Floods in Utah, 

* Magnitude and Frequency

GEOLOGICAL SURVEY 

CIRCULAR 457
Floods in Utah, Magnitude and Frequency

By V. K. Berwick

GEOLOGICAL SURVEY CIRCULAR 457

Washington 1962
United States Department of the Interior

STEWART L. UDALL, SECRETARY

Geological Survey

THOMAS B. NOLAN, DIRECTOR

Free on application to the U.S. Geological Survey, Washington 25, D. C.
CONTENTS

Page

Abstract >................-......... 1

Introduction. __-_----__------_----_-. 1

Cooperation and supervision__________ 1

Description of the area___-_-_____._-- 1

Physical features.__-------_----_-. 2

Colorado River basin ____________ 2

The Great Basin...._____________ 2

Snake River basin __-_-__-___-___ 3

Major rivers_______ _____--._-_ 3

Climatic features._________________ 3

Flood - frequency relations ____________ 3

Flood frequency at a gaging station __ 4

Basic data ______________________ 4

Flood series ____________________ 4

Station frequency curve __________ 4

Regional flood frequency......______ 4

Regional sampling............... 13

Selection of comparable floods ____ 13

Homogeneity ____________________ 13

Page

Flood-frequency relations Continued 

Regional flood frequency Continued

Composite frequency curve _______ 13

Regional analysis for summer

floods _______________________ 13

Derivation of the mean annual flood._ 15 

Basin characteristics .___._._____ 15

Mean annual flood relations.______ 15

Major rivers in Utah.._____________ 18

Cloudburst floods and mud-rock

flows. ...-.__________________

Application of flood-frequency

curves ________________________

Method _________________________

Use of flood-frequency analysis on 

major river s__ _______ ______ ._

Limitations _______________________

ILLUSTRATIONS

	Page 

Figure 1. Map of Utah showing location of gaging stations _____________________________ 5

2. Map of Utah showing flood regions.....____________________________________ 12

3. Composite flood-frequency curves, regions A and B _________________________ 14

4. Composite flood-frequency curves, regions C and D _________________________ 14

5. Map of Utah showing hydrologic areas__-_______.___________________________ 16

6. Variation of mean annual flood with drainage area and mean altitude.__________ 17

7. Colorado River, discharge of 50-year flood____________________________---__ 18

8. Green River, discharge of 50-year flood____________________________________ 18

9. Duchesne River, discharge of 50-year flood.________________________________ 18

10. Strawberry River, discharge of 50-year flood__________________________-_--_ 18

11. Price River, discharge of 50-year flood___-___-______----_---_-------_--_-_ 18

12. San Rafael River, discharge of 50-year flood.....___________________________ 19

13. San Juan River, discharge of 50-year flood _________________________________ 19

14. Bear River, discharge of 50-year flood. ____________________________________ 19

15. Weber River, discharge of 50-year flood ___________________________________ 19

16. Provo River, discharge of 50-year flood________.___________________________ 19

17. Sevier River, discharge of 50-year flood ___________________________________ 19

TABLES

Table 1. Peak discharges at gaging stations used in frequency analysis 

2. Main stem gaging-station data_____________________________

Page

6

20

HI
Floods in Utah, Magnitude and Frequency

By V. K. Berwick

ABSTRACT

This report presents a procedure for estimating the magnitude and frequency of floods, within the range of the base 

data, for any site, gaged or ungaged. From the relation of annual floods to the mean annual flood, a composite frequency 

curve was derived for recurrence intervals of 1.1 to 50 years. 

For regions of similar hydrologic characteristics, curves were 

developed by multiple correlation to express the relation of 

mean aunual flood to drainage area and mean altitude. The 

record^ of gaging stations having 5 or more years of record 

were used as base data when the natural conditions of streamflow are not affected by works of man. For major rivers where 

the flow is affected by diversion or regulation, separate 

analyses were made for each stream. The results may be 

applied to any area in Utah, except the Great Salt Lake 

Desert and a small area of the State in the Snake River basin.

INTRODUCTION

The proper design of structures in or near 

a stream should include the determination of 

the magnitude and frequency of floods. Where 

flooding may endanger human life, structures 

should be designed to withstand the greatest 

probable flood magnitude. In most instances, 

however, the risk to human life from flooding 

is small, and structures are designed to withstand a flood of some selected frequency of 

occurrence based on economics.

Floods result from the combined effects of 

climatic events and physiographic characteristics of a basin. Some of the principal 

physiographic factors affecting flood flows 

are: drainage area, altitude, geology, basin 

shape, slope, aspect, and vegetal cover.

Flood data for an individual site show what 

has occurred at that site during a definite 

period of time but could lead to erroneous 

results in the prediction of future events, even 

at that site, if the record is not representative 

of the long-term average. A composite floodfrequency curve based on many gaging-station

records adjusted to a common time base is a 

logical means for predicting future flood expectancy anywhere within a homogeneous flood 

region. This report (a) outlines the homogeneous flood regions in Utah and presents a 

composite flood-frequency curve for each, and 

(b) outlines hydrologic areas and presents 

graphs .showing the variation of mean annual 

flood with drainage area and altitude.

COOPERATION AND SUPERVISION

This report was prepared by the Geological 

Survey, in cooperation with the Utah Department of Highways and the U.S. Bureau of 

Public Roads. It was prepared in the office 

of the Geological Survey at Salt Lake City, 

Utah, under the direction of M. T. Wilson, 

district engineer. Technical guidance was 

furnished by the Floods Section, Water Resources Division, Geological Survey, Washington, D. C.

DESCRIPTION OF THE AREA

High, rugged mountain ranges are the most 

distinguishing features of the Utah landscape. 

Their presence influences the flow of air 

masses and therefore has a major affect upon 

precipitation and resulting streamflow. The 

State is divided by the Wasatch Mountains, a 

high range that runs in a north-south direction. On both sides of this divide are extensive 

deserts or arid regions with the exception of 

a humid section in the northern mountain 

ranges. The Uinta Mountains, one of the few 

mountain ranges in the Unites States with an 

east-west axis, extend eastward from the 

north-central part of the State almost to the 

Utah-Colorado State line.
FLOODS IN UTAH, MAGNITUDE AND FREQUENCY

The absence of a usable water supply in the 

arid regions of Utah has discouraged the collection of enough streamflow records to define flood-frequency relations; therefore, the 

Great Salt Lake Desert has not been included 

in this analysis.

PHYSICAL FEATURES

COLORADO RIVER BASIN

The Colorado River basin within Utah contains approximately 41,000 square miles, with 

plateaus and mountains ranging in altitude 

from 3,000 to 13,000 feet above sea level. 

