Hydrology and Effects of 

Conservation Structures,

Willow Creek Basin, 

Valley County, Montana, 

1954-68

GEOLOGICAL SURVEY WATER-SUPPLY PAPER 1532-G

Hydrology and Effects of 

Conservation Structures,

Willow Creek Basin, 

Valley County, Montana, 

1954-68

By DONALD G. FRICKEL

HYDROLOGIC EFFECTS OF LAND USE

GEOLOGICAL SURVEY WATER-SUPPLY PAPER 1532-G

A presentation of hydrologic data 

and a study of the effectiveness 

of conservation structures in a 

538-square-mile area in 

northeastern Montana

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1972
UNITED STATES DEPARTMENT OF THE INTERIOR 

ROGERS C. B. MORTON, Secretary

GEOLOGICAL SURVEY 

V. E. McKelvey, Director

Library of Congress catalog-card No. 72-600204

For sale by the Superintendent of Documents. U.S. Government Printing Office

Washington, D.C. 20402 - Price 30 cents

Stock Number 2401-02210
CONTENTS

Page

Abstract ...............--.......-.....-.................-.............-............................. Gl

Introduction and purpose of report........... ..... . .......... . .. . -- 1

Location and topography..................................................................................... 2

Climate...................................................................................................................... 4

Geology, soils, and vegetation-. . .............. ................................................... 6

Frequency analysis-- ----- ..--.----.--. ................................................................... 7

Precipitation . .. ....... .. .................................. 8

Runoff. -. .................................................................................................... 11

Analysis of data-. . .--.--.-----......... . - ................................................... 12

Erosion and sediment yield---.-----. . ....-..-- .................................................... 22

Relation to distribution of vegetation.. . ............................................ 24

Method of estimating sediment yield-.. ................................................ 28

Conservation structures....................... ............................................................. 29

Effects on runoff.. ..................................................................................... 29

Effects on sediment yield-- . ..-----....-- --.---... .. . ..-.. -- ........ .... 31

Summary.................................................................................................................. 33

References cited............ ..................................................................................... 34

ILLUSTRATIONS

Page

FIGURE 1. Index map showing location of the Willow Creek study

area, Montana----.--------..... -.... .-.--. ..--.----------.--.---------...- -.- G3

2. Map of Willow Creek basin, showing study basins and

distribution of sedimentation rates......................................... 4

3. Graph showing average monthly precipitation .................... 7

4-5. Precipitation-frequency curves showing:

4. Total annual precipitation.. ...................................- 9

5. Maximum storm precipitation----- -..---------. - 10

6. Graph showing the annual precipitation for the period of

record.. .-.....- ..- -...-..-..-......-..--.....---------- -.-- . -- ----.. 11

7-9. Flood-frequency curves showing:

7. Runoff rates . . 13

8. Variation of mean annual rate with basin area. 14

9. Runoff volume----.-..- .................................. .. ......... 15

10. Graph showing relative amounts of particles detached from

soils................................................................................................. 25

11-12. Photographs showing:

11. Typical sagebrush area................................................. 26

12. Hardpan terrace with "slick" and "semislick" areas 27

13. Cross section of Willow Creek at the gaging station, showing significant changes during the period . . .... -- 29

14. Graph showing relation between monthly sediment load

and monthly runoff.. .... ....................................................... 32

in
IV CONTENTS

TABLES

Page

TABLE 1. Reservoir capacity in Willow Creek basin.--.-......-....-.--...--.---. G2

2. Runoff measured in Northwest Burnett reservoir-.---.--..-.----.-- 16

3. Runoff measured in Cactus Flat reservoir---.----...---.-.---.- ---- 19

4. Runoff measured in Sheepshed reservoir----..----.....--...-..-..--.-..- 20

5. Sediment yield during periods between surveys..-............ .. 23

6. Annual suspended-sediment load and stream discharge

measured at Willow Creek gaging station.-----.-...---.-------.---- 24

7. Distribution of major vegetation types in the study basins

and measured yields-...--..-..-.-----.---..-.-.-..-.-.-.-..-------....--..--....-.-- 26

8. Computed sediment yields associated with major vegetation types--..---..-....-...--..-....--.-.--....... ......................................... 28
HYDROLOGIC EFFECTS OF LAND USE

HYDROLOGY AND EFFECTS OF

CONSERVATION STRUCTURES,

WILLOW CREEK BASIN, VALLEY COUNTY,

MONTANA, 1954-68

By DONALD G. FRICKEL

ABSTRACT

This report presents the results of hydrologic observations in Willow 

Creek basin in northeastern Montana for the period 1954-68. Frequency 

curves for runoff and precipitation are provided.

The average annual precipitation for the 14-year period 1954-67 was 

about 0.5-inch less than the 30-year average; also, the average for the first 

half of the period was 3.4 inches less than that for the second half. Runoff 

records show that about two-thirds of the seasonal (April through October) 

runoff occurs in two events. The average seasonal runoff volume measured 

at Northwest Burnett, Cactus Flat, and Sheepshed reservoirs was 93.9, 

96.5, and 37.5 acre-feet per square mile, respectively, for the 10-year period 

1958-67. Sediment yields from Northwest Burnett, Cactus Flat, Sheepshed, 

and Triple Crossing basins varied from 0.1 to about 2.0 acre-feet per square 

mile. The apparent relation between the sediment yield of an area and the 

occurrence of major vegetation types in that area was used as a basis for 

projecting the measured rates to other areas in the basin for estimating 

sediment yields.

During the study period numerous reservoirs and waterspreaders were 

constructed in the basin. This upstream regulation of flow has caused a 

decrease in both the channel dimensions and the suspended-sediment load at 

the gaging station near the mouth of the basin. The peak stream discharge 

recorded at the gaging station is estimated to be about 45 percent less than 

it would have been had no reservoirs or waterspreaders been in the basin. 

The annual runoff volume recorded at the gaging station is estimated to be 

18 percent less than it would be if the basin were totally uncontrolled. The 

capacity of the reservoir system is being reduced at an estimated rate of 

1.6 percent, owing to sedimentation.

INTRODUCTION AND PURPOSE OF REPORT

In the early 1950's the Bureau of Land Management initiated 

an extensive conservation program in the Willow Creek basin, 

near Glasgow, Valley County, Mont. (fig. 1). The objective of this 

program was to control runoff and sediment yield and to increase 

forage production with conservation structures. By the end of

Gl
G2 HYDROLOGIC EFFECTS OF LAND USE

1967, reservoirs providing storage capacity of about 48,000 acrefeet (table 1) had been constructed. The reservoirs detain runoff 

and sediment from approximately 75 percent of Willow Creek 

basin. Waterspreading systems supply some additional storage 

capacity and also provide irrigation to about 4,500 acres of hay 

and pastureland. Contour furrowing has been applied to some 

parts of the basin as an additional conservation treatment. Early 

in the program the U.S. Geological Survey began collecting data 

to supply the hydrologic information needed to design the conservation structures and to evaluate the effectiveness of the 

conservation measures. Initial work involved monitoring a severe 

headcut in the main channel of Willow Creek. These observations 

led to the construction of a dam to control the headcut. Observations of sediment yield were begun in three reservoirs in 1952.

TABLE 1. Reservoir capacity in Willow Creek basin

Year

1941-53 

1954.............

1955 

1956 

1957 

1958. .

1959.............

I960-.--....

Cumulative 

number of 

reservoirs

34

57

57

68

80

92

Q9

106

Cumulative 

capacity1 

(acre-ft)

1,641

7,163

7,163

U 41 Q

18,679

19,755

19,755

23,350

Year

1961............

1962............

1963............

1964............

1965............

1966............

1 q«7

Cumulative 

number of 

reservoirs

108

116

119

148

161

176

190

Cumulative 

capacity1 

(acre-ft)

30,322

32,058

32,077

40,679

46,366

47,926

47,963

1This is constructed capacity. Usable capacity may be considerably less.

Runoff and sediment measurements were begun at Northwest Burnett reservoir (hereafter referred to as Burnett reservoir) in 1954 

(fig. 2). As additional reservoirs were built, more stations were 

established to measure runoff and sediment yields from areas 

representing a variety of the terrain and vegetative conditions 

existing in the basin. This report is a compilation of the data 

collected through June of 1968 and presents an analysis of the 

effectiveness of the conservation measures in the basin.

Information on conservation structures and aerial photographs 

were provided by the Malta district of the Bureau of Land 

Management. The assistance given by the personnel of the Fort 

Peck Field Headquarters, Montana district, U.S. Geological Survey, who served as observers, is gratefully acknowledged.

LOCATION AND TOPOGRAPHY

Willow Creek drains an area of about 547 square miles (538 

square miles at gaging station) in northeastern Montana. The 

creek is on the north side of Fort Peck Reservoir and flows 

northeastward to join the Milk River about 3 miles southeast of 

Glasgow, in Valley County. It has two major tributaries 

Lone Tree Creek and Beaver Creek (fig. 2) which drain about
WILLOW CREEK BASIN, MONTANA G3

45 percent of the basin. The basin is used for grazing, forage 

production, wildlife habitat, and some farming.

