HYDROLOGIC AND GEOMORPHIC 

STUDIES OF THE 

PLATTE RIVER BASIN
Hydrologic and Geomorphic 

Studies of the 

Platte River Basin

GEOLOGICAL SURVEY PROFESSIONAL PAPER 1277

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1983
UNITED STATES DEPARTMENT OF THE INTERIOR 

JAMES G. WATT, Secretary

GEOLOGICAL SURVEY 

Dallas L. Peck, Director

Library of Congress Cataloging in Publication Data

United States. Geological Survey.

Main entry under title:

Hydrologic and geomorphic studies of the Platte River basin.

(Geological Survey Professional Paper ; 1277)

Bibliography: 258 p.

Supt. of Docs. No.: I 19.16:1277-A

Contents: Hydrologic and morphologic changes in the channels of the Platte River basin, a historical perspective/by T. R. Eschner, 

R. F. Hadley, and K.D. Crowley Effects of water development on surface-water hydrology, Platte River basin in Colorado, Wyoming, and Nebraska upstream from Duncan, Nebraska/by J. E. Kircher and M. R. Karlinger Hydraulic geometry of the Platte 

River near Overton, south-central Nebraska, by T. R. Eschner [etc.]

1. Hydrology Nebraska Platte river Watershed Addresses, essays, lectures. 2. Geomorphology Nebraska Platte River 

Watershed Addresses, essays, lectures. 3. Hydrology North Platte River Watershed Addresses, essays, lectures. 4. 

Geomorphology North Platte River Watershed Addresses, essays, lectures. 5. Hydrology South Platte River Watershed (Colo. 

and Neb.) Addresses, essays, lectures. 6. Geomorphology South Platte River Watershed (Colo. and Neb.) Addresses, essays, 

lectures.

I. Geological Survey (U.S.) II. Series.

CB705.N2H93 1983 551.48'3'09782 83-600013

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

Washington, D.C. 20402
PREFACE

The channels of the Platte River and its major tributaries, the South Platte 

and North Platte Rivers in Colorado, Wyoming, and Nebraska, have undergone 

major changes in hydrologic regime and morphology since about 1860, when the 

water resources of the basin began to be developed for agricultural, municipal, 

and industrial uses. These water uses have continued to increase with growth in 

population and land development. Diversion of flow from channels, storage of 

water in reservoirs, and increased use of ground water have affected the distribution and timing of streamflows and the transport of fluvial sediments. All 

these factors have contributed to changes in channel geometry and the riverine 

environment.

In 1979, the U.S. Geological Survey began investigations in the Platte River 

basin to determine the effects of water use on the hydrology and morphology of 

the Platte River and its major tributaries. These investigations also considered 

the relationship of hydrologic regime to factors that control or affect the habitat 

of migratory waterfowl in the Platte River valley.

This volume brings together the results of several research studies on historical changes in channel morphology, surface-water hydrology, hydraulic 

geometry, sediment-transport and bedform processes, ground-water and 

surface-water relations, stochastic models of streamflow and precipitation, and 

methods for estimating discharge required to maintain channel width. In each of 

the studies, data on some segment of the Platte River hydrologic system were 

collected and interpreted. All the studies are interrelated; together they provide 

some degree of understanding of regime changes that are occurring. The hydrologic research described in the following chapters will be useful in decisionmaking pertaining to the management of water resources and migratory waterfowl habitats.
IV CONTENTS

TABLES

Page

TABLE 1. History of canal construction in the Platte River basin, 1851-1930 A4

2. History of reservoir capacity in the Platte River basin 5

3. Channel widths of the Platte River, Nebraska, in downstream order, measured from General Land Office maps (1860) and

aerial photographs (1938-1979) 31

4. Data for channel width, braiding index, and sinuosity index for the North Platte River 38

5. Data for channel width, braiding index, and sinuosity for the South Platte River 38
CONTENTS

[Letters designate the chapters]

(A) Hydrologic and morphologic changes in channels of the Platte River basin in Colorado, Wyoming, and Nebraska: A historical perspective, by T. R. Eschner, R. F. Hadley, and 

K. D. Crowley.

(B) Effects of water development on surface-water hydrology, Platte River basin in Colorado, 

Wyoming, and Nebraska upstream from Duncan, Nebraska, by J. E. Kircher and 

M. R. Karlinger.

(C) Hydraulic geometry of the Platte River near Overton, south-central Nebraska, by T. R. Eschner.

(D) Interpretation of sediment data for the South Platte River in Colorado and Nebraska, and 

the North Platte and Platte Rivers in Nebraska, by J. E. Kircher.

(E) Relation of channel-width maintenance to sediment transport and river morphology: Platte 

River, south-central Nebraska, by M. R. Karlinger, T. R., Eschner, R. F. Hadley, and 

J. E. Kircher.

(F) A stochastic streamflow model and precipitation model for the Platte River from Gothenburg 

to Grand Island, Nebraska, by A. V. Vecchia, Jr.

(G) Simulated hydrologic effects of possible ground-water and surface-water management alternatives in and near the Platte River, south-central Nebraska, by A. W. Burns.

(H) Ground-water hydrology of the Mormon Island Crane Meadows wildlife area near Grand Island, 

Hall County, Nebraska, by R. T. Hurr.

Hydrologic and Morphologic 

Changes in Channels of the 

Platte River Basin in 

Colorado, Wyoming, and Nebraska: 

A Historical Perspective

By THOMAS R. ESCHNER, RICHARD F. HADLEY, and KEVIN D. CROWLEY 

HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

GEOLOGICAL SURVEY PROFESSIONAL PAPER 127 7-A

UNITED STATES GOVERNMENT PRINTING OFFICE, W AS H I NGTON : 1 983

CONTENTS

Abstract 

Introduction 

Acknowledgments 

Description of the area 

Development of irrigation in the Platte River basin 

South Platte River and tributaries 

North Platte River and tributaries - 

Platte River valley 

Effects of water development on hydrology 

Presettlement hydrology 

Floods 

Low flows 

Postsettlement hydrology 

Surface water 

Surface-water - ground-water relationships

Page

Al

1

2

2

2

3

5

8

8

8

9

9

10

10

10

	Page

Effects of changes in hydrology on the channel A13 

Presettlement channel and valley-floor characteristics 13 

Channel width 13 

Channel depth 13 

Bed material and bed forms 13 

Islands 14 

Vegetation 14 

Summary of presettlement characteristics 15 

Changes in Platte River morphology 15 

Changes in North Platte and South Platte River morphology 31 

Relationship of discharge regulation to channel change 31 

Processes of width reduction 32 

Some implications of future water development 34 

References cited 35

ILLUSTRATIONS

Page

FIGURE 1. Map of the Platte River in Colorado, Wyoming, and Nebraska A3

2. Cumulative usable storage in reservoirs in the Platte River basin 6

3. Historical total yearly imports of water to the South Platte River basin since 1895 7

4. Map showing location of modern and historic sites in the Platte River valley 9

5. Flow-duration curves for 10-year periods, Platte River near Overton, Nebraska 12 

6-10. Maps of channel of the Platte River near.

6. Cozad, Nebraska, in sections 25, 26, 35, and 36, T. 10 N., R. 23 W., section 31, T. 10 N., R. 22 W., and section 6,

T. 9 N., R. 22 W., in (a) 1860, (b) 1938, and (c) 1979 16

7. Kearney, Nebraska, in sections 7, 8,9,16,17, and 18, T. 8 N., R. 16 W., and sections 12 and 13, T. 8 N., R. 17 W.,

in (a) 1938, (b) 1957, and (c) 1979 19

8. Grand Island, Nebraska, in sections 1, 2,10,11,12, and 15, T. 11 N., R. 8 W., and section 36, T. 12 N., R. 8 W., in

(a) 1938 and (b) 1979 22

9. Duncan, Nebraska, in sections 3,4,8,9,10,16, and 17, T. 16 N., R. 1 W., in (a) 1860, (b) 1941, and (c) 1978 25

10. Ashland, Nebraska, in sections 15,16,17,18,19,20, and 21, T. 12 N., R. 11 E., in (a) 1941 and (b) 1971 28

11. Graph of at-a-station changes of channel width of the Platte River, Nebraska, with time 30

12. Graph of downstream changes in the percentage of 1860 channel width occupied by the channel in 1938-1941,

1957-1959,1969-1971, and 1978-1979 32 

13-16. Photographs of the Platte River

13. South of Lexington, Nebraska, facing toward the north, taken about 1910 33

14. Near the present site of Cozad, Nebraska, from the south bank toward the northwest, taken in (a) 1866 and

(b) 1979. 34

15. South of Kearney, Nebraska, from the south bank toward the north, taken (a) between 1875 and 1880 and (b) in

1981 36

16. Near Ashland, Nebraska, from the south bank toward the northeast, taken in (a) 1897 and (b) 1982 37

in

HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

HYDROLOGIC AND MORPHOLOGIC CHANGES IN CHANNELS OF THE 

PLATTE RIVER BASIN IN COLORADO, WYOMING, AND NEBRASKA:

A HISTORICAL PERSPECTIVE

By THOMAS R. ESCHNER, RICHARD F. HADLEY, and KEVIN D. CROWLEY

ABSTRACT

The channels of the Platte River and its major tributaries, the 

South Platte and North Platte Rivers in Colorado, Wyoming, and 

Nebraska, have undergone major changes in hydrologic regime and 

morphology since 1860. These changes are attributed here to 

agricultural, municipal, and industrial water use.

Although water-resource development varied temporally 

throughout the basin, the history of development along the Platte 

River and tributaries followed four stages: (1) Construction of small, 

crude ditches to irrigate flood plains; (2) constuction of larger canals 

to irrigate bench lands; (3) construction of reservoirs to store 

snowmelt runoff; and (4) accelerated development of ground-water 

resources. Despite differences in rates of development, diversion and 

storage of water for irrigation, municipal, and industrial use have 

changed streamflow patterns throughout the basin. At some stations, significant changes in flood peaks, annual mean discharges, and 

shapes of flow-duration curves have been recorded.

Changes in streamflow patterns are manifested by changes in appearance of channels of the Platte River. Prior to water development 

in the 19th century, the Platte was a wide (~2- kilometer), shallow 

(1.8- to 2.4-meter) river characterized by bankfull spring flows and 

low summer flows. Although timber generally was scarce in the 

valley, the Platte channels contained hundreds of small, timbered 

islands. Since development, the channels have changed radically. A 

comparison of surveyor's maps (General Land Office), drawn during 

the 1860's, with six sets of aerial photographs, taken between 1938 

and 1979, for six 5-kilometer reaches of the rivers shows that the 

channels have narrowed considerably above the confluence with the 

Loup River. Above the confluence with the Loup River, the width of 

the channels in 1979 ranged from 8 to 50 percent of the channel width 

in 1860, whereas below the confluence with the Loup River, the width 

of the river in 1979 was about 92 percent of the channel width in 1860. 

Above the confluence with the Loup River, width reduction has occurred by progressive encroachment of vegetation and consequent 

vertical and horizonatal accretion on sandbars in the channel. Vegetative encroachment on sandbars has occurred becaused (1) the present 

hydrologic regime provides more favorable conditions for germination and growth on sandbars, and (2) since development of the basin, 

flood peaks are no longer capable of scouring vegetation from the 

sandbars. Overbank flows evidently have become more common, 

probably because channel narrowing and vegetative encroachment 

have increased the hydraulic roughness of the channels. Moreover, 

the magnitude of low flows has increased and the days of no flows 

have decreased giving the channels a more perennial character.

INTRODUCTION

The Platte River and its tributaries in Colorado, 

Wyoming, and Nebraska (fig. 1) are typical of many 

Great Plains streams that originate in the Rocky Mountains. Much of the flow in the North Platte, South 

Platte, and Platte Rivers is derived from spring 

snowmelt in the mountains. Because the plains are 

semiarid to subhumid, most of the flow has been appropriated for irrigation of agricultural crops, municipal 

use, and industrial development. These rivers have been 

an integral part of the economy in the Platte River basin 

since the middle of the 19th century.

Migratory waterfowl also use the river and adjacent 

farmlands in the Platte River valley of central Nebraska 

during their .annual migration stopover in February and 

March. An estimated 70 to 80 percent of the world's 

lesser sandhill cranes and a small number of rare whooping cranes use the river valley between Overton and 

Grand Island, Nebraska, on their way to Canada and 

Siberia each year (Frith, 1974).

Concern for the habitat of sandhill cranes, whooping 

cranes, and other migratory-bird species prompted 

wildlife managers to document the changes that have 

occurred jn the river channels since settlement of the 

valley and the effects of these changes on wildlife 

habitat. In 1979, a study was begun in the Platte River 

basin that included hydrologic investigations by the 

U.S. Geological Survey. An integral part of these investigations is this review of the history of water development in the basin and the effects of water use and 

land use on the hydrology and morphology of the Platte 

River and its major tributaries. Site-specific investigations were centered on the critical migratory-bird 

habitat in a 96-km (kilometer) reach of the Platte River 

between Overton and Grand Island, in south-central 

Nebraska This paper presents an overview of the channel changes along the Platte River.

Al
A2 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

ACKNOWLEDGMENTS

The historical information in this report was excerpted from emigrant journals, expedition accounts, 

early photographs, and maps. The authors wish to 

thank the Grand Island, Nebraska Office of the U.S. 

Bureau of Reclamation; U.S. Geological Survey, Water 

Resources Division, Nebraska District; Burlington 

Northern Railroad; the Dawson County Historical 

Society; the Nebraska State Engineers Office; the 

Smithsonian Institution; and the Union Pacific 

Railroad for their assistance in locating maps, 

photographs, and river cross sections. Joseph Jeffrey, 

Norman Jeffrey, Emil Roeser, and personnel from the 

Colorado Historical Society, Denver Public Library, and 

Nebraska State Historical Society assisted in obtaining 

early descriptions of the Platte River valley. F. B. Shaffer provided unpublished information about reservoir 

capacity.

Carl F. Nordin, Jr. and Stanley A. Schumm read parts 

of an earlier manuscript. The manuscript was improved, 

both technically and editorially, by comments and suggestions in reviews by John E. Costa, Michael J. Ellis, 

William M. Kastner, and Garnett P. Williams. In addition, Garnett P. Williams provided many thoughtprovoking discussions. The sequence of tracings of 

maps and aerial photographs were prepared by Kenneth 

B. Rennick. Part of this research was conducted by the 

senior author while he was funded by a National Science 

Foundation grant.

DESCRIPTION OF THE AREA

The Platte River and its major tributaries, the North 

Platte and South Platte Rivers, have a drainage area of 

about 222,740 km2 (square kilometers) in Colorado, 

Wyoming, and Nebraska. The North Platte River originates in the mountains of northern Colorado, flows 

northward into central Wyoming, then southeastward 

to Nebraska. In west-central Nebraska, the river joins 

the South Platte River to form the Platte River (fig. 1). 

The South Platte River originates in the mountains of 

central Colorado and flows northeastward across the 

eastern Colorado plains into Nebraska to meet the 

North Platte River (fig. 1).

Most of the flow in the Platte River system above the 

Loup River is derived from spring snowmelt in the 

Rocky Mountains. Precipitation on the Great Plains, 

which ranges from 330 to 635 mm (millimeters), contributes additional water to the channels. Irrigation of 

agricultural lands is the major water use in the basin; 

surface water is stored in reservoirs and diverted from 

channels to canals for irrigation, for municipal use, for

power generation. Ground water is developed extensively in the basin.

DEVELOPMENT OF IRRIGATION IN THE 

PLATTE RIVER BASIN

Development of irrigation in the Platte River basin 

has had significant effects on the hydrology of the river. 

Not all of these effects have been documented owing to 

a lack of long-term hydrologic records. The earliest 

streamflow records date from 1891. Systematic flow 

records date from 1930. To understand the changes in 

hydrology that occurred prior to 1930, the history of 

irrigation development in the basin is reconstructed 

from records of canal construction and other available 

information.

Although irrigation development varied temporally 

throughout the basin, the history of development along 

the Platte River and tributaries followed four general 

stages. Each stage produced a different effect on river 

hydrology. The first stage represents the earliest period 

of irrigation. It was characterized by construction of 

small, crude ditches to irrigate irregular patches of land 

on the flood plains. The second stage was characterized 

by construction of larger and more sophisticted canals 

and ditches to irrigate lands on benches above the 

valley floor. The amount of water appropriated to these 

canals usually exceeded the summer flows of the river. 

Thus, canals with later water rights were unable to 

divert water during the irrigation season. Many canals 

were abandoned, and the number of new appropriations 

granted was reduced or eliminated.

The third stage was characterized by the construction 

of reservoirs to store water from snowmelt runoff. During this stage, many of the canals abandoned previously 

were reopened. Many new canals were constructed, and 

existing canals were enlarged. Summer flows were overappropriated during most of stage 3, and new claims for 

water each year exceeded the amount of water available 

in the basin. The fourth stage marked the end of canal 

construction in the basin. Dam construction continued, 

but at a slower pace, and water impounded above these 

structures was used to satisfy existing water rights and 

new municipal demands for water and power. New 

demands for irrigation water were satisfied with ground 

water; stage 4 marked the beginning of large-scale 

ground-water withdrawals in the basin.

Irrigation development has been documented in the 

reports of the State Engineers of Colorado, Nebraska, 

and Wyoming (State of Colorado, 1883/1884 to 1925/ 

1926; State of Nebraska, 1913/1914 to 1917/1918; State 

of Nebraska, 1919/1920 to 1931/1932; State of Wyoming, 1889-1931). Early record keeping was sporadic,
HYDROLOGIC AND MORPHOLOGIC CHANGES IN CHANNELS OF PLATTE RIVER BASIN A3

FIGURE 1. The Platte River basin in Colorado, Wyoming, and Nebraska.

and few diversion data are available prior to 1930. 

Water-right adjudication records (which list the date of 

appropriation for each canal, usually coincident with the 

date of construction or enlargement) and the amount of 

water appropriated to each canal can be used to infer in 

a qualitative sense when changes in streamflow occurred. For example, during a period when hundreds of 

canal appropriations were granted in the basin, more 

consumptive use of surface water would be expected. 

When streamflow became overappropriated, the 

number of new appropriations granted should decrease. 

Thus, canal-appropriation records should indicate: (1) 

When streamflow changes caused by canal diversions 

began; and (2) the approximate date when summer flows 

were overappropriated in the basin. Comparisons of adjudication and dam-construction records with several 

written reports of the State Engineers suggest that 

canal-construction activity can be used to indicate these 

changes.

Similarly, few storage data exist for most of the reservoirs that were constructed in the basin prior to 1910.

However, the date of closure and the usable storage 

capacity of each reservoir can be used to reconstruct 

stream flow trends. For example, the beginning of largescale reservoir construction in the basin probably marks 

the date of streamflow overappropriation. This date 

serves as a reliable check on the overappropriation date 

indicated by canal-appropriation records. Moreover, 

certain streamflow parameters, such as peak flows, are 

affected by reservoir construction.

SOUTH PLATTE RIVER AND TRIBUTARIES

The South Platte River and tributaries were the focus 

of the earliest and most extensive irrigation development in the Platte River basin. Irrigation in the basin 

was first practiced by Antoine Janis, who diverted 

water from the Cache la Poudre River 1838 (Steinel and 

Working, 1926) or 1844 (Rohwer, 1953). The first 

ditches were small and crude; irrigated lands were confined to the flood plain. Construction of the small canals
A4 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

proceeded at a slow pace until about 1860. Prior to 1860, 

28 appropriations were granted for canals in the South 

Platte River basin (table 1). The period 1840-1860 may 

be considered stage 1 in the development of irrigation in 

the South Platte River basin.

The initial impetus for large-scale development of 

irrigation was the influx of population at the time of the 

discovery of gold in the mountains west of Denver in 

1858. Water-right number one in the South Platte River 

basin dates from 1859 on Bear Creek (table 1). In the 

next decade, numerous small projects were begun and 

irrigation was important enough by 1861 that the legislature passed a law allowing landowners access to water 

whether or not their land was immediately adjacent to

the stream. The establishment of the Greeley Colony in

1870 marked the beginning of construction of large 

canals (McKinnon, 1952). This experiment demonstrated the potential value of bench or terrace land, and 

it may have served as a catalyst for the formation of 

other large canal companies. Beginning in 1874, corporations were formed to finance large-scale canal projects. A period of increased construction began that 

lasted until 1890. Between 1861 and 1870, 376 canals 

were constructed; 533 canals were constructed between

1871 and 1880, and 364 canals were constructed between 1881 and 1890 (table 1).

Appropriations granted to these canals exceeded the 

available water in the basin during the summer. HOWTABLE I. History of caned construction in the Platte River basin, 1851-19301

Number of new canals constructed or existing canals enlarged2

Date of 

earliest

River 1851-1860 1861-1870 1871-1880 1881-1890 1891-1900 1901-1910 1911-1920 1921-1930 canal

South Platte River basin

Cache la Poudre River and tributaries 

Lodgepole Creek and tributaries ..... 

Big Thompson River and tributaries . 

Bear Creek and tributaries .........

South Platte River and tributaries below mouth of the

37

0

32

22

85

31

29

4

37

75

6

3

1

28

0

0

46

26

8

3

14

10

3

7

7 1860

13 1873

2 1861

14 1859

32 1868

of the Cache la Poudre .........................

Total, South Platte basin ....................

25

28

264

376

323

533

139

364

6

63

104

313

52

141

28

96

1860

North Platte River basin

Big Laramie River and tributaries .................

North Platte River, Wyoming .....................

Tributaries to North Platte River, Wyoming, except

North Platte River and minor tributaries, Colorado ....

Total, North Platte basin ....................

0 

0 

0 

0 

0

0 

0

0

8 

0 

0 

0 

0

9 

0

17

98 

2 

0 

0 

2

91 

1

194

467 

43 

16 

19 

32

740 

310

1,627

148 

55 

36 

51 

15

410 

10

725

263 

117 

5 

30

47

801 

128

1,391

119 

46 

7 

24 

25

436 

75

732

29 

17 

1 

13 

17

161 

11

249

1868 

1880 

1888

1875 

1880

Platte River basin (except North and South Platte)

Platte River tributaries above the Loup River ........

Platte River above the Loup River .................

0 

0

0

0 

0

0

0 

0

0

1 

2

3

3

7

10

0 

0

0

6 

3

9

53 

16

69

1882

'Data compiled from Biennial Reports of the State Engineer of Colorado, 1883-1926; unpublished data from the files of the State Engineer of Colorado in Denver; Biennial Reports of the 

Department of Water Resources, Nebraska, 1913-1932; 2nd Annual Report of the Territorial Engineer, Wyoming, 1889; Biennial Reports of the State Engineer of Wyoming, 1893-1930; 

Tabulation of Adjudicated Water Rights, State of Wyoming, Water Division Number One, 1965.

*Numbers are based on appropriations to new canals or additional appropriations to existing canals exceeding 0.3 cubic meter per second.

'Based on recorded date of appropriation decree.
HYDROLOGIC AND MORPHOLOGIC CHANGES IN CHANNELS OF PLATTE RIVER BASIN A5

ever, it is difficult to pinpoint the exact year in which 

summer flows in the South Platte River basin were 

overappropriated, because development activity varied 

between the tributaries. For example, the earliest record 

of overappropriation occurred in the Cache la Poudre 

basin in 1876. Irrigation reports by the State Engineer 

of Colorado during the early 1880'5 indicate that most 

of the canals holding appropriation decrees received 

water during all but the driest years. By 1885, approximately 710 m3/s (cubic meters per second) were 

appropriated in the South Platte River basin (State of 

Colorado, 1886). Although not all canals granted appropriations were diverting water, summer flows were 

nevertheless overappropriated. Thus, overappropriation 

of summer flows in the South Platte River basin occurred between 1880 and 1885, marking the end of stage 

2.

Dams were built to increase available irrigation 

water. The earliest reservoirs impounded less than 

6.2 hm3 (cubic hectometers) in the basin in 1868. The 

dams were small structures built in natural depressions 

along or across small tributaries. Large-scale construction of dams in the basin began during the early 1880's 

(table 2). Canal-construction activity declined during 

the decade 1890-1900 (63 constructed) and increased 

again after 1900. Canal construction declined again 

after 1910. Construction of dams did not completely 

eliminate overappropriation of summer flows. In 

1911-1912, for example, only canals with appropriation 

decrees of 1882 or older received water during the 

highest flows in June. In the same years, new claims for 

water totaling 784 m3/s were made (State of Colorado, 

1914).

Although present storage is double that of 1912 (fig. 

2), only a minor amount of the increase has been for irrigation. Dam construction declined during the 1920's, increased slightly during the early 1930's, and declined 

afterward. Most of the reservoirs impounded after 1930 

were for new municipal water supplies and for flood control and recreation. Little canal-construction activity occurred after 1930. New demands for irrigation water

were satisfied with ground water. Thus, 1930 marks the 

end of stage 3 and the beginning of stage 4 in the South 

Platte River basin.

Diversion of surface water from the Colorado River 

basin and North Platte River basin provided additional 

water for the South Platte River basin. The earliest of 

these transbasin diversions was begun in the early 

1890's. Importation of water increased gradually from 

completion of the first structures to 1947, when the 

Alva B. Adams Tunnel, which imports water from the 

Colorado River basin, was completed. The large increase 

in imports of water after 1947 is shown in figure 3. 

Average annual diversions in 1974 totaled 460 hm3 

(Gerlek, 1977).

Use of ground water for irrigation dates from 1885, 

from an area near Eaton, Colorado (Rohwer, 1953). Extensive development of pump irrigation did not begin 

until 1910. The number of irrigation wells in the South 

Platte River basin increased slowly to a total of about 

735 by 1933. The drought years of the mid-1930's saw 

the number of wells almost triple, to 2,000. The use of 

ground water for irrigation has continued to increase in 

importance with time (Hurr, 1975).

NORTH PLATTE RIVER AND TRIBUTARIES

Irrigation development along the North Platte River 

and tributaries had an early history similar to that of 

the South Platte River basin. Irrigation was practiced 

in the vicinity of Fort Laramie as early as 1847 

(McKinley, 1938). Throughout the 1850's and 1860's, 

small-scale irrigation projects flourished near military 

outposts, commonly to provide produce for emigrants.

Unlike Colorado, Wyoming did not experience a 

mineral-exploration boom in the late 1850's; the dominant industries in Wyoming during this period were 

grazing and agriculture. Although canals were built to 

irrigate farmland, grazing land did not require irrigation 

water. Thus, canal construction proceeded slowly during the 1860's and early 1870's. The period 1850-1870

TABLE 2. History of reservoir capacity in the Platte River basin1

Basin

New usable storage, in cubic hectometers

1851-1860 1861-1870 1871-1880 1881-1890 1891-1900 1901-1910 1911-1920 1921-1930 1931-1940 1941-1950 1951-1960 1961-1970 1971-1980

South Platte River

North Platte River

Platte River above 

Loup River .......

0

0

0

0

0

0

8.7

0

0

142.2

0

0

167.5

11.6

0

535.3

1,408.0

0

102.6

97.7

0

0

79.2

0

186.5

1,646.8

53.9

118.3

2,402.9

0

76.0

969.9

0

0

0

0

539.0

0

0

'Data from Martin and Hanson, 1966; F. B. Schaffer, Conservation and Survey Division, University of Nebraska, written commun., 1979 (for reservoirs in excess of 6.2 cubic hectometers).
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HYDROLOGIC AND MORPHOLOGIC CHANGES IN CHANNELS OF PLATTE RIVER BASIN A7

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WATER YEAR

1950 1960 1970 1975

FIGURE 3. Historical total yearly imports of water to the South Platte River basin since 1895 (modified from Gerlek, 1977).

streams in the basin were overappropriated (State of 

Wyoming, 1889); by 1899, flows of the Laramie River 

were overappropriated (State of Wyoming, 1899); by 

1901, flows of Horse Creek and tributaries, Chugwater 

River and tributaries, Little Laramie River and 

tributaries, and upper North Platte River and 

tributaries in Colorado and Wyoming were overappropriated (State of Wyoming, 1902). Summer flows of 

the North Platte River in Nebraska were overappropriated sometime between 1914 and 1917 (State of 

Nebraska, 1914; State of Wyoming, 1918).

Flows of the North Platte Rivfer in Wyoming, below 

the mouth of the Sweetwater River, were not utilized 

until the construction of Pathfinder Dam in 1909 (fig. 2). 

The difficult terrain through which the river flowed offered few good sites for canal diversions, making the 

costs of diversion prohibitive. The Reclamation Act of 

1902 provided public funds with which canals could be

constructed along this section of the North Platte. 

Because of the lag in canal construction, overappropriation of summer flows in this section of the North Platte 

did not occur until much later than in the remainder of 

the basin. Overappropriation of summer flows in most 

of the North Platte River basin, however, occurred between 1900 and 1915. This period marks the end of 

stage 2 in the development of irrigation in the North 

Platte River basin.

Reservoir construction in the North Platte River 

basin began in 1892 (McKinley, 1938). The first reservoirs were natural lakes on the upper reaches of the 

tributaries that were modified to allow storage and 

release of water. In 1897, the Wyoming Development 

Company completed a reservoir on the Laramie River. 

By 1906, 27 small reservoirs, not listed in table 2, with 

combined storage capacities of 3.0 hm3, were operating 

in the basin (State of Wyoming, 1906).
A8 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

The impoundment of Pathfinder Reservoir marked 

the beginning of stage 3 in the development of irrigation 

in the North Platte River basin. A renewed construction 

of canals occurred with the construction of reservoirs. 

During the period 1901-1910, 1,391 canals were constructed; during the period 1911-1920, 732 canals were 

constructed; and during the period 1921-1930, 249 

canals were constructed. Canal construction declined 

after 1930. Dam construction for the purpose of irrigation in the North Platte River basin ended after 1939. 

The year 1939 marks the close of stage 3 in the development of irrigation in the North Platte River basin.

PLATTE RIVER VALLEY

Development of irrigation along the Platte River 

lagged behind that of the North Platte and South Platte 

Rivers, partly because of the unwillingness of landowners to identify their land with more arid lands to the 

west (McKinley, 1938), and partly because irrigation 

was not essential for production of marginally profitable crops (Lugn and Wenzel, 1938).

Irrigation apparently was practiced as early as 1856 

in the Platte River valley, near Wood River, about 18 

km east of Fort Kearny (Carlson, 1963). Additionally, 

small irrigation projects were attempted during the dry 

years from 1859 to 1864. The project most commonly 

cited as the beginning of irrigation in the Platte River 

basin was a canal dug by John Burke in the year 1864 

(Carlson, 1963) or 1866 (Willis, 1951), just east of North 

Platte. Little additional irrigation development occurred until 1882, when the Kearney canal was built for 

hydropower generation and irrigation. Further development occurred between 1891 and 1895, dry years in the 

Platte River valley, when six large canals were built on 

the Platte River between North Platte and Kearney. 

Between 1901 and 1930, one additional canal was constructed on the Platte River (1926), and several canals 

were constructed on the tributaries to the Platte River 

(table 1).

Construction of dams to supply canals on the Platte 

River did not result from overappropriation of flows on 

the river following canal construction. Rather, a shortage of water developed from the greater consumptive 

use of surface water upstream on the North Platte and 

South Platte Rivers. Three reservoirs, two of them offstream and Lake McConaughy on the North Platte with 

a combined usable storage capacity of 2,456 hm3, were 

built after 1930 to supply canals and provide power.

Unreliability of streamflow in the Platte River encouraged development of ground water for irrigation. 

There is some historical evidence of pumping of ground 

water for irrigation beginning in the late 1880's (Willis, 

1951), but this is not documented in the Platte River

basin until 1893 (Lugn and Wenzel, 1938). Development 

of pump irrigation was slow initially, but it increased 

steadily, particularly after 1910. Between 1911 and 

1920, 146 wells were constructed in the Platte River 

valley; between 1921 and 1930, 558 wells were constructed in the valley (Lugn and Wenzel, 1938). Most of 

the wells developed before 1930 were located west of 

Grand Island. The drought years of the 1930's hastened 

the development of ground-water irrigation, and its 

development continues to increase.

EFFECTS OF WATER DEVELOPMENT 

ON HYDROLOGY

PRESETTLEMENT HYDROLOGY

The Platte River valley served as a natural highway 

Unking the eastern part of the United States with the 

unexplored and unsettled west. The first reliable reports 

of the river were written during journeys up the valley 

in the early 19th century. The number of reports increased during the large migrations west that began in 

the early 1840's, the California Gold Rush migrations in 

the late 1840's and early 1850's, and the Pikes Peak 

Gold Rush migration in the late 1850's. Between 1800 

and 1860, a substantial number of observations were 

recorded regarding the geology, topography, geomorphology of the valley, and hydrology of the river.

Accounts written during early explorations of the 

Great Plains and Rocky Mountains by scientific expeditions, as discussed below, probably furnish the most 

reliable information about the river and valley. Location 

of historic sites and migration trails are shown in figure 

4. In most cases, these expeditions were commissioned 

for the purpose of observing and reporting on the lands 

and rivers of the region. Later accounts of the river and 

valley, written during westward migrations, probably 

are not as reliable. These accounts were written by 

travelers using the valley as a means of going west; 

their interest in the territory was secondary to the immediate task of surviving the journey. Usually, no attempts were made at systematic observation, and the 

prejudices of fellow travelers and travel guidebooks 

often were repeated in the journals. Movement of large 

numbers of settlers through the Platte River valley 

(estimated to be 350,000 persons between 1841 and 

1866 by Mattes, 1969) had a significant impact on the 

land. For example, timber, a scarce commodity in the 

valley before the first migrations, all but disappeared in 

many parts of the valley because of use by settlers and 

railroads.

The most notable expeditions that touched the Platte 

River valley were the Lewis and Clark Expedition in
HYDROLOGIC AND MORPHOLOGIC CHANGES IN CHANNELS OF PLATTE RIVER BASIN A9

EXPLANATION

 --- TRAILS

 MODERN TOWNS AND CITIES

 HISTORIC SITES

0 10 20 KILOMETERS

FIGURE 4. Location of modern and historic sites in the Platte River valley.

1804, the Long Expedition in 1820, the Fremont Expedition in 1842, and the Stansbury Expedition in 

1850-1851. Other notable explorations were the Stuart 

Exploration in 1812-1813, the Ashley-Smith Explorations in 1822-1829, and the Bonneville Exploration in 

1832. These and other accounts of the river and valley 

written during the period 1800-1860 by missionaries, 

trappers, naturalists, and settlers provide the first 

substantial historical description of the Platte River.

FLOODS

To clear the western passes before the first snowfall, 

travelers had to traverse the Platte River valley in the 

spring, during spring floods. Thus, most observations of 

the river were made during high flow. In approximately 

70 years of written records of early explorations of the 

valley, from about 1800 to the construction of railroads 

and the subsequent cessation of the great westward 

migrations in 1870, there are no accounts of oVerbank 

floods on the Platte River. In 1820, the Long Expedition (James, 1823) reported that the river was so wide 

and the banks so high that "the highest freshets pass 

off without inundating the bottoms, except in their lowest parts; the rise of the water, on such occasions, being 

no more than five or six feet." In 1849, Pritchard 

(Morgan, 1959, p. 63) wrote in his journal, that the 

banks of the Platte near Grand Island:

are low at this time (the river being high) [and] do not rise more than 

18 inches or two feet above the surface of the water. I judge that the 

bottoms at this point are rarely, if ever inundated * * *. Such is the 

breadth of the channel that an immense quantity of water would be 

required to raise it above its banks * * *.

The only observation of flooding in the Platte River 

basin was noted by Fremont (1845, p. 110), on the South 

Platte upstream of Bijou Creek, who wrote "On the 

evening of the 3rd (July) as we were journeying along 

the partially overflowed bottoms of the Platte * * *." 

The "bottoms" referred to in these accounts are probably the low, broken meadowlands that occur on either 

side of the river. These bottomlands usually contain 

abandoned channels, which, during high flow, may be 

filled with water from a rise in the ground-water table, 

rather than by overflow of the river. It is unclear from 

historical accounts, particularly the Fremont account, 

whether the bottomlands were inundated by overflow of 

the river or by a rise in the ground-water table.

LOW FLOWS

Because most of the travels along the Platte River 

valley occurred in the spring, few historical accounts exist of the river during low flow. Of particular interest is 

the behavior of the river between the junction of the 

North Platte and South Platte Rivers and the confluence with the Loup River (fig. 2). The Loup has a fairly
A10 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

constant discharge (Brice, 1964, p. 35); therefore, the 

Platte River below this confluence probably was a 

perennial stream. Little is known about low-flow 

behavior of the river above the confluence with the Loup 

prior to irrigation, about 1860. Miller (1978) concluded 

that prior to irrigation the Platte River above the junction of the Loup rarely, if ever, went dry in the summer. 

This conclusion is based primarily on indirect evidence, 

such as construction of canals along the Platte to divert 

water during the summer months.

Several observations of the Platte River during low 

flow are notable. Clarke (1902, p. 301) reported that "In 

the summer of 1863, the Platte having so nearly dried 

up as to make it difficult to secure water for cattle * * * 

We sank headless barrels in the Platte * * * to secure 

water from an underflow." Ware (1911, p. 41) noted that 

during the summer of 1864:

From Fort Kearney, for many miles up, there was no water in the 

river. The water seemed to be in "the underflow". We not infrequently 

rode down to the river, and with shovels dug watering places in the 

sand of the bed * * *. We were told that 75 miles of the river were 

then dry, and that generally about 125 miles of it were dry in the 

driest season * * *

The year 1864, however, apparently was not unusually dry. In 1864, Ward (in Root and Connelley, 1901) 

wrote of the "unprecedented flood of 1864." McKinley 

(1938) also reported the river to be unusually high during the spring of 1864.

Fremont (1845, p. 77), descending the North Platte 

River (Sept. 3,1845), wrote that the river was "merely a 

succession of sandbars, among which the channel was 

divided into rivulets a few inches deep." Upon reaching 

the Platte River, Fremont and his men constructed a 

bull boat which, when fully loaded with men and supplies, drew four inches of water; they attempted to 

navigate the river (Fremont, 1845, p. 78):

On the morning of the 15th [September] we embarked in our hide 

boat, Mr. Preuss and myself, with two men. We dragged her over the 

sands for three or four miles, then left her on a bar and abandoned entirely all further attempts to navigate this river * * *.

If the river did not go dry every summer, the flow 

became relatively insignificant, a "mere trickle of water 

among sandy shoals" (Ghent, 1929, p. 128). Between 

the junction of the North Platte and South Platte 

Rivers and the Loup River, the Platte may have gone 

dry during years of low precipitation and probably was 

reduced to a trickle in other years.

POSTSETTLEMENT HYDROLOGY 

SURFACE WATER

Diversion and storage of surface water for irrigation 

and hydropower generation have changed patterns of

streamflow in some reaches in the Platte River basin. 

At some stations changes in flood peaks, annual mean 

discharge, and the shape of flow-duration curves have 

been recorded. These changes are not found uniformly 

throughout the Platte River basin, because development of water resources has progressed differently 

along the North Platte, South Platte, and Platte Rivers.

Construction of large onstream reservoirs in Wyoming and Nebraska has decreased peak flows of the 

North Platte River. Four gaging stations on the North 

Platte River with long periods of record show that peak 

discharge decreased progressively after the closure of 

each of four major dams (Williams, 1978). Kircher and 

Karlinger (1981) determined statistically that changes 

in annual peak flows on the North Plate River at North 

Platte, Nebraska, are better described by two regression 

models, one corresponding to the period prior to construction of Kingsley Dam (1895-1935) and one corresponding to the period following construction (1936- 

1979), than by a single model. Kircher and Karlinger did 

not test the significance of differences in peak flows 

following each period of dam construction, but peak 

flows from 1895 to 1935 decreased with time. There has 

been no significant change in peak flows since 1935.

Reservoir development has been less extensive in the 

South Platte River basin than in the North Platte River 

basin. Total reservoir storage in the South Platte River 

basin increased about 100 percent from 1915 to the 

present (fig. 2) with the majority of storage in off stream 

reservoirs. Kircher and Karlinger (1981) showed that 

peak flows of the South Platte River near Kersey and 

Julesburg, Colorado, have not changed significantly 

since 1902, the beginning of the record. However, a 

statistically significant decrease in peak flows with time 

was observed on the South Platte River at North Platte, 

Nebraska, probably due to surface-water diversions 

downstream of Julesburg.

Peak flows of the Platte River are influenced by flows 

from both the North Platte and South Platte Rivers. 

Since the reduction of flood peaks on the North Platte 

River, flood peaks on the South Platte River have 

become a more significant component of flow on the 

Platte River. Peak flows on the Platte River near Overton, Nebraska, have decreased over the period of record, 

1915-1979, but have shown no statistically significant 

decrease since 1935 (Kircher and Karlinger, 1981). No 

long-term change is apparent in peak flows near Grand 

Island, Nebraska, since the record began in 1935. 

However, changes may have occurred prior to 1935.

If the entire period of record is considered, annual 

mean flows have decreased on the North Platte and 

Platte Rivers. However, since 1935, annual mean flows 

on these rivers have either not changed signficantly or 

have increased. Records for the North Platte River at
HYDROLOGIC AND MORPHOLOGIC CHANGES IN CHANNELS OF PLATTE RIVER BASIN All

North Platte and the Platte River near Overton show no 

statistically significant change in annual mean flows for 

the period 1935-1979 (Kircher and Karlinger, 1981). Annual mean flows of the Platte River near Grand Island 

have increased significantly since 1935. No long-term 

change is apparent in annual mean flows of the South 

Platte River although changes may- have occurred prior 

to the period of record. Importation of water into the 

South Platte River basin apparently has counteracted 

the effects of water development within the basin.

In addition to changes in streamflow characteristics 

that may be attributed to river regulation, one must 

consider the possible effects of climate. Droughts have 

occurred in the Great Plains roughly every 20 years 

(Hecht, 1981), although the distribution and intensity 

has been quite different for each drought period. 

Droughts in the Central Great Plains in 1911,1913, and 

1917 were short, severe, and spatially limited, whereas 

the drought of the 1930's was particularly severe in the 

Platte River basin (Hecht, 1981). Although flows, in 

general, were decreased during the 1930's drought, the 

maximum floods of record on the Platte River occurred 

in 1935 at all gaging stations (Petsch, Rennick, and 

Nordin, 1980). Therefore, trends in streamflow characteristics can be correlated with documentation of water 

development in the basin, but it is difficult to relate 

changes in hydrology to random climate variations.

The flow-duration curve is the frequency distribution 

of daily mean flows at a given site. The flow-duration 

curve graphically represents variability of streamflow 

by the shape of the curve. The position of the curve 

reflects the magnitude of the streamflow (Leopold, 

Wolman, and Miller, 1964). Curves with low slope and 

high minimum values generally indicate a large 

baseflow component of streamflow. High slope and low 

minimum values indicate a more ephemeral character 

and a quicker response to precipitation events. The 

flow-duration curve does not provide information about 

sequential relationships of flows (Hudson and Hazen, 

1964). Thus, although the curve may reveal that a given 

flow is exceeded 50 percent of the time, it cannot indicate if the flows occurred consecutively, randomly, or 

in some pattern.

The shape of flow-duration curves for most stations 

on the North Platte, South Platte, and Platte Rivers has 

changed with time (Kircher and Karlinger, 1981; 

Eschner, 1981). In general, the curves show an increase 

in the magnitude of high-frequency discharges. A 

representative example of the type of changes that have 

occurred in flow duration over time is shown in figure 5. 

The position of the curve is dependent on the volume of 

water passing the gage during the period for which the 

flow duration is computed. However, the changes in the 

shape of the flow-duration curves with time reflect the

cumulative effects of streamflow regulation and water 

use.

SURFACE-WATER - GROUND-WATER RELATIONSHIPS

Unconsolidated deposits of the Platte River valley in 

the study area consist of Quaternary sediments, which 

include Holocene alluvium. The Ogallala Formation of 

Tertiary age and Pierre Shale and Niobrara Formation 

of Cretaceous age underlie the Quaternary sediments in 

the Platte River valley. The Ogallala Formation thins to 

the east and pinches out between Kearney and Grand 

Island. The thickness of the Ogallala Formation is irregular due to deposition on an irregular Cretaceous surface and to subsequent erosion.

Quaternary sediments and, where present, the 

Ogallala Formation, are the principal aquifers in the 

Platte River valley. These two units act as a single 

aquifer in areas where the Quaternary materials overlie 

the Ogallala The Quaternary sediments comprise the 

primary aquifer where these sediments directly overlie 

the Pierre Shale or Niobrara Formation. The Niobrara 

Formation is a source of ground water at some locations 

(Bentall, 1975b). Thickness of saturated alluvium varies 

from about 6 m to more than 122 m because of an irregular bedrock surface (Bentall, 1975a).

The Platte River is hydraulically connected with the 

aquifer in the valley (Lappala, Emery, and Otradovsky, 

1979); water can move from the river to the ground 

water and from the ground water to the river. The river 

serves as a control on the ground-water system and can 

influence ground-water levels and reflect changes in 

those levels. A study near Grand Island indicates that 

ground-water levels within 0.8 km of the river in that 

area respond within 24 hours to changes in river stage 

(Hurr, 1981). It is not known if this rate of change is 

typical for other areas within the Platte River valley.

In general, ground-water pumping lowers groundwater levels. This reduction may result from drawdown 

and change in water-table gradient, rather than from appreciable loss of storage. Evapotranspiration salvage, 

or the reduction of evapotranspiration by lowering the 

water table, would offset partially the decrease in water 

level brought about by ground-water pumping in areas 

where the ground-water table is close to the surface. 

Ground-water withdrawals in relatively close proximity 

to the Platte River may influence ground-water levels in 

two ways: (1) By initiating drawdown, and (2) by causing river-stage decline that may induce a further reduction in ground-water levels downstream (Hurr, 1981).

Evapotranspiration also may result in considerable 

loss of water to the atmosphere. As vegetaton becomes 

established on the valley floor, transpiration increases.
A12 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

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O.I 0.5 2.0 5.0 10.0 20.0 50.0 70.0 90.095.0 99.099.

PERCENTAGE OF TIME DISCHARGE EQUALED OR EXCEEDED

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FIGURE 5. Flow-duration curves for 10-year periods, Platte River near Overton, Nebraska (from Kircher and Karlinger, 1981).

Dirmeyer (1975) states that about 1,136 hm3 of water 

are lost to the atmosphere through evapotranspiration 

each year between Kingsley Dam and Duncan, a distance of 386 km. This quantity was estimated by 

assuming that the vegetation on the valley floor is a 

strip 1.6 km wide, and the evapotranspiration rate is 

1.8 m/yr.

An annual evapotranspiration rate of 1.8 m is probably high for central Nebraska, although this rate has 

been documented in more arid regions. Gatewood and 

others (1950) found that cotton wood trees in the Lower 

Safford Valley of Arizona transpire about 1.8 m annually. Average annual use of ground water by cottonwood 

and willow trees along the San Luis Rey River, California, was 1.6 m with the water table at 1.2 m, and 2.5 m 

with the water table at 0.9 m (Robinson, 1958). For 

Niobrara County, Wyoming, an area more similar to 

central Nebraska than Arizona or southern California, 

Whitcomb (1965) inferred that 0.9 m was a reasonable 

rate for annual evapotranspiration by cottonwood trees. 

Total lake evaporation along the Platte River ranges 

from 1.1 to 1.3 m/yr.

Assuming a more conservative evapotranspiration 

rate of 1 m/yr and a vegetation swath 1 km wide for the 

386 km from Kingsley Dam to Duncan, the annual 

evapotranspiration loss would be 386 hm3. This is equivalent to a flow of 12.2 m3/s if the rate of evapotranspiration is constant throughout the year, or alternatively, it 

is equivalent to a flow of 24.8 m3/s if the entire volume of 

water is transpired during a six-month growing season.

Net rises in ground-water level have resulted primarily from seepage water from canals and reservoirs. Lugn 

and Wenzel (1938) noted a rise in water level over 3 m 

since 1896 near Lexington, Nebraska In general, rises 

of 3 m have occurred beneath the Central Nebraska 

Public Power and Irrigation District in Lincoln, Gosper, 

Dawson, Phelps, and Kearney Counties. The largest 

recorded rises in water levels have been 27 m for Phelps 

County, 19 m for Kearney County, and 25 m for Gosper 

County (Johnson and Pederson, 1980). Rises of more 

than 0.6 m were measured in those counties between 

October 1968 and October 1971 (Lappala, Emery, and 

Otradovsky, 1979).

Net declines in the water table have occurred over
HYDROLOGIC AND MORPHOLOGIC CHANGES IN CHANNELS OF PLATTE RIVER BASIN A13

broad areas in the Platte River valley in response to 

ground-water pumping. The greatest water-table 

declines have occurred primarily in areas where depth to 

the water table prevents evapotranspiration salvage 

(Bentall, 1975a). Since the beginning of development 

declines of less than 1.5 m have occurred extensively 

throughout Buffalo, Hall, and Merrick Counties; 

declines of up to 6.4 m have been recorded in Buffalo 

County, mainly in upland areas along the Platte RiverLoup River divide (Johnson and Pederson, 1980). 

Declines of more than 1.2 m have been measured for the 

period 1968 to 1971 for other parts of Buffalo, Hall, and 

Merrick Counties (Lappala, Emery, and Otradovsky, 

1979).

Water-level changes in the Platte River basin in 

Nebraska were simulated by Lappala and others (1979) 

for various development schemes. Projected water-level 

changes ranged from rises up to 6.1 m over some areas 

with no further development, to net declines up to 

24.4 m over the entire upper Platte subbasin, if development of ground water continues at the rate that occurred from 1960 to 1970.

EFFECTS OF CHANGES IN HYDROLOGY 

ON THE CHANNEL

PRESETTLEMENT CHANNEL AND 

VALLEY-FLOOR CHARACTERISTICS

CHANNEL WIDTH

Channel width was the most obvious characteristic of 

the Platte River in the 19th century. Most travelers, 

comparing the Platte to rivers in the Eastern United 

States, found the width of the river remarkable; comments on channel width were recorded in most journals. 

Accurately estimating distances across a wide body of 

water is difficult. Accordingly, estimates of channel 

width from historical accounts must be used with caution. In 1849, Pritchard (Morgan, 1963, p. 63) noted that 

it "is hardly possible to guess at the width of the river 

as we seldom see the whole at once, on account of the 

numerous islands that are scattered from shore to shore 

* * *." Many of the estimates of channel width included 

the width of the islands in the channel. In 1849 Gibbs 

(Settle, 1940, p. 306) noted "[the Plattel is a mile [1.6 

km] in width. Where cut up by islands, as is often the 

case, it extends to double or treble [that distance], and in 

one place is seven miles [11.3 km] wide from shore to 

shore."

Estimates of the width of the Platte River during the 

period 1800-1860 vary from 1.2 to 4.8 km, with the 

most common estimates ranging from 1.6 to 3.2 km.

There are two measured observations of channel width 

recorded in the the literature. In 1832, Captain Bonneville (Irving, 1837) measured the width of the Platte 

River 40 km below the head of Grand Island and found 

it "twenty-two hundred yards [2.0 km] from bank to 

bank." Fremont (1845, p. 21) determined the width of 

the Platte River below the confluence of the North 

Platte and South Platte Rivers to be 1.6 km.

CHANNEL DEPTH

The second most remarkable characteristic of the 

Platte River was its depth. The river could be forded 

anywhere at almost anytime of the year, except during 

spring floods. Observations of water depth are useful 

only to establish a range in flows. Most observations of 

depth range from 0.3 to 1.2 m, depending on river stage. 

Long (James, 1823) reported that the bed of the Platte 

"is seldom depressed more than six or eight feet [1.8 to 

2.4 m] below the surface of the bottoms, and in many 

places even less." Jessup (James, 1823) substantiates 

Long's report:

The range of the Platte, from extreme low to extreme high water is 

very inconsiderable, manifestly not exceeding six or eight feet [1.8 to 

2.4 m]. This is about the usual height of its banks above the surface of 

the sand which forms its bed * * *.

Warren (1858) later reported that, "when the banks are 

full, it [Platte] is about six feet [1.8 m] deep throughout, 

having a remarkably level bed."

BED MATERIAL AND BED FORMS

In general, descriptions indicate that the bed material 

consisted of sand and gravel. However, James (1823), 

the botanist and geologist of the Long Expedition, 

stated, "The alluvial deposits of which the river bottoms are formed, consist of particles of mud and sand 

* * *," implying that the bed was finer than other accounts indicated.

Quicksand was encountered in the channels of the 

Platte system. In 1812, Stuart (Rollins, 1935) wrote 

that the bed of the Platte River, near the present day 

Gosper-Phelps County border, was composed "of such 

quicksand that it was difficult for our horse to get over, 

though the water was in no place more than two feet [0.6 

m] deep." Farther downstream near Fort Kearny, 

Taylor (Williams, 1969) in 1850 noted, "The bottom is 

composed of a fine quicksand * * *." Fremont (1845) 

described the southern channel of the South Platte 

River near the confluence with the Platte River as being 

"generally quicksands."

The configuration of the channel bed and its
A14 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

ephemeral character were described in detail by several 

travelers. Bradbury (1819), recrossing the Platte, noted:

in the same place where the day before it reached to our armpits, it did 

not now reach to our waists, although the river had not fallen. Such 

changes in the bottom of this river * * * were very frequent, as it is 

composed of a moving gravel, in which our feet sank to a considerable 

depth.

Mattes (1969) cited two descriptions of the Platte River 

bed near Fort Kearny. In 1849, Pritchard (Mattes, 1969) 

noted the composition and character of the bed: "The 

bed of the river is composed of sand, and this is all the 

time shifting its position and fresh deposits are constantly being made." Evans (Mattes, 1969) wrote in 

1849 that the Platte was a wide sheet of water "running 

over a vast level bed of sand and mica * * * continually 

changing into short offsets like the shingled roof of a 

house * * *."

The account of the Long Expedition (James, 1823) 

stated of the Platte, "its bed is composed almost exclusively of sand, forming innumerable bars, which are 

continually changing their positions and moving 

downward [downstream] * * *." In their travels, 

members of the Long Expedition observed on the flood 

plain "extremely numerous natural elevations of earth, 

of some considerable degree of regularity * * * of a more 

or less oval outline" with lengths of about 30 m and 

heights of 0.6 to 1.5 m. These elevations were presumed 

to have been former sandbars, "Their existence is 

doubtless due to the action of water. Should the rivers 

Platte and Arkansas be deprived of their waters, the 

sand islands of their beds would probably present a 

somewhat similar appearance."

The water of the Platte commonly was referred to as 

muddy or turbid. The "turbid waters of the Platte" 

were noted by the Long Expedition (James, 1823). 

McKinstry (1975), although calling the Platte a river of 

sand, stated that it was "nearly as muddy" as the 

Missouri. Taylor (Williams, 1969) wrote that the river 

was, at various points, "swift and muddy ," "muddy 

and turbulent," and "broad swift and muddy." Kelly 

(1851) described the river as turbid. Ebey (Baydo, 1971) 

stated of the Platte: "The water is always muddy and 

turbid * * *." Stage coach drivers (Ghent, 1929) used to 

tell the story that the Platte never overflowed its banks 

because its flood waters carried so much mud, that as it 

rose, it built new banks.

ISLANDS

Islands were a ubiquitous feature in the Platte River 

channels. In 1852, Cole (1905, p. 29) wrote:

Looking out upon the long stretch of river either way were islands 

and islands of every size whatever, from three feet in diameter to 

those which contained miles of area, resting here and there in the 

most artistic disregard of position and relation to each other, the 

small and the great alike wearing its own mantle of the sheerest 

willow-green * * *

Islands of the Platte River can be divided into two 

groups based on size, elevation, and vegetation. The 

large, well-timbered islands were described and mapped 

by Fremont (1845, pi. 1); these are Brady Island, Willow 

Island, Elm Island, Grand Island, and five other unnamed islands. Grand Island, also called the "Great 

Island" or "Big Island," was the largest of the islands 

mapped, being 84 km long and 2.8 km wide by 

Fremont's estimate. Although no quantitative estimates were given of the elevation of the large islands, 

Fremont (1845, p. 78) described Grand Island as being 

"sufficiently elevated to be secure from the annual flood 

of the river."

In addition to the large islands, there were hundreds 

of smaller islands too numerous to map or name. These 

islands were as small as a few square meters in area; 

most supported shrubs, young willows, and cottonwoods. A particularly dense concentration of these 

smaller islands occurred between Fort Kearny and 

Grand Island: these were named "Thousand Islands" 

after the Thousand Islands of the St. Lawrence River 

(Meline, 1966, p. 21).

VEGETATION

The valley of the Platte River supported a wide variety of plant species. The Fremont Expedition collected 

and cataloged over 90 plant species in the valley; the list 

included several species of trees, such as poplar (cottonwood), elm, hackberry, box elder, willow, and juniper. 

Other tree species found in the valley included cedar, 

dogwood, ash, and aspen.

Timber was a scarce commodity; however, it grew on 

the islands in the river and could be found in scattered 

groves between the Missouri and Loup Rivers (Fremont, 1845, p. 79). In 1820, according to Bell, the banks 

of the Elkhorn River and the Platte River near the Loup 

Fork were well-timbered (Fuller and Hafen, 1957, 

p. 107). The banks of the Platte River near Buffalo 

Creek also were timbered in 1812, according to Stuart 

(Rollins, 1935, p. 217). Timber also grew on the banks of 

the Platte River from the present site of Cozad to Brady 

Island (Fremont, 1845) and on the south bank of the 

Platte River along Brady Island (Rollins, 1935; Fremont, 1845; Palmer, 1847).

The scarcity of timber in the valley has been attributed to the effects of grazing buffalo and prairie
HYDROLOGIC AND MORPHOLOGIC CHANGES IN CHANNELS OF PLATTE RIVER BASIN A15

fires (Stansbury, 1851, p. 32; Mattes, 1969). Accounts of 

prairie fires can be found in several reports. Wyeth 

(1833) noted that the ground "is covered with herbage 

for a few weeks of the year only, * * * owing to the Indians burning the prairies regularly twice a year." Bradbury (1819) observed near the mouth of the Platte:

the reflection of immense fires, occasioned by burning prairies. At 

this late season (April 28), the fires are not made by hunters to 

facilitate their hunting, but by war parties; and more particularly 

when returning unsuccessful, or after a defeat to prevent their 

enemies from tracing their steps * * *.

Several parties reported large areas of burned prairie 

along the Platte River valley. Stansbury (1851, p. 32) 

reported that the valley was burned for a distance of 

480 km above Fort Kearny.

The influences of man and climate as regulators of 

tree growth in the valley have been underemphasized. 

The Indians used cottonwood as fodder for their horses 

and for firewood. Timber use by man increased during 

westward migrations up the valley. Fremont (1845, 

p. 17) noted that, near the head of Grand Island, "with 

the exception of a scattered fringe (of trees) along the 

bank, the timber * * * is confined almost entirely to the 

island." Burnett (1904) reported that, in 1844, "near the 

head of Grand Island * * * there was not a solitary tree 

on the south side of the river." It is likely that the few 

trees that grew along the banks of the Platte River were 

used for fodder and fuel by the Indians or settlers.

Distribution of timber in the valley was inconsistent 

with that expected based on the prairie-fire hypothesis. 

Timber grew along all the large tributaries to the Platte 

River, in many of the ravines in the bluffs along the 

valley margin, and in many hollows on the valley floor. 

It is unlikely that prairie fires sweeping across the 

valley would spare the timber along the rivers and in the 

ravines and hollows. A more likely explanation is that 

distribution of timber was controlled by availability of 

water, ravines, hollows, river banks, and islands are 

situated in topographically lower areas in close proximity to water. The conditions in these areas favor germination and growth. The remainder of the valley is 

topographically higher and drier. Conditions favoring 

the germination of seeds and grdwth of trees probably 

did not exist along most of the valley.

Aridity of the valley was observed by many travelers. 

In 1820, Long christened the area "The Great American 

Desert," a description of the valley that stuck through 

most the 19th century. Several writers observed saline 

crusts on the surface over large areas of the valley. 

Townsend (1833) observed that the ground near Grand 

Island:

is in many places encrusted with an impure salt, which by taste appears to be a combination of sulphate and muriate of soda [thenardite

and halite); there were also a number of little pools, only a few inches 

in depth, scattered over the plain, the water of which is so bitter and 

pungent, that it seems to penetrate into the tongue, and almost to 

produce decortication of the mouth * * *.

Availability of water probably was the prime factor that 

determined the distribution of timber in the valley. 

Prairie fires and grazing buffalo may have been secondary regulators of growth and distribution.

SUMMARY OF PRESETTLEMENT CHARACTERISTICS

In the 1800's the Platte River averaged about 2 km in 

width; it may have been as wide as 5 km where it was 

cut by islands, or as narrow as 1.2 km where no islands 

were present in the channel. The two measured observations of width (Irving, 1837; Fremont, 1845), 2.0 and 

1.6km, fall within these average values. Flow depth 

varied between 0.3 and 1.2 m during most of the year; 

bankroll depth ranged between 1.8 and 2.4 m along 

most of the valley. Large sand deposits were common in 

the channel. The channel bed was very active; a change 

of bed elevation of 0.5 m was observed over a 1-day 

period.

The river was observed to flow at bankfull stages during the spring floods. There were no observations of 

overbank flow along the river. Above the confluence 

with the Loup, the Platte was an intermittent river. It 

carried little water during the late summer and dried up 

completely in some years.

The Platte channels contained nine large islands and 

hundreds of smaller islands; most supported timber. 

Timber grew along the banks of the Platte, along the 

banks of the tributary rivers, in the ravines cut in the 

bluffs along the margins of the river, and in hollows on 

the valley floor. Distribution of timber in the valley was 

controlled primarily by availability of water. Prairie 

fires and grazing buffalo probably were secondary regulators of timber growth and distribution.

CHANGES IN PLATTE RIVER MORPHOLOGY

Changes in channel morphology of the Platte River 

can be documented by comparison of aerial photographs 

taken between 1938 and 1979. In addition, General 

Land Office maps provide relatively accurate measurements of river width from the 1860's. Changes in the intervening years must be inferred from hydrologic data 

and records of canal and dam construction that indicate 

when changes were initiated.

The development of islands in several reaches in the 

study area from 1860 to 1979 is shown in figures 6 

through 10; the changes are summarized in figure 11.
I KILOMETER

FIGURE 6. Channel of the Platte River near Cozad, Nebraska, in sections 25, 26, 35, and 36, T. 10 N., R. 23 W., and section 31, T. 

and section 6, T. 9 N., R. 22 W., in (a) I860, (b) 1938, and (c) 1979. Shaded areas are vegetated.
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FIGURE 6. Continued.
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FIGURE 6. Continued.
HYDROLOGIC AND MORPHOLOGIC CHANGES IN CHANNELS OF PLATTE RIVER BASIN A19

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FIGURE 7. Continued.
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FIGURE 7. Continued.

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FIGURE 8. Channel of the Platte River near Grand Island, Nebraska, in sections 1, 2, 10, 11, 12, and 15, T. 11 N., R. 8 W., and section 36, T. 12 N.,

R. 8 W., in (a) 1938 and (b) 1979. Shaded areas are vegetated.
1 KILOMETER 

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FIGURE 8. Continued.

CO
A24 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

The same years are not shown for all the photo sets. 

These figures show representative island development 

that occurred throughout the study area

Development of islands near Cozad, Nebraska, is 

shown in figure 6. The channel in 1860 was broad and 

open (fig. 6). By 1938, numerous islands had formed 

within the channel and had begun to attach to the flood 

plain (fig. 6). Between 1938 and 1979, significant narrowing of the channel occurred (fig. 6). Today, almost 

the entire channel of 1860 is covered with vegetation, 

and only two or three small meandering channels are 

present (fig. 6).

By 1938, some islands had formed and had become attached to the flood plain near Kearney (fig. 7a). A group 

of en echelon islands was present near the southern 

bank of the western edge (fig. 7a). Between 1938 and 

1957, many new islands formed, and additional islands 

attached to the flood plain (fig. 7b). In 1957, almost the 

entire southern bank was lined with vegetation. In 

general, the islands present in 1938 are still present, but 

have enlarged, primarily in the downstream direction, 

or have coalesced with other islands. The dashed lines 

within the large islands in figure 7b show the locations 

of channels that separated islands at one time. These 

abandoned channels have a topographic expression on 

the island surface. By 1979, island attachment to the 

flood plain had formed a wide swath of vegetation along 

both banks within the former channel area (fig. 7c) and 

the river consisted of a series of channels braiding 

among large islands. This channel pattern near Kearney 

(in 1979) differed appreciably in appearance from both 

the channel at the same location in 1938 (fig. 7a) and 

from the channel near Cozad in 1979 (fig. 6cl.

In 1938, the percentage of channel area near Grand 

Island occupied by islands appears to have been greater 

than at the other river reaches observed for this study. 

Islands of all sizes were present in the channel, and attachment to the flood plain had begun (fig. 8a); by 1979, 

new islands had formed in this reach (fig. 8b).

Only one large island existed near Duncan, Nebraska, 

in 1860 (fig. 9a). By 1941, several small islands were 

present in the channel, and attachment of islands to the 

flood plain had begun. The large island mapped in 1860 

had decreased slightly in size (fig. 9b). Most of the 

islands evident in 1941 had become attached to the 

flood plain by 1978 (fig. 9c). Although islands continue 

to form, the channel is relatively open.

In 1941, the channel near Ashland, Nebraska, contained four large islands (fig. lOa). One large island 

along the south bank already had become attached to 

the bank. The remainder of the 5-km reach had a few 

small islands in 1941. By 1971 (fig. lOb), only one large 

island existed in the channel. Two of the islands had 

become attached to the bank and one island not present

in 1941 formed and became attached to the bank during 

the 30-year period. The net change in average channel 

width at Ashland was very small when compared to 

sites upstream (fig. 11).

Measurements of channel width taken from the 

General Land Office maps surveyed in the field during 

the approximate period 1859-1867 and six sets of aerial 

photographs for six 5-km reaches of th Platte River are 

listed in table 3. Channel widths were measured along 

six cross sections, at 1-km intervals, at each of six 

reaches, and averaged for the entire reach. To make the 

comparison of various cross sections easier, the widths 

are plotted in figure 11 as percentages of the General 

Land Office map widths. For convenience the map 

widths are called "1860 width" in figure 11. Width 

changes shown in figure 11 for individual reaches are 

termed "at-a-station" changes, because they reflect 

channel width changes for a particular reach with time.

In general, the widths of the Platte channels have 

decreased since 1860. Width changes in the Cozad, 

Overton, Kearney, Grand Island, and Duncan reaches 

are similar in character. On the average, the magnitude 

of width reduction has decreased with time since 1940. 

The decrease in width of the Platte River near Ashland, 

Nebraska, has been minor, however, and channel width 

has increased slightly since 1941.

Width increases of a smaller scale are superimposed 

on the long-term width reductions. These relatively 

minor width increases occur between 1951 and 1957, 

and 1969 and 1979 for the reach near Overton; between 

1950 and 1957 for the reach near Grand Island; and between 1941 and 1949, 1955 and 1959, and 1965 and 

1971 for the reach near Ashland. Width decreased consistently in the reaches near Kearney and Duncan.

Williams (1978) measured river widths at 35 locations 

on the North Platte and Platte Rivers from the 

Wyoming-Nebraska State line to Grand Island. He 

found that channel width was about 10 to 20 percent as 

wide in 1965 as it was in 1860 for most of the reach. The 

downstream 100 km of his study reach, from Overton to 

Grand Island, also showed a decrease in width, but to a 

lesser extent than upstream, being about 60 to 70 percent as wide in 1965 as it was in 1860.

Channel widths during the periods 1938-1941, 

1957-1959, 1969-1971, and 1978-1979, expressed as 

percentages of the 1860 channel widths, are plotted 

with distance downstream from the WyomingNebraska State line in figure 12. The width changes 

with time shown in figure 12 are here termed "downstream" changes. Generally, the greatest reductions in 

channel widths occurred between the periods 1938-1941 

and 1957-1959. At Cozad, for example, the 1938-1941 

channel occupied 87 percent of the 1860 channel width, 

whereas the 1957-1959 channel occupied only 10
1 KILOMETER

FIGURE 9. Channel of the Platte River near Duncan, Nebraska, in sections 3, 4, 8, 9,10,16, and 7, T. 16 N., R. 1 W., in (a) 1860, (b) 1941, and (c) 1978.

Shaded areas are vegetated.

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FIGURE 9. Continued.
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17 I 16

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FIGURE 10. Channel of the Platte River near Ashland, Nebraska, in sections 15,16,17,18,19, 20, and 21, T. 12 N., R. 11 E., In (a) 1941 and (b) 1971.

Shaded areas are vegetated.
HYDROLOGIC AND MORPHOLOGIC CHANGES IN CHANNELS OF PLATTE RIVER BASIN A29

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A30 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

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I860 1880 1900 1920 1940 

YEAR OF MAP OR PHOTOGRAPH

I960 1980

FIGURE 11. At-a-station changes of channel width of the Platte River, Nebraska, with time.

percent of the 1860 channel width. Additionally, the 

magnitude of change in channel width between the 

periods 1938-1941 and 1957-1959 decreases downstream. The downstream-most reach, Ashland, actually 

shows an increase of width of 3 percent between these 

periods.

Channel width has decreased consistently for most of 

the reaches during the entire period of record 

(1860-1979). However, the rate of width reduction has 

decreased since 1957-1959. That is, there is relatively 

little change in channel width between 1957-1959 and 

1961-1969 and almost no change between 1969-1971 

and 1978-1979. During 1969-1971, the last period of 

complete aerial photograph coverage, channel widths 

ranged from 10 percent of the 1860 width at Cozad, the

upstream-most reach, to 92 percent of the 1860 width at 

Ashland.

Reduction of channel width has been documented extensively and has been shown to coincide with a period 

of changing flow regime. Despite the abundance of information available from aerial photographs, channel 

changes in the period between the General Land Office 

surveys and the inception of aerial photography only 

can be conjectured.

Information from the gaging station formerly located 

south of Lexington, Nebraska, provides one precise 

morphologic description from this intervening period. 

The U.S. Geological Survey station description, prepared in 1902, states that both right and left banks 

were: "Low, not over four or five feet, but not subject to
HYDROLOGIC AND MORPHOLOGIC CHANGES IN CHANNELS OF PLATTE RIVER BASIN A31

TABLE 3. Channel widths of the Platte River, Nebraska, in downstream order, measured from General Land Office maps 

(1860) and aerial photographs (1938-1979)

Channel width, in meters

Year

Cozad Overton Kearney

Grand 

Island Duncan Ashland

1860 1,161 1,545 1,484 1,100' 826 594

1938 1,015 890 1,298 704

1941 600 515

1949 539

1950 643 543

1951 204 451 698

1955 521

1957 113 460 695 664 521

1959 533

1963 110 408 308 530

1964 448

1965 530

1969 113 387 293 472

1970 424

1971 549

1978 411

1979 110 405 247 387

'From 1898 edition 30' U.S. Geological Survey topographic map (General Land Office 

map incomplete).

overflow-sparingly wooded." The description further 

states, "Bed is composed of shifting sand. Total width 

is 3,720 feet [1,134 m]." The same cross section, as 

measured from the General Land Office maps, has a 

width of 1,134 m, the same width as that given in 1902. 

A photograph dated about 1910 of the bridge over the 

Platte River south of Lexington shows that the river 

was still wide and free of vegetation (fig. 13). A note on 

the back of the photo indicates the bridge was about 

1,450 m long (photograph on file at the Dawson County 

Historical Society Museum). The 1938 aerial photograph shows the same cross section with a width about 

one-third of the width in 1860. Although the reduction 

at the gage station was largely because of fill around the 

bridge sections, areas of the river upstream and 

downstream from the bridge show that channel narrowing and island development already had occurred. Thus, 

morphologic change of the Platte River at this site 

began after 1910, but before 1938.

Further historical evidence for the change of the 

overall character of the channel is available from 

ground-level photography at several locations along the 

river. For example, in the reach of the river near Cozad 

and Kearney, the river has changed with time from a 

broad channel with few islands (figs. 14a and 15a) to a 

series of relatively narrow, well-defined channels intertwining among large islands (figs. 14b and 15b). Below 

the confluence with the Loup River, channel change has 

been far less dramatic. For example, near Ashland, a

photograph taken in 1897 (fig. 16a) shows a broad, 

vegetation-free channel. A photograph taken from 

about the same location in 1982 (fig. 16b) shows that the 

channel changed very little. The evidence from the 

ground-level photography corroborates the at-a-station 

and downstream trends of channel width evident in 

figures 11 and 12.

CHANGES IN NORTH PLATTE AND 

SOUTH PLATTE RIVER MORPHOLOGY

Changes of North Platte River morphology have been 

similar to changes that occurred on the Platte River. 

Channel width in 1965 ranged from 5 to 40 percent of 

the channel width mapped in 1860 (table 4); it probably 

averaged about 15 percent of the 1860 channel width 

(Williams, 1978). Braiding and sinuosity (table 4) were 

determined for the channel as of 1938 and as of 1965 

(Williams, 1978). In general, braiding index, defined by 

Williams (1978) as the sum of length of islands in a 

reach divided by the length of the reach, decreased, and 

sinuosity index, defined by Williams (1978) as the 

length of a reach of existing channel divided by the 

length of channel in the same reach in 1860, increased 

for the North Platte River in Nebraska.

Morphology of the South Platte River also has 

changed. Nadler (1978) found that channel width in 

1952 averaged only about 15 percent of channel width in 

1867. From 1867 to 1952, sinuosity of the South Platte 

River increased between 5 and 15 percent. Data from individual cross sections are listed in table 5.

RELATIONSHIP OF DISCHARGE REGULATION 

TO CHANNEL CHANGE

Morphologic changes of the North Platte, South 

Platte, and Platte Rivers have been similar despite 

significant differences in the hydrology of these three 

rivers. Construction of reservoirs and diversion of 

streamflow on the North Platte River have caused 

reductions of annual peak flows and mean annual flows 

of both the North Platte and Platte Rivers. In contrast, 

there has been no reduction of peak flows on the South 

Platte River upstream of Julesburg during the period of 

record because of a relatively small amount of reservoir 

construction. Transbasin diversions into the South 

Platte River have offset diversions of water for irrigation, resulting in no net change of mean annual flows 

during the period of record.

