Some Effects 

of Fine Sediment 

on Flow Phenomena

GEOLOGICAL SURVEY WATER-SUPPLY PAPER 1498-G

Some Effects 

of Fine Sediment 

on Flow Phenomena

By D. B. SIMONS, E. V. RICHARDSON, and W. L. HAUSHILD

STUDIES OF FLOW IN ALLUVIAL CHANNELS

GEOLOGICAL SURVEY WATER-SUPPLY PAPER 1498-G

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1963
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 25, D.C.
CONTENTS

Page

Partial list of symbols..____________________________________________ v

Glossary of terms__ ___--__-_-_-_-_-___-________--_-______________ vi

Abstract__ _____________________________________________________ Gl

Introduction. _____________________________________________________ 1

Equipment, procedure, and data___________________________________ 2

Flumes______________________________________________________ 2

Bed materials._________________________________________________ 3

Fine materials__________-----_____-_-_____-_____-___-_-________ 4

General procedure.____________________________________________ 4

Basic data____________________________________________________ 12

Effect of fine sediment on fluid properties.___ _________________________ 17

Viscosity.____________________________________________________ 17

Specific weight-_---_--_-__-_--_-___-__________-__-_--__-______ 20

Effect of fine sediment on fall velocity______--_____-____-__-___-______ 20

Observed flow phenomena._________________________________________ 26

Regimes of flow and forms of bed roughness._____________________ 26

Lower flow regime.____________________________________________ 29

Ripples_________________________________________________ 29

Dunes, 8-foot flume_-----_-___---______--_--____-_______--_ 31

Dunes, 2-foot flume___-_-______ ____________________________ 32

Transition. _____-__-___ ______________________________________- 33

Sheared-out dunes, 2-foot flume._____-___-_-____-__-_-______ 33

Upper flow regime._______----_-______________--___-_-_________ 34

Standing waves, 2-foot flume________________________________ 34

Antidunes, 8-foot flume.___________________________________ 34

, Antidunes, 2-foot flume____________________________________ 35

Effect of fine sediment on resistance to flow.__________________________ 36

Effect of fine sediment on bed-material transport. _____-__--_-___--____ 36

Fine sediment transport-__-__---_-_-_______-_.__---__-_____-_----_- 42

Conclusions and recommendations._-___-_________-_--_-____----__-__ 44

Literature cited-_________________________________________________ 45

Index.___________________________________________________________ 47

ILLUSTKATIONS

Page

FIGURE 1. Schematic diagram of the 2-foot flume___-____----_ G3 

2-3. Graphs showing the particle-size distribution of:

2. The bed materials. _________________________ 3

3. The fine sediments-___________________________ 5

4. Graphs showing measured and recorded water-surface

slopes _________________________________________ 13

5. Graphs comparing bed-configuration measurements.... 16 

6-7. Graphs showing apparent kinematic viscosity of:

6. Aqueous dispersions of bentonite_______________ 17

7. Aqueous dispersions of kaolin-_________________ 18

in
IV CONTENTS

Page

FIGURE 8. Figure showing general shape of the viscosity curves 

for clay-water systems with various amounts of 

added bases._______-_________-..--_--___---___ G19

9. Graph showing the particle-size distribution of a sand

sample from the Elkhorn River, Nebr_ ________ 22

10-12. Graphs showing the variation of fall velocity:

10. With varying percentage of bentonite in water. _ 23

11. With varying percentage of kaolin in water____. 24

12. With water temperature-_____________________ 25

13-14. Photographs showing the dune bed configuration in:

13. The 8-foot flume___________________________ 27

14. The 2-foot flume___________________________ 28

15-16. Photographs showing antidunes in:

15. The 8-foot flume--.-__________________. 28

16. The 2-foot flume---___-----_-_-__... 29

17. Photograph showing lenses of fine material trapped in

the bed_ ____-_-____-_--___-___---__---___ --____ 30

18. Photograph showing ripples during clear-water run____ 31 

19-22. Graphs showing variation of:

19. Resistance coefficient; 8-foot flume data-_______ 37

20. Resistance coefficient; 2-foot flume data. _______ 38

21. Bed-material transport with varying concentration of fine material_______________________ 39

22. Bed-material transportation parameter; 8-foot

flume data._______________________________ 41

23. Photograph showing layer of bed material adjacent to

the flume floor impregnated with fine sediment______ 43

TABLES

Page

TABLE 1. Summary of data for runs in flumes__ ___--_-__-__-___----__ G6 

2. Variation of the measure of gradation with percentage of

bentonite in water______________________________________ 22
PARTIAL LIST OF SYMBOLS

DimenSymbol Description sions Units

C Chezy coefficient of discharge in ______ ___________

Vj; dimensionless form which is

equivalent to V/T7*. 

