i <tt

(N

I

03

PQ 

6:3

OH

P

O

00

Cd

OQ 

523

Channel Patterns and 

Terraces of the Loup Rivers

i,

in Nebraska

GEOLOGICAL SURVEY PROFESSIONAL PAPER 422-D

Prepared as part of the program 

of the Department of the Interior 

for development of the 

Missouri River basin

 c

CO

Channel Patterns and 

Terraces of the Loup Rivers 

in Nebraska

By JAMES C. BRICE

PHYSIOGRAPHIC AND HYDRAULIC STUDIES OF RIVERS

GEOLOGICAL SURVEY PROFESSIONAL PAPER 422-D

Prepared as part of the program 

of the Department of the Interior 

for development of the 

Missouri River basin

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1964
UNITED STATES DEPARTMENT OF THE INTERIOR 

STEWART L. UDALL, Secretary

GEOLOGICAL SURVEY 

Thomas B. Nolan, Director

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

Washington, D.C. 20402
CONTENTS

Abstract. _ ----------____-_.__________.__..____._...

Introduction.-.._._..___.__.___...'_.._.._.___...___

Pleistocene and Recent deposits.......L..............

North Loup River valley near Elba._____._..___._

North Loup River valley near Burwell..__.__._.__ 

North Loup River valley downstream from Brewster. 

North Loup River valley upstream from Brewster... 

South Loup River valley near Cumro. ____________

Summary of Pleistocene and Recent geologic history _

Geologic influences on the longitudinal river profiles.....

Influence of rock resistance---_-------..-_.--__--

Influence of regional slope and relief.....__--_--..,,

The Middle Loup River at Dunning_.___..__._.__._._ 

Hydraulic factors in relation to width.._.__.._.__, 

Hydraulic factors in relation to braiding...........

Hydraulic factors in relation to a confluence........

Page 

Dl

1

2

3

5

5

6

8

8

9

10

12

14

14

15

21

The Middle Loup River at Dunning Continued. Page 

Summary of hydraulic factors in relation to channel

pattern..__,,._______--_.___--------------,-- D21

Observations on the formation of sandbars, islands, and

valley flats--,....,..--._--.-,--_----.------------ 23

Measurement and description of channel patterns._,.___ 25

Meandering and sinuosity._____..-,..,-_._,--.,-.. 25

Braiding....---.--.....-----.I-.------,,----..--- 27

Width.. ,____.____,_,_,__..,.-_ T --, T .,._-,.-,- 31

Channel patterns of the Loup Rivers.,.,,.,____,_, 31

Relation of selected hydraulic factors to channel pattern. 32

Bank credibility.......,.._-,,..-.-.---.,.,-.,,,- 32

Discharge- ... 1 ^. 7 _..._ T , 7 .,,,,,---,,,,.--.,---, 35

Bed material a.nd suspended-sediment concentration. 37

Water temperature..__,_,.,._--_,.,-,,-,.,_,_....,- 38

Longitudinal river slope i&nd valley slope.,.,,--.,-- 39

References cited_. -_--_--,-,-_,,-._---,-,,,,...--.-. 40

ILLUSTRATIONS

Page 

FIGURE 1. Map of Loup River drainage basin_......,....._,,_..,.._.,.,.,,.,^-....,J7 ,^^-^,,^._.--,.,-,-.,,-.- D2

2. General topographic and stratigraphic relations of valley fills in the North, South, and -Middle Loup River valleys, 3

3. Generalized geologic section along northwest side of Coopers Canyon near Elba.,,_,-_.,_,.__,,.._,-,,,---,--- 4

4. Cross section in Coopers Canyon near Elbar -_-_-, r ,-..,--- T ,,-.,-,,-,--.,-, ,,-,--..',-------,-----.->------- 4

5. Geologic section of north side of North Loup River valley near Burwe.ll__.,---,_,,;.,,_-.-_,_--'l-. T _..._-__-_ 5

6. Stratigraphic diagram of valley fill of the Elba terrace and valley fill of Pe,orian age exposed in cut bank of North

Loup River about 5 miles downstream from Brewster.,,____,_,..,,,,.,_-,___._--__--__.---_--__-------- 6

7. Cross section of North Loup River valley 6 miles upstream from Brewster-_._,__ -.......I....-..----.---- 7

8. Longitudinal river profile, valley profile, and Elba terrace profile, North Loup River ..................1..... 10

9. Longitudinal river profile and valley profile, Middle Loup River, __.,.__-,, ................^............... -11

10. Longitudinal river profile and valley profile, South Loup River._._ ;._ ,__, _, _.----.---------'------------- 12

11. Location of sections on a reach of the Middle Loup and Dismal Rivers near Dunning..,_,,----.---__.---,---- 14

12. Cross profiles of Middle Loup River at Dunning......_,,,_..,__,,__,,,,_,_.,:.,._-.^...................... 14

13. Mean depth, mean velocity, local slope, and effective area in relation to effective width at sections B, Cz, E, and

A, Middle Loup River at Dunning..._______-._________._,.,,. T _,^_...___._-_--____--_-____._-----.- 16

14. Cross profiles of section A, Middle Loup River at Dunning.__,._,__,,__--,_,___--_-_-.__,._-__ ..--._-_. 18

15. Maximum depth, mean velocity, local slope, and effective area in relation to water width at half mean depth, section A, Middle Loup River at Dunning__-__.__,_________,,__,____, T ._ .....^....................... 19

16. Effective area and local slope in relation to effective width for sections upstream and downstream from confluence of Middle Loup and Dismal Rivers_ .................^......................^-....^......... 22

17. Aerial photograph and tracing of photograph, North Loup River, about 1 mile downstream from gaging station

near St. Paul.._...__._....__.__......._.__._.. ...... T .........--......-.-...._.-,---.-..-__.- 23

18. Small lobe-shaped dunes on submersed sandbar in North Loup River 8 mijes downstream from Brewster -------- 24

19. Straight reach of North Loup River, same locality as figure 18. T ...........^..............^..........--.-- 24

20. Delineation of meander belt, axis of meander belt, and channel arcs for measurement of sinuosity and symmetry. _ 25

21. Delineation of a reach of the Buyuk Menderes River, Turkey, for measurement of sinuosity and symmetry._., 26

22. Reaches that illustrate different values of the braiding index. T ,__.,-_.,,-.-_-.,___--_,--,-,---__________- 29

23. Reaches that illustrate different values of the sinuosity index,...,.-._,_-_, ,.......................^...... 30

24. Longitudinal river profile and valley profile, Calamus River.,,_-__-,..__.-,__.,_.-,-_._-_---,___-_-__-_-. 34

25. Diagrammatic relation of sinuosity index to width and bank credibility, Calamus River__. ._._..______.._-.- 34

26. Width in relation to mean annual discharge and average maximum daily discharge for different channel patterns. ..........................................,^.... r .:.........^....^.^......... T ............. 36

27. Suspended-sediment concentration in relation to temperature and discharge, sections A, JE, and B, .Middle Lpup

River at Dunning. ..............................,,^,.,....................,.l..^.................. 38

28. Velocity in relation to temperature and discharge, sections A and E, Middle Loup River at Dunning..._______ 39

29. Reach slope in relation to the average maximum daily discharges for meandering and braided reaches. ...._.-- 40

in
IV CONTENTS

TABLES

TABLES 1-2. Values of hydraulic factors at Page

1. Section A, Middle Loup River at Dunning, Nebr___._______._._______.._.__._.___.__..________-..._ D20

2. Gaging stations in the Loup River basin._______________________________________________________ 28
PHYSIOGRAPHIC AND HYDRAULIC STUDIES OF RIVERS

CHANNEL PATTERNS AND TERRACES OF THE LOUP RIVERS IN NEBRASKA

By JAMES C. BRICE

ABSTRACT

The North, South, and Middle Loup Rivers drain an area 

of about 12,000 square miles in central Nebraska. The North 

and Middle Loup, which rise in the Sandhills, 'have notably 

constant discharges because much of their flow is derived 

from ground water. Moderate sinuosity is characteristic of 

the South Loup whereas the North and Middle Loup have low 

sinuosity (except in their upper courses) and tend to be 

braided. The rivers are bordered by well-defined terraces 

which are described and interpreted historically as a background for explaining the morphology of the modern rivers. 

Valley-fill deposits ranging in age from Kansan to Recent 

are exposed along the rivers, and the fill underlying the 

youngest major terrace is assigned an age of about 10,000 

years on the basis of three carbon-14 age determinations. 

The rivers are probably slowly degrading, as the lowest terraces are cut on older fill.

Along the Middle Loup near Dunning, a decrease in channel width at constant discharge is accompanied by a decrease 

in effective area and local slope and by an increase in mean 

depth and mean velocity. In a braided section, bars submersed to a depth equal to or less than half mean depth arr 

considered equivalent to emersed bars, and the width of the 

braided section is expressed as the width of flowing water at 

half mean depth. The effect of braiding at a wide section is 

to decrease the width of flowing water, and the changes in 

hydraulic variables that accompany braiding are similar to 

the changes that accompany flow from a wide single channel 

to a more narrow single channel.

The long river profiles are less steep than the long profile 

of the Great Plains, owing mainly to the sinuosity of the 

rivers. The Great Plains profile is nearly straight, and the 

river profiles are straight for most of their length. The 

slopes of meandering reaches generally are less steep than 

the slopes of braided reaches of similar discharge, but local 

slope correlates more closely with the width of flowing water 

than with any other aspect of channel pattern. The slope of 

the long river profiles shows little or no change at the confluence of major tributaries, and it does not show any significant correlation with downstream increase in discharge, 

which is evidently accommodated mainly by changes in cross 

section. Slope is regarded as a partially independent variable.

Channel patterns are quantitatively described, for geomorphic purposes, by a braiding index and a sinuosity index. 

The greater sinuosity of the South Loup, in comparison with 

the lower courses of the North Loup and Middle Loup, is attributed to the higher concentration of silt and clay in its suspended load. Probably, the silt and clay promotes sinuosity 

as it becomes incorporated in bank materials and increases 

the cohesiveness of banks. Within the Sandhills, the North

Loup, Middle Loup, and their tributaries tend to be sinuous 

despite a very low concentration of silt and clay in the suspended load; however, swamp vegetation is common along 

the stream courses, and it probably promotes sinuosity by 

increasing bank resistance. In general, where banks are of 

sand and easily erodible, wide shallow channels tend to develop. Braiding takes place in wide shallow channels by the 

growth and stabilization of longitudinal sandbars, which probably originate from breaching of transverse bars and dunes. 

Sinuous reaches are generally narrower than braided or 

straight reaches of similar discharge. Width, although highly 

variable locally, increases downstream approximately as the 

0.5 power of bank-full discharge. The downstream relation 

of width to discharge is affected by .a downstream increase in 

variability of discharge.

INTRODUCTION

The Loup River basin (fig. 1) occupies all of central 

Nebraska. The part of the basin considered in this 

report has an area of about 12,000 square miles. Of 

this area, about 4,500 square miles is mantled with 

loess and contributes directly to surface runoff, and 

about 7,500 square miles is mantled with dune sand and 

does not contribute directly to surface runoff. (See 

fig. 1.) Annual rainfall averages about 20 inches in 

the eastern part of the basin and about 15 inches in the 

western part.

The purposes of this report are to describe the channel patterns of the Loup Rivers quantitatively and to 

determine the factors that have had the greatest influence on the development of these patterns. Among 

the factors considered were the gradients and deposits 

of ancestral rivers. Terraces and valley-fill deposits 

of late Wisconsin and Recent age were studied, and 

the geologic history of the Loup Rivers was outlined. 

River widths and channel patterns were measured on 

aerial photographs, and long profiles were prepared 

from topographic maps. Detailed measurements on 

the Middle Loup and Dismal Rivers made by the 

Geological Survey in connection with investigations of 

sediment transport were analyzed and related to 

channel pattern.

Fieldwork, which was done in the summer of 1958, 

consisted mainly of an investigation of terraces and 

terrace deposits, and the movement of dunes and bars 

in the river channels was also observed.

Dl
D2 CHANNEL PATTERN'S ANt> TERRACES OF THE LOUP RIVERS IN NEBRASKA

Rivers of the Loup basin are especially suitable for 

a study of channel patterns and other aspects of river 

morphology. Different reaches of the North and Middle Loup Rivers represent meandering, braided, 

straight, or sinuous channel patterns; and the South 

Loup River is meandering. Gaging stations are well 

distributed along the rivers (see fig. 1), and the period 

of record for most of these stations is adequately long. 

The North and Middle Loup Rivers have in their upper 

courses notably constant discharges because most of 

their flow is derived from ground water rather than 

from surface runoff. Reasonably complete data on 

suspended-sediment load are available, and investigations of total load have been made in a turbulence 

flume at Dunning. Topographic maps published between 1951 and 1955 are available for most of the basin; 

these have a scale of 1:24,000 and a contour interval 

of 10 feet. Other parts of the basin are covered on 

recently published topographic maps that have a scale 

of 1: 62,500 and a contour interval of 20 feet. Aerial 

photographs, taken in the 1930's and again in the 1950's, 

are available.

This report was written under the direction of D. M. 

Culbertson, district engineer at Lincoln, Nebr. Three 

carbon-14 age determinations were made by Meyer

Rubin. B. R. Colby, M. Gordon Wolman, and S. A. 

Schumm critically read the manuscript and offered 

many helpful suggestions.

PLEISTOCENE AND RECENT DEPOSITS

Pleistocene stratigraphic units that were distinguished in the Loup River basin are shown in figure 

2. The basin is underlain by the Ogallala Formation 

(Pliocene), which crops out at widely scattered localities along the sides of the main valleys. The 

Ogallala is composed of alluvial gravels, sands, and 

silts, from which much of the Pleistocene valley fill 

has been derived. The oldest Pleistocene deposits 

observed during the present investigation are correlated with the Kansan Glaciation on the basis of their 

stratigraphic position beneath two buried soils, of 

which the upper was identified as the Sangamon and 

the lower as the Yarmouth. The Loveland Formation 

(Illinoian) on the upland consists of dune sand and 

loess which commonly are found in alternate layers. 

Outcrops of the Sangamon soil are common along 

the valleys of minor tributaries and along roadcuts in 

the upland. Along the main valleys, the Sangamon 

soil is developed on silt, sand, or gravel that is presumably of Illinoian age.

Stapleto'n \Arnold

EXPLANATION

Stations for which records of water 

and sediment discharges only are 

available

Stations for which records of water 

discharges only are .available

1.0 20 30 40 MILES

41 41'

99 <

FIGURE 1. Map of Loup River drainage basin.
PHYSIOGRAPHIC AND HYDRAULIC STUDIES OF RIVERS D3

Peorian Loess of Wisconsin age mantles the southern half of the Loup River basin. The upland loess 

extends down the valley sides and merges with a contemporaneous valley fill of Peorian age which consists 

mostly of silt in minor tributary valleys and of silt, 

sand, and gravel in the main valleys. (See figs. 2, 3, 

4.) The physiographic expression of this valley fill 

of Peorian age, here called the Kilgore terrace, has 

been mostly obliterated by erosion, but a few distinct 

remnants of the Kilgore terrace can be seen along the 

South Loup River near Cumro.

The most conspicuous and extensive terrace in the 

main valleys stands 20-40 feet above river level, and 

many broad, flat remnants of this terrace occur along 

the lower 100 miles of the North and Middle Loup 

Rivers. This terrace is here called the Elba terrace 

because the town of Elba is built on its surface and 

because the underlying valley fill is well exposed in 

the walls of a canyon southeast of Elba. (See figs. 3, 

4.) Carbon-14 age determinations indicate that deposition of the valley fill of the Elba terrace began 

about 10,000 years B.P. Several minor terrace deposits of late Recent age stand along the main streams 

at heights ranging from a few feet to 15 feet above 

river level.

NORTH LOTTP, RIVER VALLEY NEAR ELBA

About 0.6 mile southeast of Elba, the Elba terrace 

is deeply trenched by an intermittent stream that descends from the upland and flows in a canyon northwestward across the terrace and into the North Loup

River. (See fig. 3.) Most minor tributaries of the 

river, both intermittent and permanent, have cut 

shallow valleys into the terraces that border the 

river; in the canyon southeast of Elba is one of the 

few deep cross sections to be found. This canyon, 

although unnamed on the Elba quadrangle sheet, was 

called Coopers Canyon by Miller and Scott (1955), 

and this name is used here. The entrenchment of 

Coopers Canyon is perhaps explained by the fact that 

the canyon meets the river on the outside of a meander bend where the meander has made a steep cut 

into the Elba terrace about 30 feet above river level. 

Successive shifts of the river against the mouth of the 

intermittent stream probably formed a succession of 

headcuts that advanced rapidly upstream during 

times of heavy runoff and thus formed the canyon. 

Because the history of Coopers Canyon is not representative of stream history in the Loup River basin, 

the minor late Recent terrace deposits in the canyon 

have no regional significance.

The valley fill exposed in the nearly vertical walls 

of Coopers Canyon was described in detail by Miller 

and Scott (1955). The thickness of exposed valley fill 

is about 40 feet, of which the lower 12-15 feet is white 

crossbedded sand and the upper 23-25 feet is silt. 