The Uinta Mountains bisect the Green River 

basin near the Utah-Wyoming State line, 

forming the northern boundary of the Utah 

portion of the basin. The Wasatch Mountains 

and High Plateaus form the western boundary. 

Other mountain ranges and plateaus are interspersed throughout the area. Some of the 

more prominent ranges are the LaSal, Abajo, 

and Henry Mountains. Another orographic 

barrier in the Colorado River basin, known 

as the Book Cliffs, extends in a general eastwest direction near the central part of the 

State. Drainage is predominately by streams 

with deep canyons and relatively steep'slopes. 

Drainage areas of streams used in the study 

for the Colorado River basin range from 2 to 

77,000 square miles.

The vegetal cover within the region varies 

considerably in kind and in growth depending 

largely upon the amount and seasonal distribution of precipitation. Parts of the Colorado 

River basin have an extremely shallow soil 

mantle with some large areas of exposed 

sandstone. Where these conditions exist the 

vegetal cover ranges from sparse to almost 

nonexistent.

THE GREAT BASIN

That part of the Great Basin considered in 

this study (approximately 18,000 square 

miles) includes the Wasatch Mountains and 

the western portions of the High Plateaus. 

The Wasatch Mountains extend southward 

from the Utah-Idaho State line and connect 

with the High Plateaus to form a north-south 

divide ending near the southwest corner of 

the State.

The geology of the Great Basin is complex 

and is not discussed here except in general 

terms. The Wasatch Mountains are characterized by rugged topography with high peaks 

and deep canyons. The mountains are long 

narrow ridges which rise abruptly from the 

valley floors with relatively small foothill 

areas. Several streams, including the Bear, 

Weber, and Provo Rivers, are classed as 

relatively old and have cut through the high 

mountain ranges in deep canyons. Many of 

the smaller streams in the area are younger 

in origin, and for the most part are responsible for much of the more recent erosion.

The High Plateaus consist of three parallel 

strips of tabletop formations that are common to both the Great Basin and the Colorado 

River basin. The altitudes range from 5,000 

to 10,000 feet above sea level. The streams 

originating in the High Plateaus have steep 

slopes leading to gently sloping valley floors. 

When a stream reaches the mouth of a canyon, where the gradient is lower, the flow 

often spreads out on the valley floor. In some 

places, the surface flow disappears as the 

streams cross the alluvial fans at the entrance to mountain valleys. These conditions 

are more prevalent in the Great Basin, but 

apply to some degree in the Colorado River 

basin.

The vegetal cover in the Great Basin is 

similar to that in the Colorado River basin; 

however, in the northern part of both basins, 

the average annual precipitation is higher, 

and at some altitudes the forest is denser. 

Drainage areas of streams used in this study 

for the Great Basin range from 10 to 8,000 

square miles.

The modifications of peak discharge by 

different geological formations are noticeable 

in both the Colorado River basin and the 

Great Basin hydrologic areas. One example 

of this modification is in the Logan River 

basin where extensive limestone deposits 

have a retarding effect on major floods by 

absorbing some of the surface flow. In other 

areas, the exposure of impervious formations 

hastens the rate of runoff. In general, the 

streams materially affected by geology are 

widely scattered, and because the flood data 

do not define these effects sufficiently, it is 

considered impractical to separate these
FLOOD-FREQUENCY RELATIONS

drainage basins from the larger hydrologic 

areas.

SNAKE RIVER BASIN

Flood-frequency relations for the Snake 

River basin in Utah, a small area in the northwest corner of the State, are not included in 

this report. A flood-frequency report 

(Thomas, Broom, and Cummans, 1961) for 

the Snake River basin includes that area of 

Utah.

MAJOR RIVERS

The discharges of the main stems of the 

larger rivers are so modified by diversion 

and storage that only extreme floods would 

reflect the general characteristics of geology, 

topography, and other natural factors. Furthermore, the large rivers drain more than 

one flood region. Studies of frequency and 

magnitude for the larger rivers are, therefore, considered independently of the flood 

regions. The slopes of most streams, including the main stem of the larger streams, 

are relatively steep and for most channel 

reaches, floods of 50-year recurrence interval are confined within their natural banks.

CLIMATIC FEATURES

The climate of the State of Utah ranges 

widely from arid to humid over rather short 

distances. The average annual temperature 

is about 48°F. Extreme temperature observations recorded are a maximum of 116°F at 

St. George and a minimum of -50°F at Woodruff. These temperature variations have a 

considerable effect on the accumulation of 

snow. The annual snowfall ranges from less 

than 6 inches at St. George to 346 inches at 

Silver Lake in the Wasatch Mountains.

Utah is a region of relatively low rainfall 

with an average annual precipitation of about 

12.6 inches. During an average year there 

are only 57 days on which 0.01 inch or more 

of precipitation falls anywhere in the State.

Variations in precipitation during two seasons of the year have a major effect on floods. 

During the winter months, when Pacific

storms frequent the region, precipitation occurs in the form of snow. The precipitation 

during this season is the most consistent and 

becomes the major source of streamflow. In 

the northern part of the State, most streams 

are fed chiefly from perennial snowfields and 

the amount of runoff is a function of the snowfall. The southern part of the State is also 

subject to precipitation in the form of snow, 

and snowmelt floods may be significant at 

times. However, the annual maximum floods 

are usually caused by thunderstorms, and 

only on rare occasions is the annual maximum flood produced by a combination of rain 

and snowmelt. The second season is during 

the late summer and early fall when thunderstorms occur. These storms have a different 

source than the winter storms; the moisture, 

usually following a high-pressure system, is 

carried from the Gulf of Mexico by unstable 

air masses over the arid regions of southwestern United States. Occasionally, a storm 

from the Gulf of California extends into the 

State from the southwest, and some floods 

have been caused by this condition.

Some of the thunderstorm activity develops 

over the desert areas without regard to 

change in elevation and are triggered by convection currents. The amount of moisture 

available and the ambient temperatures play 

important roles in the summer storms. An 

important factor influencing the paths of 

thunderstorms is the proximity of the storm 

to mountains. Thunderstorms usually affect 

relatively small areas; therefore, a flood at 

a site will often be caused by a high-intensity 

storm covering only a part of the drainage 

basin above that site.