Cf Concentration of fine sediment dis- ppm __ ___________

charge. 

<?/_ t Concentration of fine sediment and ppm __ ___________

bed material discharge. 

Ct Concentration of total bed mate- ppm__ ___________

rial discharge. 

d Median fall diameter of bed mate- i_____ ft

rial. 

dn Nominal diameter. The diameter L. _ _ _ _ ft

of a sphere that has the same

volume as the particle. 

dt Median fall diameter of bed mate- _£_____ ft

rial discharge. 

D Average depth of flow----------- L...__ ft

F Force_____-___-_______________ F..... Ib

F Froude number________________ ______ ___________

h Average height of bed roughness__ L..... ft

I Average spacing of bed roughness- L..... ft

L Length________________________ £_____ ft

Q Discharge of water-sediment mix- L3 /T.. cu ft per sec

ture. 

q b Rate of bed-load transport______ F/tL_ . Ib per ft-sec

2, Rate of total sediment transport- _ F/tL. _ Ib per ft-sec 

R Reynolds number; for a sediment ______ ___________

particle, R is wdjv. 

S Surface slope in steady uniform ______ ___________

flow. 

t Time_ ________________________ £_____ sec

T Temperature--._______________ ______ °C

V Average velocity based on contin- L/T... ft per sec

uity principal. 

Vs Average velocity of sand waves in LfT... ft per min

the lower flow regime. __ 

V* Shear velocity which is -\fgDS, or LIT... ft per sec

vWpV
VI STUDIES OF FLOW IN ALLUVIAL CHANNELS

DimenSymbol Description sions Units

w Fall velocity of sediment particles- i/T___ ft per sec 

wf Fall velocity of sediment in an LIT-.- ft per sec 

aqueous dispersion of fine sediment. 

7 Specific weight of an aqueous dis- F/L3 . _ Ib per cu ft

persion of sediment. 

yw Specific weight of water _________ F/L3 _ _ Ib per cu ft

ys Specific weight of sediment- _____ F/L3 - _ Ib per cu ft

Ay Difference between specific weights F/L3 -- Ib per cu ft

of air and water. 

AYS Difference between specific weights F/L3 -- Ib per cu ft

of sediment and water. 

8' Thickness of laminar sublayer.___ Z_____ ft

v Kinematic viscosity___________ L2/T-- sq ft per sec

/ Apparent kinematic viscosity of L2/T- _ sq ft per sec 

the aqueous dispersion of fine 

sediment. 

M Dynamic viscosity______________ Ft/L2 - _ Ib-sec per sq ft

p Mass density of water,__________ Ft2/L*. Slug per cu ft

ps Mass density of sediment_ _______ Ft2/L*- Slug per cu ft

<rr A measure of the gradation of the ______ _____________

sediment. 

T 0 Tractive or shear force developed F/L2 -- Ib per sq ft

on the bed, yDS.

TC Critical tractive force associated F/L2 ^. Ib per sq ft 

with beginning of bed movement.

GLOSSARY OF TERMS

Alluvial channel. A channel whose bed is composed of appreciable 

quantities of the sediments transported by the flow at a given 

or greater discharge.

Antidunes. Symmetrical sand and water surface waves which are 

in phase and which move upstream. The surface waves build up 

with time and become gradually steeper on their upstream sides 

until they break like surf and disappear. These waves generally 

form, break, and reform in groups of two or more.

Bed material. The material of which a stream bed is composed.

Dune. A sand wave of approximately triangular cross section in a 

vertical plane in the direction of flow with gentle upstream slope 

and steep downstream slope. It travels downstream as a result 

of the movement of the sediment up the upstream slope and the 

deposition of part of this material on the downstream slope.
GLOSSARY OF TERMS VII

Fine sediment. The part of the total load that is composed of particles of smaller sizes than those found in appreciable quantities 

in the bed material (referred to by some writers as wash load).