Schumm (1968) attributed decrease in size of the 

South Platte River channel to the decrease in the annual 

peak discharge. However, a decrease in the annual peak
A32 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

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1978-1979

I I I I I I I I

380 420 460 500 540 580 620 660 700 740 780

RIVER DISTANCE DOWNSTREAM FROM NEBRASKA-WYOMING 

STATE LINE, IN KILOMETERS

FIGURE 12. Downstream changes in the percentage of 1860 channel width of the Platte River occupied by the channel in 1938-1941,

1957-1959, 1969-1971, and 1978-1979.

discharge of the South Platte River upstream of Julesburg, Colorado, has not occurred during the period of 

record (Kircher and Karlinger, 1981). Thus, morphologic 

change apparently has occurred in response to irrigation 

development in the basin prior to the period of record. 

Nadler (1978) proposed that irrigation development 

along the South Platte River changed the river from intermittent to perennial. This hydrologic change caused 

a change in the vegetation that stabilized the channel. 

The temporary reduction of discharge during the 

drought of the 1930's allowed vegetation to occupy and 

become established in areas of channel. Subsequent 

floods were not able to widen the channel, as they 

presumably might have, prior to the encroachment of 

vegetation.

PROCESSES OF WIDTH REDUCTION

Six sets of aerial photographs used in this report (figs. 

6-10) allow documentation of channel width reductions 

and the processes of width reduction. These processes 

are island formation and subsquent attachment of 

islands to either the flood plain or other islands. The 

channel in the 1860's was broad and open (figs. 6a and 

13 near Cozad, Nebraska for example) with few vegetated islands, most of which were large.

By 1938, width decreased by island formation. In addition, bank locations had shifted toward the center of 

the channel, as a result of island formation and attachment to the flood plain. Island attachment resulted 

from channel abandonment or atrophication, rather
HYDROLOGIC AND MORPHOLOGIC CHANGES IN CHANNELS OF PLATTE RIVER BASIN A33

FIGURE 13. Photograph of the Platte River south of Lexington, Nebraska, facing toward the north, taken about 1910. (Photograph from

Dawson County Historical Society Museum.)

than from a migration of the river course. Most of the 

small islands near these sections are wedge- or lobeshaped; they are oriented with the pointed end downstream. Comparison of these islands with adjacent 

sandbars shows that they have the same form. Therefore, we conclude that the majority of the islands in the 

Platte River formed when vegetation established itself 

on these bars and stabilized them. Hydrologic changes, 

which began with irrigation development and were accelerated by large reservoir construction, evidently provided more favorable growing conditions on the bars, or 

decreased flood peaks that formerly had removed 

vegetation.

Once an island formed, it tended to perpetuate itself. 

The presence of vegetation encouraged further aggradation by increasing roughness and decreasing flood-water 

velocity over the bar when the island is submerged.

Thus, island elevation increased until it was at or above 

high-water stage.

Sets of maps and photographs made after 1938 show 

similar, continued development of islands. However, 

with time, the number of islands diminished, but thensize increased. Sediment was accreted at the downstream ends of islands due to decreased flow velocity at 

their downstream end. This sand substrate is a likely 

place for vegetation establishment.

The coalescence of islands occurs as the channels between islands gradually lose their water- and sedimentcarrying capabilities, becoming indistinguishable, both 

in appearance and function, from the islands they 

separate. This process has been documented in other 

studies. Nadler (1978) proposed vertical infilling of 

channel braids or branch channels, as the method by 

which the South Platte River was transformed from a
A34 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

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FIGURE 14. The Platte River near the present site of Cozad, Nebraska, from the south bank. A, looking approximately northwest, in the year 

1866. (Courtesy of Union Pacific Railroad.) B, Oblique photograph, facing toward the northwest, taken in 1979.

multiple-thalweg to single thalweg stream. Branchchannel aggradation is important in the abandonment 

of channels and subsequent attachment of islands to the 

flood plain on the Cimarron River (Schumm and Lichty, 

1963). The attachment of islands to the flood plain of 

the Loup River in Nebraska by atrophication of narrow 

channels carrying water at high discharges has been 

documented by Brice (1964).

SOME IMPLICATIONS OF 

FUTURE WATER DEVELOPMENT

Documented changes in the channels of the Platte 

River and its major tributaries that have been discussed 

in this report are attributed primarily to water development. Water use for irrigation in the basin and water 

demands from municipal, industrial, and power generation uses have significantly changed streamflow 

characteristics. These water uses have affected mean 

annual flows, peak flows, low flows, and flow distribution (Kircher and Karlinger, 1981). Also, changes in 

surface-water hydrology probably have affected sediment transport in major streams. New discharge and 

sediment-transport regimes have resulted in sand bars 

that are not scoured or removed each year. Vegetation 

has stabilized channel sand bars and transformed them 

into islands. These processes have been a major factor 

in narrowing the channels, as shown by the sequence of 

maps (figs. 6 to 10). All of these changes have contributed to progressive deterioration of the riverine 

habitat of sandhill cranes, whooping cranes, and other
HYDROLOGIC AND MORPHOLOGIC CHANGES IN CHANNELS OF PLATTE RIVER BASIN A35

FIGURE 14. Continued.

migratory birds in the critical r^ach between Overton 

and Grand Island, Nebraska

If the present migratory-bird habitat is to be t preserved from further deterioration, further research is 

needed for the relationship between streamflow, 

sediment-transport characteristics, and channel 

geometry. For example, it will be useful to estimate the 

discharge necessary to maintain a desired channel 

width necessary for preservation of the habitat. This 

discharge must be of sufficient magnitude and duration 

to cause sand bar movement and removal of vegetation 

seedlings by scour.

REFERENCES CITED

Baydo, Gerald, 1971, Overland from Missouri to Washington territory in 1854: Nebraska History, v, 52, p. 65-87.

Bentall, Ray, 1975a, Hydrology, Nebraska mid-state division and 

associated areas: Lincoln, Nebr., Conservation and Survey Division, Institute of Agriculture and Natural Resources, University 

of Nebraska, 256 p.

___1975b, Physiography, geology, soils, agriculture: Nebraska 

mid-state division: Lincoln, Nebr., Conservation and Survey Division, Institute of Agriculture and Natural Resources, University 

of Nebraska, 76 p.
A36 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

FIGURE 15. Platte River south of Kearney, Nebraska, from the south bank toward the north. A, taken between 1875 and 1880. (Photograph

from Stuhr Museum of the Prairie Pioneer.) B, taken in 1981.

Bradbury, John, 1819, Travels in the interior of America in the years

1809,1810, and 1911, in Thwaites, R. G,, ed., 1905, Early western

travels, v. 5: Cleveland, Ohio, A. H. Clarke Co., p. 25-320. 

Brice, J. C., 1964, Channel patterns and terraces of the Loup Rivers

in Nebraska: U.S. Geological Survey Professional Paper 422-D,

41 p. 

Burnett, P. H., 1904, Recollections and opinions of an old pioneer:

Quarterly of the Oregon Historial Society, v. 5, p. 64-99,

139-198,272-305,370-470. 

Carlson, M. E., 1963, The development of irrigation in Nebraska,

1854-1910: A descriptive history: Ph. D. dissertation, Lincoln,

Nebr., University of Nebraska, 153 p. 

Clarke, H. T., 1902, Freighting Denver and Black Hills: Proceedings

and Collections of the Nebraska State Historical Society, Second

Series, v. 5, p. 299-312. 

Cole, G. L., 1905, In the early days along the Overland Trail in

Nebraska territory, in 1852: Kansas City, Mo., Hudson Publishing Co., 125 p. 

Crowley, K. D., 1981, Large-scale bedforms in the Platte River

downstream from Grand Island, Nebraska: structure, process,

and relationship to channel narrowing: U.S. Geological Survey

Open-file Report 81-1059,31 p. 

Dirmeyer, Richard, 1975, More on protected streamflows: Nebraska

Resources, v. 6, p. 3-4.

Eschner, T. R., 1981, Morphologic and hydrologic changes of the 

Platte River, south-central Nebraska: M.S. thesis, Fort Collins, 

Colo., Colorado State University, 269 p.

Fremont, (Capt.) J. C., 1845, Report of the exploring expedition to the 

Rocky Mountains: Washington, D. C., Gales and Seaton, 693 p.

Frith, C. R., 1974, The ecology of the Platte River as related to sandhill cranes and other waterfowl in south central Nebraska: M.S. 

thesis, Kearney, Nebr., Kearney State College, 115 p.

Fuller, H. M., and Hafen, L. R., 1957, The journal of Captain John R. 

Bell, official journalist for the Stephen H. Long expedition to the 

Rocky Mountains, 1820: Glendale, Calif., Arthur H. Clark Co., 

349 p.

Gatewood, J. S., Robinson, T. W., Colby, B. R., and others, 1950, Use 

of water by bottom-land vegetation in lower Safford Valley, 

Arizona: U.S. Geological Survey Water-Supply Paper 1103, 

210 p.

Gerlek, Stephen, 1977, Water supplies of the South Platte River 

basin: M.S. thesis, Fort Collins, Colo., Colorado State University, 

798 p.

Ghent, W. J., 1929, The road to Oregon: New York, Longmans, 

Green, and Co., 274 p.

Hecht, A. D., 1981, The challenge of climate to man: EOS Transactions, American Geophysical Union V. 62, p. 1193-1197.
HYDROLOGIC AND MORPHOLOGIC CHANGES IN CHANNELS OF PLATTE RIVER BASIN A37

FIGURE 15. Continued.

FIGURE 16. Photograph of the Platte River near Ashland, Nebraska, from the south bank toward the northeast. A, taken in 1897.

(Photograph by N. H. Darton, U.S. Geological Survey.) B, taken in 1982.

Hudson, H. E., and Hazen, Richard, 1964, Droughts and low 

streamflow, in Chow, V. T., ed., Handbook of applied hydrology: 

New York, McGraw-Hul, p. 18-1-26.

Hurr, R. T., 1975, Effects of water-management practices on the flow 

of the South Platte River, Colorado: International Association for

Hydrological Sciences, Symposium of Tokyo, 1975, Publication 

no. 117, p. 61 1-617.

, Ground-water hydrology of the Crane Meadows wildlife

area, near Grand Island, Hall County, Nebraska: U.S. Geological 

Survey Open-File Report 81-1109, 43 p.
A38 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN 

TABLE 4. Data for channel width, braiding index, and sinuosity index for the North Platte River1

Location, 

city name, or 

township and 

range

K CO «7

R. 50 W. ..............

K AQ TX7

T /IQfVI

K AC. \\7

R 44 W

T ^ixrol 1<xn

R 49 W

R 4fl W

TCpVQtnrM*

R. 38 W. ...............

R. 36 W. ...............

R 34 w

Sutherland .............

R. 32 W. ...............

North Platte ............

Williams' 

Total channel width braiding 

(meters) index

1865

07 c

Gin

1,140

81 fi

1 9***!

1 ocn

1

f\£*f\

r.Af.

QQK

CIO

. 710

... 950

... 940

... 850

... 750

.... 740

... 790

1938

 

200 

815 

325 

410 

460 

520

1965

55 

105 

120 

130 

170 

150 

185 

200 

150 

165

45 

45 

195 

75 

45 

90

Ratio of 

1965 to 1938 1965 

1865

0.06

n 1 q

0.11

0

1 R

0.14

n 10

0

10

O 37

0.17

0.20

1.21 0.00 

0.05 1.21 0.00 

0.05 8.13 2.50 

0.23 2.23 0.26 

2.13 2.20 

0.06 3.48 1.91 

0.11 3.44 1.76

Williams' 

sinuosity 

index

1938 1965

1.06 1.00 

1.06 1.00 

1.00 1.11 

1.06 1.11 

1.05 1.30 

1.03 1.05 

1.06 1.11

'From Williams, 1978.

TABLE 5. Data for channel width, braiding index, and sinuosity for the South Platte River1

Location, 

city name, or 

township and 

range

T K XT P CK W

ftprooxr

Hardin ...........

T 4 N R fi3 W

A/f fl<jt^r<j

T 4 N f? fi9 W

Sublette ..........

T 4 N R fil W

T

K. XT "D Cf\ 1B7

Weldona ..........

T

A XT p CQ \ir

T A XT T> CO VV

Hurley ............

T

A XT "D ET 1B7

Snyder ...........

T. 4 N., R. 56 W.

Total channel width 

(meters)

1867

415

.. 335

.. 335

.. 435

Q£A

.. 425

430

CIA

.. 535

.. 430

. . 440

qon

f*f\f:

.. 425

AQti

.. 375

eqe

1952

34 

52 

91 

44 

56 

81 

39 

36 

48 

80 

73 

52 

55 

101 

75 

51 

60 

75

1977

81 

107 

61

107 

119 

109 

91

93 

91

Ratio 

of 

1952 

to 

1867

0.08 

0.16 

0.27 

0.10 

0.16 

0.19 

0.09

0.08 

0.15 

0.17 

0.12 

0.14 

0.17 

0.18 

0.10 

0.16 

0.14

Ratio 

of 

1977 

to 

1867

0.24 

0.32 

0.14

0.25

 

0.20

0.21

0.22

0.24

Braiding 

index2

1867

0.42 

0.40 

0.17

0.27

0.29

0.16

0.21

0.79

0.18

1952

0.29 

0.25 

0.21

0.76

0.30

0.31

0.50

0.49

1.78

Sinuosity3

1867

1.05 

1.04 

1.05

1.00

1.13

1.14

1.02

1.01

1.02

1952

1.21 

1.11 

1.12

1.09

1.19

1.25

1.12

1.10

1.12

'From Nadler, 1978.

2Braiding index, after Brice (1964), not equivalent to Williams' braiding index in table 4.

'Sinuosity denned as length of channel divided by down-valley distance.
HYDROLOGIC AND MORPHOLOGIC CHANGES IN CHANNELS OF PLATTE RIVER BASIN A39

Irving, Washington, 1837, The adventures of Captain Bonneville, 

Todd, E. W., ed., 1961: Norman, Okla., University of Oklahoma 

Press, 429 p.

James, Edwin, 1823, Account of an expedition from Pittsburgh to the 

Rocky Mountains: Ann Arbor, Midi., University Microfilms, 

Inc., 945 p. (This is a chronicle of the Long Expedition.)

Johnson, M. S., and Pederson, D. T., 1980, Groundwater levels in 

Nebraska, 1979: Nebraska Water Survey Paper 50,65 p.

Kelly, William, 1851, An excursion to California, over the prairie, 

Rocky Mountains, and Great Sierra Nevada: New York, Arno 

Press, 334 p. [Reprinted 1973.]

Kircher, J. E., 1981, Sediment transport and effective discharge for 

the North Platte, South Platte, and Platte Rivers in Nebraska: 

U.S. Geological Survey Open-File Report 81-53,26 p.

Kircher, J. E., and Karlinger, M. R., 1981, Changes in surface-water 

hydrology for the South Platte River in Colorado and Nebraska, 

the North Platte and the Platte River in Nebraska: U.S. Geological Survey Open-File Report 81-818,77 p.

Lappala, E. G., Emery, P. A., and Otradovsky, F. J., 1979, Simulated 

changes in ground-water levels and streamflow resulting from 

future development (1970 to 2020) in the Platte River basin, 

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resources of south-central Nebraska: U.S. Geological Survey 

Water-Supply Paper 779,242 p.

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States: U.S. Geological Survey Water-Supply Paper, 115 p.

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Nebraska State Historical Society Publications, v. XXV, 583 p.

McKinley, J. L., 1938, The influence of the Platte River upon the 

history of the valley: Minneapolis, Minn., Burgess Publishing Co., 

138 p.

McKinnon, J. C., 1952, Poudre Valley contributions to Colorado irrigation practice, in A hundred years of irrigation in Colorado: 

Denver, Colo., Colorado Water Conservation Board, p. 31-40.

McKinstry, B. L., 1975, The California gold rush overland diary of 

Byron N. McKinstry, 1850-1852: Glendale, Calif., A. H., Clark, 

401 p.

Meline, J. F., 1966, Two thousand miles on horseback: Albuquerque, 

N. Mex., Horn and Wallace, 317 p.

Miller, Gene, 1978, History of Platte River flows: U.S. Fish and 

Wildlife Service, Grand Island, Nebr., unpublished manuscript, 

typewritten, 18 p.

Morgan D. L., ed., 1959, The overland diary of James A. Pritchard 

from Kentucky to California in 1849: Denver, Colo., The Old West 

Publishing Co., 221 p.

___1963, Overland in 1846, diaries and letters of the CaliforniaOregon trail: Georgetown, Calif., Talisman Press, 825 p.

Nadler, C. T., Jr., 1978, River metamorphosis of the South Platte and 

Arkansas Rivers: M.S. thesis, Fort Collins, Colo., Colorado State 

University, 151 p.

Palmer, Joel, 1847, Journal of travels over the Rocky Mountains, 

1845 and 1846, in Thwaites, R. G., ed., 1906, Early western 

travels, v. 30: Cleveland, Ohio, A. H. Clark Co., 311 p.

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Statistical summaries of selected streamflow data South Platte 

River in Colorado and Nebraska; North Platte and Platte Rivers 

in Nebraska: U.S. Geological Survey Open-File Report 80-679, 

278 p.

Robinson, T. W., 1958, Phreatophytes: U.S. Geological Survey WaterSupply Paper 1423,84 p.

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Geological Survey, Water Resources Division, Colorado District 

Library, Denver, Colo., 9 p.

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floodplain construction along Cimarron River in southwestern 

Kansas: U.S. Geological Survey Professional Paper 352-D, 

p. 71-88.

Settle, R. W., 1940, The march of the mounted riflemen: Glendale, 

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(1917/1918).

___, Biennial reports of the State engineer Department of Public 

Works, Bureau of Irrigation, Water Power, Drainage, nos. 13 

(1919/1920) to 19 (1931/1932).

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Colorado: Fort Collins, Colo., The State Agricultural College, 

659 p.

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Mountains, in Thwaites, R. G., ed., 1905, Early western travels, 

v. 21: Cleveland, Ohio, A. H. Clark Co., 369 p.

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p. 1-99.

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New York, St. Martins Press, 483 p.

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report Annual Report of the Secretary of War, 1858 (Serial 975), 

p. 620-670.

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Niobrara County, Wyoming, with a section on Chemical quality 

of the ground water U.S. Geological Survey Water-Supply Paper 

1788,101 p.

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the journal of Clavin Taylon Nebraska History, v. 50, p. 125-148.

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Platte and Platte Rivers in Nebraska: U.S. Geological Survey Circular 781,48 p.

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Department of Roads and Irrigation, Lincoln, Nebr., 1950-1951, 

89 p.

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Ohio, A. H. Clark Co., p. 21-106.

Effects of Water Development on 

Surface-Water Hydrology, 

Platte River Basin in 

Colorado, Wyoming, and Nebraska 

Upstream from Duncan, Nebraska

By JAMES E. KIRCHERanrf MICHAEL R. KARLINGER

HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

GEOLOGICAL SURVEY PROFESSIONAL PAPER 1277-B

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON 1983

CONTENTS

Page

Abstract ........................................... 1

Introduction ........................................ 1

Physical setting ..................................... l

Climate. ............................................ 3

Present use of surface water ........................... 3

Storage reservoirs ................................ 3

Transmountain diversions ......................... 3

Irrigation ....................................... 6

Domestic and municipal uses ....................... 6

Hydrology.......................................... 6

General......................................... 6

Hydrology Continued

Site selection ..........

Flow-duration curves....

High flows ............

Low flows .............

Statistical analysis .....

Mean flows ............

Instantaneous peak flows 

Summary. ...............

References...............

Page

7

7

9

9

12

18

21

25

28

ILLUSTRATIONS

FIGURE 1. Mapof the Platte River basin showing location of data-collection sites....................................... 2

2-5. Graphs showing annual precipitation at:

2. Julesburg, Colorado (1888-1978) ............................................................... 4

3. North Platte, Nebraska(1875-1978) ............................................................ 4

4. Gothenburg, Nebraska(1895-1978)............................................................. 5

5. Grand Island, Nebraska(1890-1978)............................................................ 5

6-9. Graphs showing changes in channel area and island area near:

6. Cozad, Nebraska ............................................................................ 10

7. Overton, Nebraska .......................................................................... 10

8. Grand Island, Nebraska ...................................................................... 11

9. Duncan, Nebraska ........................................................................... 11

10. Graph showing change in channel width at four sites along the Platte River ......................................... 12

11-19. Graphs showing selected flow-duration curves at:

11. Station 06693000, North Platte River at North Platte, Nebraska (water years 1931-79) .................. 13

12. Station 06754000, South Platte River near Kersey, Colorado

(wateryears1902,1903,1906-12,1915-79) .................................................... 13

13. Station 06764000, South Platte River at Julesburg, Colorado

(wateryears 1903-06,1909-12,1914-21,1925-79).............................................. 14

14. Station 06765500, South Platte River at North Platte, Nebraska (water years 1932-79) .................. 14

15. Station 06766500, Platte River near Cozad, Nebraska (water years 1941-79) ........................... 15

16. Station 06768000, Platte River near Overton, Nebraska (water years 1931-79).......................... 15

17. Station 06770000, Platte River near Odessa, Nebraska (wateryears 1940-79) .......................... 16

18. Station 06770500, Platte River near Grand Island, Nebraska (water years 1935-79) ..................... 16

19. Station 06774000, Platte River near Duncan, Nebraska (water years 1930-79) .......................... 17

20-28. Graphs showing the mean 1-, 3-, 7-, 15-, and 30-day high flows at:

20. Station 06693000, North Platte River at North Platte, Nebraska (water years 1931-79) .................. 18

21. Station 06754000, South Platte River near Kersey, Colorado

(wateryears1902,1903,1906-12,1915-79) .................................................... 19

22. Station 06764000, South Platte River at Julesburg, Colorado

(wateryears1903-06,1909-12,1914-21,1925-79) .............................................. 20

23. Station 06765500, South Platte River at North Platte, Nebraska (water years 1932-79) .................. 21

24. Station 06766500, Platte River near Cozad, Nebraska (wateryears 1941-79) ........................... 22

25. Station 06768000, Platte River near Overton, Nebraska (water years 1931-79).......................... 23

26. Station 06770000, Platte River near Odessa, Nebraska (water years 1940-79) .......................... 24

27. Station 06770500, Platte River near Grand Island, Nebraska (water years 1935-79) ..................... 25

28. Station 06774000, Platte River near Duncan, Nebraska (wateryears 1930-79) .......................... 26

in
IV CONTENTS

FIGURES 29-37. Graphs showing the mean 1-, 3-, 7-, 14-, and 30-day low flows at: "^

29. Station 06693000, North Platte River at North Platte, Nebraska (water years 1931-79) .................. 30

30. Station 06754000, South Platte River near Kersey, Colorado

(wateryears 1902,1903,1906-12,1915-79) .................................................... 31

31. Station 06764000, South Platte River at Julesburg, Colorado

(wateryears 1903-06,1909-12,1914-21,1925-79).............................................. 32

32. Station 06765500, South Platte River at North Platte, Nebraska (water years 1932-79) .................. 33

33. Station 06766500, Platte River near Cozad, Nebraska (wateryears 1941-79) ........................... 34

34. Station 06768000, Platte River near Overton, Nebraska (water years 1931-79).......................... 35

35. Station 06770000, Platte River near Odessa, Nebraska (wateryears 1940-79) .......................... 36

36. Station 06770500, Platte River near Grand Island, Nebraska (water years 1935-79) ..................... 37

37. Station 06774000, Platte River near Duncan, Nebraska (wateryears 1930-79) .......................... 38

38-43. Graphs showing annual mean discharges at:

38. Station 06693000, North Platte River at North Platte, Nebraska (wateryears 1895-1979) ................ 39

39. Station 06754000, South Platte River near Kersey, Colorado

(wateryears1902,1903,1906-12,1915-79) .................................................... 39

40. Station 06764000, South Platte River at Julesburg, Colorado

(wateryears 1903-06,1909-12,1914-21,1925-79) .............................................. 40

41. Station 06765500, South Platte River at North Platte, Nebraska (water years 1918-79) .................. 40

42. Station 06768000, Platte River near Overton, Nebraska (water years 1915-79).......................... 41

43. Station 06770500, Platte River near Grand Island, Nebraska (water years 1934-79) ..................... 41

44-47. Graphs showing monthly mean discharges for April through September at:

44. Station 06693000, North Platte River at North Platte, Nebraska (wateryears 1931-78) .................. 42

45. Station 06765500, South Platte River at North Platte, Nebraska (water years 1932-78) .................. 43

46. Station 06768000, Platte River near Overton, Nebraska (water years 1931-78).......................... 44

47. Station 06770500, Platte River near Grand Island, Nebraska (water years 1935-78) ..................... 45

48-53. Graphs showing annual instantaneous peak discharges at:

48. Station 06693000, North Platte River at North Platte, Nebraska

(water years 1895-1979).................................................................... 46

49. Station 06754000, South Platte River near Kersey, Colorado

(water years 1902,1903,1905-12,1914-79) .................................................... 46

50. Station 06764000, South Platte River at Julesburg, Colorado (water years 1902-06,

1909-12,1914-15,1917-18,1920-24,1926-79) ................................................. 47

51. Station 06765500, South Platte River at North Platte, Nebraska

(wateryears1897,1914-15,1917,1921-79) .................................................... 47

52. Station 06768000, Platte River near Overton, Nebraska (wateryears 1915-17,1919-23,1926-79).......... 48

53. Station 06770500, Platte River near Grand Island, Nebraska (water years 1934-79) ..................... 48

54. Graph showing comparison of instantaneous peak flows on the South Platte River at North Platte,

Nebraska, and the Platte River near Overton, Nebraska.......................................... 49

TABLES

TABLE 1. Mean annual precipitation at selected sites ................................................................... 3

2. Surface-water areas as of 1962 and evaporation from reservoirs, lakes, streams, and canals ........................... 6

3. Reservoirs with capacities greater than 0.6 cubic hectometer .................................................... 8

4. Streamflow characteristics of primary data sites .............................................................. 12

5. Summary of regression and covariance analysis for the logarithms of annual mean flows ............................. 27

6. Summary of regression and covariance analysis for the logarithms of annual peak flows .............................. 27

7. Summary of regression results relating the logarithms of mean annual and peak flows of the South Platte River

and North Platte River to the logarithms of mean annual and peak flows of the Platte River ....................... 27

8. Summary of beta coefficients relating the logarithms of mean annual and peak flows of the

North Platte River and South Platte River to the logarithms of mean annual and peak flows of the Platte River ....... 28
HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

EFFECTS OF WATER DEVELOPMENT ON SURFACE-WATER

HYDROLOGY, PLATTE RIVER BASIN IN COLORADO, WYOMING, AND

NEBRASKA UPSTREAM FROM DUNCAN, NEBRASKA

By JAMES E. KIRCHER and MICHAEL R. KARLINGER

ABSTRACT

The North Platte and Platte Rivers in western and central 

Nebraska have undergone significant changes in surface-water 

hydrology since the kte 19th century. The South Platte River in 

Colorado and Nebraska has undergone much less change during the 

same period. This report presents an analysis of the changes in 

surface-water resources in the Platte River basin in Colorado, 

Wyoming, and Nebraska upstream from Duncan, Nebraska, an area 

of 157,700 square kilometers.

Nine stream-gaging stations in the basin were selected for 

analysis of streamflow changes. Flow-duration curves, 1-, 3-, 7- , 

14-, and 30-day mean low flows, and 1-, 3-, 7-, 15-, and 30-day 

mean high flows were determined for all stations. Beginning about 

1950, flow-duration curves for all stations, except .that of the South 

Platte River near Kersey, Colorado, show a change with time of the 

low-flow segment of the distribution curve in a downstream direction. The analyses indicate that high flows have been relatively 

unaffected by water development in the Platte River Basin. Low 

flows in the North Platte River increased following the closure of 

Kingsley Dam during 1941. Low flows in the South Pktte River at 

Julesburg, Colorado, increased, beginning about 1920, and at North 

Platte, Nebraska, about 1932. Statistical analyses of data from six 

selected sites were performed to determine: (1) The significance of 

major water developments that may have produced abrupt changes 

in the time series of streamflow statistics, and (2) the significance of 

water developments that caused a more gradual change or time 

trend in the streamflow statistics.

INTRODUCTION

The Plate River in Nebraska is one of the most important rivers of the Great Plains, not only because of 

the agricultural development within its basin, but also 

because it is unique as a habitat for several species of 

migrating waterfowl. Among these species are the sandhill cranes and the whooping cranes, which require a 

wide and shallow channel relatively free of vegetation 

for roosting and breeding. Maintaining these channel 

characteristics has caused concern in recent years 

because the Platte River channel has narrowed appreciably since the early 1950's. Before measures to 

prevent further narrowing can be taken, however, an 

examination of the hydrologic changes, which occurred 

along with the channel changes, is needed.

This report presents an appraisal of the changes in 

surface-water resources of the Platte River basin. In 

the appraisal, the following aspects were considered: 

(1) The present use of the surface-water supplies, (2) the 

historical flow characteristics of the streams, and (3) 

the effects of environmental factors on streamflow.

PHYSICAL SETTING

The South Platte and North Platte Rivers originate 

primarily as snowmelt streams in the Rocky Mountains of Colorado. They flow across the Great Plains to 

form the Platte River at their confluence at North 

Platte, Nebraska (fig. 1).

The South Platte originates in the central part of Colorado, flows southeastward to a point about 100 km 

(kilometers) southwest of Denver, flows 

northeastward, leaves the mountains about 50 km 

southwest of Denver, flows through Denver, and continues northeastward to the confluence with the North 

Platte River. Total drainage area of the South Platte 

River is about 62,900 km2 (square kilometers), and the 

river is about 720 river km long (Bentall, 1975, p. 6). 

The reach of the South Platte River studied extends 

from Kersey, Colorado, to the confluence with the 

North Platte River, a distance of about 380 river km.

From its origin in north-central Colorado, the North 

Platte River flows northward into east-central Wyoming near Casper, and then flows southeastward to its 

confluence with the South Platte River. The North 

Platte River drains about 80,000 km2 and is about 

1,050 river km long. The reach of the North Platte 

River studied is from Lake McConaughy near

Bl
B2 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

s

£1

c

 §

I

2 

S

I
EFFECTS OF WATER DEVELOPMENT ON SURFACE-WATER HYDROLOGY B3

Ogallala, Nebraska, to the confluence with the South 

Platte River, a distance of about 86 river km.

The Platte River is formed at the confluence of the 

North Platte and South Platte Rivers. The Platte flows 

eastward through Nebraska to the Missouri River at 

the eastern edge of the State. The reach of the Platte 

River studied extends from North Platte to Duncan, 

Nebraska, a distance of about 460 river km.

CLIMATE

Climate in the basin is affected by altitude, latitude, 

and topography. The Platte River basin has a 

continental-type climate, characterized by a large 

range of temperature and irregular annual and 

seasonal precipitation.

The mountainous region of the South Platte River 

basin has long winters, significant snowfall, and a 

short growing season. Precipitation varies in the 

mountains according to altitude; high mountainous 

areas along the Continental Divide average about 

1,000 mm (millimeters) of precipitation annually.

Annual precipitation in the foothills averages about 

400 to 500 mm. Snowfall constitutes a smaller percentage of precipitation here than in the mountains. Summer and winter temperatures in the foothills are more 

moderate than in either the mountains or the plains.

The plains region just east of the foothills has low 

humidity, warm summers, cold winters, and considerable year-to-year variation in precipitation. 

Average annual precipitation ranges from approximately 300 to 460 mm. Most of the precipitation occurs from April through September.

The climate of the North Platte River basin is about 

the same as that for the South Platte River basin. The 

climate generally can be characterized as semiarid with 

large fluctuations in temperature. Annual precipitation on most of the plains area ranges from 230 to 400

mm; in mountainous areas from about 500 to 1,000 

mm.

The climate of the eastern plains of Nebraska is different, however, from the climate of the plains nearer 

the mountains. Precipitation across Nebraska is 

variable both geographically and seasonally. Average 

annual precipitation ranges from about 380 mm at the 

western end of Nebraska to about 790 mm at the 

eastern end.

Mean annual precipitation at several locations 

within the basin is shown in table 1. Total annual 

precipitation for each year of record for four precipitation stations in the basin is shown in figures 2 through 

5.

The average annual evaporation from the basin as 

estimated by Meyers (1962) is tabulated in table 2. The 

entire basin as of 1962 had an annual evaporation of 

1,447 hma (cubic hectometers) (table 2). There have 

been reservoirs, ponds, and canals added since 1962 

that will increase this amount.

PRESENT USE OF SURFACE WATER 

STORAGE RESERVOIRS

The Platte River basin has 194 reservoirs that have 

useable-storage capacities greater than 0.6 hm3. These 

reservoirs are listed in table 3. The combined useablestorage capacity of the reservoirs is 8,829 hm3 . In addi-v 

tion to the reservoirs shown in table 3, numerous small 

lakes and stock ponds are scattered throughout the 

study area.

TRANSMOUNTAIN DIVERSIONS

The major transmountain diversions are located in 

Colorado and import water to the South Platte River. 

This imported water is collected from the Colorado 

River basin and the North Platte River basin and

TABLE l. Mean annual precipitation at selected sites

Weather Mean

Station annual

location1 precipitation 

(millimeters)

Pathfinder, Wyoming. . .

Casper, Wyoming .......

Ft. Laramie, Wyoming. .

Greeley, Colorado .......

Ft. Morgan, Colorado . . .

. .253

..347

..349 

..367

..345

. .315

..335

Period 

of 

record

1900-1978 

1911-1978 

1886-1978 

1871-1978 

1873-1978 

1888-1978 

1889-1978

Weather Mean 

station annual 

location1 precipitation 

(millimeters)

Sterling, Colorado ......

Julesburg, Colorado .....

North Platte, Nebraska. . Gothenburg, Nebraska. . 

Grand Island, Nebraska.

. .377

. .427

. .389

. .471 

. .542 

. .629

Period 

of 

record

1910-1978 

1888-1978 

1889-1978 

1875-1978 

1895-1978 

1890-1978

1 See figure 1.
B4 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

O 

g

CL

O

1000

800

600

400

200 Mean annual precipitation 

for the period of record « 

427 millimeter*

1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980

FIGURE 2. Annual precipitation at Julesburg, Colorado (1888-1978)

O 

<

OLU

cc

a.

900

800 -

700 -

600 -

500 

400 -

300

200

Mean annual precipitation 

for the period of record " 

471 millime

1870 1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 

FIGURE 3. Annual precipitation at North Platte, Nebraska (1875-1978).
EFFECTS OF WATER DEVELOPMENT ON SURFACE-WATER HYDROLOGY B5

z

*

o

Q.

u

1000

900 -

800 -

700 

600 -

500

400 -

300

Mean annual precipitation 

for the period of record * 

542 millimeters

1890 1900 1910 1920 1930 1940 1950 1960 1970 1980

FIGURE 4. Annual precipitation at Gothenburg, Nebraska (1895-1978).

IS

Ul

Q.

U

1200

1100 

1000 -

900 -

800

700

600

500

400 -

300

1890

Mean annual precipitation 

for the period of record = 

629 millimeters

1900 1910 1920 1930 1940 1950 1960 1970 1980

FIGURE 5. Annual precipitation at Grand Island, Nebraska (1890-1978).
B6 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

TABLE 2. Surface-water areas of 1962 and evaporation from reservoirs, lakes, streams, and canals (from Meyers, 1962)

[hm* = square hectometers; hma = cubic hectometers]

River basin

North Platte

River

South Platte

River

Platte River

downstream from

confluence of

North and South

Platte Rivers

State and -

Wyoming

Colorado

Nebraska

Total of

N. Platte

Wyoming

Colorado

Nebraska

Total of S.

Platte

Nebraska

Principal 

reservoirs and 

regulated lakes

Effective

(hm')

13,558

10.93

13,986

27,554.93

25.5

11,999

0

12,024.5

1,856

Annual

evapo-

(hm>)

147

.09

167

314.09

.24

120

0

120.24

22.6

Other lakes with 

areas greater than 

0.6 square hectometer

Effective

(hm'(

3,642

0

0

3,642

0

91.9

0

91.9

0

Annual

evapo-

(hm')

40.7

0

0

40.7

0

.89

0

.89

0

Principal streams 

and canals

Effective

(hm')

3,495

69.6

9,031

12,595.6

0

1,741

1,919

3,660

24,819

Annual

evapo-

<hm')

38.2

.60

107.6

146.4

0

19.2

23.1

42.3

273

Small ponds 

and reservoirs

Effective

(hm')

2,520

455

12,368

15,343

258

5,530

3,211

8,999

8,930

Annual

evapo-

(hm<)

25.9

3.88

147.2

176.98

2.57

54.7

38.35

95.62

99.1

Small s

Effective

(hm')

1,808

103

627

2,538

307

1,779

111

2,197

5,820

streams

Annual

evapo-

(hm>)

18.9

.87

7.32

27.09

3.16

18.63

1.30

23.09

64.2

Total for 

all classes

Effective

(hm2 )

25,023

639

36,012

61,674

590

21,140

5,241

26,971

41,423

Annual

evapo-

(hm>)

271

5.44

429

705.44

6.0

214

62.7

282.7

459

diverted to the South Platte River basin for municipal, 

industrial, and irrigation uses. The average annual 

water diverted from western Colorado is 414 hm8 

(Gerlek, 1977). Development of conditional water 

rights may yield an additional 271 to 308 hm8 per year 

of water from western-slope diversions.

IRRIGATION

Irrigation in the Platte River basin began during the 

early 1800's with the construction of small, wide ditches to small irrigated tracts of land on the flood plain 

adjacent to the river. Since that time, there have been 

many reservoirs built to store water and many 

elaborate canal and ditch systems built to more efficiently use surface water. The earliest development occurred on the Colorado and Wyoming plains where the 

climate necessitated having irrigation projects store 

water for use during the dry summer months.

Since the earliest irrigation projects, when only the 

land next to the rivers was used for agriculture, the irrigated land has increased to about 1.4 million hm (hectometers) in the entire basin. The area now is irrigated 

by means of direct diversions, reservoirs, and groundwater systems, and encompasses land several 

kilometers from the river.

DOMESTIC AND MUNICIPAL USES

Several cities and industrial plants within the basin 

obtain water supplies from the river or from aquifers 

that are recharged mainly from the river. The 

municipalities continue to grow at a rapid rate, 

especially along the Front Range of Colorado and coalrich eastern Wyoming. This growth has been accompanied by increased water demands.

HYDROLOGY

GENERAL

When the Platte River and its tributaries were virtually unregulated, spring runoff flowed unchecked 

down the mountain stream channels and onto the 

plains. During the summer after the snowpack melted, 

flow in these streams became very low. In the plains 

many of the rivers and tributaries were ephemeral, as 

most of the low flow infiltrated into the stream bed.

Today, after more than 100 years of irrigation and 

water-resource development in the basin, the Platte 

River and its major tributaries, the North and South 

Platte Rivers, have changed from ephemeral streams 

to perennial streams. Spring runoff from the mountains now is diverted and stored in offstream reservoirs or retained by onstream reservoirs, to be used 

later in the year as needed. Through irrigation, much of 

the water is used on large tracts of agricultural land. 

The basin water balance also has been changed further 

by imported water from adjacent river basins.

The hundreds of reservoirs and the thousands of 

kilometers of unlined canals, ditches, feeders, and 

laterals have large seepage losses. As a result of this 

and of the irrigation practices used, the water tables 

have risen over the years making the plains' streams 

effluent; in other words, they gain water from irrigation return flows. These flows then are rediverted farther downstream leaving the channel dry downstream 

from the point of diversion. This pattern of use and 

reuse extends along the length of the plains' reaches of 

the South Platte, North Platte, and Platte Rivers.
EFFECTS OF WATER DEVELOPMENT ON SURFACE-WATER HYDROLOGY B7

The balance between diversions and return flows has 

been affected in recent years by extensive pumping 

from the riparian aquifer. This has been a serious effect 

on the surface-water users who are dependent on these 

ground water seeps. Therefore, the practice of irrigation may have affected and overridden natural factors 

that normally define the hydrology of the Platte River.

Because of these changes in the hydrology during 

the last 40 years, the Platte River channel has decreased 

in cross sectional area and the island areas has increased 

(figs. 6-9). As a result, the channel has undergone considerable narrowing (fig. 10). Measurements made 

from aerial photographs were used in developing 

figures 6 through 10. These changes in the Platte River 

have caused concern among wildlife managers interested in maintaining a suitable habitat for the 

thousands of migrating waterfowl that use the Platte 

in central Nebraska. The reach of river concern extends 

from Lexington, Nebraska, to near Grand Island, 

Nebraska. This reach will be referred to throughout the 

remainder of the report as the critical habitat reach.

One of the potential consequences of the hydrologic 

changes is a change in vegetation growth along and 

within the river channel. If channel bars are exposed 

for a sufficient period of time, vegetation may become 

established, causing island formation and channel narrowing. Currier and Van Der Valk (1980) found that 

cottonwood and willow seeds begin falling about midMay and continue to fall through mid-July. They state 

that after germination these seedlings could be viable 

until the end of August. If seed germination and seedling establishment is to occur, mud flats with significant soil moisture would have to be exposed for at least 

1 to 2 weeks. Therefore, the investigation of hydrologic 

changes require special attention to the period from 

mid-May to the end of August, defined as the critical 

growth period for vegetation.

SITE SELECTION

Nine sites along the North Platte, South Platte, and 

Platte Rivers were chosen for evaluation of flow 

changes. These sites are listed in table 4. Flowduration curves and average 1-, 3-, 7-, 15-, and 

30-day mean high and 1-, 3-, 7-, 14-, and 30-day 

mean low flows were defined for all sites. For six of the 

nine sites, statistical analyses were performed on the 

records of annual mean flow and annual peak 

discharge. The six sites chosen were the North Platte 

River at North Platte, Nebraska; the South Platte 

River near Kersey, Colorado; the South Platte River 

near Julesburg, Colorado; the South Platte River at

North Platte, Nebraska; the Platte River near Overton, Nebraska; and the Platte River near Grand Island, 

Nebraska. These sites were chosen because the spatial 

and temporal coverage of flow data best represents the 

hydrology in the critical reach, as well as the reaches of 

the North Platte and South Platte Rivers that show 

the effect of the extensive development along these 

rivers that have had an effect on the critical reach. The 

results of the statistical analyses will be discussed 

later in the report.

FLOW-DURATION CURVES

Flow-duration curves for 10-year intervals within 

the period of record at each of the nine selected stations, which show the percentage of time that water 

discharges of various magnitude have been equaled or 

exceeded, are presented in figures 11 through 19. The 

flow-duration curves shown illustrate the progression 

of hydrologic change that has occurred within the 

basin. Although flow-duration curves for longer 

periods of record may have less time variability, it was 

believed that the longer-period flow duration curves 

might mask the nature of progressive change in the 

flow characteristics. For a discussion of defining the 

period or periods selected for computation of flow 

duration for a given station, see Riggs (1972).

The only station showing any major change in the 

upper end of the flow-duration is the North Platte 

River at North Platte (fig. 11). All the 10-year periods 

following the 1931-39 period were smaller in 

magnitude and had a flatter slope except for 1970-79, 

which had several years of very high flow that may 

have caused the increase. This flattening indicates a 

decrease in the magnitude of high flows resulting from 

flow regulation occurring along the North Platte 

River. The remainder of the stations show very little 

change in the high flow section of the flow-duration 

curves, indicating no or very little change in the high 

flows.

The South Platte River near Kersey, Colorado, is the 

only station that shows very little change in the entire 

flow-duration curve sequence. This can be attributed 

partly to an increase in transmountain diversions of 

surface water. These diversions have been used to meet 

1980 municipal, industrial, and agricultural demands 

thereby resulting in very little change in the native 

water supply. As water use continues to increase along 

the Front Range, however, the flow characteristics for 

the Kersey station also may change.

The changes in the flow-duration curve sequences 

are indicative of the reduction in flow variability as one
B8 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

TA

RIVER BASIN

NORTH PLATTE 

NORTH PLATTE 

NORTH PLATTE 

NORTH PLATTE 

NORTH PLATTE

NORTH PLATTE 

NORTH PLATTE 

NORTH PLATTE 

NORTH PLATTE 

NORTH PLATTE

NORTH PLATTE 

NORTH PLATTE 

NORTH PLATTE 

NORTH PLATTE 

NORTH PLATTE

NORTH PLATTE 

NORTH PLATTE 

NORTH PLATTE 

NORTH PLATTE 

NORTH PLATTE

NORTH PLATTE 

NORTH PLATTE 

NORTH PLATTE 

NORTH PLATTE 

NORTH PLATTE

NORTH PLATTE 

NORTH PLATTE 

NORTH PLATTE 

NORTH PLATTE 

NORTH PLATTE

NORTH PLATTE 

NORTH PLATTE 

NORTH PLATTE 

NORTH PLATTE 

NORTH PLATTE

NORTH PLATTE 

NORTH PLATTE 

NORTH PLATTE 

NORTH PLATTE 

NORTH PLATTE

NORTH PLATTE 

NORTH PLATTE 

NORTH PLATTE 

NORTH PLATTE 

NORTH PLATTE

NORTH PLATTE 

NORTH PLATTE 

NORTH PLATTE 

NORTH PLATTE 

NORTH PLATTE

NORTH PLATTE 

NORTH PLATTE 

NORTH PLATTE 

NORTH PLATTE 

NORTH PLATTE

NORTH PLATTE 

NORTH PLATTE 

NORTH PLATTE 

NORTH PLATTE 

NORTH PLATTE

NORTH PLATTE 

NORTH PLATTE 

NORTH PLATTE 

NORTH PLATTE 

NORTH PLATTE

BLE «J. neservoirs witn capacitie 

than 0.6 cubic hectometer

RESERVOIR NAME

ALCOVA RESERVOIR 

AQUA FRIA 

ARNOLD RESERVOIR 

8ATIS RESERVOIR 3ENNETT RESERVOIR

316 CREEK 

BOETTCHER 

BOSLER 

BUCKLIN 

BUTTE

CARLSTROM 

CARROL LAKE RESERVOIR 

CASE BIER 

CAVENOAR 

COALMONT

COW CREEK LAKE RESERVOIR 

CRYSTAL LAKE 

OARCY 

DENT ION OA« 8-2 

OUTTON CREEK RESERVOIR

GLENDO RESERVOIR 

GLOWMILL RESERVOIR 

80SHEN HOLE 

GOSHEN NO. 2 RESERVOIR 

GRANITE SPRINGS

GRAY REEF 

GUERNSEY RESERVOIR 

HAMILTON RESERVOIR 

HAWK SPRINGS 

HOG PARK

HUGHES RESERVOIR 

HUTTON LAKE 

HYANNIS 

J. FRANK WALKER 

KING NO. 1

KORTESRESERVOIR 

LA PRELE RESERVOIR 

LAKE OWEN BERG 

LAKE JOHN 

LAKE HATTIE

LAKE ALICE 

LAKE MINATARE 

LAKE MCCONAUGHY 

LAKE OGALLALA

LAUNE

LEE»S RESERVOIR 

MCFARLANE 

MEADOW CREEK 

NORTH SPRING CREEK RESERVOIR 

NORTH MICHIGAN

OLIVE RESERVOIR 

PATHFINDER RESERVOIR 

PIERCE RESERVOIR 

PINE RIDGE 

POLARIS RESERVOIR

POLE MOUNTAIN 

RAINER RESERVOIR 

RATLINS RESERVOIR

ROLE ROY

SABIN

SADDLEBACK RESERVOIR 

SA6E CREEK RESERVOIR 

SAND LAKE 

SARATOGA RESERVOIR

SEMINOE

s greater

RESERVOIR CAPACITY 

(CUBIC HECTOMETERS)

233.0 

0.9 

1.4 

3.8 

1.2

8.5 

0.8 

2.0 

0.9 

1.?

0.8 

0.7 

1.8 

0.7 

39.1

0.6 

 5.6 

0.9 

0.8 

3.2

980.5 

1.0 

6.1 

1.1 

9.1

2.2 

55.8

1.2 

20.6 

3.8

0.8 

3.1 

2.6 

0.7 

2.7

5.7 

2.5 

1.7 

8.0 

84.5

U.I 

76.7 

2401.9 

16.0 

3.7

0.6 

8.0 

6.2 

0.9 

1.6

9.2

1319.3 

4.0 

2.7 

0.7

2.3

0.7 

0.8 

11.0 

3.9

0.8 

0.7 

1.4 

1.0 

1246.3

TABLE 3.-

RIVER BASIN

NORTH PLATTE 

NORTH PLATTE 

NORTH PLATTE 

NORTH PLATTE 

NORTH PLATTE

NORTH PLATTE 

NORTH PLATTE 

NORTH PLATTE 

NORTH PLATTE 

NORTH PLATTE

NORTH PLATTE 

NORTH PLATTE 

NORTH PLATTE 

NORTH PLATTE 

SOUTH PLATTE

SOUTH PLATTE 

SOUTH PLATTE 

SOUTH PLATTE 

SOUTH PLATTE 

SOUTH PLATTE

SOUTH PLATTE 

SOUTH PLATTE 

SOUTH PLATTE 

SOUTH PLATTE 

SOUTH PLATTE

SOUTH PLATTE 

SOUTH PLATTE 

SOUTH PLATTE 

SOUTH PLATTE 

SOUTH PLATTE

SOUTH PLATTE 

SOUTH PLATTE 

SOUTH PLATTE 

SOUTH PLATTE 

SOUTH PLATTE

SOUTH PLATTE 

SOUTH PLATTE 

SOUTH PLATTE 

SOUTH PLATTE 

SOUTH PLATTE

SOUTH PLATTE 

SOUTH PLATTE 

SOUTH PLATTE 

SOUTH PLATTE 

SOUTH PLATTE

SOUTH PLATTE 

SOUTH PLATTE 

SOUTH PLATTE 

SOUTH PLATTE 

SOUTH PLATTE

SOUTH PLATTE 

SOUTH PLATTE 

SOUTH PLATTE 

SOUTH PLATTE 

SOUTH PLATTE

SOUTH PLATTE 

SOUTH PLATTE 

SOUTH PLATTE 

SOUTH PLATTE 

SOUTH PLATTE

SOUTH PLATTE 

SOUTH PLATTE 

SOUTH PLATTE 

SOUTH PLATTE 

SOUTH PLATTE

-neservoirs witn capacities greater i 

0.6 cubic hectometer Continued

RESERVOIR NAME

SEYMOUR

SIRNARO RESERVOIR 

SOUTH SPRINGS CREEK RESERVOIR

SPECTACLE LAKE 

TURPIN PEAK RESERVOIR

UPPER VAN TASSEL RESERVOIR 

UPPER ROCK CREEK 

WALOEN RESERVOIR NO 1

WALDEN RESERVOIR NO 2

WHR RESERVOIR NO i

WHR RESERVOIR NO i

WILLOW CREEK RESERVOIR 

WYOMING DEVELOPMENT CO. RESERVOIR 

WYOMING OEVELPMENT CO. RESERVOIR 

AGATE

AL8IOM LAKE 

AVTHRA (DUCK LAKE1) 

ANTERO

BADGER 

BARKER MEADOWS

BARR LAKE 

BASE LINE RESERVOIR

BILLlNGSt AR8UCKLE 

BOOTLEG 

BOULOER

BOULOER 

BUTTON ROCK 

CABIN CREEK 

CASTLEWOOD

CHERRY CREEK

CLARK COUNTY NO. 2 

CLOVER BASIN 

COALBANK WATERSHED 

O.A. LORD NO. 4 

ELEVENMILE CANYON

EMPIRE

ENGLEWOOD 

FALL RIVER RESERVOIR 

FOOTHILLS

FRANKTOWN PARKER

GEORGETOWN 

BOLD LAKE RESERVOIR 

GROSS RESERVOIR 

HAYDEN 

HIDDEN LAKE

HIGHLAND NO. 2 

HILLCREST 

HORSE CREEK

HUDSON 

JACKSON LAKE

JULESBURG RESERVOIR 

JUMBO RESERVOIR 

KENWOOO 

KIOWA 

KLOG NO. 3

LAKE CHEESMAN 

LAKE MALONEY 

LEFT HAND VALLEY 

LEFT HAND PARK 

LEG8ET

LIOOERDALE LAKE 

LOCH LOMAND 

LOST PARK 

LOVELLA 

LOWER LATHAM

nun

RESERVOIR CAPACITY 

(CUBIC HECTOMETERS)

0.6 

1.9 

0.8 

1.8 

1.6

2.3 

3.5

4*4 

0.9 

1.1

1.1 

0.9 

NO 1 18.9 

NO. 2 121.2 

12.9

1.3 

5.4 

19.6 

12.2 

15.0

39.6 

6.5 

1.2 

7.6 

21.5

9.4 

19.1 

2.3

4.2 

303.4

1.4 

0.7 

2.6 

4,3

120.6

46.5 

7.4 

1.1 

5.2

0.8

0.9 

1.7 

53.1

0.6 

4.0

4.6 

2.2

36.2

14.6 

44.0

34.7 

3.1

12.3

10.3 

0.9

97.5' 

7.4 

13.0 

1.9 

1.2

0.9 

10.8 

56.6 

8.3 

7.1

NORTH PLATTE SEPERATION LAKE RESERVOIR 0.7 SOUTH PLATTE MARSHALL LAKE 12.9

progresses downstream. The North Platte River at 

North Platte, Nebraska, the South Platte River at 

Julesburg, Colorado, and North Platte, Nebraska, and 

the Platte River near Overton, Nebraska, show a flattening in the lower end of flow-duration curves beginning about 1950 and continuing to 1979. This flattening usually is due to an increase of inflows caused by 

irrigation return flows or controlled release from reservoirs that maintain streamflow during low-flow 

periods. The period of record for the Platte River near 

Cozad, Nebraska, is too short to detect any obvious 

flattening of the flow-duration curves from those prior 

to 1940. The flow-duration curves for the gaging stations at Platte River near Odessa, Grand Island, and 

Duncan, Nebraska, are progressively flattening at the 

low-flow end. Changes in the shapes of the flow-
EFFECTS OF WATER DEVELOPMENT ON SURFACE-WATER HYDROLOGY B9

TABLE 3. Reservoirs with capacities greater than 

0.6 cubic hectometer Continued

>?IVER cfASIN

SOUTH PLATTE 

SOUTH PLATTE 

SOUTH PLATTE 

SOUTH PLATTE 

SOUTH PLATTE

SOUTH PLATTE 

SOUTH PLATTE 

SOUTH PLATTE 

SOUTH PI ATTE 

SO'ITH PLATTE

SOUTH PLATTE 

SOUTH PLATTE 

SOUTH PLATTE 

SOUTH PLATTE 

SOUTH PLATTE

SOUTH PLATTE 

SOUTH PL^TE

SOUTH PLATTE

SOUTH PI ATTE

SOUTH PLATTE

SOUTH PLATTE 

SOUTH PL4TTE 

SOUTH PLATTE 

SOUTH PLATTE 

SOUTH PLATTE

SOUTH PLATTE 

SOUTH PLATTE 

SOUTH PLATTE 

SOUTH PLATTE

SOUTH PLATTE

SOUTH PLATTE 

SOUTH PLATTE 

SOUTH PLATTE 

SOUTH PLATTE 

SOUTH PLATTE

SOUTH PLATTE 

SOUTH PLATTE 

SOUTH PLATTE 

SOUTH PLATTE 

SOUTH PLATTE

SOUTH PLATTE 

SOUTH PLATTE 

SOUTH PLATTE 

SOUTH PLATTE

PLATTF

PLATTF

PLATTE

PLATTF 

PLATTE 

PLATTE

PLATTF 

PLATTF. 

PLATTF 

PLATTF 

PLATTF.

PLATTE 

PLATTE 

PLATTE 

PLATTF 

PLATTE

PLATTF 

PLATTE

RESERVOIR NAME

MCINTIRF NO. 1 

MESA 

MILTON LAKE 

MONTGOMERY 

NOONAN NO. 2

NORTH STFRLI>'JG 

OLIVER 

PANAMA 

PANHANULF 

PARK CRFEK DAM

PETFRSOM LAKE 

PF.TERSON LAKE 

PLATTE CANYON 

PLEASANT VALLEY 

POINT OF ROCK

PREWITT 

PROSPECT 

QUINCY 

RATTLESNAKE

RESERVOIR NO. ??

RESERVOIR MO. ft 

RESFRVOIR NO. 4 

RIVFRSIOF 

SHEFP CREEK 

SIX MILF

SILVER LAKE

SOUTH GRAY 

SUTHERLAND RESFRVOIR 

TAWRYALL 

TERMINAL

TERRY LAKF 

TIMNATH 

TWIN LAKES 

UNION 

UPPFR URAO

VALMONT 

WARREN LAKE 

WASSON

WATER SIJOPLY NO. * 

WATER SUPPLY NO. 3

WILO HOBSF

WILLAMS MCCREERY 

WINDSOR

WORSTER (EATON)

BLUE STEM

8RANCHEO OAK 

CONESTOGA 

ERICSON 

GALLAGER CANYON L'AKE 

HOLMES LAKE

JFFFERY RESERVOIR 

JOHNSON RESERVOIR 

LAKF SARCOCK AND LAKE NORTH 

MIDWAY CANYOMS LAKF SYSTEM 

OLIVE CREEK

PAWNEE

PLUM CREEK LAKE 

SHERMAN RESERVOIR 

STAGE COACH 

TWIN LAKES

WAGON TRAIN 

YANKEE HILL

RESERVOIR CAPACITY 

(CUBIC HECTOMETERS)

1.1 

1.2

53.2 

6.3 

3.3

91.2 

9.? 

0.8 

1.3 

9.1

1.1 

1.5 

1.2 

3.1 

99.4

40.1 

9.4 

3.5 

2.T 

51.7

13.0 

1.6 

70.9 

2.? 

13.4

4.9 

1,* 

9.9 

16.2 

4.2

10. 0 

12.5 

21.1 

15.7 

0.9

17.2 

2.8 

1.0 

1.2 

5,9

1.0 

21.7 

19.3 

2.5 

3.7

32.0 

3.2 

2.0 

3.7 

1.5

14.2 

66.6 

5.5 

11.6 

1.8

10.5 

5.7 

85.2 

2.4 

3.5

3.1 

2.5

TOTAL RESERVOIRS TOTAL CAPACITY 8829.*

duration curves can be related to the channel width 

and area changes already shown in figures 6 through 

10.

It should be emphasized that a distinction be made 

between change in shape of flow-duration curves and 

shift in flow-duration curves for different periods of 

record. A change in the shape of a flow-duration curve 

indicates change in the characteristics of flow distribution. This is the basis of the preceding analysis. A shift

in a flow-duration curve, however, indicates a change 

in flow volume, but not distribution shape. A change in 

shape from 1940-49 to 1950-59 and a change in 

volume from 1960-69 to 1970-79 are shown in figure 

16.

Further interpretation of the flow-duration curves 

may be made using periods of records longer than 10 

years. Again using figure 16 as an illustration, an 

analysis could have been made using two periods, 

1931-49 and 1950-79. It is apparent that the resulting 

flow-duration curves would lie somewhere between the 

respective 10-year period curves as plotted. The 

resulting two curves would allow one to relate the 

changes in water use and environmental factors to flow 

characteristics between the two periods.

HIGH FLOWS

High flows, as used in this section, are defined as the 

largest mean flows occurring for durations of 1, 3, 7, 

15, or 30 consecutive days for any given year. Changes 

in the mean high flows in the study reach are presented 

in figures 20 through 28. The North Platte River at 

North Platte, Nebraska, shows a general decrease in 

the high mean flows coinciding with the establishment 

of Lake McConaughy during 1941. During 1971 and 

1973, however, a unique combination of large 

holdovers in the reservoirs and large inflows into the 

reservoirs, because of rapid snowmelt along with 

simultaneous heavy rains on the Nebraska part of the 

drainage basin, resulted in higher than normal releases 

from the reservoir (Shaffer, 1976). The two peaks on 

the high-flow graphs are not believed to indicate a sustained upward trend in mean high flows. This also was 

shown in the flow-duration curves with a flattening of 

the curves. The remainder of the stations, however, 

show little change in high flows.

LOW FLOWS

Low flows, as used in this section, are defined as the 

smallest mean flows occurring for durations of 1, 3, 7, 

14, or 30 consecutive days for any given year. The 1-, 

3-, 7-, 14-, and 30-day low flows for each of the nine 

stations are presented in figures 29 through 37. The 

North Platte River at North Platte, the South Platte 

River at North Platte, and the Platte River near Cozad 

and Overton, show an increase in the minimum level of 

low flows since about 1940, while the South Platte 

River at Julesburg, Colorado, shows an increase, starting about 1920. The South Platte River near Kersey,
g g

AREA, IN SQUARE HEC

Ol O) 

8 g 

i I i 
EFFECTS OF WATER DEVELOPMENT ON SURFACE-WATER HYDROLOGY Bll

LLJ

i

500

450

400

350

300

250

200

150

100

50

.Channel area

Island

1920 1930 1940 1950 1960 1970

FIGURE 8. Change in channel area and island area near Grand Island, Nebraska.

£

500

450

400

350

£ 30°

ui

X

£ 250

200

150

100

50

^Channel area

0

1920

1980

1930 1940 1950 1960 1970 1980

FIGURE 9. Change in channel area and island area near Duncan, Nebraska.
B12 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

1200 -

1000 -

LU 

t 8°° -

z

JC 600 -

a

400 - 

200 -

o . 

1930

Station name

North Platte River at 

North Platte, Nebraska. 

South Platte River near 

Kersey, Colorado. 

South Platte River near 

Julesburg, Colorado. 

South Platte River at 

North Platte, Nebraska.

Platte River near Cozad, 

Nebraska. 

Platte River near Overton, 

Nebraska. 

Platte River near Odessa, 

Nebraska. 

Platte River near Grand 

Island, Nebraska. 

Platte River near Duncan, 

Nebraska.

# COZAD

$ OVERTON

i

* GRAND ISLAND 

#. X DUNCAN

8 x\

*~^^rx *\

\ \ \ ft^^" ~"~~*~"" -* ^X""> ""

-

-

^^» ^ ____ ^ i* , . ,.i H

i t i i

1940 1950 1960

FIGURE 10. Change in channel width at four sites along the Platte River.

TABLE 4. Streamflow characteristics of primary data sites

[km* = square kilometers; m'/s = cubic meters per second]

Period of Drainage 

Station streamflow record area 

number (water years) (km1 )

06693000 1895-1979 80,000 

06754000 1902-03, 1905-79 24,859

06764000 1903-06, 1909-12, 1914-21, 59,927 

1925-79 

06765500 1897, 1914-15, 1917-79 62,900

06766500 1932, 1937-79 146,300 

06768000 1915-79 149,400 

06770000 1937-79 150,500 

06770500 1934-79 152,300

06774000 1895-1910, 1910-11, 157,700 

1912-15, 1928-79

1970 191

Mean annual 

discharge

(m'/s)

23.5 

22 

13.5 

9.5

14.2 

39 

35.9 

35.6 

41.2

Colorado, shows no change in low flows. The Platte 

River near Odessa, Grand Island, and Duncan, 

Nebraska, shows a slight increase in low flows, but the 

change is not as pronounced as at the upstream stations.

STATISTICAL ANALYSES

Statistical analyses were performed on annual mean 

flow and peak flow for the previously mentioned six. 

sites to make the following determinations:
EFFECTS OF WATER DEVELOPMENT ON SURFACE-WATER HYDROLOGY 

1000 E~l I I I I I | | | i | | | | | | |

B13

o 100

LU 

CO

DC 

1U 

O_

o

oo

O

Z

CO

O

10

1.0

0.1

1931-39 

1940-49 

1950-59 

1960-69 

1970-79

I I I I I I I I I I I I I I I I

0.1 0.5 2,0 5.0 10.0 20.0 50.0 70.0 90.0 95.0 

PERCENTAGE OF TIME DISCHARGE EQUALED OR EXCEEDED

99.0 99.5 99.9

FIGURE 11. Selected flow-duration curves at Station 06693000, North Platte River at North Platte, Nebraska (water years 1931-79).

1000 =~T

o

o 100 

oLLJ 

CO 

DC

00

O

10

1.0

0.1

i i

1902-03, 

1906-09 

1910-12. 

1915-19 

! 930-39

1950-59 

1970-79 

I I I I I I I I I I I I I I I___I

0.1 0.5 2.0 5.0 10=0 20.0 50.0 70.0 90.0 95.0 99.0 99.5 99.9 

PERCENTAGE OF TIME DISCHARGE EQUALED OR EXCEEDED

FIGURE 12. Selected flow-duration curves at Station 06754000, South Platte River near Kersey, Colorado

(water years 1902,1903, 1906-12,1915-79).
B14 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

1000 P=r

Q 100

O 

O

LLJ 

V)

cc

10

O

1.0

0.01

111 I I I I I

1903-06,

1909 

1910-12, 

1914-19 

1930-39

Z 1950-59

1960-69 

I I I

I I I I I I

II II III

0.1 0.5 2.0 5.0 10.0 20.0 50.0 70.0 90.0 95.0 

PERCENTAGE OF TIME DISCHARGE EQUALED OR EXCEEDED

99.0 99.5 99.9

FIGURE 13. Selecte

1000

100

Q

z O0

LLJ 

CO

cc

LLJ 10

Q.

CO

cc

LLJ

LLJ

^>

.j

_ 1

CO

D

O

e£

,

LLJ

g 0.1

X

O

CO

Q

0.01

n nni

d flow-duration curves at Station

=l I I I II I

?^S\v

- *^^^ ^^w.

~ ^^^^v^**^^

~ N>^X^^^^

 \^V<S N ^^*^x^ ^\^^^^ ^^ ^^^^^

 ^^^^^^. "**"*'' ^^*

 ^>^»lll^ *^^ ^^- * mm """""^^^ni

»

^

-

~

~

=

1940-49 

; 1950-59' 

I 1960-69 

~ 1970-79 - 

I I I I II I

06764000, South Platte River at Julesbarg, Colorado (water years 1903-79).

 1 1 \ \ \ \ 1 1 1 1 1 T|

:

=

-

^^^ ^^^» !^^^ J****^^ 

_^g3^^^r~^^^» _ ~

^^*^^^g*^^^J^^ag^^^^BiCB^^^B^^^^^^^^^ ^

^ ^ *^-^ - *x 

\ 

\ 

^^^^B^ 

**B:«^=»^^^**

\ ^^*"*^^^^

V ^^^^^^fc^ ~

\. ^^^^^^^^^ ~

V \ -

\

\

\ =

i E

}i -

i - i =

:

i i i i i i i i i i i i

0.1 0.5 2.0 5.0 10.0 20.0 50.0 70.0 90.0 95.0 99.0 99.5 99.9

PERCENTAGE OF TIME DISCHARGE EQUALED OR EXCEEDED

FIGURE 14. Selected flow-duration curves at Station 06765500, South Platte River at North Platte, Nebraska (water years 1932-79).
EFFECTS OF WATER DEVELOPMENT ON SURFACE-WATER HYDROLOGY B15

1000 pr

O 100

10

CO

O

0.1

I I I I I I T 1 T

I I I I I I I I I till

 1941 -49

I 1950-59

 1960-69

 1970-79

I I I

0.1 0.5 2.0 5.0 10.0 20.0 50.0 70.0 90.0 95.0 

PERCENTAGE OF TIME DISCHARGE EQUALED OR EXCEEDED

99.0 99.5 99.9

FIGURE 15. Selected flow-duration curves at Station 06766500, Platte River near Cozad, Nebraska (water years 1941-79).

1000 cr

100

10

1,0

0.1

0.01

I I I III I I

1931-39 -

1940-49 -

1950-59 -

1960-69 -

1970^-79 -

I I I I I I I I I I I I I I I I

0.1 0.5 2.0 5.0 10.0 20.0 50.0 70.0 90.0 95.0 

PERCENTAGE OF TIME DISCHARGE EQUALED OR EXCEEDED

99.0 99.5 99.9

FIGURE 16. Selected flow-duration curves at Station 06768000, Platte River near Overton, Nebraska (water years 1931-79).
B16 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

1000 =

o 

o

100

10

0.1

0.01

i r i r I I I I I

0 001

0.1

1940-49 

1950-59 

1960-69 

1970-79 

I I I I I I I I

0,5 2.0 5.0 10.0 20.0 50.0 70.0 90.0 95.0 

PERCENTAGE OF TIME DISCHARGE EQUALED OR EXCEEDED

99-0 99.5 99.9

FIGURE 17. Selected flow-duration curves at Station 06770000, Platte River Near Odessa, Nebraska (water years 1940-79).

8LLJ 

V)

cc

1000

100

10

O 1.0 

m

O

O

V)

0.1

0.01

0.001

T \ T

1935-39 

1940-49 

1950-59 

1960-69 

1970-79 

I I I I I

0.1 0.5 2.0 5.0 10.0 20.0 50.0 70.0 90.0 95,0 

PERCENTAGE OF TIME DISCHARGE EQUALED OR EXCEEDED

99.0 99.5 99,9

FIGURE 18. Selected flow-duration curves at Station 06770500, Platte River near Grand Island, Nebraska (water years 1935-79).
EFFECTS OF WATER DEVELOPMENT ON SURFACE-WATER HYDROLOGY BIT

1000 =r

Q

o 

o01 

V)

100

10

1.0

0.1

0.01

0.001

I I I I

1930-39 

1940-49 

1950-59 

1960-69 

1970-79 

I I I I___I I I

0.1 0.5 2.0 5.0 10.0 20.0 50.0 70.0 90.0 95.0 

PERCENTAGE OF TIME DISCHARGE EQUALED OR EXCEEDED

99.0 99.5 99.9

FIGURE 19. Selected flow-duration curves at Station 06774000, Platte River near Duncan, Nebraska (water years 1930-79).

1. The significance of major developments along the 

rivers that would cause abrupt changes in the time 

series of annual mean flow and annual peak flow and,

2. The significance of developments that would show a

more gradual change or time trend in annual peak

flow and annual mean flow.

The only major development along the Platte River 

system that was suspected to cause a drastic modification in the time series of the flow statistic was the construction of Kingsley Dam and subsequent formation 

of Lake McConaughy. Construction of coffer dams, 

diversions, and off-stream storage for Kingsley Dam 

was begun about 1935 (Shaffer, 1976), so the period of 

record for all sites was divided into two time frames, 

when available, of pre-1935 and post-1935. Water 

year 1935 was included in the post-1935 time frajne.

The significance of any major development causing 

abrupt changes in the time series of the flow variables, 

was determined by an analysis* of covariance (Riggs, 

1969; Kleinbaum and Kupper, 1978). In this analysis, 

logarithms of the flow variable were regressed against 

time with dummy variables as additional independent 

variables. The dummy variable was given a value of 1 

for the pre-1935 period and a value of 0 for the 

post-1935 period. If the partial F-statistics of the 

regression indicated that the inclusion of the dummy

variables was statistically significant to the regression, then the regression was analyzed considering the 

separate periods for time trend analyses. The level of 

significance used was the 5-percent level.

The trend analysis was performed to determine any 

gradual change of the flow variable with time. The 

trend analysis was simply a regression of the 

logarithm of the flow variable against time, for either 

the total period or for each individual period. Whether 

one or two time periods were analyzed was determined 

from the results of the analysis of covariance. If the 

hypothesis that the construction of Kingsley Dam had 

no effect on the respective flow variable is not rejected 

(corresponding to the F-statistics of the analysis of 

covariance being insignificant at the 5-percent level), 

then a single trend line would be obtained for the entire 

period of record. If, however, this same hypothesis is 

rejected then a trend line would be determined for the 

period before 1935 in addition to one for the period 

after 1935.

It is important to note that the determination of the 

trends is made only for comparative purposes, and not 

for estimations of the particular flow variable to be 

made at any site. A statistical summary of the 

covariance analyses is shown in table 5. The values in 

the table are applicable only for comparing the signifi-
B18 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

30-DAY

1930 1940 1950 1960 

WATER YEAR

1970 1980

1930 1940 1950 1960 

WATER YEAR

1970 1980

FIGURE 20. Mean 1-, 3-, 7-, 15-, and 30-day high flows at Station 06693000, North Platte River at North Platte, Nebraska

(water years 1931-79).

cant changes in hydrology between sites or between 

periods or to notice any overall trend in flow variables 

for any site.

MEAN FLOWS

Annual mean flows for the six sites are shown in 

figures 38 through 43. The North Platte River at North 

Platte, Nebraska (fig. 38), had a decrease in annual 

mean flows during the mid-1930's. From the analysis 

of covariance results of table 5, it can be seen that

there is a definite shift in the time series for mean flows 

in the North Platte around 1935. The large F-statistic 

indicates that a model of mean flow versus time should 

be broken into the pre-1935 and post-1935 time 

periods. However, the slope for each time period is not 

significantly different from zero; therefore, there was 

no significant trend in mean flow at this station during 

the period before 1935 or during the period after 1935. 

Because regressions of mean discharge versus time for 

the pre- and post-1935 periods show no change in 

mean flow with time for each period, an alternative 

test for indicating the difference in the respective
EFFECTS OF WATER DEVELOPMENT ON SURFACE-WATER HYDROLOGY B19

15-DAY

30-DAY _

1900 1910 1920 1930 1940 1950 1960 1970 1980 

WATER YEAR

0

1900 1910 1920 1930 1940 1950 1960 1970 1980 

WATER YEAR

FIGURE 21. Mean 1-, 3-, 5-, 15-, and 30-day high flows at Station 06754000, South Platte River near Kersey, Colorado

(water years 1902, 1903, 1906-12, 1915-79).

populations would be a simple t-test on the means for 

each period.