FLOOD-FREQUENCY RELATIONS

Methods developed by engineers of the 

Water Resources Division of the Geological 

Survey and others were used to compute 

magnitude and frequency relations for 

streams in Utah. Steps taken in the analysis 

were: (a) computation of a flood-frequency 

curve for each gaging station, (b) the combination of individual curves to define regions 

of homogeneous flood-frequency relations, 

and (c) computations of the mean annual flood 

from the related drainage basin characteristics.
FLOODS IN UTAH. MAGNITUDE AND FREQUENCY

FLOOD FREQUENCY AT A GAGING STATION

BASIC DATA

Streamflow records from 167 gaging stations (fig. 1) with 5 or more years of record 

were used in the analysis. Selection of 

records from 118 stations was based on the 

condition that the flood peaks resulted from 

natural flow. Records from the remaining 49 

stations are for the major rivers and are affected by diversions or storage.

The effect of diversions or storage on flood 

flow may be inconsequential for extreme 

floods but may be significant for lesser 

floods. If peak flow was not affected by more 

than 10 percent, it was assumed that the 

streamflow record could be used without adjustment. Table 1 contains a list of the gaging stations for which records were used in 

the flood-frequency analysis. The table shows 

the maximum known flood and other pertinent 

data for each station.

To place all records on a comparable 

basis, it is desirable that they be adjusted to 

the same time period. The period 1938 57 

was used for 71 stations in flood regions A 

and B (fig. 2). Except in flood regions C and D, 

the order of magnitude of the. known peaks in 

shorter records was adjusted to this base by 

correlation with p<^aks at nearby stations.

FLOOD SERIES

Two methods for analyzing floods are by 

the annual flood series and by the partialduration series. In an annual flood series, 

only the maximum instantaneous discharge 

for each water year is listed. In a partialduration series, all floods equal to or greater 

than an arbitrarily selected base are listed. 

It should be noted that, in the annual flood 

series, no consideration is given to secondary 

floods, which in some years may be greater 

than the maximum for other years. On the 

other hand, in the partial-duration series, 

some water years may have no flood as great 

as the selected base discharge.

The recurrence interval in an annual flood 

series is defined as the average interval of 

time within which the given flood will be 

equaled or exceeded once as an annual maximum. The recurrence interval in a partialduration series denotes elapsed time without

regard to the water year or any other selected time unit. There is a statistical relation 

between recurrence intervals computed by 

the two methods, as shown in the following 

table by Langbein (1949):

Recurrence intervals, in years

Annual flood 

series

Partial- duration 

series

1.16.

1.58.

2.00.

2.54.

5.52.

10.5...

20.5...

50.5...

100.5...

0.5

1.0

1.45

2.0

5.0

10

20

50

100

The annual flood series was used in this 

report. As will be noted from the table, recurrence intervals are essentially the same 

in both series for periods greater than 10 

years. For those desiring information on the 

basis of the partial-duration series, it is 

suggested that results be computed by methods described in this report and conversion 

made by use of the table.

STATION FREQUENCY CURVE

The annual peak discharge for each station 

was listed in order of magnitude with no. 1 

as the largest. The time scale, designated 

as the recurrence interval (T) and plotted as 

the abscissa on special probability paper 

(Gumbel, 1941; Powell, 1943), was fitted to 

the data by the formula

n + 1 T = ~^~

where a is the number of years of record and 

a is the relative magnitude of the event with 

the largest as 1. Corresponding peak discharges were plotted as ordinates, and a 

smooth curve was then drawn on the basis of 

the plotted points. The use of extreme value 

probability paper tends to cause the plotted 

points for many stations to fall in a straight 

line.

REGIONAL FLOOD FREQUENCY

A composite frequency curve based on records for many gaging stations is a better tool 

for estimating the magnitude of future floods
FLOOD-FREQUENCY RELATIONS

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STATUTE MILC8

Figure 1. Map of Utah showing location of gaging stations.
Table 1. Peak discharges at gaging statiMs used in frequency analysis

Station 

No.

Gaging station

Drainage 

area 

(sq mi)

Period 

of 

record

Mean 

altitude 

(feet)

Areal

Q 

2.33

(cfs)

Maximu

Date

COLORADO RIVER BASIN

9-1810

1820

1830

1840

1855

1860

1865

1870

1875

2185

2200

2205

22fiO

2265

2275

2330

2340

2640

Tributaries between Dolores River and Green River

Onion Creek near Moab, Utah_______ ___________

Castle Creek above diversions, near Moab, UtahCourthouse Wash near Moab, Utah _____________

Mill Creek near Moab, Utah ___________________

Hatch Wash near La Sal, Utah _________________

Indian Creek near Monticello, Utah. ____________

Indian Creek above. Cottonwood Creek near

Monticello, Utah.

Cottonwood Creek near Monticello, Utah ________

Indian Creek above Harts Draw, near

Monticello, Utah.

Green River basin

Blacks Fork near Millburne, Wyo ______________

East Fork of Smith Fork near Robertson, Wyo,.-.-

West Fork of Smith Fork near Robertson, Wyo___

Henry's Fork near Lonetree, Wyo__________- _

Middle Fork Beaver Creek near Lonetree, Wyo __

West Fork Beaver Creek near Lonetree, Wyo____

Carter Creek near Manila, Utah _______________

Carter Creek at mouth, near Manila, Utah ______

Ashley Creek below Trout Creek near

Vernal, Utah.

18.8

7-. 58

150

76

370

4.5

31.2

115

257

156

53

37.2

56

28

23

19

MO

27

1950-55;

1959

1950-55;

1957-59

1949-55

1914-19;

1949-59

1950-59

1949-57

1949-59

1949-57

1949-57

1939-59

1939-59

1939-59

1942-59

1948-59

1948-59

1948-54

1946-55

1943-54

5,810

9,480

4,810

7,170

6,550

9,620

7,130

7,210

6,580

10,270

10,250

9,790

10,270

10,480

10,680

10,280

9,010

9,930

677

34

2,210

1,070

939

21

93

340

2,100

1,140

497

325

522

329

302

229

565

343

Aug. 29, 1951

June 7, 1952

Aug. 5, 1957

Aug. 21, 1953

Aug. 4, 1959

Aug. 6, 1955

July 20, 1955

July 10, 1953

Aug. 30, 1957

June 7, 1957

June 13, 1953

May 30, 1950

June 13, 1953

June 12, 1953

June 13, 1953

June 3, 1952

June 4, 1952

May 19, 1948
FLOOD-FREQUENCY RELATIONS

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3385

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Boulder Creek near Boulder, Utah ____________

Escalante River at mouth, near Escalante, Utah.

