FLOOD ANALYSIS ALONG THE LITTLE MISSOURI RIVER WITHIN AND 

ADJACENT TO THEODORE ROOSEVELT NATIONAL PARK, NORTH DAKOTA

By Douglas G. Emerson and Kathleen M. Macek-Rowland 

Water-Resources Investigations Report 86-4090

Prepared in cooperation with the 

NATIONAL PARK SERVICE

Bismarck, North Dakota 

1986
UNITED STATES DEPARTMENT OF THE INTERIOR 

DONALD PAUL HODEL, Secretary

GEOLOGICAL SURVEY 

Dallas L. Peck, Director

For additional information 

write to:

District Chief, WRD 

U.S. Geological Survey 

821 East Interstate Avenue 

Bismarck, ND 58501

Copies of this report can 

be purchased from:

Open-File Services Section 

Western Distribution Branch 

U.S. Geological Survey 

Box 25425, Federal Center 

Denver, CO 80225 

(Telephone: (303) 236-7476)
CONTENTS

Page.

Abstract 1

Introduction 1

Flood frequency 3

Flood profiles 1 2

Ice jams 14

Flood-hazard assessment 33

Summary 35

References 36

ILLUSTRATIONS

Figure 1. Map showing location of Theodore Roosevelt

National Park 2

2. Map showing South Unit study reach and location

of cross sections A-A 1 through R-R 1 4

3. Map showing Elkhorn Ranch Site study reach and

location of cross sections S-S 1 through V-V 5

4. Map showing North Unit study reach and location

of cross sections W-W 1 through FF-FF 1 6

5. Graphs showing relation between the 100- and 

500-year flood discharges and drainage area 

for the Little Missouri River 9

6. Cross sections A-A 1 through L-L 1 and water-surface 

elevations for 100- and 500-year floods, Little 

Missouri River, South Unit reach 15

7. Cross sections M-M 1 through O-O' and water-surface 

elevations for 100-year flood, Knutson Creek 

reach 19

8. Cross sections P-P 1 through R-R 1 and water-surface 

elevations for 100-year flood, Paddock Creek 

reach 20

9. Cross sections S-S 1 through V-V and water-surface 

elevations for 100- and 500-year floods, Little 

Missouri River, Elkhorn Ranch Site reach 21

10. Cross sections W-W through CC-CC 1 and watersurface elevations for 100- and 500-year 

floods, Little Missouri River, North Unit 

reach 23

11. Cross sections DD-DD 1 through FF-FF 1 and watersurface elevations for 100-year flood, Squaw 

Creek reach 26

12. Profiles for 100- and 500-year floods and 

streambed, Little Missouri River, South 

Unit reach 27

111
ILLUSTRATIONS, Continued

Figure 13. Profiles for 100-year flood and streambed,

Knutson Creek reach 28

14. Profiles for 100-year flood and streambed,

Paddock Creek reach 28

15. Profiles for 100- and 500-year floods and

streambed, Little Missouri River, Elkhorn

Ranch Site reach 29

16. Profiles for 100- and 500-year floods and 

streambed, Little Missouri River, North 

Unit reach 30

17. Profiles for 100-year flood and streambed,

Squaw Creek reach 31

18. Graphs showing relation between backwater 

due to ice and water-surface elevations, 

and an envelope curve 32

19. Graphs showing water-surface elevation-frequency

curves 34

Table

3.

TABLES

Annual peak discharges and annual maximum 

water-surface elevations for the streamflow 

station Little Missouri River at Medora 

(06336000) -

Annual peak discharges and annual maximum 

water-surface elevations for the streamflow 

station Little Missouri River near Watford 

City (06337000) -

Flood discharges for selected reaches -

10

13
SELECTED FACTORS FOR CONVERTING INCH-POUND UNITS TO 

THE INTERNATIONAL SYSTEM (SI) OF UNITS

For those readers who may prefer to use the International System (SI) of 

Units rather than inch-pound units, the conversion factors for the terms used 

in this report are given below.

Multiply inch-pound unit By To obtain SI unit

Cubic foot per second

(ft3 /s) 

Foot (ft) 

Mile (mi) 

Square mile

0.02832

0.3048

1.609

2.590

cubic meter per

second 

meter 

kilometer 

square kilometer

National Geodetic Vertical Datum of 1929 (NGVD of 1929): A geodetic datum 

derived from a general adjustment of the first-order nets of both the United 

States and Canada, formerly called "mean sea level." NGVD of 1929 is referred 

to as sea level in this report.
FLOOD ANALYSIS ALONG THE LITTLE MISSOURI RIVER WITHIN AND

ADJACENT TO THEODORE ROOSEVELT NATIONAL PARK,

NORTH DAKOTA

By Douglas G. Emerson and Kathleen M. Macek-Rowland

ABSTRACT

The Little Missouri River flows through Theodore Roosevelt National Park t 

which consists of three separate units: South Unit, Elkhorn Ranch Site, and 

North Unit. The park is located in the Little Missouri badlands. Discharges 

and water-surface elevations for 100- or 500-year floods or both were computed 

for selected reaches along the Little Missouri River and three of its tributaries (Knutson Creek, Paddock Creek, and Squaw Creek) within and adjacent 

to Theodore Roosevelt National Park. The 100- and 500-year flood discharges 

for the Little Missouri River were determined from streamflow records. The 

100-year flood discharges for the three creeks were estimated using a 

multiple-regression equation based on drainage area and soil-infiltration 

index. Water-surface elevations were determined by the step-backwater method. 

The effects of ice jams on water-surface elevations were estimated from 

streamflow records.