Within the silt are several humic zones, which Miller 

and Scott interpreted as soils, developed during different interglacial episodes of the Pleistocene. The lowest and most conspicuous of these humic zones was 

named by Miller and Scott the Coopers Canyon gley 

soil. They attributed this soil to weathering during

20-

20 

40 

60-

Kilgore 

terrace

Elba 

-terrace

Valley fill \ Valley fill \ Valley fill of

is^ofKansan "\* oflHinoian* Peorian age

!|x age .\> .age \ \

5s«si\ V V ,

^Il| V \ \

^li!f;\ _ _ V _ _ _\ __(lowan and

Terraces of late 

Recent age

Valley fill of the Elba Terrace

(Recent age)

Ogallala Formation

1000

I

FIGURE 2. General topographic and stratigraphic relations of valley fills in the North, South, and Middle Loup River valleys.

Dashed lines are Inferred contacts.
D4 CHANNEL PATTERNS AND TERRACES OF THE LOUP RIVERS IN NEBRASKA

? °

\ Valley fill of the Elba terrace

Northeast

FIGURE 3. Generalized geologic section along northwest side of Coopers Canyon near Elba. Dotted line indicates Elba terrace

profile just southeast of canyon. Dashed lines are inferred contacts.

Southeast

1830

FIGURE 4. Cross section in Coopers Canyon near Elba. Section is 

1,100 feet upstream from bridge on State Route 11.

the entire interval between the end of the Kansan 

Glaciation and the beginning of the Gary Stade of the 

Wisconsin Glaciation.

In 1958 the Coopers Canyon gley soil was examined in detail by ithe writer at several places 

along the canyon walls, particularly on the northwest wall 100 feet upstream from the railroad 

bridge that crosses the canyon. Here the soil 

consists of a band of gray silty clay about 1 foot 

thick underlain by a band of calcareous silty sand 

in which snail shells are so abundant that they 

give the sand the appearance of a coquina. A 

collection of large and apparently unaltered snail 

shells from the calcareous silty sand yielded a 

carbon-14 age of 10,500±250 years (U.S. Geol. 

Survey lab. No. W-752). As the snail-bearing

layer is only about 1 foot above the sand that 

forms the base of the exposure and as the crossbedding of the sand indicates rather rapid deposition, the sand probably is not much older than 

10,000 years. Miller and Scott (1961, p. 1284) 

published a revision of their previous interpretation (1955) of stratigraphy in Coopers Canyon. 

They now consider all the alluvium and soils in 

the high terrace (here named the Elba terrace) 

as "* * * younger than the Two Creeks interstadial." 

Along Coopers Canyon upstream from the point 

at which the canyon enters the upland, the Elba terrace is absent, probably because it has been removed by lateral erosion. The sides of the canyon are composed of Peorian Loess, of valley 

fill of Peorian age, and of Loveland Formation 

overlain by Peorian Loess; set against these 

sides are minor valley fills younger than the 

Elba. About 1,100 feet upstream from the bridge 

where State Route 11 crosses Coopers Canyon, 

the Sangamon soil is well exposed in the north 

side of Coopers Canyon; the top of the soil is 

about 15 feet above the canyon bottom, and at 

one end of the exposure the soil is truncated by 

valley fill of Peorian age. (See fig. 4.) The 

appearance of the Sangamon soil at this locality 

is typical of its general appearance throughout 

Nebraska, except that, no Cca horizon has developed. The Sangamon soil that has developed in 

upland areas is commonly a soil complex (some 

of the horizons are repeated vertically); and the
PHYSIOGRAPHIC AND HYDRAULIC STUDIES OF RIVERS D5

Sangamon soil that has developed on valley fills, 

like the Sangamon soil in Coopers Canyon, may 

represent only part of this complex. The Sangamon soil in Coopers Canyon consists of a darkgrayish-brown (10T7? 4/2 moist) mimic zone 

2 feet thick underlain by a zone of clay enrichment 6 feet thick. The parent Loveland Formation consists of light-yellowish-brown (10J7? 6/4 

moist) silt underlain by sand of the same color.

NORTH LOUP RIVER VALLEY NEAR BURWELL

Pleistocene deposits ranging in age from Kansan 

to Wisconsin are well exposed in the sharply dissected 

valley side of the North Loup River 2 miles north of 

Burwell, Nebr. In the NE^NE^ sec. 11, T. 21 N., 

R. 16 W., the Sangamon soil forms a conspicuous band 

on <a steep-sided ridge (see fig. 5); and ashy silts 

crop out at the base of this ridge. Although the Yarmouth soil does not crop out in this ridge, it is well 

exposed 700 feet west of the ridge; there it is developed on about 4 feet=of ashy silt. The ashy silt is 

underlain by gravel which has been excavated for 

road building. Although the thickness of the Peorian 

Loess is only about 20 feet at this locality, it increases 

rapidly to about 70 feet a few hundred yards to the 

north.

About 3 miles east of Burwell, the uplands north of 

North Loup River is trenched by Jones Canyon, 

which is steep sided and deep. In the upper reaches 

of this canyon, in the NE^4 sec. 9, T. 21 N., R. 15 W., 

a thickness of 90 feet of Peorian Loess is exposed; the 

total thickness of the Peorian here is even greater, as 

the base is not exposed.

The valley fill of the Elba terrace and the valley fill 

of Peorian age are well exposed in a deep cut on the 

outside of a meander bend of the North Loup River 

near the center of sec. 5, T. 22 N., R. 21 W., about 5 

miles downstream from Brewster. (See fig. 6.) A 

peat bed within the valley fill of the Elba !terrace 

abuts sharply against both sides of a residual ridge of 

valley fill of Peorian age, and a radiocarbon determination on a sample of the peat (U.S. Geol. Survey lab. 

No. W-755) yielded an age of 8,400±250 years B.P. 

The surface of the Elba1 terrace, which is locally 

buried by dune sand, stands about 20 feet above the 

water level of the river. A lower terrace surface, 

which stands about 10 feet above water level, has 

been cut on valley fill of the Elba terrace; the peat 

bed within the Elba extends continuously beneath this 

lower surface.

The valley fill against which the valley fill of the 

Elba terrace abuts is 45 feet thick and consists of 

poorly sorted sand and gravel throughout; it is identified as valley fill of Peorian age only on the basis of 

stratigraphic and topographic position. Rapid deposition of this valley fill is indicated by the absence of 

buried humic zones, the absence of clay or peat beds, 

and the presence of large-scale crossbedding in the 

gravel beds.

The following stratigraphic section of dune sand 

and valley fill of the Elba terrace applies to the cutbank shown on the left side of figure 6, near the conNorth

2300'-

2250'-

2200'-

2150'-

South

FIODBK 5. Geologic section of north side of North Loup River valley near Burwell.

719-579 O-64 2
D6 CHANNEL PATTERNS AND TERRACES OF THE LOUP RIVERS IN NEBRASKA

tact between the Elba valley fill and valley fill of 

Peorian age:

Measured section of Elba Terrace about 5 miles downstream from.

Brewster

Sand, fine-grained, white, aeolian______

Humic zone in silty, clayey sand; black 

(WYR 2/1 moist)____._____________

Sand, medium- to fine-grained, yellowishgray _---________-_____-_____---__

Clay, sandy, medium-gray_-._________

Humic zone in sand; black (IQYR 2/1 

moist)__________________________

Sand, light-gray; mottled by filled worm

burrows..._____________________ 23. 7-25.0

Sand, medium- to fine-grained, yellowishgray. ............................

Sand interbedded with peaty clay and 

sand. Unit grades horizontally into 

bed of peat 3 ft thick which contains 

abundant upright Equisetum stems_

Sand, medium-grained, white; contains 

laminae of black clay_______________

Sand and gravel, poorly sorted, crossbedded- __________________________

(Water level of North Loup River 

at 41 ft)

Depth (feet) Thickness 

(feet)

0-21 21. 0

21-22

22-23

23-23. 2

23. 2-23. 7

23. 7-25.0

25-26

1.0

1.0

.2

. 5

1. 3

1.0

26-29 

29-34 

34-41

3.0 

5.0 

7.0

NORTH LOUP RIVER VALLEY UPSTREAM FROM 

BREWSTER

In the vicinity of Pitt Bridge, which crosses the 

North Loup Eiver 6 miles upstream from Brewster, 

the Elba terrace forms an extensive flat about 30 feet 

above water level on the south side of the river, and a 

succession of lower terraces forms flats on the north 

side of the river. The most extensive of these lower

terraces stands about 12 feet above water level, and 

other less extensive terraces stand at 4 feet and at 2 

feet above water level. About 1,000 feet downstream 

from the bridge, a section across the 4-foot and the 12- 

foot terraces is exposed in a meander cut. A peat bed 

crops out near water level under the 4-foot terrace surface and extends continuously under the 12-foot terrace surface. (See fig. 7.) The 4-foot terrace was 

evidently cut on the fill that contains the peat bed. 

The age of 9,000 ±250 years B.P., obtained on a log 

from the peat bed (U.S. Geol. Survey lab. No. W750), indicates that the fill on which both the 4-foot 

and the 12-foot terraces are cut is the valley fill of the 

Elba terrace. Where W-750 was collected, the fill 

underlying the 12-foot terrace is as follows:

Measured section of fill underlying 12-foot terrace 6 miles upstream 

from Brewster

Depth (feet)

Surface soil, very pale brown (IQYR 8/4 

moist); weak humic zone developed on 

fine-grained sand__________________

Sand, fine-grained, white; mottled by

 numerous filled worm burrows in

upper part______________________

Humic zone, dark-gray (10FS 4/1

moist); developed on fine-grained sand. 

Sand, medium- to fine-grained, white,

crossbedded; contains streamers of

small pebbles and a few thin layers of

dark clay_____ ____________________

Peat, dark-brown, rubbery; contains

abundant Equisetum stems and a few

small logs_-__-_______-_-____.___ 9. 5-10. 5

Sand, medium-gray, silty.____________ 10. 5-11. 0

(Water level of river at 11 ft)

0-1.2

1. 2-3. 2

3, 2-3. 5

3. 5-9. 5

Thickness 

(feet)

1.2

2.0

6.0

1.0 

. 5

West (upstream) East (downstream)

2480'

2460'-

2440'-

2420'

FIGURE 6. Stratigraphic diagram of valley fill of the Elba terrace and valley fill of Peorian age exposed In cut bank of North Loup

River about 5 miles downstream from Brewster.

Cut surface on valley fill 

of the Elba terrace
PHYSIOGRAPHIC AND HYDRAULIC STUDIES OF RIVERS D7

dnoj

8-
D8 CHANNEL PATTERNS AND TERRACES OF THE LOUP RIVERS IN NEBRASKA

SOUTH LOUP RIVER VALLEY NEAR CUMRO

An extensive terrace standing 30^40 feet above 

river level in many places along the South Loup 

River is correlated with the Elba terrace of the North 

Loup River on the basis of height, degree of dissection, and stratigraphic relation with older valley fills. 

-The fill of the Elba terrace is well exposed along the 

South Loup River at several localities upstream and 

downstream from Cumro. Silt and fine sand are the 

main constituents of the fill; however, the proportion 

of these is not uniform from place to place, and no 

uniform gradation from coarse sediment at the base 

of the fill to fine sediment toward the top was observed.

Along the South Loup River near Cumro, remnants 

of a (terrace standing 60-80 feet above river level 

were observed. This terrace is here called the Kilgore terrace because sections of the terrace fill and 

remnants of the terrace surface can be seen along 

Kilgore Creek, which is about 3 miles downstream 

from Cumro. Where sections of the fill underlying 

the Kilgore terrace are exposed along the South Loup 

River, as at Satoria, the fill consists mainly of waterlaid sand and silt. The fill underlying the Kilgore 

terrace is considered to be valley fill of Peorian age, 

contemporaneous with Peorian Loess on the upland, 

because the Kilgore terrace slopes up and merges with 

the upland without any break in topography. Moreover, the fill underlying the Kilgore terrace is the only 

fill observed that is older than the valley fill of the 

Elba terrace but younger than the Loveland 

Formation.

Minor terraces at various elevations below the Elba 

terrace surface appear in the vicinity of Cumro and 

generally along the South Loup River. These minor 

terraces could not be correlated from place to place 

along the river, and their variability in height above 

river level suggests that they are cut terraces rather 

than fill terraces. Downcutting by the South Loup 

River is indicated by the presence of abandoned channels that stand at different heights above the present 

river level and below the level of the Elba terrace.

SUMMARY OF PLEISTOCENE AND RECENT 

GEOLOGIC HISTORY

The valleys of the Loup Rivers were originally incised into the Ogallala Formation prior to Kansan 

time, perhaps as early as the late Pliocene. Exposed 

Kansan deposits are sparse along the present valleys, 

and the rivers have probably shifted their courses 

greatly during the Pleistocene. The valley fill of 

Kansan age at Burwell consists mainly of gravel and 

sand, and it filled the bedrock valleys to a height of 

about 80 feet above present river level. The valley 

fill of Kansan age was probably incised before deposition of the valley fill of Illinoian age, the top of 

which stands about 60 feet above present river level; 

however, no stratigraphic evidence of such incision 

was found.

After the development of the Sangamon soil, the 

main valleys were incised at least to the present river 

levels, and the upland was deeply gullied. Incision of 

the main valleys is indicated by the position of valley 

fill of Peorian age, which crops out near the level of 

the present rivers. At upland roadcuts, steep-sided 

hillocks cut in the Loveland Formation and buried by 

the Peorian Loess can be distinguished. The hillocks 

commonly are capped by the Sangamon soil, and on 

their buried slopes detached slabs of Sangamon soil 

are commonly incorporated in the base of the Peorian. 

The origin of these slabs is puzzling, but probably 

they were detached by erosion from near the top of 

the slope and then, after sliding some distance downslope, were incorporated in the accumulating Peorian 

Loess. The Peorian Loess accumulated to a maximum depth of about 50 feet on the upland near Ord 

and to a depth of about 90 feet on the upland near Burwell, and the valley fill of Peorian age accumulated 

in the main valleys to a height of 60-80 feet above the 

present river level. Scattered remnants of the surface 

of the valley fill of Peorian age are preserved, and 

this surface is here called the Kilgore terrace.

Deposition of the Peorian Loess and valley fill was 

followed by deep incision in the main valleys, inasmuch as the surface of the next younger valley fill 

(that of the Elba terrace) stands about 30 feet below 

the surface of the Kilgore terrace and the thickness of 

the valley fill of the Elba terrace is at least 30 feet. 

This incision in the main valleys was accompanied by 

extensive gully and drainage development in the upland. Nearly all the present tributaries, except for 

gullies of late Recent age, are bordered by remnants 

of the Elba terrace and, therefore, existed before deposition of the valley fill of the Elba terrace.

Deposition o>f the valley fill of the Elba terrace in 

the valleys of intermittent tributaries was accompanied by extensive grading of the valley sides, which 

slope smoothly down to the surface of the fill. Along 

the largest permanent streams, grading of valley sides 

is less notable, probably because these streams continued to steepen their valley sides by lateral planation during deposition of the valley fill of the Elba 

terrace. Minor buried soils are common in the valley 

fill of the Elba terrace, particularly in the upper part; 

but the number, degree of development, and position 

of these soils vary from place to place. The soils, 

which have poorly developed profiles, probably formed 

during short intervals, of perhaps no more than a few 

hundred years each, when deposition of the valley fill
D9

of the Elba terrace was temporarily halted. The 

lateral extent of each soil appears to be local rather 

than general; differences in soil characteristics over 

short lateral distances probably resulted from differences in drainage that existed during soil development. Close spacing of minor soil and humic zones in 

the upper part of the valley fill of the Elba terrace 

suggests slow and intermittent deposition of this upper 

part. Three carbon-14 age determinations on valley 

fill of the Elba terrace along the North Loup Kiver 

indicate that deposition began somewhat earlier than 

10,500 years B.P. and was still in progress 8,000 years 

B.P. Development of buried soils in the upper part 

of the fill and grading of valley-side slopes must have 

required a long period of time; hence, incision of the 

fill and dissection of the associated graded slopes are 

assigned a more recent date, perhaps 2,000 or 3,000 

years B.P.

Late Recent terrace deposits, ranging in height 

from a few feet to 15 feet above present river level, 

are attributed to lateral cutting rather than to filling 

because they are mainly underlain by valley fill of the 

Elba terrace. The Loup Eivers have been degrading 

their channels continuously during late Recent time, 

perhaps for the past 2,000 or 3,000 years, and are 

probably degrading their channels at present.

Dune sand covers much of the Loup River basin; 

however, time did not permit a study of the dunes. 

H. T. U. Smith (1955) published a brief description of 

the development of dune forms in the Nebraska Sandhills. The general northwest-southeast trend of the 

dune ridges shows clearly on aerial photographs, as 

do the remarkable longitudinal furrows that run the 

full length of many dune ridges along their crests. 

The dune ridges are roughly parallel to the prevailing 

wind direction. The troughs between ridges and the 

furrows on top of the ridges are probably erosional in 

that both begin as rounded blowouts and progress 

downwind, killing the grass in front of them and leaving behind them a furrow, much as a finger leaves 

behind a furrow as it is pushed across the surface of 

sand. Mantling of the Peorian Loess by dune sand is 

conspicuous along the north side of the North Loup 

River near Burwell; therefore, the Sandhills must 

have been extended considerably in this vicinity since 

Peorian time. The Peorian Loess is, however, remarkably free of interbedded dune sand.