Paria River basin

Paria River near Cannonville, Utah ____________

Paria River at Lees Ferry, Ariz___ ___________

Virgin River basin 

North Fork Virgin River near Springdale, Utah _

1.9

175

2,010

220

1,570

350

1950-55 

1950-55 

1950-55

1950-55 

1923-59

1913-14; 

1923-59

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8,320

6,330

6,890

6,140

7,560

9

625

4,720

1,860

5,360

2,120

Aug. 6, 1955

July 25, 1955

Aug. 4, 1951

Aug. 16, 1955 

Sept. 12, 1958

Mar. 3, 1938

THE GREAT BASIN

Bear River basin 

10- 115 Bear River near Utah-Wyoming State line_______ 176 1942-59

120 Mill Creek at Utah-Wyoming State line and 60 1942-48; 

Mill Creek near Evanston, Wyo. 1 1949-59 

160 Sulphur Creek near Evanston, Wyo_____________ 80.5 1942-59

190 Bear River near Evanston, Wyo._-----_-------_ 715 1913-56

205 Bear River near Woodruff, Utah ______________ 870 1942-59

210 Woodruff Creek near Woodruff, Utah ____------_ 65 1937-43;

1949-59 

230 Big Creek near Randolph, Utah _____------_---_ 52.2 1939-44;

1949-59 

265 Bear River near Randolph, Utah -------_-----_- 1,640 1943-59

270 Twin Creek at Sage, Wyo-__--_-----_.--------- 246 1943-59

320 Smiths Fork near Border, Wyo ______-_-_-__-__ 165 1942-59

350 Smiths Fork at Cokeville, Wyo_--_-.----_------ 275 1942-52

395 Bear River at Border, Wyo_-__-____-_-------_ 2,490 1937-59

400 Thomas Fork near Geneva, Idaho ________------ 45.3 1939-51

405 Salt Creek near Geneva, Idaho----------------- 37.6 1939-51

410 Thomas Fork near Wyoming-Idaho State line____ 113 1949-59

425 Thomas Fork near Raymond, Idaho_-_-_-_------ 202 1942-52

475 Montpelier Creek at irrigators weir, near 50.9 1942 59

Montpelier, Idaho. 

585 Bloomington Creek near Bloomington, Idaho.---- 22.1 1943-47

690 Georgetown Creek near Georgetown, Idaho..---- 22.2 1911;

1914; 

1939-56

9,770

9,320

7,930

8,130

7,930

7,900

7,370

7,470

7,180

8,270

7,810

7,390

7,170

,390

,290

.090

7,370

7,860

7,830

1,060

398

291

1,680

1,790

244

164

2,380

490

579

706

3,160

134

128

284

404

160

105

104

June 6, 1957

June 7, 1957

Apr. 23, 1952

June 14, 1921

Apr. 28, 1952

May 25, 1950

July 11, 1957

May

Mar.

June

May

May

May

8, 1952

18, 1947

7, 1957

4, 1952

11, 1952

18, 1950

.do---.--

May 

May

.do---.-- 

19, 1950 

18, 1950

June 2, 1943 

June 8, 1912

*In excess of.

Equivalent records combined.
10 FLOODS IN UTAH, MAGNITUDE AND FREQUENCY

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Tributaries between Weber and Jordan Rivers

Holmes Creek near Kaysville, Utah ___________

Farmington Creek above diversions, near

Farmington, Utah.

Stone Creek above diversions, near Bountiful,

Utah.

Jordan River basin

Salt Creek near Nephi, Utah __________________

Payson Creek above diversions, near Payson,

Utah.

Spanish Fork at Thistle, Utah___ ______________

Hobble Creek near Springville, Utah___ ______

Provo River near Kamas, Utah _______________

Provo River near Hailstone, Utah _____________

T~)e»«»T» frfflr ne*ar WfilHwnnH TTtah

Dry Creek near Alpine, Utah ____ ___________

Fort Creek at Alpine, Utah_________ ________

Sevier Lake basin

Sevier River at Hatch, Utah __________________

Sevier River near Kingston-, Utah _____________

Clear Creek at Sevier Utah

Salina Creek at Salina, Utah __________________

Pavant Valley

Chalk Creek near Fillmore, Utah ___ ________

Parowan Valley

fe»nff»T* (~1 r'e'e'\f ne*f*r PaiT»wan TTtah

Cedar City Valley

Coal Creek near Cedar City, Utah___ __________

2.49

10

4.48

95

18.8

490

105

30

230

26

9.82

6.55

340

1,110

169

298

60

60

7.9

1950-59

1949-59

1950-59

1925-38

1947-59

1908-25;

1933-59

1904-16;

1945-59

1949-59

1949-59

1938-50

1947-55

1947-55

1911-28;

1939-59

1914-59

1912-19;

1934-58

1914-19;

1942-55

1914;

1943-59

1942-50

1915-20;

1935-59

7,580

7,470

7,050

7,330

7,610

7,130

7,110

9,710

8,600

7,450

8,770

7,500

8,480

7,790

7,690

7,810

8,020

8,680

8,640

28

77

36

255

141

441

246

349

1,150

155

116

57

621

830

365

481

261

317

352

___ do ......

May 20, 1958

May 5, 1952

July 17, 1932

May 4, 1952

_ __ _do__ __

___ do ......

June 6, 1957

June 4, 1957

May 3, 1945

June 13, 1953

Aug. 4, 1951

May 26, 1922 i/ *

Mar. 4, 1938

Aug. 17, 1955 o *

July 27, 1953

May 4, 1952

Aug. 5, 1945 O *

July 9, 1936
12 FLOODS IN UTAH, MAGNITUDE AND FREQUENCY

'its* HCX" % in*

4

40-

2S 0 25 90

 =

STATUTE MILES

 3T

112" ^ A 111'

Figure 2. Map of Utah showing flood regions.

110*
FLOOD-FREQUENCY RELATIONS 13

than a curve based on records for any one 

site. To combine records, the relative magnitude of floods must be computed on a dimensionless basis. The ratio of each flood 

to the mean annual flood, or simply the flood 

ratio, is a means of satisfying this premise. 

Floods used in computing composite floodfrequency curves are expressed as the median flood ratio for each recurrence interval.

REGIONAL SAMPLING

Sampling for a flood-frequency study can 

be accomplished by two methods time and 

areal sampling. Time sampling involves the 

collection of records at a few long-term stations, while areal sampling requires a large 

number of stations to evaluate the various 

characteristics of the region, without regard 

for the length of record. Streamflow records 

at the present time do not satisfy the requirements of either method, since the longterm records or the density of stations necessary to complete a statistical approach do 

not exist. An analysis of existing records 

will be helpful until such time as additional 

information can be obtained. To combine 

records from all the stations, it is advantageous to place the flood on a comparable 

basis as to time and physical characteristics 

of the drainage basin.