Streams in the basin are naturally ephemeral; however, some 

may now have long periods of low flow as the result of outflow 

from the many detention dams in the basin. Stream channels 

are deeply entrenched and are actively eroding, thus contributing 

much sediment directly into the main channel of Willow Creek. 

This is especially true along the lower reaches. The average gradient of Willow Creek from the confluence of its South and North 

Forks to the Milk River is 4.5 feet per mile. This is a relatively 

flat gradient for a stream in the Western United States.

108° 107°

10

i

20 30 MILES

FIGURE 1. Index map showing location of the Willow Creek study area, Montana.
G4 HYDROLOGIC EFFECTS OF LAND USE

The basin has low to moderate relief, with elevations ranging 

from 2,000 feet to about 2,800 feet above sea level. The topography 

is characterized by rolling uplands interspersed with a welldefined drainage system of relatively flat floored valleys.

CLIMATE

The climate in the Willow Creek basin is of the continental 

type. The mean annual precipitation at Glasgow, about 6 miles

Modified from vegetation 

maps provided by the 

Bureau of Land Management

FIGURE 2. Study basins, main drainage channels, and areal
WILLOW CREEK BASIN, MONTANA G5

north of the Willow Creek gaging station, is 12.67 inches, based 

on 54 years of National Weather Service (U.S. Weather Bur.) 

records. Usually, most of the precipitation in any given year is 

received during the summer, with the highest amount occurring 

in June and the next highest amounts in May and in August 

(fig. 3). The storms during May and June commonly last for 

several days and contribute approximately 40 percent of the total 

annual precipitation. The late summer storms generally occur as

EXPLANATION

Study reservoir 

Boundary of gaged basins

Boundary of 

Willow Creek basin

A

Water-stage recorder

Vegetation Computed sediment yield, 

type in acre-feet

per square mile 

Grass 0.76

Saltbush .88

Sagebrush 1.51

Greasewood, upland 2.00

Greasewood, bottomland .90

Weeds, waste, barren 3.50

distribution of computed sedimentation rates in Willow Creek basin.

474-236 O - 72 - 2
G6 HYDROLOGIC EFFECTS OF LAND USE

short-duration thunderstorms. In the summer months (April 

through September) precipitation in the basin averages 9.69 

inches, whereas precipitation during the winter months (October 

through March) averages only 2.98 inches. Storm precipitation 

during the winter months occurs mostly as snow.

Northeast Montana experiences a wide range in temperatures 

annually. The average maximum daily temperature for July at 

Glasgow is 87.6°F, and the average minimum daily temperature 

for January is 1.9°F. The highest temperature ever recorded 

at Glasgow, 113°F, occurred in July of 1900; the record low, 

 59°F, occurred in February of 1936. Mean annual temperature 

is 42.3 °F and the mean for the months of April through September 

is 60.6°F. The temperature span between maximum and minimum 

daily temperatures averages about 23°F.

GEOLOGY, SOILS, AND VEGETATION

Willow Creek basin is underlain by the Bearpaw Shale of Late 

Cretaceous age. The Bearpaw, a black marine shale high in 

sodium content, is easily eroded. Along the rim of the basin, the 

Bearpaw is overlain by the relatively resistant sandstone of the 

Fox Hills and Hell Creek Formations. Glacial drift deposits are 

scattered throughout the basin, but only in thin layers of small 

areal extent. A detailed description of rock units occurring in the 

Willow Creek area is given by Jensen and Varnes (1964).

Soils in the basin reflect the characteristics of their parent 

formations. The valley alluvium, derived primarily from the Bearpaw Shale, is very fine grained and relatively impermeable. A 

significant feature of the nonflooded alluvial soils is the development of hardpan "slicks" and "semislicks." These areas, described 

by Branson, Miller, and McQueen (1962), produce very little 

forage, but they apparently have a significant effect on sediment 

yield and runoff. Soils on the valley side slopes are composed 

basically of weathered shale in which various amounts of coarser 

material are evident in some areas. The soils near the basin divide, 

derived from the Fox Hills and Hell Creek Formations, are 

sandier and produce more forage than the other soils in the basin.

Vegetation in the Willow Creek basin is typical of that in the 

High Plains. Principal plants are nuttall saltbush (Atriplex 

nuttallii), big sagebrush (Artemisia tridentata) , sandberg bluegrass (Poa secunda), blue grama (Bouteloua gracilis) , western 

wheatgrass (Agropyron smithii), and black greasewood (Sarcobatus vermiculatus) .

The distribution of plants generally varies with the changes in 

soil type. Greasewood and western wheatgrass occur on the present 

flood plains, and nuttall saltbush is the dominant species on the
WILLOW CREEK BASIN, MONTANA G7

alluvial terraces that were flooded before the present valley 

trenching began. Big sagebrush, blue grama, and sandberg bluegrass are the main species found on the valley side slopes and ridge 

tops. Big sagebrush is dominant on the shale soils, whereas the 

grasses are dominant on the sandier soils along the rim of the 

basin.

2.5-

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<

0.5-

FIGUBE 3. Average monthly precipitation at Glasgow, Mont., 1954-67.

FREQUENCY ANALYSIS

Knowledge of the magnitude and frequency of hydrologic events 

is essential to sound, economic design of conservation structures. 

Frequency curves are used to relate the magnitude of a recorded 

hydrologic event to the probable frequency of recurrence of like 

events. A single short-term station record may contain a large 

"chance" variation from the "correct" value. This variation can 

be reduced by developing a regionalized or composite frequency 

relation from a number of station records within a hydrologically 

homogeneous region. Benson (1960) showed that by using the
G8 HYDROLOGIC EFFECTS OF LAND USE

composite relation of five or more 10-year records, the 10-year 

event could be predicted within 5.7 percent of the correct value; 

however, to obtain similar accuracy by using the relation of an 

individual station, a 90-year record was required.

A regional frequency curve shows the relationship of a dimensionless quantity, called the "event" ratio (flood ratio, precipitation ratio), to its recurrence interval. The ratios are determined 

by dividing the event of a given frequency by an "index" event, 

usually the mean annual event, using values obtained from the 

frequency curves of individual stations. Ratios are computed at 

selected recurrence intervals for each station to be included. The 

median ratio values are plotted against their respective recurrence intervals to define the regional frequency curve.

In order to use the frequency curve, a means of estimating the 

index event at any point in this region is necessary. This is 

usually accomplished by relating the index event to the drainagebasin area or to some other basin characteristic (s). By use of this 

relation with the regional frequency curve, a frequency curve 

can be defined for any location within the region. Dalrymple 

(1960) described the procedure for regionalizing station data in 

detail.

Regionalized precipitation-frequency and runoff-frequency 

curves were defined for the Willow Creek area. The common time 

base used for the annual precipitation-frequency curve was 54 

years. For reasons explained later, the time base for the 1-day 

and 3-day precipitation curves was reduced to 44 years. The runoff volume and discharge curves have a time base of 14 years.

PRECIPITATION

Three regionalized precipitation-frequency curves were developed for use in the Willow Creek area. These curves (figs. 4, 

5) relate the annual precipitation and the maximum 1-day and 

maximum 3-day precipitation to the recurrence interval. They 

were developed from data published in the reports "Climatological 

Data" of the National Weather Service (U.S. Weather Bur.) for 

stations in the Willow Creek area. The 1-day, 3-day, and 1-year 

time intervals were selected on the basis of available data and 

usefulness in design and management planning. Generally, 3 

consecutive days is the maximum length of major storms in the 

area, although a small amount of the total storm precipitation may 

fall on the fourth and fifth days.

Records from weather stations at Glasgow, Frazer, Fort Peck, 

Haxby, Jordan, Brusett, Telegraph Creek, and Malta were selected 

on the basis of location and length. Willow Creek basin is within 

the area bounded by these stations (fig. 1). Records from the
WILLOW CREEK BASIN, MONTANA G9

above weather stations are for periods varying in length from 

18 to 54 years, through 1968. Only two of the records were for 

periods of less than 30 years, and one of those was a 28-year 

record. All met the test for hydrologic homogeneity.

The double-mass curve technique described by Searcy and 

Hardison (1960) was applied to the annual precipitation amounts. 

The double-mass curves for the Glasgow, Frazer, and Jordan 

stations had significant slope breaks, and the annual precipitation 

amounts for these stations were adjusted accordingly. Because 

there is no method for making adjustments on individual storm 

amounts, these stations were excluded from the analyses of maximum 1-day and 3-day storms. As a result of this exclusion, the 

common time base represented by the frequency curves was shortened to 44 years.

26 I TTT I ! I

22

18

14

71

10

I I

I I

1.1 1.5 2 2.33 345 10 

RECURRENCE INTERVAL, IN YEARS

25 50

FIGUBE 4. Annual precipitation-frequency curve for the Willow Creek area.
G10 HYDROLOGIC EFFECTS OF LAND USE

The ordinate quantities of the precipitation-frequency curves 

(figs. 4, 5) are not dimensionless. Because a satisfactory relationship for estimating the index-precipitation event at any site was 

not found, a single value was applied to the whole region, thus 

permitting actual precipitation quantities to be shown on the 

frequency curves. The value used was the median of the station 

mean annual precipitation amounts.