The South Platte River stations (figs. 39 through 41) 

indicate very little change in the annual mean flow 

with time, even with the extensive development 

upstream. The absence of change indicated by visual 

inspection of the records from the South Platte River 

stations is verified by the analysis of covariance. The 

F-statistics indicate that there has been no statistically significant shift in logarithms of mean flows between the two periods, and the total period t-statistics

on the regression slope parameter indicate that there 

was no significant trend over the entire period.

The annual mean flows for the Platte River near 

Overton (fig. 42) decreased abruptly during the 

mid-1930's. The statistical results of table 5 support 

this significant trend by indicating that a regression 

model of the logarithms of mean flow versus time for 

Overton need to be divided into the two specified 

periods. Slope parameters of the individual regressions 

are not significantly different from zero.

The logarithms of the mean flows for the Platte
B20 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

O 

O

UJ

cc

UJ

Q_

O

CO

z>

O

UJ

O

cc

<

O

900

800

700

600

500

400

300

200

100

0

900

800

700

600

500

400

300

200

100

0

900

800

700

600

500

400

300

200

100

1-DAY 15-DAY

1

3-DAY . 30-DAY -

1900 1910 1920 1930 1940 1950 1960 1970 1980 

WATER YEAR

7-DAY -

0

1900 1910 1920 1930 1940 1950 1960 1970 1980 

WATER YEAR

FIGURE 22.-Mean 1-, 3-, 7-, 15-, and 30-day flows at Station 06764000, South Platte River at Julesburg, Colorado

(water years 1903-79).

River near Grand Island (fig. 43) show an increasing 

trend for the entire period of record, which began after 

1935. This increase probably was unduly affected by 

the high flow water years 1971-74.

Monthly mean flows for the period of record for 

April through September are shown in figures 44 

through 47. These months were chosen because they 

encompass the critical growth period for vegetation as 

defined by the U.S. Fish and Wildlife Service. The 

months also include the major runoff period and irrigation season. Only four stations were used in this 

analysis to show the changes on the North Platte

River, South Platte River, and the Platte River in and 

near the critical reach.

The monthly mean flows during July and August for 

the North Platte River (fig. 44) indicate a marked increase beginning about 1945. These are two of the peak 

irrigation months and the increases are the result of 

releases from Lake McConaughy. April and May are 

the months of spring runoff and the North Platte River 

at North Platte shows a decrease in these flows following the construction of Lake McConaughy, which now 

holds back the higher flows.

The South Platte River at North Platte (fig. 45) had
EFFECTS OF WATER DEVELOPMENT ON SURPACE-WATER HYDROLOGY B21

30-DAY

1930 1940 1950 1960 

WATER YEAR

1970 1980

1940 1950 1960 1970 1980 

WATER YEAR

FIGURE 23. Mean 1-, 3-, 7-, 15-, and 30-day flows at Station 06765500, South Platte River at North Platte, Nebraska

(water years 1932-79).

little change in the monthly mean flows. The records 

for the Platte River near Overton and Grand Island 

(figs. 46 and 47) do not indicate the large change that 

occurred in the North Platte River, but do show a 

small increase in the monthly mean flows during July 

and August. The change in monthly mean flows 

possibly is damped out by the South Platte River, 

which has had little change in the mean flows.

INSTANTANEOUS PEAK FLOWS

The yearly instantaneous peak flows for six stations 

in the study reach are given in figures 48 through 53.

The North Platte River at North Platte (fig. 48) indicates the largest change in peak flows of the six stations; this is most likely a result of the on-stream construction of Kingsley Dam, which holds back the peak 

flows that once continued downstream. The statistical 

analysis (table 6) indicates that a regression model of 

the logarithms of annual peak flow versus time needs 

to be divided into two models corresponding to 

pre-1935 and post-1935 time periods. This first model 

indicates a decrease in peak flows to 1935; following 

1935 there is no significant change in the peak flows 

with time.
B22 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

15-DAY

30-DAY

1940 1950 1960 1970 

WATER YEAR

1980

1940 1950 1960 

WATER YEAR

1970 1980

FIGURE 24. Mean 1-, 3-, 7-, 15-, and 30-day flows at Station 06766500. Platte River near Cozad, Nebraska (water years 1941-79).

For the South Platte River near Kersey, Colorado, 

and the South Platte River at Julesburg, Colorado, the 

regression results indicate no shift in time series for 

the logarithms of peak flows as well as no significant 

trend with time. The F-test for the South Platte River 

at North Platte (fig. 51) indicates a homogeneity in the 

data set for the entire period, and there is a gradual 

decrease in annual peak flows throughout the entire 

period of record. The 1935 data point may have an inordinate effect on the trend of the regression.

The Platte River near Overton (fig. 52) indicates a 

single regression of the logarithms of annual peak flow 

versus time with a negative trend for the period of 

record, while statistically the 1935-present data set of

peak flows at Grand Island (fig. 53) shows no appreciable trend. The similarity of the peak flows at 

Overton compared to the South Platte River near 

North Platte, shown by both statistical results and 

visual inspection, is indicative of the important contribution of the South Platte peak flows to the Platte 

River major peak flows. The overlaid plots of peak 

flows for the South Platte River at North Platte, 

Nebraska, and the Platte River near Overton, 

Nebraska, are shown in figure 54. This is substantiated 

by Williams (1978) who stated that the North Platte 

River upstream from Lake McConaughy showed a 

decrease in peak flow after the construction of each of 

the major reservoirs in Wyoming, and the Platte River
EFFECTS OF WATER DEVELOPMENT ON SURFACE-WATER HYDROLOGY B23

15-DAY -

30-DAY -

1930 1940 1950 1960 1970 1980 

WATER YEAR

1940 1950 1960 

WATER YEAR

1970 1980

FIGURE 25.-Mean 1-, 3-, 7-, 15-, and 30-day high flows at Station 06768000, Platte River near Overton, Nebraska

(water years 1931-79).

near Grand Island, Nebraska, shows similarity of 

peak-flow occurrences (fig. 54).

In order to illustrate the effect of the peak flows and 

mean flows of the South Platte and North Platte 

Rivers on the peak flows and mean flows for the Platte 

River near Overton, regression analyses were 'performed relating the logarithms of these flow variables, 

and the results are listed in table 7. Because the timetrend analyses previously discussed for both peak and 

mean flows of the North Platte River at North Platte 

indicate that two separate time periods need to be considered in making statistical determinations regarding 

this site, the interstation regressions were performed 

for each time period.

The difference in the magnitudes of the slope coefficients of the respective North Platte River and South 

Platte River flow variables are not legitimate 

measures of the relative importance of one independent variable compared to another in affecting the flow 

variables at Overton. This is true because the size of a 

coefficient would change as a result of merely changing 

the scale of the measurements of the variable. 

However, by adjusting the ordinary least-squares 

regression-slope coefficient estimates by the ratio of 

the standard deviations of the independent and dependent variables, an objective measure of importance of 

the independent variables can be determined. These 

adjusted coefficients are called "beta coefficients"
B24 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

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15-DAY

600

500

400

0 300

553 20°

2

100

0

600

500

400

300

200

100

3-DAY

1930 1940 1950 1960 

WATER YEAR

1970 1980

7-DAY

0

1930 1940 1950 1960 

WATER YEAR

1970 1980

FIGURE 26. Mean 1-, 3-, 7-, 15-, and 30-day high flows at Station 06770000, Platte River near Odessa, Nebraska

(water years 1940-79).

(Goldberger, 1964). The beta coefficients calculated 

from the slope coefficients in table 7 are listed in table 

8.

The pre-1935 beta coefficients from table 8 indicate 

that the mean flow variable from the North Platte 

River at North Platte is the more important contributor to the mean flow variable at Overton. Similarly, the pre-1935 peak flow variable beta coefficients 

show the North Platte River peaks to be slightly more 

dominant then the peak flow variable from the South 

Platte River in affecting the peak flow variable at 

Overton. However, the post-1935 beta coefficient from

the mean flow analysis indicate that the South Platte 

River has equalized its effect on the mean flow variable 

at Overton relative to the North Platte River's effect. 

The regression analysis of the post-1935 peak flow 

variable shows that the roles of the more important 

contributor for this flow variable have reversed. This 

role reversal can be explained by the fact that the 

South Platte peak flows account for the majority of the 

significant peaks at Overton. Although the North 

Platte River is a major contributor to most annual 

peak flows at Overton, most large peaks are derived 

from the South Platte basin.
EFFECTS OF WATER DEVELOPMENT ON SURFACE-WATER HYDROLOGY B25

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o

cc

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600

500

400

300

200

100

600 

°- 500 

£ 400

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00

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500

400

300

200

100

1-DAY 15-DAY

3-DAY 30-DAY

1930 1940 1950 1960 1970 1980 

WATER YEAR

7-DAY

0

1930 1940 1950 1960 1970 1980 

WATER YEAR

FIGURE 27. Mean 1-, 3-, 7-, 15-, and 30-day high flows at Station 06770500 Platte River near Grand Island, Nebraska

(water years 1935-79).

SUMMARY

Flow in the Platte River basin is affected by t^ansmountain diversions in the headwaters, dams that 

create on-stream reservoirs, structures that divert 

water to off-stream reservoirs, ground-water pumpage 

from lands bordering rivers, return of water to channels from irrigation and hydropower releases, possible 

gain or loss of water by seepage, water demands of an 

increasing population, and the requirements of more 

vegetation that now grows in the river valley. These effects of man in the Platte River basin are the most 

logical explanation for the observed changes in flow.

Changes in surface-water hydrology and channel size 

have occurred at different times throughout the basin. 

The hydrologic changes are identified by shifts in 

levels of low flows and high flows, and the flattening of 

flow-duration curves. These changes also are illustrated in the time series of annual mean and peak 

flows. Changes in channel morphology are exhibited in 

the plots of width and area of the Platte River channels 

through time.

The hydrologic and channel changes have occurred
B26 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

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600

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400

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700

600

500

400

300

200

100

0

700

600

500

400

300

200

100

1-DAY 15-DAY

3-DAY 30-DAY

1920 1930

7-DAY

0

1920

1940 1950 1960 

WATER YEAR

1970 1980

1930 1940 1950 1960 

WATER YEAR

1970 1980

FIGURE 28.-Mean 1-, 3-, 7-, 15-, and 30-day high flows at Station 06774000, Platte River near Duncan, Nebraska

(water years 1930-79).

in such a manner that the upstream reaches were affected earliest in the period of record. Observing the 

10-year flow-duration curves and low flows at the sites 

studied indicate the stations upstream of the Platte 

River near Overton are maintaining relative stability, 

while those sites downstream of Overton still are adjusting to the changes in the hydrologic system 

upstream. This relative stability reached at each of the 

sites is as follows: The North Platte River at North 

Platte, Nebraska, about 1941; the South Platte River 

at Julesburg, Colorado, about 1920; the South Platte 

River at North Platte, Nebraska, about 1937; and the 

Platte River near Cozad and Overton, Nebraska, about

1950. The Platte River near Odessa, Grand Island, and 

Duncan, Nebraska, still is adjusting toward stability, 

while the South Platte River near Kersey, Colorado, 

has not shown any significant change for the period of 

record investigated. Therefore, in hydrologic analysis, 

caution needs to be taken in defining the period of 

record used because of the changing hydrologic 

system.

At each site, statistical analyses were performed on 

records prior to and following the construction of 

Kingsley Dam, to determine the effect on the peak and 

annual mean flows. The South Platte River in Colorado 

shows no trend in either the peak or annual mean
EFFECTS OF WATER DEVELOPMENT ON SURFACE-WATER HYDROLOGY 

TABLE 5. Summary of regression and covariance analysis for the logarithms of annual mean flows

B27

Site

North Platte River at 

North Platte, Nebraska. .

South Platte River near 

Kersey, Colorado .......

South Platte River at 

Julesburg, Colorado .....

South Platte River at 

North Platte, Nebraska. .

Platte River near 

Overton, Nebraska .......

Platte River near 

Grand Island, Nebraska. .

F-statistic

....73.9*

.....2.26

.....1.28

. . . . . 2.50

. ...20.2*

equation

2

1

1

1

2

1

Pre-1935 population

Slope (-statistic

-0.006 -1.13

-.005 -

-.006 -

_ Ofi4 _

-.031 -1.82

Post-1935 population

Slope (-Statistic

0.000 0.03

.015 -

.011 -

OHO _

.010 1.99

.013 -

Slope

0.003

-.001

-.006

.013

Total record

(-statistic

0.85

-.26

-1.16

2.30*

 Indicates statistic is significant at the 5-percent level

TABLE 6. Summary of regression and covariance analysis for the logarithms of annual peak flows

Site

North Platte River at 

North Platte, Nebraska . .

South Platte River near 

Kersey, Colorado .......

South Platte River at 

Julesburg, Colorado .....

South Platte River at 

North Platte, Nebraska . .

Platte River near 

Overton, Nebraska. .....

Platte River near 

Grand Island, Nebraska. .

F-statistic

. . . 156.4*

. .. .0.570

. . . . . 2.40

. . . . . 1.31

.....1.93

equation

2

1

1

1

1

1

Pre-1935 population

Slope (-statistic

-0»021 -3.15*

-.004 -

-.010 -

-.067 -

-.037 -

Post-1935 population

Slope (-statistic

0.001 0.24

.016 -

004 

.077 -

007 

- 007 

Slope

0.007

-.004

-.018

-.019

-.007

Total record

(-statistic

1.63

-.62

-2.22*

-4.23*

-.99

 Indicates statistic is significant at the 5-percent level

TABLE 7. Summary of regression results relating the logarithms of mean annual and peak flows of the South Platte River and North Platte

River to the logarithms of mean annual and peak flows of the Platte River.

Variable

Slope regression Slope regression

coefficient (-statistic* coefficient (-statistic*

Pre-1935 Logarithms of mean flow 

Platte River near 

Overton, Nebraska. 

Logarithms of peak flow 

Platte River near 

Overton, Nebraska.

Post-1935 Logarithms of mean flow 

Platte River near 

Overton, Nebraska. 

Logarithms of peak flow 

Platte River near 

Overton, Nebraska.

0.984

.674

.725

.288

7.99

5.17

7.09

2.07

0.166

.260

.376

.353

2.85

4.45

6.57

6.88

*A11 ( values are significant at the 5 percent level
B28 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

TABLE 8. Summary of beta coefficients relating the logarithms of 

mean annual and peak flows of the North Platte River and South 

Platte River to the logarithms of mean annual and peak flows of the 

Platte River

Variable

Beta Beta

coefficient coefficient

(North Platte) (South Platte)

Pre- Logarithms of mean flow 

1935 Platte River near

Overton, Nebraska. 0.756 0.269

Logarithms of peak flow 

Platte River near 

Overton, Nebraska. .576 .495

Post- Logarithms of mean flow 

1935 Platte River near

Overton, Nebraska. .571 .529

Logarithms of peak flow 

Platte River near 

Overton, Nebraska. .211 .702

flows. The South Platte River at North Platte, 

Nebraska, shows no trend in annual mean flows, but a 

decrease in peak flows for the period of record. The 

North Platte River at North Platte, Nebraska, and the 

Platte River near Overton, Nebraska, show a decrease 

in both the peak and annual mean flows, while the 

Platte River near Grand Island, Nebraska, shows no 

trend in the peak flows, but a slight increase in annual 

mean flows.

REFERENCES

Bentall, Ray, 1975, Hydrology, Nebraska Mid-State Division and 

associated areas: Nebraska University Conservation and 

Survey Division, Institute of Agriculture and Natural 

Resources Report, 256 p.

Bentall, Ray, and Shaffer, F. B., 1975, Availability and use of water 

in Nebraska, 1975: Nebraska University Conservation and 

Survey Division, Institute of Agriculture and Natural 

Resources Report, no. 48, 121 p.

Currier, P. J., and Van Der Valk, A. G., 1980, The vegetation of the 

Platte River, in Phytosociology, forest development, and seedling establishment: U.S. Fish and Wildlife Service, Northern 

Prairie Wildlife Research Center, Jamestown, North Dakota, 

40 p.

Gerlek, Steve, 1977, Water supply management analysis and alternative development for the South Platte River basin, v. 2: U.S. 

Army Corps of Engineers, 354 p.

Goldberger, A. S., 1964, Econometric theory: New York, John Wiley 

and Sons, 399 p.

Kleinbaum, D. G., and Kupper, L. L., 1978, Applied regression 

analyses and other multivariate methods: Belmont, California, 

Wadsworth Publishing, p. 209-226.

Meyers, J. S., 1962, Evaporation from the seventeen western 

States: U.S. Geological Survey Professional Paper 272-D, p. 

71- 100.

Riggs, H. C., 1969, Some statistical tools in hydrology: U.S. 

Geological Survey Techniques of Water-Resources Investigations, Book 4, Chapter Al, 39 p.

___1972, Low-flow investigations: U.S. Geological Survey 

Techniques of Water-Resources Investigations, Book 4, 

Chapter Bl, p. 15.

Shaffer, F. B., 1976, History of irrigation and characteristics of 

streamflow in Nebraska part of the North and South Platte 

River basins: U.S. Geological Survey Open-File Report 76-167, 

98 p.

Williams, G. P., 1978, The case of the shrinking channels-The North 

Platte and Platte Rivers in Nebraska: U.S. Geological Survey 

Circular 781, 48 p.
FIGURES 29-54
B30 HYDROIXXHC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

20

15

10

14-DAY

30-DAY

1930 1940 1950 1960 

WATER YEAR

1970 1980

7-DAY

1930 1940 1950 1960 1970 1980 

WATER YEAR

FIGURE 29.-Mean 1-, 3-, 7-, 14-, and 30-day low flows at Station 06693000, North Platte River at North Platte, Nebraska

(water years 1931-79).
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FIGURE 36. Mean 1-, 3-, 7-, 14-, and 30-day low flows at Station 06770500, Platte River near Grand Island, Nebraska

(water years 1935-79).
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1890 1900 1910 1920 1930 1940 

WATER YEAR

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FIGURE 38. Annual mean discharges at Station 06693000, North Platte River at North Platte, Nebraska (water years 1895-1979). 

70

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1900 1910 1920 1930 1940 1950 1960 1970

WATER YEAR

FIGURE 39. Annual Mean discharges at Station 06754000, South Platte River Near Kersey, Colorado

(water years 1902,1903,1906-12,1915-79).

1980
DISCHARGE. IN CUBIC METERS PER SECOND DISCHARGE. IN CUBIC ME
EFFECTS OF WATER DEVELOPMENT ON SURFACE-WATER HYDROLOGY B41

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1910 1920 1930 1940 1950 

WATER YEAR

1960 1970 1980

FIGURE 42. Annual mean discharges at Station 06768000, Platte River near Overton, Nebraska (water years 1915-79). 

120

100

80

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S

3

40

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20

1930 1940 1950 1960 

WATER YEAR

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FIGURE 43. Annual mean discharges at Station 06770500, Platte River near Grand Island, Nebraska (water years 1934-79).
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EFFECTS OF WATER DEVELOPMENT ON SURFACE-WATER HYDROLOGY B43

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MAY AUGUST

JUNE SEPTEMBER

1930 1940 1950 1960 1970 1980 1930 1940 1950 1960 1970 1980

WATER YEAR

FIGURE 45. Monthly mean discharges for April through September at Station 06765500, South Platte River at North Platte,

Nebraske (water years 1932-78).
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HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

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250

200

150

100

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1930

APRIL JULY

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UNE SEPTEMBER

1940 1950 1960 1970 1980 1930 

WATER YEAR

1940 1950 1960 1970 1980

FIGURE 46. Monthly mean discharges for April through September at Station 06768000, Platte River near Overton,

Nebraska (water years 1931-78).
300

250

200

150

100

50

0

EFFECTS OF WATER DEVELOPMENT ON SURFACE-WATER HYDROLOGY B45

APRIL JULY

AJ\

AUGUST

SEPTEMBER

1940 1950 1960 1970 1980 1930 1940 

WATER YEAR

1950 1960 1970 1980

FIGURE 47. Monthly mean discharges for April through September at Station 06770500, Platte River near Grand Island,

Nebraska (water years 1935-78).
B46 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

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1890 1900 1910 1920 1930 1940 

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FIGURE 48.-Annual instantaneous peak discharges at Station 06693000, North Platte River at North Platte, Nebraska

(water years 1895-1979).

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1900 1910 1920 1930 1940 1950

WATER YEAR

1960 1970 1980

FIGURE 49.-Annual instantaneous peak discharges at Station 06754000, South Platte River near Kersey, Colorado

(water years 1902, 1903, 1905-12, 1914-79).
EFFECTS OF WATER DEVELOPMENT ON SURFACE-WATER HYDROLOGY B47

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WATER TEAR

 Annual instantaneous peak discharges at Station 06764000, South Platte River at Julesburg, Colorado 

(water years 1902-06, 1909-12, 1914-15, 1917-18, 1920-24, 1926-79).

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FIGURE 51. Annual instantaneous peak discharges at Station 06765500, South Platte River at North Platte, Nebraska

(water years 1897, 1914-15, 1917, 1921-79).
B48 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

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WATER YEAR

1960 1970 1980

FIGURE 52. Annual instantaneous peak discharges at Station 06768000, Platte River near Overton, Nebraska

(water years 1915-17, 1919-23, 1926-79).

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FIGURE 53. Annual instantaneous peak discharges at Station 06770500, Platte River near Grand Island, Nebraska (water years 1934-79).
EFFECTS OF WATER DEVELOPMENT ON SURFACE-WATER HYDROLOGY B49

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FIGURE 54.-Comparison of instantaneous peak flows on the South Platte River at North Platte, Nebraska, and the Platte River

near Overton, Nebraska.

Hydraulic Geometry of the 

Platte River Near Overton, 

South-Central Nebraska

By THOMAS R. ESCHNER

HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

GEOLOGICAL SURVEY PROFESSIONAL PAPER 127 7-C

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1983

CONTENTS

Abstract 

Introduction 

Description of the study area 

Field study area 

Cross-section locations 

Channel characteristics 

The concept of hydraulic geometry 

At-a-station hydraulic geometry - 

Downstream hydraulic geometry 

Assumptions 

The b-f-m diagram 

At-a-station hydraulic geometry 

Summarized data 

Page 

Cl

1

2

2

3

3

5

5

5

6

6

Page

At-a-station hydraulic geometry Continued C8 

Field data 12 

Complex at-a-station hydraulic geometry 15 

Meaning of the exponents 17 

Hydraulic and morphologic information from the b-f-m 

diagram 18 

Systematic variation and analytical error 19 

Significance of complex hydraulic-geometry relations 20 

Implications and limitations of at-a-station hydraulicgeometry relations 23 

Summary and conclusions 23 

References cited 24 

Summary of statistical data 27

ILLUSTRATIONS

FIGURE 1. Index map of the Platte River basin C3

2. Map showing the location of the study area in south-central Nebraska 4

3. Divided b-f-m diagram, showing fields that represent different channel types 7 

4-15. Relation of width, depth, and velocity to discharge:

4. Platte River 30 meters downstream from gage near Cozad, Nebraska, post-1969 record 10

5. Platte River 120 meters downstream from gage near Cozad, Nebraska, 1964-1969 record 10

6. Platte River 120 meters downstream from gage near Cozad, Nebraska, post-1969 record 11

7. North channel of the Platte River 90 meters downstream from gage near Overton, Nebraska, post-1969 record 11

8. Platte River 30 meters downstream from gage near Cozad, Nebraska, for the period of record 12

9. Platte River 60 meters downstream from gage near Cozad, Nebraska, for period of record 12

10. Platte River 120 meters downstream from gage near Cozad, Nebraska, for the period of record 13

11. Platte River 60 meters downstream from gage near Odessa, Nebraska, for the period of record 13

12. Platte River 90 meters downstream from gage near Odessa, Nebraska, for the period of record 14

13. Platte River near Cozad, Nebraska 14

14. Platte River near Lexington, Nebraska 15

15. Platte River downstream from Johnson-2 Return near Lexington, Nebraska 15

16. Cross-section surveys of the Platte River at the Cozad field section 16

17. B-f-m diagram showing plotting positions of current at-a-station hydraulic-geometry exponents, and exponents from the

period of record 17 

18-21. B-f-m diagram showing changes in hydraulic-geometry exponents with time. Data from the:

18. North channel of the Platte River in the vicinity of the gage near Cozad, Nebraska 21

19. Platte River in the vicinity of the gage near Odessa, Nebraska 21

20. North channekrf the Platte River in the vicinity of the gage near Cozad, Nebraska; partitioned data sets 22

21. Platte River in the vicinity of the gage near Odessa, Nebraska; partitioned data sets 22

TABLES

TABLE 1. At-a-station hydraulic-geometry exponents for summarized data, expressed as coefficients of the power function: (log w) 

log a+6(k>g Q) C9 

2. Significance levels for at-a-station hydraulic-geometry equations from summarized data 28

ill

HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

HYDRAULIC GEOMETRY OF THE PLATTE RIVER NEAR OVERTON,

SOUTH-CENTRAL NEBRASKA

By THOMAS R. ESCHNER

ABSTRACT

At-a-station hydraulic-geometry relations were computed for a 

reach of the Platte River in south-central Nebraska containing 

habitat for sandhill and whooping cranes. The range of exponents of 

log-linear relations is large between different reaches of the river, and 

among different sections within a given reach. In general, simple 

linear regression of the logarithms of width, depth, and velocity on 

the logarithm of discharge yielded large proportionate reductions in 

the variances of the dependent variables. Examination of plots of the 

data indicates that, in many instances, the relations are log-linear, or 

power functions (Leopold and Maddock, 1953).

Use of the b-f-m diagram, a graphical representation of at-a-station 

hydraulic-geometry exponents (Rhodes, 1977), allows responses of 

width, depth, and velocity to changing discharge to be interpreted 

from physical consideratons. In general, based on simple power functions, with increasing discharge for the Platte River in the study area; 

(1) Width-depth ratio increases; (2) velocity increases more slowly 

than channel cross-sectional area; and (3) roughness increases. The 

b-f-m diagram also allows the systematic variation of the hydraulicgeometry exponents with time to be assessed. In general, the width 

exponent has decreased with time. Trends in the velocity and depth 

exponents are less apparent.

For some sections, power functions do not appear to describe adequately the observed at-a-station relations. For these sections, breaks 

in the slopes of the hydraulic geometry relations serve to partition the 

data sets. Power functions fit separately to the partitioned data 

described the width-, depth-, and velocity-discharge relations more 

accurately than did a single power function. Plotting positions of the 

exponents from hydraulic geometry relations of partitioned data sets 

on b-f-m diagrams indicate that much of the apparent variation of 

plotting positions of single power functions results because the single 

power functions compromise both subsets of partitioned data. 

Although there is for some sections a suggestion of a decrease in the 

width exponent through time even for partitioned data, in general the 

differences in plotting positions between the subsets of partitioned 

data for a given time interval are at least as great as the differences in 

plotting positions between successive time intervals for nonpartitioned data.

The shape of the complex at-a-station relations may have at least 

three causes: (1) Changes in bed roughness with discharge may not be 

linear (Richards, 1973); (2) channel shape may preclude constant rates 

of increase in water width and depth with increasing discharge; and 

(3) an insufficient range of data values may account for apparent complex behavior. Complex hydraulic-geometry relations have significance for channel maintenance and preservation of sandhill- and 

whooping-crane habitat. Nearly the entire channel bed of sections exhibiting complex hydraulic-geometry relations can be covered with 

low-magnitude discharges. Vegetation encroachment may be inhibited, preventing further channel narrowing, where non-log-linear 

relations apply. Discharges required to cover the channel bed are 

lower than discharges estimated as necessary for channel maintenance by other methods, but the former may serve as minimritn 

values for channel maintenance.

INTRODUCTION

The Platte River in south-central Nebraska in the 

mid-1800s exceeded 1 km (kilometer) in width. Descriptions of its appearance and its treacherous fords today 

seem exaggerations, because the present river width 

rarely exceeds 300 m (meters). Sandbars and islands 

have become vegetated, as have the banks and adjacent 

bottomlands. These morphologic and vegetative 

changes have resulted from continuous changes in the 

hydrology of the river. Annual discharge and annual 

peak discharge have decreased in many locations since 

the development of irrigation in the Platte River basin 

(Kircher and Karlinger, 1981). These changes in 

streamflow characteristics have decreased the capability of the river to shift sandbars and scour encroaching 

vegetation (Eschner, Hadley, and Crowley, 1981). 

Equally as important, irrigation practices apparently 

have changed the Platte River from an intermittent 

stream to a perennial stream in many locations.

Changes in hydrology and channel morphology of the 

Platte River have reduced its value as a wildlife habitat 

for some species and increased its value for others. The 

river presently is used by a wide variety of waterfowl, 

including ducks, geese, bald eagles, and sandhill and 

whooping cranes. Sandhill cranes (Grus canadensis) and 

the endangered whooping crane (Grus americana) use 

the Platte River as a staging area and stopover point. In 

March, these birds spend several weeks in the Platte 

River valley prior to completing their northward migration to breeding grounds in Canada. In the fall, the river

Cl
C2 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

is used as a stopover point when the birds return to 

wintering grounds in the southern United States (U.S. 

Fish and Wildlife Service, 1981).

Two features of the Platte River especially are desirable as crane habitat. Unvegetated sandbars in broad, 

shoal reaches of the river provide ideal night-roosting 

sites; the open character of these sites decreases the 

likelihood of predation. Wet meadows adjacent to the 

river provide important nutrients, in the form of 

invertebrates, for the cranes.

In general, changes in the hydrology and channel morphology of the Platte River have been detrimental to 

crane habitat (U.S. Fish and Wildlife Service, 1981). As 

vegetation increases in height and channel width decreases, the river loses its suitability as a night-roosting 

area Changes in river water level affect the quality of 

the wet meadows. If these meadows are not subirrigated adequately, they may be converted to pasture or 

cropland, and, therefore, will be lost as feeding grounds.

Not all of the Platte River valley in south-central 

Nebraska is presently prime habitat. Frith (1974) 

classified crane habitat along the Platte River and 

found a broad range of habitat quality. The U.S. Fish 

and Wildlife Service (1978) determined that the 100-km 

reach of the Platte River downstream from Lexington, 

Nebraska was critical habitat for the whooping crane; 

maintaining the crane habitat along this reach of the 

river is essential for the preservation of the whooping 

crane.

Studies of channel changes of the Platte River basin 

have been undertaken, at least at a preliminary level. 

Schumm (1968) described the reduction in channel 

width of the North Platte River and attributed it to the 

decrease in annual peak flows of the river. Nadler (1978) 

showed that the South Platte River had decreased in 

width and increased in sinuosity, the ratio of channel 

length to valley distance, since the beginning of irrigation. Changes in channel width, channel pattern, and 

vegetation encroachment on the North Platte and 

Platte Rivers were described by Williams (1978b). The 

processes of width reduction of the Platte River were 

documented by Eschner and others (1981).

The primary objective of this study were to compute 

at-a-station hydraulic-geometry relations at selected 

sites, to examine how the relations have changed with 

time, and to determine the significance of the relations 

for channel maintenance.

DESCRIPTION OF THE STUDY AREA

The Platte River is formed by the confluence of the 

North Platte and South Platte Rivers, about 6 km east 

of the city of North Platte, Nebraska From this confluence, the Platte River flows generally toward the east. 

Initially the river arcs to the north to Duncan, then it 

arcs south to Ashland. From Ashland, the Platte River 

flows 80 km east to its confluence with the Missouri 

River (fig. 1). The total area drained by the Platte River 

is about 233,000 km2 (square kilometers). The Loup 

River, the primary tributary to the Platte River, drains 

39,400 km2.

FIELD STUDY AREA

The field study area is a 72-km reach of the Platte 

River in south-central Nebraska, extending from the 

town of Cozad to the town of Odessa (fig. 2). The entire 

area lies within the High Plains Section of the Great 

Plains Province of the Interior Plains (Fenneman, 1931).

Annual precipitation decreases to the west across the 

study area, ranging from about 560 mm (millimeters) at 

Kearney to about 510 mm at Cozad. Most of the precipitation falls as spring and summer rains, and the largest 

amount falls in June. Total lake evaporation is about 

1,270 mm per year throughout the area

The Platte River in the study area is affected by man 

to varying degrees. Gravel pits, both active and abandoned, dot the river bottom. Water is diverted for the 

Dawson County Canal immediately upstream of the 

study area Water from the Tri-County Supply Canal 

that has been used for hydropower generation and for 

cooling is returned to the South Channel of the river 

through the Johnson-2 power return at a point about 

midway between Lexington and Overton. The amount 

of water returned depends on irrigation demand and 

power generation at hydropower plants. About 3 km 

east of the town of Elm Creek, water is diverted by the 

Kearney Canal for irrigation and hydropower. The 

banks of the river have been riprapped at various locations to reduce the erosive effect of the river against the 

banks.

Three gaging stations, operated by the U.S. Geological Survey and the Nebraska Department of Water Resources, are within the study reach. The river at the 

gage near Cozad, at the western edge of the study area, 

has a drainage area of approximately 146,300 km2. Two 

channels are present at Cozad, and each channel is 

gaged separately. Only the north channel is considered 

in the discussion of at-a-station hydraulic geometry in 

this report. These gages produced records from April 

1939, with irrigation-season records for 1932, and 1937 

to 1938. The gage near Overton, although not occupying the same site for the period of record, produced 

records from October 1914 to the present, and gage 

heights from the period July to September 1914. The 

drainage area of the Platte River at this gaging station
HYDRAULIC GEOMETRY OF THE PLATTE RIVER NEAR OVERTON, NEBRASKA

111° 104°

 .. 

C3

41'

[NEBRASKA

100 200 KILOMETERS

KEY TO NUMBERED TOWNS

1 North Platte

2 Cozad

3 Lexington

4 Overton

5 Odessa

6 Kearney

7 Grand Island

8 Duncan

9 Ashland

FIGURE 1. Index map of the Platte River basin.

is about 149,400 km2. The gaging staton near Odessa, at 

the eastern end of the study area, has had a recording 

gage since October 1938. The basin area at this gage is 

approximately 150,500 km2.

CROSS-SECTION LOCATIONS

Six river cross sections have been established within 

the study reach for field observations (fig. 2). These sections will be referred to as Cozad (section 1), Lexington 

(section 2), Johnson 2 (section 3), Overton (section 4), 

Elm Creek (section 5), and Odessa (section 6), in downstream order. The location of the Johnson-2 power 

return also is indicated in figure 2.

CHANNEL CHARACTERISTICS

The channel of the Platte River in the study area 

ranges in width from about 120 m to over 500 m. Water 

depth varies from a few millimeters over bars at low 

flow to over 2 m in the thalweg at high flow.

Vegetated sandbars occur throughout the river at 

average flows, (near mean annual); the width of these 

bars approaches two-thirds of the channel width; their 

length approaches twice the channel width. Vegetation 

comprises low weeds and grasses, with willow or cottonwood seedlings at various stages of development; these 

seedlings, if not destroyed by flood, become firmly established and cause the sandbar eventually to become 

an island. Permanent islands also occur.

Vegetation along the river bank consists of grasses, 

shrubs, and trees. The trees most commonly found are 

species of willow, cottonwood, and ash. Russian olive 

and red cedar trees grow in areas not frequently inundated. Tamerisk has been seen infrequently, and only 

within the last decade (Joe Jeffrey, rancher, oral commun., 1979).

The Platte River channel is braided at low flows, with 

threads of water intertwining among ripples, dunes, and 

sandbars. At the highest flows, water extends from 

bank to bank and flows straight through the channel. 

At many locations, the channel pattern appears to be 

meandering or anastomosing, that is, consisting of 

branches that separate and rejoin around islands.
100° 00' 99° 45' 99° 30' 99° 15'

EXPLANATION 

A GAGING STATION 

CROSS SECTION

FIGURE 2. Location of the study area in south-central Nebraska.
HYDRAULIC GEOMETRY OF THE PLATTE RIVER NEAR OVERTON, NEBRASKA C5

THE CONCEPT OF 

HYDRAULIC GEOMETRY

The term hydraulic geometry was introduced by 

Leopold and Maddock (1953) to describe the way in 

which channel characteristics vary with discharge. In 

essence, hydraulic geometry is an empirical model expressing the changes in channel and hydraulic variables 

as simple power functions of discharge. The resulting 

equations have the form:

w=aQb 

d=cQf 

v=kQm

(1)

(2)

(3)

where

w = width, 

d = mean depth, 

v = mean velocity, 

Q = instantaneous discharge, 

b, f, and m = the exponents of the equations, and 

a, c, and k = the coefficients.

For continuity, the product of width, mean depth, and 

mean velocity must be the discharge:

Q=wdv. (4)

Then the product of the hydraulic-geometry coefficients 

and the sum of the exponents must be:

Q=ack (5)

Hydraulic-geometry relations can be defined for both 

specific cross sections on a river (at-a-station hydraulic 

geometry) and different cross sections on a river at a constant frequency of discharge (downstream hydraulic 

geometry), although not necessarily in downstream 

order. The exponents of both the at-a-station and downstream relations have been studied in various physiographic and climatic regions. In addition, expected 

exponents under ideal conditions have been derived 

theoretically for both downstream and at-a-station 

geometry.

AT-A-STATION HYDRAULIC GEOMETRY

Exponents for at-a-station hydraulic geometry, 

reported in the literature, range at least from 0.0 to 0.84 

for the width exponent, 6; 0.01 to 0.84 for the depth exponent, f, and 0.03 to 0.99 for the velocity exponent, m

(Rhodes, 1978). Park (1977) calculated modal class 

values for 139 at-a-station data sets for streams in proglacial, humid temperature, semiarid, tropical, and 

"unspecified" regions. Park found that exponent values 

for width fell within the class 0.0 to 0.1, for depth within 

the class 0.3 to 0.4, and for velocity within the class (0.4 

to 0.5. Knighton (1975) reported average exponents for 

206 cross sections in the United States as 0.16 for width, 

0.43 for depth, and 0.42 for velocity. Perhaps the most 

commonly cited average exponent values are those computed by Leopold and Maddock (1953) for "a large variety of rivers* * *." The values are 6=0.26, /=0.40, and 

m=0.34.

Computed exponent values have been compared to 

theoretically derived at-a-station values. Theoretical at-astation exponent values will vary with the channel shape 

assumed for their derivation. The "most probable 

values" as generally cited (Park, 1978; Rhodes, 1978) are 

6=0.23, /=0.42, and m=0.35 (Langbein, 1964). Wolman 

and Brush (1961) derived theoretical at-a-station crosssection area (A), and width exponents based on flume 

studies of coarse noncohesive sands. For channels at or 

above the critical velocity of incipient motion, A=Q°-g 

and 6=0.90. For channels below the point of incipient 

motion, A=Q° 9 and 6=0.75. Wolman and Brush (1961) 

cited the Platte River near Grand Island, Nebraska at 

moderate stages as an example of a river in coarse noncohesive sands that behaves according to their 

derivation.

DOWNSTREAM HYDRAULIC GEOMETRY

Computed downstream exponents range at least from 

0.03 to 0.89 for width, 0.09 to 0.70 for depth, and -0.51 

to 0.75 for velocity. These values are those reported by 

Park (1978) for 72 observations. The modal classes of 

these observations are 0.4 to 0.5 for width, 0.3 to 0.4 for 

depth, and 0.1 to 0.2 for velocity. Leopold and Maddock 

(1953) listed the average exponents calculated for their 

classic study as 6=0.5, /=0.4, and m=0.1. Carlston 

(1969) computed least-square solutions for Leopold and 

Maddock's data and found the mean of the exponents to 

be 0.461 for width, 0.383 for depth, and 0.155 for 

velocity.

Theoretical exponents have been derived for downstream hydraulic geometry. Leopold and Langbein 

(1962) obtained values of 6=0.55, /=0.36, and m=0.09. 

Langbein (1964) calculated the exponents as 6=0.53, 

/=0.36, and m=0.10. Using a different method, Smith 

(1974) obtained average downstream exponent values of 

6=0.6, /=0.3, and m=0.1.

The use of average hydraulic-geometry exponents, 

even for rivers within one basin, has led to the theory
C6 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

that rivers have similar geometries despite different 

physiographic and climatic settings. Recently, however, 

the validity and usefulness of average hydraulicgeometry exponents have been questioned (Knighton, 

1975; Rhodes, 1977; Park, 1978). The large range of all 

three exponent values suggests that mean geometry 

may be an attractive, but more or less meaningless, 

concept.

ASSUMPTIONS

The concept of hydraulic geometry is based on 

assumptions, which may include the following (Thornes, 

1977; Knighton, 1977):

1. A direct causal relationship exists in the system, 

with discharge as the primary independent variable.

2. A change in the independent variable will cause a 

specific change to occur in the dependent variables.

3. The changes are continuous and reversible.

4. Mean-stream characteristics are represented by the 

relations at a particular site.

5. Simple log-linear relationships accurately describe 

the observed changes.

Although channel width is determined largely by discharge, at-a-station hydraulic geometry is a function of 

channel shape for low flows (Richards, 1976). Channel 

shape is (in turn) determined by physical properties of 

channel-perimeter sediment (Schumm, 1960) and past 

flow events (Pickup and Rieger, 1979). Thus, despite, 

the ultimate cause of channel size, the channel yields an 

at-a-station hydraulic geometry that is a relic of larger 

flows.

Hydraulic geometry relations describe observed 

changes in a channel with changing discharge; the relations are best-fit lines for the data used and do not 

necessarily represent unique values. A given change in 

discharge need not always produce the same response in 

the channel; width may adjust slightly more than depth 

on one occasion, but the reverse may occur on another 

occasion. In the same manner, channel response may 

not be reversible in a strict sense. This fact was 

documented by Leopold and Maddock (1953) with their 

example of the passage of a single flood on the San Juan 

River in Utah. Hydraulic-geometry plots from this flood 

show hysteresis, that is, channel depth, mean velocity, 

suspended-sediment load, streambed elevation, and 

water surface all responded differently to the same discharge on the rising and falling stage.

Knighton (1977) has studied the theory that mean 

stream characteristics are represented by at-a-station 

relations. He concluded that four factors were responsible for short-term variation at a given site. Measurement error is present in all discharge measurements; 

mean depth and velocity particularly are susceptible to 

error because they are computed from point measurements. Random error is also a source of variation in all 

discharge observations. Hysteresis is a random variation. Systematic variation, or variation resulting from 

progressive change of the channel, in hydraulic geometry is a third source of short-term variation at a site. 

Knighton suggests that systematic variation can be examined by looking at discrete time phases of the sample 

from a given site. The final source of short-term variation in at-a-station hydraulic geometry lies in analytical 

error.

The existence of analytical error would be a refutation 

of the assumption that simple log-linear relations adequately describe channel changes with discharge. 

Richards (1973) pointed out that, because depth and 

velocity are functions of roughness, they also should be 

functions of bed sediment and channel geometry. He 

suggested that higher-order equations, specifically logquadratic equations, may express more accurately 

hydraulic-geometry relations.

Log-quadratic or log-polynomial equations are appropriate for use in hydraulic geometry because they 

allow use of the continuity relationship. For example, 

the width-discharge power-function relation (equation 1) 

can be rewritten as:

Generalization to -a log-quadratic equation yields:

(log w;)=log a+6, (log Q) b 2 (log Q)2 (7)

By analogy to equation 6, the first derivative of equation 

7 with respect to log Q,

(8)

Q)

is the instantaneous slope of the curve. The continuity 

equation using first derivatives of log-quadratic functions becomes:

(61+/1+m1)+2(62+/2+m2)log Q= (9)

(Richards, 1973). The first derivative, therefore, is 

analogous to the exponent of the power function.

THE B-F-M DIAGRAM

Two methods of graphically representing hydraulicgeometry exponents have been proposed. Park (1978)
HYDRAULIC GEOMETRY OF THE PLATTE RIVER NEAR OVERTON, NEBRASKA C7

presented tri-axial graphs of both at-a-station and downstream hydraulic-geometry exponents to allow consideration of the simultaneous variations in the three exponents. Park concluded that there is not a tendency 

within an area or environment to establish a unique 

hydraulic-geometry relation or series of relations, either 

at-a-station or downstream.

Rhodes (1977) graphically represented hydraulicgeometry exponents by plotting them -on a triangularcoordinate system, which he termed a b-f-m diagram. 

The arrangement of the b-f-m diagram was different 

from the tri-axial graphs proposed by Park. Rhodes' 

research indicated that comparison of channels through 

assessing the similarity of exponents was inadequate. 

He proposed a series of subdivisions of the b-f-m 

diagram based on hydraulic and morphologic considerations (fig. 3). The ten fields of the diagram are created 

with five lines, as follows:

1. b=f. This line represents no change in the widthdepth ratio with changing discharge. To the right 

of this line, width-depth ratios decrease with 

discharge, and to the left of this line, width-depth 

ratios increase with discharge. Location of a point 

relative to this line may provide information 

about channel shape and stability, and bedload 

transport.

2. m=f. Rhodes (1977) suggested that the competence 

of channels plotting above this line should increase 

with discharge. This statement was based on an 

analysis of competence and the rates of change of 

velocity and depth by Wilcock (1971), and on work 

by Leopold and Maddock (1953), associating the 

ratio of the rates of change in velocity to depth 

with the rate of change of suspended load.

3. m=/72: This division is based on Froude number and 

represents a constant value. The Froude number, 

defined as:

F= (10)

where

v =velocity,

g ^gravitational constant, and

d =water depth,

can be expressed as a proportion between m and /*, 

because both velocity and depth can be expressed 

in terms of discharge. If the constants are 

eliminated, the proportion of Qvz oc Qm results. 

Thus, a constant Froude number is expressed by 

m=/72. Froude number increases above this line 

with increasing discharge and decreases below the 

line with increasing discharge.

4. m=b+f, or m=0.50: Channels plotting above this 

line show rapid increase in velocity with discharge.

FIGURE 3. Divided b-f-m diagram, showing fields that represent 

different channel types. (After Rhodes, 1977).

If the velocity (m) increases more rapidly than 

cross-sectional area (6+/), resistance must decrease 

rapidly. Rhodes (1977) indicated that this division 

provided information about channel stability. 

5. mlf =213: This line is related to the Manning roughness coefficient, n, in the Manning equation (metric 

form):

:i/2

v= (ID

where -R=hydraulic radius, the ratio of the crosssectional area to the wetted perimeter, and S=slope. 

Mean depth is assumed to be approximately equal to 

hydraulic radius for wide, shallow channels, such as 

those of the Platte River.

Expressing slope, <SocQz , and roughness, nocQy, as functions of discharge, Manning's equation may be rewritten

as:

Qm oc Q(2/3)/ X QdlVf 

Qy (12)

If m=2/3 /, the ratio Smln is constant with changing discharge. Rhodes assumed (from data from several 

sources) that slope varies little with discharge; thus, 

roughness may change appreciably. This assumption, 

although true for limited ranges of discharge, is probably not true for the full range of flows. Points below the
C8 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

line mlf =213 on the b-f-m diagram represent channels in 

which roughness increases with discharge.

AT-A-STATION HYDRAULIC GEOMETRY

Hydraulic-geometry relations were computed both for 

the six field-study sections and for several cross sections 

near the Cozad, Overton, and Odessa gages. The exponents were calculated using linear regression techniques 

on log-transformations of the data Initially, first-order 

log equations (power functions) were assumed to represent the hydraulic-geometry relations. In addition, logquadratic equations were fitted to the data sets, and 

separate power functions were fitted to discrete 

segments of the data sets for these purposes: (l)To 

decrease the residual error of the regressions; (2) to approximate more closely the apparent trend of the data; 

and (3) to meet physical constraints observed in the field. 

For the purpose of discussion, the data 

are grouped as: (1) Summarized data, those data obtained from discharge measurement summary sheets; 

and (2) field data, those data collected from field 

measurements.

SUMMARIZED DATA

These values of water width, depth, velocity, and discharge were summarized from discharge-measurement 

sheets and summary sheets in the Nebraska District Office of the Water Resources Division of the U.S. Geological Survey. The range of summarized data is relatively 

small, but the data set is large. High-flow discharge observations are missing from the summarized data; such 

measurements usually are made from bridges and do not 

represent natural sections. At lower discharges, 

measurements were made at specified distances from 

the gage or bridge. In contrast to the method employed 

by Leopold and Maddock (1953), discharge measurements for this study were grouped by specific location, 

as recorded on the individual discharge notes. For example, discharge measurements made at a given cross 

section were not grouped with measurements made 20 m 

upstream or downstream from that cross section. These 

data groupings should reduce the scatter introduced by 

the use of different sections.

Hydraulic-geometry exponents that apply for the at-astation case, for the period of record and for shorter time 

periods, are listed in table 1 for data from sections near 

the Cozad, Overton, and Odessa gages. Exponents for 

power functions based on whole data sets and partitioned data sets are listed in table 1; corresponding 

significance levels and corresponding correlation coefficients are listed in the summary of statistical data at the 

end of the report (table 2).

The range of exponents for the sections near Cozad, 

Overton, and Odessa is relatively large for each of the 

hydraulic-geometry relations computed from simple 

linear regression. The width exponent varies from 0.22 

to 0.80, the depth exponent varies from 0.11 to 0.63, and 

the velocity exponent varies from 0.09 to 0.44. The 

amount of variation of the exponent varies from area to 

area For example, the width exponent ranges from 0.21 

to 0.66 for the sections near Cozad, but the width exponent ranges only from 0.48 to 0.68 for the sections near 

Odessa Variability of all three exponents is least for the 

three sections near Odessa

For the period of record, simple linear regression of 

the logarithms of width, depth, and velocity on the 

logarithm of discharge yielded large reductions in the 

variances of the dependent variables relative to the 

variances of the logarithms of width, depth, and velocity alone. Similar reductions were found for the period 

since 1969 in most instances.

The reduction of variances of the dependent variables 

does not necessarily indicate that the relations between 

discharge and width, depth, and velocity are power 

functions, because the correlation coefficient is not a 

measure of the appropriateness of the straight-line 

model. However, examination of representative plots of 

the data (figs. 4-12) indicates that some of the relations 

are log-linear, or plot as straight lines on log-log plots.

For some sections, however, power functions do not 

appear to be the correct model for the data, although 

simple linear regression did reduce significantly the 

variances of the dependent variables (figs. 5,6, 7,9, and 

10). In general, for the period of record and for the 

period since 1969 for the sections where power functions 

do not appear to describe hydraulic-geometry relations, 

the addition of a second-order discharge term results in 

a significant proportionate reduction of the variance of 

the dependent variable relative to the variance of the 

dependent variable without the second-order discharge 

term. This is particularly true for the data sets from the 

period of record, probably because of the size of the data 

sets. The significance of higher-order terms tends to decrease as the order of the term increases. Statistics on 

the second-order terms are not included in table 1 

because although the improved fit of regression lines 

obtained from second-order discharge terms is statistically significant in some instances, it has no physical 

meaning.

On many of the hydraulic geometry plots, breaks in 

the slopes of the width, depth, and velocity-discharge 

relations are evident at a certain discharge (fig. 10). 

These breaks in slope can serve to partition the data 

sets. Power functions fitted separately to the low range 

of discharge and to the high range of discharge generally yielded large proportionate reductions in the variances of the dependent variables relative to the van-
HYDRAULIC GEOMETRY OF THE PLATTE RIVER NEAR OVERTON, NEBRASKA C9

TABLE 1. At-a-station hydraulic-geometry exponents for summarized data, expressed as

form: (log w)=log a+b(log

Distance

Platte downstream

River from gage

near: (meters)

Cozad 30

Cozad 45

Cozad 60

Cozad 60

Cozad 75

Cozad 120

Cozad 120

Overton,

north

channel . . 30

Overton,

north

channel . . 45

Overton,

north

channel . . 60

Overton,

north

channel . . 75

Overton,

north

channel . . 90

coefficients

Q)

Period of

record

1961-1979

1961-1963

1964-1969

1970-1979

1954-1979

Low

High

1954-1969

Low

High

1970-1979

High

1953-1979

Low

High

1953-1957

1958-1963

1953-1963

Low

High

1964-1969

Low

High

1970-1979

Low

High

1961-1979

Low

High

1961-1963

Low

High

1964-1969

Low

High

1970-1979

High

1951-1979

Low

High

1951-1963

Low

1964-1969

Low

High

1970-1979

Low

High

1968-1976

1968-1976

Low

High

1968-1976

Low

High

1968-1978

Low

High

1968-1978

Low

High

of power

b

0.5282

.5560

.492

.4893

.5082

.795

.3741

.5492

.755

.5998

.2782

.2351

.5339

.6788

.3576

.6610

.4944

.5728

.6801

.435

0.4468

.772

.3738

.3809

.997

.1772

.4345

.5848

.5188

.4999

.510

.6425

.5086

.752

.5435

.2155

.2553

 4QQ8 **«7«7O

.6224

.2281

0.6168

.6585

.2345

.4669

.1636

.3184

.4380

.2165

.4294

.3850

.305

.2139 *

.4100

.5226

.0474

.01813

.770

.4161

0.3154

.654

.1665

functions

Coefficients

f

0.2939

.2804

.2169

.3405

.3537

.127

.4905

.297

.245

.4002

.6274

.6847

.2720

.1273

.4503

.1637

.3473

.2450

.1395

.4359

0.2831

-.101

.4071

.4551

-.0161

.5717

qooc .OD^O

.0414

.3560

.3580

.2106

.2859

.2832

-.111

.3543

.5151

.4705

Q1 Ql .OlOl

.2067

.5790

0.2198

.1863

.5147

.3629

.6166

.5334

.5240

.5833

.3497

.3608

.307

.5465

.3658

.2684

7QQQ

. I OOO

.4815

.139

.2456

0.4331

.1923

.4806

of the

m

0.1778

.1636

.2913

.1702

.1381

.078

.1354

.153

.015

.1521

.0944

.0801

. J. 1Q41 \J^A.

.1939

.1921

.1753

.1583

.1822

.1805

.1295

fl \J»& 9701 1 UA

.329

.2190

.1640

.0192

.2511

,£t 9030 \Jtj\J

.3739

.1252

.1421

.2798

.0717

.2082

.3599

.1023

.2694

.2742

.1871

.1709

.1930

0.1634

.1551

.2508

.1702

.2198

.1482

.0380

.2024

.2210

.2543

.388

.2396

.2242,

.2090

icxq .1010

.4372

.091

.3383

0.2514

.1538

.3529

TABLE 1. At-a-station hydraulic-geometry exponents for summarized data, expressed as coefficients of power functions of the

form: (log w)=log a+b(log Q) Continued

Distance

Platte downstream Period of Coefficients

River from gage record b f m

near (meters)

Overton,

south

channel . . 30 1968-1978 .5332 .3974 .0694

Overton,

SOUtJ"!

channel . . 90 1968-1978 .3870 .3229 .2901

Overton ... 30 1961-1967 .8011 .1165 .0824

Overton ... 45 1961-1963 .914 -.048 .134

Overton ... 60 1954-1967 .6523 .1984 .1493

Low .462 .503 .034

High .4637 .3150 .2213

1954-1963 .7303 .1384 .131

Low .948 -.114 .166

High .5152 .2705 .2143

1964-1967 .6047 .247 .1484

Low .251 .721 .028

High .4550 .3435 .2014

Overton ... 75 1962-1967 0.4878 0.2386 0.2736

Low .770 .139 .091

High .4161 .2456 .3383

1962-1963 .386 .347 .267

1964-1967 .4973 .2264 .276

Low .768 .177 .0552

High .4282 .2227 .3491

Overton ... 90 1962-1967 .4729 .3207 .2064

Low .7072 .1686 .1242

High .1961 .5819 .2219

1962-1963 .5092 .3010 .1898

Low .8478 .0432 .1090

High .1283 .5905 .2812

1964-1967 .4602 .327 .2123

Low .6402 .2307 .1292

High .2157 .5787 .2056

Odessa .... 60 1962-1979 .6286 .2218 .1496

Low .6508 .1805 .1687

High .3701 .548 .082

Odessa .... 60 1962-1963 0.6807 0.1362 0.1832

Low .7100 .0994 .1906

High .320 .383 .297

1964-1969 .5868 .2940 .1193

1979 .4829 .4028 .1143

Odessa .... 75 1961-1979 .6018 .2033 .1949

Low .6138 .1718 .2144

High .256 .551 .193

1961-1963 .5963 .1615 .2922

1964-1969 .5869 .2691 .1442

Low .6224 .2258 .1519

High .254 .600 .146

1970-1979 .5692 .3084 .1224

Odessa .... 90 1953-1979 .6183 .2074 .1743

Low .6804 .1540 .1656

High .3077 .4817 .2106

1953-1963 .6343 .1974 .1683

Low .6562 .1623 .1814

High .2662 .565 .169

Odessa .... 90 1964-1969 0.5514 0.2521 0.1966

Low .7244 .1233 .1523

High .2719 .4782 .2499

1970-1979 .5077 .3295 .1698

'Negative values for the depth exponent occur only in the low range of discharges for partitioned data sets. The values result as discharge increases; spreading flow over previously

unwetted streambed, and they reflect the fact that mean depth may decrease as width increases rapidly.

ances of the variables alone (table 2, at the end of the

report).

Regressions based on partitioned data sets indicate
CIO HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

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DISCHARGE, IN CUBIC METERS PER SECOND

100

FIGURE 4. Relation of width, depth, and velocity to discharge, 

Platte River 30 meters downstream from gage near Cozad, 

Nebraska, post-1969 record.

the effect of the range of data values. For example, the 

exponent of the width-discharge power function for the 

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the gage near Cozad is 0.5082 (table 1). For the same 

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DISCHARGE, IN CUBIC METERS PER SECOND

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FIGURE 5. Relation of width, depth, and velocity to discharge, 

Platte River 120 meters downstream from gage near Cozad, 

Nebraska, 1964-1969.

function exponents are 0.795 for discharge values less 

than 1.1 cubic meters per second (m3/s), and 0.3741 

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HYDRAULIC GEOMETRY OF THE PLATTE RIVER NEAR OVERTON, NEBRASKA Cll

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gage near Overton, Nebraska, post-1969 record.

ponent for the width-discharge power function for discharges of 1.1 m3/s or greater is quite similar to the exponent for the width-discharge power function for all 

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FIGURE 8. Relation of width, depth, and velocity to discharge, 

Platte River 30 meters downstream from gage near Cozad, 

Nebraska, for the period of record.

FIELD DATA

Field data were collected at the six cross sections established for this study. Discharges were obtained by 

gaging for the Lexington, Johnson-2, and Elm Creek

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FIGURE 9. Relation of width, depth, and velocity to discharge, 

Platte River 60 meters downstream from gage near Cozad, 

Nebraska, for the period of record.

sections. At the remaining three sites (Cozad, Overton, 

and Odessa), rating curves were used to estimate 

discharge; therefore, channel depth and velocity were 

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HYDRAULIC GEOMETRY OP THE PLATTE RIVER NEAR OVERTON, NEBRASKA C13

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FIGURE 10. Relation of width, depth, and velocity to discharge, 

Platte River 120 meters downstream from gage near Cozad, 

Nebraska, for the period of record.

charges, but the data are deficient toward the middle of 

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FIGURE 11. Relation of width, depth, and velocity to discharge, 

Platte River 60 meters downstream from gage near Odessa, 

Nebraska, for the period of record.

field sections. At the Cozad, Lexington, and Johnson-2 

sections, sufficient data were collected to permit plotting of depth-discharge and velocity-discharge relations 

also. Plots of some of the field data are presented as 

figures 13 to 15.
C14 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

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FIGURE 12. Relation of width, depth, and velocity to discharge, 

Platte River 90 meters downstream from gage near Odessa, 

Nebraska, for the period of record.

The number of field data points is too small to be significant, but the figures suggest that, in some instances, 

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FIGURE 13. Relation of width, depth, and velocity to discharge, 

Platte River near Cozad, Nebraska.

width-, depth-, and velocity-discharge relations at the 

Johnson-2 section, and the width-discharge relation at 

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HYDRAULIC GEOMETRY OF THE PLATTE RIVER NEAR OVERTON, NEBRASKA C15

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DISCHARGE, IN CUBIC METERS PER SECOND

FIGURE 14. Relation of width, depth, and velocity to discharge, 

Platte River near Lexington, Nebraska.

relation between width and discharge, and between 

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DISCHARGE. IN CUBIC METERS PER SECOND

FIGURE 15. Relation of width, depth, and velocity to discharge, 

Platte River downstream from Johnson-2 Return near Lexington, 

Nebraska.

COMPLEX AT-A-STATION 

HYDRAULIC GEOMETRY

Hydraulic-geometry relations for the Platte River are 

not described adequately by power functions in all instances. This complex hydraulic geometry is not
C16 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

peculiar to the Platte River. Wolman (1955) stated of 

Brandywine Creek, in Pennsylvania, "There is a suggestion in some of the data * * * that the depth-discharge and velocity-discharge curves may actually plot 

as curved rather than straight lines on a log-log paper. 

Such a relationship of the at-a-station curves is not uncommon." Richards (1973) noted that non-linear 

changes of depth and velocity with discharge may result 

from non-linear changes of roughness with discharge. 

Richards (1976) also proposed that channel crosssection shape can produce breaks or discontinuities in 

the width-discharge relationship. Williams (1978a) 

showed that all three hydraulic-geometry exponents 

vary with discharge for the Humbolt River in Nevada. 

At least three causes may explain the complex 

hydraulic geometry in the study area The first explanation may lie in the range of discharges observed. At 

some sections only a small range of discharges was 

observed (fig. 7). The scatter of the predicted variables 

(width, depth, and velocity) may be sufficient to make 

the relation appear to be complex. This explanation 

does not apply to all sections, because at some sections

at which the range of observed discharges is low, there 

is little scatter of the data (figs. 5 and 7); and because at 

some sections at which the range of observed discharges 

is high, the relations are nevertheless complex (fig. 10 

and 12). Conversely, it may be that changes in the rates 

of adjustment of width, depth, and velocity with increasing discharge were not observed because of the 

small range of observed discharges. Secondly, the 

velocity-discharge and depth-discharge relationships 

may be complex because of changes in roughness 

(Richards, 1973). In addition to changes in roughness 

associated with dunes and other small-scale bed forms, 

changes in roughness may occur as vegetated or 

unvegetated larger bed forms, such as macroforms 

(Crowley, 1981), are inundated. Finally, and for this 

study, most importantly, channel shape may preclude a 

constant rate of water-depth and water-width increase. 

Near Cozad, for example (fig. 16), the banks are cohesive 

and near vertical at many locations. At low flows, the 

channel bottom generally is not wetted entirely. As discharge increases, width increases very rapidly as the 

channel floor is covered, but depth increases slowly.

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DATE OF SURVEY

 AUGUST 1979 

....... SEPTEMBER 1979

 MAY 1980 

_._ _ AUGUST 1980

I I

10 15 20 25 30

DISTANCE, IN METERS FROM REFERENCE MARK 1

35 40 45

FIGURE 16. Cross-flection surveys of the Platte River at the Cozad field section.
HYDRAULIC GEOMETRY OF THE PLATTE RIVER NEAR OVERTON, NEBRASKA C17

Once the entire channel bed is covered and the banks are 

reached, width cannot increase appreciably, although 

depth may increase rapidly. Such sudden decreases in 

the rate of width increase and sudden increases in the 

rate of depth increase will cause discontinuities in the 

slopes of hydraulic-geometry plots.

The shapes of the hydraulic-geometry relations have 

their bases in the physical characteristics of the channel 

and flow. Based on the channel shape (fig. 16), the 

width-discharge relation should be concave downward 

for sections at which the power function does not hold. 

In figures 4 through 15 the width-discharge relation 

either is a power function or is concave downward. 

Where the power function holds for the width-discharge 

relation, the depth-discharge and velocity-discharge 

relations both may be power functions or both may be 

complex with opposite curvature. Where the widthdischarge relation is not a power function, the depthdischarge and velocity-discharge relations each may be 

a power function or complex, with curvature in either 

direction. The channel shape, which controls the curvature of the width-discharge relation, also controls the 

shape of the depth-discharge relation. The depthdischarge relation must be concave upward if it is not a 

power function. In figures 4 through 15 the depthdischarge relation either is a straight line or it is concave up. The velocity-discharge relation varies in shape 

from concave up (figs. 5 and 7) to a power function (figs. 

4 and 8) to concave down (figs. 9 and 10). The physical 

significance of the velocity-discharge curve shapes is 

difficult to ascertain. Richards (1973, 1977) suggested 

that the curves should be concave downward because 

the increase in roughness as dunes form offsets any increased efficiency due to increased depth. Knighton 

(1979) cited data showing that the resistance-discharge 

relation for sand-bed streams is concave upward, corroborating Richards' suggestion that the velocitydischarge curve is concave downward. The velocitydischarge curves may be concave upward at sections 

where the effect of form roughness decreases as depth 

increases.

Two alternatives to power functions hve been proposed as models for hydraulic geometry. Thornes (1970) 

partitioned each set of bivariate data into two subsets 

and obtained a discrete power-function regression for 

each subset. The break between the subsets was determined by minimizing the combined error sums of 

squares of the regressions. Williams (1978a) used two 

sets of exponents to describe hydraulic-geometry relations; one set was for discharges less" than a specified 

value, the other set was for discharges greater than the 

specified value. Richards (1976) argued that fitting of 

power-law relationships to discrete subsets of a data set 

was unnecessarily complicated, although possible. He

proposed instead that polynomials be fit to the logarithms of the data, because fewer parameters need to be 

estimated than for partitioned data sets and because of 

the analogy with the power-function situation.

For this study, where a single power function did not 

adequately describe the relation, data sets were partitioned based on breaks in slope of the hydraulic 

geometry plots. Separate power functions were then fit 

to the different discharge ranges. Although cumbersome to apply, discrete power functions accurately describe the changes in hydraulic variables with increasing discharge. Polynomials compromise the relations 

that would be obtained from the partitioned data sets 

and do not allow the points to be identified at which the 

width-, depth-, and velocity-discharge relations change.

MEANING OF THE EXPONENTS

Exponents of the first-order equations represent 

the rates of change of the dependent variables with 

changing discharge. Rewritten as power functions, for 

example:

<logW)=loga+&(logQ);

first derivatives of the equations are exponents of the 

first-order equations. Thus, exponents of the power 

functions are slopes of the first-order equations. 

Because of continuity, the first derivatives or exponents 

of the width-, depth-, and velocity-discharge relationships will sum to one.

The question then is: What do the slopes of the 

hydraulic-geometry relations mean? The slopes represent the rates of change of width, depth, and velocity 

with changing discharge. Comparison of numerical 

values of the exponent indicates which variables show 

greater rates of change at which sections. However, numerical comparison of the exponents does not provide 

information about the meaning of the exponents themselves or their implications about channel conditions.

The b-f-m diagram allows the similarity or difference 

in responses of width, depth, and velocity to changing 

discharge to be interpreted based on physical considerations (Rhodes, 1977). The use of the b-f-m diagram is 

possible only when the exponents sum to one. For power 

functions, this constraint presents no problems because 

the exponents sum to one; however, in some instances 

individual exponent values are either negative numbers 

or greater than one, making plotting on the b-f-m 

diagram impossible. Expansion of the diagram to include negative values and values greater than one would 

be possible, but would make interpretation of the exponents more difficult Exponents for the first-order
CIS HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

A COZAD GAGE, PERIOD OF RECORD 

A COZAD GAGE, 1970-1979 

O ODESSA GAGE, PERIOD OF RECORD 

 ODESSA GAGE, 1970-1979

OVERTON GAGE, SOUTH CHANNEL 

OVERTON GAGE, NORTH CHANNEL

FIGURE n. B-f-m diagram showing plotting positions of current at-a-station hydraulic-geometry exponents

and exponents from the period of record.

equations for entire data sets from table 1 for the 

periods of record and since 1969 are presented graphically on a b-f-m diagram (fig. 17). Although these exponents may not in all instances represent the correct 

model, they will serve as a starting point from which to 

examine the b-f-m diagram.

HYDRAULIC AND MORPHOLOGIC INFORMATION 

FROM THE B-F-M DIAGRAM

The b-f-m diagram not only allows hydraulicgeometry exponents to be presented graphically, but 

also allows inferences to be made about hydraulic and 

morphologic parameters. Hydraulic-geometry exponents for the summarized data (for the period of 

record and since 1969) plot in six of the ten fields of the 

b-f-m diagram.

Only six of the 23 data points plot to the right of the 

line, b=f, at most sections the width-depth ratio increases with increasing discharge. Four of the six points 

to the right of the b f line represent sections in the 

vicinity of the Cozad gage on the north channel of the 

Platte River. This reach of the river is deeper relative to 

width than any other river reach within the study area. 

The remaining points to the right of the line b f are 

from the north channel near Overton. All of the points 

from the period of record, including those from the 

north channel near Cozad, plot to the left of the line, 

b=f.

None of the data points plot above the line, m=0.50.

Rapid velocity increases are not likely considering the 

shallow depth of the river and the increased wetted 

perimeter as discharge increases. In addition, vegetation present on many of the bars will increase roughness 

as it is inundated, further decreasing the possibility of 

rapid velocity increase.

Six data points plot above the line, ml'/'=2/3, which 

represents the ratio SP^In. Points above this line should 

represent sections at which roughness decreases with 

increasing discharge. Of these six points, one near 

Cozad and two near Odessa represent the entire period 

of record, and the other three represent sections near 

Overton. Thus, roughness apparently increased with increasing discharge at almost half of the sections for the 

period of record. However, for the period since 1969, 

plotting positions for exponents from unpartitioned 

data sets indicate that roughness increased with increasing discharge at 14 of 17 sections.

None of the data points from the Platte River plot 

above the line, m=f. Therefore, in all instances, the rate 

of change of velocity with increasing discharge is less 

than the rate of change of depth with increasing discharge. This implies that competence will not increase 

with increasing discharge at any of the sections studied 

(Wilcock, 1971).

The line, m=/72, represents sections at which Froude 

number is constant with increasing discharge. Six of the 

15 data points from the summarized data since 1969 

plot below the line, m=/72, in fields in which Froude 

number decreases with increasing discharge. The remaining nine points representing summarized data
HYDRAULIC GEOMETRY OF THE PLATTE RIVER NEAR OVERTON, NEBRASKA C19

since 1969 plot above the line, m=/72, representing sections at which Froude number increases with increasing 

discharge. Of these nine points, six are from the vicinity 

of the Overton gage. The remaining three points, two 

near the Cozad gage and one near the Odessa gage, 

almost plot on the line. For the eight data values from 

the period of record, only one point plots below the line, 

m=/72, although four other values lie close to the line. 

Thus, based on unpartitioned data sets for the period of 

record, Froude number .should have increased with increasing discharge at seven of eight sections.

The b-f-m diagram can be used to interpret, in a 

general sense, the way morphologic and hydraulic 

parameters adjust to increasing discharge. Exponent 

values from hydraulic-geometry relations from summarized data for unpartitioned data sets for the period 

of record plot only in fields five, seven, and nine of the 

b-f-m diagram. Thus, for these sections, the width-depth 

ratio increases with increasing discharge; the velocityarea ratio decreases with increasing discharge; Froude 

number generally increases with increasing discharge; 

and the slope-roughness ratio generally decreases, presumably indicating an increase in roughness with increasing discharge. Exponent values for the hydraulic 

geometry computed from summarized data for unpartitioned data sets since 1969 plot in fields five through 

ten of the b-f-m diagram. For these sections, the widthdepth ratio may increase or decrease; in general, it increases. The velocity-area ratio decreased in all instances. In general, both Froude number and roughness 

increased with increasing discharge.

The meaning or significance of the fields of the b-f-m 

diagram is relatively clear; the meaning of the variation 

displayed by the hydraulic-geometry exponents and 

hydraulic variables is unclear. Note, for example, the inferred differences in roughness among the Cozad sections or the Overton sections, and the differences between the Cozad and Overton sections. Changes in bedforms with increasing discharge, such as from dunes to 

plane bed with transport, may cause roughness to decrease. The question of why this should occur at only a 

few sections remains. The different changes of the 

width-depth ratio can be understood, based on the morphology of the cross sections. Variations of m=/72, indicative of the Froude number, also are less readily 

understandable. An inferred decrease in roughness may 

account for some of the sections showing an increase in 

Froude number with increasing discharge. However, 

other sections show an increase in Froude number with 

increasing discharge, and yet also show an increase in 

roughness (fields seven and eight of the b-f-m diagram).

At least four explantions can be offered for the variation of hydraulic-geometry exponents computed for 

unpartitioned data sets, and different reactions of

hydraulic and morphologic variables as inferred from 

the b-f-m diagrams.

1. Morphologic or vegetative differences between sections may be so great that all of the hydraulicgeometry exponents are influenced. This could 

cause variation in plotting position on the b-f-m 

diagram also.

2. Inferences drawn from the b-f-m diagram may be 

incorrect. The fields of the diagram may not actually group like channels or channels that respond in a similar manner to increasing discharge.

3. Part of the variation may be due to the different 

time periods used. For example, great differences 

exist between the unpartitioned data from the 

Cozad sections for the period of record and for the 

period since 1969. Data from the period of record 

represent a time average of the hydraulicgeometry exponents; whereas, the data since 1969 

presumably represent a more homogeneous period, 

due to the shorter time period. Changes in the plotting positions of the exponents then may show 

changes in the response of the river, both morphologically and hydraulically, with time.

4. Part or all of the variation of exponents and plotting 

positions may be due to the assumption in this section that single power functions are the appropriate model for hydraulic geometry. 

Two of these four explanations for the variation in exponents, systematic variation (3) and analytic error (4), 

will be examined in more detail in the next section of 

this chapter.

SYSTEMATIC VARIATION AND ANALYTICAL ERROR

Changes in channel morphology should influence the 

rates of change of width, depth, and velocity with increasing discharge. As a result, the hydraulic geometry 

computed for short time intervals of a period during 

which a channel section was undergoing substantial 

change should show systematic variation with time. Unfortunately, long-term records either are not available or 

are unsuitable for use in hydraulic-geometry computations. In most instances, early discharge measurements 

were made near bridges. Bridge sections may have been 

unaltered near the turn of the century, but they were increasingly filled to facilitate bridge construction. 