INTRODUCTION

Theodore Roosevelt National Park an area of geologic, historic, and 

scenic interest is located in western North Dakota (fig. 1) in the Little 

Missouri badlands. The park consists of three separate units: South Unit, 

Elkhorn Ranch Site, and North Unit. The Little Missouri River, a tributary of 

the Missouri River, flows north through the South Unit and Elkhorn Ranch Site 

and then turns in the North Unit and flows east. The Little Missouri badlands 

are described by Bluemle (1977) as a "Rugged, deeply-eroded, hilly area along 

the Little Missouri River; gentle slopes characterize 20 to 50 percent of the 

area and local relief is commonly over 500 feet."

The National Park Service needed information on flood potential as part of 

a general management plan for the park. They requested and funded a study to 

determine water-surface elevations along the Little Missouri River and three 

of its tributaries (Knutson Creek, Paddock Creek, and Squaw Creek) within and 

adjacent to Theodore Roosevelt National Park. The water-surface elevations 

will be used by the National Park Service as a basis for planning visitor 

activities and selecting structure sites*

The objectives of the study were to: (1) Determine water-surface elevations for 100- and 500-year flood discharges for selected reaches of the 

Little Missouri River; (2) determine water-surface elevations for 100-year
4800' -

4700" -

NORTH DAKOTA

SOUTH DAKOTA

Theodore Roosevelt 

National Park 

(North Unit)

KENZIECQ 

BILLINGSTXX

Theodore Roosevelt

National Park 

(Elkhorn Ranch Site)

Theodore Roosevelt 

National Park 

(South Unit)

10400' 10300'

Base modified from U.S. Geological

Survey Theodore Roosevelt

National Memorial Park, 0 5 10 15 20 25 MILES N. Dak. (South Unit), 1974 I r H H , h ' '

0 5 10 15 20 25 KILOMETERS

Figure 1. Location of Theodore Roosevelt National Park.
flood discharges for the areas near the mouths of Knutson, Paddock, and Squaw 

Creeks; and (3) evaluate the effects of ice jams on water-surface elevations.

The study reach for the South Unit (fig. 2) is about 8 river miles long 

and includes the area along the Little Missouri River from about 0.1 mi south 

of Medora to about 1 mi downstream from Beef Corral Bottom. The study reach 

for the Elkhorn Ranch Site (fig. 3) is about 3 river miles long and includes 

the area from about 0.5 mi south of the south boundary of the site to about 

0.05 mi north of the north boundary of the site. The study reach for the 

North Unit (fig. 4) is about 7 river miles long and includes the area from 

about 1 mi upstream from Squaw Creek Campground to the bridge on U.S. Highway 

85.

FLOOD FREQUENCY

The annual peak discharge data for the streamflow station Little Missouri 

River at Medora (06336000), which has a drainage area of about 6,190 mi^, 

were used to determine the 100- and 500-year flood discharges for the Little 

Missouri River along the South Unit reach. The flood discharges determined 

are considered to be applicable for the entire South Unit reach. The procedures described by the U.S. Geological Survey (1982) were used to determine 

flood-flow frequency. The station has a discontinuous record from May 1903 

to September 1934 and a continuous record from October 1945 to September 1976. 

The records include 50 annual peak discharges and 50 annual peak elevations 

(table 1).

Discharge data are not available for the Little Missouri River near the 

Elkhorn Ranch Site reach. Therefore, annual peak discharge data for the 

streamflow stations Little Missouri River at Marmarth (06335500), Little 

Missouri River at Medora (06336000), and Little Missouri River near Watford 

City (06337000) were used to determine the 100- and 500-year flood discharges 

for these stations. The 100- and 500-year flood discharges determined at 

these stations were then plotted against the station drainage areas (fig. 5) 

and a curvilinear line drawn through the points. The 100-year flood discharge 

for the Little Missouri River near the Elkhorn Ranch Site reach, which has a 

drainage area of about 6,680 mi^, was determined from the plot to be 69,000 

ft-Vs, and the 500-year discharge was determined from the plot to be 103,000 

ft-^/s. Flood discharges determined in this analysis are considered to be 

applicable for the entire Elkhorn Ranch Site reach.

The annual peak discharge data for the streamflow station Little Missouri 

River near Watford City (06337000), which is located near the downstream end 

of the North Unit and has a drainage area of about 8,310 mi^, were used to 

determine the 100- and 500-year flood discharges for the Little Missouri River 

along the North Unit reach. Flood discharges determined in this analysis are 

considered to be applicable for the entire North Unit reach. The station has 

a continuous record from September 1934 to the present. The record includes 

48 annual peak discharges and 48 annual peak elevations (table 2).

Discharge data are not available for Knutson and Paddock Creeks, which are 

located in the South Unit (fig. 2), or for Squaw Creek, which is located in
141 N.

R. 14O N. R. 14O N.

Base modified from 

U.S. Geological Survey 

Belfield. 1980

R. 1O2 W. R.101 W.

3 MILES

3 KILOMETERS

CONTOUR INTERVAL G5.6 FEET 

NATIONAL GEODETIC VERTICAL DATUM OF 1929

G-G'

EXPLANATION 

 CROSS SECTION

 PARK BOUNDARY

Figure 2. South Unit study reach and location of cross sections A-A' through R-R'.
47°15'00" 103°37'30" R. 102 W.^

Base modified from U.S. Geological Survey 

Roosevelt Creek West, 1974

base moamed trom u.b. ue 

Roosevelt Creek West, 1974 

Roosevelt Creek East, 1970

0

h 

0

R. 102 W.

1 MILE

V4 Vz 1 KILOMETER

CONTOUR INTERVAL 20 FEET 

NATIONAL GEODETIC VERTICAL DATUM OF 1929

EXPLANATION

S-S' CROSS SECTION 

 - - PARK BOUNDARY

Figure 3. Elkhorn Ranch Site study reach and location of cross sections S-S'.through V-V.
R. 100 W. 10320'00" R. 99 W. 103 15'00"

T.148 N.