SELECTION OF COMPARABLE FLOODS

The peak flows of a stream at a given point 

integrate all of the flood characteristics of 

the drainage basin. A suitable index for the 

effect of physical features of a basin is the 

mean annual flood. Theoretically, a peak 

discharge with a recurrence interval of 2.33 

years is the same as the arithmetical mean 

of an infinitely long series. An estimated 

value of the mean annual flood(^2.33)may be 

obtained graphically from the flood-frequency 

curve for each individual station. All of the 

floods are placed on a dimensionless basis 

by dividing the recorded floods by the mean 

annual flood; thus, flood records for all gaging stations within the region are comparable 

irrespective of flood magnitude.

HOMOGENEITY

Before a group of stations can be combined 

on a regional basis, a test of homogeneity is

necessary to show that all of the records are 

from a region of similar flood-frequency 

characteristics. A statistical test is applied 

to the slope of the individual frequency curves 

to determine whether or not the deviations 

from an average slope are due to chance 

alone. The selection of the flood regions 

shown in figure 2 was based on the results of 

the homogeneity test with consideration given 

to geographic differences.

COMPOSITE FREQUENCY CURVE

When the requirements of the homogeneity 

test were satisfied, the stations were grouped 

together and flood ratios for several recurrence intervals were computed. Ratios of 

floods from each record for the selected recurrence intervals were listed, and the median flood ratios were obtained from this 

tabulation. Each median flood ratio was 

plotted to its corresponding recurrence interval and a curve was fitted smoothly through 

these points (figs. 3 and 4). These curves, 

with the flood discharge expressed in terms 

of the ratio to the mean annual flood, were 

based on all of the significant discharge records and represent the most likely floodfrequency relation for each respective region. Ratios to. the mean annual flood for any 

recurrence interval are obtained from the 

composite flood-frequency curve. At any 

desired recurrence interval, the magnitude 

of the discharge is estimated by multiplying 

this ratio by the mean annual flood.

REGIONAL ANALYSIS FOR SUMMER FLOODS

For flood regions C and D, the length of 

Streamflow records range from 5 to 10 years 

with a few records of longer periods for 

large drainage basins. Floods in these regions are generally caused by summer thunderstorms. The extension of records and the 

determination of the order of magnitude of 

floods by correlation methods are unsatisfactory in these regions because each flood 

occurrence may be entirely independent of 

any other flood. A flood may occur on one 

stream while no flow would be experienced 

on a nearby stream.

If a station record of 1,000 years were 

available, it would be reasonable to assume 

that 20 floods having a recurrence interval 

of 50 years or more may be experienced.
14 FLOODS IN UTAH, MAGNITUDE AND FREQUENCY

1.5 2 345 10 

RECURRENCE INTERVAL, IN YEARS

Figure 3. Composite flood-frequency curves, regions A and B.

20 30 40 50

7

o 

O 

O

_» 4

<ID'

< 

LU

7

i

1.1 1.5 2 345 10 

RECURRENCE INTERVAL, IN YEARS

Figure 4. Composite flood-frequency curves, regions C and D.

20 30 40 50
FLOOD-FREQUENCY RELATIONS 15

Within regions C and D, there are records of 

690 annual peaks. If the same analogy is applied, then 2 percent of these annual peaks 

should be 50-year floods or greater. From 

an envelope curve drawn on a plot of annual 

floods versus drainage area to exclude 2 

percent of the floods, it is possible to obtain 

an estimated 50-year flood for each of the 

47 stations. The estimated flood selected 

from the envelope curve is used as a guide 

to extend the individual flood-frequency 

curves. Although it is difficult to meet all of 

the conditions set forth in an accepted regional analysis, the two composite frequency 

curves (fig. 4) should be a suitable substitute 

for predicting peak discharges until additional 

hydrologic information is available.

DERIVATION OF THE MEAN ANNUAL FLOOD

To use the regional flood-frequency curve, 

a means must be provided for the determination of the mean annual flood.

BASIN CHARACTERISTICS

Characteristics of the basin as they affect 

floods are numerous, and many are difficult 

to define or separate. The ones selected and 

investigated in this study are as follows:

1. Drainage area. Noncontributing area is 

normally deducted from the total.

2. Mean altitude. The mean altitude of a 

basin is the average altitude above a given 

point.

3. Slope. The slope of a stream is the total 

fall between any two points divided by the 

stream length between those points. The 

points selected were at 0.2 and 0.8 of the total 

stream length above the site.

4. Shape. The shape of a basin is approximated by the length-width ratio.

5. Aspect. The aspect of a basin is the 

compass direction of the main stream and is 

a measure of the usual storm pattern in the 

area as well as exposure to prevailing winds 

and sunshine. This characteristic is significant when considering the peak discharge that 

results from snowmelt.

The above five characteristics were tested 

for effect on the mean annual flood in order 

to determine which were significant. Curves 

were derived by a multiple correlation of the 

mean annual flood with the two most significant characteristics, drainage area and mean 

altitude of the basin. Use of the remaining 

three characteristics did not significantly 

improve the statistical correlation. Slope, 

shape, and aspect probably have some effect 

on the mean annual flood, but the effect, if 

any, cannot be adequately defined on the basis 

of available streamflow records.

MEAN ANNUAL FLOOD RELATIONS

The relationship of the mean annual flood 

to basin characteristics was correlated from 

the records of 188 gaging stations. Boundaries of the selected hydrologic areas (fig. 5) 

are somewhat arbitrary; however, the present program of data collection will aid in the 

verification of these boundaries. For each 

hydrologic area, a family of curves was drawn 

(fig. 6). The use of the curves is limited by 

the range of the basic data.