Riprap generally has been placed on the banks immediately upstream and downstream of the bridge section. These factors tend to establish bridge sections as 

highly modified, almost rigid boundary sections, incapable of significant morphologic adjustment to 

changes in flow.
C20 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

For this analysis, each location grouping of discharge 

measurements was further divided into time-period 

groups, the ends of which were coincident with the years 

of aerial photography. The equations of hydraulic 

geometry were computed for the individual time groupings at each location. Comparison of exponents and coefficients can be made between locations or between 

time periods, or both, if the limitation imposed by the 

limited ranges of data is recognized.

The hydraulic-geometry exponents for the different 

time groupings are listed in table 1. The success of time 

and location groupings varied from gage to gage. Five 

locations were separable from the Cozad measurements. 

At three of these locations sufficient records are available to make three time groupings. A series of gage location changes at Overton made the records difficult to 

compare directly with those from Cozad and Odessa. 

For most locations, records are available for the entire 

channel for two time periods, but starting in 1969 each 

channel was gaged independently. The records from 

Odessa allow three locations, each with three time 

periods, to be established.

In general, for the unpartitioned data the width exponent at each location for the Cozad and Odessa sites 

decreased with time. However, there are instances when 

the width exponent increased with time. The depth and 

velocity exponents for Cozad (fig. 18) and Overton generally do not show trends, either among stations or at a 

given station with time. This implies that depth and 

velocity adjust in different ways at different times. At 

Odessa depth appears to be increasing, while velocity is 

decreasing or remaining constant with time (fig. 19).

Interpretation of the changes in width exponents for 

the Overton section are not made easily. Width exponents decreased at three of the four locations for 

which records are available for the period prior to 1963 

or for the period 1964 to 1969. At the fourth station, the 

width exponent increases. Records for the post-1969 

period are available only for individual channels. In all 

cases, however, the individual channels have width 

exponents smaller than those computed for earlier 

periods.

Plots of the hydraulic-geometry exponents for unpartitioned data on b-f-m diagrams provide visual interpretations of the changes in hydraulic geometry with time 

(figs. 18 and 19). These plots show, as discussed above, a 

general decrease in the rate of width increase with discharge and, for Odessa, an increase in the rate of depth 

increase with discharge. The implication of the width 

change is that channel width is not as great for large 

discharges as it once was, a point borne out by the examination of aerial photographs. The hydraulicgeometry changes at Odessa indicate that the channel 

should be incising, as depth is increasing simultaneously with the width decrease. This conforms to 

Williams' (1978b) observed decrease in bed elevation at 

Odessa.

The apparent change in hydraulic geometry exponents with time (figs. 18 and 19) may result from 

changes in the range of discharges represented in each 

of the different time intervals, rather than from significant changes in the width-, depth-, and velocitydischarge relations themselves. If a hydraulic geometry 

relation at a site is assumed to be represented by a 

single power function, as in figure 18, when in fact it 

would be better represented using two different power 

functions (fig. 5), then the single power function exponent for that hydraulic geometry relation will be a compromise between the two exponents that would better 

describe the relation. The slope of the single relation will 

depend on the range of discharge values present. A preponderance of data values from what would be one 

subset of data if the data were partitioned, would result 

in a single exponent that approximates the exponent for 

the subset If the range of discharges represented at a 

site changes with time, the slope of a single hydraulic 

geometry relation at that site may also change with 

time. Thus, the observed changes in hydraulic geometry 

exponents with time may result because the discharge 

ranges, upon which those exponents are dependent, 

change with time.

Examples of hydraulic geometry exponents from partitioned data sets from Cozad and Odessa are plotted in 

figures 20 and 21. Although there is a suggestion in 

figure 18 that the width exponent generally has decreased with time near Cozad, partitioning of the data 

sets (fig. 20) indicates that some of the apparent reduction of the width exponent results from changes in 

the range of discharges represented in different time intervals. Nevertheless, the width exponent decreases 

with time near Cozad even within the hydraulic geometry relations for partitioned data sets. The gradual, 

systematic change of exponents through time near 

Odessa (fig. 19) does not occur when the data sets are 

partitioned (fig. 21). Although fewer points are plotted 

on figure 21 than on figure 19 because of small data 

sets, it is apparent that there is not a change in exponent values through time. Rather, the change in plot* 

ting positions on figure 21 results from partitioning of 

the data

SIGNIFICANCE OF COMPLEX HYDRAULICGEOMETRY RELATIONS

Analysis of at-a-station hydraulic geometry showed 

that some of the sections within the study reach were 

not described adequately by conventional hydraulic
HYDRAULIC GEOMETRY OF THE PLATTE RIVER NEAR OVERTON, NEBRASKA C21

PERIOD BEFORE 1958 

PERIOD BEFORE 1964 

1964-1969 

PERIOD AFTER 1969

FIGURE l8. B-f-m diagram showing changes in hydraulic-geometry exponents with time. Data from the 

north channel of the Platte River in the vicinity of the gage near Cozad, Nebraska. 0=period before 1958. 

l=period before 1964. 2=1964-1969. 3=period after 1969.

PERIOD BEFORE 1964 

1964-1969 

PERIOD AFTER 1969

FIGURE 19. B-f-m diagram showing changes in hydraulic-geometry exponents with time. Data from the 

Platte River in the vicinity of the gage near Odessa, Nebraska. 1=period before 1964. 2= 

1964-1969. 3=period after 1969.

geometry. In general, sections of this type show a rapid 

width increase as the channel bed is covered; then, a 

much slower increase in width as the channel fills with 

water; a slow depth increase until the banks are 

reached; followed by a rapid increase in depth as discharge increases. Rate of increase of velocity with increasing discharge either may be slow initially and then 

increase, or may be rapid initially and then decrease.

The significance of complex hydraulic geometry is 

twofold. Log-linear regression of partitioned data sets
C22 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

BEFORE 1963 

1964-1969 

AFTER 1969

0.5

FIGURE 20. B-f-m diagram showing changes in hydraulic-geometry exponents with time. Data from the 

north channel of the Platte River in the vicinity of the gage near Cozad, Nebraska; partitioned data sets.

BEFORE 1964 

1964-1969

FIGURE 21. B-f-m diagram showing changes in hydraulic-geometry exponents with time. Data from the 

Platte River in the vicinity of the gage near Odessa, Nebraska; partitioned data sets.

describe how width, depth, and velocity change at certain cross sections with increasing discharge more accurately than do single-power functions of the entire 

data set. Thus, at least the shape of the relations is conveyed correctly, enabling changes in the width-, depth-, 

or velocity-discharge relations to be predicted at those 

sections more accurately than they might be predicted

using power functions. Use of partitioned data sets in 

hydraulic-geometry equations, where appropriate, 

should reduce or eliminate autocorrelation of the 

residuals from the single linear relation, resulting in a 

more accurate estimation of standard errors.

The existence of a break in the slope of the widthdischarge relation is of primary importance for this
HYDRAULIC GEOMETRY OF THE PLATTE RIVER NEAR OVERTON, NEBRASKA C23

study (for example, fig. 5). Above the break, the entire 

channel width may be occupied, at a shallow depth, by a 

discharge of relatively high duration. Because vegetative encroachment and stabilization of the channel 

banks and bars is part of the process of width reduction 

on the Platte River (Eschner, Hadley, and Crowley, 

1981), the further establishment of vegetation must 

be, prevented if the existing channel width is to be 

maintained.

Seeds may be prevented from germinating if there is 

no exposed substrate on which they can grow. Young 

vegetation may be removed if it is inundated with water 

of a velocity sufficient to scour it out, or it may be killed 

if inundated for a sufficient period of time. The sections 

of channel where a single power function does not describe the hydraulic geometry may be kept free of vegetation by relatively low flows, because the bed will be 

covered completely by those flows. For example, near 

Cozad, the mean annual discharge for the period 1953 to 

1979 was 14.0 m3/s. Discharges at which the slope of the 

hydraulic-geometry relations from the north channel 

near Cozad changes (figs. 9 and 10) are much lower than 

mean annual discharge. For the section 60 m below the 

Cozad gage, the width-discharge and depth-discharge* 

relations appear to change slope at about 2 ms/s. For the 

section 120 m below the Cozad gage, the widthdischarge relation flattens out at about 3 m3/s and the 

depth-discharge relation exhibits a break in slope at 

about 3 m3/s. Thus, the discharge of the north channel 

at which the hydraulic-geometry relations change is 

less than half of the mean annual discharge for the 

entire channel near Cozad.

IMPLICATIONS AND LIMITATIONS OF

AT-A-STATION HYDRAULIC-GEOMETRY

RELATIONS

The form of some of the at-a-station hydraulicgeometry relations for the Platte River suggests that 

present channel dimensions may be related to relatively 

high-duration discharges. This analysis indicates that 

the discharges at which the rates of change of hydraulic 

and morphologic variables change are well below 

bankfull discharge, and may approximate the lower 

mean annual discharge. These discharges may not 

maintain the present channel characteristics, but it 

surely can be assumed that discharges below these 

values will probably not be able to maintain the channel. 

When these minimum values are compared with the 

values necessary for channel maintenance obtained by 

other methods, the applicability and limitations of the 

minimum values become evident.

Kircher (1981) determined the effective discharge, defined as the mean of the small range of discharges, that 

moves the most sediment during a year, for several sections along the Platte River. For the area near Overton, 

Kircher obtained a value of 40.9 m3/s as the effective 

discharge for the period 1950-1980. Mean annual discharge for the same period was 39.4 m3/s. The effective 

discharge, then, was close to the mean annual discharge. 

The effective discharge for the months May to August 

for 1950 to 1980 was determined to be 157.7 m3/s, much 

greater than the mean annual discharge. The months 

May to August were selected, because germination occurs during this period. The effective discharge for this 

period should both prevent germination and uproot 

small seedlings.

Karlinger and others (1981) applied theoretical equations developed by Parker (1978) to estimate the discharge necessary for maintaining cross-sectional 

characteristics of the Platte River channel. For a reach 

near Overton where the width is about 180 m, the necessary discharge was determined to be 107.6 m3/s. The 

depth corresponding to this discharge was estimated to 

be 0.6 m. The discharge necessary to cover the channel 

bed at this section, hence the discharge at which the 

width- and depth-discharge relations change, is 

estimated to be about 22 m3/s. The value obtained by 

Karlinger and others (1981) lies between that obtained 

from the width-discharge relation and that determined 

by Kircher (1981) as the effective discharge for the 

critical germination period.

Crowley (1981) discussed the movement of macroforms, bedforms which average 1 to V/z m in height, and 

their effect on maintenance of channel width. By 

moving downstream, these large bedforms can uproot 

vegetation. In order to move, the macroform must be 

covered by at least 20 cm of water. For the river near 

Overton, approximately 80 m3/s would be required to 

move the macroforms. This value is twice the mean annual discharge, and is about three-fourths of the value 

obtained from the theoretical equations.

SUMMARY AND CONCLUSIONS

Hydrology and morphology of the Platte River in 

south-central Nebraska have changed since settlement 

of the river basin (Eschner, Hadley, and Crowley, 1981). 

Peak discharges have decreased, and the formerly wide, 

open channel has narrowed, as sandbars have become 

vegetated and formed permanent islands. These 

changes in the Platte River have prompted concern for 

the habitat of migratory birds, particularly whooping 

cranes and sandhill cranes. This study was undertaken 

to compute at-a-station hydraulic geometry at selected 

sites, to examine how the relations have changed with
C24 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

time, and to determine the significance of the relations 

for channel maintenance.

At-a-station hydraulic geometry of the Platte River in 

south-central Nebraska is complex. The range of exponents of simple log-linear relations is large, both between different reaches of the river, and among different 

sectons within a given reach of the river (table 1). The 

at-a-station exponents plot in several fields of the b-f-m 

diagram (fig. 17) suggesting that morphologic and 

hydrologic changes with increasing discharge vary considerably. Systematic changes in the plotting positions 

of the hydraulic-geometry exponents from simple power 

functions with time indicate that the rates of change of 

the width, depth, and velocity with increasing discharge 

have varied with time. In general, the width exponent 

has decreased, although trends are not readily apparent 

in the other exponents.

Breaks in the slopes of the width-, depth-, and 

velocity-discharge relations at a certain discharge on 

plots of the hydraiilic-geometry for both data summarized from discharge notes (figs. 4 through 12) and data 

from field measurements made for this study (figs. 13, 

14, and 15) indicate that simple power functions are not 

the proper model in all instances. These breaks in slope 

can serve to partition the data sets. Power functions fit 

separately to the partitioned data fit the data significantly better than simple power functions for several 

locations. The exponents of hydraulic geometry relations based on partitioned data sets indicate the effect 

of the range of discharge values. Part of the observed 

change in plotting positions on the b-f-m diagram of the 

exponents from simple power functions results because 

the range of discharges for different time intervals is 

not the same. Much of the change of plotting positions 

is eliminated if the data sets are partitioned.

The shape of the channel cross section and, perhaps, 

changes in roughness with increasing discharge account 

for the shape of complex hydraulic-geometry relations. 

As the channel bed is inundated, width increases rapidly and depth increases slowly. Once the entire channel 

bed is covered and the banks are reached, width cannot 

increase appreciably but depth can increase rapidly.

Complex at-a-station hydraulic-geometry relations 

have significance for channel maintenance and suggest 

that existing channel dimensions may be related to 

relatively low-magnitude flows. Vegetation must not 

become established in the channel if the existing width 

is to be maintained. This can be accomplished by 

preventing germination of seeds or by uprooting young 

established seedlings. The discharge at which the entire 

channel bed is covered and at which the width- and 

depth-discharge relations change represents a minimum 

value for channel maintenance. Although this minimum 

discharge may not maintain the channel, discharges

below this value will afford channel area for seed germination and thus cannot prevent vegetation establishment. For a given cross section, the discharge at which 

the hydraulic geometry relations change is generally 

less than annual mean discharge.

REFERENCES CITED

Carlston, C. W., 1969, Downstream variations in the hydraulic geometry of streams: Special emphasis on mean velocity: American 

Journal of Science, v. 267, p. 499-509.

Crowley, K D., 1981, Large-scale bedforms in the Platte River: 

Structure process, and relation to channel narrowing: U.S. 

Geological Survey Open-File Report 81-1059,33 p.

Eschner, T. R., Hadley, R. F., and Crowley, K. D., 1981, Hydrologic 

and morphologic changes in channels of the Platte River Basin: A 

historical perspective: U.S. Geological Survey Open-File Report 

81-1125,57 p.

Fenneman, N. M., 1931, Physiography of western United States: 

New York, McGraw-HiU, 534 p.

Frith, Charles, 1974, The ecology of the Platte River as related to 

sandhill cranes and other waterfowl in southcentral Nebraska: 

MS thesis, Kearney, Nebraska, Kearney State College, 115 p.

Karlinger, M. R., Mengis, R. C., Kircher, J. E., and Eschner, T. R., 

1981, Application of theoretical equations to estimate the discharge needed to maintain channel width in a reach of the Platte 

River near Lexington, Nebraska: U.S. Geological Survey OpenFile Report 81-697,16 p.

Kircher, J. E., 1981, Sediment transport and effective discharge 

for the North Platte, South Platte, and Platte Rivers in 

Nebraska: U.S. Geological Survey Open-File Report 81-53,26 p.

Kircher, J. E., and Karlinger, M. R., 1981, Changes in surface-water 

hydrology for the Platte River basin: U.S. Geological Survey 

Open-File Report 81-818,77 p.

Knighton, A. D., 1975, Variations in at-a-station hydraulic geometry: 

American Journal of Science, v. 275, p. 186-218.

___1977, Short-term changes in hydraulic geometry, in Gregory, 

K. J., ed., River channel changes: Chichester, England, John 

Wiley,p.l01-119.

___1979, Comments on log-quadratic relations in hydraulic geometry: Earth Surface Processes, v. 4, p. 205-209.

Langbein, W. B., 1964, Geometry of river channels: American 

Society of Civil Engineers Journal of Hydraulics Division, v. 90, 

p. 301-312.

Leopold, L. B., and Langbein, W. B., 1962, The concept of entropy 

in landscape evolution: U.S. Geological Survey Professional 

Paper 500-A, 20 p.

Leopold, L. B., and Maddock, Thomas, Jr., 1953, The hydraulic 

geometry of stream channels and some physiographic implications: U.S. Geological Survey Professional Paper 252,57 p.

Nadler, C. T., Jr., 1978, River metamorphosis of the South Platte 

and Arkansas Rivers, Colorado: MS thesis, Fort Collins, Colorado, Colorado State University, 151 p.

Park, C. C., 1977, World-wide variations in hydraulic geometry exponents of stream channels: An analysis and some observations: 

Journal of Hydrology, v. 38, p. 133-146.

___1978, World-wide variations in hydraulic geometry exponents 

of stream channels: An analysis and some observations reply: 

Journal of Hydrology, v. 39, p. 199-202.

Parker, Gary, 1978, Self-formed straight rivers with equilibrium 

banks and mobile bed. Part I. The sand-silt riven Journal of Fluid 

Mechanics, v. 89, pt 1, p. 109-125.
HYDRAULIC GEOMETRY OF THE PLATTE RIVER NEAR OVERTON, NEBRASKA C25

Pickup, G., and Rieger, W. A., 1979, A conceptual model of the relationship between channel characteristics and discharge: Earth 

Surface Processes, v. 4, p. 37-42.

Rhodes, D. D., 1977, The b-f-m diagram: Graphical representation and 

interpretation of at-a-station hydraulic geometry: American Journal of Science, v. 277, p. 73-96.

___1978, World-wide variations in hydraulic geometry exponents 

of stream channels: An analysis and some observationscomments: Journal of Hydrology, v. 39, p. 193-197.

Richards, K. S., 1973, Hydraulic geometry and channel roughness: 

A non-Knear system: American Journal of Science, v. 273, 

p. 877-896.

___1976, complex width-discharge relations in natural river sections: Geological Society of America Bulletin, v. 87, p. 199-206.

JL977, Channel and flow geometry: a geomorphological perspective: Progress in Physical Geometry, v. 1, p. 65-102.

Schumm, S. A., 1960, The shape of alluvial channels in relation to 

sediment type: U.S. Geological Survey Professional Paper 352-B, 

p. 17-30.

___1968, River adjustment to altered hydrologic regimen, Murrumbidgee River and paleochannels, Australia: U.S. Geological 

Survey Professional Paper 598,65 p.

Smith, T. R., 1974, A derivation of the hydraulic geometry of steady 

state channels from conservation principles and sediment transport laws: Journal of Geology, v. 82, p. 98-104.

Thornes, J. B., 1970, The hydraulic geometry of stream channels 

in the Xingu-Araguaia headwaters: Geographical Journal, v. 136, 

p. 376-382.

___1977, Hydraulic geometry and channel change, in Gregory, 

K. J., ed., River channel changes: Chichester, England, John 

Wiley, p. 91-100.

U.S. Fish and Wildlife Service, 1978, Determination of critical habitat for the whooping crane: Federal Register, v. 43, no. 94, 

p. 20938-20942.

___1981, The Platte River ecology study: U.S. Department of the 

Interior, Fish and Wildlife Service Special Research Report, 

187 p.

Wilcock, D. N., 1971, Investigation into the relations between bedload transport and channel shape: Geological Society of America 

Bulletin, v. 82, p. 2159-2176.

Williams, G. P., 1978a, Hydraulic geometry of river cross sectionstheory of minimum variance: U.S. Geological Survey Professional 

Paper 1029,47 p.

___1978b, The case of the shrinking channels the North Platte 

and Platte Rivers in Nebraska: U.S. Geological Survey Circular 

781,48 p.

Wolman, M. G., 1955, The natural channel of Brandywine Creek 

Pennsylvania: U.S. Geological Survey Professional Paper 271, 

56 p.

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size and shape of stream channels in coarse noncohesive sands: 

U.S. Geological Survey Professional Paper 282-G, 28 p.

SUMMARY OF STATISTICAL DATA
C28 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN 

TABLE 2. Significance levels for at-a-station hydraulic-geometry equations from summarized data

Variable

w

V

D

w

V

D

w

V

D

w

V

D

w

V

D

w

V

D

w

V

D

D

V

D

w

V

D

w

V

D

w

V

D

w

V

D

w

V

Platte 

River 

near:

Cozad

Cozad

Cozad

Cozad

Cozad

Cozad

Cozad

Cozad

Cozad

Cozad

Cozad

Cozad

Cozad

Cozad

Cozad

Cozad

Cozad

Cozad

Cozad

Cozad

Cozad

Cozad

Cozad

Cozad

Cozad

Cozad

Cozad

Cozad

Cozad

Cozad

Cozad

Cozad

Cozad

Cozad

Cozad

Cozad

Cozad

Cozad

Distance 

below gage 

(meters)

30

30

30

30

30

30

30

30

30

30

30

30

45

45

45

45

45

45

45

45

45

60

60

60

60

60

60

60

60

60

60

60

60

60

60

60

60

60

Testing 

regression

YonX

YonX

YonX

YonX

YonX

YonX

YonX

YonX

YonX

YonX

YonX

YonX

YonX

Low

High

YonX

Low

High

YonX

Low

High

YonX

Low

High

YonX

Low

High

YonX

Low

High

YonX

High

YonX

High

YonX

High

YonX

Low

High

YonX

Low

High

YonX

Low

High

YonX

YonX

YonX

YonX

YonX

YonX

YonX

Low

High

YonX

Low

High

YonX

Low

High

YonX

Low

High

YonX

Low

High

YonX

Low

High

YonX

Low

High

YonX

Low

High

Period 

of 

record

1961-1979

1961-1979

1961-1979

1961-1963

1961-1963

1961-1963

1964-1969

1964-1969

1964-1969

1970-1979

1970-1979

1970-1979

1954-1979

1954-1979

1954-1979

1954-1969

1954-1969

1954-1969

1970-1979

1970-1979

1970-1979

1953-1979

1953-1979

1953-1979

1953-1957

1953-1957

1953-1957

1958-1963

1958-1963

1958-1963

1953-1963

1953-1963

1953-1963

1964-1969

1964-1969

1964-1969

1970-1979

1970-1979

n

30

30

30

3

3

3

6

6

6

21

21

21

30

8

22

30

8

22

30

8

22

9

5

4

9

5

4

9

5

4

21

18

21

18

21

18

73

25

48

73

25

48

73

25

48

11

11

11

15

15

15

26

15

11

26

15

11

26

15

11

13

3

10

13

3

10

13

3

10

34

7

27

34

7

27

Regression 

sum of 

squares

2.469174

0.279886

3.673960

0.57133

0.04949

0.14535

0.15573

0.05462

0.03028

1.09755

0.132768

0.531339

2.10585

.59899

.38114

0.155475

.00560

.04997

1.01994

.01542

.65535

1.7758

.27336

.31156

0.1384

.00011

.02003

0.52064

.02872

.13875

0.138480

.06605

0.015929

.00767

0.704423

.56005

11.49118

4.45530

.56799

1.51974

.36342

.16379

2.98305

.15681

.90036

2.7491

0.1933

0.16872

2.0328

0.20856

1.0032

3.03395

.26945

0.21365

.02390

0.12763

.27101

0.93046

.15643

.22226

0.34010

.02848

.07628

0.37346

.00268

.26363

0.675620

.15766

.03985

0.125167

.00006

.08001

Error 

sum of 

squares

0.006662

0.001833

0.007333

0.00290

0.000031

0.00353

0.00960

0.00337

0.00228

0.005369

0.001145

0.003656

0.01251

.01741

.005845

0.008515

.01163

.00821

0.01442

.00710

.01281

0.0199

.03425

.00460

0.0101

.01826

.00028

0.00394

.03425

.00460

0.002437

.00245

0.008576

.00973

0.008997

.00963

0.01671

.01960

.00827

0.01029

.02412

.00382

0.01182

.00617

.00739

0.0389

0.0497

0.00335

0.0158

0.00334

0.0123

0.02966

.01690

0.03581

.00350

0.00736

.01106

0.00483

.00649

.00126

0.00230

.00909

.00120

0.00721

.00022

.00157

0.007885

.00403

.00445

0.004224

.00060

.00462

Fstatistic

370.75

152.95

193.21

196.84

1,594.40

41.09

16.24

16.24

13.32

204.39

115.45

145.33

168.33

34.40

65.21

18.26

.48

6.09

70.73

2.17

51.16

84.49

7.98

67.75

13.76

.01

72.59

132.25

.84

30.17

56.82

26.96

1.86

.79

78.30

58.13

687.68

227.31

68.69

147.69

15.07

42.86

252.37

25.40

121.88

70.56

3.88

50.41

128.60

62.41

81.72

102.29

15.94

5.97

6.65

17.33

24.50

179.02

24.11

176.09

147.62

3.13

63.36

51.70

12.39

167.44

85.68

39.06

8.94

29.63

.10

17.14

Significance 

level

0.10

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

0.05

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

0.01

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

0.001

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X
HYDRAULIC GEOMETRY OF THE PLATTE RIVER NEAR OVERTON, NEBRASKA 

TABLE ^.-^Significance levels for at-a-station hydraulic-geometry equations from summarized data Continued

C29

Variable

D

w

V

D

w

V

D

w

V

D

w

V

D

w

V

D

w

V

D

w

V

D

w

V

D

w

V

Platte 

River 

near

Cozad

Cozad

Cozad

Cozad

Cozad

Cozad

Cozad

Cozad

Cozad

Cozad

Cozad

Cozad

Cozad

Cozad

Cozad

Cozad

Cozad

Cozad

Cozad

Cozad

Cozad

Cozad

Cozad

Cozad

Cozad

Overton,

north

channel

Overton,

north

channel

Distance 

below gage 

(meters)

60

75

75

75

75

75

75

75

75

75

75

75

75

120

120

120

120

120

120

120

120

120

120

120

120

30

30

Testing 

regression

YonX

Low

High

YonX

Low

High

Yon-X

Low

High

YonX

Low

High

YonX

Low

High

YonX

Low

High

YonX

Low

High

YonX

Low

High

YonX

Low

High

YonX

Low

High

YonX

High

YonX

High

YonX

High

YonX

Low

High

YonX

Low

High

YonX

Low

High

YonX

Low

YonX

Low

YonX

Low

YonX

Low

High

YonX

Low

High

YonX

Low

High

YonX

Low

High

YonX

Low

High

YonX

Low

High

YonX

YonX

Period 

of 

record

1970-1979

1961-1979

1961-1979

1961-1979

1961-1963

1961-1963

1961-1963

1964-1969

1964-1969

1964-1969

1970-1979

1970-1979

1970-1979

1951-1979

1951-1979

1951-1979

1951-1963

1951-1963

1951-1963

1964-1969

1964-1969

1964-1969

1970-1979

1970-1979

1970-1979

1968-1976

1968-1976

n

34

7

27

46

15

31

46

15

31

46

15

31

15

6

9

15

6

9

15

6

9

12

5

7

12

5

7

12 *5

7

19

15

19

15

19

15

153

63

90

153

63

90

153

63

90

32

28

32

28

32

28

82

42

40

82

42

40

82

42

40

39

14

25

39

14

25

39

14

25

14

14

Regression 

sum of 

squares

0.964612

.00004

.41468

1.585857

.21177

.67218

0.346376

.08656

.03916

1.103953

.00106

.31658

0.043926

.04431

.28454

0.3549

.01336

.05634

0.22520

.00757

.00354

1.12738

.10291

.16234

0.18892

.02361

.00575

0.34943

.00225

.06900

0.085085

.004352

0.132970

.05019

0.486102

.14776

19.87165

12.66166

.25444

2.785591

.95552

.18221

7.799154

1.39596

1.63983

8.4442

5.388868

0.5925

.29907

1.07189

.43142

0.34519

.18675

.02623

0.39503

.02481

.04738

1.66396

.11284

.37284

0.701922

.11042

.16778

0.151930

.00083

.14213

1.969314

.15802

1.21734

0.196206

0.051963

Error 

sum of 

squares

0.007636

.00275

.00706

0.006428

.00505

.00580

0.002718

.00164

.00219

0.005522

.00321

.00443

0.00375

.00244

.00198

0.00195

.00091

.00453

0.00371

.00075

.00205

0.00484

.00618

.00347

0.00135

.00046

.00029

0.00526

.00352

.00211

0.002278

.00249

0.001599

.00186

0.003464

.00400

0.01202

.00906

.00272

0.004004

.00746

.00153

0.009340

.00603

.00243

0.0129

.01296

0.0129

.01474

0.00682

.00661

0.00272

.00406

.00153

0.00078

.00082

.00055

0.00208

.00370

.00092

0.004423

.00515

.00218

0.002814

.00256

.00221

0.004547

.00327

.00323

0.006256

0.001103

Fstatistic

126.32

.01

58.68

246.71

41.99

115.99

127.44

52.85

17.81

199.92

.32

71.40

117.07

18.15

143.76

18.23

14.75

12.46

60.68

10.05

1.72

232.87

16.65

46.79

140.42

51.55

19.54

66.42

.64

32.60

37.35

17.47

83.16

27.04

140.33

36.97

1,65322

1,397.26

93.70

695.70

127.92

119.03

835.03

231.65

676.00

656.38

415.75

46.10

20.25

257.25

65.29

127.01

45.97

17.14

504.45

30.36

86.68

800.89

30.47

404.41

158.70

21.44

76.91

53.99

.32

64.32

433.10

48.30

376.75

31.36

47.11

Significance 

level

0.10

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

0.05

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

0.01

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

0.001

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X
C30 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

TABLE 2. Significance levels for at-a-station hydraulic-geometry equations from summarized data Continued

Variable

D

W

V

D

W

V

D

W

V

D

W

V

D

W

V

D

W

V

D

W

V

D

W

V

D

W

V

D

Platte 

River 

near

Overton,

north

channel

Overton,

south

channel

Overton,

south

channel

Overton,

south

channel

Overton

Overton

Overton

Overton,

north

channel

Overton,

north

channel

Overton,

north

channel

Overton

Overton

Overton

Overton,

north

channel

Overton,

north

channel

Overton,

north

channel

Overton

Overton

Overton

Overton

Overton

Overton

Overton

Overton

Overton

Overton

Overton

Overton

Distance 

below gage 

(meters)

30

30

30

30

30

30

30

45

45

45

45

45

45

60

60

60

60

60

60

60

60

60

60

60

60

75

75

75

Testing 

regression

YonX

YonX

YonX

YonX

YonX

YonX

YonX

YonX

Low

High

YonX

Low

High

YonX

Low

High

YonX

YonX

YonX

YonX

Low

High

YonX

Low

High

YonX

Low

High

YonX

Low

High

YonX

Low

High

YonX

Low

High

YonX

Low

High

YonX

Low

High

YonX

Low

High

YonX

Low

High

YonX

Low

High

YonX

Low

High

YonX

Low

High

YonX

Low

High

YonX

Low

High

Period 

of 

record

1968-1976

1968-1976

1968-1976

1968-1976

1961-1968

1961-1968

1961-1968

1968-1976

1968-1976

1968-1976

1961-1963

1961-1963

1961-1963

1968-1976

1968-1976

1968-1976

1954-1968

1954-1968

1954-1968

1954-1963

1954-1963

1954-1963

1964-1968

1964-1968

1964-1968

1962-1968

1962-1968

1962-1968

n

14

20

20

20

11

11

11

25

10

15

25

10

15

25

10

15

7

7

7

53

20

33

53

20

33

53

20

33

46

16

30

46

16

30

46

16

30

18

7

11

18

7

11

18

7

11

28

9

19

28

9

19

28

9

19

51

17

34

51

17

34

51

17

34

Regression 

sum of 

squares

0.130150

0.952106

0.0161493

0.528872

0.67557

0.00714

0.14293

0.326028

.03135

.01072

0.142227

.05074

.01344

0.28635

.03162

.06995

0.47005

0.00128

0.01013

0.680470

.21689

.00064

0.203593

.00762

0.541680

.05723

.17544

2.12162

.02629

.3977

0.11113

.00014

.09061

0.19631

.03116

.18349

1.57824

.02303

.20046

0.05105

.00071

.03467

0.05669

.00033

.05523

0.67519

.00608

.12427

0.04065

.00007

.02435

0.11258

.05027

.07082

0.85980

.17490

.21246

0.27048

.00246

.14042

0.20581

.00573

.07405

Error 

sum of 

squares

0.004312

0.002543

0.0009511

0.002149

0.00997

0.00163

0.00900

0.002975

.00533

.00108

0.001261

.00159

.00070

0.003402

.00696

.00101

0.00759

0.00592

0.00142

0.004211

.00700

.00134

0.001548

.00043

0.004389

.00703

.00125

0.00878

.01214

.00357

0.00301

.00424

.00204

0.00610

.00921

.00292

0.00813

.01267

.00215

0.00130

.00098

.00097

0.00479

.00846

.00173

0.00465

.00080

.00449

0.00362

.00617

.00278

0.00515

.00479

.00375

0.00436

.00492

.003344

0.00234

.001129

.00258

0.00290

.00357

.00267

Fstatistic

30.18

374.40

16.98

246.10

67.73

4.37

1.59

109.59

5.86

9.92

112.79

31.92

19.18

84.17

4.54

69.22

61.94

.21

7.13

161.59

31.02

.48

131.52

9.73

17.72

123.42

8.12

139.95

241.80

2.16

111.30

36.97

.03

44.49

32.15

3.39

62.88

194.04

1.82

93.32

39.44

.72

35.64

11.83

.04

32.04

145.20

7.56

27.67

11.22

.01

8.76

21.90

10.50

18.92

197.20

35.52

61.78

115.59

2.19

54.46

70.97

1.61

27.77

Significance 

level

0.10

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

0.05

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

0.01

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

0.001

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X
HYDRAULIC GEOMETRY OF THE PLATTE RIVER NEAR OVERTON, NEBRASKA 

TABLE 2. Significance levels for at-a-statian hydraulic-geometry equations from summarized data Continued

C31

Variable

w

V

D

W

V

D

W

V

D

W

V

D

W

V

D

W

V

D

W

V

D

W

V

D

W

V

Platte 

River 

near

Overton,

north

channel

Overton,

north

channel

Overton,

north

channel

Overton.

Overton

Overton

Overton

Overton

Overton

Overton,

north

channel

Overton,

north

channel

Overton,

north

channel

Overton,

south

channel

Overton,

south

channel

Overton,

south

channel

Overton

Overton

Overton

Overton

Overton

Overton

Overton

Overton

Overton

Odessa

Odessa

Distance 

below gage 

(meters)

75

75

75

75

75

75

75

75

75

90

90

90

90

90

90

90

90

90

90

90

90

90

90

90

60

60

Testing 

regression

YonX

YonX

YonX

YonX

YonX

YonX

YonX

Low

High

YonX

Low

High

YonX

Low

High

YonX

Low

High

YonX

Low

High

YonX

Low

High

YonX

YonX

YonX

YonX

Low

High

YonX

Low

High

YonX

Low

High

YonX

Low

High

YonX

Low

High

YonX

Low

High

YonX

Low

High

YonX

Low

High

YonX

Low

High

YonX

Low

High

YonX

Low

High

Period 

of 

record

1968-1976

1968-1976

1968-1976

1962-1963

1962-1963

1962-1963

1964-1968

1964-1968

1964-1968

1968-1978

1968-1978

1968-1978

1968-1978

1968-1978

1968-1978

1962-1968

1962-1968

1962-1968

1962-1963

1962-1963

1962-1963

1964-1968

1964-1968

1964-1968

1962-1979

1962-1979

n

8

8

8

8

8

8

43

13

30

43

13

30

43

13

30

33

10

23

33

10

23

33

10

23

23

23

23

160

75

85

160

75

85

160

75

85

41

22

19

41

22

19

41

22

19

119

53

66

119

53

66

119

53

66

55

38

17

55

38

17

Regression 

sum of 

squares

0.0012756

0.0368640

0.0447134

0.05917

0.02833

0.04782

0.79032

.11570

.20058

0.24402

.00050

.13332

0.16379

.00615

.05425

0.281233

.06885

.02127

0.178685

.00381

.09554

0.530304

.00595

.17726

0.25592

0.143793

0.178088

2.71652

1.15854

.03305

0.51750

.03573

.04231

1.24976

.06586

.29093

0.80779

.54046

.00309

0.11225

.00893

.01487

0.28229

.00141

.06553

1.90815

.63762

.03121

0.40611

.02596

.02836

0.96578

.08278

.22458

8.280655

3.79507

.01874

0.469099

.25506

.00091

Error 

sum of 

squares

0.0005457

0.0006871

0.0003512

0.00877

0.00061

0.00540

0.00370

.00296

.00355

0.00266

.00120

.00285

0.00253

.00265

.00264

0.003713

.00167

.00307

0.001486

.00114

.00121

0.001724

.00157

.00142

0.01347

0.003713

0.009934

0.00421

.00546

.00076

0.00152

.00201

.00088

0.00426

.00606

.00140

0.00549

.00400

.00031

0.00107

.00134

.00045

0.00363

.00274

.00072

0.00380

.00581

.00088

0.00168

.00232

.00101

0.00453

.00724

.00161

0.006983

.00929

.00133

0.004171

.00447

.00360

Fstatistic

2.34

53.65

127.32

6.76

46.79

8.88

213.74

39.19

56.55

91.78

.50

46.79

64.64

2.31

20.52

75.74

41.09

6.92

120.25

3.31

78.85

307.60

3.80

124.99

19.00

38.73

17.93

645.25

212.28

43.56

340.46

17.72

47.89

293.37

10.89

207.65

147.14

135.26

9.92

105.06

6.71

33.41

77.79

.52

91.58

501.76

109.83

35.52

241.49

11.16

27.98

213.45

11.42

139.24

1,185.83

408.85

14.06

112.47

57.00

.25

Significance 

level

0.10

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

0.05

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

0.01

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

0.001

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X
C32 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

TABLE 2. Significance levels for at-a-station hydraulic-geometry equations from summarized data Continued

Variable

D

w

V

D

w

V

D

w

V

D

w

V

D

w

V

D

w

V

D

w

V

D

w

V

D

w

V

D

w

V

D

w

V

D

Platte 

River 

near:

Odessa

Odessa

Odessa

Odessa

Odessa

Odessa

Odessa

Odessa

Odessa

Odessa

Odessa

Odessa

Odessa

Odessa

Odessa

Odessa

Odessa

Odessa

Odessa

Odessa

Odessa

Odessa

Odessa

Odessa

Odessa

Odessa

Odessa

Odessa

Odessa

Odessa

Odessa

Odessa

Odessa

Odessa

Distance 

below gage 

(meters)

60

60

60

60

60

60

60

60

60

60

75

75

75

75

75

75

75

75

75

75

75

75

90

90

90

90

90

90

90

90

90

90

90

90

Testing 

regression

YonX

Low

High

YonX

Low

High

YonX

Low

High

YonX

Low

High

YonX

YonX

YonX

YonX

YonX

YonX

YonX

Low

High

YonX

Low

High

YonX

Low

High

YonX

YonX

YonX

YonX

Low

High

YonX

Low

High

YonX

Low

High

YonX

YonX

YonX

YonX

Low

High

YonX

Low

High

YonX

Low

High

YonX

Low

High

YonX

Low

High

YonX

Low

High

YonX

Low

High

YonX

Low

High

YonX

Low

High

YonX

YonX

YonX

Period 

of 

record

1962-1979

1962-1963

1962-1963

1962-1963

1964-1969

1964-1969

1964-1969

1970-1979

1970-1979

1970-1979

1961-1979

1961-1979

1961-1979

1961-1963

1961-1963

1961-1963

1964-1969

1964-1969

1964-1969

1970-1979

1970-1979

1970-1979

1953-1979

1953-1979

1953-1979

1953-1963

1953-1963

1953-1963

1964-1969

1964-1969

1964-1969

1970-1979

1970-1979

1970-1979

n

55

38

17

26

15

11

26

15

11

26

15

11

19

19

19

10

10

10

60

40

20

60

40

20

60

40

20

9

9

9

45

27

18

45

27

18

45

27

18

6

6

6

187

66

121

187

66

121

187

66

121

45

18

27

45

18

27

45

18

27

134

43

91

134

43

91

134

43

91

8

8

8

Regression 

sum of 

squares

1.03098

.29176

.041148

5.39766

2.55189

.00632

0.39093

.18391

.00546

0.21598

.05000

.00907

1.66754

0.06890

0.4186

0.325985

0.018275

0.22677

8.185083

6.11130

.00355

0.858114

.74553

.00201

0.934258

.47876

.01641

3.4736

0.5731

0.25476

2.74704

1.91408

.00329

0.16580

.00395

.00109

0.57759

.25188

.01842

0.300151

0.013869

0.088113

26.01329

16.14536

.14149

2.067655

.95615

.06631

2.925669

.82710

.34679

17.0072

7.46218

.01986

1.19649

.57036

.00796

1.64721

.45667

.08951

4.53298

2.52567

.08429

0.576022

.11170

.07122

0.94740

.07312

.26072

0.926422

0.1065735

0.401328

Error 

sum of 

squares

0.01269

.01567

.00464

0.00600

.00901

.00133

0.00339

.00606

.00012

0.00846

.01351

.00137

0.00521

0.00368

0.0101

0.006496

0.005656

0.01112

0.006655

.00952

.00058

0.004192

.00544

.00080

0.005211

.00594

.00087

0.0148

0.0146

0.00424

0.00482

.00706

.00065

0.00120

.00154

.00075

0.00417

.00553

.00083

0.005752

0.001560

0.004935

0.00751

.01115

.00258

0.001675

.00221

.00136

0.006222

.00838

.00283

0.0053

.00899

.00144

0.00353

.00333

.00373

0.00739

.00881

.00428

0.00701

.01216

.00185

0.00093

.00155

.00050

0.00487

.00827

.00170

0.003596

0.0007208

0.004560

Fstatistic

81.24

18.58

8.88

900.00

283.25

4.75

115.56

30.36

45.70

25.50

3.69

6.66

320.05

18.66

41.47

50.18

3.23

20.39

229.91

641.61

6.10

204.70

137.12

2.53

179.29

80.64

18.84

235.32

39.19

60.06

569.78

271.26

5.02

138.53

73.79

1.44

138.53

45.56

22.28

52.18

8.89

17.85

3,463.82

1,448.56

54.91

1,234.42

432.64

48.86

470.21

98.80

122.54

3,188.86

829.44

13.79

338.93

171.09

2.13

222.90

51.84

20.88

646.68

207.65

45.70

619.01

72.25

143.28

194.32

8.82

153.02

257.63

147.85

88.01

Significance 

level

0.10

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

0.05

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

0.01

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

0.001

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X
Interpretation of Sediment Data for 

the South Platte River in Colorado 

and Nebraska, and the North Platte 

and Platte Rivers in Nebraska

By JAMES E. KIRCHER

HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 1277-D

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1983

CONTENTS

Abstract 

Introduction 

Acknowledgments 

Physical setting 

Data collection - 

Suspended sediment 

Bedload 

Page

Dl

1

1

1

3

3

3

Bed material 

Total sediment discharge 

Comparison of total sediment discharge methods 

Mean-daily sediment discharge 

Summary 

References cited 

Summary of data 

Page

D4

4

6

11

24

24

27

ILLUSTRATIONS

Page

FIGURE 1. Map showing location of sediment-data stations along the North Platte, South Platte, and Platte Rivers. D2 

2-29. Graphs showing:

2. Variation in sediment size with distance downstream for the North Platte and Platte Rivers, August 1979. 5

3. Variation in local channel slope with distance downstream for the North Platte and Platte Rivers. 5

4. Variation in median bed-material size with discharge for the Platte River near Overton, Nebraska. 6

5. Variation in median bed-material size with discharge for the Platte River near Grand Island, Nebraska. 6

6. Relations between water and measured total sediment discharges for the North Platte, South Platte, and Platte

Rivers. 7

7. Relation of total sediment discharge in individual size class as a function of total sediment discharge: 0.062- to

0.125-millimeter size class. 9

8. Relation of total sediment discharge in individual size class as a function of total sediment discharge: 0.125- to

0.250-millimeter size class. 10

9. Relation of total sediment discharge in individual size class as a function of total sediment discharge: 0.250- tQ

0.500-millimeter size class. 11

10. Relation of total sediment discharge in individual size class as a function of total sediment discharge: 0.500- to

1.000-millimeter size class. 12

11. Relation of total sediment discharge in individual size class as a function of total sediment discharge: 1.000- to

2.000-millimeter size class. 13

12. Relation of total sediment discharge in individual size class as a function of total sediment discharge: 2.000- to

4.000-millimeter size class. 14

13. Relation of total sediment discharge in individual size class as a function of total sediment discharge: 4.000- to

8.000-millimeter size class. 15

14. Relation of total sediment discharge in individual size class as a function of total sediment discharge: 8.000- to

16.00-millimeter size class. 15

15. Comparison of sediment discharges computed by the modified Einstein procedure for an individual particle-size class

with corresponding measured sediment discharges for the class; 0.062- to 0.125-millimeter size class. 16

16. Comparison of sediment discharges computed by the modified Einstein procedure for an individual particle-size class

with corresponding measured sediment discharges for the class; 0.125- to 0.250-millimeter size class. 17

17. Comparison of sediment discharges computed by the modified Einstein procedure for an individual particle-size class

with corresponding measured sediment discharges for the class; 0.250- to 0.500-millimeter size class. 17

18. Comparison of sediment discharges computed by the modified Einstein procedure for an individual particle-size class

with corresponding measured sediment discharges for the class; 0.500- to 1.000-millimeter size class. 18

19. Comparison of sediment discharges computed by the modified Einstein procedure for an individual particle-size class

with corresponding measured sediment discharges for the class; 1.000- to 2.000-millimeter size class. 18

20. Comparison of sediment discharges computed by the modified Einstein procedure for an individual particle-size class

with corresponding measured sediment discharges for the class; 2.000- to 4.000-millimeter size class. 19

21. Comparison of sediment discharges computed by the modified Einstein procedure for an individual particle-size class

with corresponding measured sediment discharges for the class; 4.000- to 8.000-millimeter size class. 19

22. Comparison of sediment discharges computed by the modified Einstein procedure for an individual particle-size class

with corresponding measured sediment discharges for the class; 8.000- to 16.00-millimeter size class. 20

23. Comparison between total sediment discharges computed by the modified Einstein procedure and measured total

sediment discharges. 20

HI
IV CONTENTS

Page

FIGURE 24. Comparison between total sediment discharges computed by the Colby method and measured total sediment

discharges. D21

25. Comparison between total sediment discharges computed by Colby's method and total sediment discharges computed by the modified Einstein procedure. 21

26. Flow-duration curve for the North Platte River at North Platte, Nebraska (1941-79). 22

27. Flow-duration curve for the South Platte River at North Platte, Nebraska (1941-79). 22

28. Flow-duration curve for the Platte River near Overton, Nebraska (1950-79). 23

29. Flow-duration curve for the Platte River near Grand Island, Nebraska (1935-79). 23

TABLES

TABLE 1. Number and name of sediment-data stations. D3

2. Water-sediment discharge relations, derived by log-linear regression, for selected Platte River stations. 7

3. Coefficients and statistics for linear regression equations of log-transformed values of measured total sediment discharge by

size class versus measured total sediment discharge. 8

4. Coefficients and statistics for linear regression equations of log-transformed values of total sediment discharge by the

modified Einstein procedure by size class versus total sediment discharge by the modified Einstein procedure. 8

5. Coefficients and statistics for linear regression equations of log-transformed values of measured bedload discharge by size

class versus total measured bedload discharge. 16

6. Coefficients and statistics for linear regression equations of log-transformed values of unmeasured-sediment discharges

computed by the modified Einstein procedure by size class versus total unmeasured-sediment discharge. 16

7. Coefficients and statistics for linear regression equations of log-transformed values of sediment discharges in different size

classes computed by the modified Einstein procedure and from measured sediment discharges. 16

8. Summary of mean-daily water discharge and measured total sediment discharge at four gaging stations. 24

9. Comparison of mean-daily sediment discharges obtained by varying the number of subdivisions of the flow-duration curve

for the Platte River near Overton, Nebraska 24

10. Summary of water-discharge measurements. 29

11. Summary of measured sediment-transport data 30

12. Grain-size distribution of suspended sediment. 31

13. Grain-size distribution of bedload. 32

14. Statistical data, grain-size distribution of bedload. 33

15. Grain-size distribution of bed material. 34

16. Statistical data, grain-size distribution of bed material. 36
HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

INTERPRETATION OF SEDIMENT DATA FOR THE

SOUTH PLATTE RIVER IN COLORADO AND NEBRASKA, AND THE

NORTH PLATTE AND PLATTE RIVERS IN NEBRASKA

By JAMES E. KIRCHER

ABSTRACT

Sediment data were collected on the South Platte, North Platte, 

and Platte Rivers during the 1979 and 1980 runoff seasons for a 

determination of quantity and distribution of sediment in the basin. 

These data show a decrease in median bed-material size in a downstream direction, except near Overton, Nebraska, where an increase 

in size corresponds to an increase in local slope. The median grain size 

varies little with increasing discharge at two stations along the Platte 

River.

Measured suspended sediment and bedload discharges were combined for a determination of total sediment discharge at four locations 

in the Platte River basin. The measured total sediment discharge was 

then compared to the total sediment discharges computed by the 

modified Einstein procedure and Colby method. This comparison was 

made by size class and total load for all size classes; it showed very 

close agreement indicating that field conditions in the Platte River 

approximate the principles of the two computational methods.

The measured total sediment discharge was then used for the computation of mean daily sediment discharge at four stations in the 

basin. The mean daily sediment discharges at the four locations were: 

(1) 597 metric tons per day for the North Platte River at North Platte, 

Nebraska; (2) 307 metric tons per day for the South Platte River at 

North Platte, Nebraska; (3) 1,100 metric tons per day for the Platte 

River near Overton, Nebraska; and (4) 1,130 metric tons per day for 

the Platte River near Grand Island, Nebraska

INTRODUCTION

The Platte River is one of the most important rivers 

of the Great Plains a source of irrigation water for 

agriculture and the unique habitat for several species of 

migrating waterfowl. Ongoing channel and hydraulic 

changes along the Platte River and its tributaries 

(Kircher and Karlinger, 1981) caused concern* among 

wildlife and agricultural managers. Therefore, prediction of channel response to anticipated changes in 

hydraulic factors and the determination of discharges 

required to maintain a channel of specified or existing 

cross-sectional properties are critical to management 

schemes. The prediction of channel response can aid 

managers in the planning of future projects.

Effective evaluation of management plans requires information on sediment transport in the Platte River. 

This investigation was undertaken to determine the 

quantity and distribution of sediment in transport in 

the Platte River basin. Data presented in this report 

were collected in 1979 and 1980. Data collected were 

used to determine suspended-sediment discharges, bedload discharges, bed-material sizes, and total sediment 

discharges at several locations in the basin. Changes in 

bed-material size in a downstream direction were also 

determined along the North Platte and Platte Rivers. 

Sediment-water-discharge relations and information on 

bed-material size can be used by resource managers, 

hydrologists, and other earth scientists to better 

understand and accommodate the process of sediment 

discharge in the basin. This information on the sediment characteristics of the river can be used with existing techniques to obtain an estimate of the discharge 

necessary to maintain a specified channel size.

ACKNOWLEDGMENTS

The author would like to thank the following for helping collect and reduce the data during the 1979 and 

1980 field seasons: L. E. Dobson, T. R. Eschner, E. M. 

Fryer, E. M. Held, M. R. Karlinger, L. R. Newmeyer, 

and D. Reynolds.

PHYSICAL SETTING

The South Platte and North Platte Rivers originate 

as snowmelt streams in the Rocky Mountains of Colorado, flowing across the Great Plains to form the Platte 

River at their confluence at North Platte, Nebraska 

(fig. 1 and table 1). Total drainage area of the South 

Platte River is about 62,900 km2 (square kilometers) and

Dl
D2 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

I

I
INTERPRETATION OF SEDIMENT DATA D3

TABLE 1. Number and name of sediment-data stations

Station 

No. 

in 

figure 1

1

2

3

4

5

6

7

8 

9

10

11

12

13

14

15

16

17

18

19

20 

21

U.S. 

Geological 

Survey 

station No.

06691000

06693000

06754000

06758500

06760000

06764000

06765500

06766000 

06766500

06768000

06770000

06770500

06772600

06772800

06772850

06774000

06794700

06796000

06796500

06796550 

06805500

Station name

North Platte River near Sutherland, Nebraska

North Platte River at North Platte, Nebraska

South Platte River near Kersey, Colorado

South Platte River near Weldona, Colorado

South Platte River at Balzac, Colorado

South Platte River at Julesburg, Colorado

South Platte River at North Platte, Nebraska

Platte River at Brady, Nebraska 

Platte River near Cozad, Nebraska

Platte River near Overton, Nebraska

Platte River near Odessa, Nebraska

Platte River near Grand Island, Nebraska

Platte River near Central City, Nebraska

Platte River near Clarks, Nebraska

Platte River near Silver Creek, Nebraska

Platte River near Duncan, Nebraska

Platte River near Schuyler, Nebraska

Platte River near North Bend, Nebraska

Platte River near Fremont, Nebraska

Platte River near Venice, Nebraska 

Platte River near Louisville, Nebraska

the river is about 720 river km (kilometers) long (Ben-, 

tall, 1975, p. 6). The North Platte River drains approximately 80,000 km2 and is about 1,050 km long.

The area studied includes a 380 river-km reach of the 

South Platte River from Kersey, Colorado to North 

Platte, Nebraska; a 86 river-km reach of the North 

Platte River from Lake McConaughy near Ogallala, 

Nebraska to the confluence with the South Platte River; 

and a 460 river-km reach of the Platte River from North 

Platte to Louisville, Nebraska. The major emphasis of 

the study was the 120 river-km reach between Lexington and Chapman, Nebraska; this reach was designated 

by the U.S. Fish and Wildlife Service as the habitat of 

several species of endangered migratory waterfowl.

DATA COLLECTION

Sediment data were collected at twenty-one locations 

along the North Platte, South Platte, and Platte Rivers 

(fig. 1 and table 1). Primary station identification is the 

eight digit U.S. Geological Survey station number; 

however, station numbers used in this report (fig. 1 and 

tables 10 to 16 (see Summary of Data section at end of 

report)) were assigned to each station with higher 

numbers in downstream direction (Kircher, 198la).

Sampling stations were located at bridge crossings 

for convenience of sampling at high flows. Sampling 

was done from May through September to insure that 

observations were made for a variety of bed and 

hydraulic conditions. Frequency and type of sampling 

were variable among stations. Bed-material samples

were collected at all locations, but water-discharge, 

suspended-sediment, and bedload measurements were 

made at only a few of the locations (tables 10 to 16) 

within and near the reach of river designated as critical 

habitat by the U.S. Fish and Wildlife Service.

SUSPENDED SEDIMENT

Suspended sediment is that sediment carried in suspension by the turbulent components of streamflow. 

Samples were collected by depth-integrating with either 

a DH-48 or D-74 suspended-sediment sampler according to the equal-width increments method (Office of 

Water-Data Coordination, 1977). Fifteen to twenty 

verticals were sampled to determine the average 

discharge-weighted concentrations (table 11) and 

particle-size distribution (table 12) of the sediment in 

the streamflow. Suspended-sediment discharge (in 

metric tons per day) was computed as the product of the 

discharge-weighted concentration (in milligrams per 

liter), the water discharge (in cubic meters per second), 

and a units conversion constant, 0.0864 (table 11).

BEDLOAD

Bedload is the material moving on or near the streambed by rolling and sliding, and sometimes making brief 

excursions into the flow a few particle diameters above 

the bed. Bedload particles move in a series of steps interrupted by periods of no motion. A particle moves 

whenever the lift and drag forces produced by the flow 

or the impact of another moving particle overcome the 

resisting forces and dislodge the particle. Movement of 

bedload particles deforms the bed and produces bed 

forms, which, in turn, affect flow and bedload transport. 

Because bed forms and other factors influence bedload 

transport even in steady flow, bedload discharge fluctuates with time at a point and varies substantially 

from one point to another over the bed.

Bedload was measured at several different stations in 

the study reached during the summers of 1979 and 1980 

using a Helley-Smith bedload sampler (Helley and 

Smith, 1971). The measurements supplement suspended-sediment measurements, and enabled a calculation of total sediment discharge. Procedures for the collection of bedload samples are described by Emmett 

(1980). Channel width was divided into at least 20 increments of equal width. Bedload was measured twice 

at the midpoint of each increment to define the average 

bedload discharge for the cross section (tables 13 and 

14).
D4 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

BED MATERIAL

Bed-material samples were collected at all twenty-one 

stations using a BMH-60 (Guy and Norman, 1970). 

Size distributions of the samples were determined to 

define the change in bed-material size in a downstream 

direction, and to compute total sediment discharge. By 

giving each sample a weight proportional to the increment of channel width it represents, a weighted mean 

grain-size distribution for each station was calculated 

(table 15). A statistical summary of grain-size distributions, expressed as grain diameters at given percentfiner values, is presented in table 16.

Median grain diameter (D50), defined as the size for 

which half the material, by weight, is finer and half is 

coarser, changes in a systematic way downstream. On 

the basis of synoptic sampling in August 1979, the median diameter apparently decreases in the North Platte 

River downstream to the confluence of the North Platte 

and South Platte and increases in the Platte River from 

that point downstream to Overton, where it reaches its 

maximum; from Overton, the median diameter decreases in the downstream direction (fig. 2). The increase in median diameter in the reach of the Platte 

River upstream from Overton coincides with an increase in the slope of the river channel in the same reach 

(fig. 3). The increased slope may be due to the influx of 

coarser sediment from the South Platte River, or to 

widening of the channel caused by the addition of flow 

from the large powerplant return canal between Brady 

and Overton, or a combination of both (T. R. Eschner, 

U.S. Geological Survey, written commun., 1981). Error 

bars in figure 2 were calculated by computing the median bed-material size for the cross section from different numbers of samples. The number of samples per 

cross section was varied from 2 to 15 samples and then 

each weighted again to arrive at median bed-material 

sizes. These error bars are shown to give the reader an 

indication of the variation in gradation curves that can 

be observed, if fewer cross-section samples are collected 

than were used in this report. The line drawn between 

stations passes through median particle size computed 

from the maximum number of samples, based on Hubbell's (1956) statement that numerous samples in a 

cross section should be collected to obtain a representative sample. The error bars indicate that any future 

sampling for particle sizes should be based on numerous 

samples in a cross section. Plots of median grain size 

versus water discharge for the Platte River show that 

the median diameter decreases somewhat with increasing discharge at Overton (fig. 4), but that no trend is exhibited at Grand Island (fig. 5).

TOTAL SEDIMENT DISCHARGE

Total sediment discharge was computed using three 

different methods for four sites on the North Platte, 

South Platte, and Platte Rivers between North Platte 

and Grand Island, Nebraska. The methods are: (1) Addition of the measured suspended-sediment and bedload 

discharges; (2) the modified Einstein procedure (Colby 

and Hembree, 1955); (3) and addition of the measured 

suspended-sediment discharge and unmeasured sediment computed by a graphical method presented by 

Colby (1957); this third method is hereinafter called the 

Colby method. Sediment discharge computed by the 

three methods were compared to see if all three provided 

similar rates at Platte River cross sections. The four 

sites chosen for the comparisons were: (1) North Platte 

River at North Platte, Nebraska; (2) South Platte River 

at North Platte, Nebraska; (3) Platte River near Overton, Nebraska; and (4) Platte River near Grand Island, 

Nebraska.

Adding the measured suspended-sediment discharge 

and the bedload discharge measured with a HelleySmith bedload sampler may produce an erroneous 

estimate of total sediment discharge, because part of 

the suspended-sediment discharge in the "unsampled 

depth" (bottom 0.091 m (meter)) is accounted for in both 

the measured suspended-sediment discharge and the 

measured bedload discharge. In the calculation of 

measured suspended-sediment discharge, the measured 

suspended-sediment concentration is multiplied by the 

entire water discharge. Hence, part of the suspended 

sediment in the bottom 0.091 m of flow is included in 

the measured suspended-sediment discharge. Suspended material, in the "unsampled depth" coarser 

than 0.25mm also is trapped in the Helley-Smith 

sampler. Measured suspended-sediment discharges for 

the North Platte, South Platte, and Platte Rivers were 

adjusted to represent only the suspended-sediment 

discharge in the sampled depth, by multiplying 

measured rates by the fraction of flow in the sampled 

depth (Colby and Hembree, 1955). The corrected 

suspended-sediment discharge then was added to the 

measured bedload discharge to estimate total sediment 

discharge.

The modified Einstein procedure (Colby and Hembree, 1955) is a method for computing total sediment 

discharge from suspended-sediment samples and other 

relevant data. Data required for the modified Einstein 

procedure are obtained from a single cross section and 

include the mean velocity, stream width, mean depth at 

sampled verticals, concentration, and size distribution 

of the measured suspended-sediment, size distribution
INTERPRETATION OF SEDIMENT DATA D5

§ 

Q

UJ 

N

CO

UJ UJ

UJ

m

Q 

UJ

2.0

1.5

1.0

0.5

I T

10

8 Station number from figure I

and table I

Range of D50 values resulting 

I from varying number of bed

material samples 

 Line connecting D 5o values based

on maximum number of bed

material samples

20 21 -

100 200 300 400 500 

DISTANCE DOWNSTREAM, IN KILOMETERS

600

FIGURE 2. Variation in sediment size with distance downstream for the North Platte and Platte Rivers,

August 1979.

0.00150 

0.00 I 40

0.00130

CC 

UJ 

rh- 0.00120 UJ

a. ^

3 C o-ooi 10

-i 11- 0.00100 

gco

Z UJ 0.00090

X uJ

0 2 0.00080

~~ 0.00070 

0.00060

0.00050

 Station number from 

figure I and table I

14

0 100 200 300 400 500 600

DISTANCE DOWNSTREAM, IN KILOMETERS 

FIGURE 3. Variation in local channel slope with distance downstream for the North Platte and Platte Rivers.

of the bed material, and water temperature. From these 

data, sediment discharge for each sediment size class 

can be determined and summed to obtain a total sediment discharge for the entire range of sediment sizes.

Colby's (1957) graphical method for estimating the 

unmeasured sediment discharge consists of several empirical relationships based on some of the same stream 

measurement data employed in developing the modified
D6 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

o 

Q

UJ 3.0 

N

CEUJ

CD

Q 

UJ

2.0

1.0

1 1 1 1 1 1 1 i I 1 1 1 1

ft

"ft ft

ft ftft

. * * ,

1 1 1 1 1 1 1 1 1 1 1 1 1

1

-

-

-

_

1

0 100 200 300

WATER DISCHARGE, IN CUBIC METERS PER SECOND 

FIGURE 4. Variation in median bed-material size with discharge for the Platte River near Overton, Nebraska.

o to 

Q

UJ 

N

cr

UJ

^ 0.5

Q 

UJ

I I I I I I I r I

I I I I

I I I I I

ft i

I I I L

I -

J___L

0 80 160 240 320

WATER DISCHARGE, IN CUBIC METERS PER SECOND 

FIGURE 5. Variation in median bed-material size with discharge for the Platte River near Grand Island, Nebraska

Einstein method. The graphical method is simple to apply; however, it does not give a breakdown of the unmeasured sediment discharge into size fractions, and requires a precise determination of mean velocity, because

unmeasured sediment discharge is very sensitive to 

changes in velocity.

Application of the graphical method requires mean 

stream velocity, stream width, mean depth, and meas-
INTERPRETATION OF SEDIMENT DATA D7

ured suspended-sediment concentrations of sand particles. Size distribution of bed material is not needed. 

From these measured values, an estimate of the 

unmeasured-sediment discharge is made. The unmeasured sediment discharge then is added to the measured

suspended-sediment discharge to obtain the total sediment discharge according to the Colby method.

Total sediment discharges calculated by all three 

methods were used to define water-sediment discharge 

relations for the four stations except for the South

TABLE 2. Water-sediment discharge relations, derived by log-linear regression, for selected Platte River stations

[Qg, sediment discharge in metric tans per day; Q, water discharge in cubic meters per second; hi, natural logarithm of function]

U.& Geological 

Survey station 

number

06693000

06765500

06768000

06770500

Station name

North Platte River at North Platte, Nebraska

South Platte River at North Platte, Nebraska

Platte River near Overton, Nebraska

Platte River near Grand Island, Nebraska

Regression equation*

ln(Q ) = 2.45 + 1.29 ln(Q)

ln(O ) = 2.44 + 1.39 ln(O)

ln(Qs) = 1.77 + 1.58 ln(Q)

ln(Q ) = 2.55 + 1.32 ln(Q)

ln(Qj = 2.72 + 1.32 ln(Q)

ln(O ) = 2.12 + 1.29 ln(Q)

ln(Q ) = 2.23 + 1.27 ln(Q)

ln(Qj = 1.74 + 1.36 ln(Q)

ln(Q ) = 2.34 + 1.26 ln(Q)

ln(O = 2.74 + 1.19 ln(O)

ln(Qs) = 1.44 + 1.45 ln(Q)

Type of 

equation 

(see footnotes)

(1)

(2)

(3)

(1)

(2)

(1)

(2)

(3)

(1)

(2)

(3)

Number 

of 

data points

5

5

3

7

7

7

7

4

8

8

6

 The dependent variable in the regression equation is:

(1) Total measured sediment discharge.

(2) Total sediment discharge computed using the Colby (1957) method.

(3) Total sediment discharge computed using the modified Einstein method (Colby and Hembree, 1955).

100,000 cr

5

o

§ 10.00Q

O

E

8

<

1000

100

O

LU 

V)

5

10

T I I I I IIII I I I I I I III

 NORTH PLATTE RIVER AT NORTH PLATTE

 SOUTH PLATTE RIVER AT NORTH PLATTE

 PLATTE RIVER NEAR OVERTON

 PLATTE RIVER NEAR GRAND ISLAND

I I I H

I I I I I I I I ' ' I I I I I I

10 100

DISCHARGE, IN CUBIC METERS PER SECOND

1000

FIGURE 6. Relations between water and measured total sediment discharges for the North Platte, South Platte, and Platte

Rivers (Kircher, 1981b).
D8 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

Platte River at North Platte, where sufficient data were 

not available for the modified Einstein procedure; 

curves were defined by least-squares regression on the 

log-transformed data. Equations of these curves are 

presented in table 2. The measured total sediment 

discharge relations are presented in figure 6 (Kircher, 

1981b) for all four stations for a comparison of station 

variability.

COMPARISON OF TOTAL SEDIMENT 

DISCHARGE METHODS

The three total sediment discharge methods were 

compared to determine if they all could be applied to the 

Platte River system, because some methods are more 

simple to use than others. Total sediment discharges 

computed by the modified Einstein procedure were first 

compared to measured total sediment discharges by individual size classes. Relations expressing the total 

sediment discharge in each particle-size class as functions of total sediment discharge were determined for 

both the measured total sediment discharge and the 

modified Einstein total sediment discharge. A leastsquares linear regression of the log-tranformed data was 

used to obtain an equation for each size class from 0.062 

to 16.00 mm. The equation obtained is of the form:

ln(qs)=A+B(]n(Qs)) (I)

where In = natural logarithm,

qs = total sediment discharge by size class in

metric tons per day, and 

Qs = total sediment discharge, in metric tons per

day.

Regression equations and statistics are presented in 

table 3 for measured total sediment discharge and in 

table 4 for the modified Einstein total sediment 

discharge. The ratio Y/X is included in these tables. It 

is the ratio of the mean of the dependent variable to the 

mean of the independent variable, computed prior to 

transforming the data. This ratio gives an indication of 

what percentage of the total sediment transport is in 

each size class. Mean percentages will not add to 100, 

because the sediment transport finer than 0.062 mm is 

not included, and also because the mean value of total 

bedload is variable. Graphs showing individual data 

points for various particle-size classes together with the 

least-square line, are presented in figures 7 to 14. The 

least-square lines are also shown except where the coefficient of determination (r2) was less than 0.50. The 

modified Einstein total sediment discharge data were 

omitted for the size classes 4.000 to 8.000 mm because

TABLE 3. Coefficients and statistics for linear regression equations of 

log-transformed values of measured total sediment discharge by size 

class versus measured total sediment discharge.

[<7S, total sediment discharge in each size class; Qs< total sediment discharge; hi, natural

logarithm]

Particle-size 

class 

(millimeters)

0.062- 0.125 

.125- .250 

.250- .500 

.500- 1.000 

1.000- 2.000 

2.000- 4.000 

4.000- 8.000 

8.000-16.000

Number of 

data points

17

17 

17 

17 

17 

17 

17 

17

ln(<;s)=A+B<ln<es))

A

-3.38 

-1.42 

-1.35 

-2.22 

-3.52 

-5.19 

-17.9

B

1.16 

.977 

.945 

.998 

1.10 

1.22 

2.58

H

78.4 

89.5 

91.4 

87.4 

82.6 

79.3 

56.1

SE 

(log units)

0.64 

.35 

.31 

.40 

.53 

.66 

2.36

Y/X 

(percent)

5.47 

16.69 

22.85 

17.21 

11.07 

7.13 

3.84 

1.10

TABLE 4. Coefficients and statistics for linear regression equations of 

log-transformed values of total sediment discharge by the modified 

Einstein procedure (Colby and Hembree, 1955) by size class versus 

total sediment discharge by the modified Einstein procedure.

\q , total sediment discharge in each size class; Q , total sediment discharge; In, natural

logarithm]

Particle-size 

class

(millimeters)

0.062- 0.125 

.125- .250 

.250- .500 

.500- 1.000 

1.000- 2.000 

2.000- 4.000 

4.000- 8.000 

8.000-16.000

Number of 

data points

17

17 

17 

17 

17 

17 

17 

17

ln<<;s)=A+B<ln<es))

A

-2.44 

-3.02 

-2.69 

-4.47 

-14.3

B

1.08 

1.16 

1.11 

1.29 

2.23

H

88.0 

92.2 

96.4 

86.4 

71.8

SE 

(log units)

0.47 

.40 

.25 

.60 

1.62

Y/X 

(percent)

5.99 

20.01 

23.52 

19.46 

13.41 

2.47 

.19 

.0004

most of the data points were equal to zero and zero 

values cannot be used in log-transformed regressions.

Statistical data from linear regressions of logtransformed data are summarized for the measuredbedload discharge in table 5 and for the computed 

unmeasured sediment discharge from the modified 

Einstein procedure in table 6. The curves presented in 

figures 7-14 and the equations in table 3 to 6 reflect the 

way the percentage of material in each size class varies 

with the corresponding computed sediment discharge 

(modified Einstein procedure or measured sediment discharge). The coefficients depend only on the percentage 

of material in a size class associated with each computed (measured) sediment discharge, and in no way 

relate to the absolute accuracy of the total sediment 

discharge or the sediment discharge in each size class. 

As such, the equations for a given procedure are unrelated in absolute terms to the equations developed for a 

different procedure. Therefore, these figures and tables 

should only be used to determine the respective load in 

each size class for the particular method used.
INTERPRETATION OF SEDIMENT DATA D9

 z. to "z.

UJ O

LU

Q 

LU 

CO

10,000

1000

100

10

CO

en

_] 

o

LU 

N

CO 

I

0<

pQ O.I 

tree

< LU 

O.Q.

°'01

l0 ' 000

1000

100

10

O.I

0.01

i i i nun I i i nun i i i him i i i iluii i i i mid i i i mi

t

MEASURED TOTAL SEDIMENT DISCHARGE :

(0.062-0.125 MILLIMETER SIZE CLASS) ft

ft *

ft .*»*

i i i nun 11111 linn i unit i i i mm i i i mil

- TOTAL SEDIMENT DISCHARGE BY 

MODIFIED EINSTEIN METHOD

| (0.062-0.125 MILLIMETER 

SIZE CLASS)

i i nun i i i iiu i i

ft i 

>

* «*

*»**

i nun mill nun iiiiiin ium i mil

O.I I 10 100 1000 IO,OOO 100,000 

TOTAL SEDIMENT DISCHARGE, IN METRIC TONS PER DAY

FIGURE 7. Relation of total sediment discharge in individual size class as a function of total sediment discharge:

0.062- to 0.125-millimeter size class.

Sediment discharges in individual particle-size 

classes, as computed by the modified Einstein procedure and determined from measured discharges, have 

been compared by least-squares linear regression, using 

log-transformed discharge values (table 7). Graphs (figs. 

15-22) show the data and the least-squares line for 

regressions in which the coefficient of determination (r2)

was greater than 0.50; the line of perfect agreement also 

is shown.

The agreement between the methods is good for particle sizes finer than 2.000 mm. However, for those 

greater than 2.000 mm, the modified Einstein procedure 

yields smaller sediment discharges than the measured 

sediment discharge method does.
D10 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

O

UJ 

M

CO 

UJ .

ft

01 (Z 

< UJ 

Q- CL

UJ O

CO 

Q

IUJ

Q 

UJ 

CO

O

10,000

1000

100

10

O.I

CO 0.01

o 10,000

1000

100

10

O.I

0.01

i irnirir i iiiiini i

MEASURED TOTAL SEDIMENT DISCHARGE

(0.125-0.250 MILLIMETER SIZE CLASS)

Least squares

i i mnt mm i i i mm i i i nun i i i inn

:i TOTAL SEDIMENT DISCHARGE BY 

MODIFIED EINSTEIN METHOD

| (0.125-0.250 MILLIMETER 

SIZE CLASS)

Least squares

i i 11 mi i iii inn j_i 11inn i i i i inn i i iiinn i i i 11 in

O.I I 10 100 1000 10,000 100,000 

TOTAL SEDIMENT DISCHARGE, IN METRIC TONS PER DAY

FIGURE 8. Relation of total sediment discharge in individual size class as a function of total sediment discharge:

0.125- to 0.250-millimeter size class.

Total sediment discharges determined by the three 

methods are compared in figures 23-25. These figures 

show the data plotted around the line of perfect agreement. Although they do not agree perfectly, this exemplifies how close the results are. Agreement among the 

discharges is better than that among individual size 

class discharges. The agreement among these relations

implies that the Colby and modified Einstein methods 

might be used for bed-material sizes beyond those for 

which they were developed. It appears that the field 

conditions seem to approximate the principles of the 

modified Einstein procedure and the Colby method well, 

indicating that the suspended sediment can be used as 

an index to the bedload movement in the Platte River
INTERPRETATION OF SEDIMENT DATA Dll

V)

o

UJ 

N

<S> i

|S

< LU 

CL Q.