GEOLOGIC INFLUENCES ON THE LONGITUDINAL RIVER 

PROFILES

The slope and direction of flow of a river are initially determined by the geologic setting in which the 

river becomes established. Geologic setting includes 

not only the resistance of the rocks traversed by the

river but also the regional slope of the land surface. 

For modern rivers that flow in valleys made by ancestral rivers, geologic setting includes the gradients and 

deposits of the ancestral rivers. Rubey (1952, p. 135) 

pointed out that a river flowing on a predetermined 

gradient may more nearly or more readily attain 

equilibrium by the development of a wide, shallow 

cross section than by the development of a flatter 

gradient. Development of a flatter gradient might 

be inhibited by resistant consolidated rock or by 

gravel beneath the river bed. Development of a wide, 

shallow cross section would be promoted by easily 

erodible river banks.

Geologic influences on the long profile of a river can 

be evaluated by relating the river profile to the regional slope, to the valley gradients of ancestral 

rivers, and to the distribution of different rock units 

traversed by the river. Inasmuch as the Loup Rivers 

are flowing mainly on the deposits (valley fill of the 

Elba terrace), of an ancestral river, the modern 

rivers have been influenced both by the lithology of the 

fill of the Elba terrace and by the gradient of the 

Elba surface. Similarly, the ancestral Loup Rivers 

were doubtless influenced by the regional slope of the 

Great Plains and by the lithology of the underlying 

Ogallala Formation.

Longitudinal river profiles and valley profiles were 

prepared for the North Loup (fig. 8), Middle Loup 

(fig. 9), and South Loup' (fig. 10). Profiles of the 

North Loup from altitudes of 1,745 to 2,500 feet were 

measured on Geological Survey topographic maps, 

scale 1: 24,000, contour interval 10 feet; and from altitudes of 2,500 to 3,200 feet, on Geological Survey topographic maps, scale 1:62,500, contour interval 20 feet. 

Profiles of the Middle Loup from altitudes of 1,745- 

2,560 feet were measured on 1:24,000-scale Geological 

Survey topographic maps having a contour interval 

of 10 feet; and from altitudes of 2,560-3,300 feet, on 

1:62,500-scale Geological Survey topographic maps 

having a contour interval of 20 feet. Profiles of the 

South Loup from altitudes of 1,880 to 1,982 feet were 

measured on 1:24,000-scale Geological Survey topographic maps having a contour interval of 10 feet; and 

from altitudes of 1,982 to 3,000 feet, on 1: 250,000-scale 

Army Map Service maps having contour intervals 50 

or 100 feet. For the river profiles, horizontal distances along the stream were measured with a map 

measurer. For the valley profiles, horizontal distances were measured along a line drawn through the 

inflection points of curves in the stream, and altitudes 

were taken on the streambank at an inflection point. 

Between any two points of given elevation, the ratio 

of valley slope to stream slope is a measure of the
D10 CHANNEL PATTERNS AND TERRACES OF THE LOUP RIVERS IN NEBRASKA

sinuosity of the stream; indeed, sinuosity may be 

defined in this way (Lane, 1957, p. 98). The regional 

slope of the Great Plains, which is shown for comparison with the profiles, was measured on Army 

Map Service maps (scale, 1:250,000; contour interval, 

100 ft) over the same section of the Great Plains as 

that crossed by 'the Loup Rivers. A straightedge 

was laid perpendicular to the trend of the contour 

lines that indicate the regional slope of the plains. 

The prevailing elevation of the upland in the area 

marked by the east end of the straightedge was subtracted from the prevailing elevation at the west end, 

and the horizontal distance (about 150 miles) was 

measured along the straightedge.

INFLUENCE OF BOCK RESISTANCE

At some places, the channels of the Loup Rivers 

may be cut into the Ogallala Formation. Certain 

lithologic units of the Ogallala, particularly the 

carbonate-cemented sandstone, are moderately resistant to channel erosion. The conspicuous bulge in the 

long profile of the South Loup (fig. 10) between Cumro 

and Ravenna is attributed to resistant bedrock although no outcrops were observed in the river channel. Information from drilling and from gravel 

pumping indicates that the channels of the Loup Rivers generally are underlain not by the Ogallala Formation but rather by several tens of feet of alluvial 

gravelly sand.

From place to place along all the Loup Rivers, 

gravel for road building is pumped from beneath the 

river channel or from low terraces along the river. 

However, test drilling has shown no commercial deposits of gravel for long distances along the rivers. 

For example, no gravel has been found along the 

South Loup between Arnold and Ravenna. Test drilling at gravel-producing localities has shown that the 

thickness and distribution of gravel are sporadic even 

within an area of a few acres.

3300

3100

2900

2700

2500

2300

\

Brewster

14

X

X

Ord

1900

1700

220 200 180 160 140 120 100 80 60

DISTANCE FROM CONFLUENCE WITH MIDDLE LOUP RIVER, IN MILES

40 20

FIGURE 8. Longitudinal river profile, valley profile, and Elba terrace profile, North Loup River, Nebr. Regional slope of Great Plains la

shown for comparison. Numbers refer to gaging stations in table 2.
Dll

Gravel is pumped from depths as great as 40 feet, 

and nearly all this gravel is less than 1 inch in diameter. Coarser gravel, which is rejected by the 

Nebraska Highway Department, is separated by 

screening. The rejected gravel probably represents 

less than 2 percent of the ^total sand and gravel 

pumped, and it consists mostly of pebbles less than 2 

inches in diameter; although cobbles as much as 6 

inches in diameter were seen, they represent less than 

5 percent of the rejected gravel. Competency of the 

Middle Loup to transport pebbles as much as 1 inch 

in diameter is indicated by the occasional observance 

of such a pebble in the artificial turbulence flume at 

Dunning.

Gravel deposits do not seem to be concentrated beneath the bed of the river, but rather they seem to be 

interbedded with sand and silt down to the maximum 

depths reached by the pumps. Most of the commercial gravel deposits are probably within the valley fill

of tfie Elba terrace. Gravel lenses in ;the fill of the 

Elba terrace were probably derived from older gravel 

deposits exposed upstream. Some commercial deposits are within older valley fills (of Kansan, Illinoian, or Peorian age) that have been recently exposed by lateral migration or by downcutting of the 

rivers. The sporadic lateral and vertical distributions of the gravel as well as its small size indicate 

that gravel has not prevented the rivers from adjusting their gradients by incision.

In general, the valley fills of ancestral rivers are 

easily erodible and permit the development of wide, 

shallow cross sections. Nearly everywhere the river 

banks are formed by terraces cut in late Recent time 

which are underlain by valley fill of the Elba terrace. 

This fill consists dominantly of sand along the braided 

North Loup and Middle Loup and of silty sand along 

the meandering South Loup.

3300

3100

2900

2700

2500

2300

2100

1900

1700

200 180 160 140 120 100 80 60 

DISTANCE FROM CONFLUENCE WITH NORTH LOUP RIVER, IN MILES

40 20

FIGURE 9. Longitudinal river profile and valley profile, Middle Loup River, Nebr. Regional slope of Great Plains is shown for comparison. Numbers refer to gaging stations in table 2.
D12 CHANNEL PATTERNS AND TERRACES' OF THE LOUP RIVERS IN NEBRASKA

3300

3100

2900

2700

uJ 2500 

Q

2300

2100

1900

1700

Stapleton

Arnold

Stapleton\

Arnold IN

\

X10

220 200 180 160 140 120 100 80 60

DISTANCE FROM CONFLUENCE WITH MIDDLE LOUP RIVER, IN MILES

40 20

FIGURE 10. Longitudinal river profile and valley profile, South Loup River, Nebr. Kegional slope of Great Plains is shown for

comparison. Numbers refer to gaging stations in table 2.

INFLUENCE OF REGIONAL SLOPE AND BELIEF

The influence of regional slope and relief on the long 

profiles of rivers can be shown either by comparing 

the profiles of rivers in mountainous regions with the 

profiles of rivers on plains or by noting the profile 

changes along a single river as it flows across different physiographic provinces. For example, the profile of the Arkansas River in the Rocky Mountains 

upstream from Canon City, Colo., is steep and irregular; it is nearly straight across the Great Plains, but 

it flattens across the Interior Lowlands and flattens 

still more as the river traverses the structural trough 

of the Arkansas Valley and enters the Gulf Coastal 

Plain. Miller (1958) investigated the characteristics 

of streams that flow across resistant rocks in mountainous areas onto unconsolidated deposits of the Rio 

Grande depression. He concluded that channel slope 

is "* * * a partially independent variable, determined by inherited conditions that the stream can 

gradually modify, but only within certain limits."

In accounting for the shape of long river profiles, 

many writers give insufficient attention to the influence 

of regional slope. However, Rubey (1952, p. 135) 

stressed the significance of regional slope in his discussion of the long profiles of the Missouri and Platte 

Rivers. He noted that the Missouri River, from 

about 2,000 miles upstream from Great Falls, Mont., 

to its mouth, flows at an approximately uniform distance below the older uplands that border it. He remarked that "* * * one is forced to believe either 

that the discharge and load of the present Missouri 

River are such that they almost exactly fit the slopes 

of these old upland surfaces * * * or, as seems 

more likely, that the profile of the present stream has 

been greatly influenced by the slope of the earlier surfaces on which it began its work." Also, he suggested 

that the Platte River flows on a preexisting slope on 

which it has attained equilibrium by development of a 

very shallow cross section rather than a flatter 

gradient.
D13

The direction of the Loup Kiver courses is closely 

related to the direction of slope of the Great Plains. 

In this part of Nebraska the surface of the Great 

Plains dips about S. 75° E. at about 9.5 feet per mile 

(0.0018 ft per ft). The upper courses of both the 

North Loup and the Middle Loup trend about S. 70° 

E. that is, almost directly down the dip of the Plains. 

Beyond the Sandhills, the courses of the two rivers remain generally parallel but swing southward to about 

S. 40° E. In its upper course the South Loup trends 

S. 60° E., but between Cumro and Ravenna it swings 

northward and trends slightly north of east. The 

trend of the Calamus River is generally uniform at 

about S. 55° E.

The river slopes and the valley slopes of the Loup 

Rivers are similar although somewhat less steep than 

the slope of the Great Plains. (See figs. 8, 9, 10). 

The slopes are less steep owing to the sinuosity of the 

rivers and their valleys rather than to the incision below the surface of the Great Plains. In fact, the manner of incision of the rivers tends to make their slopes 

steeper than the slope of the Great Plains because the 

incision is deeper in the lower courses than in the 

headwaters. For example, the upper reaches of the 

North Loup (in the Big Galls quadrangle) are incised 

to a depth of about 100 feet below the surrounding upland whereas the lower reaches, near the confluence 

with the South Loup (about 215 river miles downstream), are incised to a depth of about 200 feet below 

the upland. The long profiles of the Loup Rivers and 

the profile of the Great Plains are alike in being 

nearly straight. Although the profile of the North 

Loup flattens at its lower end and steepens alt its upper 

end, the straightness of most of the profile can be 

demonstrated by laying a straightedge along it. The 

profile of the Middle Loup, which is nearly straight 

from the headwaters to the confluence with the North 

Loup, has an average slope of about 0.00125 as compared with a slope of 0.0018 for the Great Plains.

One explanation for the similarity between the profiles of the Loup Rivers and the profile of the Great 

Plains is that all are a result of gradation by 

eastward-flowing streams of similar hydraulic characteristics. There is, however, no convincing evidence 

that the eastward slope of the Great Plains is fundamentally a result of stream gradation. Instead, the 

surface of the Great Plains may have been merely 

flattened originally by subaerial processes generally, 

then tilted eastward by tectonic movements related 

to Cenozoic uplift of the Rocky Mountain region. As 

shown by geologic sections across Nebraska (Condra 

and others, 1950, fig. 8), the fluvial formations of Cenozoic age (Chadron, Brule, and Ogallala Formations)

were deposited generally parallel to an erosional surface on rocks of Cretaceous age. A similar relation 

between the Ogallala and this erosional surface is 

shown on geologic sections by Frye and others (1956, 

p. 19), who also presented convincing stratigraphic 

evidence that the Ogallala does not represent a series 

of coalescent alluvial fans sweeping eastward from 

the Rocky Mountains. Instead, the Ogallala represents a series of alluvial fills in shallow eastwardtrending valleys cut in rocks of Cretaceous age; the 

fills overlapped laterally onto the gently sloping valley 

sides, buried the interstream divides, and eventually 

formed a coalescent alluvial plain. But the thickness 

of the Ogallala does not change greatly from west to 

east, and its total thickness (about 400 ft) is insufficient to have much effect on the slope of the Great 

Plains, which are about 400 miles in breadth. The 

origin of the eastward slope of the erosdonal surface 

on rocks of Cretaceous age remains in doubt, but the 

overlap of the Ogallala across the Chadron and Brule 

suggests either a differential tectonic downwarping of 

the Great Plains or a differential upwarping of the 

source areas to the west (Frye and others, 1956, p. 

50). In addition, the initial eastward dip of the Ogallala probably has been increased by tectonic movements in post-Ogallala time.

The profiles of the Loup Rivers have probably been 

inherited from the Great Plains profile. Many river 

profiles are characterized by a downstream decrease 

in slope which generally is attributed to a downstream 

increase in discharge or to a downstream decrease in 

particle size of load. Because average discharge remains nearly constant for long distances along the 

middle courses of the North Loup and Middle Loup, 

downstream decrease in slope is perhaps not to be expected. Also, there is very little downstream change 

in particle size of load for any of the Loup Rivers. 

However, bank-full discharge shows a rather sharp 

rate of increase downstream along the North Loup and 

Middle Loup. Both average discharge and bank-full 

discharge increase downstream along the South Loup, 

which has a notably straight long profile. Long profiles of the Loup Rivers are not significantly altered 

by substantial increases in discharge at the confluence 

of major tributaries. For example, the average discharge of the Middle Loup is increased by a factor of 

nearly two below the confluence of the Dismal River; 

yet, this increase in discharge is not accompanied by 

any significant change in slope. If, as seems apparent for the Loup Rivers, slope is not changed in response to variations in discharge or channel pattern, 

then the rivers would have little tendency to modify 

an inherited slope. Hydraulic adjustment to changes

719-579 O-64 3
DH CHANNEL PATTERNS AND TERRACES OF THE LOUP RIVERS IN NEBRASKA

in discharge and channel pattern is made mostly by 

change in cross section.

THE MIDDLE LOUP RIVER AT DUNNING 

HYDRAULIC FACTORS IN RELATION TO WIDTH

In their report on sediment transportation, Hubbell 

and Matejka (1959) presented detailed tables of basic 

hydraulic data on different sections of the Middle 

Loup River at Dunning, Nebr. The location of sections discussed herein is as shown in figure 11. Sections A and E mark the limits of a reach about 7,900 

feet in length. Section A has a bank-full width of about 

340 feet, and the channel contains emergent bars during ordinary stages. The bank-full width of section 

C2 is about 85 feet, and that of section E is about 150 

feet. Section C2 is free of emergent sandbars, but at 

section E emergent bars may form near the center of 

the channel at low flows. The flow at section B is confined by bridge abutments to a width of about 65 feet, 

but the flow at other sections is hot artificially confined, except perhaps by vegetation and by some brush 

riprap at section C2 . Cross profiles of sections A, C2 , 

and E, measured at a discharge about equal to average 

discharge, are shown in figure 12. The data for each 

of these sections permit an analysis of the hydraulic 

adjustments made by the river at constant discharge 

as it flows through sections of distinctly different 

widths.

The relative variation in river width along the reach 

at Dunning is typical of the variation along many 

reaches of the North Loup and Middle Loup. The bed

and bank materials are nearly uniform along tihe reach 

at Dunning; therefore, variations in width cannot reasonably be assigned to variations in particle size of 

bank materials. Variations in width might be assigned 

to variations in vegetal growth on the banks; yet, the 

present vegetation at section A is similar to that at 

section E. At both sections, the left bank has a dense 

growth of willows and other trees whereas the right 

bank is sodded. Variations in width are perhaps related to past conditions of vegetal growth on the banks. 

Photographs of the sections are reproduced by Hubbell 

and Matejka (1959).

Basic data for each section include measurements of 

discharge ($), effective width (TPe ), effective area 

(Ac ), mean suspended-sediment concentration, local 

slope, reach slope, and water temperature. Mean 

velocity was calculated from Q/Ae and mean depth

FIGURE 11. Location of sections on a reach of the Middle 

Loup and Dismal Rivers near Dunning, Nebr.