The annual precipitation in the Willow Creek area varied from 

7.01 inches to 17.37 inches in the 14-year period during which 

runoff records were collected (fig. 6). The annual amounts are 

the averages of the amounts recorded at eight National Weather 

Service (U.S. Weather Bur.) stations. The average annual precipitation was 11.94 inches, which is about 0.5 inch less than the

5.0

4.0

3-day storm.

Ld 

03.0

1-day storm

02-0

1.0

I I

1.1 1.5 2 2.33 345 10

RECURRENCE INTERVAL, IN YEARS

25 50

FIGURE 5. Maximum storm precipitation-frequency curves for the Willow Creek area.
WILLOW CREEK BASIN, MONTANA Gil

30-year average. The average for the first half of the period was 

3.4 inches less than the average for the second half.

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14-year mean (1954-67) 11.94 

7-year mean (1954-60) 10.25

7-year mean (1961-67) 13.64

30-year mean (1938-67) 12.39

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_

1954 55 56 57 58 59 60 61 62 63 64 65 66 1967

FIGURE 6. Annual precipitation in the Willow Creek area, 1954-67. Bars show the average of 

amounts recorded at the following National Weather Service (U.S. Weather Bur.) stations: 

Glasgow, Frazer, Fort Peck, Haxby, Jordan, Brusett, Telegraph Creek, and Malta.

RUNOFF

Runoff in Willow Creek basin results from either snowmelt or 

rainstorms. The peak discharge and maximum daily volume in a 

given year may result from either type of event. Runoff rates are 

generally high because of the relatively impervious soils in the 

basin.

Runoff data were obtained by measuring the inflow to a reservoir located at the mouth of each gaged basin1 . Continuous waterlevel recorders monitored the reservoir stage. Stage-capacity 

relations were developed from topographic surveys of the reservoirs and were adjusted for sediment accumulation on the basis 

of periodic resurveys. Outflow relations were developed from the 

recession hydrographs and were verified, when possible, by current-meter measurements of outflow, after the inflow had stopped. 

Inflow was then calculated as change-in-storage plus outflow.

!The term "gaged basin (s) " refers to the following upland watersheds where data were obtained 

by using a reservoir as a runoff- and sediment-collecting device: Burnett, Cactus Flat, Sheepshed, 

and Triple Crossing. The "gaged basins" are located within the boundaries of Willow Creek basin.
G12 HYDROLOGIC EFFECTS OF LAND USE

Seepage and evaporation during the inflow periods were considered 

to be negligible in all reservoirs.

Runoff data collected at three reservoirs are given in tables 2, 

3, and 4. Although the recording season varied from year to year, 

it generally included the months of March through October. 

Streamflow records (U.S. Geological Survey, "Surface Water 

Supply of the United States," pt. 6-A, 1954-67) at Willow Creek 

gaging station show that more than 90 percent of the annual 

runoff occurs during these months.

ANALYSIS OF DATA

The average seasonal runoff to Burnett, Cactus Flat, and 

Sheepshed reservoirs was 93.9, 96.5, and 37.5 acre-feet per square 

mile, respectively, for the 10-year period 1958-67. The average 

runoff at Burnett reservoir for the 14-year period 1954-67 was 

88.1 acre-feet per square mile, and the average at Sheepshed 

reservoir for the period 1955-67 was 30.9 acre-feet per square 

mile.

General appearance of Burnett and Cactus Flat drainage basins 

would suggest that there should be a higher average runoff at 

Cactus Flat than at Burnett. The relatively impermeable hardpan 

terraces covering 26 percent of Burnett basin are believed to be 

a factor in producing this higher than expected runoff. The soils 

and vegetation of Sheepshed drainage suggest less runoff than at 

the other two basins. However, the measured difference seems 

extreme. Part of the difference may be due to an instrumentation 

deficiency. Sheepshed reservoir was instrumented primarily to 

measure maximum runoff events, and it is possible that a number 

of small events were not recorded. As this record of runoff volume 

is somewhat questionable, it was not used to develop the runoffvolume curves presented in this report. Runoff rates were probably 

unaffected by this particular instrumentation problem.

The time distribution of runoff must be considered in many 

management and design decisions. Analysis of reservoir inflow 

on a single-event basis shows that a major part of the annual 

inflow usually occurs in a few events. On the average, 34 percent 

of the annual runoff occurs in response to snowmelt, commonly 

from one event of several days' to a week's duration. Of the remaining annual runoff (about 66 percent), about half is produced 

by a single rainstorm in June or July, and half by smaller storms 

throughout the rest of the summer. Thus, approximately twothirds of the annual runoff usually occurs from only two events.

Instrumentation used in this study did not provide for determination of instantaneous runoff rates. Average runoff rates were 

computed by dividing the inflow during a short time interval by
WILLOW CREEK BASIN, MONTANA G13

that time interval. Although average rates are not directly comparable with instantaneous rates, they may be more meaningful 

than instantaneous rates for reservoir design, because they show 

how long the rate was sustained. Rates computed for the Willow 

Creek area are based on a 30-minute time interval, which is the 

shortest interval that could be defined with reasonable accuracy 

for all the records.

An annual flood-frequency curve and two volume-frequency 

curves were defined for the Willow Creek area. The annual floodfrequency curve (fig. 7) gives the relation between the recurrence 

interval and the ratio of the maximum annual runoff rate to the 

mean annual runoff rate. This curve represents the annual series 

of runoff rates for a 30-minute period and is not interchangeable

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Runoff rates based

during a 30-minute

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1.01 1.1 1.5 2 2.33 345

RECURRENCE INTERVAL, IN YEARS 

FIGURE 7. Flood-frequency curve for Willow Creek basin.

10 20

474-236 O - 72 - 3
G14 HYDROLOGIC EFFECTS OF LAND USE

with curves representing rates for other time intervals. It is 

used in conjunction with figure 8 which gives the variation of the 

mean annual runoff rate with basin size. These curves were 

developed from the records of Sheepshed, Cactus Flat, and Burnett 

reservoirs. The paucity of points in figure 8 may cause concern 

but the relation should give satisfactory estimates of the mean 

annual floods for basins that are 5 to 11 square miles in area. 

The mean annual floods of the three gaged basins may be estimated 

from the curve to within 10 percent of the measured values. 

Several of the authors' colleagues agree that the measured values 

indicated in figure 8 are reasonable for the soil, topographic, and 

vegetative conditions existing in the gaged basins. These basins 

were originally selected as being representative of the conditions 

prevailing in Willow Creek basin. Inasmuch as this curve and the 

related curve in figure 7 are based on a minimum of data, it is 

extremely important that the use of the limitations listed elsewhere be strictly adhered to.

The two volume-frequency curves (fig. 9) are based on the 

records of Cactus Flat and Burnett reservoirs. Because of the 

similarity in the size and the runoff amounts of the two basins, 

the ordinate values of the two curves are volumes based on the 

average mean annual volumes. The 6-month-volume curve represents the total volume of runoff for the recording season, which 

accounts for most of the runoff for the whole year.

RUNOFF RATE, MEAN ANNUAL 

IN FEET PERHUNDREDS OFCUBIC SECOND

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DRAINAGE AREA, IN SQUARE MILES

FIGURE 8. Variation in mean annual runoff rate with drainage area.

20
WILLOW CREEK BASIN, MONTANA G15

To apply the flood-frequency curve to a specific basin, use figure 

8 to estimate the mean annual runoff rate for that basin. Then 

determine the flood ratio for the required recurrence interval 

from figure 7. The product of the mean annual runoff rate (fig. 

8) and the flood ratio (fig. 7) is the estimated runoff rate. A 

complete flood-frequency curve for a basin can be produced by 

plotting the runoff rates for several recurrence intervals and 

fitting a smooth curve through them. The 3-day or 6-month runoff 

volume of a given recurrence interval can be found for a specific 

basin by multiplying the basin area by the unit runoff (fig. 9).

The runoff-frequency curves given herein are based on a comparatively small number of records, but, as explained previously, 

composite curves provide a given degree of accuracy more often 

than do curves applied on an individual basis. Use of these curves 

should be restricted to Willow Creek basin and those immediately 

surrounding areas where the topography, soils, and vegetation 

are similar to those in Willow Creek basin. The curves represent 

basins 5 to 11 square miles in area, and their use on basins whose 

areas are outside this size range is not recommended. The curves 

should not be extended to higher recurrence intervals.

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1.01 1.5 2 2.33 345 

RECURRENCE INTERVAL, IN YEARS

10 20 30

FIGURE 9. Runoff volume-frequency curves for Willow Creek basin.
G16 HYDROLOGIC EFFECTS OF LAND USE

TABLE 2. Runoff measured in Northwest Burnett reservoir

Location. Lat 48°05' N., long 107°08' W., SE^4 sec. 24, T. 27 N., R. 35 E., 

on Lone Tree Creek, about 18 miles upstream from the confluence with 

Willow Creek, near Glasgow, Mont. 

Drainage area. 5.0 sq mi.

Records available. 1954-67, summer months only. 

Gage. Water-stage recorder.

Runoff and discharge determinations. Contents of reservoir and volume of 

inflow computed from stage-capacity curve of the reservoir. Average 

discharges determined from runoff hydrograph.

Capacities. Capacities of the reservoir at the spillway elevation are as 

follows:

Aug. 1954........146 acre-ft,

Sept. 1955........143 acre-ft,

Sept. 1962........143 acre-ft,

Sept. 1963 .143 acre-ft, 

June 1968........140 acre-ft.