 (f) 

UJ O

1000

100

I0

O.I

0.01

cc 

< o

X

~ 10,000

o

o

iUJ

O 

LJ 

CO

HO

cr

1000

100

10

O.I

o.oi

i i nun i i nun ii nun nun i iiniiii i rime

~ MEASURED TOTAL SEDIMENT DISCHARGE f

" (0.250-0.500 MILLIMETER SIZE CLASS)

squares

i i i mm i i i mi i i \\\ \ i iiini

i i i mm i i mm i i i Mini r i i nun i 1 1 inn i i i i II

TOTAL SEDIMENT DISCHARGE BY 

MODIFIED EINSTEIN METHOD

(0.025-0.500 MILLIMETER SIZE CLASS)

Least squares

iii iui i iiiini i i limit nn

O.I I 10 100 IOOO 10,000 100,000 

TOTAL SEDIMENT DISCHARGE, IN METRIC TONS PER DAY

FIGURE 9. Relation of total sediment discharge in individual size class as a function of total sediment discharge:

0.250- to 0.500-millimeter size class.

system. Of the two computational methods, the Colby 

method is the easier to use, and it could be used for 

estimates of total sediment discharge within the study 

reach investigated in this report. However, as the 

hydraulic conditions and sediment characteristics 

deviate from those for which the total- discharge 

methods were formulated, the advantages of measuring 

bedload increase.

MEAN-DAILY SEDIMENT DISCHARGE

Mean-daily sediment discharge can be determined by 

calculating the expected value of sediment discharge 

[E(QS)]. The expected value is defined as:

(2)
D12 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

CO 

CO

O

LLJ 

N

COi

LJ

O 5

P°

<£

_ CO

2

UJ O

tr

1000

100

10

o.i

o.oi

10,000

1000

LJ

Q 

LJ 

CO

100

'0

O.I

O.OI

E 1 1 1 1 Mill 1 1 Mill 1 1 Mill (Mill 1 1 1MB

MEASURED TOTAL SEDIMENT DISCHARGE

(0.500-1.000 MILLIMETER SIZE CLASS)

 XL.east squares

i i i nun i i i nun linn i i i ini mm mil

= i i i i inn inn i 1 ml

TOTAL SEDIMENT DISCHARGE BY 

MODIFIED EINSTEIN METHOD

(0.500-1.000 MILLIMETER 

SIZE CLASS)

1 1 MB

Least squares

mm iim tin inn mm i mm i i il

O.I I 10 100 1000 10,000 100,000 

TOTAL SEDIMENT DISCHARGE, IN METRIC TONS PER DAY

FIGURE 10. Relation of total sediment discharge in individual size class as a function of total sediment

discharge: 0.500- to 1.000-millimeter size class.

where Qs = sediment discharge in metric tons per

day,

= sediment density function, and 

= expected value of the sediment discharge or mean daily sediment discharge in tons per day. 

For the Platte River stations, the sediment density

function is unknown, because of the lack of comprehensive sediment discharge data, but Qs is a known function of water discharge from the water-sediment 

discharge relations. Therefore, by probability theory, 

the following substitution can be made for equation 2:

(3)
INTERPRETATION OF SEDIMENT.DATA D13

CO 

CO<t

_J 

o

UJ 

N

CO 

i

Ld_l>- 

0<

< UJ 

O.Q.

2

UJ O

CD ho

UJ 

CO

Io I10,000

1000

100

10

O.I

0.01

if 10,000

1000

too

10

O.I

0.01

gill 11 Illl iMIII i r i nuii i mrim i i IMIIII i i ima

- MEASURED TOTAL SEDIMENT DISCHARGE

~s (1.000-2.000 MILLIMETER SIZE CLASS)

Least squares

i_i i i tiiu i ill tun i i 11 iiiii 11 illl Ill I Mill I III till

I IIIII Illl IIIII I I I I III

^ TOTAL SEDIMENT DISCHARGE BY 

MODIFIED EINSTEIN METHOD

I (1.000-2.000 MILLIMETER SIZE CLASS)

Least squares

i linn 11 HIM i i i mm i nun i i mm i i inn

O.I I 10 100 1000 10,000 100,000 

TOTAL SEDIMENT DISCHARGE, IN METRIC TONS PER DAY

FIGURE 11. Relation of total sediment discharge in individual size class as a function of total sediment

discharge: 1.000- to 2.000-millimeter size class.

where g(Q) = Qs, in metric tons per day, and

f(Q) = the water-discharge density function. 

The water-discharge density function can be obtained 

from the flow-duration curve. The cumulative frequency 

of daily mean water discharges at a gaging station 

defines a flow-duration curve. Flow-duration curves 

show the percentage of time a specific water discharge

was equaled or exceeded during the period of record. 

Flow-duration curves based on several years of record 

described the approximate probability of various daily 

mean water discharges being equaled or exceeded. Flowduration curves used in this report were defined during 

a period in which large changes in flow and channel morphology no longer occur (Kircher and Karlinger, 1981)
D14 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

c/

o

UJ 

N

UJ

H Q

o: ~

1000

100

10

O.I

±C/> 0.01

UJQ

op

rr

<o 10,000

o

ui

S

o

UJ 

CO

1000

100

O.I

0.01

MEASURED TOTAL SEDIMENT DISCHARGE

(2.000-4.000 MILLIMETER SIZE CLASS)

Least squares

llllll Illllll Illllll 1 1 llllll 1 1 Illllll 1 1 Illlll

Eli 1111111 i i Miim i i i MIIII r r iiinn

TOTAL SEDIMENT DISCHARGE BY 

MODIFIED EINSTEIN METHOD

I (2.000-4.000 MILLIMETER SIZE CLASS)

1 ml i i 1 1 ii

Least squares

nun i i 1 1 inn mint i it nun i i imii i i Min

O.I I 10 100 K>00 10,000 100,000 

TOTAL SEDIMENT DISCHARGE, IN METRIC TONS PER DAY

FIGURE 12. Relation of total sediment discharge in individual size class as a function of total sediment

discharge: 2.000- to 4.000-millimeter size class.

(figs. 26-29). Although the analytical form of the flowduration curve is unknown, the integral in equation 3 

can be approximated by a summation of the discretized 

integrand, which has the following form:

N

(4)

With this form, the expected value of the Qs is determined by first dividing the discharge scale of the flowduration curve into N equal intervals. Then, the 

midpoint of each interval is used to obtain the corresponding sediment discharges from the water sediment 

discharge relations for each station. The sediment discharge is then multiplied by the probability of occur-
INTERPRETATION OF SEDIMENT DATA D15

UJ 

N

<p 10,000

UJ

Po 1000 

o: 

< cr

Q. UJ 

Q.

-en 100

UJ§

< o 10

^UJ

OS ,

SEDIMEN 'OTAL

CLASS, II

? 0

O L.

O

|tii nun i i i mm i i i mm i i i mm i i 1 1 Inn i 1

1 MEASURED TOTAL SEDIMENT DISCHARGE

I (4.000-8.000 MILLIMETER SIZE CLASS)

i J{

; /\

~ >/Least squares

5

§

i | i mm i i i UJIK | i i linn ill mm i i i nun i i

1 » 10 100 1000 10,000

i me

i

!

5

-

5

!

i mil

IOO.C

TOTAL SEDIMENT DISCHARGE, IN METRIC TONS PER DAY

FIGURE 13. Relation of total sediment discharge in individual size class as a function of total sediment

discharge: 4.000- to 8.000-millimeter size class.

UJ 

N

LU 

0<

< UJ 

Q. Q.

UJ O 

<^

T. tr oiUJ

10,000

1000

100

io

ho

MIIII i nun i i i MIIII i i i nun i i i mm

; MEASURED TOTAL SEDIMENT DISCHARGE

= (8.000-16.00 MILLIMETER SIZE CLASS)

Least squares

i i i mm i i i mm mm i i MIIII inn

O.I I 10 100 1000 10,000 100,000

TOTAL SEDIMENT DISCHARGE, IN METRIC TONS PER DAY 

FIGURE 14. Relation of total sediment discharge in individual size class as a function of total sediment

discharge: 8.000- to 16.00-millimeter size class.

rence of the associated water discharge f(Qj) AQ to yield 

a weighted quantity of sediment. The summation of all 

g(Qj}f(Qj}&Qj values gives the expected value of the sediment discharge which is an approximation of the meandaily sediment discharge. The mean-daily sediment 

discharge based on the measured total sediment
D16 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

TABLE 5. Coefficients and statistics for linear regression equations of 

log-transformed values of measured bedload discharge by size class 

versus total measured bedload discharge.

fog, measured bedload discharge in each size class; Qg, total measured bedload discharge; hi, 

natural logarithm]

TABLE 7. Coefficients and statistics for linear regression equations of 

log-transformed values of sediment discharges in different size classes 

computed by the modified Einstein procedure (Colby and Hembree, 

1955) and from measured sediment discharges

totaj sediment discharge computed by the modified Einstein procedure; QM> total

ln(<7B)=A+B<ln<QB))

Particle-size Number of ' __ 

class data points A B r* SE Y/X

(millimeters) dog units) (percent)

0.062- 0.125 17 - - 0.005

.125- .250 17 -3.08 0.961 79.4 0.53 .016 

.250- .500 17 - .44 .873 93.3 .25 3.95 

.500- 1.000 17 -1.13 .985 98.2 .14 24.82 

1.000- 2.000 17 -1.85 1.03 98.4 .14 29.69 

2.000- 4.000 17 -3.21 1.15 95.3 .28 19.87 

4.000- 8.000 17 -4.82 1.27 91.0 .44 12.79 

8.000-16.000 17 -17.4 2.73 67.1 2.05 6.90

TABLE 6. Coefficients and statistics for linear regression equations of

by the modified Einstein procedure by size class versus total 

unmeasured-sediment discharge

tou> unmeasured sediment discharge in each size class; Qu, total unmeasured-sediment 

discharge; In, natural logarithm)

ln<QMEP)-A+Bfln<QM))

Parade-size Number of 

class data points A B r" SE Y/X

0.062- 0.125 17 0.741 0.911 99.1 0.13 127.75 

.125- .250 17 .562 .972 98.7 .15 140.04 

.250- .500 17 -1.42 1.22 87.4 .51 120.21 

.500- 1.000 17 - .609 1.11 74.6 .67 132.06 

1.000- 2.000 17 -1.31 1.26 74.9 .82 141.48 

2.000- 4.000 17 -6.99 2.03 69.7 1.69 40.50 

4.000- 8.000 17 - - 5.85

O /\/\/\ 1 G f\/\f\ 1 ^7 f\A

Total 17 -0.47 1.07 92.9 0.31 116.78

discharge relations, for the South Platte River at North 

Platte, the North Platte River at North Platte, the

Particle-size 

class 

(millimeters)

0.062- 0.125 

.125- .250 

.250- .500 

.500- 1.000 

1.000- 2.000 

2.000- 4.000 

4.000- 8.000 

8.000-16.000

Number of 

data points

17 

17 

17 

17 

17 

17 

17 

17

A

-1.57 

-2.41 

-2.48 

-4.01 

-13.5

Wg

B

0.922 

1.12 

1.15 

1.31 

2.27

u)=A+B(ln(Qu»

r1

81.3 

93.9 

98.1 

89.1 

74.3

SE 

dog units)

0.52 

.33 

.19 

.54 

1.55

Y/X 

(percent)

2.11 

12.25 

25.44 

30.42 

21.60 

3.98 

.31 

.0006

Platte River near Overton, and the Platte River near 

Grand Island were computed based on N = 69 (table 8). 

From equation 4 it can be seen that as N increases, 

the closer the approximation of the mean-daily sediment 

should be to the value obtained from equation 3. The 

variation of mean-daily sediment discharge with increasing N can be seen in table 9. The flow-duration 

curve was divided into 35, 69, 103, and 137 equal 

discharge intervals and an expected value of sediment 

discharge computed. The flow-duration curve was also

10,000 e

UJ

cc

< O 1000 =

UJ O 

OQ: O

cc uj o:

^ Q_ Q_

X 100

o w z

£2* 10

UJrr UJ

U.

Q 

O

O.I

Least squares 

D

Perfect agreement

O.I I 10 100 1000 10,000

MEASURED SEDIMENT DISCHARGE, 

IN METRIC TONS PER DAY

FIGURE 15. Comparison of sediment discharges computed by the modified Einstein procedure for an individual 

particle-size class with corresponding measured sediment discharges for the class; 0.062- to 0.125-millimeter 

size class.
INTERPRETATION OF SEDIMENT DATA 

10,000 = j i i i 111 it I I I i Mill I i i i i nil 1

D17

LU

o: 

> 5 1000 * ^T ^J

LU Q LU

£0:0 ? LU a:

o 0- 0- 100

C/)CO 2 

a^UJ

10

^Qr LU

Q LU Q 

LU5 LJ

 Q 

O

O.I

= (0.125-0.250 MILLIMETER SIZE CLASS)

Least squares

L i 11 nn i i i t mi

0. 10 100 1000 10,000

MEASURED SEDIMENT DISCHARGE, 

IN METRIC TONS PER DAY

FIGURE 16. Comparison of sediment discharges computed by the modified Einstein procedure for an individual 

particle-size class with corresponding measured sediment discharges for the class; 0.125- to 0.250-millimeter 

size class.

10,000 b , | | ,

LU 

O:

x=>

,.< Q 

LUQ LU 

O O

<LU o: IQ- a. 

o

(/)(/) 2 

Q 0 iJ

1000

100

LU 10

fEhQLU Q

"II 

O 

S

O.I

i mrri i FT i MIII

E (0.250-0.500 MILLIMETER SIZE CLASS)

Least squares

Perfect agreement

i i i inn i i i nun 1111 till i i i i 11 in

0.1 10 100 1000 10,000

MEASURED SEDIMENT DISCHARGE, 

IN METRIC TONS PER DAY

FIGURE 17. Comparison of sediment discharges computed by the modified Einstein procedure for an individual 

particle-size class with corresponding measured sediment discharges for the class; 0.250- to 0.500-millimeter 

size class.

divided into 35,69,103, and 137 equal logarithmic intervals in an attempt to reduce the error caused by the 

skewness of the flow distribution.

It can be seen in table 9 that the variation in the 

number of intervals does cause a variation in the meandaily sediment discharge; however, the difference is less
D18 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN 

10,000

UJ

o:

UJO UJ

o o 

cco: o

1000

O "00 

C0<2 2

^- o z: jo 

aujp

LJ ^ UJ

co Q7

 Q 

O

O.I

= I I I I Mill I I 1TITTTI I Fill I \ I I ITIll

: (0.500-1.000 MILLIMETER SIZE CLASS)

O.I 10 100 1000 10,000

MEASURED SEDIMENT DISCHARGE, 

IN METRIC TONS PER DAY

FIGURE 18. (Comparison of sediment discharges computed by the modified Einstein procedure for an individual 

particle-size class with corresponding measured sediment discharges for the class; 0.500- to 1.000-millimeter 

size class.

LJO

o trtr

10,000

UJ

oc 

>: Q 1000

IQ. 100

co

^. 10

QUJ

 Q 

O

O.I

I I I I I Mil I II I Mill I I I I I III! I

E (1.000-2.000 MILLIMETER SIZE CLASS)

M mi

O.I 10 100 1000 10,000

MEASURED SEDIMENT DISCHARGE, 

IN METRIC TONS PER DAY

FIGURE 19. Comparison of sediment discharges computed by the modified Einstein procedure for an individual 

particle-size class with corresponding measured sediment discharges for the class; 1.000- to 2.000-millimeter 

size class.
INTERPRETATION OF SEDIMENT DATA 

10,000 E I I I Mlill 

LU

< LUCE 0-0.

1000

100

10

(/)

 Q 

O

O.I

Illl Mil I I I I Mil I

: (2.000-4.000 MILLIMETER SIZE CLASS)

Least squares

a

1111 mi i i 11 ILII I Mil

O.I 10 100 1000 10,000

MEASURED SEDIMENT DISCHARGE, 

IN METRIC TONS PER DAY

FIGURE 20. Comparison of sediment discharges computed by the modified Einstein procedure for an individual 

particle-size class with corresponding measured sediment discharges for the class; 2.000- to 4.000-millimeter 

size class.

LU

LU Q LU

e> o 0:0:0 2*2

QOLU

202 

CCLU

10,000

1000

100

10

CO U_ *E 

o

O.I

I I I Mill I Illl I

E (4.000-8.000 MILLIMETER SIZE CLASS)

Perfect agreement

I I MUM J . I I I Illl POl JllMllB °. III! I Illl

O.I 10 100 1000 10,000

MEASURED SEDIMENT DISCHARGE, 

IN METRIC TONS PER DAY

D19

FIGURE 21. Comparison of sediment discharges computed by the modified Einstein procedure for an individual 

particle-size class with corresponding measured sediment discharges for the class; 4.000- to 8.000-millimeter 

size class.
D20 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

10,000 E i i i iiiiu

- (8.000-16.00 MILLIMETER SIZE CLASS)

O.I

10 100 1000

MEASURED SEDIMENT DISCHARGE, 

IN METRIC TONS PER DAY

FIGURE 22. Comparison of sediment discharges computed by the modified Einstein procedure for an 

particle-size class with corresponding measured sediment discharges for the class; 8.000- to 16.00- 

size class.

10,000

individual 

millimeter

100,000

I

oc

UJ

Q.

(/}

Isr

10.000

SI

O ui

- 0 

O ui

IIO ~

± 1000

I I I I I I I I

* *

Perfect agreement

Mill I I I I L

100 1000 10,000 

MEASURED TOTAL SEDIMENT DISCHARGE, IN METRIC TONS PER DAY

100.000

FIGURE 23. Comparison between total sediment discharges computed by the modified Einstein procedure (Colby and Hembree,

1955) and measured total sediment discharges.
INTERPRETATION OF SEDIMENT DATA D21

100,000

a. 

to

O

10.000 -

LU _

S 0

LU LU 2 s

<£

58co o 5 ~~

tLU

5 

Q

LU 

tO

1

1000 -

100

100 1000 10,000 

MEASURED TOTAL SEDIMENT DISCHARGE, IN METRIC TONS PER DAY

100,000

FIGURE 24. Comparison between total sediment discharges computed by the Colby method and measured total sediment discharges. 

100,000

CO

o

10,000

1000

LU

Q

LU 

CO

10]

I I \ I

Perfect agreement 

I III I I I I J L I I I

foo 1000 10,000 100,000 

TOTAL SEDIMENT DISCHARGE, tN METRIC TONS PER DAY (MODIFIED EINSTEIN PROCEDURE)

FIGURE 25. Comparison between total sediment discharges computed by the Colby's method and total sediment discharges computed by the modified Einstein procedure (Colby and Hembree, 1955).
D22 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

1000.0

100.0

10.0

1.0

0.1

I I i r i i r i III I i

i i i i i i i I I I

0.1 0.5 2.0 5.0 10.0 20.0 50.0 70.0 90.0 95.0 99.0 99.5 99.9

PROBABILITY OF DISCHARGE BEING EQUALED OR EXCEEDED

FIGURE 26. Flow-duration curve for the North Platte River at North Platte, Nebraska (1941-79).

1000.0 cr

o

UJ 

CO

100.0

O

00

3

2

10.0

1.0

0.1

r i i i i i I I

I I I I I I I I I I I I

0.1 0.5 2.0 5.0 10.0 20.0 50.0 70.0 90.0 95.0 99.0 99.5 99.9 

PROBABILITY OF DISCHARGE BEING EQUALED OR EXCEEDED

FIGURE 27. Flow-duration curve for the South Platte River at North Platte, Nebraska (1941-79).
INTERPRETATION OF SEDIMENT DATA D23

1000 JO cr

o

S 100.0

85

o.

£

|

o 10.0

00

2

< 

o

(O

5

1.0

0.1

1 I I I I II I I

I I I I I I I 1 I I I I I___I I I I I

0.1 0.5 2.0 5.0 10.0 20.0 50.0 70.0 90.0 95.0 

PROBABILITY OF DISCHARGE BEING EQUALED OR EXCEEDED

99.099.6 99.9

FIGURE 28. Flow-T oration curve for the Platte River near Overton, Nebraska (1950-79).

1000.000*

O 100.000

CO

tc

a! 10.000

gID

i

o

00

3

1.000

UJ

g 0.100 

<

5

(O

O

0.010

0.001

r~i i i i * i r I I I I I \ I

\ I I I 1 I 1 1 1 1 L I I I I I I

0.1 0.5 2.0 5.0 10.0 20.0 50.0 70.0 90.0 95.0 99.0 99.5 99.9

PROBABILITY OF DISCHARGE BEING EQUALED OR EXCEEDED

FIGURE 29. Flow-duration curve for the Platte River near Grand Island, Nebraska (1935-79).
D24 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

TABLE 8. Summary of mean-daily water discharge and measured total sediment discharge at four gaging stations.

(km*, square kilometers; m'/s, cubic meters per second; tyd, metric Urns per day]

U.S. Geological

Survey station

number

06693000

06765500

06768000

06770500

Station name

North Platte River at North Platte, Nebraska

South Platte River at North Platte, Nebraska

Platte River near Overton, Nebraska

Platte River near Grand Island, Nebraska

Drainage

area

(km2)

80,000

62,900

149,400

152,300

Mean

daily

discharge

(m'/s)

23.5

9.5

39

35.6

Mean daily

total measured

sediment

discharge

(ttt)

597

307

1,100

1,130

TABLE 9. Comparison of mean-daily water sediment discharges 

obtained by varying the number of subdivisions of the flow-duration 

curve for the Platte River near Overton, Nebraska

[t/d, metric tons per day; In, natural logarithm]

Type of intervals

Equal water discharge 

Equal water discharge 

Equal water discharge 

Equal water discharge 

Equal ln(water discharge) 

Equal ln(water discharge) 

Equal ln(water discharge) 

Equal ln(water discharge)

Number 

of 

intervals

35 

69 

103 

137 

35 

69 

103 

137

Mean-daily 

measured 

total sediment 

discharge

(t/d)

1115 

1110 

1107 

1107 

747 

1095 

1100 

1108

than 2 percent if the 35-interval equal-logarithmic intervals value is omitted.

SUMMARY

Streamflow and sediment data were collected at 

several locations along the Platte River and its major 

tributaries, the North Platte River and the South Platte 

River. The data were analyzed to determine the change 

in bed-material size in a downstream direction, and also 

to determine relations between water and total sediment discharges at four locations in the study reach.

The median bed material decreases in a downstream 

direction except near Overton, Nebraska, where it increases as a result of an increase in local slope at the 

same location. The median bed material at two locations 

in the Platte River was found to vary little with increasing water discharge.

Total sediment discharge was calculated by three 

methods for four stations in the critical reach. The four 

stations were the North Platte River at North Platte, 

Nebraska; the South Platte River at North Platte, 

Nebraska; the Platte River near Overton, Nebraska; 

and the Platte River near Grand Island, Nebraska The 

three methods were: (1) summing measured bedload and 

suspended-sediment discharges; (2) summing measured 

suspended sediment discharge with unmeasured sediment discharge computed by Colby (1957) method; and 

(3) using the modified Einstein procedure (Colby and 

Hembree, 1955). Total sediment discharges computed 

by the, three methods were compared and found to agree 

closely. From this comparison it was found that the 

sediment and hydraulic characteristics of the Platte 

River closely approximate the principles of the Colby 

method and modified Einstein procedure, indicating 

that the suspended sediment can be used as an indicator 

of bedload. When the modified Einstein and measured 

total sediment discharge were compared by particle-size 

class the agreement between the two methods was good 

for particle sizes finer than 2 mm; however, for sizes 

greater than 2mm the modified Einstein procedure 

yielded smaller sediment discharges than were 

measured.

The mean daily sediment discharge for the four locations was computed by combining the relations between 

water discharge and measured total sediment discharge 

with the stations respective flow-duration curve. The 

mean daily sediment discharge for each site was found 

to be: (1) 579 t/d (metric tons per day) for the North 

Platte River at North Platte, Nebraska; (2) 307 t/d for 

the South Platte River at North Platte, Nebraska; (3) 

1,100 t/d for the Platte River near Overton, Nebraska; 

and (4) 1,130 t/d for the Platte River near Grand Island, 

Nebraska

REFERENCES CITED

Andrews, E. D., 1980, Effective and bankful discharges of streams in 

the Yampa River basin, Colorado and Wyoming: Journal of 

Hydrology, v. 46, 20 p.

Bentall, Ray, 1975, Hydrology, Nebraska mid-state division and associated areas: Nebraska University Conservation and Survey 

Division, Institute of Agriculture and Natural Resources Report, 

256 p.

Colby, B. R., 1957, Relationship of unmeasured sediment discharge to 

mean velocity: Transactions of the American Geophysical Union, 

v. 38, no. 5, 9 p.

Colby, B. R., and Hembree, C. H., 1955, Computations of total sediment discharge, Niobrara River near Cody, Nebraska: U.S. 

Geological Survey Water-Supply Paper 1357, 187 p.

Emmett, W. W., 1980, A field calibration of the sediment-trapping 

characteristics of the Helley-Smith bedload sampler: U.S. 

Geological Survey Professional Paper 1139, 43 p.
INTERPRETATION OF SEDIMENT DATA D25

Guy, H. P., and Norman, V. W., 1970, Field methods for measurement 

of fluvial sediment: U.S. Geological Survey Techniques of WaterResources Investigations, Book 3, Chapter C2, 59 p.

Helley, E. J., and Smith, Winchell, 1971, Development and calibration 

of pressure-difference bedload sampler U.S. Geological Survey 

open-file report, 18 p.

Hubbell, D. W., and others, 1956, Progress Report Number 1- Investigations of some sedimentation characteristics of a sand-bed 

stream: U.S. Geological Survey open-file report, 78 p.

Kircher, J. E., 1981a, Sediment analysis for selected sites on the 

South Platte River in Colorado and Nebraska, and the North 

Platte and Platte Rivers in Nebraska Suspended sediment,

bedload, and bed material: U.S. .Geological Survey Open-File 

Report 81-207, 48 p. 

_1981b, Sediment transport and effective discharge of the

North Platte, South Platte, and Platte Rivers, Nebraska: U.S. 

Geological Survey Open-File Report 81-53, 26 p.

Kircher, J. E., and Karlinger, M. R., 1981, Changes in surface water 

hydrology, Platte River basin in Colorado, Wyoming, and 

Nebraska upstream from Duncan, Nebraska: U.S. Geological 

Survey Open-File Report 81-818, 77 p.

U.S. Geological Survey, 1977, National handbook of recommended 

methods for water-data acquisition: Office of Water-Data Coordination, 100 p.

SUMMARY OF DATA

INTERPRETATION OF SEDIMENT DATA

TABLE 10. Summary of water-discharge measurements 

[m, meters; m'/s, cubic meters per second; m/s, meters per second; C, degrees Celsius]

D29

Station 

number 

in 

figure 1

1

1

2

2

2

2

2

2

3

3

3

3

3

4

4

4

4

4

5

5

5

5

5

6

6

6

6

7

7

7

7

7

7

7

7

8

9

9

10

10

10

10

10

10

10

10

10

10

11

11

12

12

12

12

12

12

12

12

12

16

16

18

Date

8/ 9/79

8/11/79

8/ 8/79

8/12/79

5/13/80

6/ 5/80

8/ 4/80

8/ 5/80

6/27/79

7/15/79

8/21/79

9/25/79

5/ 6/80

6/20/79

6/26/79

7/18/79

8/16/79

9/26/79

6/20/79

6/25/79

7/17/79

8/17/79

9/27/79

7/ 2/79

7/17/79

8/15/79

9/27/79

7/28/79

8/ 8/79

5/22/80

6/ 5/80

6/12/80

6/22/80

6/26/80

6/29/80

8/10/79

7/15/79

8/ 8/79

7/18/79

8/15/79

5/ 1/80

6/ 4/80

6/11/80

6/21/80

6/23/80

6/24/80

6/25/80

6/28/80

7/17/79

8/15/79

8/16/79

4/30/80

5/15/80

5/21/80

6/ 3/80

6/10/80

6/20/80

6/24/80

6/27/80

7/24/79

8/17/79

8/20/79

Time

800

1555

940

930

1630

1630

930

930

1200

1055

930

955

1230

1200

1200

1200

1200

1200

1700

1250

1430

1230

820

1400

900

1230

1255

930

745

1300

1300

1100

1230

1025

1115

1145

1200

1530

1030

1130

1330

1150

1000

815

750

830

900

1800

1630

1500

1045

1200

1145

930

1210

1600

1000

940

1100

1100

1030

1230

Stage 

(m)

0.59

.69

1.02

1.19

1.07

1.22

1.50

1.50

1.64

.91

1.79

1.05

2.78

2.53

1.83

.99

1.58

1.19

2.76

2.41

1.19

1.73

1.11

1.52

.87

1.01

1.00

1.63

1.51

3.44

2.98

2.72

2.52

2.33

2.18

.80

.48

.49

.50

.40

1.08

1.37

.99

.86

.79

.97

.59

.43

.48

.39

.43

1.01

1.32

1.32

1.35

1.13

.98

.97

.84

.52

.26

.46

Discharge 

(m 3/s)

22.6

27.9

16.2

31.4

17.5

26.3

58.4

58.4

71.2

11.9

98.8

20.5

351

234

92.7

9.80

53.2

17.7

253

107

7.50

39.5

4.30

36.6

2.18

5.21

5.64

8.18

4.50

351

189

113

78.3

47.2

32.4

19.1

1.50

1.08

16.7

6.54

146

254

126

89.3

65.4

70.5

46.8

22.7

8.69

1.93

8.10

142

271

250

304

207

124

115

63.0

22.7

4.81

42.3

Width 

(m)

83.5

89.3

76.2

75.3

76.5

76.5

89.3

89.3

96.0

49.4

111

51.2

197

105

88.4

38.4

83.8

39.6

302

85.6

40.5

72.5

27.7

92.4

16.5

23.8

21.3

30.8

31.7

146

148

139

142

122

121

65.5

22.9

20.4

116

81.1

198

204

200

192

188

189

154

116

83.5

29.9

138

266

268

268

268

260

242

243

230

194

98.8

248

Mean 

Depth

(m)

0.39

.49

.32

.59

.40

.55

.73

.73

.85

.32

1.04

.51

1.91

1.64

.95

.38

.70

.56

1.06

1.21

.66

.28

.49

.24

.33

.40

.36

.22

1.53

1.11

.71

.59

.44

.41

.50

.15

.32

.29

.20

.86

1.13

.79

.61

.46

.49

.44

.32

.21

.16

.15

.65

1.02

.97

1.06

.79

.60

.59

.41

.24

.15

.35

Mean 

Velocity

(m/s)

0.70

.64

.67

.70

.58

.63

.90

.90

.87

.76

.86

.79

.93

1.36

1.10

.67

.90

.79

.79

1.03

.82

.56

.80

.55

.67

.65

.74

.66

1.57

1.15

1.14

.94

.87

.65

.b9

.45

.17

.50

.40

.8b

1.10

.80

.76

.75

.76

.69

.62

.50

.39

.40

.83

.99

.96

1.07

1.00

.86

.80

.66

.48

.32

.49

Area 

(m2 )

32.3

43.7

24.3

44,6

30.4

42.0

64.8

64.8

81.4

15.6

115

26.1

376

172

84.2

14.6

59.0

22.3

321

104

47.9

7.7

45.5

4.0

7.8

8.6

11.1

6.9

224

164

99.0

83.4

54.1

50.0

32.5

3.3

6.5

33.1

16.2

171

231

158

IH

87.2

92.9

67.9

36.8

17.4

4.9

20.4

172

273

261

285

206

145

144

95.4

47.3

15.0

85.7

Water 

Temperature

(°C)

21.0

21.0

23.0

18.5

17.0

27.5

20.0

20.0

21.5

23.0

17.0

13.5

23.0

17.5

20.5

23.0

16.0

24.0

15.0

22,0

22.5

22.0

19.0

23.5

22.5

23.0

27.0

23.0

21.0

17.0

17.5

24.0

22.0

20.5

23.0

24.5

24,0

30.0

18.0

18.0

15.0

18.2

22.0

26.0

21.0

24.5

27.5

24.0

25.5
D30 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

TABLE 11. Summary of measured sediment-transport data

[m'/s, cubic meters per second; mg/L, milligrams per liter, tons/d, metric tens per day; kg/s/m, kilograms per second per meter]

Station 

number

in 

figure 1

1

1

2

2

2

2

2

2

3

3

3

3

3

4

4

4

4

4

5

5

5

5

5

6

6

6

7

7

7

7

7

7

7

7

10

10

10

10

10

10

10

10

10

12

12

12

12

12

12

12

Date

8/ 9/79

8/11/79

8/ 8/79

8/12/79

5/13/80

6/ 5/80

8/ 4/80

8/ 5/80

6/27/79

7/15/79

8/21/79

9/25/79

5/ 6/80

6/20/79

6/26/79

7/18/79

8/16/79

9/26/79

6/20/79

6/25/79

7/17/79

8/17/79

9/27/79

7/17/79

8/15/79

9/27/79

7/28/79

8/ 8/79

5/22/80

6/ 5/80

6/12/80

6/22/80

6/26/80

6/29/80

7/18/79

8/15/79

6/ 4/80

6/11/80

6/21/80

6/23/80

6/24/80

6/25/80

6/28/80

8/16/79

5/15/80

5/21/80

6/ 3/80

6/10/80

6/20/80

6/24/80

Water 

discharge

(m3 /s)

22.6

27.9

16.2

31.4

17.5

26.3

58.4

58.4

71.2

11.9

98.8

20.5

351

234

92.7

9.80

53.2

17.7

253

107

7.50

39.5

4.30

2.18

5.21

5.64

8.16

4.50

351

189

113

78.3

47.2

32.4

16.7

6.54

254

126

89.3

65.4

70.5

46.8

22.7

8.10

2H

250

304

207

124

115

Suspendedsediment 

concentration

(mg/L)

370

120

170

350

1430

140

310

370

710

140

1000

84

950

190

410

580

400

100

520

900

900

1350

100

130

62

1160

570

390

350

190

170

69

240

220

190

130

110

70

100

330

270

270

120

230

180

Suspendedsecfiment 

discharge

(tons/d)

720

290

240

950

2160

320

1560

1870

4370

140

8540

150

28800

3840

3280

490

1840

150

11400

8320

580

4610

100

35200

9310

3810

2370

770

480

5270

2400

1470

730

670

280

100

7730

5830

7090

2150

2460

1790

Unit 

bedload 

transport 

rate 

(kg/s/m)

0.058

.059

.043

.048

.043

.028

.123

.089

.087

.267

.026

.070

.013

.008

.036

.033

.038

.670

.371

.313

.250

.125

.045

.051

.009

.353

.105

.091

.130

.107

.045

.017

.010

.241

.293

.366

.185

.107

.121

Bedloadtransport rate

(tons/d)

420

450

280

310

281

184

944

688

383

28300

87.5

239

18.6

17.3

66.7

88.0

104

8410

4720

3740

3060

1310

470

511

63.6

6210

1810

1500

2100

1740

602

169

113

5570

6780

8920

4150

2230

2530

12 6/27/80 63.0 120 650 .075 1490
INTERPRETATION OF SEDIMENT DATA 

TABLE 12. Grain-size distribution of suspended sediment

D31

Station 

number 

in 

figure 1

1

1

2

2

2

3

3

3

3

4

4

4

4

4

5

5

5

5

6

6

6

7

7

7

7

10

10

10

10

10

10

12

12

12

12

12

12

Date

8/ 9/79

8/11/79

8/12/79

8/ 4/80

8/ 5/80

6/19/79

6/27/79

8/21/79

5/ 6/80

6/26/79

8/16/79

8/16/79

9/26/79

9/26/79

6/20/79

6/25/79

7/17/79

8/17/79

6/14/79

7/ 2/79

8/15/79

5/22/80

6/ 5/80

6/22/80

6/26/80

6/11/80

6/11/80

6/21/80

6/23/80

6/24/80

6/25/80

8/16/79

5/15/80

5/21/80

6/10/80

6/24/80

6/27/80

Percentage finer than indicated sieve size; 

sieve size (millimeters)

1.0

100

100

100

100

100

69

100

100

100

100

100

100

100

100

100

100

100

100

97

100

92

68

100

100

100

100

100

100

100

100

100

100

100

100

100

100

100

0.7

100

100

100

100

100

62

95

100

100

100

100

97

100

100

100

98

100

100

85

100

63

65

100

100

100

100

100

100

100

100

100

100

100

99

100

100

100

0.5

94

100

95

99

98

53

78

99

100

99

97

96

100

100

98

92

97

97

66

100

45

63

98

98

99

99

99

100

100

100

100

97

99

97

100

100

100

0.35

64

97

95

96

97

43

58

99

87

96

92

89

100

99

90

84

95

90

46

97

34

60

91

95

97

96

96

98

100

100

100

94

98

89

91

98

100

0.25

57

94

92

87

84

34

49

95

85

89

81

82

98

95

74

75

82

82

38

89

24

57

80

86

88

91

91

96

97

97

100

89

70

67

64

92

98

0.175

49

75

83

73

65

28

41

91

66

82

64

75

83

83

47

62

39

69

31

72

23

54

69

78

77

80

80

90

87

81

99

85

40

43

49

71

84

0.125

35

44

69

50

41

26

38

86

60

74

52

73

77

73

3b

55

31

61

28

54

23

53

64

7<»

74

74

74

85

83

75

98

78

22

28

41

62

78

0.088

21

38

49

25

14

26

36

82

57

71

48

fl

62

67

31

51

30

47

27

52

23

53

63

73

/2

ro

70

83

82

72

95

70

19

25

40

59

74

0.062

10

30

26

21

9

26

36

78

53

70

47

68

56

64

31

49

30

42

26

51

23

52

61

71

69

69

69

81

80

69

89

61

18

2

40

59

73
D32 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN 

TABLE 13. Grain-size distribution of bedload

Station 

number 

in 

figure 1

1

1

2

2

2

2

2

2

3

3

4

4

6

6

6

7

7

7

7

7

7

7

7

10

10

10

10

10

10

10

10

10

10

12

12

12

12

12

12

12

12

12

Date

8/ 9/79

8/11/79

8/ 8/79

8/12/79

5/13/80

6/ 5/80

8/ 4/80

8/ 5/80

9/25/79

5/ 6/80

7/18/79

9/26/79

7/17/79

8/15/79

9/27/79

7/28/79

8/ 8/79

5/22/80

6/ 5/80

6/12/80

6/22/80

6/26/80

6/29/80

7/18/79

8/15/79

5/ 1/80

6/ 4/80

6/11/80

6/21/80

6/23/80

6/24/80

6/25/80

6/28/80

8/16/79

4/30/80

5/15/80

5/21/80

6/ 3/80

6/10/80

6/20/80

6/24/80

6/27/80

Percentage finer than indicated sieve size; 

sieve size (millimeters)

16.0

100

100

100

100

100

100

100

100

97

88

100

100

100

100

100

100

100

93

100

100

100

100

100

100

100

94

100

100

100

100

100

100

100

100

100

100

100

98

100

100

100

100

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

8.0

99.0

99.0

100.0

100.0

100.0

100.0

97.0

99.0

94.0

79.0

98.0

99.0

100.0

99.0

100.0

99.0

100.0

90.0

94.0

95.0

97.0

98.0

99.0

99.0

100.0

93.0

96.0

95.0

98.0

98.0

97.0

99.0

99.0

100.0

98.0

99.0

98.0

94.0

98.0

99.0

99.0

99.0

4.0

94.0

93.0

97.0

98.0

96.0

98.0

89.0

94.0

83.0

63.0

90.0

93.0

97.0

96.0

96. 0

88.0

94.0

80.0

82.0

85.0

87.0

91.0

96.0

95.0

97.0

84.0

86.0

85.0

90.0

88.0

86.0

89.0

93.0

98.0

94.0

94.0

92.0

86.0

91.0

96.0

94.0

96.0

2.0

84.0

80.0

89.0

91.0

90.0

90.0

77.0

86.0

66.0

43.0

75.0

78.0

89.0

89.0

83.0

68.0

75.0

61.0

67,0

70.0

72.0

77.0

87.0

85.0

85.0

68.0

69.0

68.0

74.0

71.0

69.0

71.0

80.0

91.0

81.0

83.0

79.0

72.0

80.0

88.0

83.0

89.0

1.0

61.0

59.0

74.0

73.0

76.0

77.0

59.0

72.0

46.0

25.0

54.0

56.0

72.0

74.0

60.0

41.0

43.0

37.0

48.0

52.0

52.0

57.0

68.0

68.0

65.0

48.0

45.0

46.0

53.0

49.0

45.0

42.0

62.0

75.0

59.0

61.0

60.0

51.0

64.0

73.0

63.0

71.0

0.5

26.0

35.0

47.0

40.0

47.0

53.0

33.0

47.0

25.0

13.0

30.0

28.0

37.0

38.0

27.0

11.0

13.0

13.0

24.0

26.0

24.0

24.0

33.0

32.0

28.0

22.0

17.0

23.0

21.0

23.0

20.0

15.0

27.0

43.0

24.0

30.0

27.0

23.0

36.0

44.0

33.0

36.0

0.25

3.0

6.0

7.0

5.0

5.0

8.0

4.0

5.0

4.0

3.0

4.0

5.0

3.0

10.0

4.0

0.6

O.J

2.0

2.0

3.0

2.0

0.9

2.0

2.0

2.0

3.0

2.0

7.0

3.0

3.0

2.0

0.3

2.0

4.0

3.0

5.0

4.0

3.0

5.0

7.0

5.0

2.0

0.125

0.0

0.0

0.1

0.2

0.2

0.2

0.2

0.2

0.0

0.1

0.1

0.2

0.0

1.0

0.1

0.1

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.3

0.0

0.0

0.2

0.0

0.0

0.0

0.0

0.1

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.062

0.0

0.0

0.0

0.0

0.0

0.0

0.0

o.o

0.0

0.1

0.0

0.0

0.0

0.7

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.1

0.0

0.0

0.1

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0
INTERPRETATION OF SEDIMENT DATA 

TABLE 14. Statistical data, grain-size distribution of bedload

D33

Station 

number 

in 

figure 1

1

1

2

2

2

2

2

2

3

3

4

4

6

6

6

7

7

7

7

7

7

7

7

10

10

10

10

10

10

10

10

10

10

12

12

12

12

12

12

12

12

12

Date

8/ 9/79

8/11/79

8/ 8/79

8/12/79

6/ 5/80

8/ 4/80

8/ 5/80

5/13/80

9/25/79

5/ 6/80

7/18/79

9/26/79

7/17/79

8/15/79

9/27/79

8/ 8/79

7/28/79

6/ 5/80

5/22/80

6/12/80

6/22/80

6/26/80

6/29/80

7/18/79

8/15/79

5/ 1/80

6/ 4/80

6/11/80

6/21/80

6/23/80

6/24/80

6/25/80

6/28/80

8/16/79

6/ 3/80

4/30/80

5/15/80

5/21/80

6/10/80

6/20/80

6/24/80

6/27/80

Particle-size (millimeters) at given percentage finer; 

percentage' finer paramenter

5

0.3

0.2

0.2

0.3

0.2

0.3

0.3

0.2

0.3

0.3

0.3

0.2

0.3

0.2

0.3

0.4

0.4

0.3

0.4

0.3

0.3

0.3

0.3

0.3

0.3

0.3

0.3

0.2

0.3

0.3

0.3

0.4

0.3

0.3

0.3

0.3

0.3

0.3

0.3

0.2

0.3

0.3

16

0.4

0.3

0.3

0.3

0.3

0.4

0.3

0.3

0.4

0.6

0.4

0.4

0.4

0.3

0.4

0.6

0.6

0.4

0.6

0.4

0.4

0.4

0.4

0.4

0.4

0.4

0.5

0.4

0.4

0.4

0.5

0.5

0.4

0.3

0.4

0.4

0.4

0.4

0.4

0.3

0.4 0'.4

25

0.5

0.4

0.4

0.4

0.4

0.4

0.4

0.4

0.5

1.0

0.5

0.5

0.4

0.4

0.5

0.7

0.7

0.5

0.7

0.5

0.5

0.5

0.5

0.5

0.5

0.5

0.6

0.5

0.6

0.5

0.6

0.7

0.5

0.4

0.5

0.5

0.5

0.5

0.4

0.4

0.4

0.4

35

0.6

0.5

0.4

0.5

0.4

0.5

0.4

0.4

0.7

1.5

0.6

0.6

0.5

0.5

0.6

0.9

0.9

0.7

1.0

0.6

0.7

0.6

0.5

0.5

0.6

0.7

0.8

0.7

0.7

0.7

0.8

0.9

0.6

0.5

0.7

0.6

0.6

0.6

0.5

0.4

0.5

0.5

50

0.8

0.8

0.5

0.6

0.5

0.8

0.5

0.5

1.1

2.6

0.9

0.9

0.6

0.6

0.8

1.2

1.3

1.1

1.5

1.0

1.0

0.9

0.7

0.7

0.8

1.1

1.1

1.1

0.9

1.0

1.1

1.2

0.8

0.6

1.0

0.8

0.8

0.8

0.7

0.6

0.8

0.7

65

1.1

1.2

0.8

0.8

0.7

1.2

0.8

0.8

2.0

4.4

1.4

1.3

0.9

0.8

1.1

1.6

1.8

1.9

2.3

1.6

1.5

1.3

0.9

0.9

1.0

.8

.8

.8

.4

.6

1.8

1.7

1.1

0.8

1.5

1.2

1.1

1.2

1.0

0.8

1.1

0.9

75

l.b

1.7

1.0

1.1

0.9

1.8

1.1

1.0

2.8

6.7

2.0

1.8

1.1

1.1

l.b

2.0

2.4

2.8

3.3

2.b

2.2

1.8

l.J

1.3

1.4

2.6

2.5

2.6

2.0

2.3

2.5

2.3

1.6

1.0

2.2

1.6

l.b

1.7

1.6

1.1

l.b

1.1

84

2.0

2.4

1.5

1.5

1.4

2.9

1.8

1.4

4.1

11.6

2.9

2.5

1.6

1.6

2.1

2.6

3.4

4.4

5.3

3.9

3.4

2.7

1.8

1.9

1.9

4.1

3.7

3.9

2.9

3.2

3.7

3.2

2.4

1.4

3.6

2.3

2.1

2.5

2.4

1.6

2.1

1.6

90

2.9

3.2

2.1

1.9

2.0

4.2

2.8

2.0

5.8

19.2

4.0

3.3

2.2

2.2

2.7

3.3

4.3

6.0

8.7

5.3

4.5

3.9

2.4

2.6

2.5

6.3

4.9

5.3

4.0

4.3

4.9

4.1

3.3

1.9

5.4

3.1

2.9

3.5

3.6

2.3

2.9

2.2

95

4.5

4.6

3.1

2.8

2.9

6.1

4.4

3.3

9.7

32.8

5.4

4.6

3.1

3.6

3.7

4.3

5.5

8.5

25.1

7.8

6.2

5.6

3.6

3.9

3.4

25.2

6.9

8.0

5.6

6.0

6.7

5.1

4.8

2.6

9.1

4,6

4.4

5.1

5.4

3.5

4.4

3.4
D34 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN 

TABLE 15. Grain-size distribution of bed material

Station 

number 

in 

figure 1

1

1

1

2

2

2

2

2

2

2

3

3

3

3

3

4

4

4

4

5

5

5

5

5

6

6

6

6

6

6

7

7

7

7

7

7

7

7

7

8

8

9

9

9

10

10

10

10

10

10

10

10

10

10

11

11

12

12

12

12

Date

6/28/79

8/ 9/79

8/11/79

8/ 8/79

8/12/79

8/21/79

5/13/80

6/ 5/80

8/ 4/80

8/ 5/80

6/27/79

7/16/79

8/21/79

9/25/79

5/ 6/80

6/20/79

6/26/79

7/18/79

9/26/79

6/20/79

6/25/79

7/17/79

8/17/79

9/27/79

6/14/79

6/27/79

7/ 2/79

7/17/79

8/15/79

9/27/79

7/28/79

8/ 8/79

8/21/79

5/22/80

6/12/80

6/22/80

6/26/80

6/29/80

7/26/80

6/28/79

8/10/79

7/15/79

7/20/79

8/ 8/79

7/18/79

8/15/79

5/ 1/80

6/ 4/80

6/11/80

6/21/80

6/23/80

6/24/80

6/25/80

6/28/80

7/17/79

8/15/79

8/16/79

8/27/79

4/29/80

4/30/80

Percentage finer than indicated sieve size; 

sieve size (millimeters)

16.0

100.

99.

98.

100.

100.

100.

100.

100.

100.

100.

98.

95.

98.

95.

95.

99.

99.

100.

100.

99.

100.

100.

100.

100.

100.

100.

100.

100.

98.

100.

98.

96.

96.

100.

87.

98.

89.

100.

100.

100.

100.

100.

98.

99.

100.

96.

100.

100.

100.

100.

99.

100.

98.

99.

100.

100.

100.

100.

100.

100.

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

8.0

100.0

96.0

95.0

98.0

99.0

99.0

99.0

99.0

98.0

98.0

94.0

84.0

93.0

84.0

86.0

94.0

93.0

95.0

97.0

97.0

98.0

97.0

99.0

98.0

97.0

99.0

98.0

95.0

90.0

97.0

93.0

91.0

87.0

98.0

92.0

90.0

80.0

96.0

97.0

100.0

98.0

100.0

90.0

96.0

80.0

92.0

96.0

97.0

98.0

9*8.0

94.0

94.0

89.0

93.0

97.0

98.0

99.0

98.0

99.0

99.0

4.0

99.0

89.0

89.0

89.0

97.0

95.0

94.0

97.0

94.0

94.0

82.0

68.0

84.0

74.0

72.0

85.0

83.0

82.0

86.0

92.0

94.0

87.0

90.0

91.0

91.0

93.0

91.0

87.0

76.0

90.0

78.0

78.0

76.0

94.0

84.0

78.0

65.0

86.0

87.0

98.0

89.0

97.0

79.0

82.0

57.0

80. 0

89.0

87.0

92.0

93.0

82.0

82.0

74.0

82.0

92.0

88.0

94.0

94.0

94.0

96.0

a.o

92.0

75.0

77.0

77.0

89.0

87.0

85.0

92.0

87.0

88.0

62.0

43.0

70.0

63.0

57.0

65.0

61.0

59.0

64.0

83.0

84.0

69.0

78.0

79.0

79.0

72.0

74.0

64.0

60.0

75.0

54.0

59.0

64.0

85.0

72.0

64.0

52.0

72.0

74.0

91.0

76.0

88.0

60.0

66.0

39.0

62.0

76.0

71.0

80.0

82.0

68.0

67.0

58.0

68.0

86.0

74.0

82.0

82.0

82.0

88.0

1.0

76.0

54.0

60.0

62.0

73.0

69.0

71.0

79.0

72.0

74.0

45.0

28.0

54.0

48.0

44.0

42.0

40.0

46.0

43.0

76.0

69.0

52.0

61.0

61.0

66.0

49,0

54.0

45.0

44.0

51,0

35.0

37.0

4.6.0

65.0

59.0

48.0

42.0

54.0

57.0

70.0

57.0

72.0

44.0

46.0

23.6

40.0

59.0

58.0

58.0

63.0

50.0

49.0

42.0

51.0

74.0

52.0

66.0

71.0

64.0

74.0

0.5

46,0

32.0

38.0

41.0

43.0

41.0

51.0

53.0

45.0

50.0

26.0

13.0

31.0

28.0

29.0

18.0

17.0

29.0

19.0

65.0

45.0

28.0

30.0

34.0

44.0

20.0

26.0

22.0

22.0

23.0

16.0

14.0

25.0

32.0

29.0

26.0

27.0

25.0

27.0

30.0

29.0

28.0

23.0

22.0

9.0

18.0

33.0

42,0

27.0

32.0

25.0

28.0

23.0

24.0

39.0

24.0

37.0

47.0

39.0

45.0

0.25

10.0

15.0

12.0

11.0

9.0

9.0

26.0

20.0

12.0

18.0

9.0

3.0

10.0

15. 0

18.0

5.0

4.0

6.0

4.0

45.0

20.0

6.0

9.0

4.0

18.0

3.0

8.0

3.0

4.0

5.0

3.0

0.9

8.0

6.0

4.0

4.0

6.0

2.0

2.0

5.0

5.0

2.0

3.0

5.0

1.0

3.0

10.0

21.0

8.0

7.0

7.0

7.0

5.0

6.0

5.0

5.0

7.0

8.0

8.0

11.0

0.125

1.0

5.0

2.0

2.0

0.9

0.5

11.0

8.0

0.8

2.0

2.0

0.5

1.0

9.0

16.0

2.0

0.4

0.4

2.0

18.0

6.0

0.6

2.0

0.2

2.0

0.1

3.0

0.1

0.3

0.3

0.1

0.0

1.0

0.7

0.2

0.3

0.4

0.0

0.0

0.2

0.1

0.0

0.7

0.8

0.0

0.2

0.8

8.0

0.9

0.2

0.3

0.1

0.3

0.1

0.3

0.0

0.2

0.3

0.7

0.1

0.062

0.2

0.7

0.2

0.2

0.0

0.0

1.0

1.0

0.1

0.0

0.8

0.1

0.2

3.0

15.0

0.6

0.1

0.1

2.0

5.0

1.0

0.1

0.5

0.0

0.9

0.0

0.9

0.0

0.1

0.0

0.0

0.0

0.3

0.1

0.1

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.2

0.0

0.0

o.b

4.0

0.1

o.o

0.0

0.0

0.0

0.0

0.2

0.0

0.1

0.0

0.3

0.0
INTERPRETATION OF SEDIMENT-DATA 

TABLE 15. Grain-size distribution of bed material Continued

D35

Station 

number 

in 

figure 1

12

12

12

12

12

12

12

13

14

15

16

16

17

18

19

20

21

Date

5/15/80

5/21/80

6/ 3/80

6/10/80

6/20/80

6/24/80

6/27/80

8/18/79

8/18/79

8/18/79

8/17/79

8/18/79

8/18/79

8/20/79

8/19/79

8/19/79

8/19/79

Percentage finer than indicated sieve size; 

sieve size (millimeters)

16.0

100

100

100

100

100

100

100

100

100

100

100

100

100

100

100

100

100

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

8.0

98.0

100.0

97.0

98.0

99.0

100.0

98.0

99.0

100.0

99.0

99.0

99.0

97.0

100.0

99.0

100.0

100.0

4.0

92.0

95.0

90. 0

92.0

94.0

96.0

95.0

93.0

95.0

92. 0

95.0

97.0

93.0

97.0

96.0

99.0

98.0

2.0

83.0

86.0

77.0

84.0

81.0

87.0

86.0

81.0

83.0

82.0

85.0

91.0

87.0

91.0

86.0

96.0

91.0

1.0

66.0

69.0

57.0

68.0

61.0

73.0

70.0

62.0

65.0

63.0

66.0

75.0

78.0

81.0

73.0

89.0

82.0

0.5

36.0

40.0

29.0

40.0

35.0

43.0

41.0

30.0

34.0

32.0

34.0

40.0

56.0

56.0

53.0

68.0

62.0

0.25

6.0

7.0

6.0

8.0

7.0

9.0

10.0

4.0

5.0

5.0

5.0

6.0

11.0

12.0

18.0

19.0

25.0

0.125

0.0

0.0

1.0

0.1

0.1

0.2

0.5

0.1

0.0

0.1

0.0

0.2

0.7

0.7

4.0

2.0

10.0

0.062

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

o.o

0.0

0.0

0.1

0.1

2.0

0.4

9.0
D36 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

TABLE 16. Statistical data, grain-size distribution of bed material

Station 

number 

in 

figure 1

1

1

1

2

2

2

2

2

2

2

3

3

3

3

3

4

4

4

4

5

5

5

5

5

6

6

6

6

6

6

7

7

7

7

7

7

7

7

7

8

e

9

9

9

10

10

10

10

10

10

10

10

10

10

11

11

12

12

12

12

Date

6/28/79

8/ 9/79

8/11/79

8/ 8/79

8/12/79

8/21/79

5/13/80

6/ 5/80

8/ 4/80

8/ 5/80

6/27/79

7/16/79

8/21/79

9/25/79

5/ 6/80

6/20/79

6/26/79

7/18/79

9/26/79

6/20/79

6/25/79

7/17/79

8/17/79

9/27/79

6/14/79

6/27/79

7/ 2/79

7/17/79

8/15/79

9/27/79

7/28/79

8/ 8/79

8/21/79

5/22/80

6/12/80

6/22/80

6/26/80

6/29/80

7/26/80

6/28/79

8/10/79

7/15/79

7/20/79

8/ 8/79

7/18/79

8/15/79

5/ 1/80

6/ 4/80

6/11/80

6/21/60

6/23/80

6/24/80

6/25/60

6/Z8/80

7/17/79

8/15/79

8/16/79

8/27/79

4/Z9/80

4/30/80

Particle size (millimeters) at given percentage finer; 

percentage finer parameter

5

0.2

0.1

0.2

0.2

0.2

0.2

0.1

0.1

0.2

0.2

0.2

0.3

0.2

0.1

0.0

0.3

0.3

0.2

0.3

0.1

0.1

0.2

0.2

0.3

0.2

0.3

0.2

0.3

0.3

0.3

0.3

0.4

0.2

0.2

0.3

0.3

0.2

0.3

0.3

0.2

0.2

0.3

0.3

0.3

0.4

0.3

0.2

0.1

0.2

0.2

0.2

0.2

0.3

0.2

0.2

0.3

0.2

0.2

0.2

0.2

16

0.3

0,3

0.3

0.3

0.3

0.3

0.2

0.2

0.3

0.2

0.3

0.6

0.3

0.3

0.1

0.5

0.5

0.4

0.5

0.1

0.2

0.4

0.3

0.4

0.2

0.5

0.4

0.4

0.4

0.4

0.5

0.5

0.4

0.4

0.4

0.4

0.4

0.4

0.4

0.4

0.4

0.4

0.4

0.4

0.7

0.5

0.3

0.2

0.4

0.3

0.4

0.4

0.4

0.4

0.3

0.4

0.3

0.3

0.3

0.3

25

0.4

0.4

0.4

0.4

0.4

0.4

0.2

0.3

0.3

0.3

0.5

0.9

0.4

0.4

0.4

0.6

0.7

0.5

0.6

0.2

0.3

0.5

0.4

0.4

0.3

0.6

0.5

0.6

0.6

0.5

0.7

0.7

0.5

0.4

0.5

0.5

0.5

0.5

0.5

0.5

0.5

0.5

0.5

0.6

1.1

0.6

0.4

0.3

0.5

0.4

0.5

0.5

0.5

0.5

0.4

0.5

0.4

0.4

0.4

0.4

35

0.4

0.6

0.5

0.4

0.4

0.5

0.3

0.4

0.4

0.4

0.7

1.4

0.6

0.6

0.7

0.8

0.9

0.7

0.8

0.2

0.4

0.6

0.6

0.5

0.4

0.7

0.6

0.8

0.8

0.7

1.0

0.9

0.7

0.5

0.6

0.7

0.7

0.7

0.6

0.6

0.6

0.6

0.8

0.7

1.7

0.9

0.5

0.4

0.6

0.5

0.7

0.6

0.8

0.7

0.5

0.7

0.5

0.4

0.5

0.4

50

0.5

0.9

0.7

0.7

0.6

0.6

0.5

0.5

0.6

0.5

1.2

2.4

0.9

1.1

1.*

1.3

1.4

1.3

1.3

0.3

0.6

0.9

0.8

0.8

0.6

1.0

0.9

1.2

1.3

1.0

1.7

1.5

1.2

0.7

0.8

1.1

1.7

0.9

0.9

0.7

0.9

0.7

1.3

1.1

3.1

1.4

0.8

0.7

0.8

0.8

1.0

1.0

1.4

1.0

0.6

0.9

0.7

0.5

0.7

0.6

65

0.8

1.4

1.2

1.1

0.8

0.9

0.8

0.7

0.8

0.8

2.2

3.6

1.6

2.2

2.8

2.0

2.2

2.3

2.1

0.5

0.9

1.7

1.1

1.1

1.0

1.6

1.4

2.0

2.4

1.5

2.7

2.4

2.1

1.0

1.*

2.1

4.0

1.5

1.4

0.9

1.3

0.9

2.4

1.9

5.0

2.2

1.2

1.4

1.2

1.1

1.8

1.9

2.7

1.8

0.8

1.5

1.0

0.8

1.0

0.8

75

1.0

2.0

1.8

1.8

1.1

1.2

1.2

0.9

1.1

1.1

3.0

5.3

2.b

4.2

4.5

2.7

3.0

3.1

2.7

0.9

1.3

2.4

1.8

1.7

1.6

2.1

2.1

2.7

3.8

2.0

3.7

3.6

3.7

1.4

2.3

3.5

6.2

2.3

2.1

1.1

1.9

1.1

3.4

2. a

6. U

3.2

1.9

2.3

1.7

1.5

2.7

2.8

4.2

2.8

1.1

2.1

1.4

1.3

1.5

1.0

84

1.3

3.0

2.8

2.9

1.5

1.7

1.9

1.3

1.7

1.6

4.4

8.1

4.0

6.0

7.1

3.8

4.3

4.3

3.8

2.2

2.1

3.5

2.8

2.6

2.6

2.8

2.9

3.6

5.7

2.9

5.1

S.4

6.6

1.9

4.0

5.5

10.7

3.6

3.4

1.5

2.9

1.6

5.3

4.3

8.4

4.8

3.0

3.4

2.4

2.2

4.3

4.3

6.0

4.5

1.8

3.1

2.2

2.2

2.2

1.6

90

1.8

4.4

4.3

4.2

2.1

2.4

2.8

1.8

2.6

2.5

6.1

10.7

5.9

10.9

10.0

5.5

6.1

5.6

4.8

3.3

2.9

4.6

4.0

3.8

3.8

3.5

3.8

4.9

8.0

4.0

6.7

7.6

9.6

2.8

6.5

8.1

17.5

4.9

4.7

1.9

4.1

2.2

8.0

5.4

9.2

6.8

4.4

4.7

3.5

3.2

5.8

5.8

8.3

6.3

3.1

4.3

3.0

3.0

3.1

2.2

95

2.4

7.2

8.0

5.8

3.2

3.9

4.4

2.9

4.4

4.6

9.3

15.4

9.5

16.0

15.3

8.6

9.1

7.8

6.5

5.5

4.4

6.4

5.2

5.4

6.2

4.7

5.6

7.6

11.2

6.3

10.1

13.1

14.4

4.5

4.8

11.4

32.8

7.1

6.7

2.7

5.8

3.2

11.4

7.4

10.3

13.3

7.3

6.8

5.0

5.1

8.3

8.3

11.6

9.2

5.9

5.9

4.5

4.6

4.4

3.6
INTERPRETATION OF SEDIMENT DATA 

TABLE 16. Statistical data, grain-size distribution of bed material Continued

D37

Station 

number 

in 

figure 1

12

12

12

12

12

12

12

13

14

15

16

16

17

18

19

20

21

Date

5/15/80

5/21/80

6/ 3/80

6/10/80

6/20/80

6/24/80

6/27/80

8/18/79

8/18/79

8/18/79

8/17/79

8/18/79

8/18/79

8/20/79

8/19/79

8/19/79

8/19/79

Particle size (millimeters) at given percentage finer; 

percentage finer parameter

5

0.2

0.2

0.2

0.2

0.2

0.2

0.2

0.3

0.3

0.2

0.3

0.2

0.2

0.2

0.1

0.2

0.0

16

0.4

0.3

0.4

0.3

0.3

0.3

0.3

0.4

0.4

0.4

0.4

0.3

0.3

0.3

0.2

0.2

0.2

25

0.4

0.4

0.5

0.4

0.4

0.4

0.4

0.5

0.4

0.4

0.4

0.4

0.3

0.3

0.3

0.3

0.3

35

0.5

0.5

0.6

0.5

0.5

0.4

0.5

0.6

0.5

0.5

0.5

0.5

0.4

0.4

0.4

0.3

0.3

50

0.7

0.6

0.8

0.6

0.7

0.6

0.6

0.8

0.7

0.7

0.7

0.6

0.5

0.5

0.5

0.4

0.4

65

1.0

0.9

1.3

0.9

1.1

0.8

0.9

1.1

1.0

1.1

1.0

0.8

0.7

0.6

0.7

0.5

0.5

75

1.4

1.2

1.0

1.3

1.6

1.1

1.2

1.6

1.4

1.5

1.3

1.0

0.9

0.8

1.1

0.6

0.8

84

2.2

1.8

2.8

2.0

2.3

1.7

1.8

2.4

2.1

2.3

2.0

1.4

1.5

1.2

1.8

0.8

1.1

90

3.3

2.5

4.0

3.2

3.1

2.4

2.5

3.3

2.8

3.4

2.7

1.9

2.6

1.8

2.5

1.1

1.8

95

5.3

3.9

6.2

5.2

4.5

3.7

3.9

4.7

4.1

4.8

4.1

3.0

5.0

3,0

3.7

1.8

2.6

Relation of Channel-Width 

Maintenance to Sediment Transport 

and River Morphology: Platte River, 

South-Central Nebraska

By MICHAEL R. KARLINGER, THOMAS R. ESCHNER, RICHARD F. HADLEY, 

and JAMES E. KIRCHER

HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 127 7-E

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1983

CONTENTS

Abstract 

Introduction 

Description of the study area 

Physical characteristics of the channel

Channel geometry 

Channel pattern 

Width 

Depth 

Slope 

Bed forms 

Sediment characteristics 

Bed sediment 

Bank sediment 

Vegetation effects 

El

1

2

3

3

3

3

4

5

5

6

7

9

9

Page

Discharge-related theoretical methods for maintaining channel 

width E9 

Effective discharge 9 

Macroforms and channel width 12 

Bed-bank sediment interchange 14 

General theory and concepts 14 

Regime equations 15 

Calibration of sediment size input 15 

Special considerations concerning the calibration

curve 17 

Summary 17 

References cited 18

ILLUSTRATIONS

Page

FIGURE 1. Map showing the study area in Nebraska E2

2. Photograph showing the Platte River near Overton, Nebraska 3

3. Graph showing variation in channel width with distance downstream for the Platte River, Nebraska 3

4. Graph showing variation in local channel slope with distance downstream for the Platte River, Nebraska 4

5. Vertical photograph showing external geometry of the Platte River macroforms, Platte River near Grand Island, Nebraska 5

6. Graph showing selected grain-size distributions of bed material from the Platte River, Nebraska 6

7. Graph showing variation in sediment size with distance downstream for the Platte River, August 1979 7

8. Plot showing change in median bed-material particle size with increasing discharge for the Platte River near Overton and

Grand Island, Nebraska 9 

9-11. Graphs showing:

9. Grain-size distributions of bank sediment for the Platte River, Nebraska 10

10. Sediment-water discharge relations for the Platte River near Overton, Nebraska 11

11. Flow-duration curves for the Platte River near Overton from 1950 to 1979, and Grand Island from 1935

to 1979 11

12. Schematic diagram showing procedure for computation of effective discharge 12

13. Sketch showing macroform geometry 13 

14-16. Graphs showing:

14. Selected solutions of Parker's regime equations (16) and (17a) 16

15. Width-sediment size design curve for Cozad, Lexington 1 and 2, Overton, and Odessa sites 17

16. Particle-size distribution curves for bed material at Cozad, Lexington 1 and 2, Overton, and Odessa sites 18

ill
IV CONTENTS

TABLES

TABLE 1. Channel widths of the Platte River, Nebraska, in downstream order, measured from General Land Office maps (1860) and 

aerial photographs (1938-1979) 

2. Channel slope for selected reaches of the Platte River, Nebraska 

3. Grain-size distribution of bed and bank sediment from the Platte River, Nebraska 

Page

E5 

6 

8

4. Variation in computed effective discharge resulting from variation of the number and type of water-discharge intervals 12

5. Cross-sectional characteristics and sediment sizes for given discharges 16

LIST OF SYMBOLS

a = regression coefficient 

a' = regression coefficient 

a = acute angle formed by intersection of channel bank with

macroform crestline (degrees) 

dc = center (average) depth of channel (m) meters 

Ds = bed-material particle size for which s percent is finer (mm)

millimeters

A = difference operator 

E(-) = expected value of sediment discharge (t/d) metric tons per

day

/( ) = water discharge density function 

g(-) = sediment discharge-water discharge relation 

g = acceleration of gravity (m/s2) meter per second per second 

G = channel slope (m/m) meter per meter 

hg = depth of scour (m) meter 

h(-) = sediment density function 

H = height of macroform (m) meter 

j = summation index 

Lf = length of macroform (m) meter

X L = distance of macroform movement oblique to channel (m)

meter 

\L = distance macroform must move in downstream direction to

achieve scour depth hg (m) meter 

n' = regression coefficient 

n regression coefficient

N = number of increments in numerical integration 

Q = water discharge (ms/s) cubic meter per second 

Qs = total sediment discharge (tld) metric tons per day 

QE = effective discharge (ms/s) cubic meter per second 

Rc = relative smoothness (roughness) of channel 

R. = VsNRDg dimensionless fall velocity expression 

R = difference in specific gravity between sediment and water

(1.65) 

0 = acute angle of downstream sloping face of macroform with

horizontal (degrees)

tL time required to move macroform one wavelength (days) 

txf = time required to move macroform distance \L (days) 

V* = particle fall velocity (mis) meter per second
HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

RELATION OF CHANNEL-WIDTH MAINTENANCE TO SEDIMENT

TRANSPORT AND RIVER MORPHOLOGY: PLATTE RIVER,

SOUTH-CENTRAL NEBRASKA

By MICHAEL R. KARLINGER, THOMAS R. ESCHNER, 

RICHARD F. HADLEY, and JAMES E. KIRCHER

ABSTRACT

Study of the physical characteristics of the Platte River channel 

provides a basis for understanding channel-forming processes in the 

river. These physical characteristics and an understanding of 

channel-forming processes are used to estimate discharges necessary 

to maintain channel width. Maintenance of channel width is important for preservation of migratory-bird habitat in south-central 

Nebraska.

Channel width, depth, and slope are spatially variable; but, in addition, width has decreased significantly at many sites during the last 

80 years. Bed sediment generally decreases in size in a downstream 

direction, with some anomalies because of local inflows.

Bedload movement in the Platte River results in two scales of bed 

forms: (1) Ripples and dunes, and (2) macroforms (large bars and 

islands). The bed forms cause the channel pattern to change as water 

discharge changes: at low flows, the river has a distinct braided appearance, while, at higher flows, the river has a straight, single 

channel Insufficient water discharge has resulted in macroform 

stabilization, island formation, and subsequent channel narrowing 

along the river.

To estimate water discharge needed to maintain the present channel width, three methods were developed, based on the relationship 

between sediment transport and channel width. In the first method, 

an empirical estimation of effective discharge is computed from a 

sediment-water-discharge relation and flow statistics. This sedimentwater-discharge relation is combined with a flow-duration curve to 

produce a frequency-dependent sediment volume. The second method 

is developed from the geometry of macroforms and their migration in 

the Platte River downstream from Grand Island, Nebraska. The 

depth of scour necessary to uproot vegetation on the stoss (upstream) 

side of macroforms is related to downstream movement of the forms. 

Macroforms must be inundated with at least 20 centimeters of water 

for movement to occur, discharges of this magnitude are relatively infrequent. A third method, based on works by Parker (1977), analyzes 

channel formation from the theoretical perspective of bed-bank sediment interchange. Our data are used to calibrate Parker's equations 

for applications to the Platte River in south-central Nebraska.

INTRODUCTION

The Platte River in south-central Nebraska (fig. 1) is a 

prominent feature in the economy and environment of 

the region. In the middle of the 19th century, the Platte 

River valley marked the route of early westward migrations. Beginning in the latter part of the 19th century 

and continuing until 1982, an increasing proportion of 

the river flow has been appropriated for irrigation, 

municipal, industrial, and hydropower uses. In addition, 

migratory birds long have used the valley as a stop-over 

in their annual migration.

The regulation of the river flow in the past century 

has had a marked influence on the channel morphology 

(Eschner, Hadley, and Crowley, 1982; Williams, 1978) 

by reducing flood peaks, extending low-flow periods, 

changing sediment-transport characteristics, and allowing increased vegetation growth in the channels. Channel changes that have occurred in the Platte River and 

its tributaries since about 1860 have significantly 

changed the migratory bird habitat. Optimum roosting 

conditions occur when at least 75 m (meters) or more of 

unobstructed view exist (U.S. Fish and Wildlife Service, 

1981). Thus, a minimum unobstructed channel width of 

150 m is required for optimum roosting conditions. The 

changes in flow regime, sediment-transport characteristics, and vegetation-growth patterns have reduced 

channel width to less than 150 m at many locations in 

the study area.

This paper will examine the channel-forming processes in the Platte River, describe how these processes 

have changed the channels, and consider solutions of

El
E2 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

40°

1 KEYSTONE

2 NORTH PLATTE

3 BRADY

4 COZAD

KEY TO NUMBERED TOWNS

9 KEARNEY 17 COLUMBUS

10 GIBBON

11 WOOD RIVER

12 GRAND ISLAND

5 LEXINGTON 1 and 2 13 CENTRAL CITY

6 OVERTON 14 CLARKS

7 ELM CREEK 15 SILVER CREEK

8 ODESSA 16 DUNCAN

FIGURE 1. The study area in Nebraska

18 SCHUYLER

19 NORTH BEND

20 FREMONT

21 VENICE

22 ASHLAND

23 LOUISVILLE

the problem of preserving channel characteristics 

through knowledge of the fluvial processes. The 

primary objective of preserving these characteristics is 

to prevent deterioration of the riverine habitat used by 

migratory birds.