Section A, Sept 9, 1949, 399 cfs Section C,, Aug 16,

50 100 150 200 250 300 350 400 0

WIDTH,IN FEET

Section E, May 6, 1952, 366 cfs Sectiort S, Oct 3, 1956, 724 cfs

50 100 150 0 50 100 150 200 

WIDTH, IN FEET

250 300 350 400

FIOUKB 12. Cross profiles of Middle Loup River at Dunning, Nebr. Section A, C2, and E after Hubbell and Matejka (1959) ; section S

after Hubbell (1960).
PHYSIOGRAPHIC AND HYDRAULIC STUDIES OF RIVERS D15

from A G /We . Effective width is defined as the length 

of a discontinuous line that crosses the channel and 

that is normal to the direction of flow at every point 

on the line. Width of sandbars is not included in effective width. Effective area is the sum of the products 

of effective width and measured depth for each section 

of a water-discharge measurement. Local slopes 

Avere measured with staff gages placed 300 feet upstream and 300 feet downstream from a section. At 

section A, the slope determined from the readings of 

these gages is questionable because the slope differed 

from one individual channel to another and also because transverse flow at the section caused local differences in slope along each bank. The reach slope 

is based on the difference in water-surface elevation 

between sections A and E. For each of the hydraulic 

properties listed above, except slope, 33 measurements 

were available for section A, 37 for section B, 23 for 

section C2 , and 49 for section E. Of local slope, 20 

measurements were available for section A, 11 for 

section G2 , 31 for section E, and none for section B. 

Some water temperatures were estimated by the writer 

on the basis of past records of water temperatures for 

that calendar date, and others were extrapolated from 

temperature measurements made at another section 

on the same date.

In figure 13, mean value of mean depth, mean velocity, local slope, and effective area are plotted, on 

rectangular-coordinate paper, against effective width 

at sections B, C2 , E, and A. The mean values were 

obtained from measurements grouped according to 

discharge.

Mean velocity and mean depth decrease as effective 

width increases whereas effective area and slope increase as effective width increases. Unfortunately, 

the scope of the data is insufficient to define adequately the form of the equations that would relate effective width to the cither variables. Moreover, the 

effective widths at section A are not strictly comparable with the effective widths at the other sections 

because bars, submersed to shallow depth, are commonly present at section A but are rarely present at 

the other sections. A bar submersed to a depth of 6 

inches, for example, would not influence the effective 

width at section A, but it would influence the hydraulic 

characteristics of the channel. A measure of width at 

section A that is about comparable with the effective 

width at the other sections is the water width at half 

mean depth. The mean value of the water width at 

half mean depth at section A, for discharges of 350- 

399 and 400^49 cfs, is about 215 feet. The points 

representing these discharges at section A should 

probably be moved to the left to an effective width of

about 215 feet. At the other sections, the effective 

width as plotted is about equal to the water width at 

half mean depth.

The increase in effective area with increasing width 

at constant discharge has been noted for many other 

sandibed streams (B. K. Colby, oral communication, 

1961). An explanation of this increase must take into 

account the necessity for continuity in both bed-material discharge and water discharge from section to 

section, regardless of the width of the section. If only 

water discharge were involved, many different combinations of hydraulic adjustments might be possible; 

for example, the cross-sectional area might remain 

constant, and slope might increase enough to increase 

average velocity (in spite of decreasing depth). Continuity of bed-material discharge, however, requires 

a decrease in bed-material discharge per foot of stream 

width as the stream widens; if the width of the stream 

is doubled, the discharge of bed material per foot of 

width must be decreased by half. The decrease in 

bed-material discharge per foot of width requires a 

decrease in velocity and an increase in effective area.

The reach slope remains constant at about 0.0013 

foot per foot for the whole range of discharges and 

widths shown in figure 13. This reach slope corresponds to the local slope expected for a discharge of 

450-500 cfs at a width of about 225 feet, which is the 

average width of the reach. Average width of the 

reach was determined by dividing the surface area of 

the reach by its length. Average discharge at Dunning is about 385 cfs and bank-full discharge is about 

570 cfs. The reach slope may therefore be adjusted to 

a discharge between average discharge and bank-full 

discharge.

Data were grouped and graphs were prepared to 

investigate the relation of local slope to discharge and 

suspended-sediment concentration at sections A and 

E. For the range of measurements available, local 

slope showed no definite relation either to discharge or 

to suspended-sediment concentration.

HYDRAULIC FACTORS IN RELATION TO BRAIDING

For a shallow stream of uniform depth that is flowing at bank-to-bank width, the growth of bars or 

islands in the channel not only divides the flow into 

braids but also reduces the water width to a value less 

than bank-to-bank width. The reduction in water 

width is a measure of the degree of braiding. Section 

A has well-defined banks, and its bank-to-bank width 

remained at about 340 feet during the period of measurement (1949-56). The section is in a nearly straight 

reach of the river; therefore, no tendency for the thalweg to remain near one bank would be expected. At
MEAN OF EFFECTIVE AREAS 

IN SQUARE FEET

MEAN OF LOCAL 

SLOPES

MEAN OF MEAN VELOCITIES 

IN FEET PER SECOND

M

"" ff 2, 2,

. <n

 3 sr Q 8
PHYSIOGRAPHIC AND HYDRAULIC STUDIES OF RIVERS D17

discharges of 350-500 cfs, the width of flowing water 

would extend from bank to bank if no bars were present, and the effective width would approximate the 

bank-to-bank width.

To investigate the changes in channel configuration 

from time to time at section A, 30 cross profiles were 

plotted (from notes of water-discharge measurements 

made during the period 1949-56) on a horizontal scale 

of 40 feet to the inch and a vertical scale of 2 feet to 

the inch. Seven of these profiles, mostly pertaining to 

water discharge measurements of 400-449 cfs, are 

shown in figure 14. The position of greatest depth in 

the cross profile shifts apparently at random through 

the width of the stream, although there is some tendency for the deeper channels to be near the banks 

rather than midway between the banks. Cross profiles 

of the channel on successive days (such as on Aug. 30 

and 31, 1949) show no major changes in configuration, 

but in a period of 2 weeks the configuration can change 

completely. For example, compare the cross profile 

of April 12,1950, with that of April 25.

The effect of a bar submersed to a depth of a few 

tenths of a foot is not very different from the effect 

of an emersed bar on the flow of water through a given 

cross section. The waiter velocity in the shallow 

depth above the submersed bar is low, and the crosssectional area of the stream above shallowly submersed bars is only a small part of the total 

cross-sectional area. Shallowly submersed bars do 

not confine the flowing water at the surface of the 

stream, and their width enters into the measurement 

of effective stream width only if the water above the 

bar is nearly motionless.

To evaluate the effect of all bars and islands on 

such hydraulic variables 'as effective area and mean 

velocity, some means of expressing numerically the 

configuration of the channel cross profile is needed. 

Many schemes were tried in an effort to derive a single 

number that would take into account all the irregularities of the cross profile, but none led to a number that 

was unique for a particular configuration. However, 

a measure of water width was devised to take into account the effect of bars submersed to shallow depth. 

This measure is called the water width at half mean 

depth. It was measured by laying a straightedge 

across the plotted cross profile at a distance from the 

water surface equal to half mean depth; the width of 

bars that intersected the straightedge were excluded, 

and the increments of water width at this depth were 

summed.

The choice of half mean depth as a suitable depth 

at which to measure water width was made by trialand-error measurement on the 30 plotted cross profiles at section A. Absolute depth was not chosen because such a choice might lead to the statement of a 

water width of zero for a very shallow cross section. 

Of the different fractions of mean depth that were 

tried, half mean depth seemed most appropriate. 

Inspection of the velocities and cross-sectional area 

above bars submersed to a depth equal to or less than 

half mean depth indicated that only a small part of 

the water discharge is transmitted above such bars, 

whereas a significant part of the discharge is transmitted above bars submersed to greater depths. Even 

where bars submersed to a depth equal to or less than 

half mean depth occupy much of the width of the 

cross section, only a small percentage of the total discharge is transmitted above these bars. For example, 

only about 11 percent of the total discharge was being 

transmitted above the shallowly submersed bars on the 

cross section dated Sept. 13,1949 (fig. 14). The.water 

width at half mean depth is only 54 percent of the effective width measured at the water surface For the 

30 cross profiles that were plotted, the mean value of 

half mean depth is 0.36 foot, the standard deviation is 

0.04 foot, and the range is 0.28 to 0.47 foot.

The graphs of figure 15 show effective area, local 

slope, mean velocity, and maximum depth at section 

A in relation to the water width at half mean depth. 

(See table 1.) In addition, points representing mean 

values of effective area and mean velocity at sections 

B, C2 , and E (and mean values of local slope at sections C2 and E) are shown for comparison. Maximum 

depth is not the absolute maximum depth, which is 

too fortuitous to be significant, but it is the maximum 

depth above which lies 95 percent of the effective area. 

It was measured by laying a straightedge across the 

bottom of the plotted profile, sliding the straightedge 

upAvard until it reached the level below which lay 5 

percent of the effective area, and then taking the water 

depth at that level. Mean velocity is computed from 

discharge divided by effective area. Local slope, 

which is not available for all the plotted points, is 

from Hubbell and Matejka (1959, p. 82). Effective 

area is from the same source and from the original 

notation of water-discharge measurements.

Curves were fitted to the points applying to section 

A by the method of least squares; correlation coefficients and fitted curves are shown on the graphs. A 

linear relation is assumed because the range of data is 

insufficient to warrant the investigation of more complex relations. The correlation coefficients indicate 

a significant positive correlation with effective area 

at the 1-percent level and indicate a significant negative correlation with maximum depth and mean 

velocity, also at the 1-percent level. No significant
D18 CHANNEL PATTERNS AND TERRACES OF THE LOUP RIVERS IN NEBRASKA

X"^ -~\ / -_/

^X"^\

 ^

"X ^

/

/

"T-n-r-r? V

Jul;

^^

/27, 1! J51.4C

*^^*. 

3 cfs

 ----,

\r

Aug30, 1949, 374 cfs

o

Jf

cc

ID 

C/5

o: 'UJ

/^k/

/^Y/////' '///&»,u s^ / ~^ "^^ v

/ ~^

\

Auj

/^

/ 

31,15

\

49,42

A4 cfs

^ 1

\ I

^

^-r-r-r r77>^

^

^=

^

\

/

/

 - ,

 *»-^ _____

Api 25,1? 50,42

. -

3 cfs

- ^

J AAV \ /^ s."1 /

V

/

^\ ^

V

fa,

y

y//////, y////////////, y//W>\ fifo//

Apr

^/>f^/

12,1?

y///%/>

50,43

Vr^

^N »

? cfs

\

\

^

\

\

^/

X

////// y//////y///// ^ ^\/

Sep

~^^

t 13, 1

\

349,4!

r~

9 cfs

-^ -.^J

320 280 240 200 160 

WIDTH,IN FEET

120 80 40

FIGURE 14. Cross profiles of section A, Middle Loup River at Dunning. Bar widths that are above half mean water depth

are indicated by shading.
EFFECTIVE AREA, IN SQUARE FEET

a 50 »

8 s

2. 3" B

H> PS 

* 8

P3

P R a °" 

H <?

a O«

Ni O 

O O

m ivj O o

-5 ^ S B M

^ K)

m ho

> o

en

o

i

en

O

O

O

o

LOCAL SLOPE 

pop 

o o o 

rvj 4^ en

MEAN VELOCITY, 

IN FEET PER SECOND

M

_>8

0

D>

x°

C

0 >

X

0

X

II 

1 

P

IV) 

00

X

oX

X

)

X
D20 CHANNEL PATTERNS AND TERRACES OF THE LOUP RIVERS IN NEBRASKA

correlation with local slope is indicated at the 5-percent 

level; therefore, the curve is not shown.

Unlike the points representing mean values at sections B, C2 , and E, the points representing individual 

measurements at section A show no alinement according to discharge. This is attributed in part to the fact 

that significant differences in channel configuration 

apply to points in the same discharge range; water 

width at half mean depth is an imperfect measure of 

channel configuration. In addition, much of the 

scatter of points is related to differences in water temperature. For example, of the 12 points that lie above 

the velocity curve, 10 represent measurements made 

at a water temperature of less than 50°F, whereas only

2 represent measurements made at a water temperature of more than 50°F. Of the 14 points below the 

velocity curve, only 2 represent measurements made 

at a water temperature of less than 50°F, and the 

others represent measurements made at a temperature of more than 50°F. The mechanism by which 

water temperature affects velocity in the Loup Rivers 

is complex in that it involves not only a change in 

water viscosity but also accompanying changes in 

suspended-sediment concentration and bed form.

The relations shown in figure 15 indicate that the 

forming of emersed and shallowly submersed bars in a 

wide, shallow channel renders the channel hydraulically similar, at least in effective area and mean

TABLE 1. Values of hydraulic factors at section A, Middle Loup River at Dunning, Nebr.

Date

1949 

Aug. 30.. ______________________________

31-----..--........,.. .... .....

Sept. 7.. .----_--._--_.._...--_..._.....

9... --..___......__.-..._._.__.._.

13.. ...... .._.__.-_.._ .... .....

1950 

Mar. 1.. ...__.-.._....... .

21

Apr. 12.. _..._...._...--...___..._._...

25----------..-...................

May 9... __________ ....... _ . _

23. ---___--.__.___________________

June 6. ----___--__-______________ _____

July 6_-_ __________ ....... ________

18. _________________________ ____.

Aug. !---________ ._._.__._____...._____

Oct. 4... -._..-..-.._.___._ .... _ _

Nov. 7-------.--. .....__. .

29. _______________________________

1951 

Feb. 19_. .-___._._....._.______.. .. ..

Mar. 13. _______________________________

Apr. 25. ---------_---------__--.._____-

June 25. ---____--._______ . ___

July 27-.... ...-...__.__.________

Aug. 15_. ----_-.._______...____..._---.

Sept. 20_. ___._._. __ ..__ _

Dec. 4... ___ ... _______ _ _ .

1953 

Oct. 22.... ____ . ___ .

1954 

May 26_. ________________________ .....

Aug. 3. -.....---....-.._............_..

1956 

May 8__ _______________________________

Discharge 

(cfs)

374

424

379

399

41 Q

426

430

432

426

477

OQ1

356

366

402

364

380

399

405

427

404

452

391

403

ocn

417

4.CO

4.S1

386

361

416

Effective 

width 

(feet)

273

272

279

275

258

299

230

229

285

325

236

244

266

318

320

260

330

256

276

160

282

288

323

336

256

qqrj

288

282 q/iq

1QQ

Width at 

half mean 

depth 

(feet)

270

268

252

242

140

202

206

160

254

190

156

142

214

242

216

232

202

202

228

118

230

155

302

224

150

94.4.

168

140

136

142

Effective 

area 

(sq ft)

194

229

213

221

187

168

190

172

194

197

171

178

196

221

198

190

191

162

183

135

190

198

230

210

199

91 3

220

186

1Qfi

186

Mean 

. velocity 

(fps)

1.93

1. 85

1.78

1. 81

2. 24

2. 54

2.26

2. 51

2.20

2. 42

2.29

2.00

1. 87

1.82

1.84

2.00

2.09

2.50

2.33

2.99

2. 38

1. 97

1.75

1. 67

2. 10

2. 12

2. 19

3. 13

1.84

2.24

Mean 

depth 

(feet)

0 71

84

76

80

72

56

83

75

68

61

72

73

74

70

62

73

58

63

66

85

67

69

72

62

78

64

.76

.66

.57

.93

Maximum 

depth 

(feet)

0.8

1. 1

1.2

1. 4

1.5

1.0

1. 1

1. 7

1.6

1.3

1.9

1.7

1. 1

1.6

1. 4

1. 0

1. 4

1. 2

1.2

1. 5

1. 1

1.8

.9

1.6

2.0

1.0

2.3

1.7

1.5

1.7

Local 

slope (ft 

per ft)

0 0013

0013

00125

0013

00145

00145

00125

0016

0014

0013

00155

0013

0014

00125

.6613

.0015

. 00125

. 00125

. 0014

Water 

temperature (°F>

64

64

61

59

55

35

35

40

41

50

70

70

66

64

70

44

48

38

38

32

48

78

81

72

67

35

45

70

70

50
PHYSIOGRAPHIC AND HYDRAULIC STUDIES OF RIVERS D21

velocity, to a more narrow channel. Also, the greater 

the width of bars in the channel, the greater is its 

maximum depth. Because the width of section A is 

very great relative to its depth, the effect of banks is 

insignificant, and two or three channels transmit a 

given water discharge at approximately the same effective area and mean velocity as a single channel of 

the same total width.

Although the growth of emersed bars in a channel 

necessarily causes braiding, a decrease in water width 

results only if the bank-to-bank width remains constant. If the growth of bars or islands is accompanied 

by bank erosion, the water width may remain constant or even increase. Also, a reduction in water 

width can take place without braiding if a single channel is formed. Braiding cannot be equated with a reduction in water width unless a constant bank-to-bank 

width and the presence of emersed bars or islands are 

stipulated. The bank-to-bank width at section A, during the period of measurement, possibly remained constant only because the bars were transient.

HYDRAULIC FACTORS IN RELATION TO A 

CONFLUENCE

The confluence of the Middle Loup and Dismal Rivers is hydraulically and morphologically similar to the 

joining of two channels of a braided stream that have 

been separated by a stabilized alluvial island. In discharge, slope, suspended-sediment concentration, and 

particle size of load, the Dismal River is similar to 

the Middle Loup River upstream from the confluence. 

Therefore, hydraulic adjustments made at the confluence are pertinent to a consideration of adjustments 

made in a braided stream where channels join or 

divide.

Measurements made on the same day and at about 

the same discharge have been given by Hubbell (1960) 

for six Sections on the Middle Loup and Dismal Rivers 

(see fig. 11); the measurements of water temperature, 

water discharge, effective area, effective width, and 

local slope are for all six sections and for 7 different 

days during 1956. Local slope was measured for a 

reach 300 feet upstream and 300 feet downstream from 

each section. In addition, Hubbell reported similar 

measurements made on 4 days at four additional sections (here designated Si, S2 , Ti, and T2 ), which are 

300 feet upstream and 300 feet downstream from sections S and T, respectively. The cross profiles of 

sections E and S are shown in figure 12.