Flow regime. A range of flows with similar bed forms, resistance 

to flow, and mode of sediment transport.

Lower flow regime. Flow with bed forms of ripples, ripples on 

dunes, and dunes.

Median diameter. The midpoint in the size distribution of a sediment such that one-half of the weight of the material is composed 

of particles larger than the median diameter, and the other onehalf is composed of particles smaller than the median diameter.

Plane bed. A bed without elevations or depressions larger than the 

maximum size of the bed material.

Ripple. Small triangular-shaped sand waves, similar to dunes in 

shape but smaller in magnitude, which have rather small width 

normal to the direction of flow.

Sand waves. Crests and troughs (such as ripples, dunes, or symmetrical undulations) on the bed of an alluvial channel formed 

by the movement of the bed material.

Sediment. Fragmental material that originates from weathering of 

rocks and is transported by, suspended in, or deposited by water.

Sediment concentration. The ratio of dry weight of sediment to 

total weight of the water-sediment mixture, expressed in parts per 

million.

Standard fall diameter or fall diameter. The diameter of a sphere 

that has a specific gravity of 2.65 and the same terminal uniform 

settling velocity as the particle (any specific gravity) when each 

is allowed to settle alone in quiescent distilled water of infinite 

extent and at a temperature of 24° C.

Standing waves. Symmetrical sand and water waves which are in 

phase and which gradually build up and die down. Waves of 

this type are virtually stationary and generally develop in series 

and often reform, somewhat periodically, after disappearing.

Suspended load. The sediment moving in suspension in a fluid as 

a result of turbulent currents and (or) by colloidal suspension.

Total load. The total amount of sediment that is transported by 

water past a section in a given length of time.

Upper flow regime. Flow with bed forms of plane bed with movement, standing waves, and antidunes.

STUDIES OF FLOW IN ALLUVIAL CHANNELS

SOME EFFECTS OF FINE SEDIMENT ON FLOW 

PHENOMENA

By D. B. SIMONS, E. V. RICHARDSON, and W. L. HAUSHILD

ABSTRACT

Fine material (bentonite and kaolin clays) dispersed in water has a very 

definite effect on the viscosity and specific weight of the fluid. Tests at 24° C. 

with a Stormer viscosimeter showed that the apparent kinematic viscosity of 

an aqueous dispersion consisting of 10 percent by weight bentonite was 8.75 

times greater than that, of pure water, and a dispersion consisting of kaolin was 

1.40 times greater. The change is viscosity and density of the fluid changes the 

fall velocity of the bed material. The effect of fine material on the fall velocity 

of the bed material can be determined, as a first approximation, with the visual 

accumulation tube by using aqueous dispersions of clay as the sedimentation 

liquid. The results from visual accumulation analyses .are comparable to those 

obtained by computation using the Reynolds number, drag relation, and the 

viscosity of the aqueous dispersion of clay as obtained from the Stormer viscosimeter.

Experiments conducted in flumes at Colorado State University demonstrated 

that when changes in fall velocity caused by the changes in fluid properties 

occurred, the form of bed roughness was altered. Resistance to flow and 

sediment transport, because they are dependent on the form of bed roughness, 

were appreciably affected.

INTRODUCTION

Many controversial statements regarding the influence and effect 

of very fine sediment (clay and silt) on the mechanics of flow in alluvial channels are prevalent. Fine material is most commonly referred to as wash load; wash load has been defined by Einstein (1950) 

as "that part of the sediment load which consists of grain sizes finer 

than those in the bed." Even the term "wash load" is controversial 

and for the most part is referred to as fine-material load in this 

report. Einstein (1950) pointed out that the fine-material load does 

not appear to be a function of the flow, but that it is usually related 

to supply and that the stream's capacity to transport it is always 

vastly in excess of the available supply. He did not indicate that 

its presence is apt to influence the mechanics of flow in any way.

668688 O 63 2 Gl
G2 STUDIES OF FLOW IN ALLUVIAL CHANNELS

Similarly, Brown, in "Engineering Hydraulics" (Rouse, 1950), stated 

that the fine-sediment load plays a negligible role in normal stream 

behavior.