DESCRIPTION OF THE STUDY AREA

The North Platte and South Platte Rivers originate 

as snowmelt-runoff streams in the Rocky Mountains of 

Colorado. They flow across the Great Plains and form
RELATION OF CHANNEL-WIDTH MAINTENANCE TO SEDIMENT TRANSPORT AND RIVER MORPHOLOGY E3

the Platte River at their confluence at North Platte, 

Nebraska (fig. 1). Downstream from North Platte, the 

Platte River flows generally eastward through Nebraska to the Missouri River at the eastern edge of the 

State. The Platte River downstream from North Platte 

has a drainage area of about 79,000 km2 (square kilometers) and is about 460 river km (kilometers) long. The 

study area for this report extends from North Platte to 

Ashland, Nebraska, along the Platte River (fig. 1).

PHYSICAL CHARACTERISTICS 

OF THE CHANNEL

The Platte River is diverse in channel form; in general, it is wide and shallow. The sand and gravel bed has 

bed forms of various scales. Generally, channel banks 

do not exceed 2 m in height and are silt, sand, and 

gravel. Channel pattern varies from meandering to 

island-braided to straight. Numerous sandbars cause 

the degree of braiding to vary with discharge.

CHANNEL GEOMETRY

CHANNEL PATTERN

The pattern of the Platte River varies with time, 

space, and discharge. Since development of irrigation, 

channel patterns have changed by formation of islands 

and their subsequent attachment to the flood plain. The 

formerly broad open channel has been transformed at 

many locations upstream from Grand Island into a 

series of small channels intertwining among islands of

FIGURE 2. The Platte River near Overton, Nebraska View is to the

northwest. Note the heavily vegetated banks and braided channels

(taken in 1979).

various sizes (Eschner, Hadley, and Crowley, 1982; 

Williams, 1978). The well-defined channels in the upper 

Platte River (near Cozad) disappear downstream into 

numerous channels and islands (near Overton) (fig. 2). 

Downstream from Grand Island, the Platte River flows 

primarily in a single broad channel with relatively few 

islands. Large bed forms within the channel cause the 

pattern to change as discharge changes. At low flows, 

emergent bed forms give the river a braided appearance. 

At high flows, water fills the channel from bank to 

bank, submerging all bed forms. Although the pattern 

at high flow appears straight, major flow lines meander 

within the bankfull channel.

WIDTH

Channel width is defined here as the width of unvegetated bed within the channel banks at a given section,

1500

1000

d

z 

z

5 500

Relation based on 1860 map

Relation based on 1971 1979 

aerial photographs

I I I I 1

100 200 300 400 500 600 

DISTANCE DOWNSTREAM, IN KILOMETERS

FIGURE 3. Variation in channel width with distance downstream for 

the Platte River, Nebraska
E4 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

excluding islands. Thus, the width is a maximum channel bed width. Many of the width measurements reported here were made from aerial photographs rather 

than from measurements in the field.

Width of the Platte River ranged from about 100 m to 

over 500 m in 1979 (table 1). In general, channel width 

varies considerably, but increases in a downstream 

direction (fig. 3). Some of this variation can be related to 

diversions from the river or to returns of surface water. 

For example, the relatively large width at Overton may 

be due to the Johnson-2 Power Return, (Lexington-2 on 

figure 1) 12 km upstream. This return accounts for 

about 60 percent of the flow at Overton. Part of the local 

variation in channel width in other reaches probably can 

be attributed to variations in sediment characteristics 

and channel slope.

The downstream increase in channel width evident in 

the 1970's is in contrast to the downstream decrease in 

channel width evident in the 1860's (fig. 3). The large

decrease in channel width of the upstream part of the 

Platte River channel has resulted from hydrologic 

changes that have occurred since the development of irrigation in the basin (Eschner, Hadley, and Crowley, 

1982; Kircher and Karlinger, 1982; Williams, 1978). The 

relative lack of change further downstream perhaps can 

be attributed to the small initial size of the channel, and 

the diminished effect on surface water of irrigation development downstream from the junction with the Loup 

River near Columbus, Nebraska

DEPTH

Depth was measured by topographic surveys at low 

water, and by sounding at higher stages. Mean channel 

depth was obtained from the sounded water depth by 

relating the surface to a known elevation. Channel 

depth is variable in space and with discharge, because

0.0015

LLJ

CC 

LLJ

O.

s

LLJ

O.

O

0.0010

0.0005

II

O

< 

8

O

I I I I I

CO

O

I _L

100 200 300 400 500 

DISTANCE DOWNSTREAM, IN KILOMETERS

600

FIGURE 4. Variation in local channel slope with distance downstream for the Platte River, Nebraska
RELATION OF CHANNEL-WIDTH MAINTENANCE TO SEDIMENT TRANSPORT AND RIVER MORPHOLOGY E5

TABLE I. Channel widths of the Platte River, Nebraska, in downstream order, measured from General Land Office maps (I860) and 

aerial photographs (1938-1979) from Eschner, Hadley, and Crowley 

(1982)

Year Cozad Overtoil Keamey

Grand 

Island Duncan Ashland

Channel width, in meters

1860

1938

1941

1949

1950

1951

1955

1957

1959

1963

1964

1965

1969

1970

1971

1978

1979

1,161

1,015

204

113

110

113

110

1,545

890

451

460

408

387

405

1,484

1,298

698

695

308

293

247

I.IDO1 

704

643

664

530

472

387

826

600

543

521

448

424

411

594

515

539

521

533

530

549

1From 1898 edition 30' U.S. Geological Survey topographic map (General Land Office 

map incomplete).

at least some of the bed sediment is moved readily by all 

flows. The cross section and longitudinal profile at a station along the channel also change with time. For example, high flows during the spring of 1980 moved a 

large bedform into a cross section near Lexington, shifting the thalweg about 50 m toward the right bank. 

Lower flows gradually shifted the thalweg back to the 

left. Water depths at low flow may range from a few mm 

(millimeters) to more than 1 m. Maximum channel 

depths generally do not exceed 2 m.

SLOPE

Channel slope was measured from U.S. Geological 

Survey 7.5-minute topographic quadrangles for several 

reaches along the river (table 2). The measured segments were a minimum of 20 times the channel width. 

Slope was calculated as the average rate of elevation 

change per unit distance. The slope of the Platte River 

ranges from about 0.00070 to about 0.00135; slope generally decreases downstream from Cozad (fig. 4). This 

downstream variation of slope may relate to changes in 

channel sediment size. The slope near Overton is an exception to the downstream trend: channel slope increases from Cozad to Overton. This increase in slope 

may be a response to the return flow from the Johnson-2 

(Lexington-2 on figure 1) power plant upstream from 

Overton.

BED FORMS

At least two scales of bed forms exist in the Platte 

River: (1) Ripples and dunes small bed forms of the 

lower flow regime; and (2) macroforms large bed forms 

proportional to the channel dimensions (Crowley, 

198la), which are submerged only during the highest 

flows.

In plan view, macroforms are situated obliquely, at 

about 30°, to the direction of flow (fig. 5). Width of 

macroforms is about 0.6 times the channel width, and 

length is about 1.9 times the channel width. The height 

of macroforms generally does not exceed 2 meters. A 

steep slipface forms the downstream end of a 

macroform. Small channels, oriented about perpendicular to the slipface, occur near the downstream end of

FIGURE 5. Vertical photograph showing external geometry of the Platte River macroforms, Platte River near Grand Island, Nebraska (from

Crowley, 1981a).
E6 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

TABLE 2. Channel

Reach

Brady

Cozad

Overton

Kearney

Gibbon

Wood River

Grand Island

Central City

Silver Creek

Duncan

Schuyler

North Bend

Fremont

Venice

Ashland

slope for selected reaches

Nebraska

Distance downstream

from Keystone, Nebraska

(kilometers)

112

159

200

234

252

289

311

339

374

390

424

459

479

496

532

of the Platte River,

Slope

(meters per

meter)

0.00123

.00117

.00132

.00130

.00125

.00123

.00123

.00121

.00119

.00104

.00096

.00094

.00094

.00088

.00072

macroforms. These channels carry only a small percentage of the flow in the channel. The thalweg of the channel lies immediately downstream from the macroform 

slipface.

The formation of macroforms is not well understood. 

Crowley (1981b) has concluded that macroforms are not 

large-scale equivalents of ripples and dunes. Flow 

separation and reattachment, generally thought to form 

dunes, are only weakly developed over macroforms at 

high flows. Ratios of macroform dimensions and flow 

variables are generally at least an order of magnitude

t/3

O

LU

s

o

larger than corresponding ratios for ripples and dunes. 

In addition, macroforms are not sensitive to small 

changes of flow regime. Macroforms move only during 

the highest flows when they are submerged; they move 

by downstream migration of smaller bed forms, such as 

ripples and dunes, superimposed on the macroforms. 

The smaller forms transport sediment across the stoss 

side of the macroform to the crest, where the sediment 

slides down the slipface. Downstream migration rates of 

1.0 to 1.5 m/hr (meters per hour) were measured in the 

Platte River during 1980 high flows. Long-term rates of 

migration, computed from measurements on aerial 

photographs, varied between about 10 and 24 m/yr 

(meters per year). The rate of migration apparently increases downstream, perhaps as a result of downstream 

increase in discharge (Crowley, 198la).

SEDIMENT CHARACTERISTICS

Unconsolidated deposits in the Platte River valley 

overlie rocks of Pennsylvanian to Tertiary age. These 

unconsolidated sediments consist of loess, alluvium, 

and proglacial deposits up to 125 m thick. Recent 

alluvium, ranging in size from clay to gravel, is exposed 

on the channel bed.

In a study of the relative percentages of quartz, 

potassium feldspar, and plagioclase in Platte River

cc.

LU

in

LU 

O

LUe?

iLU 

O 

CC,

LU

O.

i i i nmrv i i i i i 1111 i i i i i 1111 i i i i i 11 r

0.01 1.0 

PARTICLE SIZE, IN MILLIMETERS

10.0 100.0

FIGURE 6. Selected grain-size distributions of bed material from the Platte River, Nebraska (data from Kircher,

1981a).
RELATION OF CHANNEL-WIDTH MAINTENANCE TO SEDIMENTTRANSPORT AND RIVER MORPHOLOGY E7

sand, Hayes (1962) concluded that quartz increases uniformly downstream, and both potassium feldspar and 

plagioclase decrease downstream. Hayes' (1962) data 

suggest that the quartz and feldspar contents of Platte 

River sediment are relatively stable upstream from the 

Loup River confluence. Mineralogy of the bed sediment 

changes with distance downstream from the Loup confluence: the percentage of quartz increases; whereas, the 

percentages of feldspars decrease.

There are many possible sources for Platte River sediment. Erosion in the Rocky Mountains yields sediment 

to both the North and South Platte Rivers. Direct erosion of bedrock beneath the Platte River rarely occurs 

because of the thickness of unconsolidated deposits. 

However, reworking of valley fill beneath and adjacent 

to the Platte River provides sediment to the river. Sediment contributions from tributaries may be significant. 

For example, sediment from the Loup River system 

probably accounts for the change in mineral composition of Platte River sediment downstream from the 

Loup confluence.

BED SEDIMENT

Bed-material samples were collected with a BMH 60 

sampler at 14 cross sections along the Platte River 

(Kircher, 1981a). Sampling was done from May to September to insure a variety of bed conditions. Samples 

were sieved (table 3), and the percentages in size classes 

were plotted to determine the size distributions. 

Selected representative distributions are plotted in 

figure 6.

The size of bed material in the Platte River ranges 

from less than 0.062 mm (millimeters) to greater than 

16mm; grain-size distributions are listed in table 3. 

Median size (D50), defined as the diameter of which half 

the particles of the sample are finer, somewhat changes 

systematically downstream. Median diameter increases 

downstream to Overton, but then decreases downstream from Overton (Kircher, 1982) (fig. 7). A secondary peak of large median diameter occurs from Central 

City to Silver Creek. Examination of figure 9 indicates 

that not only median diameter but also overall sizes 

change downstream. Bed material at Overton is coarser 

for almost all percentiles than bed material at Brady. 

Grain sizes at all percentiles become finer with increasing distance downstream from Overton for the reaches 

sampled.

The median bed-material particle size varies little 

with changes in discharge, at two stations for which 

data are available. Plots of median grain size (D50) of bed 

material and discharge for the Platte River show no positive trend, or decrease in grain size with increasing discharge near Overton (fig. 8), and no significant trend 

near Grand Island (fig. 8). The increase in bed material

2.0

1.5

o in

2 1.0

<

6

< 

Q

0.5

0.0

Range of DgQ values resulting from 

various bed material samples

 Line connecting D^n values 

based on maximum number of 

bed material samples

.1.1.1

100 200 300 400 500 

DISTANCE DOWNSTREAM, IN KILOMETERS

600

FIGURE 7. Variation in sediment size with distance downstream for the Platte River, August 1979. 

Zero on the distance scale (abscissa) corresponds to the North Platte River near Keystone, Nebraska 

(from Kircher, 1982).
E8 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN 

TABLE 3. Grain-size distribution of bed and bank sediment from the Platte River, Nebraska

[Data from Kircher (1981a) and Eschner (1981)]

Distance downstre 

Section from Keystone, Nebr 

on the North Platte I 

in kilometers

Eun 

aska, nBte

liver 32

Percent finer than indicated size, 

in millimeters

16 8 4 2 i 0.5 0.25 0.125 0.0625

Median 

grain 

size, in 

millimeters

Bed Sediment

Brady 112

Cozad 159

Overton 200

Odessa 223

Grand Island 311

Grand Island 311

Central City 339 

Clarks 357

Silver Creek 374

Duncan 390

Schuyler 424 

North Bend 459

Fremont 479

Venice 496

Louisville 533

6/28/79

8/10/79

7/15/79

7/20/79

81 8/79

7/18/79

8/15/79

5/ 1/80

6/ 4/80

6/11/80

6/21/80

6/23/80

6/24/80

6/25/80

6/28/80

7/17/79

8/15/79

8/16/79

8/27/79

4/29/80

4/30/80

5/15/80

5/21/80

6/ 3/80

6/10/80

6/20/80

6/24/80

6/27/80

8/19/79 

8/18/79

8/18/79

8/17/79

8/18/79

8/18/79 

8/20/79

8/19/79

8/19/79

8/19/79

100

100

100

98

99

100

96

100

100

100

100

99

100

98

99

100

100

100

100

100

100

100

100

100

100

100

100

100

100 

100

100

100

100

100 

100

100

100

100

100

98

100

90

96

80

92

96

97

98

98

94

94

89

93

97

98

99

98

99

99

98

100

97

96

99

100

98

99 

100

99

99

98

97 

100

99

100

100

98

89

97

79

82

57

80

89

87

92

93

82

82

74

82

92

88

94

94

94

96

92

95

90

92

94

96

95

94 

95

92

95

95

93 

97

96

99

98

91

76

88

60

66

39

62

76

71

80

82

68

67

58

68

86

74

82

82

82

88

83

86

77

84

81

87

86

83 

83

82

65

89

87 

91

86

96

91

70

57

72

44

46

23

40

59

58

58

63

50

49

42

51

74

52

66

71

64

74

66

69

57

68

61

73

70

64 

65

63

66

77

78 

81

73

89

82

30

29

28

23

22

9

18

33

42

27

32

25

28

23

24

39

24

37

47

39

45

36

40

29

40

35

43

41

32 

34

32

34

48

56 

56

53

68

62

5

5

2

3

5

1

3

10

21

8

7

7

7

5

6

5

5

7

8

8

11

6

7

6

8

7

9

10

5 

5

5

5

9

11 

12

18

19

25

0.2

.1

.0

.7

.8

.0

.2

.8

8

.9

.2

.3

.1

.3

.1

.3

.0

.2

.3

.7

.1

.0

.0

1

.1

.1

.2

.5

.1 

.0

.1

.0

.4

.7 

.7

4

2

10

0.0

.0

.0

.0

.2

.0

.0

.0

4

.1

.0

.0

.0

.0

.0

.2

.0

.1

.0

.3

.0

.0

.0

.0

.0

.0

.0

.0

.0 

.0

.0

.0

.0

.1 

.1

2

.4

9

0.7

.9

.7

1.3

1.1

3.1

1.4

.8

.7

.8

.8

1.0

1.0

1.4

1.0

.6

.9

.7

.5

.7

.6

.7

.6

.8

.6

.7

.6

.6

.7 

.7

.8

.7

.5

.5 

.5

.5

.4

.4

Bank Sediment

Cozad 159 

Lexington-1 189 

Lexington-2 190 

Overton 200 

Elm Creek 215 

Odessa 223

1980 

1980 

1980 

1980 

1980 

1980

99.6 

92.2

99.4 

92.8 

99.3 

82.6 

98.1 

99.8

size does not occur that might be expected as increasing 

discharge removes finer particles from the bed. The 

apparent decrease in grain size with increasing dis98.6 

85.7 

95.2 

73.3 

95.8 

99.4

96.1 

75.5 

90.4 

68.1 

91.6 

93.8

93.7 

61.1 

83.3 

60.0 

84.9 

69.4

87.3 

41.5 

68.0 

45.7 

76.9 

31.0

70.7 

17.5 

38.1 

28.5 

55.4 

10.2

40.3 

4.7 

11.8 

11.7 

22.4 

5.2

charge near Overton may be due to the 

lag gravel, as sand is removed from 

discharges.

21.0 

2.2 

4.3 

5.1 

14.7 

3.2

.16 

.68 

.33 

.63 

.23 

.71

accumulation of 

the bed at low
RELATION OF CHANNEL-WIDTH MAINTENANCE TO SEDIMENT TRANSPORT AND RIVER MORPHOLOGY E9

* 2

OVERTON

i I i

100 200 300

Q

LLJ 

OQ 0.5

0.0

GRAND ISLAND 

. . . I .

0 80 160 240 320 

WATER DISCHARGE, IN CUBIC METERS PER SECOND

FIGURE 8. Change in median bed-material particle size with increasing discharge for the Platte River near Overton and Grand Island, 

Nebraska (from Kircher, 1982).

BANK SEDIMENT

Composite bank material samples were collected at 

six sections from Cozad to Odessa The variability of 

bank sediment is high, ranging from less than 0.062 mm 

to greater than 16 mm (fig. 9 and table 3). Median grain 

sizes (DM) are generally lower than median grain sizes of 

the bed at corresponding locations. Grain size distributions do not show a progression in a downstream direction and the curves do not all have the same shape. 

Variability in grain size of bank sediment may result 

from the limited number of samples.

VEGETATION EFFECTS

Many species of vegetation are present along? the 

Platte River. Annual and biennial grasses odcur along 

banks and on islands along the entire river. Shrubs and 

trees are particularly common in'the upper parts of the 

study reach. The most common trees are cottonwood, 

willow, elm, and ash. Extensive vegetation in the Platte 

River valley is a relatively recent phenomenon (Eschner, 

Hadley, and Crowley, 1982). Accounts of explorers and 

early settlers indicate that timber was scarce in many

places as recently as 1860. Hydrologic changes in the 

Platte River since 1860, such as reduction of flood 

peaks, have made conditions more favorable for germination and preservation of vegetation. Vegetation has, 

in turn, had a significant effect on channel morphology 

and processes. For example, establishment of vegetation on sandbars is the chief method by which channel 

width is reduced (Eschner, Hadley, and Crowley, 1982). 

The total amount of sediment in transport is also 

changed, because of reduction of channel width and the 

presence of vegetation on low bars within the channel.

DISCHARGE-RELATED THEORETICAL

METHODS FOR MAINTAINING

CHANNEL WIDTH

Geomorphic processes in a river involve the interrelationships between channel cross-section characteristics, 

sediment transport, and hydrology. Although channel 

cross-sectional configuration is partly a function of sediment movement, sediment discharge is difficult to 

study directly. However, the relationship between 

water discharge and sediment discharge allows channel 

maintenance to be related to water discharge.

This chapter describes three methods that use this 

dependence between water and sediment discharge to 

estimate the functional relationships between channel 

width and water discharge. The three methods have 

been calibrated in the Platte River. Sediment transport 

plays an important role in all three methods.

In the first method, a sediment-water discharge rela-, 

tion is combined with a steady-state flow-duration curve 

to empirically estimate an effective discharge, defined 

here as the water discharge that maintains the present 

channel cross section. The second method is based on 

results of field studies of macroform formation and 

migration in the Platte River downstream from Grand 

Island, Nebraska If these bed forms are not moved 

downstream, they can become stabilized with vegetation to form islands, thereby narrowing the channel. 

The third method analyzes channel formation from the 

theoretical perspective of bed-bank sediment interchange. Data used to calibrate regime equations from 

this latter method were collected in a reach of the river 

from Cozad downstream to Odessa, Nebraska

EFFECTIVE DISCHARGE

The rate of sediment movement in a channel depends 

in part on the magnitude of water discharge. The relationship between water discharge and sediment discharge can be expressed by a sediment-discharge rating 

curve of the form:
E10 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

LJJ 

M

CO

Q

LJJ

S

o

Q

<

I I 

oc

LJJ

CO 

LJJ

O

LJJ

CD

LJJ 

O 

OC

 COZAD

 LEXINGTON-1 

LEXINGTON -2 

OVERTON 

ELM CREEK 

ODESSA

0.01 0.1 1.0 10.0 

PARTICLE SIZE, IN MILLIMETERS

100.0

FIGURE 9. Grain-size distributions of bank sediment for the Platte River, Nebraska (from Eschner, 1981).

where

Qs = sediment discharge;

Q = water discharge; and

a and n = regression coefficients, here determined by

regression analysis.

The sediment-water discharge relation should accurately describe the period under consideration; a 

sediment-water discharge relation does not necessarily 

remain constant over many years. For example, figure 

10, representing data from the Platte River near Overton, shows that the sediment-water discharge relation 

for this station has changed since the 1950's. The sediment discharge near Overton in 1980 at water discharges less than 74 m3/s (cubic meters per second) was 

greater than the sediment discharge for corresponding 

water discharges in the 1950's; but, the rate of increase 

of sediment discharge with increasing water discharge 

was less in 1980 than it was in the 1950's.

The significance of a given discharge in moving a 

quantity of sediment during a specified period depends 

on frequency of the discharge. Frequency with which a 

given discharge occurs is represented by the flowduration curve (fig. 11). The most frequent discharges 

are small and transport relatively small amounts of 

sediment; large discharges are less frequent, but they 

transport greater amounts of sediment.

Relative effectiveness of a given water discharge to 

influence channel morphology can be described by the 

maximum product of sediment discharge and the frequency of occurrence associated with the corresponding 

flow (fig. 12). A range of intermediate flows transports 

most of the annual sediment load. This range of discharges may be represented by the maximum sediment 

load; the midpoint of this range will be called the effective discharge (Andrews, 1980). Therefore, the effective 

discharge can be described as the discharge that maintains the channel by virtue of its frequency of occurrence and transporting capacity, by transporting, on 

the average, more sediment during the period of record 

than any other discharge.

Effective discharge can be obtained from the computations necessary for determination of mean annual 

sediment discharge. Mean annual sediment discharge is 

determined by calculating the expected value of sediment discharge E(QS). The expected value is defined as:

)=l? Qsh(Qs)dQs (2)

where

E(QS) = expected value of the sediment discharge or 

mean annual sediment discharge in tons 

per day;
RELATION OF CHANNEL-WIDTH MAINTENANCE TO SEDIMENT TRANSPORT AND RIVER MORPHOLOGY Ell

10,000

g

1,000

100

QO. 

O </>

l a

$e 10

2 <?

3! 5

0.1

Data from 1950's 

(M.R.B.C., 1975)

Data from 198 

(Kircher. 1981b)

1 10 100 1.000 

DISCHARGE, IN CUBIC METERS PER SECOND

FIGURE 10. Sediment-water-discharge relations for the Platte River

near Overton, Nebraska (from Missouri River Basin Commission,

1975; and Kircher, 1981b).

Qs = sediment discharge in metric tons per day; 

and

h(Qs) = sediment discharge density function. 

The sediment-density function, h(Qs), is unknown, but 

Qs is a known function of water discharge from the 

sediment-water-discharge relation (fig. 12A). Therefore, 

by probability theory, the following substitution can be 

made for equation 2:

)=ff g(Q)f(Q)dQ (3)

where

g(Q) = Qs, in metric tons per day; and 

f(Q) = the water-discharge density function. 

The water-discharge density function (fig. 12B) can be 

obtained from a flow-duration curve, such as the type 

shown in figure 11. Although the analytical form of the 

flow-duration curve is unknown, the integral in equation 

3 can be approximated by a summation of the discretized integrand (fig. 12C) which has the following 

form:

1000

100

o

10

tc

LU

0. 1

* 0.1 

5 1000

o 

z 100

LU

g 10

i 1

CO

o

0.1

0.01

0.001

OVERTON

0.10.5 5.0 10.0 50.0 90.0 95.0 99.0 99.9 

PROBABILITY OF DISCHARGE BEING EQUALED OR EXCEEDED

FIGURE 11. Flow-duration curves for the Platte River near Overton

from 1950 to 1979, and Grand Island from 1935 to 1979 (from

(Kircher, 1981b).

N 

7=1

(4)

where

Qj = midpoint of discretized interval. 

With this form, the flow-duration curve can be divided 

into N equal intervals. The midpoint of each interval is 

then determined and inserted into the sediment-waterdischarge relation for each station, thus providing a 

sediment-discharge value. This sediment-discharge 

value is then multiplied by the probability of occurrence 

of that associated water discharge, flQjlAQj, to yield a 

weighted quantity of sediment. The discharge that carried the most sediment during a period of record is the 

peak of the integrand in equation 3 or the peak summand in equation 4. An example of a plot of the summand in equation 4 is shown in figure 12C for the Platte 

River near Overton.

Equation 4 with N equal to about 20 is the form most 

commonly used (Andrews, 1980; Benson and Thomas, 

1966). However, the location of the peak summand is 

dependent on N. The greater the number of intervals,
E12 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

. vj A a

a

WATER DISCHARGE

B

f(Q)

f(Qj)

Q:

WATER DISCHARGE

AVE SEDIMENT LOAD

g(Q)f(Q)AQ 

9(Qj)*

f(Qj)*

AQ:

WATER DISCHARGE

FIGURE 12. Procedure for computation of effective discharge.

the closer the result will be to the true value. Variation 

of the resulting effective-discharge by varying N can be 

seen in table 4 for the Platte River near Overton and the 

Platte River near Grand Island. Flow-duration curves 

were also divided into equal natural logarithm (log) 

(water-discharge) intervals to reduce the error caused by 

skewness of the flow distribution. The computation of 

effective discharge for these two stations is based on the 

total sediment-water-discharge relations of each.

TABLE 4. Variation in computed effective discharge resulting from

variation of the number and type of water-discharge intervals

[N, number of intervals; E(X), expected value of mean annual total-sediment discharge;

QE, effective discharge; t/d, metric tons per day; m3/s, cubic meters per second]

Platte River near

Overton, Nebn

Type of interval

Arithmetic

Logarithmic

N

35

69

103

137

171

35

69

103

137

E(X)

(t/d)

1115

1110

1107

1107

1101

747

1095

1100

1108

iska

QE

(m3/s)

46

35

34

31

32.5

33

41

44

46

Platte River near

Grand Island, Nebraska

N

35

69

103

137

171

35

69

103

137

E(X)

(t/d)

1099

1086

1098

1075

1076

1064

1066

 

1073

QE

(m3/s)

46

45

40.5

36

32.5

59.5

55

 

43

Effective discharge varies considerably with N and 

the type of intervals used. Table 4 shows that the maximum number of divisions give results differing by as 

much as 29 percent, when compared to the minimum 

number of divisions. Because a constant sedimentwater-discharge relation and flow-duration curve were 

used in all cases for each station, study of the differences in effective discharge can be limited to the discretized approximation of the flow-duration curve. Further research is necessary to determine if the differences 

are due to the errors in the integration approximation, 

or if the method yields a statistically inconsistent 

estimator of effective discharge.

Nonstationarity of the hydrologic record may introduce a second source of error. Use of a flow-duration 

curve developed for a period of changing flow would 

result in an effective discharge that is time-averaged. 

As a result, errors associated with the averaging of the 

flow-duration curve will carry over to the computation 

of the effective discharge.

MACROFORMS AND CHANNEL WIDTH

Formation of islands and their subsequent attachment to the flood plain is a major cause of channel narrowing in the Platte River (Eschner, Hadley, and 

Crowley, 1982). Islands form as vegetation becomes 

established on macroforms and stabilizes them. Vegetation also increases hydraulic roughness over the 

macroform and promotes deposition of sediment. Vegetation continues to proliferate on the newly deposited 

sediment, increasing both the stability of the 

macroform and the likelihood of further deposition. In 

this manner, a macroform can grow vertically until the 

surface is at the same elevation as the flood plain.

Prevention of seedling germination and removal of 

vegetation from macroforms inhibit stabilization of 

macroforms. Seeds can be removed from the macroform 

surface and seedlings uprooted by scour on the stoss 

side of the macroform. The depth of scour is a direct 

function of downstream translation of the macroform as 

explained in the following paragraph. The maximum 

scour depth (the macroform height) is obtained if the 

bed form is translated a distance equal to its length.

In cross section, macroforms are triangular, with a 

stoss side dipping gently upstream and a steep slipface 

downstream of the macroform crest (fig. 13). The relationship between the depth of scour and the distance 

through which a macroform moves is developed by 

using plane geometry; it is based on the work of Crowley (198la). This development requires specification of 

the depth of scour, hs, the amplitude or height of the 

macroform, H, the macroform length, Lp and the acute
RELATION OF CHANNEL-WIDTH MAINTENANCE TO SEDIMENTTRANSPORT AND RIVER MORPHOLOGY E13

EXPLANATION

v A --(1 ~ (L ~

L~ H f~ tan 0

A' L MACROFORM TRANSLATION PERPENDICULAR TO SLIPPAGE

hs EROSION DEPTH ON STOSS SIDE

H AMPLITUDE

Lf MACROFORM LENGTH

6 SLIPPAGE ANGLE

B CHANNEL WIDTH

a ANGLE FORMED BY MACROFORM AND CHANNEL BANK 

FIGURE 13. Macroform geometry (from Crowley, 1981 a).

angle of the downstream sloping face with the horizontal, 6. Because the crestlines of macroforms are not 

perpendicular to the flow, a correction must be made 

which is a function of the acute angle, a, formed by the 

intersection of the channel bank with the crestline. 

From proportionality of right triangles, the expression 

for the distance of macroform movement, \'L, oblique to 

channel banks is:

\'L = (5)

To establish the macroform movement in the downstream direction, \L, that is, parallel to the flow, \'L must 

be divided by sina:
E14 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

X^ = X^/sina =

H

 7//(tan6sina)) (6)

Crowley (198la) reports that macroform heights average about 2 m, and lengths average about 300 m, for the 

Platte River below Grand Island. The angle 6 is approximately 30°, and the angle a averages about 28°. Therefore, the factor HI(tanQsma) is negligible compared to 

. Equation 6 can thus be simplified:

X =

H

(7)

An estimate of flow and its duration required to transport a macroform a distance, XL, and insure a scour 

depth, hs, can now be made for a given Ly and sedimenttransport rate per unit width of channel, Qs. The time 

required to move a unit width of macroform a distance 

of one (macroform) length, tL . is obtained from the conservation of sediment transport for a triangular bed 

form:

±HLf =Q,tLf

or

(8a)

(8b)

The following identity holds for a constant speed of the 

macroform:

(9)

Equations 8b and 9 can be combined to yield:

t\ = AL 2Q,

(10)

where

tx is the time required to move a unit width of 

macroform a distance XL.

Inserting the expression for \L (eq. 7) into equation 10 

gives the time necessary to scour the stoss side of the 

macroform to a depth, hs:

 /sina) (11)

Kircher (1981b) presents unit width regression relationships for sediment discharges as functions of water 

discharge, Q, for several stations along the Platte River.

These relationships are of the form: 

Qs = <*Qn (12)

where a and n are regression coefficients. If equation 12 

applies to the reach of interest, an expression for the 

water discharge as a function of scour depth and translation time can be obtained by combining equations 11 

and 12:

(LWsina)

l/re

(13)

This direct substitution of equation 12 into equation 

13 presents some statistical inconsistencies. Because Q 

is the independent variable in equation 12, technically it 

should not be expressed as a function of the regression 

parameters a and n. However, if the explained variation 

of the equations given in equation 12 is reasonably high, 

then the effects of this direct substitution are minimal. 

If the explained variation of the equations (12) is not 

large enough, then a new regression of Q on Qs should 

be performed; in which case:

(14)

where a' and n' are regression coefficients; 

and

= a

2t\ sina

n'

(15)

As noted previously, incipient motion of sediment 

particles on the macroforms in the Platte River occurs 

when there are approximately 20 cm (centimeters) of 

water over the bed form. Therefore, the admissible discharges obtained from equation 13 or 15 are limited to 

those discharges associated with the river stage necessary to barely cover the macroforms.

BED-BANK SEDIMENT INTERCHANGE

GENERAL THEORY AND CONCEPTS

If riparian vegetation is absent, the channel width of 

an alluvial river depends on the relative balance between scour and deposition of sediment along the 

banks. Excess scour along the base of the banks erodes 

the banks by undercutting, resulting in channel widening. This process is hastened where bank sediment is 

noncohesive and streamflow is perennial. When bed
RELATION OF CHANNEL-WIDTH MAINTENANCE TO SEDIMENT TRANSPORT AND RIVER MORPHOLOGY E15

scour is counterbalanced by deposition of suspended 

sediment in slack water along channel banks, for 

relatively constant discharge, erosion decreases and an 

equilibrium width is established. However, a decrease in 

discharge followed by reduced movement of bed 

material along the banks may induce vegetation 

growth. If this vegetation is not uprooted by subsequent floods, the banks become stabilized and the channel resists further widening by erosion.

Various empirical regime relations have been developed that estimate changes in channel width as a function of channel depth (Lane, 1937), or changes in channel 

width and depth as power functions of discharge 

(Leopold and Maddock, 1953). Parker (1977) developed 

regime equations that go beyond similar studies by 

theoretically examining the multivariate structure of 

the empirical relations. These equations comprise an 

algorithm that is unique, in that channel cross-sectional 

characteristics (top width and maximum depth in a 

uniform bed) are mathematically integrated with bedmaterial size, sediment load, channel slope, and 

discharge.

This report compares theoretically determined channel characteristics, using Parker's method, to onsite 

Platte River data. This analysis was made for five sites 

in or near the reach from Lexington to Grand Island, 

Nebraska.

REGIME EQUATIONS

Parker (1977) uses concepts of water and sediment 

movement that specify conditions for balance of bedload transport and lateral diffusion of suspended sediment necessary to attain channel equilibrium. These 

conditions are integrated into a set of three regime equations that relate channel slope, G, center depth of channel, dc, width of channel, B, water discharge, Q, total 

bed material load, Qs, and the particle size, of which s 

percent of the bed material is finer, Ds. In Parker's 

development, the channel bed was assumed uniform, 

with center depth equaling maximum depth. Because 

the bed in the Platte River is irregular, due to bed forms, 

center depth does not retain its % connotation of the 

theory; therefore, average depth will be used in lieu of 

center depth.

Using Parker's terminology, the first regime equation 

relates relative roughness of channel to slope, depth, 

and particle size. Parker's expression of relative 

roughness (dJDg) is the reciprocal of the conventional 

definition of relative roughness and may be more appropriately termed relative smoothness.

Rc = dcIDs = 46.5 (16)

where

R

= relative smoothness (roughness) of channel;

= center (average) depth of channel (meter);

= bed-material particle size, in meters, for

which s percent is finer; 

= VSNR Dsg dimensionless fall velocity expression;

Vs = particle-fall velocity (meter per second); 

R = difference in specific gravity between sediment and water (1.65); 

g = acceleration of gravity (9.8 meter per second

per second);

G = channel slope (m/m) meter per meter. 

The remaining two regime equations establish water 

discharge, Q, and sediment discharge, Qs, as functions 

of particle size and channel features.

Q=0.958 Rc3 G ln(1.06 Rc2 G)*

[Bldc -0.921 R G1 '2 Rf1 ] (17)

Qs=0.601 Rcnl2 G9'2 *

[B/dc -1.41 Rc112 Gll2 Rf ] +2.97*10-"

*RC 2 G912 Rf1 In (1.06 Rc3 G)*

\Bldc -1.33 R112 G1/2

In equations 17 and 18: 

B = channel top width, in meters.

A graph of selected solutions to equations 16 and 17 

for various combinations of variables is given in figure 

14. Equation 16 is solved first, using particle attributes 

Vs, R, and Ds, and channel slope G. The resulting value 

of Rc is then inserted into equation 17 with the other required variables, to solve for Q. Depth is shown, because 

it is determined by equation 16 through a choice of sediment size and slope. The selection of dependent and independent variables shown in figure 14 reflects the intent to estimate water discharge necessary to maintain 

a desired width of channel.

The particle-fall velocity for a given sediment size is 

required to calculate Rf in the regime equations. Fall 

velocities were obtained from the U.S. Inter-Agency 

Committee on Water Resources (1957), using the 20 °C 

(degrees Celsius) temperature curve for naturally worn 

quartz particles having a shape factor of 0.7. Channel 

slopes were obtained from topographic maps.

CALIBRATION OF SEDIMENT SIZE INPUT

Parker (1977) bases his conclusions on three primary 

assumptions: (1) Regime equations apply only to
E16 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

TABLE 5. Cross-sectional characteristics and sediment sizes for given discharges (modified from Karlinger and others, 1981)

[B, maximum width, in meters; Q, water discharge, in cubic meters per second; d, depth, in meters; G, channel slope, (dimensionless) in meters per meter; D, sediment size, in millimeters;

D , design size of sediment, in millimeters]

Site

Obtained from onsite measurements

D

"maximum

Cozad

Lexington

Lexington 2

Overton

Odessa

(m)

31

201

201

178

229

Q

(m3/s)

11

8

85

102

122

142

159

184

127

198

B

(m)

31

30

.137

152

168

183

183

198

178

229

d

(m)

0.62

.53

.61

.66

.70

.76

.79

.91

.70

.64

G

(m/m)

.00125

.00125

.00114

.00114

.00114

.00114

.00114

.00114

.00119

.00112

D15

(infer

0.36

.37

.31

.37

.38

50lhank>

(mmT1

0.15

.68

.33

.44

.71

DS

(mm)

0.20

.18

.25

.26

.27

.28

.29

.30

.27

.29

Calculated from 

regime equations

B

(m)

30

28

133

144

162

172

178

191

171

222

d

(m)

0.37

.32

.52

.55

.57

.60

.63

.66

.56

.64

straight reaches of channel; (2) bed and bank material 

are noncohesive; and (3) particle size is uniform throughout the channel. Of the three, only the assumption of 

uniform particle size is not met in an approximate way 

for the Platte River. Therefore, there is some question 

as to the best value to use for Ds in equations 16 and 17; 

this question was not satisfactorily resolved in Parker's 

(1977) study.

To determine an input sediment size for application of 

regime equations to the Platte River, a trial solution 

procedure based on measurements from five locations

was used. These measurements were made near Cozad, 

Overton, and Odessa, Nebraska; measurements were 

made at two sites near Lexington, Nebraska At each 

site, cross-sections were surveyed at several water discharges. Bed-material samples were also obtained at 

each cross section. Water-surface widths and their corresponding discharges obtained from the field measurements were used with local channel slope and depth as 

input variables in equations 16 and 17, to determine 

that sediment size, Ds, necessary for calculated width to 

equal measured width for the given discharge. These

400

Q 300

O

uj 200 c/j

cc

LJJ 

Q.

O

00

O

100

O

10

I I I I I M

I__I I I I I I

CHANNEL SLOPE SEDIMENT SIZE 

/DIMENSIONLESS) (MILLIMETERS)

G = 0.001

G = 0.001

G = 0.0005 

G = 0.001

G = 0.002

D c =0.30

Ds =0.25

Ds = 0.20 

Ds =0.20

Dc =0.20

MEAN

CHANNEL DEPTH 

(METERS) 

d = 0.72

d=0.56

d = 0.63 

d=0.41

d = 0.27

10 100 200 300 

WIDTH (B) IN METERS

FIGURE 14. Selected solutions of Parker's regime equations (16) and (17a) (from Karlinger and others, 1981).
RELATION OF CHANNEL-WIDTH MAINTENANCE TO SEDIMENT TRANSPORT AND RIVER MORPHOLOGY E17

0.40

0.35 -

0.30

0.25

7Z 0.20

0.15

0.10

0.05

0.00

O COZAD

A LEXINGTON - 1

A LEXINGTON - 2

n OVERTON

 ODESSA

50 100 150

WIDTH. IN METERS

200 250

FIGURE 15. Width-sediment size design curve for Cozad, Lexington 

1 and 2, Overton, and Odessa sites (from Karlinger and others, 1981).

sediment sizes were plotted against width to establish a 

design relation (fig. 15) to apply equations 16 and 17 for 

any site within the reach. Data used to develop figure 15 

are summarized in table 5.

SPECIAL CONSIDERATIONS CONCERNING THE 

CALIBRATION CURVE

The calibration curve (fig. 15) derived from data obtained at the five sites is acceptable only:

1. If the sediment sizes estimated from figure 15 are 

within the sediment-size distribution of each site. 

Parker (1977) also proposed that an appropriate effective particle size might be among the smaller sizes. 

These smaller sizes would be dominant in the bed-bank 

interchange.

2. For the calibration curve to be useful at any other 

site within the Cozad-Odessa reach, sediment-size distribution at such sites must also contain the calibrated 

size. The particle-size distribution curves of figure 16 indicate that both of these requirements are met for this 

reach of the Platte River. As can be seen from figure 16, 

all of the calibrated sediment sizes are acceptably 

within the sediment-size distribution curves and are in 

the lower range of the size distribution. Parker (1977) 

found that an estimate of D16 for the bed material gave 

the best results in a study of the Niobrara River in 

Nebraska Overlap of the distribution curves strongly 

indicates a homogeneity in sediment-size distribution 

for all intermediate sites within this reach.

Sediment size as a function of width only is shown in 

figure 15. However, channel slope, is an implicit additional independent variable in the graph. For a given 

width, sensitivity of discharge to slope is much smaller 

than sensitivity of discharge (fig. 14) to sediment size. 

Therefore, dependence of the design sediment size on 

channel slope is assumed to be negligible for the calibration curve.

Another consideration in the use of figure 15 is that 

maximum widths were constraints in development of 

the figure. For all sites, especially Cozad and Overton, 

stabilizing vegetation on the banks prevents any widening of the channel in response to increasing discharge; 

any increase in conveyance is reflected in an increase in 

depth. Therefore, to apply the proposed procedure to 

any intermediate site, a maximum width needs to be 

estimated if there is constraining vegetation; larger 

values than this width would render the method 

inappropriate for determining a maintenance discharge.

SUMMARY

Physical characteristics of the Platte River channels 

and the sediment that forms channel boundaries may 

serve as bases for assessing the effects of watermanagement decisions on channel changes. Channel 

geometry and hydrologic data, used with analysis data 

of bed and bank sediment, can estimate channel response to changes in river flow regime.

Channel characteristics of the Platte River have been 

documented sufficiently for the period 1900-80 to permit correlation of channel response to historical changes 

in hydrology, including water use. The channel has narrowed by 50 percent near Duncan, Nebraska, since 

about 1900; the width has decreased as much as 90 percent since 1900 near Cozad, Nebraska The channel, 

which was once broad and relatively free of vegetation 

and islands, has been transformed at many locations 

into a series of narrow channels separated by islands of 

various sizes. Sediment transport also has been altered 

extensively because of reduced flow in narrow channels,
E18 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

99.9 

M 99.8 S 99-5

UJ 99.0

< 98.0 

O

Q 95.0

Z

Z 90.0

cc

UJ

80.0 

70.0

_ 60.0 

E 50.0 

ft 40.0 

Q 30.0 

fe 20.0

°- 10.0

u_

0 5.0

UJ

O 

cc

2.0 

1.0 

0.5

0.2 

0.1

I I I i \ I I I I

ODESS LEXINGTON - 1

COZAD

I I I I I I I I I I I I I I I I I I I I I I I I I I

0.1 1.0 10 

PARTICLE SIZE, IN MILLIMETERS

100

FIGURE 16. Particle-size distribution curves for bed material at Cozad, Lexington 1 and 2, Overton, and Odessa sites

(from Karlinger and others, 1981).

some of which are clogged with vegetation, islands, and 

aggrading bed forms. How much more will these channels change as a result of future water-management 

practices?

Three methods relating water discharge to channel 

cross-section characteristics have been presented to 

allow assessment of the consequences of future rivermanagement practices. A statistically based effective 

discharge computation is presented, but it lacks a 

physical basis for understanding fluvial processes. The 

methods involving movement of macroforms and bed 

and bank sediment interchange are both more physically based than the effective discharge method, but 

both may be subject to errors because theoretical 

assumptions are only approximated for the Platte River 

channels. Each of the three methods has limitations for 

determining channel-maintenance discharges. However, 

with some understanding of the fluvial processes operating in the channels and the relationship of water 

discharge to sediment discharge, channel-maintenance 

discharges may be estimated.

REFERENCES CITED

Andrews, E. D., 1980, Effective and bankfull discharges of streams 

in the Yampa River basin, Colorado and Wyoming: Journal of 

Hydrology, v. 46,20 p.

Benson, M. A., and Thomas, D. M., 1966, A definition of dominant 

discharge: Bulletin of the International Association of Scientific 

Hydrology, v. 11, no. 2, p. 76-80.

Crowley, K. D., 1981a, Large-scale bedforms in the Platte River downstream from Grand Island, Nebraska: Structure, process, and 

relationship to channel narrowing: U.S. Geological Survey OpenFile Report 81-1059,31 p.

___1981b, Hierarchies of bedforms: Princeton University, Princeton, New Jersey, pt. 1, unpublished Ph. D. dissertation, 98 p.

Eschner, T. R., 1981, Morphologic and hydrologic changes of the 

Platte River, south-central Nebraska: Colorado State University, 

Fort Collins, M. S. thesis, 269 p.

Eschner, T. R., Hadley, R. F., and Crowley, K. D., 1983, Hydrologic and morphologic changes in channels of the Platte River 

basin: A historical perspective: U.S. Geological Survey Professional Paper 1277-A, 39 p.

Hayes, John R., 1962, Quartz and fieldspar content in South Platte, 

Platte, and Missouri River sands: Journal of Sedimentary Petrology, v. 32, no. 4, p. 793-800.
RELATION OF CHANNEL-WIDTH MAINTENANCE TO SEDIMENT TRANSPORT AND RIVER MORPHOLOGY E19

Karlinger, M. R., Mengis, R. C., Kircher, J. E., and Eschner, T. R., 

1981, Application of theoretical equations to estimate the discharge needed to maintain channel width in a reach of the Platte 

River near Lexington, Nebraska; U.S. Geological Survey OpenFile Report 81-697,16 p.

Kircher, J. E., 1981a, Sediment analysis for selected sites on the 

South Platte River in Colorado and Nebraska, and the North 

Platte and Platte Rivers in Nebraska Suspended sediment, bedload, and bed material: U.S. Geological Survey Open-File Report 

81-207,48 p.

___1981b, Sediment transport and effective discharge of the 

North Platte, South Platte, and Platte Rivers in Nebraska; U.S. 

Geological Survey Open-File Report 81-53,26 p.

Kircher, J. E., 1983, Interpretation of sediment data for the South 

Platte River in Colorado and Nebraska, and the North Platte and 

Platte Rivers in Nebraska; U.S. Geological Survey Professional 

Paperl277-D,37p.

Kircher, J. E., and Karlinger, M. R., 1983, Changes in surface water 

hydrology, Platte River basin in Colorado, Wyoming, and 

Nebraska upstream from Duncan, Nebraska; U.S. Geological 

Survey Professional Paper 1277-B, 49 p.

Lane, E. W., 1937, Stable channels in erodible material: American

Society of Civil Engineers Transactions 63, p. 123-142.

Leopold, L. B., and Maddock, Thomas, Jr., 1953, The hydraulic 

geometry of stream channels and some physiographic implications: U.S. Geological Survey Professional Paper 252,57 p.

Missouri River Basin Commission, 1975, Land conservation and 

sedimentation, Platte River basin, Nebraska Level B Study, 

Technical Paper Omaha, Nebraska, 214 p.

Parker, Gary, 1977, Self-formed straight rivers with stable banks and 

mobile bed in non-cohesive alluvium. Part I. The sand-silt river: 

Dept. of Civil Engineering, University of Alberta, Alberta, 

Canada, 56 p.

U.S. Fish and Wildlife Service, 1981, Platte River ecology studySummary report: U.S. Department of the Interior, Northern 

Prairie Wildlife Research Service, Jamestown, N. Dak., 187 p.

U.S. Inter-Agency Committee on Water Resources, 1957, Some 

fundamentals of particle size analysis, Report No. 12, in A Study 

of methods used in measurement and analysis of sediment loads 

in streams: Minneapolis, Minnesota, St. Anthony Falls Hydraulic 

Laboratory, 55 p.

Williams, G. P., 1978, The case of the shrinking channels the North 

Platte and Platte Rivers in Nebraska; U.S. Geological Survey Circular 781,48 p.

A Stochastic Streamflow Model and 

Precipitation Model for the 

Platte River from Gothenburg to 

Grand Island, Nebraska

By ALDO V. VECCHIA, JR.

HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 12 7 7-F

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1983

CONTENTS

	Page

Abstract F 1

Introduction 1

Acknowledgments 3

General modeling scheme 3

Precipitation model 4

Single-station models 4

Combined-station model 9

Calculation of drought probabilities 11

	Page

Streamflow model F19

. 19

_ 25

 29

 33

 33

. 35

Single-station models 

Combined-station model 

Simulation and evaluation of probabilities 

Pretipitation-streamflow correlation 

Selected references

ILLUSTRATIONS

FIGURE 1. Map showing location of study area 

2. Graph of monthly precipitation at Gothenburg, 1939-1978 

3. Graph of monthly precipitation at Kearney, 1939-1978 

4. Graph of monthly precipitation at Grand Island, 1939-1978 

5. Graph of autocorrelations and spectral density of monthly precipitation at Kearney, 1939-1978 

6. Graph of autocorrelations for residuals at Gothenburg, Kearney, and Grand Island with 95-percent confidence limits

7. Graph of histograms of residuals for Gothenburg and Grand Island 

8. Graph of monthly precipitation simulation of 40 years for Gothenburg 

9. Graph of monthly precipitation simulation of 40 years for Kearney 

10. Graph of monthly precipitation simulation of 40 years for Grand Island 

11. Graph of actual monthly means versus means from 10 simulations for Kearney 

12. Graph of historical sequence of seasonal discharges at Overton gaging station, 1943-1979 

13. Graph of historical sequence of seasonal discharges at Odessa gaging station, 1943-1979 

14. Graph of historical sequence of seasonal discharges at Grand Island gaging station, 1943-1979 

15. Graph of seasonal autocorrelations 

16. Graph of residuals for Odessa 

17. Graph of 50-year simulation of streamflow at Overton from combined-station model 

18. Graph of 50-year simulation of streamflow at Odessa from combined-station model 

19. Graph of 50-year simulation of streamflow at Grand Island from combined-station model 

Page 

.F 2

5

6

7

8

9

10

12

13

14

17

21

22

23

24

26

29

30

31

TABLES

Page

TABLE 1. Precipitation statistics for Gothenburg, Kearney, and Grand Island, 1934-1978 F 4

2. Residual statistics for Gothenburg, Kearney, and Grand Island 1934-1978 11

3. Monthly means and standard deviations for actual precipitation data and 10 model simulations of 40 years each for

Gothenburg statistics 15

4. Monthly means and standard deviations for actual precipitation data and 10 model simulations of 40 years each for

Kearney statistics 15

5. Monthly means and standard deviations for actual precipitation data and 10 model simulations of 40 years each for

Grand Island statistics 16

in
IV CONTENTS

TABLE 6. Quantiles of actual data versus simulation F17

7. Drought severity levels and corresponding estimates of cumulative distribution function 18

8. Probabilities of some droughts of duration m years or longer for Gothenburg 20

9. Probabilities of some droughts of duration m years or longer for Kearney 20

10. Probabilities of some droughts of duration m years or longer for Grand Island 20

11. Probabilities of some droughts of duration m years or longer for 3-station average 20

12. Flow statistics for Overton, Odessa, and Grand Island, 1943-1979 24

13. Individual-station streamflow models 25

14. Statistics of residuals from individual-station models, 1945-1979 25

15. Matrices of autocorrelation of residuals 26

16. Seasonal statistics for actual streamflow data and 10 model simulations for Overton 27

17. Seasonal statistics for actual streamflow data and 10 model simulations for Odessa 27

18. Seasonal statistics for actual streamflow data and 10 model simulations for Grand Island 27

19. Significant cross correlations between residuals from individual-station models 28

20. Full-rank decompositions of seasonal-covariance matrices 32

21. Estimates of probability of level x being surpassed at least m times over next 50 years 33

22. Estimated correlations between monthly precipitation at Gothenburg and at Grand Island with monthly streamflow at

Overton - 34

23. Estimated correlations between monthly precipitation at Gothenburg and at Grand Island with monthly streamflow at

Grand Island 34

24. Estimated correlations between seasonal precipitation at Gothenburg and at Grand Island with seasonal streamflow at

Overton 35

25. Estimated correlations between seasonal precipitation at Gothenburg and at Grand Island with seasonal streamflow at

Grand Island 35

CONVERSION TABLE

Multiply

inches

cubic feet per second

By

0.0254 

0.028

To Obtain

meters

cubic meters per second

LIST OF SYMBOLS

E = expected value

C = nonnegative transformation constant

F = mass function value

/ = counter based on drought limits

J = total number of stations

j = station index

k = season index

L = size of random sample in drought calculation

( = rainfall level in drought analysis (inches)

N = length of precipitation record

n = year index

s = number of seasons per year

t = time index (years)

U = March-April precipitation totals (inches)

V = May-August precipitation totals (inches)

variable representation for seasonal time series

variable representation for transformed series

vectors of parameters in precipitation model

residual component for Grand Island streamflow 

= residual component in precipitation model (inches) 

= independent normal random variate 

= streamflow covariance matrix 

= residual component for Overton streamflow model (cubic feet

X =

Z =

a =

8 =

X = parameter in Box-Cox transformation

£ = residual component for Overton streamflow model (cubic feet

per second) 

a = standard deviation of residual component in precipitation

models (inches)
HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

A STOCHASTIC STREAMFLOW MODEL AND

PRECIPITATION MODEL FOR THE PLATTE RIVER FROM

GOTHENBURG TO GRAND ISLAND, NEBRASKA

By ALDO V. VECCHIA, JR.

ABSTRACT

A stochastic model of monthly precipitation at Gothenburg, 

Keamey, and Grand Island, Nebraska, is developed. The model 

allows for simulation of single-station or joint-station precipitation 

and estimation of probabilities of future precipitation events. Some 

probabilities of droughts of differing severities and durations over the 

next 50 years are estimated by using the resulting model.

A stochastic model of seasonal streamflow at the Overton, Odessa, 

and Grand Island, Nebraska, gaging stations of the Platte River is 

also presented. Three seasons were chosen to correspond to differing 

periods of flow and vegetation development along the riven (1) Season 

1 consists of aggregated flows for September through February (base 

flow period); (2) season 2, aggregated flows for March and April 

(snowmelt flows); and (3) season 3, aggregated flows for May through 

August (time of seed drop by riparian vegetation). The model can be 

used for single-station or joint-station simulation of streamflow and 

estimation of probabilities.

Finally, it is recognized that the precipitation series may have an effect on the streamflow series. Although this effect is not modeled 

because of limited data collection, some cross correlations between 

the two hydrologic series are presented to allow preliminary estimation of the changes in streamflow resulting from changes in 

precipitation.

INTRODUCTION

A reach of the Platte River in south-central Nebraska 

has been designated a critical habitat reach for migratory waterfowl, especially sandhill and whooping 

cranes. These birds are attracted to the area partly 

because of the local geomorphic characteristics of the 

river channel; to maintain these geomorphic processes 

and preserve these habitat characteristics, the 

hydrology of the region must be effectively managed. 

Perhaps the two most critical elements for properly 

managing both the habitat and the economic development along the river valley are understanding and predicting the hydrology.

This report presents stochastic models of precipitation and streamflow for the critical reach of the Platte 

River, which is defined as the reach extending from Lexington to Grand Island, Nebraska (fig. 1). Precipitation 

stations at Gothenburg, Keamey, and Grand Island, 

Nebraska, are assumed to represent adequately the precipitation patterns within the critical reach. Data from 

these stations are used to model joint-monthly precipitation values. A three-season flow series is jointly modeled for the gaging stations at Overton, Odessa, and 

Grand Island, Nebraska, because of complexity of the 

monthly streamflow time series. The three flow seasons 

are defined as September through February (season 1), 

March and April (season 2), and May through August 

(season 3). season 1 represents the base flow period; 

season 2 represents the period of high flows from snowmelt in the Rocky Mountains; and season 3 represents 

the approximate time of seed drop by riparian vegetation and seedling germination and establishment in the 

channel.

The precipitation and streamflow models are used for 

simulation and evaluaton of probabilities pertaining to 

events of interest, including periods of low precipitation 

and high or low streamflow occurrences. These events 

become important when causes of channel narrowing, 

such as vegetation encroachment and maintenance of 

wetland environment, are studied.

The precipitation and streamflow models were developed individually rather than jointly because of time 

and resource limitations. A joint model would involve a 

detailed study of the effects of drought on nearby irrigation pumping, and, in turn, on the operating rules of the 

many diversions and timed reservoir releases of this 

highly regulated river. Some statistical correlations between the precipitation and streamflow series are presented in a later section of this report.

Fl
SOUTH DAKOTA

43'

104° 103° 102

______ ^S^STPlattc River

KANSAS

FIGURE 1. Location of the Platte River Study area from Gothenburg to Grand Island.
STOCHASTIC STREAMFLOW AND PRECIPITATION MODELS FOR PLATTE RIVER, NEBRASKA F3

Both the precipitation and streamflow models are designed to maintain cross correlation between stations, 

to allow simultaneous simulation of the three station 

series; however, individual models for each station remain autonomous, to allow concentration on a single 

station for special purpose studies. The interstation correlation structure is maintained by allowing residuals 

from the single-station models to be correlated.

ACKNOWLEDGMENTS

The author wishes to express his gratitude to the following for their valuable assistance: M. R. Karlinger, 

R. F. Hadley, and C. F. Nordin, Jr. In addition, part of 

this research was conducted by the author under a grant 

from the National Science Foundation that was supervised by Prof. D. C. Boes, Department of Statistics, 

Colorado State University, Fort Collins, Colorado.

GENERAL MODELING SCHEME

Both the precipitation and streamflow models are 

applications of a general technique for modeling 

multistation seasonal time series. This technique is 

briefly outlined in this section. A discussion of alternative modeling methods will not be given; the method 

used here is justified by showing its applicability to the 

precipitation and streamflow series.

Suppose one has observed a seasonal time series consisting of s seasons per year for each of N consecutive 

years, at each of J interrelated stations. Denote this time 

series as:

7=1,2,..., J,n=0,l,..., N-l, fc= } ,

where

j is the station index;

n is the year index;

k is the season index; and 

t(n,k}=ns + k is the cumulative time index. 

The likelihood of certain extreme events involving the 

process over the years N, AH-1,..., N+M, where M is 

large in comparison to N, can be determined by using a 

stochastic model based on the observed series.

Let -Xy? ,i = X® ,. + e, denote the model for

the 7th station, where X® , . is the deterministic or pre- r, .

t(n,k)

dieted component of ,. , and e ,, is the random t(n,k) t\n,K)

or residual component. To allow both autonomy of the 

individual station models and recursive simulation of

the time series, X® , . is assumed to be the linear func- 1\nji)

tion of previous values of the series at the 7th station, and 

of certain parameters that may be dependent on seasons 

but not on years:

where ak (/), k = 1,2..., s, are vectors of parameters to be 

estimated. The single-station model residuals, which 

could be correlated, are assumed to follow a normal 

distribution with mean 0. Correlation of the withinstation residuals occurs in the streamflow model but not 

in the precipitation model. Interrelations between stations can be maintained in the model by allowing residuals from single-station models to be correlated between 

stations. For example, if a high (low) value for station 1 is 

usually accompanied by a high (low) value for station

2, then e

(D

t(n,k) would be positively correlated.

Many types of time-series models useful for analysis of 

hydrologic data fit the general form given in the previous paragraph. Some examples are auto-regressive 

integrated moving average (ARIMA) models (Box and 

Jenkins, 1975), periodic autoregression models (Pagano, 

1978), and trigonometric linear models (Graybill, 1976). 

Trigonometric linear models were chosen for the precipitation model and periodic autoregressions with moving 

average components in the residuals were chosen for the 

streamflow model. Parameters were estimated by the 

method of least squares.

The assumption that residuals are normally distributed is often not true when untransformed time series 

are modeled, especially hydrologic data. To achieve normality for residuals, a Box-Cox transformation often can 

be utilized (Box and Cox, 1964). This transformation 

follows the form (the station index is dropped for 

convenience):

t)\=

where

, \ \ogjx M

is the untransformed series, and 

Cis the nonnegative constant, for which 

for all t(n,k), n=0,l,..., N-l, 

s.

The value of X for which residuals from the model of the

resulting series, {(zt(n Jx}> most closely followed a normal distribution was determined for both the precipitation and streamflow series, using a maximum likelihood
F4 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

technique. For details of this technique and for an 

analytic interpretation of the resulting transformation, 

see Vecchia (198 la).

PRECIPITATION MODEL

The time series used for development of the precipitation model consists of monthly precipitation totals, in inches, at the Gothenburg, Kearney, and Grand Islands, 

Nebraska stations, from January 1934 through 

December 1978. Monthly means and standard deviations of these series are listed in table 1. The large 

differences in means and standard deviations among 

months must be accounted for in the model either by inclusion of seasonally varying mean and variance components or by transforming the raw data; the Box-Cox 

transformation is adequate for removing seasonally in 

the variances; a periodically varying deterministic component is added to account for the monthly means. 

Graphs of the series (figs. 2, 3, and 4) show that the data 

truncated at zero and positively skewed, indicating that 

a model fit to the untransformed data would have a nonnormally distributed random component. For example, 

if the deterministic part of the model yields a value of 0.5 

inch for January 1951, then the random component for 

that month cannot be less than 0.5 inch, because 

negative precipitation values are impossible. The BoxCox transformation of the data alleviated this problem.

SINGLE-STATION MODELS

Estimated autocorrelations and spectral density for 

Kearney (fig. 5) indicate a strong periodicity of 12 

months. Two classes of models that can be fit to series 

exhibiting periodic autocorrelation structure are autoregressive integrated moving average (ARIMA) models 

(Box and Jenkins, 1975) and trigonometric linear 

models (Graybill, 1976). For a complete description of

the fitting of these two types of models to the singlestation series, as well as a comparison between models, 

see Vecchia (198la). Only the trigonometric models are 

presented here, because they fit the observed series 

better than the ARIMA models, and because they are 

easier for simulation and evaluation of drought 

probabilities.

Let \X^\ t=1,2,3...} denote the precipitation series 

for the 7 th station with 7=1 corresponding to Gothenburg; j=2 corresponding to Kearney; and 7=3 corresponding to Grand Island, with t=l corresponding to 

January 1934. The values X=l/3 and C=0.01 yielded the 

optimal Box-Cox transformation for all three stations, 

so the original series were transformed to:

Zf =[(x,</)+.Ol)1/3 -l]* 3,7=1,2,3.

The cube-root transformation has been analyzed by 

quantifying an explanation of skewness in precipitation 

distributions (Stidd, 1970). The transformed series were 

modeled as follows:

Gothenburg: 

41 )=0.2009-1.1956*cos^-0.1595*sin

\.2i

(1)

12

+0.1293*cos-+0.1089*sin

o 4

where e^ are iid (independent, identically distributed) normal (0,0.8612); R2=50.2 percent.

Kearney:

(2)

ZS2>=0.3492-1.1637*cos 0.1708*sin 

i Zt 12

+0.1699*sin -0.1367*sin-^+el2>; 4 6

where {42>} are iid normal (0.0.8982); R2=47.0 percent.

TABLE 1. Precipitation statistics for Gothenburg, Kearney, and Grand Island, 1934 to 1978

Month

Jan.

Feb.

Mar.

Apr.

May.

June.

July.

Aug.

Sept.

Oct.

Nov.

Dec.

Gothenburg

Mean 

(inches)

0.459

.500

1.220

2.156

3.431

4.118

2.587

2.493

1.892

1.045

.597

.473

Standard deviation 

(inches)

0.381

.440

.881

1.516

2.120

2.279

1.610

1.285

1.453

1.163

.588

.344

Mean 

(inches)

0.511

.688

1.357

2.420

3.915

4.141

2.962

2.410

2.451

1.348

.730

.576

Keamey

Standard deviation 

(inches)

0.401

.539

1.138

1.670

2.227

2.781

1.911

1.479

1.986

1.252

.849

.473

Grand Island

Mean 

(inches)

0.525

.786

1.238

2.421

3.864

3.871

2.710

2.447

2.443

1.031

.787

.603

Standard deviation 

(inches)

0.390

.641

1.067

1.493

2.080

2.331

2.040

1.621

2.153

.951

.837

.550
12.0

24 48 72 96 120 144 168 192 216 240 264 288 312 336 360 384 

MONTHS

FIGURE 2. Monthly precipitation at Gothenburg, January 1, 1939 through December 31,1978.
15.0

13.5

12.0

ft 10.5

I 

O

^ 9.0

g 7.5

I

9: 6.0 

O

LLJ

cc

°- 4.5

3.0

1.5

0.0

1 T

24 48 72 96 120 144 168 192 216 240 264 288 312 336 360 384 

MONTHS 

FIGURE 3. Monthly precipitation at Kearney, January 1,1939 through December 31,1978.
I I I I I I

264 288 321 336 360 384 

120 144 168 192 216 240

MONTHS
F8 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

1.0

0.5

ui

cc

§ 0.0 

O

-0.5

-1.0

10 20 30 

LAG, IN MONTHS

40 50

1.2

1.0

0.8

0.6

O ui

§5 0.4

0.2

CO 

Z 

Ul

Q

0.0

100 12.0 5.0 3.4 

PERIOD, IN MONTHS

2.5 2.0

FIGURE 5. Autocorrelations and spectral density of the monthly precipitation totals at Kearney, January 1, 1939 through

December 31, 1978.

Grand Island:

2?rt 2ir£ 43>=0.3187-1.117*cos -+0.1988*sin

J.^ 4

+0.1216*sin-0.1097*sin 6 12 (3)

where {ej31} are iid normal (0,0.8952); R2=45.1 percent.

Residuals from each of the above models were examined to insure that the following assumptions were not 

violated: (1) The residuals et are mutually independent; 

and (2) et is distributed normally, with mean 0 and 

variance a2 for all t. A visual inspection of the graphs of 

the residuals versus time for each station indicated no
STOCHASTIC STREAMFLOW AND PRECIPITATION MODELS FOR PLATTE RIVER, NEBRASKA F9

1.0

0.5

0.0

-0.5

-1.0

Gothenburg

1 .U

RELATION

3 O

3 01

GC \jf\j

O 

0

e

< -0.5

.1 n

I I I I III

Kearney

- -

I I I I III

1.0

0.5

0.0

-0.5

-1.0

I I

Grand Island

10 15 20 25 30 35 40

LAG, IN MONTHS 

FIGURE 6. Autocorrelations for residuals at Gothenburg, Kearney, and Grand Island within 95-percent confidence limits.

trends or abnormalities. Graphs of the autocorrelations 

of the residuals for each station, along with 95-percent 

confidence limits assuming white noise (fig. 6), show that 

the residuals have no significant autocorrelation. A 

histogram of the residuals for Gothenburg and Grand 

Island (fig. 7), with the series statistics (table 2), show 

that the residuals appear to be normally distributed, but 

that some differences exist in the means and standard

deviations among the months. The differences were considered minor enough for the model to be used.

COMBINED-STATION MODEL

Models were determined for each station individually. 

However, if joint probability statements are to be made 

about the three stations, a multivariate structure must
F10 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

0.6

0.4

0.2

O

a- °-°

LU 0.6

LU

cc

0.4

1 I I

Grand Island

211

195

61

10

53

10

0.2

0,0

I I I 

Gothenburg

213

55

I

198

64

J_L

<-2.0 -1.5 -05 0.5 1.5 >2.0 

MIDPOINT OF IIMTERVAUIIM INCHES

FIGURE 7. Histograms of residuals for Gothenburg and 

Grand Island.

be added to the model. Because the stations are geographically near each other, they are assumed to be 

similar in their precipitation patterns. Therefore, if the 

error in predicting rainfall at any one station is a large 

positive number (the rainfall is much greater for that 

month than the model predicts), then the errors at the 

other stations should tend to be positive. This is indeed 

the case, as the estimated covariance matrix of the computed residuals is:

GothenA burg 

£= Kearney 

 Grand

Island ,

Gothen- Grand 

burg Kearney Island

0.741

.546

.484

0.546

.805

.622

0.484

.622

.799 ;and

the corresponding estimate of the correlation matrix is: 

Gothen- Grand 

burg Kearney Island 

Gothen1.0 0.706 0.628 

.706 1.0 .773

A burg 

R= Kearney 

~~ Grand

.628 .773 1.0

Therefore, the final model for the joint monthly 

precipitation series at Gothenburg, Kearney, and Grand 

Island is:

Gothenburg: 

Kearney: 

Grand Island:

(4a) 

(4b) 

(4c)

where ^ are the deterministic components given in 

equations 1, 2, and 3 of the previous section and the sequences {!t}={(et(1), et(2)' ((3))} are independent and identically distributed trivariate normal random vectors, 

with mean Q and covariance matrix £. The deterministic 

components are periodic functions with period 12 (t l 

corresponding to January).

The purpose of the model is to make probability statements about events in the future, not to predict specific 

future precipitation values. If direct evaluation of the 

probability of an event from the model is not possible, 

then a number of future realizations can be generated to 

determine frequency of the event. The simulation of 

joint-station precipitation for a particular month proceeds as follows:

1. Generate three independent normal random variates with mean 0 and variance 1, fotl, r)t2, r)t3), from 

an existing normal random generator

2. Compute (1) =0.8608*r;a, e (,2) =0.6346*r;tl 

+0.6347*i;t2, and ef} =0.5627*r;tl +0.4167*i;t2 

+0.5557*r?t3;

3. add the corresponding deterministic components 

to the residuals of (4) to obtain ti]\ Zf, and ZJf\ 

and

4. Untransform 7^ to get precipitation in original 

units:
STOCHASTIC STREAMFLOW AND PRECIPITATION MODELS FOR PLATTE RIVER, NEBRASKA 

TABLE 2. Residual statistics for Gothenburg, Kearney, and Grand Island, 1934 to 1978

Fll

Month

Jan.

Feb.

Mar.

Apr.

May.

June.

July.

Aug.

Sept.

Oct.

Nov.

Dec.

Total

Gothenburg

Mean 

(inches)

0.059

-.100

-.023

-.030

.021

.117

-.128

.169

-.158

-.065

.074

.062

0.0

Standard deviation 

(inches)

0.690

.699

.756

.947

1.017

.911

.934

.718

1.048

1.025

.887

.628

Mean

(inches)

-0.054

-.026

.093

-.064

-.046

.099

-.016

-.093

.088

.011

-.089

.098

0.0

Kearney

Standard deviation 

(inches)

0.631

.714

.870

.894

1.064

1.003

.869

.805

1.056

.969

1.074

.779

Grand Island

Mean 

(inches)

-0.120

.041

-.003

-.044

.001

.105

-.099

.010

.125

-.234

.108

.109

0.0

Standard deviation 

(inches)

0.653

.705

.848

.895

.912

.915

1.042

.831

1.079

1.002

.999

.784

Graphs of 40-year model simulations are presented for 

Gothenburg (fig. 8), Kearney (fig. 9), and Grand Island 

(fig. 10).

One method of evaluating model adequacy is to determine how well it reproduces monthly means and standard deviations of past data Note that the historical 

record is assumed to be one possible realization from an 

underlying model driving the system. Therefore, the purpose is not to reproduce past statistics exactly, but to 

determine that the realization that occurred could have 

come from the developed model within a reasonable 

margin of accuracy (which depends on the purpose of the 

model). Monthly means and standard deviations for the 

actual data and for 10 model simulations of 40 years 

each are presented in table 3 (Gothenburg), table 4 

(Kearney), and table 5 (Grand Island). A graphical 

display of the means for Kearney is shown in figure 11. 

Data in the tables indicate that values for January and 

February seem too large in the simulations for Kearney 

and Grand Island, and the September simulations may 

be slightly distorted. The distribution of values for all of 

the months combined is another check of the adequacy 

of the model. Although these values do not represent a 

random sample from a single distribution, the simulated 

sequences should closely resemble the past data. Some 

quantile values of actual versus simulated data are 

shown in table 6.

CALCULATION OF DROUGHT PROBABILITIES

The discussion in this section shows how the precipitation model can be used: (1) For direct evaluation of the 

probability of a precipitation shortage of given severity 

in any particular month; and (2) for determination of the 

probabilities of multi-station and multi-month events. 

The probabilities from (1) and (2) are used to determine 

the likelihood of droughts of given severity and durations over the next 50 years.

Yn=f({ X$ ,7=1,2,3, *= 1,2, ...,12})

Where / is any real-valued function of the monthly 

precipitation values of year n. Under the precipitation 

model, Yn and Ym are independent and identically 

distributed random variables for all m ^ ra. This allows 

easy calculation of probabilities involving the series Y^, 

YN+I, ..., YN+M (where N I is the current year) from 

the cdf (cumulative distribution function) of Yn, 

FY(x)=P[Ym <x], because (YN, YN+l, ..., YN+M) is a 

random sample of size M+l from a population with cdf 

FY(x). The calculation of FY(x) for two cases proceeds as 

follows:

1. To evaluate the probability of the rainfall at a particular station in a month k of year n falling below level 

f, first let Yn=X^nk^ (the station index is dropped for 

convenience). Because the Box-Cox transformation, 

Zfaft, is monotone increasing in X^n^, probability 

statements about X^n^ can be directly related to probability statements about

Letting £'={(£ -I- .01)1/3 -l}* 3, this probability becomes:

(5)

where fj-^k) *s the deterministic component for season 

k and a is the residual standard deviation for the particular station of interest (see the previous section). This 

probability is easily evaluated from standard normal 

tables, since e^k) /a *s normally distributed with mean 0 

and unit variance. For example, to compute the probability that the rainfall at Grand Island in June of any

STOCHASTIC STREAMFLOW AND PRECIPITATION MODELS FOR PLATTE RIVER, NEBRASKA F13

«

I

!