T. 147 N.

R.100 W.

Base modified from 

U.S. Geological Survey 

Watford City, 1982

R. 99 W.

3 MILES

0123 KILOMETERS

CONTOUR INTERVAL 65.6 FEET 

NATIONAL GEODETIC VERTICAL DATUM OF 1929

W-W

EXPLANATION 

 CROSS SECTION

- PARK BOUNDARY

Figure 4. North Unit study reach and location of cross sections W-W through FF-FF'.
Table 1 . Annual peak discharges and annual maximum watersurface elevations for the streamflow station 

Little Missouri River at Medora (06336000)

Date

Peak discharge 

(cubic feet per second)

Maximum

water-surface

elevation

(feet above

sea level)

June

July

June

June

June

May

Mar.

May

July

Apr.

June

Mar.

Apr.

June

Feb.

Sept

June

Apr.

May

June

June

Mar.

Mar.

Mar.

Mar.

Apr.

Mar.

Apr.

Apr.

June

9,

2,

8,

24

6,

31,

16

17,

8,

3,

16

16

4,

7,

25

. 1

22

28

24,

12

24

23

23

21

27

8,

22

1,

8,

21

1904

1905

1906

, 1907

1908

1909

, 1910

1911

1912

1914

, 1915

, 1916

1924

1929

, 1930

3, 1930

, 1931

, 1932

1933

, 1934

, 1946

, 1947

, 1948

, 1949

, 1949

1950

, 1951

1952

1952

, 1953

11

8

13

29

10

12

7

5

5

1

24

6

18

38

4

1

12

20

1

9

65

24

14

25

5

42

8

,600

,500

,900

,000

,800

,400

,550

,540

,750

,850

,700

,630

,500

,700

,700

,610

,500

,800

,850

,310

,000

,100

,600

,600

,200

,500

,820

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

i

,

i

i

f

i

i

i

i

i

i

t

i

i

i

i

i

t

i

i

t

i

i

t

i

i

i

257

256

258

262

257

258

256

255

255

253

260

255

260

263

255

251

256

259

251

255

267

260

259

-

259

255

265

-

254

.95

.95

.75

.75

.45

.25

.25

.35

.45

.05

.75

.85

.55

.95

.15

.27

.41

.19

.25

.50

.25

.25

.75

-

.75

.75

.10

-

.96
Table 1. Annual peak discharges and annual maximum watersurface elevations for the streamflow station Little 

Missouri River at Medora (06336000) Continued

Date

Peak discharge 

(cubic feet per second)

Maximum

water-surface

elevation

(feet above

sea level)

Apr. 7, 1954

June 27, 1955

Mar. 20, 1956

Mar. 27, 1956

June 22, 1957

July 4, 1958

Mar. 20, 1959

Mar. 22, 1960

May 24, 1961

May 30, 1962

Mar. 3, 1963

June 10, 1964

Apr. 3, 1965

Mar. 14, 1966

May 11, 1 967

Mar. 7, 1968

Mar. 23, 1969

May 9, 1970

June 6, 1971

Mar. 11, 1972

Mar. 1, 1973

June 20, 1973

May 21, 1974

May 9, 1975

June 21, 1976

4,320

25,600

2,030

7,900

5,050

6,650

8,100

3,540

10,800

11,000

9,170

15,000

6,800

15,700

3,000

11,200

6,550

21,200

40,000

3,820

5,230

22,800

6,000

2,252.74

2,260.65

2,251.51

2,254.20

2,252.65

2,254.22

2,255.47

2,251.97

2,256.60

2,261 .05

2,255.86

2,259.30

2,254.73

2,258.48

2,252.10

2,256.75

2,254.06

2,259.57

2,265.43

2,254.45

2,253.65

2,260.75

2,253.81
I/)

LJ

o: 

<

Z)

a

9000

8000

7000

6000

5000

4000

100-YEAR FLOOD

UTTLE MISSOURI RIVER 

NEAR WATFORD CITY \ 

(06337000)

'ESTIMATED DISCHARGE OF 

UTTLE MISSOURI RIVER ~ 

FOR ELKHORN RANCH 

SITE REACH

UTTLE MISSOURI RIVER AT 

MEDORA (06336000)

UTTLE MISSOURI RIVER AT MARMARTH (06335500)

40.000 50.000 60.000 70.000 80.000

FLOOD DISCHARGES. IN CUBIC FEET PER SECOND

 0.000

<

LJ

a:

LJ

o

Q

9000

8000

7000

6000

5000

4000

LITTLE MISSOURI RIVER NEAR 

WATFORD CITY (06337000)

500-YEAR FLOOD

ESTIMATED DISCHARGE OF 

UTTLE MISSOURI RIVER FOR 

ELKHORN RANCH SITE REACH

UTTLE MISSOURI RIVER AT 

MARMARTH (06335500) UTTLE MISSOURI RIVER AT 

MEDORA (06336000)

70.000 80.000 90.000 100.000 110.000

FLOOD DISCHARGES. IN CUBIC FEET PER SECOND

120.000

Figure 5. Relation between the 100- and 500-year flood discharges and drainage area 

for the Little Missouri River.
Table 2. Annual peak discharges and annual maximum watersurface elevations for the streamflow station Little 

Missouri River near Watford City (06337000)

Maximum

water-surface

elevation

(feet above

Date (cubic feet per second) sea level)

Peak discharge 

(cubic feet per second)

July

Mar.

June

Mar.

Mar.

Sept

June

Mar.

Feb.

Apr.

Mar.