Figure 16 shows the relation of effective area and 

local slope to effective width for sections upstream 

and downstream from the confluence. Measurements 

of effective width and area at each section have been

placed into two groups according to discharge and 

water temperature, and the means of the values within 

each group are plotted. The upstream sections have 

been paired and summed as E plus R and F plus P, 

so that the combined discharge of each pair approximately equals the discharge downstream from the 

confluence. Hubbell (1960, p. 29) used dimensionanalysis and multiple-regression techniques to demonstrate the relations of hydraulic variables at individual 

sections upstream and downstream from the confluence. The purpose of figure 16 is to show graphically 

the relations that are considered to be of greatest geomorphic significance. Points in the same discharge 

group show a linear distribution when plotted on double log paper, and the variables are probably related 

by a power function. (A power function is also suggested by the distribution of points in fig. 13.) The 

curves are visually approximated rather than statistically constructed because the scatter of points is 

small and because no particular significance is attached to the slope value of the curve.

In general, the sum of the widths of the Middle Loup 

and the Dismal upstream from the confluence is less 

than the width of the Middle Loup downstream from 

the confluence. Also, the sum of effective areas for 

two sections upstream from the confluence is less than 

the effective area downstream from the confluence. 

Increase in width at the confluence is probably related 

to a fortuitous change in bank erodibility, inasmuch as 

vegetal growth along the banks is generally dense except along the left bank downstream from the confluence (Hubbell, 1960, p. 42). Despite some scatter of 

points, figure 16 indicates a regular increase in effective area with increase in effective width, regardless 

of whether effective width applies to the sum of two 

channel widths or to the width of a single channel. A 

similar increase in effective area with increasing 

width has been shown for a single channel (fig. 13).

SUMMARY OF HYDRAULIC FACTORS IN RELATION 

TO CHANNEL PATTERN

Among the major aspects of channel pattern are the 

total width of flowing water and the manner in which 

this width is distributed in the cross section whether 

in a single channel or (as in the braided pattern) in 

multiple channels. The Middle Loup River at Dunning afforded a good opportunity for investigation of 

the relation of width, at constant discharge, to other 

hydraulic variables. The river flows through sections 

of greatly differing width along a short reach that has 

no significant downstream increase in discharge. Also, 

there was available a large'number of measurements
D22 CHANNEL PATTERNS AND TERRACES OF THE LOUP RIVERS IN NEBRASKA

at sections having greatly different widths and a narrow range of discharges. In effect, the variable of 

discharge was held constant, so that the relation of 

width to effective area, mean velocity, mean slope, 

and mean depth could be distinguished. Hydraulic 

changes that occur when water flows from a wide section to more narrow sections were then compared with 

hydraulic changes that occur when channel width decreases, owing to braiding, at section A. Also avail0.02

able were detailed measurements of width and other 

hydraulic variables upstream and downstream from 

the confluence of the Middle Loup and Dismal Rivers 

near Dunning. The confluence of these two rivers is 

considered analogous to the confluence of two channels 

in a braided stream; therefore, sections upstream and 

sections downstream from the confluence were compared as to the relation of total width to hydraulic 

variables.

0.015

0.01

 o

F + P

E+R

O

E+R

m~

ST

T

O

Tl

n

T

*

S l

os c

S2

 s 2

»

400

150

100 200 300 400 

MEAN OF EFFECTIVE WIDTHS, IN FEET

500 600 700

O Discharge < 750 cfs, temperature > 50°F 

 Discharge >750 cfs, temperature < 50°F 

Letters refer to sections

FIGURE 16. Effective area and local slope In relation to effective width for sections upstream and downstream from confluence of

Middle Loup and Dismal Rivers.
PHYSIOGRAPHIC AND HYDRAULIC STUDIES OF RIVERS D23

The conclusions drawn from these investigations are 

that the effect of braiding at section A is to decrease 

the width of flowing water and that the changes in effective area and mean velocity accompanying braiding 

are similar to the changes accompanying flow from a 

wide single channel to a narrower single channel. In 

other words, the effect of braiding on a wide channel 

is to render it hydraulically similar, at least in effective area and mean velocity, to a narrower single channel. Similarly, if effective width downstream from a 

confluence is greater than the sum of effective widths 

upstream from the confluence, effective area is increased and mean velocity is decreased. No definite 

relation between width and local slope was discerned, 

partly because the range of data for local slope was 

less than that for the other variables. Local slope 

perhaps increases as width increases from section to 

section; however, no significant correlation was discerned between local slope and braiding at section A 

or between local slope and width upstream and downstream from the confluence of the Middle Loup and 

Dismal Rivers.

OBSERVATIONS ON THE FORMATION OF SANDBARS, 

ISLANDS, AND VALLEY FLATS

In laboratory experiments by Leopold and Wolman 

(1957), braiding began with the deposition of an initial central bar which consisted of coarse particles that 

could not be transported under local conditions. In 

natural streams, such a bar may become vegetated 

and grow into an island, which divides the flow of the 

stream so that the channel pattern is braided. Bars 

and islands of the Loup Rivers are built of fine- and 

medium-grained sand, which is the ordinary bed material of the rivers; their origin cannot be explained as 

the selective deposition of coarser particles.

As seen on aerial photographs, most submersed bars 

in the Loup Rivers are either lobe shaped or wedge 

shaped, and the point of the lobe or wedge is generally 

oriented downstream. (See fig. 17). A typical bar 

is about 300 feet long and about 200 feet wide at its 

widest part. Small lobe-shaped dunes having heights 

as much as 6 inches and lengths as much as several 

feet were seen in shallow water on the surface of bars 

(fig. 18) and elsewhere.

l,.\ $\N 

jtf>*\

. »&-& \ 

V: - v « \ "* i

'^V' : -'

,«.!»»*««.,:.

FIGURE 17. Aerial photograph and tracing of photograph, North Loup Elver, about 1 mile downstream from gaging station near St. Paul. 

On tracing, submersed bars are shown in lightly stippled pattern emersed bars in heavily stippled pattern, and islands are blank. 

Biver flows toward right.
D24 CHANNEL PATTERNS AND TERRACES OF THE LOUP RIVERS IN NEBRASKA

FIGURE 18. Small lobe-shaped dunes on submersed sandbar in North 

Loup River 8 miles downstream from Brewster. River flows toward 

right. Sandbar is being rapidly eroded as salient at lower right 

migrates upstream.

The large bars and the small dunes probably 

acquired their similar shapes in the same general 

way. The forming of small dunes was observed in 

shallow water at the river edge. First, nearly straight 

dune ridges several feet long and oriented transversely 

to the current were formed. The ridges advanced 

downcurrent and grew rather uniformly in height until the current broke through them in several places, 

forming scallops from which lobes of sand were built 

ahead of the original dune ridge. Some lobes increased in height as they were built forward. Increase 

in height was augmented if a lobe advanced up the 

backslope of another lobe ahead.

The bar of figure 18 is in a straight, narrow reach of 

the North Loup River; the reach is shown in the background of figure 19. The bar is not typical of those 

previously described, but it was studied because the 

high adjoining bank (Elba terrace surface) afforded 

a vantage point not found at many places along the 

Loup Rivers. The channels on either side of the bar 

are kept clear of sand deposits by high water velocity 

and by sand boils, which are nearly vertical clockwisemoving eddies that rise from the stream bottom and 

carry sand in suspension. Erosion of the downstream 

end of the bar was observed to take place along a deep 

salient, shown in figure 18, that moved rapidly upstream.

Many Loup River bars probably originate from sand 

ridges built across the river bed at right angles to the

FIGURE 19. Straight reach of North Loup River, same locality as 

figure 18. Elba terrace, at right, stands 34 feet above river. Note 

small willow-covered island in foreground. 

prevailing current. Channels are formed where the 

current breaks through the ridges, and lobe-shaped 

bars are built in front of these channels. If a lobeshaped bar increases sufficiently in height, the current 

is diverted around it and forms channels on either side; 

the bar may continue to grow in the quieter water between these channels by the advance of small dunes 

on its surface. The downstream end of the bar may 

become pointed by the convergence of channels on 

either side, and the bar as a whole may become wedge 

shaped. Diversion of current around submersed bars 

creates braided patterns, observable on aerial photographs (fig. 17), that are the same as the patterns 

made by diversion around emersed bars and islands. 

Bars are built during a high river stage to heights that 

are above the water level during an average river 

stage. Some of these bars emerge when the river recedes, and they then become islands if vegetation 

grows on them (fig. 19) and prevents their destruction. 

The valley flats (flood plains) of the North and 

Middle Loup Rivers are built by a modification of the 

lateral accretion process: islands are successively 

added to the valley flat as the course of the river shifts 

laterally. Many islands are separated from the valley 

flat by a single narrow channel that is dry during an 

average river stage. (See island at lower center, fig. 

17.) Aerial photographs show many former islands 

that have become part of the valley flat by the disappearance of narrow channels which separated them 

from the flat. A succession of vegetation begins with 

weeds on recently emersed bars; weeds are replaced 

by willows as the bar becomes an island; and finally, 

after the island has become part of the valley flat, the
PHYSIOGRAPHIC AND HYDRAULIC STUDIES OF RIVERS D25

willows are replaced by grass. Grassed areas that 

are still recognizable as former islands are higher than 

the younger willow-covered islands. This greater 

height cannot be attributed to a thicker accretion of 

overbank deposits that accumulated over a longer period of time because overbanks flows are rare in the 

upper courses of the North Loup and Middle Loup. 

Moreover, grassed former islands show a succession 

of heights as much as about 8 feet above present river 

level. This succession of heights is an indication of 

degradation by the river.

MEASUREMENT AND DESCRIPTION OF CHANNEL 

PATTERNS

According to the usage of Leopold and Wolman 

(1957), the term "channel pattern" applies to the plan 

view of a river reach and includes meandering, 

braided, and straight channels. The channel pattern 

of a river usually varies from place to place.

MEANDERING AND SINUOSITY

Leopold and Wolman (1957) computed the sinuosity 

of a reach as the ratio of thalweg length to valley 

length. Lane (1957) computed a "tortuosity ratio" as 

the ratio of the length of the stream channel to the 

length of the stream measured along the axis of the 

valley. Many rivers on. broad valley floors have 

meander belts that are curved. For such rivers, the 

sinuosity that is a function of the size, shape, and repetition of individual channel arcs should be considered 

separately from the sinuosity that is a function of the 

curvature of the meander belt. Otherwise, a different 

measure of sinuosity would be obtained for two reaches 

whose channel arcs are identical but whose meander 

belts are differently curved. If the axis of a series 

of symmetrical sine curves is bent, the sinuosity as 

measured in relation to a straight line joining the ends 

of the axis is changed; but the radius of curvature of 

individual arcs remains the same. Figure 20 illustrates the delineation of the meander-belt axis, which 

passes through the inflection points of arcs. Individual 

channel arcs are thus delineated above and below the 

meander-belt axis. The channel sinuosity of a reach, 

here called the sinuosity index (S.I.), is the ratio of 

length of channel to length of meander-belt axis. 

Where no meander belt can be distinguished, the sinuosity index is the ratio of length of channel to length of 

valley axis. Sinuosity of a meander belt, if desired, 

may be determined from the ratio of length of meander-belt axis to length of valley axis.

Channel arc

 Center-line of channel

 . Limits of meander belt \

 Axis of meander belt

 ------ Height of channel arc_____

FIGURE 20. Delineation of meander belt, axis of meander belt, and 

channel arcs for measurement of sinuosity and symmetry.

Sinuosity is easy to define and measure, but meandering is difficult to define and measure. A discussion 

and a definition of meandering are given by Lane 

(1957), and a summary of the geometry and hydraulics 

of river meandering is provided by Leopold and Wolman (1960). According to general usage, a meandering stream has a moderate to high degree of sinuosity, 

and the sinuosity is somewhat symmetrical. In defining meandering, some writers specify a migration of 

meander bends. Leopold and Wolman (1957) stipulated that meandering reaches have a greater sinuosity 

than irregularly sinuous reaches and that a sinuosity 

of 1.5 or greater indicates meandering. However, the 

use of sinuosity alone is not satisfactory for identification of a meander; on the basis of other criteria, these 

authors recorded a meander that has a sinuosity of 

1.12 (Leopold and Wolman, 1960, p. 792). They reported consistent correlations between meander length 

and channel width; large rivers have large bends and 

small rivers have small bends, so that the general aspect of both large and small meandering rivers is 

similar in plan view.

The symmetry of a reach consisting of several channel arcs depends both on the properties of individual 

arcs and on the group properties of the sequence of 

arcs. An individual arc may be described by its 

mean radius; its form may be described by the 

ratio of length to height, which is here called the 

form ratio. The arc length is the length of the 

meander-belt axis that is intercepted by the arc, and 

the radius of an arc is approximately equal to half the 

arc length. Group properties of a sequence of arcs 

include the statistical variation in arc length, height, 

and form ratio, the regularity of repetition for arcs of 

average size and form, and the sinuosity of the 

meander-belt axis. The average arc height, length, 

and form ratio may be determined for a reach. The 

symmetry of the reach may then be compared with an 

ideal reach that consists of this average arc regularly 

repeated along a straight line of the same length as the 

actual meander-belt axis. If the consistency in size, 

form, and repetition of arcs in this ideal reach is con-
D26 CHANNEL PATTERNS AND TERRACES OF THE LOUP RIVERS IN NEBRASKA

= 100 

sidered to be 100-percent symmetry, then the symmetry of the actual reach may be expressed as a 

percentage of 100 according to the following scheme: 

Percentage symmetry of

arc length

 inn ^^ (mean deviation of length) 

mean length

arc height

100 (mean deviation of height) 

mean height

form ratio

100 (mean deviation of form ratio)

mean form ratio

The aspect of symmetry that depends on the regular 

repetition of arcs can be expressed roughly by dividing the number of arcs of approximately average size 

in the actual reach by the number of arcs in the ideal 

reach. Arcs in the actual reach whose length does not 

deviate more than 25 percent from average length may 

be considered to be of approximately average size. 

Finally, the sinuosity of the actual meander-belt axis 

relative to the straight axis of the ideal reach may be 

expressed as a percentage by dividing the sinuosity 

into one, which is the sinuosity of a- straight line.

In order to evaluate the significance of symmetry in 

the definition of meandering, measures of symmetry 

were applied to a reach of the river from whose name 

the term "meander" is derived the Maiandros River 

in Turkey (now named the Buyuk Menderes). This 

reach, shown in figure 21, is redrawn from a longer

-Centerline of river 

. Axis of meander belt

.__ Axis of Valley

........ Height of channel arc

FIGURE 21. Delineation of a reach of the Buyuk Menderes River, 

Turkey, for measurement of sinuosity and symmetry.

reach reproduced by Lane (1957) on a scale of 1 inch 

to 10,000 feet. Symmetry of the reach is perhaps adequately indicated by the following measures:

Arc length. mean, 2,600 ft; mean deviation, 800

ft; percent symmetry, 70. 

Arc height. mean, 1,700 ft; mean deviation, 570

ft; percent symmetry, 66.

Form ratio. mean, 1.8; mean deviation, 0.6; 

percent symmetry, 67.

Repetition of arcs. number of arcs of approximately average size, 10; number of arcs in 

ideal reach, 33; percent symmetry, 30.

Straightness of meander-belt axis. sinuosity, 

1.3; percent straightness, 77.

Sinuosity index of channel. 1.56.

If these measures of symmetry are valid and if this 

reach is representative of the Buyuk Menderes, then 

the type example for meandering rivers has a rather 

low degree of symmetry. If symmetry is to be stipulated in applying the term "meandering" to randomly 

selected reaches, some arbitrary limit of symmetry 

will have to be established. No simple and rapid 

means of expressing symmetry quantitatively is apparent although a great many different ways of expressing symmetry could be devised.

An experiment carried out by Friedkin (1945, p. 15) 

indicated that a minor lack of homogeneity in bank 

materials has a pronounced effect on both symmetry 

and sinuosity. When a small percentage of cement 

was distributed unevenly through the bank materials, 

a laboratory river developed low symmetry and a sinuosity index of 1.17, as compared with a high symmetry 

and a sinuosity of 1.4 for a similar laboratory river in 

homogeneous bank materials.

In this report, sinuous reaches are described by 

means of the sinuosity index, and no attempt is made 

to describe the symmetry of the sinuosity. If the sinuosity index of a reach is 1.3 or greater, the reach is 

further described as meandering, whether the sinuosity 

is symmetrical or not. Ideally, a straight reach has 

a sinuosity index of 1, but reaches that have sinuosity 

indices of less than 1.05 are described as straight. 

Reaches that have sinuosity indices between 1.05 and 

1.3 are described as sinuous. The term "meandering" 

is more satisfactory for the description of a stream 

course in general than for the description of short randomly selected reaches. The term "meandering" thus 

is applied to a sinuous stream that has, from place to 

place along its course, one or a series of symmetrical 

arcs, the length of which is related to the width of the 

stream.