In contrast, Langbein (1942) reported changes in bed form and 

increased antidune activity as the concentration of fine sediment 

increased. Blench (1957) also implied that fine-sediment load exerts 

a measurable effect on flow in alluvial channels. He stated that the 

velocity distribution and the resistance to flow are affected by the 

concentration and the characteristics of the suspended-sediment load. 

In addition Bingham (1922) showed that fluidity, the reciprocal of 

viscosity, of aqueous suspensions of clay varied markedly with the 

volume percentage of clay.

As a part of the U.S. Geological Survey's study of fluvial mechanics 

at Colorado State University an investigation was made of the effects 

of fine-sediment load on flow phenomena in a large 8-foot flume 

and a small 2-foot flume. Also, the properties of aqueous dispersions were studied in the sediment laboratory. This investigation, 

the results of which are reported here, covered the effect of concentrations of fine sediment on (1) the physical properties of the liquid 

and the hydraulic properties of the bed material, (2) the forms of 

bed roughness, (3) the resistance to flow, and (4) the bed-material 

transport.

EQUIPMENT, PROCEDURE, AND DATA

In the 8-foot flume a series of 54 equilibrium rims were completed 

in which slope was varied from 0.00046 to 0.0096 foot per foot, the 

discharge was varied from 6.9 to 21.4 cfs (cubic feet per second), and 

the concentration of fine sediment was varied from 0 to 42,000 ppm 

(parts per million). Flow conditions ranged from the lower flow 

regime with ripples to the upper flow regime with antidunes.

In the 2-foot flume 39 equilibrium runs were completed which 

covered the range of forms of bed roughness from plane bed prior 

to movement of sediment to antidunes. The ranges in the basic variables were: slope from 0.00016 to 0.0144 foot per foot, discharge from 

1.1 to 7.9 cfs, depth from 0.59 to 0.91 feet, and concentrations of fine 

sediment from 0 to 64,000 ppm. The basic data are presented in 

table 1.

FLUMES

The larger flume was a tilting recirculating flume 150 feet long, 8 

feet wide, and 2 feet deep. The flume was the same as that described 

by Simons and others (1961) except that a plastic window was installed in the flume wall between stations 90 and 96 so that bed configuration, dune velocity, sediment transport, and flow could be directly observed.
EFFECTS OF FINE SEDIMENT ON FLOW PHENOMENA G3

A schematic drawing of the smaller jflume is shown in Figure 1. 

The flume was 60 feet long, 2 feet wide, and 2i/£ feet deep with i^-inch 

clear-plastic sidewalls and a floor of ^-inch stainless-steel plate. The 

flume was adjustable to any slope from horizontal to 0.1 foot per foot, 

and it recirculated the mixture of water and sediment.

FIGURE 1. Schematic diagram of the flume. Explanation: a, pumping unit; 1), motor ; c, 

center support; d, orifice ; e, flexible connection ; /,, jacks; g, manifold] diffuser; h, head 

box; i, baffles and screens; j, rails; k, instrument carriage; I, flume (2X2.5X60 ft) ; 

m, tailgate; n, total-load sampler; o, tailbox.

BED MATERIALS

The sand used as bed material for the flume runs was the same as 

that used in the study by Simons and others (1961). However, the 

characteristics of the sand had changed slightly. (See figure 2.) In 

the study using the 8-foot flume, the median fall diameter d increased 

slightly, 0.47 versus 0.45 mm, and the measure of gradation o> de0.1

2 5 10 20 30 40 50 60 70 80 90 95 

PERCENT OF PARTICLES FINER THAN INDICATED SIZE

FIGURE 2. Particle-size distributions of the bed materials.

98 99 99.5 99.8
G4 STUDIES OF FLOW IN ALLUVIAL CHANNELS

creased slightly, 1.54 versus 1.60. Also, in the study using the 2-foot 

flume the median fall diameter was 0.54 mm, and the measure of 

gradation was 1.50. These changes are attributed to the continued 

wastage of a small quantity of water introduced through the bearings 

of the pumps to protect them from sediment; this water carried away 

some of the fine sand during preceding periods of flume operation.

FINE MATERIALS

A bentonite clay was used in the flume studies to determine the 

effect of fine sediment on resistance to flow, transport of bed material, 

and flow phenomena. Bentonite was selected because it was commercially available in large quantities and is typical of much of the 

fine material found in streams in the semiarid West. In addition, 

the effect of the bentonite and a kaolin clay on the properties of the 

fluid and on the hydraulic properties of the bed material was studied 

in the sediment laboratory.