Maxima. Maximum storm inflow 512.0 acre-ft, or 102.4 acre-ft per sq

mi, July 25-26, 1965.

Remarks. Records fair, except those with spill which are poor. Has two 

24-inch outlet pipes.

Date

of

flow

Inflow

stored

(acre-ft)

Spill1 

(acre-ft)

Inflow

Total 

(acre-ft)

Acre-feet 

per square mile

1954

May 4-6..-...-.....-.....--..... 0 44.6 44.6 8.9

June 10-12-..-.. ........-... 0 138.0 138.0 27.6

June 29-30 ........................ 0.8 13.7 14.5 2.9

July 9-10 .............................. 0.3 15.2 15.5 3.1

Aug. 5-6 .............................. 6.0 0 6.0 1.2

Aug. 9-10 ..................... 47.9 0 47.9 9.6

Aug. 15-21. ...................... 91.6 18.4 110.0 22.0

Sept. 5-6 .............................. 9.0 0 9.0 1.8

Sept. 15-16.............................. 18.0_________.5______18.5________3.7

For year... .. .... 173.6______230.4 404.0 80.8

1955

May 2-5.. ............................ 0 104.0 104.0 20.8

May 15-19 .......................... 0 279.0 279.0 55.8

July 26-27............................... 0_______59.1______59.1______11.8

For year- ... .. 0 442.1 442.1 88.4

1956

Mar. 16-20 0 106.3 106.3 21.3

May 6.... 0 14.2 14.2 2.8

May 28-29 . 0 9.2 9.2 1.8

June 22-23. ................... 0 38.9 38.9 7.8

July 29-Aug. 3 ... 3.5 24.7 28.2 5.6

Aug. 31 - 1.8______26.6_____28.4______5.7

For year . . 5.3 219.9 225.2 45.0

1957

Mar. 19-26 ........................... 4.6 156.9 161.5 32.3

Apr. 22-24............................... 2.7 9.5 12.2 2.4

May 22-23 . ... 2.9 27.6 30.5 6.1

June 9-10. .. 2.9 3.5 6.4 1.3

June 12-17.............................. 6.4 29.5 35.9 7.2

June 21-22.............................. 2.2 60.8 63.0 12.6

Aug. 30-Sept. I. . 3.9 47.5 51.4 10.3

Sept. 4-5 .............................. 2.8 16.2 19.0 3.8

Sept. 18-19 ....................... 2.8 13.3 16.1 3.2

Oct. 28-29 ......................... 2.9______2.3______5.2______1.0

For year 34.1 367.1 401.2 80.2
WILLOW CREEK BASIN, MONTANA G17 

TABLE 2. Runoff measured in Northwest Burnett reservoir Continued

Date Inflow g ., ________Inflow_________________

°f stored (acre-ft) Total Acre-feet 

___________flow____________(acre-ft)_____*_____'_____(acre-ft) per square mile

1958 

July 8-9.................................... 1.7 13.3 15.0 3.0

Dec. 3-4 .................. 2.4 40.5 42.9 8.6

For year...................... 4.1 53.8 57.9 11.6

1959

Apr. 18-19............................... 2.6 2.3 4.9 1.0

June 17..................................... 0 15.5 15.5 3.1

June 26-27............................. 0 3.6 3.6 .7

July 4........................................ 1.9 0 1.9 .4

Sept. 28.................................... 2.0 0 2.0 .4

Oct. 6........................................ 2.3 4.3 6.6 1.3

Oct. 9........................................ 2.4 1.3 3.7 .7

For year...................... 11.2 27.0 38.2 7.6

1960 

Mar. 17-23............................... 6.1 370.1 376.2 75.2

Apr. 29-May 1....................... 3.4 67.3 70.7 14.1

June 22..................................... 5.1 7.9 13.0 2.6

For year...................... 14.6_____445.3 459.9 91.9

1961

Apr. 24...................................... 5.8 0.0 5.8 1.2

May 30-31.......................... 10.0 7.0 17.0 3.4

June 13..................................... 1.8 .0 1.8 .4

June IS........ ...................... 2.5 .5 3.0 .6

July 31.. ............................. 5.0 1.2 6.2 1.2

Sept. 2...................................... 13.5 8.1 21.6 4.3

Sept. 18.................................... 6.4 .4 6.8 1.4

Oct. 31...................................... 6.1 .5 6.6 1.3

For year...................... 51.1 17.7 68.8 13.8

1962

Mar. 21-26 ........................ 43.8 115.4 159.2 31.8

May 13-14............................... 9.0 34.8 43.8 8.8

May 15...................................... .2 .2 .4 .1

May 16 .............................. 17.6 23.5 41.1 8.2

May 20-22 ................... 43.1 65.2 108.3 21.7

June 3-5 ........................... 42.0 47.9 89.9 18.0

June 14-15... .................... 2.3 12.3 14.6 2.9

June 20 .............................. .9 .6 1.5 .3

June 22-23- ...................... 17.6 38.7 56.3 11.3

July 2.. .............................. .9 1.3 2.2 .4

July 13-14............................... 120.0 225.0 2345.0 69.0

Oct. 15-16-.-.. .. 11.4 15.2 26.6 5.3

For year ... 308.8 580.1 888.9 177.8

1963

Before Feb. 28. . 4.2 5.1 29.3 1.9

Feb. 28-Mar. 2 .6 10.0 10.6 2.1

Apr. 10 .............................. 2.3 .4 2.7 .5

Apr. 17-18 . . 2.8 9.8 12.6 2.5

May 9-13 . 5.8 45.2 51.0 10.2

June 5-7.. 25.4 61.6 87.0 17.4

June 21-22- . ... 25.0 58.6 83.6 16.7

June 28-29... . 8.8 25.3 34.1 6.8

July 10. .............................. 19.7 28.0 47.7 9.5

Aug. 25-26.. . 9.0 50.6 59.6 11.9

Sept. 3 ................................. .2 12.3 12.5 2.5

For year .............. 103.8 306.9 410.7 82.0
G18 HYDROLOGIC EFFECTS OF LAND USE

TABLE 2. Runoff measured in Northwest Burnett reservoir Continued

Date 

of 

flow

Inflow

stored

(acre-ft)

Spill1 

(acre-ft)

Inflow

Total 

(acre-ft)

Acre-feet 

per square mile

1964

Mar. 30-Apr. 1....................... 2.2 6.1 8.3 1.7

Apr. 8-9................................... 5.1 16.4 21.5 4.3

Apr. 26..................................... 2.6 .8 3.4 .7

May 3....................................... 40.1 27.8 67.9 13.6

May 3-4........................... 83.6 60.2 143.8 28.8

June 18-19 ........................ 40.1 45.3 85.4 17.1

June 20 . .... 10.2 29.6 39.8 8.0

July 3... .............................. 20.9 40.6 61.5 12.3

July 10 - 4.1 5.5 9.6 1.9

Aug. 20 15.9______15.6_____31.5______6.3

For year....................... 224.8 247.9 472.7 94.7

1965

Apr. 12 .............................. 86.2 12.2 98.4 19.7

Apr. 22 .3 .0 .3 .1

May 6-7 126.4 188.8 315.2 63.0

May 30-31.. .... 2.6 1.9 4.5 .9

June 1. .. .............. 3.3 10.6 13.9 2.8

June 13.... ...... ............. 1.6 1.6 3.2 .6

June 14-16.......................... . 37.1 59.6 96.7 19.3

June 25-26............................... 127.6 384.4 512.0 102.4

June 29 .................... 1.8 6.1 7.9 1.6

July 10...................................... 18.6 34.5 53.1 10.6

Aug. 5-6- ................ 82.4 77.9 160.3 32.1

Sept. 4...................................... 1.8 1.8 3.6 .7

Sept. 9 .............................. .1 .0 .1 .0

Sept. 15.................................... .3_______A_______.3_______.!_

For year...................... 490.1_____779.4 1,269.5_____253.9

1966

Mar. 12-16 2.0 140.9 142.9 28.6

May 14-16............................... 1.6 8.7 10.3 2.1

July 2-5 ............................. 2.5 107.5 110.0 22.0

July 12-13 ..................... 137.8 118.2 256.0 51.2

Oct. 21-22................................ 6.7______4.3_____11.0______2.2

For year...................... 150.6 379.6 530.2 106.1

1967

Up to Mar. 3. 52.6 43.7 96.3 19.3

Mar. 8-9-- 16.1 44.9 61.0 12.2

Mar. 12-Apr. 4-. .. 34.3 38.9 73.2 14.6

Apr. 6-7 .............................. .1 16.1 16.2 3.2

Apr. 23 ............................. .2 .0 .2 .0

Apr. 25-May 2 2.0 126.0 128.0 25.6

June 12-15. ................. .9 17.0 17.9 3.6

June 18.. . .1 .0 .1 .0

Sept. 13-15 6.8 61.3 68.1 13.6

Oct. 1 . .7 .2 .9 .2

Oct. 5-6 ................................ 1.4_____33.7_____35.1______7.0

For year. 115.2 381.8 497.0 99.3

'Includes pipe outflow. All spill goes to waterspreader. 