For all hydrologic areas except 3, and 9, 

the mean annual flood was found to be directly 

related to drainage area and mean altitude of 

the basin. In area 3 the effects of limestone 

deposits are known to change the characteristics of streamflow when compared with that 

from surrounding drainage basins where 

limestone deposits are not present or predominant. Also, in area 3, mean altitude was 

not used as a parameter because of relatively 

few gaging-station records. In hydrologic 

area 9, where the peak discharge generally 

results from summer storms, the mean annual flood is directly related to the drainage 

area; however, it is inversely related to the 

mean altitude of the basin. One condition 

which could contribute to this fact is the 

marked change in vegetal cover with respect 

to altitude. Vegetal cover is almost nonexistent at the lower altitudes, whereas at the 

higher altitudes the cover is sufficient to retard runoff. In area 9, winter precipitation in 

the form of snow at the higher altitudes aids 

the growth of a vegetal cover. Frequently, 

summer storms are triggered before reaching the higher altitudes, thus causing larger 

floods to occur at lower altitudes.
16 FLOODS IN UTAH, MAGNITUDE AND FREQUENCY

25 0 2MP"I 

STATUTE MILES

114" 11 112* 'N 111*

Figure 5. Map of Utah showing hydrologic areas.

no* __l 37«
FLOOD-FREQUENCY RELATIONS 17

§ 1000

0

2

8 10°

o

_l

X

x

i>"ff^ 

ARE

X

A 3

Li_ 10

_J

< 3000

Z 

Z

1000

Z

100

UJ

>,,. \

-.'* 

100 300

1000

2000

1000

10.000

1000 10 100

DRAINAGE AREA, IN SQUARE MILES

1000

1000 5000

Figure 6. Variation of mean annual flood with drainage area and mean altitude.
18 FLOODS IN UTAH, MAGNITUDE AND FREQUENCY

MAJOR RIVERS IN UTAH

Inmost reaches of the major rivers, nearly 

complete development of the water siipply for

o

1°

< Q

* O i ftrt

fr

o uj 80

u!'s>

*

I

* - _

EXPLANATION

Gaging station

a

1

L

c

I

S

I

5 i

120 150 180 210 240 270 300 33

DISTANCE, IN MILES, ABOVE UTAH-ARIZONA STATE LINE

Figure 7. Colorado River, discharge of 50-year flood within the 

State of Utah.

50-YEAR FLOOD, THOUSANDS INOF CUBIC PER SECOND FEET 

8 S9

Green Rivr > 

>

n= '

o

CLx «> «

o

>

1

c «l

r=

 

i

EXPLANATION

Gaging station

a

C

«

ST,

c o 

« o

ill

ity or town

200 300 400 500 

DISTANCE, IN MILES, ABOVE MOUTH

50-YEAR FLOOD, iN THOUSANDS 3OF CUBIC FEET PER SECOND

P Mro *- He5 o ^o '"re 01 

8. Green River, discharge of 50-year flood below 

Wyoming -Utah State line.

5

K

&In*

!

 - 

20

S

.c 

u 

a 

Q

Tabioni ir 

EXPLAr

City o

!;!

Liiil

4ATION 

1

i 

r town

40 60 80 100 120 14

"

10 20 30 40 50 

DISTANCE, IN MILES, ABOVE MOUTH

Figure 10. Strawberry River, discharge of 50-year flood.

50

30

3"- 20

2 

1

 Near We

 \

^^

'ellington

yNearV Vellingtor

X

S. «

 3-JL

CL « S

C. «

k^

a ^

«

X

EXPLA

4

i _ Gaging

City c

2

\j

NATION

station.

i 

r town

20 40 60 80 100 120 14

DISTANCE, IN MILES, ABOVE MOUTH

Figure 9. Duchesne River, discharge of 50-year flood.

DISTANCE, IN MILES, ABOVE MOUTH

Figure 11. Price River, discharge of 50-year flood.

irrigation and power is reflected by the absence of homogeneity with the tributary 

streams. The major rivers are not homogeneoiis among themselves; therefore, the use 

of a composite ratio curve for estimating 

flood frequencies similar to methods used for 

the smaller streams is unsatisfactory. Each 

major river was treated individually for estimating the magnitude and frequency of 

floods. Table 2 contains a list of gaging stations for which records were analyzed on the 

above basis. The data shown for each station 

are drainage area, length of annual peak record, and estimated discharge for the 50-year 

flood. The discharge for the 50-year flood at 

each gaging site was plotted against the corresponding river miles above the mouth (figs. 

7 17). With the regimen of the rivers affected 

by regulation and diversion, it was impractical to compute the magnitude of the floods for 

recurrence intervals of less than 50 years.
FLOOD-FREQUENCY RELATIONS 19

50-YEAR FLOOD. IN THOUSANDS OF

CUBIC FEETSECOND PER 

£5 8m 

,N

Green Ri

1

\

\

EXPLANATI 

Gaging stat

\

"»

Castle Ir

^

3N 

»n

0 20 40 60 80 100 120 140 

DISTANCE, IN MILES, ABOVE MOUTH

Figure 12. -San Rafael River, discharge of 50-year flood below 

Perron Creek.

iia 8

gs* S

z «-

p

i

00 120 140 160 180 200 220 240 

DISTANCE. IN MILES, ABOVE MOUTH

13. San Juan River, discharge of 50-year flood below 

Shiprock, N. Mex.

50-YEAR THOUSANDS FLOOD, IN OF

CUBIC FEETSECOND PER Jo»o * M 

 b 

a

o

I

£

to

^

I

I

c

 -CM \

EX

C

»

'i « 

PLANATI

ging stati 

a 

ity or tow

%

I }

"TO

DN

on 

n

40 80 120 160 200 240

DISTANCE, IN MILES, ABOVE MOUTH 

Figure 14. Hear River, discharge of 50-yearflood.

10

8 

6

4 

2

8

 5

PI Near 

nU.S. Am 

- disch 

regul

ni

o

^*^

a

*~*~*

i

tj

EXPLANATION 

Gaging station

a 

City or tov

-1

ly Engin 

urge unc 

>tion for

vers esti 

er propo 

flood co

m

mated rr 

sed rese 

ntrol.

,

I

1 _

aximum 

rvoir 

,

~~\

 

1

(flows Creek halkinto reservoi 

Coalvllle'

Reservoir, Echo

tl1 

a

1

:!

1 | in

Res* Rockyport 

10 20 30 40 50 60 

DISTANCE. IN MILES, ABOVE MOUTH

70

Figure 15. Weber River, discharge of 59-year flood and U.S. 

Army Engineers'estimated maximum discharge under proposed 

flood-control project below Rockport Reservoir.

0

iiis a

x "

1- 1C

O ".

io 

ft oa

i

3 FLOOD, THOUSANDS 50-YEAR IN OF*§CUBIC FEET PERSECOND 

" 010 - ea 

.,^4

tt^

^

 i 

|

I

EXPLAf

ft

s

I

ATION

Gaging, station 

a 

City or town

!

LJ

I

0

r

i

-1-

S 10 IS 

DISTANCE, IN MILES, ABOVE MOUTH

16. Provo River, discharge of 50 -year flood below Deer 

Creek Reservoir.