Feb.

Mar.

Mar.

Mar.

Mar.

Apr.

Mar.

Mar.

Apr.

Mar.

June

June

June

July

June

Mar.

Mar.

Mar.

May

11

10

15

15

22

i

i

i

t

t

. 23

11

11

22

8,

14

24

25

17

24

28

9,

25

27

10

25

22

14

28

30

23

25

20

22

24,

i

i

t

t

i

i

i

i

i

i

t

i

i

i

t

i

i

i

i

i

t

1935

1936

1937

1938

1939

, 1940

1941

1942

1943

1944

1945

1946

1947

1948

1948

1949

1950

1951

1951

1952

1953

1953

1954

1955

1956

1957

1958

1959

1960

1961

20

8

8

14

26

4

13

12

25

32

30

8

110

16

26

60

18

42

7

10

17

2

6

12

12

18

2

i

i

i

i

i

t

i

,

t

t

i

i

i

t

t

i

i

i

i

i

t

t

i

i

t

i

500

800

990

600

500

270

000

600

000

600

000

000

000

000

000

000

000

000

.-

650

200

600

770

890

000

800

900

920

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

,939

,937

,936

,938

,942

,935

,938

,938

,947

,943

,943

,937

,953

,943

-

,942

,950

,942

-

,944

,937

-

,937

,938

,935

,936

,938

,939

,938

,932

.63

.03

.88

.43

.08

.86

.03

.62

.03

.43

.43

.78

.03

.63

-

.73

.45

.97

-

.56

.58

-

.40

.99

.03

.83

.97

.16

.86

.79

10
Table 2. Annual peak discharges and annual maximum watersurface elevations for the streamflow station Little 

Missouri River near Watford City (06337000) Continued

Date

May 31, 1962

Mar. 5, 1963

July 5, 1964

Apr. 8, 1965

Apr. 10, 1965

Mar. 12, 1966

Mar. 22, 1967

Mar. 1, 1968

Mar. 23, 1969

May 9, 1970

Mar. 28, 1971

Mar. 13, 1972

Feb. 28, 1973

Feb. 2, 1974

May 21, 1974

May 11, 1975

Mar. 19, 1976

June 24, 1976

June 17, 1977

Mar. 30, 1978

Mar. 18, 1979

Apr. 17, 1979

Mar. 23, 1980

June 14, 1980

Oct. 23, 1980

Feb. 18, 1981

Feb. 21, 1982

Mar. 13, 1982

Peak discharge 

(cubic feet per second)

12,100

10,000

12,000

20,000

12,000

30,000

7,900

15,300

13,400

31,000

52,800

7,500

6,750

17,500

7,600

6,400

31,500

10,000

865

1,390

11,000

__

Maximum 

water-surface 

elevation 

(feet above 

sea level)

1,935.74

1,938.93

1,936.85

1,946.96

 

1,936.36

1,945.10

1,935.41

1,937.07

1,936.33

1,944.30

1,943.71

1,935.45

1,935.33

 

1,937.43

1,938.42

1,934.43

1,940.11

1,935.70

1,932.84

1,933.31

1,942.06

11
the North Unit (fig. 4). The 100-year flood discharges were estimated using a 

multiple-regression equation based on drainage area and soil-infiltration 

index (O. A. Crosby, U.S. Geological Survey, written commun., 1984). The 

equation,

Q100 = 927A°- 65Si-1 - 00 ,

where Q-joo = t-*16 1 00-year flood discharge, in cubic feet per second;

A = the drainage area, in square miles; and 

Si = the soil infiltration index, in inches;

is based on 47 streamflow stations with most of the stations having 18 years 

of record. The average standard error of estimate is 98 percent.

A summation of the 100- and 500-year flood discharges for the Little 

Missouri River and the 100-year flood discharges for the three creeks is 

listed in table 3. The 100-year flood discharges on the Little Missouri River 

range from 65,300 to 78,800 ft3 /s, whereas the 500-year flood discharges range 

from 99,300 to 113,500 ft3 /s. The 100-year flood discharges on the three 

creeks range from 18,500 to 31,800 ft3 /s.

FLOOD PROFILES

The water-surface profiles for the flood discharges listed in table 3 

for the various reaches were computed using the U.S. Geological Survey's 

E431 program (Shearman, 1976). The program computes water-surface profiles 

for gradually varied, subcritical flow by the step-backwater method. The 

computations that were used to define water-surface elevations are based on 

hydraulic equations that depend on the following assumptions: (1) Stream 

discharge remains constant in the subreach defined by the two cross sections; 

(2) the flow regime in the subreach is entirely critical, critical and subcritical, or subcritical; (3) the longitudinal water-surface and channel 

slopes are small enough that normal depths and vertical depths may be considered equal; (4) the water surface is level across each individual cross 

section; (5) effects from sediment and air entrainment are negligible; and 

(6) all losses are correctly evaluated.

Starting elevations for downstream ends of the South Unit reach, the 

Elkhorn Ranch Site reach, and the three creeks were obtained using a slopeconveyance technique together with computed 100- or 500-year discharges or 

both discharges. The starting elevations for the downstream end of the North 

Unit reach were obtained using the relationship between elevation and 

discharge for the streamflow station Little Missouri near Watford City 

(06337000), which is located at the downstream end of the North Unit reach. 

Gradually varied flow does not exist where the creeks enter the Little 

Missouri River flood plain. Because of this, the flood profile for the creeks 

cannot be computed using this method for the area within the Little Missouri 

River flood plain. The computed flood profiles for the three creeks are for 

reaches upstream of the Little Missouri flood plain.

Roughness coefficients (Mannings H n H ) used in the computations were chosen 

from experience and by using results of coefficient-verification studies by 

Barnes (1967). Limited cross-sectional data were obtained from field surveys.