2Recorder not operating ; amounts based on high-water marks.
WILLOW CREEK BASIN, MONTANA G19

TABLE 3. Runoff measured in Cactus Flat reservoir

Location. Lat 47°59' N., long 106°46' W., Ey2 sec. 24, T. 26 N., R. 38 E., 

on Wilderness Coulee about 1 mile upstream from the confluence with 

Willow Creek, near Glasgow, Mont.

Drainage area. Contributing area 6.4 sq mi.

Records available. 1958-67, summer months only.

Gage. Water-stage recorder.

Runoff and discharge determinations. Contents of reservoir and volume of 

inflow computed from stage-capacity curve of the reservoir. Average discharges determined from runoff hydrograph.

Capacities. Original capacity 254 acre-ft at spillway (gage height 6.5 

ft), survey of July 30, 1958; capacity 185.6 acre-ft, survey of Sept. 9, 1962; 

capacity 176.8 acre-ft, survey of September 29, 1963; capacity 169 acre-ft, 

survey of October 10, 1964; capacity 159 acre-ft, survey of October 6, 1966.

Maxima. Maximum storm inflow 1,177.4 acre-ft, or 184.0 acre-ft per sq 

mi, May 18-25, 1960.

Remarks. Records fair, except those with spill which are poor. Has two 

24-inch outlet pipes.

Date 

of 

flow

1958 

Dec. 3-4 

For year... ..

1959 

Before Mar. 7. ... . Oct. 8-9 - 

Oct. 14 

For year

Outflow (acre-ft) _, , ,

Lower Upper outflow 

pipe Pipe and ( acre-ft) 

v v spillway

. .............. .............. 0.0

.............. .... 0.0

2.3 ..... .... ..... 2.3

. ............... .............. 2.3

Inflow 

stored 

(acre-ft)

27.5

27.5

206.0 

47.6 

5.2

258.8

Inflow

Total 

(acre-ft)

27.5

27.5

206.0 

47.6 

7.5

261.1

Acre-feet 

per 

square mile

4.3

4.3

32.2

7.4 

1.2

40.8

1960

Mar. 18-25 

Apr. 24-25-- 

Apr. 28-May 1... ...

For year. ...

. 397.4

11.3

664.7 1,062.1

.............. .0

.............. 11.3

.............. 1,073.4

115.3

2.7

22.0

140.0

1,177.4

2.7

33.3

1,213.4

184.0

.4

5.2

189.6

1961

June 13-14.. .-. 7.8 ..........

June 18 .. .............. ..........

Sept. 2 - .............. ..........

Sept. 9-10 .- .............. ..........

Sept. 11.................... .............. ..........

Sept. 18. .............. ..........

For year..... .............. ..........

7.8

.0

.0

.0

.0

.0

7.8

93.5

1.7

3.5

9.6

4.0

.8

113.1

101.3

1.7

3.5

9.6

4.0

.8

120.9

15.8

.3

.6

1.5

.6

.1

18.9

1962

21.4

57.4

Mar. 21-22 

Mar. 24-26 

May 13 .............. ............

May 21-23

July 13-14 . 170.0 610.0 

For year. .............. .............

21.4

57.4

.0

13.9

780.0

100.2

17.0

.3

79.3

121.6

74.4

.3

193.2

2780.0

19.0

11.6

.0

14.6

121.9

872.7 196.8 1,069.5 167.1
G20 HYDROLOGIC EFFECTS OF LAND USE

TABLE 3. Runoff measured in Cactus Flat reservoir Continued

Date 

of 

flow

1963 

May 12-13. 

June 5-6 

June 23-July 1 

July 10^11 

Aug. 25-26 

For year.....

1964 

Mar. 18 . .

May 2-4..... ........

For year. .

1965 

Apr. 3-15 

May 5-10 

July 4-5 

July 7-8 

July 10-11.. 

Aug. 6-7 ..... .......

For year ..

1966 

Mar. 12-17 

May 14 

July 2-4.. 

July 13 

Aug. 20-21 

For year. .

1967 

Mar. 1-3- .

Mar Q

Mar. 3...... .......

May 2 

Sept. 14 . 

For year......

Outflow

Lower 

pipe

40.6 

36.0

82.6 

61.0 

13.9

84.2

441.5 

50.6 

8.2 

6.8 

13.6 

20.7 

78.0

105.8 

2.2 

20.6

11.6

88.1 

9.6 

53.0

48.0

(acre-ft)

Upper 

pipe and 

spillway

6.4

55.9 

1.6

61.6

216.8 

185.5

2.6 

14.1 

9.5

Total 

outflow 

(acre-ft)

40.6 

42.4 

82.6 

116.9 

15.5

298.0

15.0 

145.8

160.8

658.3 

236.1 

8.2 

6.8 

16.2 

34.8 

87.5

1,047.9

105.8 

2.2 

20.6 

.0 

11.6

140.2

88.2 

9.6 

53.0 

.0 

48.0

198.8

Inflow 

stored 

(acre-ft)

0.0 

176.7 

9.1 

190.5

147.2

523.5

0.0 

226.5

226.5

67.5 

258.4 

5.3 

7.4 

113.9 

141.2 

61.3

655.0

10.7 

6.2 

6.8 

.1 

4.3

28.1

10.5 

7.2 

125.0 

.8 

63.5 

.8

207.8

Inflow

Total 

(acre-ft)

40.6 

219.1 

91.7 

307.4 

162.7

821.5

115.0 

1372.3

387.3

725.8 

494.5 

13.5 

14.2 

130.1 

176.0 

148.8

1,702.9

116.5

8.4 

27.4 

.1 

15.9

168.3

98.7 

16.8 

1178.0 

.8 

1111.5 

.8

406.6

Acre-feet 

per 

square mile

6.3 

34.2 

14.3 

48.0 

25.4

128.2

2.3 

58.2

60.5

113.4 

77.3 

2.1 

2.2 

20.3 

27.5 

23.2

266.0

18.2 

1.3 

4.3 

.0 

2.5

26.3

15.4 

2.6 

27.8 

.1 

17.4 

.1

63.4

1CIock not operating ; amounts estimated from range of chart trace. 

2Recorder not operating ; amounts estimated from high-water marks. 

3Date uncertain.

TABLE 4. Runoff measured in Sheepshed reservoir

Location. Lat 47°53' N., long 107°09' W., SE^ sec. 26, T. 25 N., R. 35 E., 

on Willow Creek about 56 miles upstream from gaging station near Glasgow, Mont.

Drainage area. 10.8 sq mi.

Records available. 1955-67, summer months only.

Gage. Water-stage recorder.

Runoff and discharge determinations. Contents of reservoir and volume 

of inflow computed from stage-capacity curve of the reservoir. Average 

discharges determined from runoff hydrograph.

Capacities. Original capacity 550 acre-ft at spillway (gage height 16.1 

ft), survey of Sept. 24, 1955; capacity 518 acre-ft, survey of Sept. 14, 1962; 

capacity 488 acre-ft, survey of June 25, 1968.
WILLOW CREEK BASIN, MONTANA G21

TABLE 4. Runoff measured in Sheepshed reservoir Continued

Maxima. Maximum storm inflow 777.5 acre-ft, or 72.0 acre-ft per sq mi, 

July 13-14, 1962.

Remarks. Record poor. Some inflow not recorded because of recorder location relative to low point in reservoir and outlet pipe. Has 6-inch and 21- 

inch outlet pipes.

Date 

of 

flow

1955 

July 26-29 

For year.... .

1956 

Mar. 24........... ........

July 3-4 ............

Aug. 29...... ....... ......

For year.....

1957 

Aug. 19 

Sept. 1-4........ ........

For year.....

1958

July 30 ........ ..

For year.....

1959 

Mar. 2.. ...... ......

Apr. 17...... ...... ........

Apr. 26-27 

May 2-3 

May 9-10 .... ....... . May 19. 

Oct. 20.... ....... .........

For year... ..

1960 

Mar. 18-22.... ...

Apr. 292 .......

June 22........ ..........

For year.....

1961*

1962 

Mar. 20-26 

Mar. 22 

July 13-14. .

July2.. ......................

For year... ..

1963 

Feb. 25-27 

June 21-22. ..

June 29-30 

July 10 .

For year

Outflow (acre-ft)

Pipe1 Spillway1

81.0 ....... .......

1.3

15.4 ....... .......

.2 ..............

0.1 ....... .......

82.9 ..............

3.2 

374.1 ...... ........

34.7 ..............

74.3 102.1 

58.7 ....... .......

106.4 ..............

35.9 ....... .......

56.2 ..............

4.6 ..............

65.2 ..............