The sinuosity index is greatly influenced by the 

choice of reaches to be measured. Few streams meander continuously along their courses, and very sinuous 

reaches are usually separated by less sinuous reaches. 

If the reach to be measured is restricted to the more 

sinuous parts, then a higher sinuosity index will obviously be obtained than if the reach is extended 

beyond the more sinuous parts. In this study, reaches 

were not selected on the basis of channel pattern but 

on the basis of location at a gaging station. Each
PHYSIOGRAPHIC AND HYDRAULIC STUDIES OF RIVERS D27

reach is about 2 miles in length along the stream and 

extends about 1 mile upstream and about 1 mile downstream from a gaging station. If the sinuosity index 

of a reach chosen in this way is about 1.3 or greater, 

the reach is meandering in the sense that seems to be 

generally accepted. For example, the small-scale 

rivers considered to be meandering by Friedkin (1945, 

pis. 33,41) have sinuosity indices of 1.25-1.3.

BBAIDING

Leopold and Wolman (1957) defined a braided river 

as "* * * one which flows in two or more anastomosing channels around alluvial island." Friedkin 

(1945) stipulated that the braided channel is extremely 

wide and shallow and that the flow passes through a 

number of small interlaced channels separated by 

bars. According to Lane (1957), "* * * a braided 

stream is characterized by having a number of alluvial 

channels with bars or islands between meeting and 

dividing again, and presenting from the air the intertwining effect of a braid." Also, Lane proposed a 

genetic classification of braided streams in which the 

major categories are "braiding due to> steep slope" 

and "braiding due to aggradation." Within each 

major category, streams are further classified according to whether they are degrading, at equilibrium, or 

aggrading. The term "multiple channel streams" was 

proposed by Lane to include not only streams having 

a distinctly braided appearance but also streams having scattered islands (such as the lower Illinois Eiver). 

Also included are distributaries on deltas and anastomosing distributaries on deltas and on alluvial fans.

The term "multiple channel" has much merit, but 

the classification of multiple-channel streams on a 

purely genetic basis is impractical. The causes of 

braiding are poorly understood, and a sound descriptive classification is a first step toward understanding 

braiding. Several descriptive features of probable 

genetic significance and of use in descriptive classification may be suggested. One such feature is the size 

of the islands relative to the width of the channel. 

Small islands are probably formed by the growth of 

bars in the channel whereas very large islands are 

more likely formed by diversion and splitting of the 

channel during overbank discharge, as in the crevassing of the natural levees of delta distributaries. The 

location of islands near the entrance of minor tributaries probably has genetic significance, as Rubey 

(1952) suggested. High sinuosity of individual channels of braided streams, together with the presence of 

lakes and undrained depressions on islands, may be 

characteristic of low-slope braided streams such as the 

Upper Mississippi River near Waukon, Iowa.

No scheme for describing quantitatively the braided 

pattern of a reach or for distinguishing between 

braided and not braided reaches was found in the 

literature. Leopold and Wolman (1957) specified that 

islands develop from bars that emerge and become 

stabilized by vegetation. The presence or absence of 

vegetal cover seems to be the only practical criterion 

for distinguishing an island from a bar in the field and 

on aerial photographs. As defined here, an island has 

vegetal cover and is ordinarily emersed during a bankfull stage; a bar has no vegetal cover and is ordinarily 

submersed during a bank-full stage, but it may be 

emersed during lower stages. Braiding that changes 

in pattern with river stage is characterized by bars 

and is termed "transient." Braiding that remains 

nearly constant in pattern is characterized by islands 

and is termed "stabilized." The following ratio, called 

the braiding index (B.I.), has been found satisfactory 

for description of channel braiding, either transient or 

stabilized:

R T _ 2 [sum of lengths of islands and (or) bars in reach] 

length of reach measured midway between banks

The braiding index is a measure of the sum of island 

or bar perimeters in a reach and hence of the increase 

in bank length that results from braiding. Most 

islands or bars are narrow, and their perimeters are 

approximately twice their lengths. Lengths of islands 

or bars in a reach can be measured and summed in 

the same operation by use of a chartometer (map 

measure). The stabilized-braiding index is determined 

by measuring islands only; the transient-braiding index, by measuring bars only; and the total-braiding 

index, by measuring both islands and bars or by adding the other two indices. Submersed bars are not 

measured. Aerial photographs are much more satisfactory than topographic maps for measurement of 

the braiding index because the braided channel pattern 

is conventionalized on many topographic maps. Also, 

the representation of a particular feature in the channel as an island or as a bar depends on the judgment 

of the cartographer. Bars are not shown on many 

maps.

The stabilized-braiding index for a particular reach 

should remain nearly constant for different river 

stages whereas the transient-braiding index will 

change greatly with changing river stage. A decision 

must be made as to which index of braiding transient, 

stabilized, or total most satisfactorily represents the 

channel morphology of a particular river. For the 

Loup Rivers, the total-braiding index was used because both bars and islands are characteristic features
D2S CHANNEL PATTEKNS AND TERRACES OF THE LOUP RIVERS IN NEBRASKA

of the river channels. A reach that is both meandering and braided may be described by using both the 

sinuosity index and the braiding index.

Although the braiding index as defined herein is useful for morphologic description, it has little quantitative hydraulic significance. The braiding index has no 

consistent relation to water width, which is, as previously shown for the Middle Loup at Dunning, the dimension to which hydraulic variables can be related. 

The writer was not able to devise a braiding measure 

that has both morphologic and hydraulic significance.

Distinction between braided reaches and reaches 

having few islands or bars is arbitrary, but a consistent 

distinction may be made by means of an appropriate 

value of the braiding index. For the Loup Rivers, a 

value of 1.5 for the total-braiding index was selected 

to distinguish braided from not braided reaches, because reaches having an index of less than 1.5 did not

have a braided appearance. The braiding index, like 

the sinuosity index, is influenced by the choice of 

reaches: short reaches that are restricted to the vicinity 

of islands will have a higher braiding index than long 

reaches sampled at random. Most of the bias that results from the selection of short reaches can be avoided 

by specifying an adequate reach length in terms of bankfull widths; for example, a reach having a length equal 

to 10 bank-full widths would probably be satisfactory. 

The braiding indices shown in table 2 apply to reaches 

about 2 miles long, extending about 1 mile upstream 

and 1 mile downstream from each gaging station. 

Channel patterns of reaches having different indices 

of braiding and sinuosity are illustrated in figures 22 

and 23. These reaches were selected to illustrate the 

range of channel patterns of the Loup Rivers and do 

not correspond exactly to the reaches referred to in 

table 2.

TABLE 2. Values of hydraulic factors at gaging stations in the Loup River "basin

Gaging station

Middle Loup River:

2. At Dunning.......

Dismal River: 

3. At Dunning.... ...

Middle Loup River: 

4. NearMilburn. _ . 

5. At Walworth.....

7. At Arcadia.. __ ..

8. At Loup City.--.-

South Loup River:

12. At St. Michael....

North Loup River: 

13 At Brcwstcr

Calamus River: 

16. Near Burwell..... 

17. Near Harrop. .....

North Loup River: 

18. AtOrd............

20. Near Cotesfleld... 

21. Near St. Paul.....

Average discharge 

for 

period 

of 

record 

to 1957 

(cfs)

201 

385

316

786 

799 

813 

799 

823 

804

165 

198 

248

378 

448 

485

288 

250

826 

828 

903 

888

Number of 

years of 

record 

to 1957

4 

12

12

5 

12 

5 

12 

7 

2

7 

12 

12

6 

12 

5

12 

( )

5 

12 

6 

12

Average of maximum 

daily discharges 

(cfs)

308 

570

460

1,250 

1,550 

1,470 

2,580 

2,000 

4,340

1,535 

3,645 

4,830

830 

1,120 

1,215

550 

450

2,250 

4,250 

4,300 

5,850

Coefficient of deviation, discharge

0.16 

.38 

.21 

.81 

.40

.91 

.81 

1.06

.29 

.41 

.46

.19

.54

.58

Mean 

width 

(feet)

100 

160

80

345 

530 

595 

320 

587 

581

11? 

205 

209

267 

270 

320

170 

67

453 

515 

417 

501

Standard deviation, 

width 

(feet)

98 

229 

175 

185 

155 

113

26 

63 

52

98 

93 

90

43 

19

140 

125 

113 

108

Coefficient of variation, 

width (percent)

28.4 

43.2 

29.4 

57.8 

26.4 

19.4

23.2 

30.7 

24.9

36.7 

34.4 

28.1

25.3 

28.4

30.9 

24.3 

27.1 

21.6

Channel slope i 

(ft per 

ft)

0.00137 

.0013

.0013

.00156 

. 00159 

. 00135 

.00120 

. 00131 

. 00127

.00083 

. 00108 

.00096

.00119 

. 00133 

. 00147

.00109 

.00102

.00110 

. 00121 

. 00120 

.00107

Index of braiding

Total

<0.1 

<.l

<.l

1.0 

1.8 

2.2 

2.5 

2.5 

2.3

<.l 

.5 

.5

.8 

1.5 

1.6

.2 

.1

1.7 

1.5 

1.2 

1.5

Stabilized

<0.1 

<.l

<.l

.2 

.9 

.5 

1.2 

<.l 

.4

<.l 

<.l 

<.l

.3 

.7 

.3

.2 

.1

.4 

.7 

<-l 

<.l

Transient

<0.1 

<.l

<.l

.8 

.9 

1.7 

1.3 

2.5 

1.9

.1 

.5 

.5

.5 

.8 

1.3

<.l 

<.l

1.3 

.8 

1.2 

1.5

Index 

of sinuosity

1.3 

1.06

1.3

1.05 

1.06 

1.05 

1.07 

1.15 

1.06

2.4 

1.6 

1.4

1.04 

1.03 

1.15

1.05 

1.6

1.06 

1.09 

1.04 

1.2

Suspended sediment

Concentration 

(ppm)»

«770 «800

<940

«820 

<900 

< 1, 100 

* 1, 250 

« 1, 200 

U.250

« 2, 100 

'3,000 

» 3, 170

<510 

«600 <680

<360

<800 

< 1,000 

« 1, 100 

 1, 430

<0.062 

mm 

(percent) 3

21

17 

23

68

81 

19

23

29

28 

62

. Bed material

<0.062 

mm (percent)

0

0 

0

1.0

.1 

.1

0

2.0 

0

<0.50 

mm (percent)

73

91 

91

92

69 

73

66

75 

75

<2 

mm 

(percent)

92

99 

99

99

92 

91

92

95 

97

1 Measured from topographic map. 

3 Discharge weighted. 

3 Average of samples.

* Based on periodic measurements.

 Based on daily measurements. 

6 Partial record.
PHYSIOGRAPHIC AND HYDRAULIC STUDIES OF RIVERS D29

A-CALAMUS RIVER NEAR BURWELL, OCT 22, 1949 

(TOTAL B. I.. 0.2;S. I.. 1.05)

5.-NORTH LOUP RIVER UPSTREAM FROM TAYLOR. 

OCT 22, 1949 (TOTAL B. I., 1.6 ;STABI LIZED B. I., 1.3; 

S. I., 1.1)

C.-MIDDLE LOUP RIVER UPSTREAM FROM ARCADIA, 

OCT 24, 1949 (TOTAL B. I., 2.7; STABILIZED B. I., 1.1; 

S. I., 1.05)

FIGURE 22. Reaches that Illustrate different values of the braiding Index. Sandbars are shown In stippled pattern, Islands are blank,

and scarps of minor cut terraces are hachured. Traced from aerial photographs.
D30 CHANNEL PATTERNS AND TERRACES OF THE LOUP RIVER'S IN NEBRASKA

.-CALAMUS RIVER NEAR HARRUP, OCT 28,1949 

IS. I.. 1.7; TOTAL B.I.., O.O8)

5.-SOUTH LOUP RIVER IN VICINITY OF CUMRO, 

OCT 11, 1949 (S. I., 2.1)

C.-SOUTH LOUP RIVER AT ST. MICHAEL, NOV 8,1951 

(S. I.. 1.6; TOTAL B. I..O.5)

\

FIGURE 23. Reaches that Illustrate different values of the sinuosity index. Sandbars are shown in stippled pattern, Islands are blank,

and scarps of minor cut terraces are hachured. Traced from aerial photographs.
D31

WIDTH

For each of the gaging stations listed in table 2, except Middle Loup River near Seneca, river width at 

the gaging station, at six sections upstream, and at six 

sections downstream was measured on aerial photographs. Width of the Middle Loup near Seneca was 

measured on a Geological Survey topographic map. 

Sections were spaced about 800 feet apart; therefore, 

the reach between the end sections was about 9,600 

feet in length. Mean width for each 9,600-foot reach 

was determined from the 13 individual measurements 

of width. At each section, width was measured between river banks, which are stabilized by vegetation 

and are clearly shown on the aerial photographs. For 

braided reaches, the widths of vegetated islands were 

not included in river width; therefore, the river widths 

represent the total widths of the stabilized channels. 

The widths of unvegetated sandbars in the channel, 

whether emersed or submersed, were included in the 

measurement of channel width. The widths as measured thus differ from the effective widths reported by 

Hubbell and Matejka (1959) for the Middle Loup at 

Dunning; there emersed sandbars were excluded from 

measurements of width. Coefficients of width variation, as determined by dividing standard deviation by 

mean width, range from about 19 percent to about 58 

percent.

CHANNEL PATTERNS OF THE LOUP RIVERS

A general impression of the sinuosity of the Loup 

Rivers may be obtained from figures 8, 9, and 10 by 

comparing each river profile with the corresponding 

valley profile. For a given reach, the ratio of valley 

slope to river-channel slope equals the sinuosity index; 

and where the two slopes are nearly parallel, the reach 

is nearly straight. At most places along the North 

Loup and Middle Loup, no meander belt can be distinguished; and the valley width, which includes the 

width of the Elba terrace surface, is no more than 20 

times the width of the river. The maximum width of 

the South Loup valley is nowhere more than twice the 

width of the meander belt. For the Loup Rivers, therefore, slope of meander belt and slope of valley axis are 

nearly equal.

The North Loup has a sinuosity index of about 1.6 

in its upper reaches. This value gradually decreases 

downstream, and below .Brewster the sinuosity is so 

low that the valley slope and stream slope are nearly 

parallel. Symmetrical, well-defined meanders are present only in a short reach near Brewster and in a reach 

near the confluence with the Middle Loup. Most of the 

lower 130 miles of the North Loup. trends in broad arcs 

(S.I. = 1.1-1,05) or in nearly straight reaches (S.I.=

1.01-1.05) that commonly meet to form a right-angle 

bend. Scattered islands divide the channel from place 

to place, but in general the North Loup is only slightly 

braided. The reach at Ord (total B.I., 1.7; stabilized 

B.I., 0.4) is typical of the more braided reaches of the 

river. For the reaches measured at gaging stations 

(table 2), the average total B.I. is 1.4 and the average 

stabilized B.I. is 0.4.

According to Leopold and Wolman (1957), extremely 

short reaches of a channel may be straight, but 

reaches that are straight for distances exceeding 10 

times the channel width are rare. They did not specifically define what is meant by a straight channel, 

but the straight channels in their illustrations show a 

slight degree of sinuosity. Long reaches that have a 

sinuosity index of less than 1.01 are fairly common 

along the North Loup and Middle Loup. A reach of 

the North Loup downstream from Scotia is 2,y2 miles 

long (a distance of about 30 times river width) and 

has a sinuosity index of 1.01. The straightness of 

Loup River reaches may be exceptional.

In general, the Middle Loup is somewhat less sinuous than the North Loup and somewhat more braided. 

Both of these rivers have a low degree of braiding as 

compared with a river such as the Platte. In a 2-mile 

reach near the village of Silver Creek, Nebr., the 

Platte had a total braiding index of about 8 on May 2, 

1951. For the reaches measured at Middle Loup 

gaging stations, the average total B.I. is 1.6 and the 

average stabilized B.I. is 0.4. Although a comparison 

of the North Loup and Middle Loup as represented on 

Geological Survey topographic maps (scale 1:24,000 

issued 1951-55) would indicate that the Middle Loup 

is much more highly braided than the North Loup, no 

great difference between the rivers could be seen on 

the aerial photographs from which the maps were 

made. The maps were evidently drawn by different 

cartographers who had different opinions about the 

representation of a braided stream. The Middle Loup 

is moderately sinuous in its upper reaches, but the 

parallelism of its stream slope and valley slope (fig.

9) shows that its sinuosity is generally very low. A 

few symmetrical meander arcs may be seen in the 

river course near Dannebrog and at Boelus, but other: 

wise the sinuosity of the Middle Loup shows little 

symmetry.

The sinuosity of the South Loup is apparent from a 

comparison of its river slope with its valley slope (fig.

10). Except for the reach between elevations 2,000 

and 2,150 feet, which has a steep slope and low sinuosity, the average sinuosity index of the river is about 

1.4. The degree of symmetry shown by most reaches 

is represented by figure 23Z?; but a higher symmetry,
D32 CHANNEL PATTERNS AND TERRACES OF THE LOUP RIVERS IN NEBRASKA

represented by figure 236", is possessed by a few 

reaches. Channel arcs gradually .increase in size 

downstream as water discharge and river width increase. (See figs. 23#, C.) Small vegetated islands 

and emersed bars occur from place to place in the 

channel of the South Loup, particularly in the lower 

20 miles of its course; but the degree of braiding is 

generally very slight.