The size distributions of the bentonite and the kaolin are given in 

figure 3. The size distributions of the bentonite and the kaolin were 

determined by standard U.S. Geological Survey sieve-pipette analyses 

with the samples chemically and mechanically dispersed in water.

GENERAL PROCEDURE

In conducting the experiments to determine the effect of fine sediment on resistance to flow and on bed material transport, specific discharges and slopes were selected, and runs were made with varying 

concentration of fine material. The mixture of water and sediment 

was recirculated at a given slope and discharge until equilibrium was 

achieved. Equilibrium was considered established when: (1) the bed 

configuration was completely developed for the full length of the 

flume, excluding the sections influenced by entrance and exit conditions; and (2) the average water-surface slope remained essentially 

constant with respect to time.

In the 8-foot flume the first run of a series was started using clear 

water, and after equilibrium was established, the data that described 

the run were collected. Then, without stopping the pumps, altering 

the bed configuration, or changing the external controls (such as tail 

gate and valves), a measured portion of fine material was added at a 

time. After the addition of each portion of fine material, the run was 

continued long enough, at least 24 hours in the lower flow regime, to 

insure equilibrium, and then the data for the run were collected. 

When the maximum concentration of fine sediment was reached for a 

particular series of runs, the process was usually reversed. The slope 

or discharge or both were changed before starting another maximumconcentration run. Other new runs were then made with the concentration of fine sediment reduced in measured portions between runs
EFFECTS OF FINE SEDIMENT ON FLOW PHENOMENA G5

U.i 

0

1

j

j j

» 

r

i 

d 0.01

: 

5

0.001 

4

/

/

^

-f

/

i

1

Bento

H- /

-v 7-

1 o 

iitev _/ Arf /7

/

/

/<v Kaolin

r

/

/

V

^^

^

/

-^

/

y

3 50 60 70 80 90 95 98 99 99.5 99.8 99.9 99.?

PERCENT OF PARTICLES FINER THAN INDICATED SIZE 

FIGURE 3. Particle-size distribution of the fine sediments.

by adding water and washing fine material and water through the 

tail-box overflow.

In the 2-foot flume 15 water-sand runs were made prior to the 

bentonite runs to define the regimes of flow and the forms of bed roughness for the flume. After the 15 water-sand runs were completed, six 

series of runs were made to determine the effect of fine sediment. 

These series of runs covered the range of bed forms from dunes to 

antidunes, and each series consisted of a water-sand run without 

bentonite plus three to five runs at different concentrations of fine sediment. When a series of runs were completed, excluding series 15, the 

aqueous dispersion of bentonite was discarded, and the system and the 

bed material were washed free of bentonite in preparation for the next 

series of runs.
TABUE 1. Summary of data for runs 

Run 8X102 (Cfs)

D

(ft)

V

(ft/?ec)

xX105 »X10S

Sq ft per sec

T

(°C)

c

(pp

0.47 mm sand in the 8-foot flume

46

47 

48 

49 

85

86 

87 

88 

90 

89

93 

92 

91 

82 

51

52 

73 

74 

76 

75

53 

77 

96 

94 

83

54 

56 

55 

57 

58

95 

78 

59

0.084 

.042 

.052 

.173 

.047

.046 

.046 

.049 

.053 

.065

.072 

.'090 

.117 

.248 

.236

.222 

.222 

.215' 

