Research Work Units are maintained in:

Boise, Idaho

Bozeman, Montana (in cooperation with
Montana State University)

Logan, Utah (in cooperation with Utah
State University)

Missoula, Montana (in cooperation with
University of Montana)

Moscow, Idaho (in cooperation with the
University of Idaho)

Provo, Utah(in cooperation with Brigham
Young University)