Most of the smaller flowing tributaries in the Sandhills (such as Goose Creek, which enters the North 

Loup upstream from Brewster) are meandering. The 

Calamus River meanders for most of its course, but 

the last 7 miles upstream from its confluence with the 

North Loup is characterized by wide, nearly straight 

reaches that contain abundant sandbars. In the loessmantled part of the Loup River basin, most tributaries 

(such as Clear Creek, Oak Creek, and Mud Creek) are 

meandering, and the meanders seem to be incised.

Channel stability of the North Loup River was 

studied by comparing aerial photographs made in 

August 1938 with photographs made in May 1957. 

Measurements were made on photographs of a reach 

near Ord, Nebr. Islands in this reach showed no measurable change in size, number, or position during the 

19-year interval. The pattern of sandbars was of 

smaller scale and greater complexity on the 1938 

photograph. The outside of a bend had migrated laterally by about 80 feet in 19 years, but the inside of the 

same bend showed little change. A straight reach 

showed a maximum of about 50 feet of lateral migration at one place, but at most places the river banks 

showed little change.

RELATION OF SELECTED HYDRAULIC FACTORS TO 

CHANNEL PATTERN

Lane (1957) discussed the factors affecting streamchannel form or shape. He did not specifically define 

the terms "channel form" and "channel shape," but 

he used these terms interchangeably to mean the aspects of a stream channel in plan view and in cross 

profile. Since his paper mainly is on the aspect of a 

stream channel in plan view, his conclusions about 

channel form readily apply to channel pattern. According to Lane, the major factors that affect channel 

form are water discharge, longitudinal slope, sediment 

load, resistance of bed and banks to scour by flowing 

water, vegetation, temperature, geology, and work of 

man. Some of these factors influence channel form directly; some, indirectly. In selecting the fewest factors for adequate differentiation of channel forms, 

Lane considered not only the relative magnitude of the 

effect of each factor but also both the feasibility of 

expressing each quantitatively and the availability of

data for each. A major objective of his paper is to 

show that differences in channel form can be satisfactorily explained by differences in slope, bed-bank 

material, and average discharge.

The factors described by Lane are undoubtedly the 

major variables in the determination of channel pattern; and his selection of slope, bed-bank material, 

and average discharge as adequate variables for explaining channel pattern is reasonable. However, the 

usefulness of average discharge may depend on its 

correlation with other measures of discharge (such as 

bank-full discharge), inasmuch as an average discharge will not move the bed or bank material of many 

streams (M. G. Wolman, written communication, 

1961). The writer regards bank credibility as the 

most significant single variable, and bank erodibility 

depends mainly on the particle size of bank material 

and on vegetal growth along the banks.

The influence of diversion dams on channel patterns 

of the Loup Rivers has not been evaluated in this report. Diversion dams for irrigation have been built 

on the North Loup near Taylor, Burwell, and Ord and 

on the Middle Loup near Sargent and Arcadia. In addition, the Boelus Power Canal diverts water from the 

Middle Loup into the South Loup near the confluence 

of the two rivers. Most of the irrigation works have 

been built since 1945, although the Boelus Power Canal 

has been in operation since 1936. Comparison of river 

reaches immediately upstream from diversion dams 

with reaches immediately downstream indicates that 

the diversion has had little effect on previously established bank-full widths or on vegetated islands.

BANK EBODIBILITY

Loup River banks are typically low and overgrown 

by grass or other vegetation, but cut banks were found 

and examined at many localities. The banks of the 

North and Middle Loup Rivers are dominantly of sand. 

The sand generally contains streamers of fine gravel. 

Most cut banks contain a few layers of silty sand; and 

in several places, layers of dark clayey sand, probably 

deposited under swampy conditions, were seen. The 

low banks and point-bar deposits of the South Loup 

are of silty sand but in many places the Elba terrace 

deposits, against which the river has cut laterally, are 

mainly of silt and clay. The generally meandering 

pattern of the South Loup is attributed to the silt and 

clay content of its banks; such a content gives these 

banks a moderate degree of resistance to erosion. In 

comparison with the North Loup and Middle Loup, the 

much higher content of particles less than 0.062 millimeter in diameter in the suspended load of the South 

Loup, as well as the higher suspended-sediment con-
PHYSIOGRAPHIC AND HYDRAULIC STUDIES OF RTVEES D33

centration, is considered to be a satisfactory indication 

of the higher silt and clay content of the South Loup's 

bank materials.

Schumm (1960) reported a relation between the 

width/depth ratio of a channel and the silt-clay content of its bed and banks. As the percentage of silt 

and clay in the bed and banks increases, the channel 

becomes deeper and narrower. In a later paper 

(1963), Schumm showed, for some alluvial rivers on 

the Great Plains, that sinuous channels are characterized by a high percentage of silt and clay in their perimeters. The writer was unable to devise a sampling 

procedure that would give a significant representation 

of the silt-clay content of banks along the Loup Rivers. 

The cohesive effect of silt and clay depends not only 

on its amount but also on its distribution in the bank 

materials. For example, silt and clay concentrated 

in layers gives a very different cohesive effect than 

would the same amount of silt and clay distributed 

uniformly through the bank materials.

No attempt has been made to describe quantitatively 

the influence of vegetation on bank erodibility, but this 

influence is significant. In the Sandhills, where the 

water table is high, swamp vegetation grows along the 

river courses and confines the channels. The meandering of the courses of the Calamus River and minor 

flowing tributaries in the Sandhills is attributed to the 

influence of swamp vegetation, which decreases bank 

erodibility.

The ability of bank materials to confine a stream depends partly on the discharge of the stream. As the 

discharge of a stream increases, the depth and mean 

velocity increase, and the banks not only are higher 

but also are subjected to greater erosive action. For 

bank materials of a given cohesiveness, a small stream 

would be expected to have a channel of lower 

width/depth ratio than a large stream.

The Calamus River is described in detail because 

it exhibits variations in channel pattern that are attributed to the influence of vegetation on bank erodibility. The major factors that influence channel pattern, 

except the factor of vegetation, seem to be constant. 

For a distance of about 7 river miles upstream from 

its confluence with the North Loup, the Calamus has 

low sinuosity and is slightly braided (fig. 224). 

Farther upstream, the Calamus becomes distinctly 

meandering (fig. 234). Discharge measurements for 

a section near Harrop, which is about 25 miles upstream from the confluence, and for another section 

near the confluence at Burwell show that discharge 

over the lower 25 miles of the river course is nearly 

constant. (See table 2.) Bank materials are derived 

from dune sand and are uniform from place to place.

Differences in bank erodibility are attributed to differences in vegetal growth along the banks; swamp 

vegetation is denser along the upper course of the 

river, probably because of the higher water table. The 

water table is higher along the upper course of the 

river because the sand dunes that border the river 

valley are higher than those along the lower course, 

which is near the edge of the Sandhills. At some 

places within the Sandhills, such as near Ashby, Nebr., 

the water table stands sufficiently high that flat areas 

between the dunes are marshy or are occupied by 

lakes.

The long profile of the lower 25 miles of the Calamus 

is shown in figure 24. The profile was drawn from 

Geological Survey topographic maps (scale, 1: 24, 000; 

contour interval, 10 ft), and plotted points represent 

locations at which successive 10-foot contours cross 

the river. The slope is about 0.0011 foot per foot for 

the entire 25-mile river profile except for two minor 

bulges in the profile. The valley slope is slightly 

steeper in the upper part of the profile. Sinuosity indices and mean widths were measured on the topographic maps for 15 reaches, each of which is bounded 

by successive 10-foot contour lines and represents a 

10-foot drop in altitude and a horizontal distance of 

about 10,000 feet along the river. The reaches range 

in sinuosity index from 1.01 to 2.1, and they range in 

mean width from 50 to 300 feet. The wider reaches, 

which are within 5 miles of the confluence, are slightly 

braided (braiding index, about 0.1) but contain numerous submersed sandbars.

River slope of the Calamus, as measured on the topographic maps, shows no consistent relation to width 

nor to sinuosity index. A reach having a mean width 

of about 50 feet has the steepest slope (0.0016), and 

another reach having the same mean width has the 

gentlest slope (0.0008). Along many of the 10,000-foot 

reaches, the river shows little variation in width, and 

any significant difference in slope between uniformly 

narrow reaches and uniformly wide reaches would 

have been recorded by the 10-foot contours. Like the 

Middle Loup at Dunning, the Calamus River evidently 

adjusts from wide sections to narrow sections not by 

change in slope but by change in effective crosssectional area. Valley slope, as measured along a 

line that passes through the inflection points of river 

bends, also shows no consistent relation to width or to 

sinuosity index.

Figure 25 shows the relation between width and sinuosity index. Inasmuch as slope and discharge are 

nearly uniform, width may be regarded as the practical measure of bank erodibility the wider a section, 

the more erodible its banks. Low sinuosities are asso-
D34 CHANNEL PATTEKNS AND TERRACES OF THE LOUP RIVERS IN NEBRASKA

2310

2290

2150

2130

140 130 120 110 100 90 80 70 60 50 40 30 20 

DISTANCE FROM CONFLUENCE WITH NORTH LOUP RIVER, IN THOUSANDS OF FEET

10

3.0 

2.5

X

Ixl

§2.0

fc

CO

f,5

CO

1,0

LOW

s

< 

/

s

-M(

s

DDE

i

/

RAT

'N

3ANK ERODIE

E >

XN N N

X

ilLITY 

h

X

N

<

 >

IGH

X

N

4

V

FIQURE 24. Longitudinal river profile and valley profile, Calamus River, Nebr. Profile extends 25 miles upstream from confluence with

North Loup River.

ences in bank erodibility are mainly determined by 

vegetal growth along the banks. Valley slope is 

mainly predetermined by regional slope and by the 

slope of the Elba terrace. A moderate degree of bank 

erodibility, controlled by swamp vegetation in the 

upper part of the river segment under consideration, 

led to the development of a meandering pattern and a 

moderately narrow width. Along reaches where vegetal resistance to bank erosion was high, the river 

course is nearly straight and tends to be narrow. 

Along reaches having low vegetal resistance to bank 

erosion, as in the lower part of the segment, the river 

developed a broad, shallow, and somewhat braided 

course. The general slope of the long river profile is 

rather uniform, and hydraulic adjustment to local 

variations in width is mostly made by changes in crosssectional area rather than by changes in slope.

Friedkin (1945) attributed changes in channel pattern along the length of the Mississippi River to differences in bank erodibility. His experiments with 

small-scale rivers showed that entirely resistant banks 

led to the development of a deep, narrow channel having a flat channel slope and that less resistant banks

50 60 70 80 90100 200 

WIDTH, IN FEET

300

FIGURE 25. Diagrammatic relation of sinuosity index to width 

and bank erodibility, Calamus River. Width is regarded as a 

practical measure of bank erodibility.

ciated with high and low bank credibilities, and high 

sinuosities are associated with intermediate bank 

erodibilities.

The relations among channel pattern, bank erodibility, and slope along the Calamus River, as interpreted by the writer, are summarized as follows: For 

a given discharge, channel pattern is determined 

mainly by bank erodibility and valley slope. Differ-
PHYSIOGRAPHIC AND HYDRAULIC STUDIES OF RIVERS D35

led to a slowly meandering channel having a moderately flat slope. A braided pattern having steep slopes 

was developed where banks were very erodible.

Friedkin's conclusions apply satisfactorily to the 

Loup Rivers except that a braided reach may have an 

only slightly greater channel slope than a meandering 

reach of nearly the same discharge. Also, a lush 

growth of vegetation may serve to confine a stream 

between otherwise erodible banks.

DISCHARGE

Leopold and Wolman (1957) tentatively concluded 

that channel width is mainly a function of discharge 

and that the quasi-equilibrium width of a channel is 

determined by bank-full or barely overbank discharges. 

Width also is related to average discharge. Leopold 

and Haddock (1953) showed that, for many rivers, 

width increases downstream as the 0.5 power of average discharge. The Loup Eiver system is exceptional 

among the eight rivers plotted by Leopold and Maddock, inasmuch as width increases downstream as the 

0.75 power of average discharge.

The concept of bank-full discharge is difficult to apply to the upper reaches of the Loup Rivers, which 

have such constancy of discharge that they rarely attain the bank-full stage. In addition, the Loup Rivers 

are bordered by a series of low terraces of different" 

heights. The height of the river banks varies from 

place to place and depends on which terrace level the 

river has cut against laterally. For an approximation 

of bank-full discharge, an average of the maximum 

daily mean discharges for the years of available record 

during the period 1946-57 was computed for each gaging station. For some stations, only 2 years of record 

was available for the period. (See table 2.) For those 

reaches attaining a bank-full or overbank stage, the 

average of the maximum daily mean discharges agrees 

reasonably well with the bank-full discharge as estimated from gage heights.

For the Loup Rivers, mean width was plotted 

against average discharge and also against bank-full 

discharge. Very different results were obtained from 

the two plots. Width increases for each river according to the following powers of average discharge: 

South Loup, 1.8; Middle Loup, 1.3; and North Loup, 

0.7. Width increases for each river according to the 

following powers of bank-full discharge: South Loup 

0.6; Middle Loup, 0.8; and North Loup, 0.45. In general, therefore, bank-full width increases at a greater 

rate relative to average discharge than to bank-full 

discharge.

Figure 26 shows the relation of width to mean annual 

discharge and bank-full discharge for Loup River 

reaches at the gagin stations listed in table 2. When

all points on the plot are considered, the visually approximated curve for meandering reaches has a slope 

of about 0.5. The point representing the Middle Loup 

near Seneca does not fall on this curve. However, 

the measurements for the Middle Loup near Seneca 

were made on a topographic map of scale 1:62, 500 

whereas measurements for the other reaches were 

made on aerial photographs. Points (representing 

braided or sinuous reaches and straight reaches are 

widely scattered; but the widths represented are generally greater than the widths of meandering reaches. 

Much of the scatter of points is attributed to the pronounced local variation in width that is characteristic 

of the North Loup and Middle Loup. This variation 

in width is, in turn, attributed to banks whose erodibility is high insofar as particle si?'e is concerned 

but whose erodibility is much decreased locally by 

vegetation.

Variability of discharge is a possible factor in the 

development of channel pattern and river width. A 

rought measure of variability of discharge was obtained by relating the discharge for the month having 

the'highest flow during a water year to the discharge 

for the month having the lowest flow. For the period 

1946-57, averages were computed for the maximum 

monthly discharges and for the minimum monthly discharges. The mean deviation of the average monthly 

maximums and minimums (relative to the average 

discharge for the period of record) was divided by the 

average discharge to give a coefficient of deviation of 

discharge. (See. table 2.) An accurate variability 

index, such as that proposed by Mitchell (1957), requires the use of flow-duration curves, which are not 

available for the Loup Rivers.

For the Loup Rivers, no direct relation between 

variability of discharge and channel pattern is apparent, but variability of discharge may have a significant 

effect on increase in width with downstream increase 

in discharge. The channel pattern of the Calamus 

River changes greatly along the. last 25 miles of its 

course despite the fact that variability of discharge is 

low- and constant. The reach having the highest coefficient of deviation of discharge (1.06 for the South 

Loup River at St. Michael) is meandering, and many 

reaches in the upper Middle Loup that have low coefficients of devaition (probably less than 0.2) are also 

meandering. Downstream increase in width with increasing average discharge higher for the Loup 

Rivers than for other rivers plotted by Leopold and 

Maddock (1953) may perhaps be attributed to the 

downstream increase in variability of discharge shown 

by the Loup Rivers (table 2). River width increases 

not only with downstream increase in all measures of
D36 CHANNEL PATTERNS AND TERRACES OF THE LOUP RIVERS IN NEBRASKA

1000

100

40

11

10

o c

12 S O 

16. 

J 

17

O

13.

2

~3*j

-\

+ 

14

15

a

19

5.

18

4

6

ti

m20

7

100 1000

MEAN ANNUAL DISCHARGE, IN CUBIC FEET

PER SECOND

+ Braided reach, total B. I. > 1.5

 Reach having B. I. <1.5, S.I. <1.3

O Meandering reach, S. I. >1.3

y Standard deviation of width

1000

100

10

>

17

:?:

^

-18-

^t_

19

20

21

100 1000 10,000 

AVERAGE MAXIMUM DAILY DISCHARGE, IN CUBIC FEET PER SECOND

100,000

FIGURE 26. Width in relation to mean annual discharge and average maximum daily discharge (approximately bank-full discharge) 

for different channel patterns. Numbers refer to gaging stations listed in table 2.
PHYSIOGRAPHIC AND HYDRAULIC STUDIES OF RIVERS D37

discharge but also with increase in bank-full discharge 

relative to average discharge.

BED MATERIAL AND SUSPENDED-SEDIMENT 

CONCENTRATION

In the northern part of the Loup Kiver basin, where 

the flow of the Loup Rivers is derived mainly from 

ground water rather than from surface runoff, the 

rivers derive most of their total sediment load from 

bank erosion. Any material supplied by surface runoff is fine- or medium-grained sand because the ground 

is almost entirely mantled by dune sand. In the loessmantled southern part of the basin, surface runoff 

makes substantial contributions to streamflow, and the 

sediment supplied is mainly silt.