12
Table 3. Flood discharges for selected reaches

Reach

Recurrence 

interval 

(years)

Probability 

(percent)

Discharge

(cubic feet per

second)

Little Missouri River 

South Unit

Little Missouri River 

Elkhorn Ranch Site

Little Missouri River 

North Unit

Knutson Creek 

Paddock Creek 

Squaw Creek

100

500

100

500

100

500

100

100

100

1 

0.2

1 

0.2

1 

0.2

1

1

1

65,300

99,300

69,000

103,000

78,800

113,500

31,800

18,500

24,600

13
The locations of the field-surveyed cross sections are shown in figures 2-4. 

These cross sections and computed water-surface elevations for the various 

reaches are shown in figures 6-11. Limited resources dictated the number of 

field-surveyed cross sections. Additional intermediate cross sections 

required for computational purposes were synthesized from the field-surveyed 

data and topographic maps. The average velocities for the 100-year flood for 

the Little Missouri River are about 4.8 ft/s for the South Unit reach, 4.9 

ft/s for the Elkhorn Ranch Site reach, and 3.6 ft/s for the North Unit reach. 

The average velocities for the 500-year flood are about 0.2 ft/s higher than 

the average velocities for the 100-year flood. The average velocities for the 

100-year floods on the three creeks are about 7.8 ft/s for Knutson Creek, 4.6 

ft/s for Paddock Creek, and 6.6 ft/s for Squaw Creek. The flood profiles of 

the various reaches are shown in figures 12-17. The average water-surface 

slope for the floods on the Little Missouri River is about 0.0005 ft/ft, and 

the difference between the 100- and 500-year flood elevations averages about 

3.5 ft.

ICE JAMS

"An ice jam may be defined as an accumulation of ice in a stream which 

reduces the cross sectional area available to carry the flow and increase the 

water-surface elevation. The accumulation of ice is usually initiated at a 

natural or manmade obstruction or a relatively sudden change in channel slope, 

alignment, or cross section shape or depth. In northern regions of the United 

States, where rivers can develop relatively thick ice covers during the 

winter, ice jamming can contribute significantly to flood hazards. When 

historical records are examined, ice jams are typically found to occur in the 

same locations. This is because the necessary conditions for genesis of an 

adequate ice supply and obstruction of its downstream transport determine the 

specific areas where ice jams will occur." (Federal Emergency Management 

Agency, 1982, p. A 3-1).

An analysis of ice jams is subjective. The Little Missouri River at 

Medora (06336000) and the Little Missouri River near Watford City (06337000) 

are the only streamflow stations having data available for analysis. The 

backwater due to ice versus the water-surface elevations for discharge 

measurements was plotted for these two stations (fig. 18). All discharge 

measurements for the Little Missouri River at Medora (06336000) were used to 

develop a maximum observed backwater envelope curve. Cross section C-C' of 

the Little Missouri River, South Unit reach, is located at this site. From 

September 1934 to October 1959, the streamflow station Little Missouri River 

near Watford City (06337000) was located about 1 mi upstream from its present 

location. Only the measurements made during that period were used to develop 

a maximum observed backwater envelope curve. Cross section AA-AA 1 of the 

Little Missouri River, North Unit reach, is located about 200 ft upstream from 

this site. A maximum observed backwater envelope curve was not developed for 

the present streamflow-station location because of the lack of high-flow 

measurements.

Although the curves represent only maximum observed backwater and the 

number of measurements decreases at higher flows, the curves represent a trend

14
A1

2280

2270

2260

2250 -

2240

I 7

500-YEAR FLOOD ELEVATION (2276.1 FEET)

100-YEAR FLOOD ELEVATION (2271.9 FEET)

0 200 400 600 800 1000 1200 1400 1600 1BOO 2000

DISTANCE, IN FEET

LJ

<

Ul

Ul

O 

CD

LJ 

LJ

z 

o

1

B'

2280

2270

2260 -

2250 -

2240

500-YEAR FLOOD ELEVATION (2274.6 FEET) 

100-YEAR FLOOD ELEVATION (2270.7 FEET)

200 400 600 BOO

DISTANCE, IN FEET

2280

2270

2260

2250

2240

C'

/ / / rv / / / /\/ / / /,

RAILROAD IRID6C STRINGERS ,,500-YEAR FLOOD ELEVATION (2273.6 FEET) 

,100-YEAR FLOOD ELEVATION (2269.8 FEET)

VERTICAL LINES WITHIN 

SECTION ARE BRIDGE PIERS

0 200 400 600

DISTANCE, IN FEET

Figure 6. Cross sections A-A' through L-L' and water-surface elevations for 100- and 

500-year floods. Little Missouri River, South Unit reach.

15
D'

2280

2270

2260

2250

2240

I l 

UEOORA BRIDGE STRINGERS

/

V/////////7T7A/

500-YEAR FLOOD ELEVATION (2272.0 FEET) 

100-YEAR FLOOD ELEVATION (2268.4 FEET)

VERTICAL LINES WITHIN 

SECTION ARE BRIDGE PIERS

0 200 400 600

DISTANCE, IN FEET

a

UI 

O

o 

m

ui ui

E'

2280

2270

2260

2250

2240

MO-YEA.R FLOOD ELEVATION f??7l.« FEETi

100-YEAR FLOOD ELEVATION (2267.J FUT)

\

-800 -600 -400 -200

UI

0 200 400 600

DISTANCE, IN FEET

BOO tOOO 1200

izou 

2270 

2260 

2250 

it AH

/////////I/////1 ////, 

INTERSTATE 14 BRIDGE STRINGERS

t

T

L. ' 

\

\

. **

N

7__^---

*

500-YEAR FLOOD ELEVATION (2265.5 FEET) 

tOO-YEAR FLOOD ELEVATION (2262.2 FEET)

VERTICAL LINES WITHIN 

SECTION ARE BRIDGE PIERS

200 400 600 BOO

DISTANCE. IN FEET

Figure 6. Cross sections A-A' through L-L' and water-surface elevations for 100- and 

500-year floods. Little Missouri River, South Unit reach Continued.