Total 

outflow 

(acre-ft)

81.0

81.0

1.3 

15.4 

.2

16.9

0.0 

.0

.0

0.0 

.1

.1

82.9 

3.2 

.0 

.0 

.0 

.0 

.0

86.1

374.1 

.0 

.0

374.1

34.7 

16.0 

176.4 

58.7 

106.4

392.2

35.9 

56.2 

4.6 

65.2

161.9

Inflow 

stored 

(acre-ft)

28.0

28.0

42.5 

79.9 

.8

123.2

23.6 

5.8

29.4

31.3 

14.7

46.0

98.8 

.8 

3.6 

5.5 

3.0 

2.2 

1.3

115.2

219.6 

3.2 

16.8

239.6

101.6 

22.5 

601.1 

45.2

24.8

795.2

33.1 

151.8 

2.1 

15.0

202.0

Inflow

Total 

(acre-ft)

109.0

109.0

43.8 

95.3 

1.0

140.1

23.6 

5.8

29.4

31.3 

14.8

46.1

3181.7 

4.0 

3.6 

5.5 

3.0 

2.2 

1.3

201.3

593.7 

33.2 

16.8

613.7

3136.3 

38.5 

777.5 

3103.9 

3131.2

1,187.4

69.0 

208.0 

6.7 

80.2

363.9

Acre-feet 

per 

square mile

10.1

10.1

4.1

8.8

a

13.0

2.2 

.5

2.7

2.9 

1.4

4.3

16.8 

.4 

.3 

.5 

.3 

.2 

.1

18.6

55.0 

.3 

1.6

56.8

12.6 

3.6 

72.0 

9.6 

12.1

109.9

6.4 

19.2 

.6

7.4

33.6
G22 HYDROLOGIC EFFECTS OF LAND USE

TABLE 4. Runoff measured in Sheepshed reservoir Continued

Date 

of 

flow

1964 

May 4.......................

June 18-19... ..........

June 20...................

For year.....

1965 

Mar. 19...................

Apr. 1-3.................

Apr. 8-9.................

Apr. 10-11.............

Apr. 12-14.............

May 6-8.................

For year.....

1966 

Mar. 10-12.............

For year.....

1967 

Feb. 25-Mar. 2...... 

Mar. 21-24.............

Apr. 27-29.............

May 1-2..................

For year..... .

Outflow (acre-ft)

Pipe1 Spillway1

31.6 ..............

53.8 ..............

22.4 ..............

6.4 ..............

119.3 ..............

4.3 ..............

30.6 ..............

98.3 ..............

71.8 ..............

68.4 ..............

80.6 ..............

247.5 ..............

33.3 ..............

21.3 ..............

Total 

outflow 

(acre-ft)

31.6 

53.8 

22.4

107.8

6.4 

119.3 

4.3 

30.6 

98.3 

71.8

330.7

68.4

68.4

80.6 

247.5 

33.3 

21.3

382.7

Inflow 

stored 

(acre-ft)

73.9 

204.9 

 11.5

267.3

12.1 

17.3 

1.1 

.1 

40.2 

147.4

218.2

32.6

32.6

26.0 

178.8 

22.0 

8.4

235.2

Inflow

Total 

(acre-ft)

105.5 

258.7 

10.9

375.1

18.5 

136.6 

5.4 

30.7 

138.5 

219.2

548.9

101.0

101.0

106.6 

426.3 

55.3 

29.7

617.9

Acre-feet 

per 

square mile

9.8 

24.0 

1.0

34.8

1.7 

12.6 

.5 

2.8 

12.8 

20.3

50.7

9.4

9.4

9.9 

39.5 

5.1 

2.8

57.3

1Water returns to channel.

2Date uncertain.

'Clock not operating ; amounts estimated from range of chart trace.

*No runoff recorded.

EROSION AND SEDIMENT YIELD

The most notable examples of channel erosion are the many 

deep gullies and headcuts along the lower reaches of Willow Creek 

and its tributaries. The gullies are in all stages of development 

and contribute sediment directly to the main channels. Hardpan slicks and semislicks on the stream terraces show little evidence of sheet and rill erosion and probably serve as a barrier to 

sediment transport because of their low gradient. Steeper upland 

slopes show various amounts of erosion, depending on the soils 

and the amount of vegetative cover. The coarser sediment removed 

from the upland slopes is often redeposited within a short distance 

and does not reach the main channels. This is especially noticeable 

where the grass is moderately heavy.

Sediment data were obtained by surveying selected reservoirs. 

The reduction in storage capacity shown by the surveys was taken 

as the volume of sediment deposited for the intervening time 

period. No adjustments were made for sediment that may have 

escaped with spill or for increases in reservoir capacity due to
WILLOW CREEK BASIN, MONTANA G23

compaction of older sediment. These losses are believed to be 

small, for the reasons discussed by Peterson (1962).

Suspended-sediment volumes passing the Willow Creek gaging 

station were determined by taking representative samples of the 

flow. (See "Quality of Surface Waters of the United States," Pt. 

6, "Missouri River Basin" [U.S. Geological Survey, 1954-63] for 

methods of sampling and computing sediment volumes.)

The amounts of sediment measured in four reservoirs in Willow 

Creek basin are given in table 5. Sediment amounts measured at 

three other reservoirs for the period 1952-55 were given by Peterson (1962). Measurements at these three reservoirs were discontinued after 1955 because of their high frequency of spill. 

Suspended-sediment amounts measured at the Willow Creek 

gaging station are given in table 6.

The average annual rate of sediment deposition in the measured 

reservoirs varied from 0.09 acre-foot per square mile at Burnett 

to 2.00 acre-feet per square mile at Triple Crossing for the periods 

of record. This rate variation presumably reflects the difference 

in the sediment-producing characteristics of the four basins.

TABLE 5. Sediment yield during periods between surveys

Sediment

________Total_______ Annual

Reservoir Period Acre-feet Acre-feet

Acre-feet per per

square mile square mile

Northwest 

Burnett.

Cactus Flat...

Sheepshed...... 

Triple

Crossing.

Aug. 1954-Sept. 1955 

Sept. 1955-Sept. 1962 

Sept. 1962-Sept. 1963 

Sept. 1963-June 1968. 

Aug. 1954-June 1968 .

.....July 1958-Sept. 1962 

Sept. 1962-Sept. 1963 

Sept. 1963-Oct. 1964-- 

Oct. 1964-Oct. 1966 

July 1958-Oct. 1966 

 Sept. 1955-Sept. 1962 

Sept. 1962-June 1968 

Sept. 1955-June 1968 

May 1960-Oct. 1964 . 

Oct. 1964-June 1968. -

May 1960-June 1968.. 

3.00 

.00 

.02 

3.13 

6.15

RQ ?n

8.62 

5.76

8 QQ

92.57

33.64 

25.33 

58.97

45>1 0

63.6

484.6

0.6 

.0 

.0 

.6 

1.2

10.81

1.35 

.90

1.40

14.46

3.12 

2.34 

5.46

9.98

1.51

11.49

6.09

1.81

".42

1.44

The amount of sediment deposited in Triple Crossing reservoir 

for the period 1964-1968 was considerably less than the amount 

deposited during the period 1960-64. Examination of the construction records of the Bureau of Land Management show that 

the drainage area contributing to Triple Crossing reservoir was 

diminished by nearly 50 percent with the construction of numerous small reservoirs during 1965-66. Much of the sediment that 

otherwise would have been deposited in Triple Crossing reservoir
G24 HYDROLOGIC EFFECTS OF LAND USE

was probably retained by these newer reservoirs. The rate shown 

in table 5 for this reservoir was adjusted to 2.00 acre-feet per 

square mile on the basis of the Cactus Flat record. Computed 

sedimentation rates for the various vegetation types, given later 

in this report, are based on a rate of 2.00 acre-feet per square mile 

from Triple Crossing basin. The reader is reminded that the 

quantity of sediment deposited in a reservoir is not a measure of 

the total sediment movement in the basin. Total sediment movement is the quantity of sediment measured in the reservoir plus 

the sediment deposited within the basin plus the sediment lost 

through spill.

TABLE 6. Annual suspended-sediment load and stream 

discharge measured at Willow Creek gaging station*

Calendar

year

1954...............

1955...............

1956 

1957 ....

1958 

1959...............

I960 

1961...............

1962- .

1963...... .........

1964...............

1965 . 

1966.. .........

1967. . .

Total 

11-year

14-year

Suspended-sediment load2

(acre-ft)

.................... 661

.................... 934

.................... 176

..................... 203

.................... 8

.................... 522

...... .............. 336

.................... 58

.................... 1,662

........ ............ 536

..................... 3492

.................... 5,588

average..... 508

average... ............ ......................

Stream discharge

(acre-ft)

30,815

53,182

9,113

16,452

2,302

48,247

43,062

4,562

104,292

47,217

43,982

114,700

11,150

37,300

566,376

36,657

40,455

^rom U.S. Geol. Survey reports on surface water and quality of surface 

water, in the United States (1954-67).

2Based on a density of 1,750 tons per acre-foot. 

3Through September 30.

RELATION TO DISTRIBUTION OF VEGETATION

The range in sediment yields suggests that there are significant 

differences in the sediment-producing characteristics of these 

basins; thus, the use of a simple average of the rates for estimating purposes may not be adequate. A statistical determination of 

the significant characteristics was not possible because of insufficient data. The reliability of vegetative measurements as 

indices of the runoff and sediment yields of an area was tested 

by Branson and Owen (1970), and the possibility of using, the 

distribution of vegetation as a guide for estimating sediment yield 

in Willow Creek basin was investigated.