S3HONI Nl 'NOIlVlldlOBUd
I I I I

216 240 264 288 312 336 

MONTHS
STOCHASTIC STREAMFLOW AND PRECIPITATION MODELS FOR PLATTE RIVER, NEBRASKA F15

TABLE 3. Monthly means and standard deviations for actual precipitation data and 10 model simulations of 40 years each for Gothenburg

statistics

[Mean values (upper number) standard deviations (lower number) in inches]

Jan. Feb. Mar. Apr. May. June. July. Aug. Sept. Oct. Nov. Dec.

Actual Data

0.440 

.381

0.500 

.440

1.220 

.881

2.156 

1.516

3.431 

2.120

4.118 2.587 

2.279 1.610

2.493 

1.285

1.892 

1.453

1.045 

1.163

0.597

.588

0.473 

.344

Simulations

1

2

3

4

5

6

7

8

9

10

.^02 

.569

.475 

.361

.545 

.523

.404

.548

.457 

.414

.574 

.536

.510 

.453

.405 

.602

.450 

.370

.499 

.597

.553

.585

.506 

.659

.735 

.671

.632 

.520

.719

.785

.569 

.614

.580 

.639

.579 

.572

.491 

.556

.626 

.562

TABLE 4. Monthly means and

.968 

.632

1.434 

1.264

1.265 

1.112

1.556 

.940

1.306 

1.127

1.133 

1.112

1.292 

.822

1.485 

1.132

1.320 

.952

1.455 

1.312

1.842 

1.281

2.027 

1.075

2.557 

1.503

2.300 

1.646

2.158 

1.721

1.940 

1.323

1.992 

1.065

2.405 

1.381

2.098 

1.441

1.940 

1.264

standard deviations

3.266 

2.070

3.198 

1.633

2.950 

1.531

3.617 

2.143

3.440 

2.318

3.191 

1.851

2.744 

1.703

3.256 

1.767

3.290 

2.159

3.575 

1.929

4.146 2.825 

2.271 1.855

3.802 2.594 

1.806 1.435

3.447 2.694 

1.927 1.414

3.700 2.606 

1.981 1.862

3.774 2.728 

2.015 1.613

4.446 2.317 

2.384 1.455

4.097 2.508 

1.888 1.686

3.782 3.134 

2.406 2.108

3.661 2.230 

2.329 1.182

4.474 3.439 

2.691 2.247

for actual precipitation data and 

statistics

1.736 

1.160

2.182 

1.496

2.702 

1.656

2.209 

1.632

2.506 

2.238

2.231 

1.326

2.711 

1.832

2.249 

1.518

2.110 

1.568

2.591 

1.673

2.169 

1.696

2.407 

1.383

2.101 

1.649

2.037 

1.596

1.883 

1.744

2.260 

1.495

2.524 

1.733

1.840 

1.186

2.249 

1.533

2.053 

1.108

10 model simulations

.918 

.978

1.096 

1.372

1.146 

.977

.942 

.773

1.045

.727

1.045 

.936

1.101 

.860

.985 

.880

.977 

.857

.817 

.788

.447 

.404

.511 

.566

.517 

.516

.463 

.436

.631 

.619

.596 

.679

.581 

.595

.528 

.581

.697 

.806

.649 

.707

of 40 years each

.423 

.423

.521 

.543

.432 

.380

.408 

.374

.588 

.622

.496

.478

.410 

.617

.333 

.399

.721 

.894

.698 

.832

for Keamey

[Mean values (upper number) standard deviations (lower number) in inches]

Jan. Feb. Mar. Apr. May. June. July. Aug. Sept. Oct. Nov. Dec.

Actual Data

0.511 

.401

0.688 

.539

1.357 

1.138

2.420 

1.670

3.915 

2.227

4.141 2.962 

2.781 1.911

2.410 

1.479

2.451 

1.986

1.348 

1.262

0.730 

.849

0.576 

.473

Simulations

1

2

3

4

5

6

7

8

9

10

.702 

.804

.730 

.570

.737 

.888

.537

.827

.629 

.663

.757 

.609

.832 

.694

.557 

.601

.941 

1.066

.600 

.547

.747 

.653

.635 

.780

.977 

1.099

.663 

.589

.927 

.992

.689 

.786

.653 

.608

.881 

.862

.617 

.606

.771 

.786

1.081 

.891

1.316 

1.148

1.142 

1.142

1.288 

.799

1.261 

1.316

1.002 

1.169

1.176 

.859

1.264 

.780

1.169 

.929

1.379 

1.179

1.950 

1.102

2.706 

1.317

2.960

1.787

2.545 

1.477

2.406 

1.552

2.422 

1.530

2.735 

1.605

3.065 

1.929

2.483 

1.531

2.382 

1.572

.70 

1.863

3.878 

1.776

3.727 

2.033

4.208 

2.224

3.936 

2.163

3.353 

1.688

3.424 

1.954

3.909 

1.801

4.170 

2.801

4.159 

1.944

3.876 2.868 

2.177 1.921

3.296 3.063

1.887 1.747

3.646 2.915 

2.122 1.675

3.667 3.172 

2.157 2.627

3.716 2.663 

1.939 1.598

4.222 2.951 

2.314 2.100

3.835 2.853 

1.888 2.056

3.593 3.274 

2.203 2.313

4.329 2.569 

2.528 1.494

4.568 3.862 

2.870 1.940

2.072 

1.482

2.829 

1.663

2.912 

1.867

2.387 

1.627

2.710 

2.237

2.639 

1.895

2.969 

1.917

2.316 

1.417

2.339 

1.814

2.761 

1.528

2.444 

1.554

2.474 

1.678

2.150 

1.432

1.972 

1.402

2.170 

1.925

2.673 

2.031

2.636 

1.696

1.915 

1.218

2.057 

1.349

2.330 

1.580

1.122 

.966

1.579 

1.606

1.506 

1.026

1.147 

1.015

1.408 

1.066

1.283 

1.453

1.317 

.913

1.038 

1.060

1.233 

1.171

1.039 

.840

.591 

.634

.640 

.539

.713 

.813

.705 

.652

.817 

.680

.904 

.739

.703 

.666

.644 

.594

.659 

.655

.789 

.794

.372

.477

.501

.447

.457 

.483

.616 

.654

.541 

.509

.530 

.509

.452 

.514

.396 

.409

.728 

.948

.694 

.733

Combined simulations

1-10

.702 

.734 

.109

.756 

.615 

.092

1.208 

1.025 

.153

2.567 

1.537 

.229

3.846 

2.024 

.302

3.875 3.021 

2.202 1.952 

.328 .291

2.593 

1.741 

.260

2.282 

1.586 

.236

1.267 

.122 

.182

.717 

.674 

.100

.529 

.585 

.087
F16 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

TABLE 5. Monthly means and standard deviations for actual precipitation data and 10 model simulations of 40 years each for Grand Island

statistics

[Mean values (upper number) standard deviations (lower number) in inches]

Jan. Feb. Mar. Apr. May. June. July. Aug. Sept. Oct. Nov. Dec.

Actual Data

0.525

.390

0.786 

.641

1.238 

1.067

2.421 

1.493

3.864 

2.080

3.871

2.331

2.710 

2.040

2.447 

1.621

2.443 

2.153

1.031 

.951

0.787 0.603 

.837 .550

Simulations

1

2

3

4

5

6

7

8

9

10

.789 

.882

.680 

.436

.847 

.712

.715 

1.002

.673 

.668

.835 

.582

.892 

.873

.585 

.503

.899 

.788

.609 

.597

.872 

.929

.610 

.766

1.086 

1.491

.809 

.680

1.004 

1.108

.691 

.626

.726 

.636

.774 

.782

.729 

.642

.738 

.633

1.241 

1.051

1.435 

1.239

1.108 

.966

1.437 

.664

1.276 

1.100

1.028 

1.189

1.298 

.977

1.289 

.873

1.301 

1.212

1.191 

.810

1.966 

1.350

2.586 

1.739

2.632 

1.642

2.287 

1.364

2.513 

1.325

2.349 

1.529

2.680 

1.413

2.724 

1.684

2.716 

1.944

2.111 

1.392

3.668 

2.021

3.716 

2.131

3.323 

1.943

4.023 

2.719

3.885 

2.292

3.632 

1.790

3.549 

1.853

3.697 

1.481

4.161 

2.698

3.849 

1.992

3.559 

2.217

3.148 

1.761

3.281 

1.766

3.167 

1.707

3.124 

1.721

3.724 

2.581

3.721 

1.978

3.232 

1.681

4.033 

2.304

4.065 

2.479

2.616 

1.582

3.199 

1.626

3.041 

1.694

21682 

2.128

2.807 

1.608

2.555 

1.797

2.790 

2.221

3.084 

1.945

2.383 

1.186

3.409 

2.005

1.896 

1.217

2.588 

1.743

2.770 

2.023

2.368 

1.396

2.481 

1.880

2.370 

1.767

2.773 

2.032

2.176 

1.171

2.351 

1.655

2.876 

1.765

2.249 

1.541

2.432 

1.491

2.088 

1.457

1.836 

1.252

2.034 

1.513

2.489 

1.769

2.319 

1.501

1.845 

1.202

2.198 

1.759

1.964 

1.162

1.042 

.904

1.200 

.937

1.508 

1.189

1.130 

.960

1.405 

1.494

1.132 

1.009

1.281 

.875

1.188 

1.509

1.118 

1.023

.933 

.852

.483 .386 

.506 .457

.748 .436 

.687 .350

.708 .433 

.747 .385

.704 .650 

.717 .719

.795 .539 

.586 .449

.888 .607 

.723 .565

.582 .589 

.561 .872

.711 .421 

.800 .565

.817 .742 

.819 .070

.816 .719 

.819 .855

year will be less than 1 inch, set k=6 and (=1. Then 

refer to the model for Grand Island (eq. 3 of the previous 

section) to obtain:

^6) =0.3187-1.1174*cos 7r+0.1988*sin Sic 

-0.1216*sin 27r-0.1097*sin 7r=1.4361.

With the above result and a«a=0.895 and f '=0.00997 

then:

P [43> >6) < l]=/> [eg> (6) /0.895< -1.5934]

=/)[Standard normal random variable < 1.5934J 

=0.056 (see equation 5).

2. For the case when Yn is a function of several 

months and (or) stations, such as Y= total precipitation 

for May through August at Grand Island, direct evaluation of FY(x) becomes difficult. However, FY(x) can be 

determined from model simulations. Using the simulation method outlines in the previous section, generate a 

random sample of Yn of size L, (ylt ..., yL) where L is a 

large number as determined below. If a certain number, 

say M, of the values ylt y2» » VL are ^ess ^an or equal to 

jc, and if L is large, than a good estimate of P\ym <x] 

would be FL (x) = Af/L, the proportion of the L values

which did not exceed x. To be more precise, define the 

sample cdf of Yn, FL(x), as:

where

liy.)

0, otherwise

By the Glivenko-Cantelli theorem (Gibbons, 1971) FL(x) 

converges uniformily with probability one to Fy(x). 

Therefore, FL(x) can be used as a approximation to Fy(x), 

if L is large enough to achieve accurate estimates for 

small values of x. As a general rule in this report, the 

sample cdf will be assumed to adequately estimate the 

true cdf for all x for which:

E > 10.

This rule can be used to pick L by noting that: 

L , fVi] E

1=1

=LFy(x).
STOCHASTIC STREAMFLOW AND PRECIPITATION MODELS FOR PLATTE RIVER, NEBRASKA F17

ACTUAL MEAN RANGE OF 10 

SIMULATED MEANS

O

O 2

Jan. Feb. Mar. April May June July Aug. Sept. Oct. Nov. Dec.

MONTHS 

FIGURE 11. Actual monthly means versus means from 10 simulations for Kearney.

TABLE 6. Quantiles (all months combined) of actual data versus simulation

Rainfall 

(percent 

less than 

tabular values)

10 

20 

30 

40 

50 

60 

70 

80 

90

Gothenburg

Actual 

(inches)

0.16 

.31 

.58 

.83 

1.22 

1.66 

2.19 

2.97 

4.26

Simulated 

(inches)

0.12 

.32 

.50 

.82 

1.07 

1.45 

2.12 

2.97 

3.82

Kearney

Actual 

(inches)

0.21 

.45 

.70 

.99 

1.42 

1.79 

2.40 

3.40 

4.71

Simulated 

(inches)

0.15 

.33 

.56 

.87 

1.33 

1.78 

2.32 

3.19 

4.44

Grand Island

Actual 

(inches)

0.19 

.45 

.68 

.95 

1.30 

1.68 

2.36 

3.26 

4.51

Simulated 

(inches)

0.17 

.32 

.60 

.93 

1.24 

1.58 

2.31 

3.17 

4.31

For example, if a value xm for which the precipitation exceeds with probability, 0.99 is the smallest x value of interest, then Fy(;cm)=0.01, and L would be 1,000, for one 

to expect, on the average, that:

W ,=io.

1=1

For the drought analyses in this report, 2,000 years of 

joint monthly precipitation from March through August 

were simulated for the Gothenburg, Kearney, and Grand 

Island stations. In addition, the monthly simulations 

were averaged over the stations to obtain an average 

precipitation series:

)+ 4V 3-The followingrandom
F18 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

variables were computed for each of the 2,000 years of 

simulated precipitation:

,j= 1,2,3;

7=1,2,3 ;

Un=Xt(n,3)+ Xt(n,4)> 

Vn=Xt(n,5)+ Xt(n,6)+ X t(n,7)+ Xt(n,8)'

U corresponds to precipitation totals for March and 

April (snowmelt season); V corresponds to totals for May 

through August (seed-germination period). The sample 

cdf's were computed for each of the above random 

variables at various values of x (the drought severity 

levels); they are given in table 7. The values of x were 

determined as follows: The precipitation record 

(1934-78) was used to estimate the mean rainfall, p, for 

each season-station combination in table 7, and severity 

levels were defined as /K, %/K, %/K, %/K, and %^. The rationale 

for using data rather than the model to estimate \i is that 

it is assumed because of the stationarity of the precipitation present environment in the critical reach was maintained during the period of record. Therefore, changes in 

precipitation, because of their effect on the river in environment, should be evaluated with reference to 

historical patterns. A value in table 7 under the column 

heading "cdf" is an estimate of the probability that the 

precipitation will fall below the corresponding severity 

level in any given year (for the corresponding seasonstation combination). Because L was chosen to be 2,000, 

cdf values below 0.005 are not very reliable estimates.

The probability of a drought of duration m years or 

longer during the 50-year planning period can be estimated by using table 7. Suppose a drought is said to occur whenever Yn is less than a certain amount x, and 

that the duration of the drought is the number of years

in a row that Yn is less than x. The problem above would 

reduce to finding distribution of the longest number of 

successes in a row a sequence of Bernoulli trials, with 

success probability equal to probability [yra <jc]. David 

and Barton (1962) show that if a sample of size r is drawn 

(with replacement) from an urn consisting of black balls 

and white balls, then, given that rj white and r2 = r TJ 

black balls were selected, the distribution of the longest 

run K of white balls is:

w

)=!-£

t=0 tl

r(tm+t) 

r(tm+t) '

where z^=tth factorial power of z=z(z l)...(e 1+1). Let 

M be the largest number of successes in a row in a sequence of 50 Bernoulli trials with success probability p; 

then:

=n]'P[N=n];

50

P[M>m+l]= £

n=0

where N is the total number of successes in the 50 trials 

(hence AT has a bionomial distribution). Therefore:

50

P[M>m+l]= P\N=n]

50

= £

where Pk{m,5Q,n) can be evaluated as accurately as 

desired. Note that the summation in Pj^m,r9 r^ is not 

really an infinite sum for fixed m, r, and rlf because the 

terms become zero, whenever t> r2 + 1 or tm+t > r±. In 

this context, the probability of one or more droughts of 

m+1 years or longer during the next 50 years would be:

TABLE 1. Drought severity levels and corresponding estimates of cumulative distribution function 

In, historical mean of season; cdf, cumulative distribution function]

Gothenburg

Season

March

and

April

May

through

Aug.

M

5/6 \i

4/6 \i

3/6/i

2/6 n

n

5/6 \i

4/6 \i

3/6 \i

2/6 n

Severity

level

(inches)

3.376

2.813

2.251

1.688

1.125

12.629

10.524

8.419

6.314

4.210

cfd

0.544

.416

.258

.141

.045

.580

.353

.139

.027

.001

Kearney

Severity

level

(inches)

3.777

3.147

2.518

1.888

1.259

13.428

11.190

8.952

6.714

4.476

cdf

0.560

.426

.277

.145

.053

.531

.312

.122

.025

.003

Grand Island

Severity

level

(inches)

3.659

3.049

2.439

1.829

1.220

12.892

10.743

8.595

6.446

4.297

cdf

0.541

.414

.267

.140

.051

.556

.327

.145

.026

.002

Three-station 

average

Severity

level

(inches)

3.604

3.003

2.403

1.802

1.201

12.783

10.819

8.655

6.491

4.328

cdf

0.538

.392

.233

.106

.028

.562

.294

.105

.015

.001
STOCHASTIC STREAMFLOW AND PRECIPITATION MODELS FOR PLATTE RIVER, NEBRASKA F19

where

p=Prob[Yn <*]

and a drought occurs whenever Yn < ;c._The probabilities of some droughts involving U$, V$, Un, and Vn are 

presented in tables 8 through 11.

STREAMFLOW MODEL

The streamflow time series consists of monthly 

average discharges (in cubic feet per second) from 

September 1942 through August 1979 (September 1942 

and water years 1943 to 1979) at the Overton, Odessa, 

and Grand Island gaging stations (see fig. 1). These 

series can be obtained from Petsch and others (1980). 

The streamflow model is a model of 3-season flow series 

obtained for each station by aggregating the monthly 

series as follows: Season 1 flows consist of the sum of the 

monthly series from September through February; 

season 2 flows consist of the sum of the monthly series 

of March and April: and season 3 flows consist of the 

sum of the monthly series from May through August. 

The year of season 1 will be designated by the year in 

which it ends (that is, season 1 of 1943 consists of 

September 1942 through February 1943). Graphs of 

these 111 seasonal flow totals in the 37-year period from 

water years 1943 to 1979 for each station are presented 

in figures 12 through 14. Seasonal statistics for Overton, 

Odessa, and Grand Island are summarized in table 12. 

The means and standard deviations appear to be 

significantly different across seasons (parameters will be 

included in the models which can account for these differences). Also, the positive skewness and kurtosis coefficients indicate that flows for individual seasons are not 

normally distributed. This distribution problem is 

solved by a Box-Cox transformation (see precipitation 

model) of the original flows to achieve a model in which 

residuals are nearly normal.

SINGLE-STATION MODELS

Autocorrelations of the flow series will be important in 

determining the appropriate model to fit to the data. In 

ordinary autoregressive-moving average (ARMA) timeseries modeling, the autocorrelation structure of the 

series is assumed to be the same for each season, an 

assumption which does not appear to be true in this case 

(fig. 15). An explanation of the term seasonal autocorrelations follows. LetX^^, n=0,l,2,..JV 1, £=1,2,..., s, be 

a seasonal time series, where t(n,k) = ns+fc; n is the year 

index (there are s seasons per year); and k is the season

index. The lag defined for members of the series X^n^ is 

a seasonal lag and not a yearly lag. For example, 

 %t(nji)-2' wnere & =3, is season number one of year n, 

and X^n^_4, where &=3, is season number 2 of year 

(n 1). The autocorrelation for season k at lagj is defined 

to be PkJ= Corr (x^^, X^^ and is assumed 

throughout to be independent of n. The values graphed 

in figure 15 are estimates p^-, &=1,2,3, 7=1,2,... 6 obtained by using the formula

_ i (V v v

- 77 n^Q ( Yt(n,k) Yt(n,k)-j>

where

N

and Y^nj^i_j=Q for t(n,k) 7<0. The class of periodic 

autoregression models are useful in modeling time series 

that have heterogeneous correlation structure among 

seasons. The models used to describe the single-station 

series fall under this class, for which a substantial base 

of theory has been developed (Pagano, 1978; Parzen and 

Pagano, 1979; Troutman, 1979). Only the statement of 

the models will be given here. For a complete exposition 

of the model fitting and parameter estimation, see Vecchia (1981b).

Results for the three stations are summarized in 

table 13. The notation has been changed slightly by 

dropping the cumulative time index, t\ Xn^k denotes the 

streamflow in season k of year n. The R2 value for season 

k is interpreted as the percentage of the variation of the 

observed data for season k from 1945 to 1979 (allowing 

for lag considerations), which is accounted for by the 

nonrandom component of the model. Note that the last 

season has a low R2 value. This does not indicate model 

inadequacy, but rather shows that season 3 variation is 

nearly random with respect to previous values in the 

series. However, season 3 is important in predicting 

season 1 of the following year; hence, it should be included in the model.

It is assumed for each station that {enj are iid normal 

random variables, with E(en)=Q, and Cov (en)=D (a 

diagonal matrix), or that the errors are independent from 

season to season. Residuals from the models from 1945 

to 1979 were examined to check these assumptions. 

Some statistics of the residuals are in table 14, which 

reveals no obvious deviations from normality, or from 

the assumption that E(en)=Q. A graph of the residual 

series for Odessa from 1945 to 1979 is shown in figure 

16; it is observed that no obvious trends are taking place. 

To check the assumption of no correlation between 

seasons, lag autocorrelation matrices for the residuals 

were examined. The lag k autocorrelation matrix of the
F20 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN 

TABLE 8. Probabilities of some droughts of duration m years or longer for Gothenburg

\li, historical mean of drought period, in inches]

Season

March

and

April

May

through

Aug.

Severity

level1

0= 3.376

5/60= 2.813

4/60= 2.251

3/60= 1.688

2/6,t= 1.125

0=12.629

5/6 0=10.524

4/6 0= 8.419

3/60= 6.314

2/6 0= 4.210

l

1.000

1.000

1.000

.999

.900

1.000

1.000

.999

.745

.049

2

1.000

.999

.939

.584

.091

1.000

.994

.574

.034

.000

3

0.994

.911

.475

.110

.004

.998

.785

.106

.001

.000

4

0.908

.596

.146

.016

.000

.951

.393

.015

.000

.000

m years

5

0.688

.298

.039

.002

.000

.788

.155

.002

.000

.000

6

0.446

.131

.010

.000

.000

.562

.056

.000

.000

.000

7

0.262

.055

.002

.000

.000

.363

.020

.000

.000

.000

8

0.147

.023

.001

.000

.000

.221

.007

.000

.000

.000

9

0.080

.009

.000

.000

.000

.130

.000

.000

.000

.000

'The severity level is the value (in inches) that defines the occurrence of a drought

TABLE 9. Probabilities of some droughts of duration m years or longer for Kearney

\ji, historical mean of drought period, in inches]

Season

March

and

April

May

through

Aug.

Severity 

level1

0= 3.777

5/60= 3.147

4/60= 2.518

3/6 0= 1.888

2/60= 1-259

0=13.428

5/6 0=11.190

4/6/*= 8.952

3/6/*= 6.714

2/6/*= 4.476

i

1.000

1.000

1.000

.999

.934

1.000

1.000

.998

.718

.139

2

1.000

.999

.960

.604

.123

1.000

.982

.485

.029

.000

3

0.996

.925

.544

.119

.007

.992

.665

.074

.001

.000

4

0.929

.627

.186

.018

.000

.887

.273

.009

.000

.000

m years 

5

0.735

.325

.053

.003

.000

.649

.091

.001

.000

.000

6

0.497

.148

.015

.000

.000

.405

.029

.000

.000

.000

7

0.305

.064

.004

.000

.000

.231

.009

.000

.000

.000

8

0.177

.027

.001

.000

.000

.125

.003

.000

.000

.000

9

0.100

.008

.000

.000

.000

.066

.001

.000

.000

.000

'The severity level is the value (in inches) that defines the occurrence of a drought

TABLE 10. Probabilities of some droughts of duration m years or longer for Grand Island

[/i, historical mean of drought period, in inches]

Season

March

and

April

May

through

Aug.

Severity 

level1

0= 3.659

5/6 0= 3.049

4/60= 2.439

3/6 0= 1.829

2/60= 1-220

0=12.892

5/6 0=10.743

4/6 0= 8.595

3/6 0= 6.446

2/6 0= 4.297

i

1.000

1.000

1.000

.999

.927

1.000

1.000

.999

.732

.095

2

1.000

.999

.950

.579

.122

1.000

.988

.604

.032

.000

3

0.994

.909

.508

.108

.006

.996

.712

.119

.001

.000

4

0.903

.589

.164

.015

.000

.924

.315

.018

.000

.000

m years 

5

0.680

.292

.045

.002

.000

.723

.112

.002

.000

.000

6

0.436

.128

.012

.000

.000

.484

.037

.000

.000

.000

7

0.255

.053

.003

.000

.000

.294

.012

.000

.000

.000

8

0.142

.022

.001

.000

.000

.169

.004

.000

.000

.000

9

0.077

.009

.000

.000

.000

.091

.000

.000

.000

.000

'The severity level is the value (in inches) that defines the occurrence of a drought.

TABLE \\.-ProbabiUties of some droughts of duration m years or longer for the three-station average

[/i, historical mean of drought period, in inches]

Season

March

and

April

May

through

Aug.

Severity 

level1

0= 3.604

5/6/*= 3.003

4/6 M= 2.403

3/60= 1.802

2/60= 1.201

0=12.983

5/6 0=10.819

4/60= 8.655

3/60= 6.491

2/60= 4.328

i

1.000

1.000

1.000

.996

.758

1.000

1.000

.996

.530

.049

2

1.000

.998

.900

.397

.039

1.000

.973

.392

.011

.000

3

0.993

.872

.384

.050

.001

.997

.604

.049

.000

.000

4

0.899

.518

.102

.005

.000

.932

.226

.005

.000

.000

m years 

5

0.671

.237

.024

.001

.000

.740

.070

.001

.000

.000

6

0.427

.097

.006

.000

.000

.504

.021

.000

.000

.000

7

0.247

.038

.001

.000

.000

.310

.006

.000

.000

.000

8

0.137

.015

.000

.000

.000

.181

.002

.000

.000

.000

9

0.074

.002

.000

.000

.000

.103

.000

.000

.000

.000

'The severity level is the value (in inches) that defines the occurrence of a drought.
STOCHASTIC STRE AMFLOW AND PRECIPITATION MODELS FOR PLATTE RIVER, NEBRASKA F21

co 

O

CO

<UJ 

CO

ce

UJ 

CO

5

D

O

o

 a

o

2-01 X SH1NOW-QN003S «3d I33d Nl 'NOSV3S «0d 39aVHOSIQ dO WHS
(M 

I

O

O

O 

O

oc

LJU

a.

266

228

190

UJ 152

o

m

D 

O

z

114

<LJU 

(/>

flC

S 76 

LJU

8

<

§

Q 38

12 24 36 48 60 72

CUMULATIVE NUMBER OF SEASONS

84 96 

FIGURE 13. Historical sequence of seasonal discharges at Odessa, Nebraska gaging station, water years 1943-1979.
STOCHASTIC STREAMFLOW AND PRECIPITATION MODELS FOR PLATTE RIVER/NEBRASKA F23

CO

to

<LU 

CO

D 

Z

LU

>

O

2-01. X SH1NOW-QNO03S H3d 133J 01800 Nl 'NOSV3S HOJ 39«VHOSia JO WflS
F24 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

TABLE 12. Flow statistics for Overton, Odessa, and Grand Island,

Nebraska, water years 1943 to 1979

[ft3/s-months, cubic feet per second-months]

Overton

Odessa

Grand Island

Season

1

2

3

1

2

3

1

2

3

Average

season 

total

(ft3/s-months)

8093.2

3641.9

4809.7

7585.5

3662.9

4363.8

7219.4

4068.6

4653.6

Standard 

deviation

(ft3/s-months

3922.6

2044.5

5108.1

3864.5

2062.8

4960.7

4184.1

1973.1

4643.8

Skewness

2.918

3.043

2.904

2.676

2.618

2.669

2.860

2.065

2.448

Kurtosis

11.068

11.927

8.554

9.757

9.438

7.368

10.962

6.564

6.456

residual vector en is defined as Cov (en, en _k) (note that 

lags are now in years). Estimates of these matrices for 

k=0,1,2,3 appear in table 15. Each estimate is based on 

about 35 observations, and an approximate standard error of the estimate is 1/V§5=0.17. Therefore, any value 

below about 0.3 in absolute value can be considered insignificant. The only problem is the lag 1 correlation for 

season 2 (Corr (en2 tn -i 2)). which is about 0.4 for each 

station, but drops off to near zero for the remaining lags.

This correlation can be preserved in the model by allowing en 2 to follow a moving-average process of order 1 

(Box and Jenkins, 1975). In other words, tn<2=Vn,2+® 

^n-i 2 wit*1 {^»,2' rc=0,l,...} a white-noise process. Moment estimates of 6 were determined to be 6=0.63 for 

Overton, and 0=0.5 for Odessa and Grand Island. A 

precise statement of the models with moving-average 

components included will be given in the next section. 

As a final check, the models were used to simulate 10 

realizations of 37 years each, the same length as the 

historical series, and the properties of the simulations 

were compared to the historical series. Some statistics of 

the simulations are in tables 16,17, and 18. Care must be 

taken in interpreting the tables owing to high variability 

of the skewness and kurtosis coefficients for such short 

data sets. The standard deviations for most of the 

simulations are lower than the respective observed standard deviations. This could indicate two things: (1) The 

observed standard deviation is higher than the long term 

standard deviation; (2) the standard deviations of model 

simulations are biased, possibly owing to the inverse 

transformation of model output. For purposes of this 

report, these differences did not warrant further investigation. Season 2 and 3 are of primary interest;

SEASON 1

OVERTON 

SEASON 2 SEASON 3

1.0 

0.8 

0.6 

0.4 

0.2 

0.0

ODESSA

O

1-

3

cc

cc 

O

O 

Ol -^

I.U

0.8

0.6

0.4

0.2

n.n

11111

-

.

-

 "

i i i i i

GRAND ISLAND

1.0 

0.8 

0.6 

0.4 

0.2 

0.0

01 23456 0123456 

LAG, IN SEASONS

FIGURE 15. Seasonal autocorrelations.

01 23456
STOCHASTIC STREAMFLOW AND PRECIPITATION MODELS FOR PLATTE RIVER, NEBRASKA F25

TABLE 13. Individual station streamflow models.

[Z, transformed streamflow variable X, seasonal streamflow; tt, residual component: R2, explained variation due to model]

Overton

tt )--i-ll(-0.1)-ni,i= 1,2,3 

Seasonal mean vector n'=(m, n* n3 ,)=(5.9000, 5.548, 5.569) 

Zn>1 =0.3632 * Zn _ 1>3 +0.1449 * Zn .^+^ 

ZBt2=1.0756*Zllil +6lli2 

Zn>3 =0.4646 * Zn, 2 +0.2631 * Zn _2i3 +6n>3 

Season: 123 

.R2: 67 76 12.4 

_______ percent percent percent

Overall R2=33 percent

Cov(en)=diag (0.00706, 0.00825, 0.08944)

Odessa

Zn>I.=log.(Xll> ,.+0.01)-w,i=l,2,3 

^'=(8.8427, 8.0965, 7.9568) 

Zn>1 =0.3423 * Zn _ u+0.1461 * Zn _ u+en ^ 

Zn>2 =0.9168 * Zn<1 -0.0982 * Zn _ u+e,,i2 

Zn>3 =0.7850 * Zn, 2 +eni3

Season: 123 

R1: 67 66 12

percent percent percent

Overall ,R2=28 percent

Cov(en)=diag (0.05082, 0.06616, 0.77623)

Grand Island

)-/*,-, i= 1,2,3 

/=(8.7668, 8.2185, 8.0729)

ZBil =0.4198 * Zn _ 1>3 -0.0469 * ZII _ 1>1 +0.1284 * Zn _ 2^+en ^ 

Zn 2 =0.6715 * Znti-0.0949 * Zn _ u +e,,i2

Season: 

.R2:

1

68 

percent

2

50 

percent

3

8.2 

percent

Overall ,R2 =26 percent

Cov(eJ=diag (0.07431, 0.08806, 0.74906)

TABLE 14. Statistics of residuals from individual-station models 1945 to 1979 (water years)

Overton

Mean 

Variance 

Skewness 

Kurtosis 

Maximum values 

Minimum values

Odessa

Mean 

Variance 

Skewness 

Kurtosis 

Maximum values 

Minimum values

Grand Island

Mean 

Variance 

Skewness 

Kurtosis 

Maximum values 

Minimum values

Sept. to Feb.

0.004 

.007 

.053 

-.761 

-.175 

.174

Sept. to Feb.

0.003 

.051

.098 

-.499 

-.493 

.500

Sept. to Feb.

0.011 

.074

.218 

.362 

-.658 

.610

March to April

-0.002 

.008 

-.055 

1.216 

-.261 

.222

March to April

0.000 

.067 

-.563

.287 

-.675 

.528

March to April

-0.002 

.088 

-.110 

.124 

-.632 

.654

May to Aug.

0.000 

.089 

.253 

-.872 

-.569 

.625

May to Aug.

0.004 

.776 

-.045 

-.107 

-2.206 

1.732

May to Aug.

-0.006 

.749 

-.110 

.124 

-2.259 

1.713

however, most of the season 2 skewness and kurtosis 

coefficients for the Odessa and Grand Island simulations are smaller than the observed values. This problem 

is not considered serious enough to cast doubt on the 

validity of the model.

COMBINED-STATION MODEL

Thus far, cross correlations between streamflow stations have not been considered. However, if simulations 

of more than one station are generated, these simula-
F26

2.5

1.5

0.5

HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

CO

Q

CO 

LU 

DC

-0.5

-1.5

-2.5

I I T

 

* * ' 

 

 

 

I I

12 24 36 48 60 72 

CUMULATIVE NUMBER OF SEASONS

84 96 108

FIGURE 16. Residuals (synthesized minus observed) for Odessa, Nebraska

TABLE 15. Matrices of autocorrelation of residuals

Lag

(years)

Season

0 1

2

3

1 1

2

3

2 1

2

3

3 1

2

3

i

1.0

-.053

.178

-.266

-.234

-.049

.125

-.088

.067

-.014

.178

.246

Overton

Season

2

-0.053

1.0

-.011

-.194

.446

.083

-.247

.107

-.058

-.197

.006

-.047

3

0.178

-.011

1.0

.020

-.150

-.070

.032

-.127

.045

.006

-.204

-.042

i

1.0

.064

.207

-.214

-.246

.047

.024 '--.178

.119

.024

.120

.200

Station

Odessa

Season

2

0.064

1.0

-.018

-.188

.403

-.015

-.131

.110

.059

-.163

-.108

-.051

3

0.207

-.018

1.0

-.003

-.024

-.200

.191

.004

.231

.056

-.215

-.086

i

1.0

-.105

.113

-.117

-.243

.077

-.057

-.261

.102

.013

.116

.245

Grand Island

Season

2

-0.105

1.0

.016

-.124

.396

-.046

-.074

-.039

.160

-.163

-.097

-.104

3

0.113

.016

1.0

.029

-.048

-.182

.099

.152

.214

.115

-.169

-.066

tions should maintain continuity between the stations. 

This will allow simulation of average flow series for two 

or three of the stations by simulating from the

combined-station model and averaging the appropriate 

values. Station continuity is maintained in the model by 

allowing the residual vectors, en, to be correlated from 

station to station. Let £ be the residuals for Overton, yn 

the residuals for Odessa, and dn the residuals for Grand

Island. The results are easier to interpret if the residuals 

are grouped together by season rather than by station, 

so define [e<i>]'=(£m, yni, 6J for i=l,2,3 and en '=(eM', en®', 

ej3)'). The autocorrelation matrices Corr (en, en_k) (note 

that lag values are now in years) were estimated for 

£=0,1,2,3; no significant values were found among the 

submatrices Corr (e$, 4/-J' k=Q,...,3 and M=j (a value is 

considered significant if it is greater than 0.3 in absolute
STOCHASTIC STREAMFLOW AND PRECIPITATION MODELS FOR PLATTE RIVER, NEBRASKA F27 

TABLE 16. Seasonal statistics for actual streamflow data and 10 model simulations for the same length for Overton, Nebraska

[Means and standard deviations are in cubic feet per second-months]

September through February

Mean

Standard

deviation Skewness Kurtosis Mean

March and April

Standard

deviation Skewness Kurtosis Mean

May through August

Standard

deviation Skewness Kurtosis

Actual data

8093 3923 2.918 11.068 3642 2044 3.043 11.927 4810 5108 2.904 8.554

Simulations

1 8489

2 6972

3 7796

4 7990

5 8972

6 8101

7 6902

8 7040

9 8159

10 8398

2822

2993

2730

3471

4044

3074

1825

2684

4082

3396

0.194

1.146

1.132

.899

1.795

1.085

.426

.725

.933

1.994

-0.602

.764

.558

-.161

4.885

.826

-.178

.222

.222

5.601

3750

3399

3705

3709

4674

4006

3145

3032

3705

3724

1550

2172

1676

1727

2989

1936

1040

1109

1809

1668

0.990

1.811

1.372

.853

2.830

1.789

.629

.455

1.010

3.605

1.411

2.897

1.591

.510

10.202

4.161

-.056

-.104

.693

16.009

4952

3592

4017

4173

5367

5153

3282

3630

5286

4218

4399

2965

3456

4661

3749

4867

1927

3752

5275

3806

3.029

1.757

2.489

3.216

1.200

3.274

.903

2.838

2.022

3.184

11.913

3.838

6.001

11.305

1.293

13.135

-.251

9.369

4.708

12.057

TABLE 17. Seasonal statistics for actual streamflow data and 10 model simulations for the same length for Odessa, Nebraska

[Means and standard deviations are in cubic feet per second-months]

September through February

Mean

Standard

deviation Skewness Kurtosis Mean

March and April

Standard

deviation Skewness Kurtosis Mean

May through August

Standard

deviation Skewness Kurtosis

Actual data

8093 3923 2.918 11.068 3642 2044 3.043 11.927 4810 5108 2.904 8.554

Simulations

1 7325

2 7645

3 6779

4 7513

5 7691

6 6533

7 7219

8 7183

9 6656

10 6734

2612

3642

2505

2839

2939

2666

3479

2282

2281

1939

0.108

1.325

1.189

1.638

1.036

1.125

1.670

.704

.751

.635

-0.785

1.685

1.156

3.144

1.075

.701

3.358

2.169

.946

-.061

3423

3671

3379

3863

3526

3707

3487

3311

3222

3150

1469

2208

1518

1594

1705

1510

1839

1340

1285

1158

1.168

1.438

.922

1.219

2.283

1.093

1.068

1.016

.583

.483

2.012

1.806

.227

1.180

7.422

1.422

.115

1.314

-.084

-.616

3612

4518

3987

4645

4965

3349

3877

3219

3483

2833

2679

4921

6098

5465

4829

3755

4559

2221

2695

2103

0.984

2.181

4.452

2.307

2.079

1.816

3.184

.939

1.608

1.851

0.197

5.366

21.502

4.597

4.661

2.204

11.803

-.153

2.713

3.834

TABLE 18. Seasonal statistics for actual streamflow data and 10 model simulations for the same length for Grand Island, Nebraska

[Means and standard deviations are in cubic feet per second-months]

September through February

Mean

Standard

deviation SkewnesS Kurtosis Mean

March and April

Standard

deviation Skewness Kurtosis Mean

May through August

Standard

deviation Skewness Kurtosis

Actual data

7219 4184 2.860 10.962 4068 1973 2.065 6.564 4653 4644 2.448 6.465

Simulations

1 7670

2 8815

3 7634

4 7784

5 6952

6 6865

7 6750

8 7843

9 9154

10 7694

4679

4068

3819

4386

3715

3160

3355

4111

5016

3351

2.179

1.153

1.654

2.818

1.536

1.229

1.619

.947

1.391

.383

5.272

1.661

3.667

10.631

2.913

1.382

2.105

-.210

1.998

-.942

4228

4502

3440

4028

3638

4279

4203

4727

4883

4173

1874

1920

1472

1812

1851

1671

2028

2956

2291

1968

2.005

.814

.704

1.002

1.564

.707

1.164

1.770

1.331

1.073

6.137

.212

-.178

1.162

3.146

.186

.783

4.042

1.867

.758

4400

6232

8386

5502

5903

4414

4896

6093

7523

4941

4816

4701

4929

8219

8254

3996

6069

8237

8093

4364

2.877

1.233

1.785

4.739

3.608

1.582

2.633

3.968

2.613

.995

9.581

.865

3.398

23.758

15.341

1.794

6.810

18.084

7.681

-.371
F28 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

value). All correlations between the residuals occur 

within the same season. Among the matrices Corr (e®, 

4fJk), the only significant values occur for &=0; i=1,2,3; 

k=l; and i=2. These matrices are given in table 19.

Recall from the individual models that a 

average component was added to the residuals for the 

second season. In particular, we have 

£-1. %t2=7;+0.5 -£-1, 5n2=6;+0.5 6;_! where 

6jJ and (£t, y*t 6*) are independent for n & t.

*l\ [f* * £*\ -fc,, %,.« ) 

It is straightfoward to show that if

Cov(e*)=

then Corr (e^, 42)) =

and Corr

0.00591 0.01586 0.01772

.01586 .05293 .05558

.01772 .05558 .07045

1.0 0.893 0.864]

.893 1.0 .910

.864 .910 1.0

[0.450 0.428 0.414

.339 .400 .364

.328 .364 .400

ils occur 

Corr (eg, 

i=l,2,o; 

Iel9. 

moving 

s for the

re (£*, 7*,

TABLE 19. significant cross correlations beti 

individual-station models

[Lag, in years]

Overton

Season 1

(September LagO Overton 1.0 

through Odessa .941 

February) Grand Island .871

Season 2

(March and Lag 0 Overton 1.0 

April) Odessa .893 

Grand Island .864

Lag 1 Overton .446 

Odessa .387

Grand Island .420

Season 3

(May through Lag 0 Overton 1.0 

August) Odessa .945 

Grand Island .918

Odessa

Z (0d) =0.9168* Z<0d)-0.0982*Z < 0d>+T*

n,2 n,l n-1,1 "

Z (W =0.7850* Z<0d>+7n ,

n,3 n,2 n'3

Z<G/) =0.4198* Z<G/> -0.0469*Z(G/)

ueen residi

Odsessa

0.941 

LO 

.913

.893 

1.0 

.910

.436 

.403

.410

.945 

1.0 

.988

+.5 7*_j

lals from

Grand 

Island

0.871

.913 

1.0

.864 

.910 

1.0

.430 

.395

.395

.918 

.988 

1.0

(7b)

(7c)

It is evident that the lag 1 matrix for season 2 in table 19 

can be explained by the moving average components.

It should be noted that the same parameter estimates 

obtained for the single-station models were used for the 

combined model rather than estimating the parameters 

in a multivariate sense. These estimates can easily be 

shown to correspond to the ordinary least squares 

estimates. This should not greatly affect the performance of the model for simulation.

The statement of the combined-station model is: Let 

transformed and mean standardized

values for Overton; let Zjjjp be the transformed and 

mean standardized values for Odessa; and let {z^f1 } be

the transformed and mean standardized values for 

Grand Island. (See table 13.) The final model becomes:

Z (Ov) =0.3632* Z<°u) +0.1449*Z(Ou) +£ ,

n,l n-1,3 n-1,1 n>1

Overton

= 1.

n,3

=0.4646* Z*0") +0.2631*Z<0t;> +£ ,

n-2,3 n'6 n,2

Z <0d> =0.3423* Z*0^ +0.1461*Z(0d> +7

n,l n-1,3

+0.1284* Z<G/) +6n1 n-2,3 "-1

n-1,1

Grand 

Island

=0.7757* Z<G/)+5

n,3 n,2

(8a)

=0.6715* Z<G/>+0.0949*Z(G/) +5*+.5 d* , (8b)

n,2 n,l n-1,1 " n-1

(80

Let MfNfe..!. Vi' ^ (42))'=fe V, 4 (43))'=(^3, 

7n3, 6n3). Then: ejf, 7=1,2,3, n=0,l,... are independent 

normal random vectors with

n-1,3 n-1,1 Yn,l

for

es:

<6a)

(6b)

(6c)

(7a)

Cov(cj?>)=

Cov (e<2>)=

.00706

.01782

.01993

.00591

.01586

.01772

COV (ej^)= .08944

.24913

.23767

Ee^=0 for 7= 1,2,3.

.01782

.05082

.05608

.01586

.05293

.05558

.24913

.77623

.75345

.01993

.05608

.07431

.01772'

.05558

.07045

.23767

.75345

.74906
STOCHASTIC STREAMFLOW AND PRECIPITATION MODELS FOR PLATTE RIVER, NEBRASKA F29

Graphs of 50-year simulations from the combinedstation model are given in figures 17, 18, and 19. The 

unusually high discharge values for the 72nd simulated 

values at Odessa and Grand Island (73,396 ft3/s-months 

for Odessa and 96,266 ft3/s-months for Grand Island) 

may seem at first to point to a model inadequacy. However, out of five hundred 50-year combined-station simulations from the next section, only eight contained 

values greater than 90,000, which indicates that this particular simulation happened to be an extreme case.

SIMULATION AND EVALUATION OF 

PROBABILITIES

The model of the previous section can easily be used 

for simulation of 3-station, 3-season flow series over the 

next 50 years. The complicated dependence structure be400

tween seasons and between stations causes direct 

evaluation of probabilities of most events of interest to 

be difficult. However, if one obtains N 50-year simulations from the model, n of which exhibit a certain event, 

then an estimate of the probability of that event occurring over the next 50 years would be n/N, assuming that 

all simulations are equally likely.

Suppose one has data for years 0, 1,..., t (t corresponds to 1979 here) and wants to simulate from the 

model for years t+1,..., t+50. Referring to table 13 and 

to any of the equations of the last section, one would proceed as follows:

1. Obtain the values of the series from years t and 

t l that are needed in the chosen equation for 

year t+1; these values are transformed as in 

table 13.

12 24 36 48 60 72 84 

CUMULATIVE NUMBER OF SEASONS

108 120 132 144 156

FIGURE 17. Fifty-year simulation of streamflow at Overton, Nebraska from the combined-station model.
______I_____I_____L

48 60 72 84 96 

CUMULATIVE NUMBER OF SEASONS

FIGURE 18. Fifty-year simulation of streamflow at Odessa, Nebraska from the combined-station model.
IN 

I 

O

X

CO

I

UJ 

CO

oc

o

u.

UJ

U 

oc

O

CO

O

S 

D

280

240

Q

Z 

O

a 200

CO 

oc

UJ

Q.

£ 160

O 

00

O

Z 120

O 

CO

80

40

12 24 36 48 60 72 84 96

CUMULATIVE NUMBER OF SEASONS

108 120 

FIGURE 19. Fifty-year simulation of streamflow at Grand Island, Nebraska from the combined-station model.
F32 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

2. Generate random vectors t+j> (2) f (2) (3) 

t ' e t+j' e t + j »

7 = 1,2,..., 50. The easiest way to do this is to generate a vector of three independent standard normal random variables for each season and each 

year and then transform them to obtain the 

desired covariance matrices. For instance, if Cov

(e^)=£., then E. can be written as T' r., where T- is 1 J J » J j J

3X3 of rank 3. Hence, if e^ is a 3X1 standard 

normal random vector (Cov (gj:(j.1 )=/), then

*7eH-i =4+i*s a normal random vector, with 

covariance matrix TJ r.=E.. r'. for jf=l, 2, 3 is

shown in table 20. 

Note that for season 2, ef^ is not observable

from the past series. The following is observable:

£+0.63 £_!, 7*+0.5 £_!, 6*+0.5 d*^.

There are ways to estimate ef* from the available 

data, but since the initial effect of e^ on the 

simulations will die off quickly and the simulations are so long, the effect of using ef^ generated 

as above will be negligible.

3. Now all the quantities necessary for the generation of Zt+l for each station are secured. Using 

the chosen equation, generate Zt+1 fl followed by 

^t+i,2 an(^ ^t+i,3 f°r eac^ station. Once Zt+j is 

generated, Zt+j+l can be generated by using Zt+j

and f(k) t=i o o t+j+i> " x » z* 6'

4. Untransform the simulated values to get the series 

in terms of the original units.

Results of a simulation study involving some flow 

events for season 2 (March through April) and season 3 

(May through August) are presented in table 21. The 

flow events represent a range of discharges that can be 

related to certain habitat characteristics.

Based on a study by R. T. Hurr (1981) it was found 

that ground-water levels at Mormon Island would rise to 

within 8 inches of the land surface if the discharge in the

TABLE 20. Full-rank decompositions of seasonal-covariance matrices

Season 1 T( =

Season 2 To =

Season 3 1% =

0.08402

.21208

.23719

.07688

.20631

.23050

.29906

.83303

.79471

.07643

.07557

.10182

.07883

.28686

.31873

.11108

.10538

.12612

channels was 3,000 fts/s. For season two, this is equivalent to a seasonal sum of 6,000 fts/s-months. A seasonal 

value of 8,000 fts/s-months would raise the levels to 

within about 4 inches of land surface, while a value of 

4,000 fts/s-months would drop the levels to about one 

foot below land surface. These values are assumed to encompass the critical ground-water levels necessary for 

an acceptable wet-meadow habitat in this area Probability values based on these flows are presented also 

for Overton and Odessa, although the ground-water 

streamflow relationships regarding possible wetmeadow complexes in these areas have not been 

determined.

Season 3, May through August, is the seedgermination period within the critical habitat reach. If 

the process of channel maintenance is to occur during 

this period, the flows should be sufficient to prevent 

seedling establishment, as well as to transport the sediment necessary for erosional processes of channel formation. Channel-geometry plots from Eschner (1981) show 

that a width of 500 feet near Odessa is associated with 

an instantaneous discharge of approximately 3,000 fts/s. 

This width is estimated as the minimum unobstructed 

width necessary for suitable crane habitat. Therefore, as 

an approximation for each reach, seasonal streamflow 

means of 4,000, 12,000, and 20,000 fts/s-months were 

chosen as channel-maintenance discharge reference 

points for calculation of exceedence probabilities. These 

streamflow means are presented as seasonal values 

because of limited model resolution. They do not imply 

that these discharges are necessary throughout season 3 

to maintain the channel; in fact, flows listed in table 10 

are probably necessary for no more than 15 percent of 

season 3 to maintain the channel.

Critical discharge levels for maintenance of both wet 

meadows and channel cross sections can be compared to 

the probabilities of achieving these levels over the next 

50 years using table 21. This comparison guide should 

assist habitat managers and water users in the area to 

plan effective utilization of available flows to satisfy projected water demands. Five hundred 50-year simulations 

were generated; probabilities of the events of table 21 

were evaluated by counting the number, n, of the 500 

simulations that satisfied the event, and taking n/500 as 

an estimate of the probability. To achieve an approximate estimate for the variability of these probability 

estimates, assume that each of the simulations is independent of the others. This assumption is not quite valid 

since the observed streamflow values for 1978 and 1979 

were used as input to start each of the simulations. 

However, this transience will not significantly affect the 

results presented here. If p is the true probability of the 

event A (A could be any event involving the future of the 

streamflow series), and n is the number out of 500
STOCHASTIC STREAMFLOW AND PRECIPITATION MODELS FOR PLATTE RIVER, NEBRASKA F33

TABLE 21. Estimates of the probability of level X being surpassed at least m times over the next 50 years

[ft'/s-month, cubic feet per second-month]

Season ftVmonth Station 16 20 24 30

2

2

2

3

2

3

4,000

6,000

8,000

4,000

12,000

20,000

Overton

Odessa

Grand Island

Overton

Odessa

Grand Island

Overton

Odessa

Grand Island

Overton

Odessa

Grand Island

Overton

Odessa

Grand Island

Overton

Odessa

Grand Island

1.0

1.0

1.0

0.93

.98

1.0

.60

.68

.83

1.0

1.0

1.0

.89

.96

.97

.43

.61

.68

1.0

1.0

1.0

0.83

.91

.99

.31

.38

.59

1.0

1.0

1.0

.69

.83

.90

.18

.27

.36

1.0

1.0

1.0

0.67

.79

.91

.13

.17

.37

1.0

1.0

1.0

.49

.62

.71

.06

.09

.12

1.0

1.0

1.0

0.52

.66

.90

.06

.06

.20

1.0

1.0

1.0

.28

.40

.53

.02

.04

.05

1.0

1.0

1.0

0.39

.47

.80

.02

.02

.09

1.0

1.0

1.0

.16

.22

.33

.01

.01

.02

1.0

1.0

1.0

0.27

.34

.67

.01

.01

.04

1.0

1.0

1.0

.12

.12

.18

.00

.00

.00

1.0

1.0

1.0

.17

.23

.54

.00

.00

.02

1.0

1.0

1.0

.06

.06

.11

.00

.00

.00

0.96

1.0

1.0

.09

.14

.43

.00

.00

.01

1.0

1.0

1.0

.03

.02

.06

.00

.00

.00

0.49

.56

.94

.00

.00

.00

.00

.00

.00

.80

.71

.89

.00

.00

.00

.00

.00

.00

0.25

.25

.71

.00

.00

.00

.00

.00

.00

.56

.35

.54

.00

.00

.00

.00

.00

.00

0.07

.06

.34

.00

.00

.00

.00

.00

.00

.31

.09

.21

.00

.00

.00

.00

.00

.00

0.01

.00

.04

.00

.00

.00

.00

.00

.00

.05

.00

.00

.00

.00

.00

.00

.00

.00

simulations in which A is observed, then, under the independence assumption:

Var n 1 p(l-p) 

500 500

PRECIPITATION-STREAMFLOW 

CORRELATION

The precipitation and streamflow models are intended 

as tools for simulation and calculation of probabilities of 

specific precipitation and streamflow conditions. The 

streamflow model can be used with channel-geometry 

models and stream discharge-ground-water level models 

to evaluate future wildlife-management alternatives. 

The precipitation model is useful in estimating probabilities of drought severity and duration that otherwise 

could not directly be estimated because of the short 

record.

Because of the presumed interrelationship between 

precipitation and streamflow, the joint effects of precipitation and streamflow on water use, including 

ground-water pumping, can only be determined from 

more extensive data collection and more sophisticated 

modeling procedures. Nevertheless, the correlation between precipitation and streamflow may allow initial 

estimates to be made of the effects of changes in precipitation on channel characteristics.

Some estimated correlations between precipitation in 

each of the 12 months, and streamflow (in average cfs) 

in the same month and 12 subsequent months, are presented in the Gothenburg and Grand Island precipitation stations, with the Overton streamflow station

(table 22) and the Grand Island streamflow station 

(table 23). Data used for the estimations consists of 

monthly precipitation tables from September 1941 to 

August 1978, and monthly streamflow series from September 1942 to August 1978, at the respective stations. 

Values below 0.3 in absolute value can be considered 

statistically insignificant. The same series as above 

were aggregated over the three streamflow seasons 

(September through February, March and April, and 

May through' August), and used to estimate correlations between precipitation in each of the seasons and 

streamflow in the same season and six following 

seasons. Results are presented in tables 24 and 25. Once 

again, absolute values below 0.3 are considered insignificant. There seems to be essentially no correlation of 

precipitation in seasons 2 and 3 with streamflow in subsequent seasons.

Significant correlations observed in tables 22 and 23 

indicate that monthly precipitation could be used effectively as a predictor of monthly streamflow. However, tables 24 and 25 indicate that the advantage of a 

joint precipitation-streamflow model for evaluation of 

streamflow probabilities would be lost when model output is aggregated over seasons.

SUMMARY

This report presents the development of stochastic 

precipitation and streamflow models for a critical 

wildlife-habitat reach of the Platte River. The habitat, 

defined as the reach of the Platte River from Lexington 

to Grand Island, Nebraska, is assumed to be adequately 

represented in terms of precipitation by basing the relevant models on data collected at Gothenburg, Kearney,
F34 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

TABLE 22. Estimated correlations between monthly precipitation at Gothenburg (A) and at Grand Island (B) with monthly streamflow at

Overton

Streamflow

lead

(in months)

Sept. Oct. Nov. Dec. Jan. Feb. Mar. Apr. May. June. July. Aug.

A. Gothenburg

0

1

2

3

4

5

6

7

8

9

10

11

12

-0.44

.32

.38

.37

.31

.36

.42

-.08

-.11

.02

-.05

-.09

-.17

0.07

.12

.06

.06

.08

.10

.05

.10

.38

.07

-.04

-.02

-.08

0.39

.33

.28

.24

.22

.29

.21

.07

.51

.24

.26

.27

.16

0.28

.34

.42

.39

.05

.09

.10

.23

.19

.18

.13

.06

-.06

-0.08

-.02

-.02

.01

.04

.20

-.13

.08

.20

-.04

.12

-.03

-.12

0.04

-.08

.03

.01

-.06

-.26

-.24

-.21

-.18

-.14

-.09

-.13

-.15

0.22

.31

.30

-.12

.13

.24

.31

.28

.27

.14

.18

.23

.28

0.26

.11 -.13

.02

.03

-.02

.00

.14

.15

.12

.10

.04

-.03

0.18

.16

.08

.20

.23

.35

.25

.24

.40

.33

.22

-.00

-.11

0.50

.27

.02

-.11

-.05

-.01

-.00

.02

.00

-.05

-.12

.00

.02

0.28 -0.09

.28 -.11

.23 -.09

.32 -.14

.27 -.09

.21 -.03

.27 -.07

.32 -.20

.29 -.01

-.07 .05

-.10 .27

-.05 -.01

.11 .10

B. Grand Island

0

1

2

3

4

5

6

7

8

9

10

11

12

0.66

.53

.59

.53

.43

.49

.57

.16

.10

-.02

-.01

-.01

-.00

0.21

.25

.22

.21

.22

.17

.09

.15

.50

.29

.14

.07

.08

0.41

.36

.37

.38

.39

.23

.20

.16

.42

.28

.25

.22

.18

0.35

.40

.40

.38

.23

.16

.04

.19

.35

.30

.23

.24

.19

-0.16

-.05

-.01

.11

.16

.33

-.01

.11

.06

.02

.10

.05

.00

0.01

-.06

.30

.33

.13

-.03

-.02

-.00

.21

.23

.26

.28

.21

0.08

.50

.40

-.07

.28

.55

.60

.50

.45

.36

.43

.58

.60

-0.07

-.17

-.05

.04

-.07

-.12

-.12

-.04

-.01

.00

-.05

-.08

.08

0.14

.06

.16

.15

.24

.39

.33

.28

.43

.39

.23

.15

.10

0.49

-.01

-.17

-.23

-.18

-.11

-.12

-.20

-.21

-.27

-.31

-.29

-.14

0.07 -0.04

-.05 -.15

-.00 -.14

.13 -.04

.02 -.05

.00 -.03

.07 -.04

.01 -.05

-.02 -.02

.02 .07

.06 -.01

.16 -.20

.16 -.15

TABLE 23. Estimated correlations between monthly precipitation at Gothenburg (A) and at Grand Island (B) with monthly streamflow at

Grand Island

Streamflow

lead

(in months)

0

1

2

3

4

5

6

7

8

9

10

11

12

Sept.

0.50

.41

.40

.42

.27

.26

.39 -.11

-.11

.01

-.05

-.17

-.18

Oct.

0.22

.14

.00

.03

.05

.14

.04

.11

.29

.00

-.10

-.08

-.06

Nov.

0.39

.25

.32

.23

.20

.30

.20

-04

.40

.16

.21

.22

.17

Dec.

0.45

.39

.50

.34

.03

.11

.05

.21

.16

.19

.13

.09

-.01

Jan.

A.

-0.06

.14

.09

.05

.05

.10

-.23

.05

.03

-.04

.07

-.00

-.10

Feb.

Gothenburg

0.14

.01

.02

-.03

.03

-.16

-.21

-.20

-.16

-.04

-.18

-.08

-.19

Mar.

0.26

.35

.27

-.10

.10

.21

.28

.26

.19

.14

.16

.17

.27

Apr.

0.29

.09 -.13

-.09

-.01

-.07

-.08

.02

.05

.08

.06

.08

.02

May.

0.24

.19

.18

.27

.25

.39

.21

.18

.40

.25

.21

-.01

-.14

June.

0.48

.28

.02

-.10

-.05

.04

-.09

.04

.09

-.09

-.13

-.02

.05

July.

0.43

.26

.25

.31

.34

.08

.24

.36

.29

-.06

-.11

-.10

.15

Aug.

-0.01

-.05

-.03

-.20

-.07

-.06

-.05

-.17

-.05

.11

.30

.06

.16

B. Grand Island

0

1

2

3

4

5

6

7

8

9

10

11

12

0.70

.61

.56

.57

.40

.38

.50

.15

.06 -.06

-.08

-.08

.02

0.35

.23

.19

.21

.29

.21

.07

.15

.40

.22

.29

.02

.10

0.51

.36

.40

.42

.37

.25

.19

.06

.32

.18

.20

.17

.19

0.51

.47

.47

.36

.21

.15

.03

.24

.32

.30

.23

.32

.28

-0.16

.08

.07

.12

.20

.29

-.08

.09

.03

-.03

.15

-.01

.01

0.14

-.07

.26

.24

.23

.09

.01

-.01

.20

.27

-.02

.28

.14

0.16

.54

.37

-.06

.23

.52

.58

.47

.44

.42

.40

.46

.58

-0.01

-.17

-.08

-.12

-.06

-.14

-.11

-.08

.04

.03

-.02

-.07

.08

0.13

.09

.15

.22

.28

.46

.29

.26

.45

.38

.27

.16

.09

0.46

-.00

-.16

-.23

-.19

-.11

-.22

-.20

-.17

-.33

-.34

-.31

-.11

0.31

-.04

.04

.14

.07

.07

.12

.12

.03

.03

.06

.14

.17

0.02

-.13

-.09

-.08

-.00

-.05

-.02

-.04

-.05

.02

.10

-.31

-.11
STOCHASTIC STREAMFLOW AND PRECIPITATION MODELS FOR PLATTE RIVER, NEBRASKA F35

TABLE 24. Estimated correlations between seasonal precipitation 

at Gothenburg (A) and at Grand Island (B) with seasonal 

streamflow at Overton

Streamflow

lead

(in seasons) i

Season

2 3

A. Gothenbuig

0

1

2

3

4

5

6

0.42

.42

.11 -.02

.02

.17

.14

-0.02

.23

.12

.13 -.19

-.03

-.02

0.09

.19

.18 -.09

-.02

-.00

.03

B. Grand Island

0

1

2

3

4

5

6

0.59

.55

.29

.22

.21

.09

.14

-0.05

.13

.21

.27 -.15

-.13

-.12

-0.03 -.00

-.04

-.11

.10

.07

.09

TABLE 25. Estimated correlations between seasonal precipitation 

at Gothenburg (A) and at Grand Island (B) with seasonal 

streamflow at Grand Island

Streamflow

lead 

(in seasons)

A. Gothenburg

0.49

-.05

-.01 

.18 

.10

0.02 

.21 

.05 

.20

-.16 

.05 

.05

0.17 

.19 

.21 -.10

-.00 

.05 

.08

B. Grand Island

0.64 

.61 

.24

.18 

.16 

.12 

.08

0.10 

.12 

.21 

.31 -.16

-.07

-.13

0.66 

.03 

.05

-.13 

.16 

.08 

.09

and Grand Island. The streamflow models are developed using data collected at Overton, Odessa, and 

Grand Island.

For modeling purposes, three seasons were defined to 

correspond approximately to periods of significantly 

different flows and vegetation development. Season 1, 

comprising the months September through February, 

represents the base flow period. Season 2, March and 

April, represents the period of high flows from snowmelt in the Rocky Mountains. Season 3, from May 

through August, represents the approximate time of 

seed drop by riparian vegetation, and, consequently, the 

period of seedling germination and establishment.

Each hydrologic variable, defined as the seasonal

value at the appropriate station, is modeled both independently of the other stations for the particular variable, and as part of a combined station model. The 

combined station model allows for expression of the 

interrelationship between stations for the given 

variable.

The precipitation models are used primarily in this 

report to estimate probabilities of droughts of given 

severities and durations. Drought severities are defined 

relative to the historical mean at the stations and the 

durations are presented as consecutive years. The 

streamflow models are used to estimate exceedence 

probabilities for specified levels of flows that are related 

to the maintenance of channel characteristics and wet 

meadow environments.

It is recognized that streamflow may not be independent of precipitation in the study reach. Although the 

interrelationship was not modeled, tables of the correlation between precipitation and streamflow (tables 

22-25) may allow initial estimates of the effects of 

changes in precipitation on streamflow to be made.

Because the resolution for both the precipitation and 

streamflow models allows only seasonal estimation, the 

models are intended as initial screening tools for 

evaluating management alternatives for the habitat. In 

order to more exactly evaluate consequences of operating rules of water releases or diversions of water for proposed development, models allowing finer estimation of 

the hydrology would have to be developed. The development of these models, however, would require a more extensive data collection and model development research 

effort.

SELECTED REFERENCES

Box, G. E. P., and Cox, D. R., 1964, An analysis of transformations: 

Journal of the Royal Statistical Society, Ser. B, 26, p. 211-252.

Box, G. E. P., and Jenkins, G. W., 1975, Time series analysis, forecasting and control: San Francisco, Calif., Holden-Day, p. 67-70.

David, F. N., and Barton, D. E., 1962, Combinatorial chance: New 

York, Hafner, p. 228-231.

Eschner, T. R., 1981, Morphologic and hydrologic changes of the 

Platte River, south-central Nebraska: Fort Collins, Colorado 

State University, MS Thesis, 269 p.

Gibbons, J. D., 1971, Nonparametric statistical inference: New York, 

McGraw-Hill,p.75.

Graybill, F. A., 1976, Theory and application of the linear model: 

North Scituate, Mass., Duxbury Press, p. 310-324.

Hurr, R. T., 1981, Ground-water hydrology of the Crane Meadows 

wildlife area, near Grand Island, Hall County, Nebraska: U.S. 

Geological Survey Open-File Report 81-1109,43 p.

Pagano, Marcello, 1978, On periodic and multiple autoregressions: 

Annals of Statistics, v. 6, no. 6, p. 1310-1317.

Parzen, E., and Pagano, M., 1979, An approach to modeling seasonally stationary time series: Journal of Econometrics, v. 9, 

p. 137-153.
F36 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

Petsch, H. E., Jr., Rennick, K. B., and Nordin, C. F., Jr., 1980, Statistical summaries of selected streamflow data, South Platte 

River in Colorado and Nebraska: North Platte and Platte Rivers 

in Nebraska, U.S. Geological Survey Open-File Report 80-679, 

278 p.

Stidd, C. K, 1970, The nth root normal distribution of precipitation: 

Water Resources Research, v. 6, no. 4, p. 1095-1103.

Troutman, B. M., 1979, Some results in periodic autoregression: Biometrika, v. 66, no. 2, p. 219-228.

Vecchia, A. V., Jr., 1981a, Precipitation model for the Platte River 

valley from Gothenburg to Grand Island, Nebraska: U.S. Geological Survey Open-File Report 81-130,44 p.

Vecchia, A. V., Jr., 1981b, A stochastic streamflow model of the 

Platte River at Overton, Odessa, and Grand Island, Nebraska* 

U.S. Geological Survey Open-File Report 81-1188,42 p.
Simulated Hydrologic Effects of 

Possible Ground-Water and 

Surface-Water Management 

Alternatives in and Near the 

Platte River, South-Central Nebraska

By ALAN W. BURNS

HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN 

U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 127 7-G

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1983

CONTENTS

Abstract 

Introduction 

Purpose and scope 

Background and approach

Description of study area 

Stream-aquifer interaction 

Page

Gl 

1

1

2

2

2

Page

Computation of stream depletions G14

Effects of water-management alternatives on stream stage 19

Conclusions 22

References cited 24

Appendix Fortran model to compute stream depletion 27

ILLUSTRATIONS

FIGURE 1. Map showing location of study area G3 

2-10. Graphs showing:

2. Stream-aquifer response function 5

3. Stream-depletion factor (SDF) response functions 7 

4-8. Unit response function for stream-depletion factor (SDF)=

4. 10 days 8

5. 100 days 9

6. 1,000 days 10

7. 10,000 days 11

8. 100,000 days 12

9. Relative scales for various values of the stream-depletion factor (SDF) 13

10. Illustration of the convolution of aquifer recharge with unit response function to yield stream accretion 14

11. Map showing stream-depletion factor (SDF) regions, in days 16

12. Diagram showing simulated components of the soil zone 17

13. Graph showing annual net ground-water recharge and annual stream depletion 18 

14-17. Graphs showing stream-stage frequency curves for four water-management alternatives affecting stream depletion:

14. Annually 20

15. September through February 21

16. March through April 21

17. May through August 22 

18-21. Graphs showing stream-stage frequency curves for four water-management alternatives directly affecting upstream 

flow:

18. Annually 23

19. September through February 23

20. March through April 24

21. May through August 25

TABLES

TABLE 1. Well and acreage data by stream-depletion factor (SDF) bands 

2. Average net ground-water recharge rates, by irrigation category and soil type, 1941-77

3. Acres irrigated per well, by SDF band and county 

4. Acreages and stream depletion for current and predicted conditions 

5. Regression coefficients for stage-discharge relationships for the Platte River 

Page

G15 

17 

17 

19 

19

in
IV HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

METRIC CONVERSIONS

Inch-pound units used in this report may be converted to metric (SI) units by using the following conversion factors:

Multiply inch-pound units By To obtain

acre 0.0040 square kilometer

acre-foot (acre-ft) 1,233 cubic meter

acre-foot per year (acre-ft/yr) 1,233 cubic meter per year

cubic foot per second (ft3/s) 0.2832 cubic meter per second

foot (ft) 0.3048 meter

foot per day (hid) 0.3048 meter per day

inch per year (in/yr) 25.4 millimeter per year

mile (mi) 1.609 kilometer

foot squared per day (ft2/d) 0.093 meter squared per day
HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

SIMULATED HYDROLOGIC EFFECTS OF POSSIBLE

GROUND-WATER AND SURFACE-WATER MANAGEMENT ALTERNATIVES 

IN AND NEAR THE PLATTE RIVER, SOUTH-CENTRAL NEBRASKA

By ALAN W. BURNS

ABSTRACT

Digital-computer models were developed and used to simulate the 

hydrologic effects of hypothetical water-management alternatives on 

the wetland habitat area near Grand Island, Nebr. Areally distributed 

recharge to and discharge from the aquifer system adjacent to the 

Platte River between Overton and Grand Island were computed for 

four hypothetical water-management alternatives: (1) Current 

methods; (2) increasing the acreage irrigated by surface water about 

270,000 acres; (3) increasing the acreage irrigated by ground water by 

about 270,000 acres, replacing as much subirrigated area as possible; 

and (4) increasing the acreage irrigated by ground water by about 

270,000 acres without replacing subirrigated areas. Using streamaquifer response functions, the stream depletions resulting from the 

computed aquifer recharge and discharge, averaged over a 50-year 

planning period, were 125,000, 53,000, 174,000, and 177,000 acre-feet 

per year, respectively.

Frequency curves of the stage in the river near the wildlife habitat 

area were computed from the 50-year sequences of monthly 

streamflows for each of the management alternatives. The differences 

in the stage-frequency curves were minimal for the four watermanagement alternatives.

For comparative purposes, three additional water-management 

alternatives were simulated which had direct effects on the 

streamflow entering the study area: (1) Assume an importation of 

240,000 acre-feet per year for irrigation of 100,000 acres downstream 

from the study area; (2) assume a diversion of 240,000 acre-feet per 

year for irrigation of 100,000 acres upstream from the study area; and 

(3) assume a reservoir or diversion which would store or divert any incoming monthly streamflow greater than 2,000 cubic feet per second. 

The average streamflow for the current-conditions simulation was 

1,274 cubic feet per second, whereas the average for each of these 

hypothetical management alternatives was 1,606, 1,045, and 1,102 

cubic feet per second, respectively. Translating these different 

streamflow sequences to stage-frequency curves indicates a mpch 

greater change in stream stage than the four water-management 

alternatives previously evaluated.

INTRODUCTION

This study is part of the Platte River Study, a 

multidisciplinary study being conducted by agencies of 

the U.S. Department of the Interior concerned with the

critical habitat of the whooping crane and other 

migratory waterfowl along the Platte River in central 

Nebraska Hydrologic investigations have been an important subset of the Platte River Study and have attempted to identify the hydrologic system as it relates 

to the habitat, and thus how water-management alternatives could affect the habitat. This particular report 

presents the simulations of the hydrologic effect on the 

river caused by potential water-management alternatives in and near the Platte River between Overton 

and Grand Island, Nebr.

PURPOSE AND SCOPE

The purpose of the part of the Platte River Study 

described in this report was to determine the range of effects on the streamflow and3 stage of the river near the 

habitat area due to possible water-management practices in a 70-mile reach of the river upstream from the 

habitat area The analysis considered only hypothetical 

water-management alternatives rather than actual proposed projects. A 50-year planning period was used to 

be compatible with the rest of the Platte River Study. 

The area of analysis was limited to the reach of the 

Platte River between the two gaging stations at Overton and Grand Island (fig. 1). The area extended outward from the river to a distance at which the effects 

of water management would be negligible during the 

50-year period. This report does not consider the effect 

of water managment on the habitat areas directly, nor 

does it directly consider effects of additional groundwater diversions upstream from Overton. However, it 

does provide information that can be used with other 

reports in this study to do such an evaluation.