J. C. Busby (written communication, Nebraska Univ. 

1950) investigated the bed material, particularly the 

sands, of the Middle Loup River. The bed material 

was sampled at depths ranging from 1 inch to 10 feet 

by driving an iron casing into the river bed at seven 

locations. Penetration by the casing into the bed at 

some of the sampling points was halted by coarse gravel or clay at a depth of about 5 feet, but the river bed 

at most points was free of gravel to a depth of at 

least 9 feet. In general, the median diameter of the 

sand increases somewhat as the depth below the surface of the stream bed increases. A typical increase 

is shown by the sampling of the Middle Loup River 

near Loup City in that the median diameter of bed 

material is about 200 microns in the first foot and about 

400 microns in the ninth foot.

Busby computed the average median diameter for 

the first 3 feet in each cross section and plotted the results to show downstream changes. The averages 

were 0.27 millimeter at Thedford, 0.38 millimeter at 

Dunning, 0.25 millimeter at Walworth, 0.26 millimeter 

at Loup City, and 0.29 millimeter at Rockville. Very 

little sand coarser than 0.8 millimeter was found in 

any of the samples. In general, the bed material is 

well sorted, and the size distribution is only slightly 

skewed.

In their report on sediment transportation in the Middle Loup River at Dunning, Hubbel and Matejka (1959) 

discussed size analyses of bed material taken with a 

piston-type sampler from cores about 2 inches in diameter and about 6 inches in length. For the coarest of 

187 samples analyzed, 80 percent of the material was 

finer than 4 millimeters and 27 percent was finer than 

0.5 millimeter. The samples were collected at irregular 

intervals between September 1949 and September 1952. 

Bed material has been sampled by the Geological 

Survey at four stations along the North Loup over 

periods ranging from 1 year at Cotesfield to 4 years at 

Burwell. For the South Loup River, bed material has

been sampled only at St. Michael. Analyses of 24 

samples collected by the Geological Survey during 1952 

and 1953 indicate that the bed material of the South 

Loup is mainly fine- to medium-grained sand. Bed 

material of the South Loup is somewhat finer than 

that of the North Loup or Middle Loup, but all three 

rivers have sandy beds.

Averages of particle-size analyses of bed material 

from the Loup Rivers are shown in table 2. According 

to these analyses, most of the bed material of the 

Loup Rivers is medium- or fine-grained sand; there 

is little difference in size of bed material from one 

river to the next or from place to place along the same 

river.

Even where the Loup Rivers appear to be only 

slightly turbid, the suspended-sediment discharge is 

obviously a significant part of the total sediment discharge. The measured suspended-sediment discharge 

of the Middle Loup River at Dunning, where the river 

appears to be clear rather than muddy, averages about 

one-half of the total sediment discharge as measured 

at the turbulence flume (Hubbell and Matejka, 1959). 

Average suspended-sediment concentrations, in parts 

per million, were computed for each station by J. C. 

Mundorff of the Quality of Water Branch in Lincoln, 

Nebr. The South Loup River, which exhibits the most 

consistently meandering pattern, also has the highest suspended-sediment concentration. The average 

amount of clay (particles less than 0.004 mm in diameter) in the suspended sediment of the South Loup 

River at Cumro is about 24 percent, whereas the average amount for stations on the North Loup and Middle 

Loup is about 9 percent.

Schumm (1963, p. 1094) suggested that the silt-clay 

content of the bed and banks may be representative of 

the type of sediment load transported by a stream. 

The higher the percentage of total sediment load transported as wash load (silt and clay), the higher is the 

silt-clay content of bed and banks and the more sinuous is the stream likely to be. This suggestion seems 

valid and it is supported by comparison of the South 

Loup with the North Loup and Middle Loup. Unfortunately, information on total sediment load is not 

available for most rivers.

The braided pattern is sometimes attributed to an 

excess of total load supplied to the stream that is, to 

a supply of sediment that exceeds the capacity of the 

stream. The capacity of a stream is difficult to determine either by theory or by measurement. An excess 

of total load might be indicated by aggradation, and no 

excess of total load might be indicated by degradation. 

Geological evidence indicates that the Loup Rivers are 

slowly degrading.
D38 CHANNEL PATTERNS AND TERRACES OF THE LOUP RIVERS IN NEBRASKA

WATER TEMPERATURE

Hubbell (1960, p. 22) discussed the significant influence of water temperature on the hydraulics of the 

Middle Loup River at Dunning. Dune heights on the 

river bed become distinctly lower as water temperature decreases, and the bed is smoothest at water temperatures near 32° F. Small sediment discharges and 

large flow resistances are associated with high temperatures whereas large sediment discharges and 

small flow resistances are associated with low temperatures. Hubbell also noted that the shallowest depths, 

narrowest widths, and highest velocities are associated 

with the lowest temperatures.

Figures 27 shows the relation of suspended-sediment 

concentration to water temperature and discharge at 

sections A, E, and B on the Middle Loup at Dunning. 

Data from Hubbell and Matejka (1959) were grouped 

according to temperature and discharge, and means of 

the groups were plotted. Means of water temperature 

applied to measurements grouped according to successive 10°F temperature intervals, beginning with the 

interval 30°^100 F. Within each temperature interval, means of mean suspended-sediment concentration 

were based on measurements grouped according to 

discharge. For example, a mean was computed for 

all suspended-sediment concentrations listed for discharges of 350-399 cfs at water temperatures of 40°- 

49° F. For a given discharge range, suspended-sediment concentration decreases sharply as temperature 

increases. .

Figure 28 shows the relation of velocity to water temperature and discharge at sections A and E. Means 

of the variables were grouped as described for figure 

27. The decrease in velocity with increase in temperature accounts for part of the scatter of points in 

figure 15, for which temperature was not taken into 

account.

For the Middle Loup at Dunning, temperature has 

a significant effect on suspended-sediment concentration and velocity as well as an effect (probably indirect) on bed form; however, these effects do not 

necessarily apply to streams in general. Because 

much of the suspended sediment in the Middle Loup 

is fine sand, increase in viscosity with decrease in 

temperature has a significant effect on the vertical distribution of suspended sediment. For streams whose 

suspended sediment is mostly silt and clay, increase in 

viscosity has less effect on vertical distribution of suspended sediment. The change in bed form of the Middle Loup is probably related to a slight change in 

velocity through a critical value, above which dunes 

are built and below which dunes are flattened. For

other streams, change in temperature might not cause 

velocity to change through this critical value.

A measurable effect of temperature on channel pattern and slope might be expected because of the significant influence of temperature on Loup River 

hydraulics. The measurements at sections A and E 

on the Middle Loup at Dunning were analyzed to detect any effect of temperature on effective width, effective area, or slope. The number of measurements 

made at similar discharges for the whole range of 

water temperatures was insufficient for any definite 

conclusions to be drawn. However, both effective

2000

^ Oo o

X

\

\

 v 

 

\x

o

k 

\

\

o

\

A

rO

SECTION A

1 1

0

\

\

\

0

Discharge groups 

 300-349 cfs 

o 350-399 cfs 

x 400-449 cfs 

A 450-500 cfs

1000

200 

3

A

O

X

0

A

'6

e

SEC'

A

X

O

0

ION

A

X

*

B

A

O

_.

h0 50 9(

O

A

\

X * X

\ (*\

\l

.

SEC"

\

noN

A

VH

Ss

E

\

1 

0

^

X

O

50

MEAN OF WATER TEMPERATURES, 

IN DEGREES FAHRENHEIT

90

FIGURE 27. Suspended-sediment concentration In relation to temperature and discharge, sections A, B, and B, Middle Loup 

River at Dunning, Nebr.
'PHYSIOGRAPHIC AND HYDRAULIC STUDIES OF RIVERS D39

o c:

2.0

1.5

A

-

SECTION A

A

+

o

 A

o

+ o

O

3.5j 

3.0

i 5

2.0

*

o

SECTION E

+

O

+

o

*

'* « :

-

-

9

30 40 50 60 70 80 90 100

MEAN OF WATER TEMPERATURES, 

IN DEGREES FAHRENHEIT

Discharge groups

o. 300-349 cfs + 400-449 cfs 

o 350-399 cfs A 450-500 cfs

FIOCRB 28. Velocity In relation to temperature and discharge, 

sections A and E, Middle Loup River at Dunning, Nebr.

width and effective area show a general tendency to 

increase as temperature increases. At section A, 

for discharges in the range of 400^449 cfs, mean effective width increases by 20 percent as water temperature increases from 35° to 65°F, and mean 

effective area increases by 30 percent. At section E, 

for discharges in the range of 350-399 cfs, mean effective width does not change as temperature increases from 34° to T4°F, but effective area increases 

by 21 percent. Changes in local slope could not be 

related to changes in water temperature. In spite 

of the influence of temperature on width at section 

A. there is nevertheless a significant correlation of 

width to effective area, mean velocity, and maximum 

depth. (See fig. 15.)

Inspection of figures 8, 9, and 10 shows that the 

longitudinal river profiles of the North, South, and 

Middle Loup Rivers are nearly straight except for 

some steepening in the upper reaches and some flattening in the lower reaches. River profiles of the North 

Loup and Middle Loup are similar in slope, but in valley profile the Middle Loup is slightly steeper than the 

North Loup. The general river slope of the South 

Loup (0.0011 ft per ft) is somewhat gentler than that

of the Middle Loup (0.00125 ft per ft). The general 

valley slope of the South Loup (0.0018 ft per ft) is 

steeper than that of either the Middle Loup or North 

Loup. General straightness of the river profiles is 

attributed mainly to the straightness of the predetermined slope over which the rivers flow the slope of 

the Great Plains.

Because of the near constancy of slope that accompanies a significant variation in discharge and channel 

pattern, no good correlation of slope with discharge 

and channel pattern would be expected. However, 

river slopes of the 9,600-foot reaches at gaging stations 

were measured on topographic maps and plotted 

against bank-full discharge (fig. 29). The plot shows 

that the slopes of most meandering reaches are less 

than the slopes of most braided reaches of similar discharge. The points for both meandering and braided 

reaches represent an insufficient range in slope and discharge for any general relations to be established. 

Also, channel width should be taken into account simultaneously with the other variables. Indeed, analysis of channel characteristics of the Middle Loup at 

Dunning indicates that local slope shows little or no 

correlation with any variable except width.

For a given discharge and size of bed material, 

braided reaches of rivers in general probably have 

steeper channel slopes and greater effective widths 

than meandering reaches. Lane (1957) plotted slopedischarge relations for meandering sandbed streams, 

for braided sandbed streams, and for streams in gravel. 

He proposed that, for streams in each of these categories, slope varies inversely as the fourth root of average discharge. Also, meandering sandbed streams 

have lower slopes than braided sandbed streams of the 

same average discharge. Leopold and Wolman (1957) 

plotted channel slope against bank-full discharge for 

rivers that represent a wide range of discharges and 

bed-bank materials. A line, whose slope varies inversely as the 0.44 power of discharge, separates meandering streams from braided streams on their plot; 

and meandering streams have lower slopes than 

braided streams of similar bank-full discharge.

Lane (1957, p. 36) discussed the influence of valley 

slope on channel pattern. According to one viewpoint, 

a river meanders on a steep slope to reduce channel 

slope to an equilibrium value; therefore, the steeper 

the valley slope, the more sinuous the channel. Lane 

argued against this viewpoint; he maintained that 

steep valley slopes promote the braided pattern and 

that low valley slopes promote the meandering pattern. 

The lower the valley slope, the more sinuous the 

stream is likely to be, except that the sinuosity may 

be again reduced on very low slopes.
D40

u.uu^ 

o

o

cr

UJ

Q.

0 

O

LJUJ

Q0

<7> 0.001

_i

z

z

I

o 

0.0007 

200 '

© 3

©

to17

2

16 *

13

,-

4 +

* e

+14 "

10 ®

h8

+

+18its

1

©

11

9 +9

20

©

"*"

12

21

1000 7OC

AVERAGE MAXIMUM DAILY DISCHARGE, IN CUBIC FEET PER SECOND

+ Braided reach, total B. I. > 1.5

 Reach having B. I. <1.5,S. I. <1.3

® Meandering reach, S. I. ^1.3

FIGURE 29. Reach slope in relation to the average maximum daily discharges for meandering and braided reaches. Numbers refer to

gaging stations listed in table 2.

Experiments were done by Friedkin (1945, p. 10), to 

investigate the effect of valley slope on sinuosity. 

Within the range of slopes used in the experiments 

(0.006-0.009), sinuosity (and also the length and width 

of individual bends) increased as valley slope increased. However, the rate of increase in sinuosity was 

much reduced as the slopes became higher, and further 

increase in valley slope would perhaps have resulted in 

a decrease in sinuosity.

No generalities about the relation between valley 

slope and channel pattern are valid without the specification of other variables, of which bank erodibility, 

bed material, and discharge are probably the most significant. Under suitable conditions, streams will 

meander on steep slopes. For example, Leopold and 

Wolman (1960, p. 774) described a meandering channel having a slope of 0.023 and a discharge of about 

2.4 cfs that was carved in glacier ice by streams of 

melt water flowing on the glacier surf ace. Dury (1959) 

described meandering gullies on a steep-sided "spoilheap." Relations between discharge and bank erodibility that are favorable for development of the 

meandering pattern probably cause development of 

maximum sinuosity at some optimum value of valley 

slope and cause a decrease in sinuosity at slopes both 

greater and smaller than this optimum value.

The reach of the South Loup that is on the steepest 

segment of the longitudinal valley profile (fig. 10) has

the lowest sinuosity index. Elsewhere, the valley 

slope is nearly constant, but different reaches have 

considerably different sinuosities. The differences in 

sinuosity are attributed to local differences in bank 

erodibility. For a given valley slope, river slope necessarily decreases as sinuosity increases. Because the 

valley slope of the South Loup is nearly constant upstream from the steep segment of its profile, the river 

slope upstream from this segment decreases as sinuosity index increases.

Condra, G. E., Reed, E. C., and Gordon, E. D., 1950, Correlation of the Pleistocene deposits of Nebraska: Nebraska Geol. Survey Bull. ISA, p. 1-2.

Dury, G. H., 1959, The face of the earth: Baltimore, Md.,

Penguin Books, 223 p. 

Friedkin, J. F., 1945, A laboratory study of the meandering

of alluvial rivers: Vicksburg, Miss., U.S. Waterways

Expt. Sta., 40 p. 

Frye, J. C., Leonard, A, B., and Swineford, Ada, 1956,

Stratigraphy of the Ogallala formation (Neogene) of

northern Kansas: Kansas Geol. Survey Bull. 118, p.

1-92. 

Hubbell, D. W., 1960, Investigations of some sedimentation

characteristics of sand-bed streams, Progress reports:

U.S. Geol. Survey open-file rept., 78 p., 15 figs. 

Hubbell, D. W., and Matejka, D. Q., 1959, Investigations of

sediment transportation, Middle Loup River at Dunning,

Nebraska: U.S. Geol. Survey Water-Supply Paper 1476,

123 p.
PHYSIOGRAPHIC AND HYDRAULIC STUDIES OF RIVERS P41

Lane, E. W., 1957, A study of the shape of channels formed 

by natural streams flowing in erodible material: U.S. 

Army Corps of Engineers, Missouri River Div., Omaha, 

Nebr., Sediment Ser. 9,106 p., 15 figs.

Leopold, L. B., and Maddock, Thomas, Jr., 1953, The hydraulic geometry of stream channels and some physiographic implications: U.S. Geol. Survey Prof. Paper 

252, 57 p.

Leopold, L. B., and Wolman, M. G., 1957, River channel 

patterns braided, meandering, and straight: U.S. Geol. 

Survey Prof. Paper 282-B, 85 p.

 1960, River meanders: Geol. Soc. America Bull., v, 

71, p. 769-794.

Miller, J. P., 1958, High mountain streams effect of geology 

on channel characteristics and bed material: New Mexico Inst. Mining and Technology Mem. 4, 53 p.

Miller, R. D., and Scott, G. R., 1955, Sequence of alluvia- 

 tion along the Loup Rivers, Valley County area, Nebraska: Geol. Soc. America Bull., v. 66, p. 1431-1448.

Miller, R. D., and Scott, G. R., 1961, Late Wisconsin age of

terrace alluvium along the North Loup River, central

Nebraska a revision: Geol. Soc. America Bull., v. 72,

p. 1283-1284. 

Mitchell, W. D., 1957, Flow duration of Illinois streams:

Springfield, Illinois Dept. Public Works and Buildings,

Div. Waterways, 189 p. 

Rubey, W. W., 1952, Geology and mineral resources of the

Hardin and Brussels quadrangles (in Illinois) : U.S.

Geol. Survey Prof. Paper 218, 179 p. 

Schumm, S. A., 1960, The effect of sediment type on the

shape and stratification of some modern fluvial deposits:

Am. Jour. Sci., v. 258, p. 177-184. 

 1963, Sinuosity of alluvial rivers of the Great Plains:

Geol. Soc. America Bull., v. 74, p. 1089-1100. 

Smith, H. T. U., 1955, Use of aerial photography for interpretation of dune history in Nebraska, U.S.A.: Internal.

Congr., 4th, Rome-Pisa 1953, Assoc. for Study of the

Quaternary, 7 p.

U.S. GOVERNMENT PRINTING OFFICE : 1964 O 719-579