EXPLA 

- Gagini 

Crtye

'5 M

C

-4

NATION

ir town

-*

b

 1

i 

J

Gunnison

s iFi -I *1 %

U-lL? r

fc e

J 1

LJ

1

1

0 40 80 120 160 200 240 280

DISTANCE, IN MILES, ABOVE MOUTH

Figure 17. Sevier River, discharge of 50-yearflood below Piute 

Reservoir.
20 FLOODS IN UTAH, MAGNITUDE AND FREQUENCY

Table 2. Main stem gagwfl-station data

Station 

No. Gaging station

Drainage

area 

(sq mi)

Period of 

record

50-year 

flood 

(cfs)

COLORADO RIVER

9-1635__ Colorado River near Colorado-Utah State line___. 

1805__ Colorado River near Cisco, Utah_______________.

3350__ Colorado River at Kite, Utah _._._.__...__.___..

GREEN RIVER

2255__ Green River near Linwood, Utah ________________

2345._ Green River near Greendale, Utah ______________

2610__ Green River near Jensen, Utah _________________

3070__ Green River near Our ay, Utah__________________

3150__ Green River at Green River, Utah_______________

DUCHESNE RIVER 

2740__ Duchesne River near Hanna, Utah _______________

2770.. Duchesne River at Hanna, Utah .................

2775.. Duchesne River near Tabiona, Utah __.___.._....

2795__ Duchesne River at Duchesne, Utah ______________

2950__ Duchesne River at Myton, Utah ....._......_....

3020._ Duchesne River near Randlett, Utah_____________

STRAWBERRY RIVER

2850._ Strawberry River near Soldier Springs, Utah..... 

2885.. Strawberry River at Duchesne, Utah____________.

PRICE RIVER 

3115__ Price River near Scofield, Utah.._..............

3130__ Price River near Heiner, Utah._________________

3135__ Price River near Helper, Utah__________________

3140__ Price River near Wellington, Utah ______________

3145__ Price River at Woodside, Utah._________________

17,900

24,100

76,600

1951-59 

1914-17, 

1923-59 

1947-58

61,000

76,000

123,000

14,300

15,100

25,400

35,500

40,600

1929-59

1951-59

1904, 1906,

1947-59

1948-55,

1957-59

1895-

1905,

1906-59

23,000

24,000

59,000

71,000

70,000

78

230

352

660

2,750

3,920

1922-23,

1946-59

1954-59

1919-59

1918-59

1900-59

1943-59

1,640

2,860

2,550

4,500

14,000

18,000

212

1,040

1943-56

1909-10,

1914-59

3,050

3,600

163

455

530

850

1,500

1918-20,

1926-27,

1929-31,

1939-44,

1946-59

1935-59

1905-06,

1908-11,

1913-34

1950-58

1909,

1946-59

1,320

12,500

12,500

21,800

30,000
FLOOD-FREQUENCY RELATIONS

Table 2. Main stem gagmg-sfation data Continued

21

Station 

No.

Gaging station

Drainage

area 

(sq mi)

Period of 

record

50-year 

flood 

(cfs)

SAN RAFAEL RIVER

9-3280.. San Rafael River near Castle Dale, Utah.-..-... 

3285.. San Rafael River near Grten Rivtr, Utah - --,

SAN JUAN RIVER

3680.. San Juan River at Shiprock, N. Mex __,---_____, 

3795.. San Juan River near Bluff, Utah................

BEAR RIVER

10- 440__ Bear River at Harer, Idaho......._, .,..,.....

905.. Bear River near Preston, Idaho.____ _________.

1180,. Bear River near Collinston, Utah ,___.._._..__.

WEBER RIVER 

1295.. Weber River near Wanship, Utah______.________

927

1,690

1948-59

1909-18,

1946-59

7,100

27,000

12,900

23,000

1928-59

1915-17,

1927-59

99,000

85,000

2,780

4,300

6,000

1914-59

1890-98,

1900-02,

1904-16,

1944-59

1890-

1959

4,450

7,650

11,600

1305.

1320.

1335.

1360.

1365.

1370.

1410.

Weber River near Coalville, Utah. 

Weber River at Echo, Utah-_____. 

Weber River at Devils Slide, Utah. 

Weber River near Morgan, Utah . 

Weber River at Gateway, Utah.-..

Weber River at Ogden, Utah ______

Weber River near Plain City, Utah

320

438

732

1,100

1,610

2,060

1951-55,

1958

1927-59

1927-58

1905-55

1951-55

1890-93,

1895-99,

1901,

1921-59

1951-58

1905-59

4,800

6,500

8,000

9,800

9,200

10,000

PROVO RIVER

1595.

1605.

1610.

1630.

Provo River below Deer Creek Dam, Utah 

Provo River near Wildwood, Utah____ ___

Provo River at Vivian Park, Utah ________

Provo River at Provo, Utah _____________

560

590

600

680

1954-59

1939-49

1912-59

1903-05,

1934,

1937-59

2,870

3,030

3,200

2,550

SEVIER RIVER

1915.

1940.

Sevier River below Piute Dam, near Marysvale,

Utah. 

Sevier River above Clear Creek, near Sevier, Utah

2,440

2,700

1912-59

1914-16, 

1939-55

2,700

2,700
22 FLOODS IN UTAH. MAGNITUDE AND FREQUENCY

Table 2. Main stem gaging-station data Continued

Station

No. Gaging station

Drainage 

area 

(sq mi)

Period of 

record

50-year 

flood 

(cfs)

SEVIER RIVER Continued

10-1955__

2050_.

2170__ 

2190..

2240_.

2280..

2315__

Sevier River at Sevier, Utah. ___________________

Sevier River near Sigurd, Utah _________________

Sevier River below San Pitch River, near 

Gunnison, Utah. 

Sevier River near Juab, Utah ___________________

Sevier River near Lynndyl, Utah _________ _______

Sevier River near Delta, Utah __________________

Sevier River at Oasis. Utah ____________________

2,850

3,340

4,880 

5,120

6,270

7,380

8.080

1917-29

1915-59

1918-59 

1912-59

1914-19,

1943-59 

1913-19

1913-27

2,900

2,500

2,700 

2,200

1,740

1,600

1.580

CLOUDBURST FLOODS AND MUD-ROCK FLOWS

Cloudburst floods and mud-rock flows are 

common to the southern parts of both the 

Colorado River basin and the Great Basin in 

Utah. These phenomena occur at less frequent intervals in other areas of the State. 