The primary objective of this substudy was to determine the effects of possible ground-water development 

between Overton and Grand Island on the streamflow

Gl
G2 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

of the Platte River. Secondary objectives were to compare the effects of possible ground-water developments 

to similar irrigation developments using surface water 

and to compare the effects of these possible developments, which are transmitted through the aquifer 

system to the river, to the effects of developments 

which would directly affect the incoming streamflow at 

Overton. This report is a brief discussion of a rather 

brief and general analysis for a topic that could involve 

considerably greater effort to evaluate in more detail.

BACKGROUND AND APPROACH

The hydrologic system in this reach of the Platte 

River is typical of the entire Platte River drainage 

system throughout the Great Plains. Surface water is 

hydraulically connected to the ground water in the adjacent aquifers. The diversion of streamflow for irrigation, 

the withdrawal of ground water for irrigation, the 

return flow of excess irrigation applications, and the 

ground-water use by native and agricultural phreatophytes are components of this highly complex and integrated hydrologic system. Within a certain area of influence controlled by geologic boundaries, ground-water 

withdrawals that are consumptively used will deplete 

-the streamflow in the Platte River either by reducing 

return flow or by inducing infiltration from the river to 

the aquifer. Recharge in excess of withdrawals will augment streamflow either by increasing return flow or by 

reducing infiltration from the river to the aquifer.

Based on information available from previous studies, 

the study area was partitioned into subareas, each of 

which can be characterized by the response of the river 

to changes in water-management practices that are 

transmitted through the aquifer system. Scenarios of 

possible water-management alternatives then were 

selected, and the effects of those alternatives on the 

river were simulated.

DESCRIPTION OF STUDY AREA

The study area for this report is shown in figure 1. It 

includes those areas for which land-use data were available and where water use will affect the flows in the 

Platte River. Much of this area is on the south side of 

the Platte River where both the surface water and 

ground water flow away from the Platte River. This 

area is included in the study area because there is no 

hydrologic boundary which would prevent water withdrawals or accretions from affecting the flows of the 

Platte River. This area is generally flat. Normal 

precipitation is about 23 in/yr, with almost half of that 

occurring from April through June. The primary use of

the land is for agriculture, with corn being the predominant crop.

The Platte River flows through this region, providing 

an important source of water for both agricultural use 

and for wildlife. The river-bottom area is wide, and the 

river generally is shallow and extensively braided in 

sandy channels through the bottom area These features 

contribute to a closely connected stream-aquifer 

system. Other prominent surface waters in this region 

include the Wood River and the many irrigation canals 

that tend to parallel the Platte River.

Large volumes of ground water occur in the Quaternary deposits adjacent to the Platte River and in the 

underlying Tertiary Ogallala Formation. The Quaternary deposits include various units of alluvial and eolian 

deposits. The Ogallala Formation, which contains an extensive aquifer from Texas to South Dakota, underlies 

most of the Quaternary deposits in this area Below the 

Ogallala Formation is the Cretaceous Pierre Shale or the 

Niobrara Formation, which serves as the bottom of the 

aquifer system.

All of these deposits can be considered a single unconfined aquifer system (Lappala and others, 1979, p. 18), 

consisting of clay, silt, sand, and gravel. The saturated 

thickness of the aquifer ranges from 100 to 360 ft. The 

transmissivity ranges from 5,000 to 30,000 ft2/d, and 

the specific yield probably ranges from about 0.10 to 

0.20.

Irrigation is an important aspect of agriculture in this 

area Surface water diverted from the Platte River is 

delivered to the farms by extensive canal systems. In 

many areas, the water table is close enough to land surface for natural subirrigation to occur. In these areas, 

roots of the crops (or native riparian vegetation) grow 

deep enough to get water directly from the aquifer. In 

other areas, ground water is pumped for irrigation from 

wells using high-capacity pumps.

STREAM-AQUIFER INTERACTION

The effects of losses from the ground-water system by 

pumpage or subirrigation and the effects of gains by 

recharge from precipitation or excess irrigation applications are transmitted through the aquifer system to the 

river as accretions or depletions to streamflow. Withdrawals from the aquifer do not necessarily cause direct 

losses of water from the river; for example, groundwater withdrawals may not cause river water to enter 

the aquifer but rather may just reduce the amount of 

ground water that previously had been entering the 

river.

The magnitude and timing of the effects of these 

stresses (pumpage or recharge) which are transmitted
99°00' 98°30'

40°30' h

Base from U.S. Geological Survey 

1:500 000 State base map, 1965

I ^WM&ffl/

j j Study area ^^ 

Jj==n=

10 20 30 KILOMETERS 

FIGURE 1. Location of study area
G4 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

through the aquifer to the river depend upon the transmissive properties of the aquifer (transmissivity); the 

storage properties of the aquifer (specific yield for this 

water-table aquifer); the hydraulic connection between 

the stream and aquifer; and the distance from the point 

of stress to the stream. Procedures to describe these 

response functions can be derived from the theory of 

ground-water hydraulics. The general form of a 

response of a straight stream in perfect connection to an 

ideal aquifer to a stress on the ground-water system is:

q/Q=erfc

eTY

(1)

where:

q is the instantaneous rate of depletion or accretion 

from the stream measured at time t, in cubic feet 

per second; 

Q is the rate of stress on the ground-water system,

in cubic feet per second; 

erfc is the complementary error function; 

x is the distance from the point of stress to the

stream, in feet;

Sy is the specific yield of the aquifer under watertable conditions; 

T is the transmissivity of the aquifer in feet

squared per day; and 

t is the time since the stress was commenced, in

days.

The assumptions necessary in the derivation of this 

function and the definition of an ideal aquifer are:

(1) The aquifer is semi-infinite, homogeneous, and 

isotropic;

(2) the transmissivity is constant with time;

(3) the water is released instantaneously from 

storage;

(4) the stream is straight, hydraulically connected to 

the aquifer, and fully penetrating;

(5) the water temperature is the same in the stream 

and aquifer and is constant with time;

(6) the stress is continuous and steady; and

(7) the stress affects the entire saturated thickness

instantaneously.

A curve illustrating this response function for a given 

set of parameters is shown in figure 2. This curve indicates that the rate of stream depletion (accretion) 

would be 25 percent of the pumping (injection) rate after 

6 months, 50 percent after 18 months, and 75 percent 

after 80 months.

Equation 1 is typically integrated over time to evaluate the volume of stream response to the volume of the 

stress. The solution of this integration is:

v~Qt

2Tt

+ 1 erfc

e 

4Tt

(2)

where v is the volume depleted from the stream through 

time t.

Jenkins (1968a) has developed a "lumped" parameter 

known as the SDF (stream-depletion factor), that 

uniquely characterizes a response curve. The SDF is 

equal to the distance squared times the specific yield 

divided by the transmissivity (x2Sy/T) for the idealized 

assumptions stated earlier. Response curves of the integrated equation (2) for different SDF values are shown 

in figure 3. These curves indicate the percent of the 

volume pumped (or injected) that comes from (or goes 

to) the stream. Using an SDF value of 100 as an example, streamflow would be depleted by about 8 percent of 

the first month's pumpage, by about 40 percent of the 

first 6-months' pumpage, by about 65 percent of the 

first 30-months' pumpage, and by about 92 percent of 

the first 50 years of pumpage.

The SDF becomes a very important parameter when 

evaluating stream-aquifer interactions for large regions. 

Using a detailed, distributed parameter, digital groundwater flow model, arbitrary points within the model can 

be stressed and the response of the stream to those 

stresses can be simulated. Using a type-curve analysis 

similar to that used in fitting aquifer-test data to 

theoretical curves, a theoretical curve is fit to the 

simulated stream-depletion values and the respective 

SDF values are assigned to each of the points in the 

model. Thus all the vagaries of boundary conditions, 

variable transmissivities, and a sinuous river can be accounted for with the SDF parameter within the limits of 

resolution of the corresponding digital model.

The curves in figures 2 and 3 are for a continuous 

stress. A representation of the response data which 

proves more useful for analysis with time-varying 

stresses are discrete unit response functions (figs. 4-8) 

for unit periods of stress, such as a month. These step 

functions represent the percent by volume that stream 

depletion (or accretion) is of a monthly stress and the 

continuing future effects beyond the termination of the 

stress. Notice the differences between the magnitude of 

the peak of the response curves for different SDF values 

(see fig. 9, which demonstrates the differences in scales 

of figs. 4-8) and the differences in time when the peak 

occurs. Using an SDF value of 10, for example, streamflow would be depleted by about 50 percent of the
HYDROLOGIC EFFECTS, GROUND-WATER AND SURFACE-WATER MANAGEMENT ALTERNATIVES G5

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TIME SINCE PUMPING BEGAN, IN MONTHS

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FIGURE 9. Relative scales for various values of the stream-depletion factor (SDF).
G14 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

monthly pumpage during the month that the pumpage 

occurred and by about 24 percent of the pumpage 

(which has now ceased) during the following month. On 

the other hand, for an SDF value of 1,000, the maximum 

monthly stream depletion would be only about 3 percent of the pumpage, and it would occur about 5 months 

after the pumpage had ceased. The extreme example is 

for an SDF of 100,000, in which the maximum monthly 

stream depletion would be only about 0.07 percent of 

the pumpage and would occur about 45 years after the 1 

month of pumping.

The unit response function [U(k)] and a time series of 

aquifer stresses [Q(k)] are used with the discretized version of the convolution equation (Eagleson and others, 

1966, p. 756-757) to compute the time series of stream 

depletions (or accretions) [q(i)] at time i:

(3)

This computation is shown in figure 10, where the time 

series of stream accretions due to aquifer recharge for 

each month are added to the stream accretions due to 

the aquifer recharge in each subsequent month, resulting in the total stream accretions.

COMPUTATION OF STREAM 

DEPLETIONS

The SDF values computed for this study were 

primarily based on the ground-water model used for the 

Missouri River Basin Commission Level B Study (Lappala and others, 1979). The model of the Middle Platte 

reach of the Upper Platte subbasin of the Level B Study 

extended east and west beyond the area of interest for 

this current study, using a constant grid network with 

nodes 2.5 mi by 2.5 mi. For the Level B Study, the 

southern extent of the modeled area was the approximate ground-water divide between the Platte River and 

the Republican River or the Blue River. To account for 

this arbitrary boundary, the Level B model maintained 

a constant gradient along the boundary. The effect of 

this assumption was simulation of equal rates of development (withdrawal or recharge) on both sides of the 

boundary of the modeled area. This current study considered a more realistic distribution of potential development in the area south of the ground-water divide and 

thus could not use the arbitrary boundary previously 

used for the Level B Study. The constant gradient 

boundary conditions in the Level B model were removed 

and the data set for that model was used with another 

similar ground-water flow model (Taylor, 1971) for this 

study.

A. Simplified aquifer recharge possibly due 

to excess irrigation applications of surface water

3<

fcEE

Q lo

LU LU

D I-

§1

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0.6

0.4

0.2

T I 1 1

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B. Simplified unit response function

4 6 

MONTHS

C. Stream accretion due to A. convolution of 

aquifer recharge and B. unit response

FIGURE 10. Illustration of the convolution of aquifer recharge 

with unit response function to yield stream accretion.

Taylor's model simulates the stream response to a 

single pumping well, and fits the simulated response to 

the theoretical response at the point where the response 

is 28 percent of the pumpage. This point is where the
HYDROLOGIC EFFECTS, GROUND-WATER AND SURFACE-WATER MANAGEMENT ALTERNATIVES G15

pumping period is equal to the SDF value on the theoretical curve (see Jenkins, 1968b). The SDF values for 

the study area south of that covered by the Level B data 

set were computed for three cross sections. Aquifer 

characteristics were estimated based on the geologic 

cross sections published by Johnson (1960). These cross 

sections were extended south beyond the limit of landuse data such that the arbitrarily chosen no-flow boundary would have minimal effect on the SDF values computed along the cross section. The SDF values were 

then contoured and bands of equal SDF values were 

assigned the mean SDF value between the contour intervals (fig. 11).

Data enumerating the total acreage, number of wells, 

acreage irrigated by surface water, soil type, irrigable 

acreage, and subirrigated acreage for quarter townships 

(5,760 acres for most quarter townships) were provided 

by the U.S. Bureau of Reclamation (F. J. Otradovsky, 

written commun., 1981). An SDF-band value was assigned to each quarter township. When discretizing the 

area by quarter townships, the distances were such that 

no SDF value less than 1,000 existed except within 

quarter townships which intersected the river. Ah 

assumed distribution of SDF values was assigned to 

each quarter township which is intersected by the river. 

This assumed distribution was based on an average 

location of the river within a quarter township. This 

assumed distribution was the same for every quarter 

township which intersected the river, and thus the 

acreages and number of wells for some of the bands in 

table 1 are identical.

TABLE l. WeU and acreage data by stream-depletion factor (SDF)

bands

Band

1

2

3

4

5

6

7

8

9

10

11

12

13

SDF

value

10

30

60

100

300

600

1,000

3,000

6,000

10,000

30,000

60,000

100,000

Total

acreage

17,000

8,800

8,800

19,000

29,400

29,400

35,000

176,000

97,900

248,000

488,000

445,000

319,000

Wells

114

55

55

123

191

191

248

1,260

719

1,600

2,480

1,990

954

Acreage

irrigated

with surface water

314

157

157

340

523

523

419

6,630

1,210

29,700

62,400

3,220

926

Irrigable

acreage

7,400

3,700

3,700

8,000

12,300

12,300

17,400

102,000

64,400

182,000

309,000

190,000

77,200

Subirrigated

acreage

15,200

7,600

7,600

16,500

25,400

25,400

28,200

59,200

21,200

8,900

1,600

6,400

8,200

To compute the depletion of streamflow from the 

Platte River between the Overton gage .and Grand 

Island gage due to stresses in the aquifer, the net 

ground-water recharge for the area within each SDF 

band was calculated. A computer model (see appendix) 

was developed to calculate the monthly net groundwater recharges within each SDF band and then convolute them with their respective response functions. 

The amount of net ground-water recharge in an area is a 

function of the soil type, available soil moisture, the 

amount of irrigation water applied and precipitation on 

the land surface, the plants' consumptive use, and the 

amount of water withdrawn from the aquifer. To determine the amount of water recharged to or withdrawn 

from the aquifer, four basic land-irrigation categories 

were identified within the study area: Dryland (for nonirrigated land), irrigated land using surface water, irrigated land using ground water, and subirrigated areas.

The amount of land characterized by each of these 

land categories was determined for each SDF band and 

each of four soil types (see table 2 for brief description) 

from the data which were summarized in table 1. Net 

ground-water recharge rates (in feet per month) were 

computed for each of the four soil types by the U.S. 

Bureau of Reclamation (Fred Otradovsky, written commun., 1981), using a soil-moisture model. Lappala and 

others (1979) described the soil-moisture model as 

follows:

Net ground-water recharge was computed with a water-balance 

model of the soil zone developed by the Nebraska Reclamation Office, 

U.S. Bureau of Reclamation, Grand Island, Nebr. The model operates 

on a monthly basis and is adapted from the daily irrigation scheduling 

program developed by Jensen and others (1969). The soil zone was 

modeled as a lumped system for a given topography, soil type, and 

crop distribution. Inputs and outputs from the soil zone are shown in 

figure 12. Inputs to the model are monthly values of precipitation and 

potential evapotranspiration (ET). Potential ET was computed using 

the Jensen-Haise method (Jensen and others, 1969). Runoff was 

abstracted from precipitation using monthly rainfall-runoff relationships derived from data obtained by the Agricultural Research Service at Rosemont, Nebr. (U.S. Department of Agriculture, 1956-68). 

These relationships considered soil type, slope, crop cover, and farming practices.

Outflow from the soil zone consisted of gravity drainage and ET. 

Gravity drainage, or assumed recharge to the water table, occurred 

when infiltration from precipitation and applied irrigation water exceeded ET plus soil-moisture-retention capacity. Net ground-water 

recharge for land irrigated with ground water was equal to recharge 

from precipitation plus irrigation seepage minus total ground-water 

withdrawal. For land irrigated with surface water, net ground-water 

recharge was equal to recharge from precipitation plus seepage 

losses. Potential ET was computed for Grand Island, Nebr., by using 

air temperature and solar radiation (Jensen and others, 1969). 

Relative humidity, elevation, and crop type were used to adjust 

potential ET to obtain actual consumptive use. Four major crop 

types were used for this study: Row crops, small grains, alfalfa, and 

pasture. Annual net recharge to the water table and ground-water 

withdrawals were computed using typical cropping patterns for these 

crops under dryland conditions and irrigation with ground water and 

surface water.

Annual average net ground-water recharge rates for 

each soil type and land category computed from these 

data are shown in table 2. Data provided by the U.S. 

Bureau of Reclamation (table 1) had to be supplemented 

with additional soil data and well-pumping data. Soil 

types for much of the southern part of the study area
EXPLANATION

REG IONS OF SDF, IN DAYS

GAG

40e 30'

._L

Base from U.S. Geological Survey 

1:500 000 State base map, 1965 D

1 

3 10

10

I

I 

20

20 3

I

I 

30 KILOMETERS

30 MILES

FIGURE 11. Stream-depletion factor (SDF) regions, in days.
HYDROLOGIC EFFECTS, GROUND-WATER AND SURFACE-WATER MANAGEMENT ALTERNATIVES G17

TABLE 2. Average net ground-water recharge rates, by irrigation

category and soil type, 1941-77 

[Computed from U.S. Bureau of Reclamation soil-moisture model. Data are in feet per year]

Sol type

Bottomland 

Terrace land 

Silty uplands -

Sandy uplands

Land irrigated with

Dryland

0.27

.13

.13

.40

Ground water

-0.42

-.47

-.81

-.27

Surface water

1.10

.62

.56

.83

Subirrigated

land

-1.05

 

 

 

EVAPOTRANSPIRATION PRECIPITATION

Runoff

Deep percolation when storage capacity 

is exceeded

FIGURE 12. Simulated components of the soil zone.

were assigned using the Soil Conservation Service maps 

for Phelps (U.S. Department of Agriculture, 1973) and 

Adams (U.S. Department of Agriculture, 1974) Counties. To compute acreage irrigated by ground water, the 

acreage irrigated per well was needed. This acreage 

value was assumed to vary according to SDF band and 

county (table 3) and was computed to match countywide 

data provided by the U.S. Bureau of Reclamation.

The 37 years of net ground-water recharge rates provided by the U.S. Bureau of Reclamation had to be 

extended to provide the needed 50 years of data This 

extension was computed by multiple regression using 

two terms for the sine and cosine of time to compute a 

seasonally factor and monthly precipitation at

TABLE 3. Acres irrigated per well, by SDF band and county

[SDF, stream-depletion factor; USBR, U.S. Bureau of Reclamation]

SDF 

band

1-6 

7-9 

10-13 

County

Adams 

Buffalo - 

Dawson 

Hall Kearney 

Phelps ~

Acres north of river

40 

40 

50

Acres computed using 

SDF band data

98

47 

46

93 

93

Acres south of river

40 

80 

100

Acres computed using 

USBR county data

92 

61 

46

C£

92

77

Kearney. The model then was run for two consecutive 

50-year periods to generate estimates of current 

streamflow depletions. The first 50-year sequence (an 

approximation of 1880-1930 conditions) was based on 

the assumption that there was no ground-water pumpage, no surface-water irrigation on the south side of the 

river, and that all of the quarter townships intersected 

by the river were naturally subirrigated. Also, subirrigated acreage was increased from current conditions 

in all other SDF bands. The second 50-year sequence 

(an approy'"nation of 1930-80 conditions) was based on 

the assumption of instantaneous implementation of the 

Tri-County project, which is on the south side of the 

river and accounts for most of the acreage irrigated by 

surface water in the study area The number of wells 

was assumed to increase linearly from zero to the present total, and the number of subirrigated acres was assumed to decrease linearly to the present number. Estimates of the net ground-water recharge over the study 

area and the resultant stream depletion are shown in 

figure 13. Estimates of streamflow depletion were computed by averaging the last 5 years of data and are 

shown on the first line of table 4. The average stream 

depletion of 32, 300 acre-ft/yr compares favorably with 

the 38,800 acre-ft/yr computed for the 1931-78 pointflow study of the U.S. Bureau of Reclamation (F. J. 

Otradovsky, written commun., 1981).

Four water-management alternatives for the area between Overton and Grand Island were simulated to 

identify possible ranges of future streamflow depletions: (1) Continue current management practices, (2) 

irrigate all remaining irrigable land with surface water, 

(3) irrigate all remaining irrigable land with ground 

water, replacing areas of subirrigation, and (4) irrigate 

all remaining irrigable land with ground water, without 

replacing subirrigated areas. Each of these conditions 

was assumed to start instantaneously and was modeled 

for a 50-year period following the 100-year sequence 

discussed earlier. The distribution of acreage, the average stream depletion, and the average monthly stream
ACRE-FEET IN RECHARGE, NET ANNUAL 

ACRE-FEET IN DEPLETION, STREAM ANNUAL 

8IO OIOOIOHOAH ONV OIHJHOWO3O S3IOTILS dO 3HI, aLLVId H3AIH NISVa 
Water 

management 

activity

HYDROLOGIC EFFECTS, GROUND-WATER AND SURFACE-WATER MANAGEMENT ALTERNATIVES G19 

TABLE 4. Acreages and stream depletion for current and predicted conditions

Areas, in acres

Surface- Ground- SubDryland water water irriirrigated irrigated gated

Average streamflow depletion for the last 5 years, 

in thousands of acre-feet

50- 

year

Jan. Feb. Mar. Apr. May June July Aug. Sep. Oct. Nov. Dec. Total age

1930-1980 (') (') (') (') 3.9 3.1 2.3 0.9 1.1 3.2 7.0 9.1 8.8 7.9 6.4 5.1 59.1 32 

conditions.

Continue 944,000 106,000 617,000 197,000 10.4 9.5 8.8 7.4 7.6 9.6 13.3 15.4 15.0 14.1 12.6 11.4 135 125 

current 

practices.

Surface- 716,000 378,000 617,000 154,000 3.1 2.6 1.9 .5 .4 1.8 4.4 5.9 5.8 .3 4.4 3.7 39.8 53.2 

water 

development

Ground- 742,000 106,000 889,000 128,000 16.6 15.8 15.1 13.5 13.3 15.0 19.2 21.8 21.2 20.0 18.6 17.6 207.7 174 

water replacing 

subirrigation.

Ground- 716,000 106,000 889,000 154,000 16.9 16.0 15.4 13.8 13.6 15.3 19.6 22.2 21.6 20.4 19.0 17.9 212 177 

water 

development.

'Varies with time.

depletion occurring in the last 5 years of the 50-year sequence are shown in table 4 for each alternative.

The four alternatives simulated resulted in a range of 

stream depletions. If the current water-management 

practices continue, the predicted 50-year average 

stream depletion would be 125,000 acre-ft/yr. If the 

available 270,000 acres of irrigable land were irrigated 

with some imported source of water, the average depletions would be reduced to 53,200 acre-ft/yr. If that same 

acreage were irrigated with ground water, replacing 

where possible subirrigated acreage, the depletions 

would average 174,000 acre-ft/yr. If the existing subirrigated areas were not replaced by the new irrigated 

acreage, the stream depletion would average 177,000 

acre-ft/yr.

EFFECTS OF WATER-MANAGEMENT 

ALTERNATIVES ON STREAM STAGE

Changes in the streamflow and stage of the Platte 

River will affect ground-water levels in wildlife-refuge 

areas along the Platte River (Hurr, 1981). To relate the 

effects of changes in stream discharge due to management practices to the stream stage along the habitat 

area, a relationship between stream discharge and 

stream stage was developed. The stage-discharge rating 

tables for the gaging stations, Platte River near Cozad, 

near Overton, near Odessa, and near Grand Island were

all fit to regression lines. The general form of the equation is:

h=aQb (4)

where:

h is river stage above zero flow, in feet;

Q is river discharge, in cubic feet per second; and 

a and b are regression coefficients. 

The relationship for the Cozad station differed from the 

other sites because two channels are present there, but 

the regression coefficients for the other sites (table 5) 

were remarkably similar. Based on these results, a generalized description of the stage-discharge relationship 

for the habitat area was modeled as:

/i=0.033Q05. (5)

TABLE 5. Regression coefficients for stage-discharge relationships 

for the Platte River

Regression coefficients

Station

Platte River near Overton 

Platte River near Grand Island 

Platte River near Cozad (channel 1) 

Platte River near Cozad (channel 2) 

a

(\ noo

 .040

 .020

 .414

1 Q£

b

0.479 

.484 

.549 

.333 

.382
G20 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

As a tool to evaluate the effects of various watermanagement alternatives, a frequency curve of predicted stream stage along the habitat area was computed. The historical streamflow data for the Platte 

River near Overton were used for the period 1941-77. 

To extend this record to the same 50-year sequence 

used for the net ground-water recharge rates (see section 

on "Computation of Stream Depletions"), the monthly 

flows were regressed with the monthly flows for the 

South Platte River at Julesburg, Colo. Historically, flow 

diversions between the gages near Overton and Grand 

Island have been made by the Kearney Canal and Elm 

Creek Canal. The Elm Creek Canal, abandoned in 1963, 

was not considered in this analysis of future conditions. 

Much of the water diverted to the Kearney Canal is used 

for power production and is returned to the river. The 

net amount diverted, as modeled, was based on the 

monthly average data provided by the U.S. Bureau of 

Reclamation point-flow study (F. J. Otradovsky, written commun., 1981). Thus the streamflow used to compute the frequency curve of stream stage along the habitat area is the historical Overton streamflow (1,270 ft3/s 

average), less the average Kearney Canal diversion 

(23,000 acre-ft/yr), less the stream depletion computed

for each water-management activity (see table 4) for 

50-year average. The frequency curves were computed 

not only for the entire year (fig. 14), but also for the different "hydrologic seasons" applicable to the habitat 

area. These seasons include September through February (fig. 15), March through April (fig. 16), and May 

through August (fig. 17). As can be seen in these figures, the various management alternatives have only 

minimal effect on the stage of the river.

Some hypothetical water-management alternatives 

which would affect streamflow directly were selected to 

compare their effects with the effects of the four watermanagement alternatives previously discussed. The 

possible water-management alternatives which affect 

the upstream inflow to the study area include: (1) Increase current flows in the Platte River by importing 

the water needed to irrigate 100,000 acres (average flow 

is 1,610 ft3/s); (2) decrease current flows in the river by 

diverting the water needed to irrigate 100,000 acres 

(simulated flow is 240,000 acre-ft/yr; average flow is 

1,040 ft3/s); and (3) decrease current flows in the river by 

storing or diverting all monthly flow that exceeds 2,000 

ft3/s (average flow is 1,100 ft3/s). All of these flows were 

adjusted by subtracting the monthly average Kearney

3.0

2.5 -

GROUND-WATER 

DEVELOPMENT

SURFACE-WATER 

DEVELOPMENT

GROUND WATER REPLACING 

SUBIRRIGATION

1.0 -

0.5 -

99 98 90 80 70 60 50 40 30 20 

PROBABILITY OF A GREATER STAGE

10

FIGURE 14. Annual stream-stage frequency curves for four water-management alternatives affecting stream depletion.
HYDROLOGIC EFFECTS, GROUND-WATER AND SURFACE-WATER MANAGEMENT ALTERNATIVES

2.5

G21

i i i i i i

CURRENT CONDITIONS

GROUND-WATER 

DEVELOPMENT

 SURFACE-WATER 

DEVELOPMENT

 GROUND WATER REPLACING 

SUBIRRIGATION

99 98 95 90 80 70 60 50 40 30 20 10 5 

PROBABILITY OF A GREATER STAGE, IN PERCENT

2 1

FIGURE 15. September through February stream-stage frequency curves for four water-management

alternatives affecting stream depletion.

CURRENT CONDITIONS

GROUND WATER REPLACING 

SUBIRRIGATION AND 

GROUND-WATER 

DEVELOPMENT

SURFACE-WATER 

DEVELOPMENT

95 90 80 70 60 50 40 30 20 

PROBABILITY OF A GREATFR crAr,p , N

10

FIGURE 16. March through April stream-stage frequency curves for four water-management alternatives

affecting stream depletion.
G22 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

4.0

3.5

3.0

2.5

2.0

1.5

1.0

0.5

"1 I I I r~

 CURRENT CONDITIONS

GROUND-WATER 

DEVELOPMENT

 SURFACE-WATER 

DEVELOPMENT

 GROUND WATER REPLACING 

SUBIRRIGATION

l___l i | |____I I____I_____I

99 98 95 90 80 70 60 50 40 30 20 10 5 21 

PROBABILITY OF A GREATER STAGE, IN PERCENT

FIGURE 17. May through August stream-stage frequency curves for four water-management alternatives

affecting stream depletion.

Canal diversion and the predicted stream depletion 

based on current conditions, previously discussed in the 

section on "Computation of Stream Depletions," to 

compute the frequency curves of stream stage. The annual frequency curves are shown in figure 18, and the 

frequency curves for the three hydrologic seasonsSeptember through February, March through April, 

and May through August are shown in figures 19, 20, 

and 21, respectively. Though no quantitative analysis of 

the stage-frequency curves was made, it is obvious that 

there is a much greater deviation among these sets of 

curves than for the previous sets of curves.

CONCLUSIONS

The effects of water-management practices in the area 

of the Platte River between Overton and Grand Island 

caused an average of about 32,300 acre-ft/yr of simulated stream depletion over the last 50 years. This depletion would increase to about 124,900 acre-ft/yr over a 

50-year period, even if no changes occur in the watermanagement activities due to the delayed effects of the 

historical increase in ground-water pumpage to the current level. Adding about 270,000 acres of new surfacewater irrigated acreage would reduce the depletions to
HYDROLOGIC EFFECTS, GROUND-WATER AND SURFACE-WATER MANAGEMENT ALTERNATIVES G23

AVERAGE FLOW WITH 

IRRIGATION INCREASE

AVERAGE FLOW WITH 

IRRIGATION DECREASE

AVERAGE FLOW <2000 

CUBIC FEET PER 

SECOND

98 95

_L 

90 80 70 60 50 40 30 20 10

PROBABILITY OF A GREATER STAGE, IN PERCENT

FIGURE 18. Annual stream-stage frequency curves far four water-management alternatives directly affecting upstream flow.

AVERAGE FLOW WITH 

IRRIGATION INCREASE

AVERAGE FLOW WITH 

IRRIGATION DECREASE

AVERAGE FLOW <2000 

CUBIC FEET PER 

SECOND

99 98 90 80 70 60 50 40 30 20 10 

PROBABILITY OF A GREATER STAGE, IN PERCENT

FIGURE 19. September through February stream-stage frequency curves for four water-management alternatives directly affecting upstream flow.
G24 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

3.0

2.5

2.0

~ 1.5

1.0

0.5

-- AVERAGE FLOW

 - AVERAGE FLOW WITH 

IRRIGATION INCREASE

 AVERAGE FLOW WITH 

IRRIGATION DECREASE

 AVERAGE FLOW <2000 

CUBIC FEET PER 

SECOND

0

99 98 95 90 80 70 60 50 40 30 20 10 

PROBABILITY OF A GREATER STAGE. IN PERCENT

FIGURE 20. March through April stream-stage frequency curves for four water-management alternatives

directly affecting upstream flow.

an average of 53,200 acre-ft/yr over a 50-year period. If 

ground water were used to irrigate about 270,000 acres 

of irrigable land, some in areas of current subirrigation, 

the computed 50-year average depletion would be increased to 174,000 acre-ft/yr. If the increased groundwater irrigated areas did not replace subirrigated areas, 

the computed 50-year depletion would average 177,000 

acre-ft/yr. The hydrologic effect of these possible watermanagement alternatives would be minimal on the 

stage of the river along the habitat area, as shown by 

the frequency curves. The effects of importing or diverting the 240,000 acre-ft/yr necessary to irrigate 100,000 

acres, or storing or diverting all high flows in excess of 

2,000 ft3/s, would .be much more significant to the river 

stage, as shown in the frequency curves.

REFERENCES CITED

Eagleson, P. S., Mejia-R, Ricardo, and March, Frederic, 1966, Computation of optimum realizable unit hydrographs: Water Resources 

Research, v. 2, no. 4^p. 755-764.

Hurr, R. T., 1983, Ground-water hydrology of the Mormon Island 

Crane Meadows wildlife area, near Grand Island, Hall County, Nebraska: U.S. Geological Survey Professional Paper 1277-H, 12 p.

Jenkins, C. T., 1968a, Computation of rate and volume of stream 

depletion by wells: Techniques of Water-Resources Investigations of the U.S. Geological Survey, Book 4, Chapter Dl, 17 p.

___1968b, Electric-analog and digital-computer model analysis of 

stream depletion by wells: Ground Water, v. 6, no. 6, p. 27-34.

Jensen, M. E., Wright, J. C., and Pratt, B. J., 1969, Estimating soil 

moisture depletion from climate, crop, and soil data: American 

Society of Agricultural Engineers Paper 69-941.

Johnson, C. R., 1960, Geology and ground water in the PlatteRepublican Rivers watershed and the Little Blue River basin 

above Angus, Nebraska: U.S. Geological Survey Water-Supply 

Paper 1489,142 p.

Lappala, E. G., Emery, P. A., and Otradovsky, F. J., 1979, Simulated 

changes in ground-water levels and streamflow resulting from 

future development (1970-2020) in the Platte River basin, 

Nebraska: U.S. Geological Survey Water-Resources Investigations 

79-26,82 p.

Taylor, O. J., 1971, A shortcut for computing stream depletion by 

wells using analog or digital models: Ground Water, v. 9, no. 2, 

p. 9-11.

U.S. Department of Agriculture, 1956-68, Hydrologic data for experimental watersheds in the United States, annual reports: Agricultural Research Service, Rosemont, Nebr., miscellaneous publications.

U.S. Department of Agriculture, Soil Conservation Service, 1973, Soil 

survey of Phelps County, Nebraska: 88 p.

___1974, Soil survey of Adams County, Nebraska: 102 p.
HYDROLOGIC EFFECTS, GROUND-WATER AND SURFACE-WATER MANAGEMENT ALTERNATIVES

4.0

G25

3.5

3.0

2.5

- 2.0

1.5

1.0

0.5

r i i \

AVERAGE FLOW

AVERAGE FLOW WITH 

IRRIGATION INCREASE

AVERAGE FLOW WITH 

IRRIGATION DECREASE

AVERAGE FLOW <2000 

CUBIC FEET PER 

SECOND

99 98 95 90 80 70 60 50 40 30 20 10 

PROBABILITY OF A GREATER STAGE, IN PERCENT

FIGURE 21. May through August stream-stage frequency curves for four water-management alternatives

directly affecting upstream flow.

APPENDIX

FORTRAN MODEL TO COMPUTE STREAM 

DEPLETION
G28 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

C 

C 

C

c

C 

C 

C 

C 

C 

C 

C 

C 

C 

C 

C 

C 

C 

C 

C 

C 

C

PROGRAM PLTRSP ( INPUT f OUTPUT »TAPElfTAPE2*TAPE3f TAPE* » 

1 TAP£5aINPUTfTAPE6aOUTBuT)

DIMENSION I8ANOU25) *!SOILU25) ,KOUNTY(125) »ACRES(125) ,NWS(12S> f 

1 CANALSU25) fSUBSU25)

DIMENSION ETDRY(600»4) ,ETS*(600«4) tETGW(600»4) »ETSUB(600) 

DIMENSION PERSU8U3) t ACPRWL (6* 13) *PRESNTU2) tFIX(l?)

DIMENSION UNIT(13*600) 

DIMENSION STRMQP(601)

ETORY - NET RECHARGE FOR DRYLAND

ETSW - NET RECHARGE FOR SURFACE WATER IRRIGATION

ETGW - NET RECHARGE FOR GROUND WATER IRRIGATION

ETSUR - NET RECHARGE FOR AREAS OF SUBIRRlGATlON

PEPSU8 - PERCENTAGE ADJUSTMENT OF SU8IRRIGATED AREAS (BY SAND)

ACPRWL - ACREAGE PER WELL <8Y BAND AND COUNTY)

PRFSNT - 5 YEAR AVERGE OF CURoENT MONTHLY STREAM DEPLETION

UNIT - STREAM RESPONSE TO AQUIFER STRESS (BY MONTH AND SAND) 

STRMOP - FUTURE STREAM DEPLETION

	- SDF B4NO NUM9R 

ISOIL - SOIL TYPE NUMBER 

KOUNTY - COUNTY NUMRER 

ACRES - TOTAL ACREAGE 

NWS - NUMBER OF WELLS

CANALS - ACREAGE IRRIGATED 8Y SURFACE WATER

SURS - ACREAGE THAT IS SU8IRRIGATEO

DATA POESNT /i2*o./

DATA OPMAX /IS./ AVGULO /lO./ f AVG8LD /5./ 

DATA FIX /I. »1. *1. . 1. «1. f l.*.9». 8,. 9tl. »!-.»!./

READ <5«1000) NMONTH,N

READ (5»1010) PERSUB

DO 5 I = 1»6

5 PEAD (5*1010) UCPPWL(ItJ) »Jal»l3l

DO 10 7 s 1»N

READ (It 1020) I SAND (I) »KOUNTY(I) »ISOIL(D ACRES (I) »NWS(I) 

1 CANALS(I) *SU8S(T) 

10 CONTINUE

DO 12 jalf4 

12 READ (2»1030) (ETDRY ( I » J) f 1=1 »NMONTH)

DO 14 jsl*4 

14 READ (2,1030) (ETGWdf J) f lalfNMONTH)

00 16 Jalf4 

16 READ (2*1030) (ETSW(I«J) >Ial f iMMONTW)

°EAD (2,1030) (ETSU8(I) f lal

HO 18 I a l,NMONTH

TM = (I-1J/12

IM a I - IM*12
HYDROLOGIC EFFECTS, GROUND-WATER AND SURFACE-WATER MANAGEMENT ALTERNATIVES G29

18 ETSUS(I) = ETSU8(I)*FIX(IM) 

C

READ (3) UNIT 

C

C MODEL THE PEPIOO 1379-1928 

C

oo so IMONTH a I*NMONTH 

R = o.

DRY s 0.

5'* = 0.

SB a 0.

Gw = 0.

DO 60 I = 1,N

DEPTH s AVGULD

TTLAC = ACRES(I)

CANAL s 0.

IF (KOUNTY(I) .EG. 5 .OR. KOUNTY(I) .EQ* 6) GO TO 20

CANAL = CANALS*I)

TTLAC s TTLAC - CANAL 

20 18 s IRANO(I)

IF (IB .LT. 3) GO TO 30

SUB s SUBS(I)*P£RSU8(I8>

IF (SUB .GT. TTLAC) GO TO 30*

GO TO 40 

30 SUB a TTLAC

DEPTH s AVG8LD 

^0 TTLAC s TTLAC - SUR

IS s ISOILCI)

DEPTH s DPMAX (DOMAX-OEPTH)*SUB/4CRES(I)

RCHGNT s TTLAC*ETDRY(IMONTH,IS) * CANAL* TSW(IMONTH,IS) * 

1 SUB* TSU8<IMQNTH)»(OPMAX-OePTH)/DPMAX ' R s R * RCHGNT

DRY s ORY * TTLAC

sw a sw * CANAL

SB = SR * SUB 

DO 50 IK = 1«NMONTH

STRMOP(IK) » STRMOP(IK) - RCHGNT«UNIT(IR»IK) 

50 CONTINUE 

60 CONTINUE

WRITE (6»2000) lMONTH»ORY»SW f GW»Sfl.P»STRMDP(l) 

DO 70 IK = ItNMONTH 

STRMDP(IK) = ST«MOP(IK * 1) 

70 CONTINUE 

30 CONTINUE 

C

C MODEL THE PERIOD 1929-1978 

C

DO 150 IMONTH s UN-MONTH 

p = o. 

Q*Y = o.

GW a 0. 

SW a 0. 

SB = 0. 

DO 120 I = 1,N
G30 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

DEPTH s AVGULO

K = KOIJNTY(I)

TTLAC * ACRES(I)

CANAL 3 CANALS(I)

TTLAC r TTLAC - CANAL

18 s ISAND(I)

IGW s (IMONTH -1)/12

XGW s IG* * 1

GWAC = (XGW/50.)»N"rfS(I)»ACPRWL(K»I3)

IF (GWAC .GT. TTLAC) GWAC = TTLAC

TTLAC 3 TTLAC - GWiC

IF (IB ,LT. 3) GO TO 90

SUB = SU8S(I)»P£PSU8(I3)**«50.-XGW)/49>

£0 TO 100 

90 SUB = SUBS(I) - (TTLAC-SU8S(I))» UGw-50 .)/49.

DEPTH = AVG8LD 

100 IF (SUfl .GT. TTLAC) SU8 = TTLAC

TTLAC s TTLAC - SU8

IS r ISOIL(I)

DEPTH s OPMAX - (OPMAX-OEPTH)»SU8/ACRES(I)

PCHGNT s TTLAC*£TDRY(IMONTHtIS) * CANAL*£TSW(IMONTW,IS) * 

1 GWAC*ETGW(IMONTH,IS) * SU8»ETSUB(IMONTH)*(DPMAX-OEPTH)/OPMAX

O = R * RCHGNT

DRY s -ORY * TTL4C

SW s SW * CANAL

GW s GW * GWAC

SB s SP * SUB

DO 110 IK s IfMMONTH

STRMOP(IK) s STRMOP(IK) - RCHGNT^UNIT{IB*IK) 

110 CONTINUE 

120 CONTINUE

IM s IMONTH * NMONTH

WRITE (6»2000) IH»DPY»Sw*GW,s8fPfSTRMOP(l) 

IF (IMONTH .LT. 541) GO TO 130 

IJ s (IMONTH-D/12

u s IMONTH - U»12

RRESNT(IJ) s PRESNT(IJ) * STRMOPd) 

130 DO 140 IK = ItNHONTH

STRMOP(IK) 3 STRMQpdK * 1) 

140 CONTINUE 

150 CONTINUE

00 160 1-MONTH = 1»12 

PRFSNT(IMONTH) * PRFSNT(IMONTH)/5. 

WRITE (6*2000) IMONTHfPRESNT<IMONTH) 

160 CONTINUE

wRITc! (4) STRMDP 

STOP

1000 FORMAT (215) 

1010 FORMAT (13F4.Q)

1020 FORMAT <I*»2l7tF10.0«I6«F9.0,llx»Fl2.0) 

1030 FORMAT (4X»12F7.2) 

2000 FORMAT (I5»5F8.0>G15.7) 

END
Ground-Water Hydrology of the 

Mormon Island Crane Meadows 

Wildlife Area Near Grand Island, 

Hall County, Nebraska

By R. THEODORE HURR

HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

GEOLOGICAL SURVEY PROFESSIONAL PAPER 1277-H

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1983

CONTENTS

Abstract HI

Introduction 1

Purpose and scope 1

Methods of investigation 3

Acknowledgments 3

Regional description 3

Geography 3

Geology 3

Hydrology 3

Description of study area 5

Description of study area Continued 

Geography 

Geology 

Hydrology 

Ground-water hydrology 

Water levels 

Analysis of data 

Effects of water-management changes 

Summary and conclusions 

Selected references 

H5 

5 

5

7

7

7

10

11

12

ILLUSTRATIONS

FIGURES 1-4. Maps showing:

1. Location of study area 

2. Location of observaton wells, including recorder wells, and river-stage recorders

3. Water-table configuration beneath the study area, June 1,1980 

4. Water-table configuration beneath the study area, August 10,1980 

5-8. Hydrographs showing:

5. River stage, South Channel Platte River 

6. Ground-water levels in well 5, piezometer group 3 

7. Ground-water levels in well 5, piezometer group 1 

8. Ground-water levels in well 39 

9. Graph showing relationship between rainfall and change in ground-water level 

H2

4

6

8

9

9

9

9

10

CONVERSION FACTORS

Inch-pound units used in this report may be converted to the International System of Units (SI) by use of the following conversion factors:

Multiply inch-pound unit By

inch

foot

mile

gallon per minute

foot squared per day

25.4 

0.3048 

1.609

6.309X10"2 

1.075 X10~8

To obtain SI unit

millimeter

meter

kilometer

liter per second

meter squared per second

National Geodetic Vertical Datum of 1929: A geodetic datum derived from a general adjustment of the first-order level nets of both the 

United States and Canada, formerly called mean sea level.

in

HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

GROUND-WATER HYDROLOGY OF THE

MORMON ISLAND CRANE MEADOWS WILDLIFE AREA NEAR 

GRAND ISLAND, HALL COUNTY, NEBRASKA

By R. THEODORE HURR

ABSTRACT

In and near the Mormon Island Crane Meadows wildlife area in 

south-central Nebraska, the Platte River flows generally eastward in 

a broad, flat valley. The river banks and many areas adjacent to the 

river support thick stands of cottonwood, elm, and willow trees. 

Brush, grass, pastureland, and cultivated fields occupy most of the 

remaining area Seasonally, much of the lower, non-cultivated areas 

are wetlands due to a high water table. This is the habitat for many 

types of wildlife that live in the area or stop over in the area during 

annual migrations. Sandhill cranes and whooping cranes, are part of 

the annual migrations. There is concern that water-management 

changes, such as changes in surface-water diversions or ground-water 

withdrawals for irrigation, may adversely affect the hydrologic environment of the wetland areas and be harmful to the wildlife habitat.

In order to determine some of the possible effects changes in water 

management might have on ground-water levels in the wetland areas, 

detailed data were collected from Mormon Island Crane Meadows 

wildlife area, which is on an island in the Platte River, 81A miles south 

of Grand Island, Nebr., and which is representative of other wetland 

areas along the Platte River in south-central Nebraska The island is 

approximately 10 miles long and 1 mile wide. Ground-water levels and 

river stage were monitored for 7 months in 1980 to determine the relationships between ground water and surface water for the alluvial 

aquifer-river system.

Ground-water levels beneath the island respond .to changes in river 

stage, to recharge from snowmelt and precipitation, and to evapotranspiration by riparian vegetation and from areas where the water 

table is close to the land surface. The data for the island show that 

ground-water levels in the general area along the Platte River respond 

rapidly to changes in river stage usually within 24 hours in areas 

along the river's edge as much as 2,500 feet wide. Thus, temporary 

changes in river stage due to changes in surface-water diversions will 

have an almost immediate effect on ground-water levels, and the 

change in ground-water level will be maintained as long as the change 

in river stage exists. There will be no long-term residual effect on 

ground-water levels if the river is returned to its original stage.

Changes in ground-water withdrawals will have the simultaneous 

effects of (1) directly changing ground-water levels due to water-level 

declines beneath habitat areas and (2) indirectly changing groundwater levels due to changes in river stage caused by the depletion of 

streamflow. Due to the aquifer characteristics and the distance of 

withdrawals from the habitat areas, the effects of the withdrawals 

will develop slowly and be long lasting, perhaps weeks or months. If 

most of the changes in withdrawal occur farther than 2,500 feet from 

the river, however, the resulting change in ground-water levels within

2,500 feet of the river probably will average less than 1 or 2 feet. 

These changes could be modified on a short-term basis by controlling 

the river stage through controlling diversions and reservoir releases.

INTRODUCTION

In and near the Mormon Island Crane Meadows wildlife area in south-central Nebraska, the Platte River 

flows generally eastward in a broad, flat valley. Braiding of the river channel creates numerous islands of 

various sizes. The river banks and many areas adjacent 

to the river support thick stands of cottonwood, elm, 

and willow trees. Brush, grass, pastureland, and cultivated fields occupy most of the remaining area. Seasonally, much of the lower, non-cultivated areas are wetlands due to a high water table. This is the habitat for 

many types of wildlife that live in the area or stop over 

in the area during annual migrations. Sandhill cranes 

and whooping cranes are part of the annual migrations 

which include ducks, geese, and other nongame birds. 

There is concern that water-management changes, such 

as changes in surface-water diversions or ground-water 

withdrawals for irrigation, may adversely affect the 

hydrologic environment of the wetland areas and be 

harmful to the wildlife habitat.

PURPOSE AND SCOPE

It is the purpose of this report to describe some of the 

possible effects that management changes would have 

on the ground-water system of the habitat area. The objectives of the study were to determine the relationship 

between ground water and surface water so that the effects of any increase or decrease in surface-water diversion or ground-water withdrawal that changes river 

flow and the resulting river stage or ground-water level 

directly can be used to predict the changes in groundwater levels in habitat areas. These predictions of

Hi
H2 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

changes in ground-water levels can be used by botanists 

and wildlife biologists to determine the effects on the 

habitat in terms of depth, area, and duration of standing 

water, and in the assemblage and vigor of plant communities. Rather than study the entire valley, the U.S. 

Geological Survey selected a typical area, the Mormon 

Island Crane Meadows wildlife area on an island in the

Platte River near Grand Island, Nebr., for detailed 

study (fig. 1). Although the study area takes its name 

from Mormon Island, it is not actually on Mormon 

Island. It was beyond the scope of this study to discuss 

or evaluate particular management plans or the effects 

any given plan might have on ground-water levels or 

river flow.

Grand Omaha\

Z& Island/^ ^ 

S I 

Lincoln \

..A

41°00'

40°45'

ADAMS COUNTY

5 10 MILES

10 KILOMETERS

FIGURE 1. Location of study area
GROUND-WATER HYDROLOGY, MORMON ISLAND CRANE MEADOWS WILDLIFE AREA, NEBRASKA H3

METHODS OF INVESTIGATION

Previously published reports by the U.S. Geological 

Survey and the Conservation and Survey Division, University of Nebraska, have defined the general geologic 

and hydrologic framework of the area. Detailed data on 

the Mormon Island Crane Meadows study area were obtained by drilling 60 test holes into the alluvium of the 

island to determine the lithology. These test holes were 

cased and used as either observation wells or piezometers in order to monitor water levels. Three of the six 

wells and piezometers equipped with continuous waterlevel recorders provided continuous water-level records. 

Fifty-four wells and piezometers were measured 

manually on a weekly basis (fig. 2). Two river-stage 

recorders were installed one on either side of the island 

(fig. 2). Ground-water levels and river stage were monitored for approximately 7 months, beginning in April 

and ending in November 1981.

The data were analyzed to quantitatively determine 

the relationship between river stage and ground-water 

levels. The analysis included comparing measured 

ground-water-level fluctuations with measured riverstage fluctuations, and by comparing calculated with 

measured ground-water-level fluctuations. Groundwater-level fluctuations were calculated both analytically and by digital-model simulation of a generalized 

vertical section.

ACKNOWLEDGMENTS

Mormon Island Crane Meadows wildlife area is owned 

by the Platte River Whooping Crane Critical Habitat 

Maintenance Trust and is managed by the Nature Conservancy. Farming and ranching operations are leased 

to Quirk Land and Cattle Co., of Hastings, Nebr. The 

cooperation of these organizations in allowing the U.S. 

Geological Survey to drill test holes and to collect data 

is appreciated. Weekly water-level measurements were 

made under contract by Mr. and Mrs. Russ Hettinger, 

who manage the farming and ranching operations. Their 

contribution to this study is greatly appreciated.

REGIONAL DESCRIPTION 

GEOGRAPHY

The Platte River in south-central Nebraska is in a 

broad, flat valley. The habitat along the river generally 

includes the river itself, wetland or wet meadows on the 

islands or areas adjacent to the river, and dry pastures 

and cultivated fields. Much of the bottomland near and

adjacent to the river is covered with cottonwood and 

willow trees as well as smaller scrub vegetation and 

brush. Although some birds, such as the sandhill crane, 

may feed in fields considerably distant from the river, 

the habitat area that can be affected by watermanagement changes generally is restricted to within 

about half a mile on either side of the river.

GEOLOGY

The Platte River in south-central Nebraska is underlain by alluvial clay, silt, sand, and gravel of Quaternary 

age deposited in a series of broad troughs eroded into 

the underlying clay, silt, sand, and gravel of Tertiary 

age and shales and limestones of Cretaceous age. The 

Tertiary formation is the Ogallala Formation. The Cretaceous rocks are the Pierre Shale and the Niobrara 

Formation.

The Quaternary alluvium contains the principal aquifer in the area and consists of interfingering lenses and 

beds of unconsolidated clay, silt, sand, and gravel. The 

lower one-half of this unit is predominantly clay or silt 

and the upper one-half is predominantly sand and gravel 

with some beds of clay or silt.

The Ogallala Formation consists of interfingering 

beds of clay, silt, sand, and gravel. The material in the 

sand and gravel beds is fine to medium grained, poorly 

sorted, and arkosic. The lithology can vary laterally and 

vertically within short distances. Sandstone beds are 

common. Calcium carbonate cement forms widespread 

distinctive "mortar beds," and locally, secondary silica 

has cemented the sand into quartzite (Dreeszen and 

others, 1973). Sand, gravel, and some sandstones in the 

Ogallala Formation are both porous and permeable, and 

transmit water and supply water to wells.

The Pierre Shale is a gray to black marine shale, 

which locally contains very thin layers of bentonite. The 

Niobrara Formation is predominantly gray to orange, 

argillaceous chalk and limestone with some interbedded 

chalky shale. Within the area both the Pierre Shale and 

the Niobrara Formation are relatively impermeable and 

form the lower boundary to the flow system of the 

shallow alluvial aquifer.

HYDROLOGY

The Platte River is the principal river in the area. Its 

flow is the result of the combined flows of the North 

Platte and South Platte Rivers, runoff from precipitation, surface-water diversions and return flows, and 

ground-water seepage to or from the river. The Wood 

River is tributary to the Platte River 20 miles east of
39R

EXPLANATION

U.S. GEOLOGICAL SURVEY 

OBSERVATION WELL AND 

NUMBER- R indicates recorder

RO W.

GroupIR SITE AND NUMBER OF FIVEWELL GROUP OF U.S. GEOLOGICAL SURVEY PIEZOMETERS - 

R indicates recorder

A RIVER- STAGE RECORDER

98°27'30"

T.10N.

40°47'30"

T.9N

Base from U.S. Geological Survey 

Alda, Nebraska, 1962 0 

photorevised 1974

1 MILE

0 1 KILOMETER

CONTOUR INTERVAL 5 FEET 

NATIONAL GEODETIC VERTICAL DATUM OF 1929

FIGURE 2. Location of observation wells, including recorder wells, and river-stage recorders.
GROUND-WATER HYDROLOGY, MORMON ISLAND CRANE MEADOWS WILDLIFE AREA, NEBRASKA H5

and downstream from Grand Island. The Loup River is 

tributary another 45 miles further downstream.

The flow of the North Platte River is regulated by 

releases from Lake McConaughy, a large, on-channel 

reservoir in western Nebraska The flow of the South 

Platte River is largely the result of seasonal fluctuations, and surface-water diversions and return flows.

Recharge to the alluvial aquifer along the Platte River 

is from rainfall, snowmelt, applied irrigation water, and 

seepage from the Platte River. Precipitation in Hall 

County averages about 24 inches per year, most of 

which occurs in the spring and summer. The average annual snowfall is 25 inches, most of which falls during 

February and March (Keech and Dreeszen, 1964).

Ground-water movement is generally to the east 

throughout the area Upstream from Kearney, Nebr., 

which is about 35 miles west of and upstream from 

Grand Island, ground water contributes to the flow of 

the Platte River as indicated by the configuration of the 

water table (Gutentag and Weeks, 1980). From Kearney 

downstream past Grand Island to about the confluence 

with the Wood River, the ground water has a component of flow away from the Platte River towards the 

Wood River on the north and towards the Blue River 

system on the south (Freethey, 1973; Gutentag and 

Weeks, 1980).

Discharge from the alluvial aquifer is by groundwater seepage to streams, by evapotranspiration by 

phreatophytes and from areas of shallow depth to the 

water table below land surface, and by withdrawal by 

wells.

DESCRIPTION OF STUDY AREA 

GEOGRAPHY

The unnamed island on which the Mormon Island 

Crane Meadows wildlife area is located is in the Platte 

River SYz miles south of Grand Island in Hall County, 

south-central Nebraska (fig. 1). Mormon Island, from 

which the study area gets its name, is immediately to 

the north of the unnamed island and is separated from it 

by a channel of the Platte River. The unnamed island is 

approximately 10 miles long by VA miles wide and is 

one of the many permanent islands within the braided 

channel of the Platte River. The land surface of the 

island is nearly flat, as is the land on both sides of the 

river. Along the edges of the island, the banks of the 

river channels are nearly vertical. The altitude of the 

center of the island is several feet lower than the 

margins of the island.

Most of the Crane Meadows study area is pastureland 

with various types of grasses. Some land is cultivated

and planted with row crops, such as corn. Cottonwood, 

willow, and varous scrub vegetation and brush grow 

around the edges of the island.

GEOLOGY

Beneath the study area both the Ogallala Formation 

and the Pierre Shale were removed by erosion prior to 

the deposition of the Quaternary alluvium. The Niobrara Formation is the base of the shallow hydrologic 

system in the area (Keech and Dreeszen, 1964). The 

Quaternary alluvium is approxiamtely 270 to 275 feet 

thick, of which the lower 120 to 150 feet is clay or silt. 

This lower part, although probably saturated with 

water, is not considered to be a significant part of the 

aquifer system. The upper part is 120 to 155 feet thick 

and consists of interfingering beds and lenses of sand 

and gravel with some clay and silt. The sand is medium 

to very coarse, and subrounded. The gravel is very fine 

to medium, and subrounded. The grains of the sand and 

gravel are mostly quartz with some feldspar and 

granitic fragments. In the study area this material is 

saturated to within a few feet of the land surface and 

supplies water to wells, including irrigation wells. The 

aquifer, which is part of this alluvium, is in hydraulic 

connection with the Platte River when water is present 

in one or more of the channels.

HYDROLOGY

The island on which the study area is located is 

bounded on the south by South Channel Platte River, 

which is the main channel of the river, and is bounded 

on the north by interconnecting channels between 

South Channel and Middle Channel Platte River. Middle Channel is V* to 1A mile north of the study area The 

flow of the river usually is highest in the spring due to 

snowmelt and rainfall runoff. The flow decreases during 

the summer due to upstream diversions for irrigation 

and decreasing runoff. Frequently, the flow of Middle 

Channel and the interconnecting channels ceases altogether. Occasionally, even South Channel goes dry. In 

the fall when irrigation diversions stop altogether, the 

flow of the river increases and remains approximately 

steady or decreases only slightly through the winter to 

the next spring.

Water in the alluvial aquifer is in hydraulic connection with the river when water is present in the river. 

The ground-water level is controlled by the presence and 

altitude of the river as it passes by the island. The direction of ground-water movement beneath the island, as 

inferred from the water-table contours (fig. 3), is to the
EXPLANATION

 U.S. GEOLOGICAL SURVEY 

OBSERVATION WELL

o SITE OF FIVE-WELL GROUP OF 

U.S. GEOLOGICAL SURVEY 

PIEZOMETERS

-7500 WATER-TABLE CONTOUR-Shows

altitude of water table. Contour 

interval 1 foot.

R.10W.

T.10N.

Base from U.S. Geological Survey 

Alda, Nebraska, 1962 0 

photorevised, 1974 r~

1 MILE

1 KILOMETER 

CONTOUR INTERVAL 5 FEET 

NATIONAL GEODETIC VERTICAL DATUM OF 1929

FIGURE 3. Water-table configuration beneath the study area, June 1,1980.
GROUND-WATER HYDROLOGY, MORMON ISLAND CRANE MEADOWS WILDLIFE AREA, NEBRASKA H7

northeast parallel to the principal direction of flow of 

the river. North and south of the river adjacent to the 

study area, the ground water has a slight component of 

flow away from the river as water from the river recharges the aquifer (Freethey, 1973; Gutentag and 

Weeks, 1980).

Changes in river stage will alter the direction of 

ground-water flow locally. When the river stage is high, 

the direction of flow of ground water immediately adjacent to the river will tend to become more perpendicular 

to the river's edge as water flows from the river into the 

aquifer. When the river stage is low, the direction of 

ground-water flow will tend to become more parallel to 

the river's edge, although flow still continues to be from 

the river into the aquifer. In general the ground-water 

level beneath the island and beneath the land adjacent 

to the river in the vicinity of the island is lower than the 

level of water in the river. This is due mostly to 

evapotranspiration by riparian vegetation and from 

areas where the water table is close to land surface as 

observed during the period of this study. North and 

south of the river it is also due, probably even during 

wintertime, to (1) natural flow away from the Platte 

River to other, lower river systems, such as the Wood 

River and the Blue River systems (Freethey, 1973), and 

(2) to ground-water withdrawals by wells in areas adjacent to the river.

The aquifer beneath the island supplies water to one 

irrigation well, two domestic wells, and several stock 

wells. The irrigation well is seldom used. No water is 

diverted from the river for irrigation in this area.

GROUND-WATER HYDROLOGY

WATER LEVELS

Water levels in the aquifer beneath Mormon Island 

Crane Meadows wildlife area range from land surface to 

approximately IVz feet below land surface, depending 

on the location and the time of year. Water levels are 

highest in the late spring or early summer. During this 

time, when there is water in the channels on both sides 

of the island, recharge from the river enters the groundwater system along the edges of the island and flows 

toward the center of the island, curving northeastward 

along the downstream trend of the island (fig. 3). Most 

of this water never returns to the river. It either is consumed by evapotranspiration or flows back to the north 

after the channel on the north side of the island becomes 

dry during mid- to late summer. The water-table configuration of the area in August 1980 when the channel 

on the north side of the island was dry is shown in figure 

4. Recharge from the river was still occurring along the

south side of the island. Along the north side of the 

island, the channel had dried up, recharge had stopped, 

ground-water levels were below the bottom of the channel, and the direction of ground-water flow was northward and eastward in response to more regional flow 

conditions.

The altitude of the Platte River at the stage recorder 

on South Channel (fig. 2) is shown in figure 5. The 

altitudes of ground-water levels at three sites across the 

width of the island (see fig. 2 for location) are shown in 

figures 6, 7, and 8. Comparisons between these hydrographs show rises in ground-water levels attributed to 

recharge from snowmelt (fig. 6, April 1-3, 1980) and 

rainfall (figs. 6 and 7, May 16 and May 31, 1980), with 

little or no change in river stage; general rises and declines in ground-water levels that are in direct response 

to changes in river stage; and diurnal fluctuations in 

ground-water levels that are caused by diurnal changes 

in the rate of evapotranspiration.

At three sites on the island (fig. 2), groups of piezometers were installed to monitor the hydraulic head at different depths within the aquifer. Each group consisted 

of five piezometers drilled within a circle of 25-foot 

radius. The piezometers were set at five different 

depths, approximately 30 feet apart, starting at a depth 

of 25 feet. Piezometers are different from observation 

wells in that piezometers are only open to the aquifer at 

a specific depth and provide a measure of the pressure 

or hydraulic head at that specific depth.

Water levels in each of these piezometer groups 

showed only 'a slight difference in hydraulic head from 

the top of the aquifer to the bottom. The maximum difference in hydraulic head was less than 0.2 foot higher 

near the top of the aquifer than near the bottom. This 

difference occurred during the maximum water-level 

stage (May 31 to June 1,1980).

ANALYSIS OF DATA

The response of ground-water levels to changes in 

river stage is rapid. Measured changes of water levels in 

the piezometers at piezometer group 1, about 2,500 feet 

from the nearest channel of the river, occur within 24 

hours of a change in river stage. Trial-and-error comparison of measured ground-water changes with calculated changes indicated a hydraulic diffusivity for the 

aquifer (transmissivity divided by specific yield) of approximately 200,000 feet squared per day. The calculated changes were obtained by using estimated 

values of transmissivity and specific yield in the analytical drain formula (Stallman, 1962) and by using a 

cross-sectional ground-water flow model.

It was not possible to calculate changes in groundwater levels that exactly duplicated the measured
 7500-

EXPLANATION

U.S. GEOLOGICAL SURVEY 

OBSERVATION WELL

SITE OF FIVE- WELL GROUP OF

U.S. GEOLOGICAL SURVEY

PIEZOMETERS 

WATER-TABLE CONTOUR - Shows

altitude of water table. Contour

interval 1 foot.

R.10W.

T.10N.

40°47'30"

T.9N

Base from U.S. Geological Survey 

Alda, Nebraska, 1962 0 

photorevised, 1974

1 MILE

0 1 KILOMETER

CONTOUR INTERVAL 5 FEET 

NATIONAL GEODETIC VERTICAL DATUM OF 1929

FIGURE 4. Water-table configuration beneath the study area, August 10,1980.
GROUND- OF ALTITUDE 

FEET IN LEVEL. WATER 

1929 OF NGVD ABOVE 

GROUND- OF ALTITUDE 

FEET IN LEVEL. WATER 

1929 OF NGVD ABOVE 

CO CO 00 

o o to 

CJ1 O Ul 

I I I I I 

MstMJJJJJ

GROUND- OF ALTITUDE 

FEET IN LEVEL. WATER 

1929 OF NGVD ABOVE 

8 8 I 

RIVER OF ALTITUDE 

FEET IN STAGE. 

1929 OF NGVD ABOVE 

S

CO CO 

-» o 

Ul O 

CT

9

' NOWHOW ONVISI aNvno adncniMSMoavaw 'vanv vHsvnaaN 6H
H10 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

change because of some complicating factors. Much of 

the land surface in the interior of the island is below the 

altitude of the river, even at low stage. Consequently, 

the ground-water level can rise only so high just until 

the water table intersects and rises slightly above land 

surface before ground water begins to run off as 

surface-water flow in the topographic lows and sloughs 

that drain the interior of the island. Also, the response 

of ground-water levels to changes in river stage is 

mitigated by changes in the rate of evapotranspiration 

as the depth to water below land surface changes.

Evapotranspiration causes diurnal fluctuations in the 

ground-water level which range from zero to approximately 0.3 foot, depending on weather conditions, time 

of the year, and the depth to water below land surface.

1.8

1.5

1.0

0.5

0.5 

RAINFALL, IN INCHES

1.0

FIGURE 9. Relationship between rainfall and change in ground-water

level.

A 0.3-foot change and an estimated daily evapotranspiration of 0.03 foot (F. J. Otradovsky, U.S. Bureau of 

Reclamation, oral commun., 1981) would indicate the 

specific yield for the upper few feet of the aquifer to be

0.10.

The river-stage hydrograph for South Channel (fig. 5) 

also shows diurnal fluctuations. The magnitude of these 

fluctuations is smaller than the magnitude of the fluctuations in ground-water levels, indicating that the 

river is not the cause of the ground-water fluctuations. 

In fact, the reverse is probably the case: the river-stage 

fluctuations are the combined result of direct evaporation from the water surface of the river and the loss of 

streamflow to the ground-water system to replace the 

water lost by evapotranspiration from the aquifer.

Direct recharge to the aquifer from precipitation is 

shown by the hydrograph of ground-water levels in 

figure 6. Sharp rises in ground-water levels on May 16, 

18, 20, and 31, and June 2 and 22 correspond to smaller 

rises in river stage. Rainfall measured at the Grand 

Island Airport for these dates plotted against the 

change in ground-water levels is shown in figure 9. If 

the same rainfall occurred on the island as was measured at the airport and if all of the rainfall was recharge 

to the aquifer and distributed uniformly over the aquifer, the rise would indicate a specific yield of 0.07.

The transmissivity of the aquifer in the vicinity of the 

island is approximately 20,000 feet squared per day, 

based on the diffusivity and specific-yield value of 0.10. 

This is the .transmissivity for the upper part of the 

alluvial aquifer beneath the island. A test hole showed 

this part to be 135 feet thick. Below this the formation 

became much finer grained, mostly silt and clay. This 

lower, fine-grained part of the aquifer does not contribute to the short-term ground-water responses measured 

in the upper part of the aquifer.

EFFECTS OF 

WATER-MANAGEMENT CHANGES

Ground-water levels affect the wet-meadows environment in two ways. The first way is by directly controlling the depth and areal extent of standing and slowmoving water where the water table intersects and 

stands above the land surface. The second way is the effect that the water level has on plant communities 

where the water level is below land surface. The depth to 

water, and, therefore, the water available to the root 

systems, is a factor in determining the types and varieties of plants in the community and the vigor with 

which they can grow.

Any change in water-management practices that affects the flow of the river, and consequently the river
GROUND-WATER HYDROLOGY, MORMON ISLAND CRANE MEADOWS WILDLIFE AREA, NEBRASKA Hll

stage, will have a rapid and almost direct effect on the 

ground-water level beneath Mormon Island Crane 

Meadows study area and adjacent areas. The change of 

ground-water level will occur within approximately 24 

hours in areas along the river's edge as much as 2,500 

feet wide. A rise in river stage will produce a rise in 

ground-water levels that is somewhat decreased in 

magnitude, due to an increase in the rate of evapotranspiration from the water table that is closer to the land 

surface. A decline in river stage will produce a decline in 

ground-water levels that is smaller in magnitude due to 

a decreased rate of evapotranspiration. The degree to 

which evapotranspiration will modify the magnitude of 

water-level change depends on the evapotranspirationdepth relationship and the seasonal evapotranspiration 

rate.

These changes in ground-water levels will last only as 

long as the change in river stage is maintained. There 

would be no long-term effects on the ground-water 

levels if the river were to be returned to its original 

stage.

Changes in net ground-water withdrawals also would 

have the effect of changing water levels in the aquifer 

because of increased or decreased drawdown related to 

the change in rate of net withdrawal. In general, however, this effect would only occur in areas adjacent to 

the main river channels, and not in areas or islands between the channels, where there is very little groundwater withdrawal by wells. The areas or islands between 

channels, however, would be affected only by changes in 

river stage caused by changes in river flow resulting 

from the decrease or increase in ground-water 

withdrawal.

Ground water withdrawn by wells is derived from 

change of storage within the aquifer, salvage of water 

from evapotranspiration, and depletion of streamflow. 

Because most of the ground-water pumpage along the 

Platte River is at distances greater than 2,500 feet from 

the river, the greatest drawdowns and changes in 

ground-water storage due to increases in net groundwater withdrawals will occur beyond that distance from 

the river. These changes in water levels will have little 

effect on any wildlife habitat because little habitat that 

is affected by depth to water exists beyond 2,500 feet 

from the river. The effect of increases in net groundwater withdrawals at distances closer to the river than 

2,500 feet will be to salvage evapotranspiration by 

lowering the water table and to increase streamflow 

depletion by increasing the gradient away from the 

river. Estimates and calculations of these quantities indicate that an average change in water level of not more 

than 1 or 2 feet should provide enough water from these 

sources to satisfy anticipated increases in net groundwater withdrawals for irrigation. Depletion of streamflow also would change the 'stage of the river, which 

would have the same effect on ground-water levels as 

previously discussed for changes in surface-water 

management.

Increases or decreases in ground-water withdrawals 

would have effects on water levels and river flow that 

develop more slowly and last longer than the effects 

caused by increases or decreases in surface-water diversions. The magnitude, occurrence, and duration of the 

effect from changes in ground-water withdrawals would 

depend on the magnitude of the change, the distance 

from the river, and the properties of the aquifer. The rise 

or decline of ground-water levels adjacent to the river 

could be decreased on a short-term basis by upstream 

control of diversions and reservoir releases.

SUMMARY AND CONCLUSIONS

Ground-water levels in the alluvial aquifer beneath 

the island and areas adjacent to the Platte River are 

controlled by the presence and stage of the Platte River 

in its various channels, by evapotranspiration by 

vegetation and from areas of shallow depth to water, by 

regional effects of pumpage and recharge, and by 

ground-water flow to lower river systems. Changes in 

the stage of the river rapidly affect ground-water levels. 

Ground-water responses to changes in river stage occur 

within 24 hours for areas along the river's edge as much 

as 2,500 feet wide. These water-level changes will exist 

as long as the change in river stage is maintained. Once 

the river is returned to its original stage, the groundwater level will quickly return to its original level. The 

only permanent effects may be on the plant communities if water levels are changed for prolonged periods of 

time.

Increases or decreases in the rate of net ground-water 

withdrawal from the aquifer in areas adjacent to the 

Platte River will have two simultaneous effects on the 

ground-water levels adjacent to the river. First, groundwater levels will decline or rise due to increased or decreased net withdrawal itself. Due to the aquifer characteristics and the distance of withdrawals from the 

habitat areas, the effects of the withdrawals will 

develop slowly and be long lasting, perhaps weeks or 

months. If most of the increase or decrease in 

withdrawal occurs farther than 2,500 feet from the 

river, the average ground-water level change within 

2,500 feet of the river will be less than about 1 or 2 feet. 

Ground-water levels beneath islands and areas between 

flowing river channels will not be affected directly 

unless, of course, the withdrawals are on the islands 

themselves. Second, ground-water levels will respond to 

the changes in river stage as the flow of the river increases or decreases due to changes in ground-water
H12 HYDROLOGIC AND GEOMORPHIC STUDIES OF THE PLATTE RIVER BASIN

pumpage. This change in river stage will affect groundwater levels adjacent to the river as well as beneath 

islands and between channels. Some of these rises or 

declines in ground-water levels will be decreased by accompanying increases or decreases in rates of evapotranspiration as the depth to ground water below land 

surface decreases or increases. Some water-level 

changes can be decreased by controlling the stage of the 

river on a short-term basis.

SELECTED REFERENCES

Dreeszen, V. H., Reed, E. C., and Burchett, R. R., 1973, Bedrock 

geologic map showing thickness of overlying Quaternary 

deposits, Grand Island quadrangle, Nebraska and Kansas: U.S. 

Geological Survey Miscellaneous Geologic Investigations Map 

1-819.

Freethey, G. W., 1973, Configuration of the water table, 1971, Grand 

Island quadrangle, Nebraska: Lincoln, University of Nebraska, 

Conservation and Survey Division, scale 1:250,000.

Gutentag, E. D., and Weeks, J. B., 1980, Water table in the High 

Plains aquifer in 1978 in parts of Colorado, Kansas, Nebraska, 

New Mexico, Oklahoma, South Dakota, Texas, and Wyoming: 

U.S. Geological Survey Hydrologic Investigations Atlas 

HA-642, scale 1:250,000,000.

Keech, C. F., and Dreeszen, V. H., 1964, Availability of ground water 

in Hall County, Nebraska: U.S. Geological Survey Hydrologic Investigations Atlas HA-131.

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