The relative amounts of the major vegetation types in each of 

the study basins and for the whole of Willow Creek basin were 

determined from vegetation maps provided by the Bureau of Land 

Management and are shown in table 7. The measured sediment
WILLOW CREEK BASIN, MONTANA G25

yields for these basins are also shown. The vegetation in Sheepshed basin is about 76 percent grassland and 24 percent sagebrush; 

in Burnett basin the vegetation is about 74 percent grassland and 26 percent saltbush. Although both basins have low 

sediment yields compared with the other gaged basins, the sediment yield at Sheepshed is 5 times that at Burnett. This suggests 

that the sediment-producing characteristics of the two areas 

the one supporting sagebrush and the other saltbush are diverse. Data collected by I. S. McQueen and K. W. Ratzlaff (written commun., 1969) on soil erodibility in conjunction with 

infiltrometer tests show the same diversity. (See McQueen, 1963, 

for description of equipment and method.) Soil particles detached 

from the surface by simulated raindrop impact were collected and 

weighed. Figure 10 shows the relative amounts of sediment 

detached from soils supporting three vegetation types. Sediment 

amounts obtained by this method indicate the relative ease with

SAGEBRUSH

GRASS

SALTBUSH

VEGETATION TYPES

FIGURE 10. Relative amounts of particles detached from soils supporting different vegetation types.
G26 HYDRO-LOGIC EFFECTS OF LAND USE

which particles are detached and moved from the soil surface and 

represent the erosion potential of the soil.

TABLE 7. Distribution of major vegetation types in the study basins and 

measured sediment yields

Basin

Burnett ....................

Sheepshed...... ...............

Cactus Flat.................

Willow Creek... ..... ......

Amount of basin covered by 

indicated vegetation type (percent)

Grass

74

60

76

0

34

Sagebrush

0 

5 

24

84 

27

Saltbush

26 

9 

0 

10 

14

Greasewood

0

26 

0 

0 

18

Other1

0 

0 

0 

6

7

Sediment 

yield 

( acre-f t/ 

mi2 )

0.09 

2.00 

.44 

1.81 

21.40

Annual weeds, waste, barren. 

Estimated.

Sagebrush in Willow Creek basin is generally found on the 

steeper, shale slopes (fig. 11). The erosiveness of the sagebrush 

areas is indicated by the Cactus Flat data. The saltbush type 

occurs mainly on the old unflooded terraces that have developed 

"slick" and "semislick" areas (fig. 12). The soil chemistry of these 

areas is such that infiltration is greatly restricted, and a smooth 

silty crust forms on the surface (Branson and others, 1962).

.«.* 

^"-t £i$p* vr-w- ._> ?** *

* *

^tfj&tfS..* ,-* -*>-- »f-S£>.&g

. * ?.;. «*> -A

FIGURE 11. Typical sagebrush area in Willow Creek basin. Photograph taken in 1960 by R. F.

Miller.
WILLOW CREEK BASIN, MONTANA G27

FIGURE 12. Typical hardpan terrace with a "slick" area in the foreground and a "semislick" 

area in the background. These areas produce high runoff but little sediment. Photograph taken 

in 1960 by R. F. Miller.

The result is that a high percentage of the precipitation falling on 

these areas runs off, but the crust and low gradient tend to limit 

the erosion and inhibit the movement of sediment from the steeper 

slopes to the main channels. The high runoff and low sediment 

yields measured at Burnett basin suggest that the incidence of the 

saltbush type may have a significant effect on the hydrology 

of an area.

The preceding evidence suggests that the relative amounts of 

major vegetation types in an area may be used as a guide for 

applying sedimentation rates to the area. An average sedimentation rate was computed for each major vegetation type that 

occurred in a gaged basin. The measured rate for each basin was 

weighted by the percentage of basin area covered by a given 

vegetation type (table 7). The four-basin average of these 

weighted values is the computed sedimentation rate (table 8). 

Sedimentation rates were not computed for annual weeds, waste, 

and barren areas, as these types were mapped in only a small 

part of one gaged basin. These types generally occur on steep
G28 HYDROLOGIC EFFECTS OF LAND USE

slopes with loose fine-grained surface material, and they appear 

to have a higher sedimentation rate than any of the other types. 

A sedimentation rate of 3.5 acre-feet per square mile or greater 

should be applied where annual weeds, waste, and barren types 

occur. The rate shown for greasewood applies to upland sites 

only. Greasewood sites on alluvial bottomlands probably have a 

sedimentation rate similar to the saltbush type.

The computed sediment rates, shown in table 8, were applied 

to the uncontrolled areas of Willow Creek basin. It is assumed 

that 95 percent of the sediment from the controlled areas is 

retained by reservoirs. The computed estimate of sediment yield 

from the average uncontrolled area for the period 1954-64 is 507 

acre-feet per year. This compares closely with the 500 acre-feet 

per year2 measured at the gaging station.

TABLE 8. Computed sediment yields associated with 

major vegetation types

Vegetation Annual sediment

Grass................................................................. 0.76

Sagebrush........................................................... 1.51

Saltbush.............................................................. .88

Greasewood, upland....---.....----... --... -.. . - 2.00

Greasewood, bottomland....... ......... .......... ........ .90

Weeds, waste, barren..... ................ ...... ........... 3.50

METHOD OF ESTIMATING SEDIMENT YIELD

To estimate the sediment yield for a particular basin, determine 

the number of square miles of each vegetation type in the basin 

from figure 2. Multiply each value by its corresponding sedimentation rate from table 8. The sum of these products is the 

estimated annual sediment yield of the basin, in acre-feet. Nonaverage local conditions, such as extreme gullying, may dictate 

adjustment of this value for a more realistic estimate.

In using vegetation type as an indicator of sediment yield, 

the vegetation is assumed to represent the net result of integrating 

all factors which affect plant growth in an area. The degree of 

erosion in the area is related to some of the same factors and may 

itself be a factor affecting plant growth. Plants survive over a 

range of conditions, and different types often coexist. As this 

method considers only major types, the results are partly dependent on how delineations between types were mapped in areas 

where two or more types are present in nearly equal densities. It is 

possible that more reliable estimates would be obtained if the 

vegetation types were subdivided; however, the gaged basins 

do not represent an adequate number of subdivisions for this

2Datum from table 6 adjusted for sediment that passed through the reservoirs.
WILLOW CREEK BASIN, MONTANA G29

purpose. The method, as presented, provides a means of projecting 

the sedimentation data from small basins to a larger area for 

the purpose of making realistic sediment-yield estimates. The 

sedimentation rates given are averages derived from a minimum 

of data and should be used accordingly.

CONSERVATION STRUCTURES

Reservoirs and waterspreaders, such as those in Willow Creek 

basin, do not always function as intended, either individually or 

as a system. Indeed, under certain combinations of conditions, a 

structure system can actually aggravate the flooding it is supposed 

to alleviate. Therefore, a periodic evaluation of the effects of the 

system is desirable to determine whether a structure's performance 

is adequate or whether additional (or alternate) measures are 

needed. These evaluations should also be helpful in planning future 

structure systems.

The effects of the conservation structures in Willow Creek basin 

are difficult to assess because construction continued throughout 

the data-collection period. Each new reservoir changed the size 

of the contributing area of the basin, making it difficult to relate 

data to a specific area. It is in this context that the following 

evaluations are offered.

EFFECTS ON RUNOFF

The most significant effect of reservoirs and waterspreaders 

should be the reduction of peak discharges. As no records were 

collected prior to the beginning of construction, a "before" and 

"after" comparison was not attempted. However, there is evidence 

that the flow regime of Willow Creek has changed. The width of 

the channel at the gaging station (fig. 2) has narrowed significantly since 1955 (fig. 13). This change of channel geometry presumably occurred in response to reduced peak discharges and 

prolonged periods of low flow brought about by the detention 

reservoirs constructed in the basin.

25

IUJ yn 

UJ "

U_

- 15

H

I

s 10

x 

3 5

3

0

0 25 50 75 100 125 150 175

DISTANCE FROM INITIAL POINT, IN FEET

FIGURE 13. Cross-sections of the Willow Creek channel at the gaging station, showing a significant change in shape during the period 1955-67.
G30 HYDROLOGIC EFFECTS OF LAND USE

The highest discharge recorded at the Willow Creek gaging 

station during the period 1954-67 was 12,400 cfs (cubic feet per 

second) on July 14, 1962. Inspection of a number of reservoirs 

after this flood indicated that most of the reservoirs whose outflow would contribute directly to the flood peak were nearly filled, 

but few, if any, spilled significantly. The composite pipe outflow 

from these reservoirs was about 2,180 cfs. After reducing the 

measured peak by 2,180 cfs, the unit discharge for the 197 square 

miles of uncontrolled area between the reservoirs and the gaging 

station was computed as 52 cfs per square mile. The same computations were made for the smaller Beaver Creek drainage. An 

indirect measurement of discharge was made at a point near its 

confluence with Willow Creek, and the flow was computed as 

4,590 cfs. This is about 68 cfs per square mile of uncontrolled 

area after subtraction of reservoir outflow. Based on a logarithmic 

plot of unit discharge and drainage area, the projected unit discharge from 538 square miles is 42 cfs per square mile. At the 

rate of 42 cfs per square mile, and had there been no reservoirs 

to detain flow, the discharge at the gaging station would have 

been 22,600 cfs. Based on these estimates, it appears that the 

conservation structures in the basin reduced the peak discharge 

of this storm about 45 percent.