Most of the annual flood peaks in the southern 

regions occur during the summer storm 

period, as previously described, and are included in the flood-frequency relations for 

that region. In contrast to the annual floods 

observed in the snowmelt regions, occasional 

peak flows resulting from cloudburst storms 

in the central and northern parts of the State 

may have yields of 5,000 cfs (cubic feet per 

second) per square mile or more from small 

drainage basins. This is not to imply that 

these excessive flows occur more frequently 

in any one section of the State; instead, it is 

to acquaint the reader with the fact that these 

events have been observed. Although cloudburst storms may occur on many days in one 

season and may be distributed over a rather 

wide area, the high-intensity rainfall is limited to very small areas, often less than 1 

square mile. Observations of rainfall intensities from unofficial observers have shown 

that as much as 7 inches fell in less than 1 

hour during one of these storms. The probability of a cloudburst or high-intensity rainfall recurring in the same small drainage 

area during consecutive years is rather remote. Experience shows that in some drainage basins, the frequency of floods may vary 

from three in one year to one in each of three 

consecutive years to none in several years.

Some drainage basins are subject to more 

cloudburst floods than others in the same 

general locality because of physical features 

such as topography, aspect, vegetal cover, 

and other contributing factors. One example 

is Pleasant Creek near Mount Pleasant where 

a large alluvial cone covering more than 12 

square miles is evidence of frequent cloudburst flooding.

A cloudburst flood may occur without producing a mud-rock flow. Although mud-rock 

flows may be associated with cloudburst 

floods, the presence of certain soil conditions 

are required to produce them. Mud-rock 

flows are flows of mud, rock, debris, and 

water, mixed to a consistency similar to that 

 of wet concrete. A wide variety of these 

flows has been observed from those carrying a small load of sediment to others moving 

large amounts of mud, rock, and other debris. 

Some flows have just enough water to lubricate the mass of moving material and usually 

travel at a relatively slow velocity. Because 

of infrequent observation of these flows, it is 

difficult to estimate the probable recurrence 

interval at any given site. It has been noted 

by Wooley (1946) that the total discharge of 

debris and water can exceed 2,000 cfs per 

square mile.

The cost of replacing bridges, culverts, 

and sections of highway and other economicfactors will determine whether design should 

be for rare floods of the above type which 

may have a recurrence interval in excess of 

50 years.
LIMITATIONS 23

APPLICATION OF FLOOD-FREQUENCY CURVES

The application of flood-frequency curves 

to any drainage basin within the scope of this 

report required analysis of the basin characteristics vfrhich effect peak discharge. 

The significant characteristics are those 

most readily available from topographic 

maps.

METHOD

To obtain the magnitude and frequency of 

floods for any basin within the study area, 

except on major rivers, the procedure is as 

follows:

1. Determine the drainage area above the 

site by planimeter or other acceptable procedure.

2. Locate site on figures 2 and 5 and determine the flood region and hydrologic area 

involved.

3. Determine the mean altitude for drainage basin above the selected site, unless basin is in hydrologic area 3. In this report the 

mean altitude was determined by using a grid 

system of rectangular coordinates as an 

overlay on topographic maps. From a list of 

the average altitudes of each square, an arithmetical mean was computed. The squares 

were of equal size and small enough to give 

a representative sampling, but not of a known 

scale. Contour maps of the Army Map Series, 

scale 1:250,000 were used.

4. Determine the mean annual flood for the 

site from hydrologic area curve selected in 

step 2 (fig. 6). One exception is that to determine the mean annual flood of the Dirty 

Devil River near Kite, Utah (9-3335), use hydrologic area 8 curve. This exception applies 

only to the main stem and should not be used 

for the tributary streams of the Dirty Devil 

River outside of area 8.

5. Determine the flood ratio to the mean 

annual flood for the selected recurrence interval from the appropriate flood-frequency 

curve obtained in step 2 (figs. 3 and 4). When 

the drainage area above the site is near another flood region or lies in two regions with 

widely different flood ratios, it is suggested 

that a weighted average of the two flood ratios be used.

6. Estimate the magnitude of the flood by 

multiplying the mean annual flood (step 4) by 

the flood ratio (step 5).

A complete frequency curve for a site may 

be derived by repeating steps 5 and 6 for 

various recurrence intervals.

USE OF FLOOD-FREQUENCY ANALYSIS ON MAJOR RIVERS

To determine the magnitude of the flood 

for a 50-year recurrence interval at a given 

location on a major river, scale the mileage 

of the main stem from a known reference 

point as indicated on each graph (figs. 7 17). 

Use of the main stem analysis will require 

some knowledge of local conditions and the 

operation of any reservoirs involved. The 

Weber River is the only major stream that 

has a specific flood-control plan. The proposed magnitude of the controlled flow is 

shown(fig. 15) with the flood experience prior 

to the initiation of this plan.

LIMITATIONS

The results of this study may be used to 

estimate the magnitude and frequency of 

floods, with recurrence intervals up to 50 

years, for any drainage area in the State with 

the exception of the Great Salt Lake Desert 

and the Snake River basin.

The relationships of the hydrologic features of the drainage basins were defined 

from the records on streams with natural 

flows. To obtain the magnitude of any flood 

on any regulated stream, adjustments should 

be made for manmade development. Also, the 

varying effects of geology and vegetal cover 

were not given detailed consideration in this 

study. An investigation and evaluation of 

these factors may be justified in some specific areas.

The results obtained from the floodfrequency study are limited by the basic data 

available. The degree of confidence that can 

be placed in the results is closely related to 

the quantity of data used in defining the various curves. Extrapolation of curves beyond 

the limits shown is not recommended, and 

values obtained by such practice may be 

greatly in error.
24 FLOODS IN UTAH, MAGNITUDE AND FREQUENCY

SELECTED BIBLIOGRAPHY

Bodhine, G.L., and Thomas, D.M., 1960, Floods 

in Washington, magnitude and frequency: 

U.S. Geol. Survey open-file report.

Fisher, R. A., 1954, Statistical methods for 

research workers: New York, Hafner Publishing Co.

Gumbel, E. J., 1941, The return period of 

flood flows: Annals Math. Statistics, v. 12, 

no. 2, p. 163-190.

Langbein, W. B., 1949, Annual floods and the 

partial-duration flood series: Am. Geophys. Union Trans., v. 30, p. 879-881.

Linsley, R. K., Jr., Kohler, M. A., and Paulhus, 

J. L. H,, 1949, Applied hydrology: New York, 

McGraw-Hill Book Co.

Powell, R. W., 1943, A simple method of estimating flood frequency: Civil Eng. v. 13.

Thomas, C. A., Broom, H. C., and Cummans, 

J. E., 1961, Magnitude and frequency of 

floods in the United States, Part 13, Snake 

River basin: U.S. Geol. Survey WaterSupply Paper 1688 (in press).

Woolley, Ralph, R., 1946, Cloudburst floods 

in Utah, 1850-1938: U.S. Geol. Survey 

Water-Supply Paper 994.

INT.DUP..D.C.62-^1*6