16
G'

2270

2260

2250

2240

2230

500-YEAR FLOOD ELEVATION (22*1.7 FEET)

100-YEAR FLOOD ELEVATION (2256.1 FEET)

-1000 -800 -COO -400 -200 0 200 400 BOO BOO 1000 1200 1400

DISTANCE, IN FEET

UJ

>

<

UJ 

V) 

UJ

o 

m

UJ

u.

z 

g

ILJ 

LJ

H

2270

2260

2250

2240

2230

500-YEAR FLOOD ELEVATION (2251.S FEET)

100-YEAR FLOOD ELEVATION (2255.7 FEET)

H'

-600 -400 -200 0 200 400 600

DISTANCE, IN FEET

BOO 1000 1200

2270

2260

2250

2240

2230

500-YEAR FLOOD ELEVATION (2257.2 FEET)

100-YEAR FLOOD ELEVATION (2253.4 FEET)

-400 -200 200 400 600 800 1000 1200 1400 1600 1800

DISTANCE. IN FEET

Figure 6. Cross sections A-A' through L-L' and water-surface elevations for 100- and 

500-year floods. Little Missouri River, South Unit reach Continued.

17
J'

2260

22SO

2240 -

2230 -

2220

MO-YEAR FLOOD ELEVATION Q2»t.4 rctT) 7

-1000 -800 -tOO -400 -200 0 200 400 tOO 100

DISTANCE, IN FEET

UJ 

LJ

o ffi

UJ 

UJ

O

I

yUJ

K'

2260

2250

2240

2230

2220

-400 -200

MO-YEAR FLOOD ELEVATION (2252.4 FEET) 

100-YEAR FLOOD ELEVATION (2248.S FEET)

200 400 §00 aoo tooo 1200 MOO 

DISTANCE, IN FEET

L'

2260

2250

2240

2230

2220

50Q-YCAR FLOOD ELEVATION (2250.5 FEET)

100-YEAR FLOOD ELEVATION (2241.7 FEET)

-1600 -1400 -1200 -1000 -800 -600 -400 -200 0

DISTANCE, IN FEET

200 400 600

Figure 6. Cross sections A-A' through L-L' and water-surface elevations for 100- and 

500-year floods. Little Missouri River, South Unit reach Continued.

18
M

M'

2275

2270

2265

2260

2255

2250

100-YEAR FLOOD ELEVATION (2211.9 FEET)

300 400 500 600 700 800 900 1000 1100 1200 1300

DISTANCE, IN FEET

N'

Ld

< 

Ld

UJ

O 

CD

IUJ

2265

2260

2255

2250

2245

2240

I \ I l I I 

100-YEAR FLOOD ELEVATION (2211.9 FEET)

100 200 300 400 500 600 700

DISTANCE. IN FEET

0'

2265

2260

2255

2250

2245

2240

I I I T

100-YEAR FLOOD ELEVATION (22»t.« FEET)

-100 0 100 200 300 400 500

DISTANCE, IN FEET

Figure 7. Cross sections M-M' through O-O' and water-surface elevations for 100-year 

flood, Knutson Creek reach.

19
2270

22fO -

2250 -

2240 -

2250

ttO-YKA« ruOOO CUVATION (22M.4 rVCYj ^L

-100 0 100 200 500 400

DISTANCE. IN FEET

Ul 

Ul

<

Ul 

V)

Ul

O 

ffi

Ul 

Ul

Ul 

Ul

2270

2210

2250

2240

2250

-200 -100

Q'

100-YCAR riOOO ELEVATION (2257.7 ftCT)

100 200 500 400 500 COO

DISTANCE. IN FEET

700 BOO 900 1000

22CO

2250

2240

R 1

I I i I l 

tOO-YEAR riDOD ELEVATION (2251.0

2250

-1000 -tOO -BOO -700 -COO -500 -400 -500 -200 -100 0

DISTANCE. IN FEET

100 200

Figure 8. Cross sections P-P' through R-R' and water-surface elevations for 100-year 

flood, Paddock Creek reach.

20
2150

2140

2130

2120

UJ

a

Ul

> 

o

00

2110

MO-YEAR FLOOD ELEVATION (2U8.1 FEET)

IQQ-YEXft FLOOD ELEVAT10M (2134.S FEET)

S'

-400 -200 200 400 fOO 100 1000 1200

DISTANCE, IN FEET

1400 1*00 1800 2000

UJ 

UJ

 z. 

o

I

a

UJ

2140

21SO

2120

2110

500-YEAR FLOOD ELEVATION (21S5.I FEET)

200 400 fOO 800 1000

DISTANCE, IN FEET

1200 1400

Figure 9. Cross sections S-S' through V-V and water-surface elevations for 100- and 500-year 

floods. Little Missouri River, Elkhorn Ranch Site reach.

21
2140

2130

2120

> 

UJ

UJ

> 

o ffi

2110

I I I I I T 

500-YEAR FLOOD ELEVATION (2134.5 FEET)

100-YEAR FLOOD ELEVATION (2131.1 FEET)

U'

-BOO -SOO -400 -200 0 200 400 SOO

DISTANCE, IN FEET

800 1000 1200 1400

Ul

2140

2130

2120

2110

2100

I i i i i r

MO-YEAR FLOOD ELEVATION (2132.J FEET)

100-YEAR FLOOD ELEVATION (212J.O FEET)

-200 200 400 SOO 800

DISTANCE, IN FEET

1000 1200

Figure 9. Cross sections S-S' through V-V and water-surface elevations for 100- and 500-year 

floods, Little Missouri River, Elkhorn Ranch Site reach Continued.