Reservoirs and waterspreaders reduce the runoff volume from 

Willow Creek basin, though not by a major amount. About 17 

percent of the basin is controlled by waterspreading systems 

(dikes and supply reservoirs), which contribute virtually no runoff to Willow Creek. Reservoirs reduce runoff volume by increasing 

the time during which seepage and evaporation losses can occur. 

These losses were not evaluated because of insufficient data. 

Permanent storage in the reservoirs is small compared with their 

total runoff volume. On the basis of the average runoff measured 

at Burnett and Cactus Flat reservoirs, the gross annual runoff 

from Willow Creek basin is estimated to be about 49,000 acrefeet. The average annual runoff measured at the gaging station 

is about 18 percent less than this. The difference represents all 

losses incurred, including losses due to the presence of structures 

and normal transmission losses. Channel losses are believed to 

be small, owing to the low permeability of the fine-textured alluvium in which the channels are incised. No data are available 

for evaluating transmission losses or the extent to which these 

losses are affected by the structures.

The primary function of Willow Creek reservoirs is to supply 

water for livestock and irrigation and to reduce flood peaks. An 

inherent weakness of reservoirs is that they gradually fill with 

sediment, thus reducing their capacity to function as intended.
WILLOW CREEK BASIN, MONTANA G31

Some of the smaller retention reservoirs in high-sediment-yield 

areas have become filled in just 3 to 4 years. The retention of 

sediment reduces downstream pollution for the present, but it 

could result in the destruction of the reservoirs and the sudden 

release of this sediment later. Because it is generally too costly 

to attempt to prolong the life of reservoirs by removal of the 

sediment, the effective life of the system is determined by the 

rate at which sediment is delivered to the reservoirs.

EFFECTS ON SEDIMENT YIELD

The effect of reservoirs on downstream sediment yield is indicated by the data from Triple Crossing reservoir. The 1965-68 

measurement period, during which a number of small reservoirs 

were built in the basin, shows a large decrease in sediment yield 

compared with that during the 1960-64 period. Much of this 

reduction is believed to be due to retention of the sediment by 

the small reservoirs, although some may be due to runoff differences. Measurements at the gaging station on the main stem of 

Willow Creek indicate a significant reduction in sediment concentration from 1954 to 1964. The relation of monthly sediment 

load and monthly runoff volume for two 3-year periods the years 

1954-56 and 1962-64 was determined by least-squares regressions (fig. 14). The curves are nearly parallel and show, on the 

average, 55 percent less sediment per unit of runoff during the 

1962-64 period. This decrease in sediment concentration is presumably due to the retention of sediment in the additional reservoirs constructed during the period 1957-64.

It is not known how much sediment has been retained by the 

reservoirs in Willow Creek basin, as only a few reservoirs have 

been measured. Based on the distribution of vegetation types, 

the entire basin is estimated to yield an average of 751 acre-feet 

of sediment annually. Eleven years of suspended-sediment discharge (1954-64) at Willow Creek gaging station show that about 

500 acre-feet per year was removed from the basin, assuming 

trap efficiency of 95 percent. This means that a total of 251 

acre-feet of sediment was retained by the reservoirs each year.

If one assumes that 251 acre-feet of sediment is retained each 

year, the composite annual loss of original reservoir capacity in 

Willow Creek basin is 1.6 percent, based on the average storage 

capacity of reservoirs constructed through 1963. The four gaged 

basins show a composite annual loss of original capacity of 1.6 

percent, also. At the rate of 1.6 percent, the average life of the 

reservoirs would be about 62 years; however, the useful life 

would be much shorter because reservoirs begin to lose their 

effectiveness as soon as the capacity allotted to sediment storage 

has been filled.
G32 HYDROLOGIC EFFECTS OF LAND USE

1000

100

0- 10

UJ

w

Q

UJ 

0

 1954-56 

o 1962-64

10 100 

WATER DISCHARGE, IN HUNDREDS OF ACRE-FEET

500

FIGURE 14. Relation between monthly sediment load and monthly runoff at Willow Creek gaging 

station for tne periods 1954-56 and 1962-64.

Some observers may feel that the loss of reservoir capacity in 

Willow Creek basin occurs at a much higher rate than that 

indicated above. Many reservoirs are filled with sediment to the 

elevation of the outlet pipe within a few years after construction. 

It must be remembered that there is a wide variation in sedimentation rates throughout the basin, as indicated by the measured 

yields. The high-sediment-yield areas receive the most attention, 

and this tends to leave the impression that sedimentation rates 

throughout the entire basin are similar. But there are other 

reservoirs in which capacity-loss rates are very low, and these 

reduce the average capacity-loss rate for the whole basin. Also, 

reservoirs because of their shape initially lose depth very
WILLOW CREEK BASIN, MONTANA G33

rapidly. Thus, the reservoirs in the basin appear to be filling 

very rapidly, especially those in high-sediment-yield areas, lending 

support to the impression that the sedimentation rate for the 

entire basin is much higher than it actually is.

SUMMARY

Runoff and sediment-yield data from Willow Creek basin, for 

the period 1954-68, are presented for use in future structure 

design and management planning. The effects of conservation 

structures on both runoff and sediment yields were evaluated on 

the basis of available data. Frequency curves for the area were 

developed for 1-day- and 3-day-duration storms, annual precipitation, maximum 3-day-runoff volume, 6-month-runoff volume, and 

peak runoff rates.

Annual precipitation during the 14-year period 1954-67 varied 

from 7.01 to 17.37 inches and averaged 11.94 inches, which is 

slightly less than the 30-year average (12.39 in.). Although the 

runoff records for three reservoirs vary in length, they run 

concurrently for the 10-year period 1958-67. For that 10-year 

period, the following average annual values, in acre-feet per 

square mile, were recorded: Burnett, 93.9; Cactus Flat, 96.5; and 

Sheepshed, 37.5. The amount recorded at Sheepshed reservoir is 

suspect because of an instrumentation deficiency. About 34 percent of the runoff in the gaged basins occurred as the result of 

snowmelt, and about 66 percent occurred in response to summer 

rainstorms. About one-third of each year's runoff was produced 

by a single storm.

Sediment yield varies greatly in Willow Creek basin. Measured 

yields ranged from 0.09 to 2.00 acre-feet per square mile. The 

apparent relation between sediment yield of an area and the 

vegetation which the area supports was used to estimate the 

sediment yield of the entire basin. Although the evidence is not 

conclusive, it is believed that realistic estimates of sediment yield 

within the basin can be made on the basis of vegetative type. 

Additional data are needed to verify this method.

Conservation structures in the basin are apparently very effective in reducing peak discharge. Best estimates indicate the peak 

discharge of the 1962 flood at the gaging station was about 45 

percent less than it would have been without these structures. 

Reservoirs and waterspreading systems constructed since 1962 

may have increased this percentage considerably. A reduction in 

annual runoff volume of about 18 percent is indicated, but it is 

not known how much of this was due directly to structures and 

how much was due to normal transmission losses. Suspended-
G34 HYDROLOGIC EFFECTS OF LAND USE

sediment concentrations at the gaging station were reduced about 

55 percent during an 11-year period. Reservoir storage in the 

Willow Creek basin is being reduced by 1.6 percent annually.

REFERENCES CITED

Benson, M. A., 1960, Characteristics of frequency curves based on a theoretical 1,000-year record, in Dalrymple, Tate, Flood-frequency analysis: 

U.S. Geological Survey Water-Supply Paper 1543-A, p. 51-74.

Branson, F. A., Miller, R. F., and McQueen, I. S., 1962, Effects of contour 

furrowing, grazing intensities, and soils on infiltration rates, soil moisture, and vegetation near Fort Peck, Montana: Jour. Range Management, 

v. 15, no. 3, p. 151-158.

Branson, F. A., and Owen, J. R., 1970, Plant cover, runoff and sedimentyield relationships on Mancos Shale in western Colorado: Water Resources Research, v. 6, no. 3, p. 783-790.

Dalrymple, Tate, 1960, Flood frequency analysis: U.S. Geol. Survey WaterSupply Paper 1543-A, 80 p.

Jensen, F. S., and Varnes, H. D., 1964, Geology of the Fort Peck area, 

Garfield, McCone and Valley Counties, Montana: U.S. Geol. Survey 

Prof. Paper 414-F, 49 p.

McQueen, I. S., 1963, Development of a hand portable rainfall-simulator 

infiltrometer: U.S. Geol. Survey Circ. 482, 16 p.

Peterson, H. V., 1962, Hydrology of small watersheds in Western States: 

U.S. Geol. Survey Water-Supply Paper 1475-1, p. 217-356.

Searcy, J. K., and Hardison, C. H., 1960, Double-mass curves, with a section 

on Fitting curves to cyclic data, by W. B. Langbein: U.S. Geol. Survey 

Water-Supply Paper 1541-B, p. 31-66.

U.S. Geological Survey, issued annually, Surface-water supply of the United 

States, pt. 6-A, Missouri River Basin above Sioux City, Iowa: U.S. 

Geol. Survey Water-Supply Papers.

 issued annually, Quality of surface waters of the United States, pt. 

6, Missouri River Basin: U.S. Geol. Survey Water-Supply Papers.

U. S. GOVERNMENT PRINTING OFFICE : 1972 O - 474-236