.203 

.204

.235 

.199 

.201 

.237 

.200

.240 

.242 

.237 

.259 

.233

.180 

.320 

.326

14.54 

9.59 

15.26 

21.32 

7.11

6.92 

6.96 

7.10 

6.97 

7.08

7.20 

7.14 

7.12 

8.16 

8.11

8.01 

8.20 

8.18 

8.49 

8.24

8.01 

8.76 

8.31 

11.30 

15.58

15.36 

15.36 

15.36 

15.39 

15.28

15.38 

11.52 

15.36

1.11 

.75 

1.23 

1.33

.78

.76 

.75 

.74 

.60 

.60

.62 

.63 

.58 

.64 

.62

.55 

.61 

.65 

.63 

.64

.57 

.65 

.53 

.81 

.91

.92 

.90

.74 

.87 

.90

.80 

.72 

.65

1.64 

1.60 

1.55 

2.00 

1.13

1.14 

1.16 

1.20 

1.45 

1.47

1.45 

1.43 

1.53 

1.60 

1.62

1.81 

1.67 

1.58 

1.69 

1.60

1.77 

1.68 

1.94 

1.74 

2.14

2.08 

2.14 

2.04 

2.20 

2.11

2.39 

2.00 

2.96

1.30 

1.36 

1.36 

1.38 

1.31

1.77 

1.11 

1.13 

1.17 

1.12

1.24 

1.12 

1.14 

1.00 

1.28

1.20 

1.06 

1.05 

1.08 

1.05

1.16 

1.11 

1.12 

1.28 

1.19

1.18 

1.03 

1.12 

1.05 

1.08

1.12 

1.07 

1.04

1.32 

1.37 

1.50 

1.39 

1.42

1.33 

1.42

1.26. 

1.24 

1.31 

1.38 

1.36

1.52 

1.52 

1.93

1.25 

1.11 

1.26 

1.19 

1.25

2.03 

1.41 

1.20

13.1 

11.5 

11.5 

11.0

12.7

17.0 

19.1 

18.3 

17.1 

18.5

14.7 

18.5 

18.0 

23.2 

13.1

16.0 

20.7 

21.0 

20.0 

21.2

17.2 

19.1 

18.6 

13.5 

16.2

16.6 

22.1 

18.5 

21.3 

20.1

18.7 

20.3 

21.7

4

8

11

6

9

6

8

1

5

7

9

9

10

12

25

1

2

4

4

5

28

12

4
60

61 '

71

72

70

63

64

65

66

80

81

62

67

79

84

69

68

98

100

99

97

.342

.355

.531

.550

.640

.570

.578

.571

.575

.643

.634

.622

.646

.651

.740

.734

.740

.821

.790

.806

.960

21.35

21.32

8.22

8.26

8.14

15.50

15.61

15.60

15.52

15.27

21.35

21.23

20.87

21.31

15.36

15.54

20.94

15.80

21.42

21.27

12.01

.62

.61

.32

.32

.30

.43

.41

.42

.45

.39

.55

.54

.53

,55

.41

.43

.53

.44

.51

.50

.37

4.28

4.36

3.21

3.26

3.41

4.48

4.76

4.63

4.34

4.91

4.85

4.89

4.91

4.82

4.67

4.48

4.95

4.51

5.28

5.32

4.07

1.06

1.00

1.04

1.08

1.08

1.05

1.05

1.04

1.01

1.04

1.38

.98

1.02

1.05

1.23

1.02

1.00

1.11

1.29

1.09

1.10

1.18

1.20

1.18

1.31

1.20

1.16

1.26

1.34

1.38

1.43

1.12

1.36

1.46

1.24

1.23

2.46

1.96

1.29

21.1

23.2

21.4

20.2

20.2

21.2

21.2

21.6

23.0

21.8

10.7

24.5

22.7

21.0

15.0

22.4

23.5

19.0

13.3

19.6

19.5

3

6

3

7

3

3

6

9

12

12

4

11

12

7

7

42

26

5

0.54 mm sand in the 2-foot flume

1234650

208

8A

8E

8B

8C

8D7

14

14A

14C

14B

19

0.016

.019

.026

.038

.170

.201

.336

.338

.351

.331

.248

.293

.294

.198

.388

.399

.366

.377

.339 

.408

1.06

1.12

1.21

1.59

2.45

3.12

4.28

4.74

3.82

3.82

3.69

3.84

3.83

3.77

3.42

4.77

4.78

4.80

4.84 

3.82

0.61

.60

.62

.59

.72

.81

.91

.72

.78

.84

.88

.85

.86

.72

.72

.89

.82

.87

.70 

.76

0.89

.96

1.00

1.37

1.74

1.95

2.39

3.36

2.51

2.33

2.15

2.30

2.28

2.65

2.44

2.74

2.95

2.82

3.51 

2.58

1.20

1.16

1.17

1.14

1.12

1.10

1.24

1.08

1.11

1.12

1.00

1.04

1.02

.96

1.06

1.10

.98

1.03

1.02 

1.04

1.31

1.46

1.70

1.79

3.20

1.27

1.74

2.41

15.9

17.4

16.9

18.0

18.6

19.2

14.7

20.2

18.9

18.7

23.3

21.5

22.4

25.0

20.6

19.3

24.3

22.2

22.3 

21.5

5

14

20

24

63

9

22

44
TABLE 1. Summary of data for runs in flu

Run SX102

Q

(cfs)