22
13A31 V3S 3A08V 133J Nl 'NOLLVA313

Figure 10. Cross sections W-W through CC-CC' and water-surface elevations for 100- 

and 500-year floods, Little Missouri River, North Unit reach.

23
M

M

13A31 V3S 3A08V 133J Nl 'NOI1VA313

Figure 10. Cross sections W-W through CC-CC' and water-surface elevations for 100- 

and 500-year floods. Little Missouri River, North Unit reach Continued.

24
AA

1970 

1960 

1950 

1940

1 1 1 1 1 1 1 1 1 

500-YEAR FLOOD ELEVATION (1958.2 FEET)

100 -YEAR FLOOD ELEVATION (1954.3 FEET)

1 1 

/

1930 1 1 1 1 1 1 ________ 

I

0 200 400 600 800 1000 1200 1400 1600 1800 20

AA1

DISTANCE, IN FEET

UJ

>

UJ

>

O

m

UJ 

UJ

UJ _l

UJ

BB

I960

1950

1940

1930

tatn

\

1 1 1 1 1 1 1 

500-YEAR FLOOD ELEVATION (1952.7 FEET)

_ ^~~~ ~- -^400-YEAR FLOOD ELEVATI ^^"

-

ON (194B.B FEET) _

-

^ 1 -

1 1 1 1 1 1 1

BB'

200 400 600 800 1000 1200

DISTANCE, IN FEET

1400 1600

CC'

1950

500-YEAR FLOOD ELEVATION (1951.0 FEET) 

100-YEAR FLOOD ELEVATION (1947.4 FEET)

VERTICAL LINES WITHIN 

SECTION ARE BRIDGE PIERS 1940 -

1930 -

1920

800 1000 1200 1400 1600

DISTANCE, IN FEET

Figure 10. Cross sections W-W through CC-CC' and water-surface elevations for 100- 

and 500-year floods, Little Missouri River, North Unit reach Continued.

25
1980 100-YEAR FLOOD ELEVATION (1979.9 FEET)

1975

1970 -

1965

100 200 300 400 500 600

DISTANCE, IN FEET

700 800

Ul

O

CO

Ul 

Ul

u.

Ul

EE1

1970 -

1965 -

1960

 100-YEAR FLOOD ELEVATION (1977.8 FEET)

100 200 300 400 500 600

DISTANCE, IN FEET

FF

1980

FF'

1975

1970

1965

1960

1955

100-YEAR FLOOD ELEVATION (1974.6 FECT)

100 200 300 400 500 600

DISTANCE, IN FEET

Figure 11. Cross sections DD-DD' through FF-FF' and water-surface elevations for 

100-year flood, Squaw Creek reach.

26
2280

bJ 

bJ

bJ 

(/)

LJ

o

CD

LJ 

LJ

LJ 

LJ

2270 -

2260 -

2250 -

2240 -

2230 -

2220

10.000 20.000 30,000

DISTANCE, IN FEET

40,000 50.000

Figure 12. Profiles for 100- and 500-year floods and streambed, Little Missouri 

River, South Unit reach.

27
2270

Ul

Ul 

(Si 

Ul

>

O 

m

2260

ui ui 

u.

 2250 z"

O

1ui _j

Ul

2240

CROSS 

SECTIONS

1000 2000

DISTANCE, IN FEET

3000

Figure 13. Profiles for 100-year flood and streambed, 

Knutson Creek reach.

2260

ui

Ul 

V)

UJ 2250 

O

m

ui

Ul

 2240 z"

O

1

u.

Ul

2230

FV.OOO

CROSS a 

SECTIONS

 " ^ZZZZZZZZZZ

1000 2000 3000

DISTANCE, IN FEET

4000

Figure 14. Profiles for 100-year flood and streambed. Paddock Creek reach.

28
UJ 

LJ

UJ

(/)

UJ

O

00

UJ

_J 

UJ

2140

2130

2120

*f

\

2110

2100

CROSS 

SECTIONS

2000 4000 6000

DISTANCE, IN FEET

8000 10000

Figure 15. Profiles for 100- and 500-year floods and streambed. Little Missouri River, 

Elkhorn Ranch Site reach.

29
1980

Ld 

LJ

t/)

LU

O 

CD

bJ

1970 -

1960 -

1950 -

1940

1930 -

1920

10.000 20,000 30.000

DISTANCE, IN FEET

40.000 50.000

Figure 16. Profiles for 100- and 500-year floods and streambed. Little Missouri River, 

North Unit reach.

30
1980

LJ 

LJ

LJ 

V)

LJ 

>

o

CD

LJ 

LJ

2

«t

2 

O 

hLJ 

LJ

1970

1960

1950

500 1000

DISTANCE. IN FEET

1500

Figure 17. Profiles for 100-year flood and streambed, Squaw Creek reach.

31
UJ

LITTLE MISSOURI RIVER AT 

MEDORA (06336000)

Ld 

O

2257 2259 2261 2283 2285 2267 2269

ELEVATION, IN FEET ABOVE SEA LEVEL

O

a:

LdI

o

CD

LITTLE MISSOURI RIVER NEAR WATFORD CITY (06337000)

/OLD GAGE LOCATION ABOUlA 

1 MILE UPSTREAM FROM ^PRESENT SITE )

1938 1940 1942 1944 1946 1948 1950 1952

ELEVATION, IN FEET ABOVE SEA LEVEL

1954

Figure 18. Relation between backwater due to ice and water-surface elevations, 

and an envelope curve.

32
in which the backwater decreases as the discharge increases. For both 

streamflow stations, the backwater due to ice approaches zero before reaching 

the elevation computed in the step-backwater computations for the 100-year 

flood discharge.

The water-surface elevation of a flood causes the most concern whether or 

not the elevations are during an ice jam or free flow. Elevation frequencies 

for areas subject to ice-jam flooding can be based on the development of 

elevation-frequency relationships for two different populations (ice-jam flood 

elevations and free-flow flood elevations when adequate data are available). 

These relations can be combined into a single composite curve for flood 

elevation at a site under study. Because a combined frequency is needed, 

separating the annual maximum water-surface elevations into values for ice-jam 

and free-flow conditions, developing separate elevation frequencies, and 

then combining the two frequencies is not warranted. Therefore, a single 

elevation-frequency curve was developed by assigning Weibull plotting 

positions to both ice-jam and free-flow elevations and fitting a curve to 

these points on log-normal probability paper.

All of the annual maximum water-surface elevations (table 1) for the 

streamflow station Little Missouri River at Medora (06336000) were used to 

develop an elevation-frequency curve (fig. 19) for that site. Only the 

annual maximum water-surface elevations prior to October 1959 (table 2) for 

the streamflow station Little Missouri River near Watford City (06337000) 

were used to develop a curve (fig. 19) for that site. The Weibull plotting 

position was used to plot the elevations and the graphical method was used 

to fit a curve to the points. Caution must be exercised when comparing the 

elevations from the elevation-frequency curve to elevations associated with 

the flood discharges (figs. 6 and 10) because: (1) The graphical method 

requires no assumptions as to the type or characteristics of the distribution, 

and (2) only 20 years of elevation record were used to compute the elevationfrequency curve compared to 48 years of discharge record used to compute the 

discharge-frequency curve for the streamflow station Little Missouri River 

near Watford City (06337000). Because ice jams normally are location 

oriented, these ice-jam analyses apply to the specific location of the streamflow stations.

FLOOD-HAZARD ASSESSMENT

Flooding from the Little Missouri River and the three creeks causes a 

hazard to persons and property. The flood hazard of the Little Missouri River 

alone is very different from that of the three creeks. The Little Missouri 

River has a relatively large drainage basin and the threat of a flood may be 

known days in advance. The velocity of flood flows in the flood plain is considerably less than that in the main channel. In contrast, flooding from the 

three creeks most likely will be caused by intense, localized thunderstorms, 

and the threat of a flood may be known only hours in advance. The flood water 

will fill the flood plain of the creek and will flow at fast velocities. Once 

the flood water of a creek reaches the flood plain of the Little Missouri 

River, the water will spread out, reducing the velocities and depths.

33
2290

2280-

LITTLE MISSOURI RIVER AT MEDORA 

(06336000)

70 60 50 40 30 20 10 5 21 0.5 0.2 0.1 

EXCEEDANCE PROBABILITY, IN PERCENT

EXPLANATION 

 FREQUENCY CURVE

1980

1970

O

ILJ 

_J 

UJ 

LJJ 

O

2 1960 

CC

CO

CC 1950

LJJ

I1940

OBSERVED ANNUAL PEAKS

193C

LITTLE MISSOURI RIVER

NEAR WATFORD CITY

(06337000)

70 60 50 40 30 20 10 5 21 0.5 0.2 0.1 

EXCEEDANCE PROBABILITY, IN PERCENT

Figure 19. Water-surface elevation-frequency curves.

34
SUMMARY

Flood analyses were performed on selected reaches along the Little 

Missouri River and its tributaries (Knutson, Paddock, and Squaw Creeks). 

Streamflow records were used in the flood flow frequency analysis for the 

Little Missouri River. The 100-year flood discharge determined for the Little 

Missouri River South Unit reach was 65,300 ft^/s; the discharge determined for 

the Little Missouri River Elkhorn Ranch Site reach was 69,000 ft^/s; and the 

discharge determined for the Little Missouri River North Unit reach was 78,800 

ft^/s. A multiple-regression equation based on drainage area and infiltration 

index was used in the flood flow frequency analysis for the creeks. The 

100-year flood discharge determined for Knutson Creek reach was 31,800 ft^/s; 

the discharge determined for Paddock Creek reach was 18,500 ft^/s; and the 

discharge determined for Squaw Creek reach was 24,600 ft^/s. Cross-sectional 

data were obtained by field surveys. Water-surface elevations were computed 

using step-backwater methods.

Streamflow records for two stations on the Little Missouri River were used 

to develop maximum observed backwater envelope curves and elevation frequency 

curves. The maximum observed backwater envelope curves show a trend in which 

the backwater decreases as the discharge increases. The backwater due to ice 

approaches zero before reaching the computed elevations for the 100-year 

discharges.

35
REFERENCES

Barnes, H. H., Jr., 1967, Roughness characteristics of natural channels: U.S. 

Geological Survey Water-supply Paper 1849, 213 p.

Bluemle, J. P., 1977, The face of North Dakota, the geologic story: North 

Dakota Geological Survey Educational Series 11, 73 p.

Federal Emergency Management Agency, 1982, Guidelines and specifications for 

study contractors: Washington, D.C., 132 p.

Shearman, J. O., 1976, Computer applications for step-backwater and floodway 

analyses: U.S. Geological Survey Open-File Report 76-499, 103 p.

U.S. Geological Survey, 1982, Guidelines for determining flood flow frequency: 

Interagency Advisory Committee on Water Data, Office of Water Data 

Coordination, 28 p.

36