D

(ft)

V

(ft/sec)

«X105 j/XlOs

Sq ft per sec

T

(°C)

c

(pp

0.54 mm sand in the 2-foot flume Cont

9

10

18

ISA 

18B

18C

15

15A 

15B 

15C

13

11

16A 

16B 

16C

17

17A 

17B 

12

0.433

.486

.520

.508 

.790

.900 

.551

.550 

.537 

.628

.768

.980 

1.075 

1.305

1.175

1.365 

1.928 

1.438

4.16

5.33

7.62

7.57 

7.59

7.59 

6.94

6.99 

6.96 

6.99

6.37

7.48

7.82 

7.84 

7.86

7.89

7.83 

7.86 

7.84

0.72

.64

.71

.76 

.69

.70 

.74

.75 

.75 

.73

.72

.66

.67 

.66 

.65

.65

.65 

.68 

.64

2.93

4.30

5.44

5.11 

5.62

5.54 

4.75

4.76 

4.73 

4.85

5.80

5.92 

6.03 

6.14

6.21

6.17 

5.87 

6.27

1.15

1.07

1.02

1.02 

1.00

.99 

1.04

1.02 

.99 

.99

1.14

1.08

1.00 

.96 

.96

1.02

1.02 

.99 

1.17

1.44 

1.70

3.00

1.47 

2.27 

2.98

1.35 

1.93 

2.32

2.27 

2.60

17.7

20.3

22.6

22.5 

23.3

23.7 

21.7

22.5 

23.7 

24.0

18.1

19.9

23.5 

25.0 

25.1

22.5

22.3 

24.0 

16.9

13

37

58

14

40, 

58, 

11

31, 

44, 

39, 

51
Run

Bed material

dXlQs

(ft)

w'

Sand waves

I

(ft)

h 

(ft)

Vs

(fpm)

0.47 mm sand in the S-foot flume

[w computed on the basis of average median fall diameter (0.47 mm) and water temperatu

median fall diameter (0.47 mm) taking into account the effect of fine sedimen

46

47

48

49

85

86

87

88

90

89

QQ

92

91

51

73

74

76

75

53

96

83

56

57

58

95

78

1. 502

1.437

1.521

1.640

1.355

1.619

1.610

1.679

1.417

1.565

1.627

1.456

1.443

1.564

1.581

1.588

1.624

1.633

1 469

0

1.518

1.535

1.771

1.453

1.56

1.56

1.54

1.54

1.48

1.55

1.58

1.47

1.52

1.55

1.51

1.47

1.59

1.53

1.52

1/54

1.54

1.51

1.53

1.39

1.48

1.60

1.49

0.217

.214

.214

.212

.227

.230

.227

.230

.230

.229

.240

917

.224

.235

.236

.234

.236

.232

.231

.225

.238

.230

.237

.234

.231

.235

0.223

.224

.220

.221

.223

.231

.229

.217

.205

.224

.236

.227

.232

.230

.203

.223

5.98

8.20

6.24

7.28

1.20

.96

91

1.00

1.63

1.62

4.56

4.33

4.12

5.55

5.33

5.45

5.50

5.71

4.37

5.81

5.12

4.31

5.21

5.78

6.54

5.30

5.87

5.12

5.36

7.36

0.41

.22

.32

.35

.07

.06

.06

.07

.06

.06

.25

.28

.20

.26

.34

.30

.28

.34

.29

.24

.32

.43

.41

.29

.27

.29

.26

.33

.39

0. 035

.030

.080

.0074

.0033

.0055

.0015

.027

.030

.039

.050

.084

.17

.19

.18

.26

.17

.16

.15

.11

.091

.20

.28

.16

.33

.20

.23

.29

.21

.31

.34
TABLE 1. Summary of data for runs in flum

Run

Bed material

dXlO3

(ft)

<Tr W

10 '

Sand waves

I

(ft).

A

(ft)

Fs

(fpm)

0.47 mm sand in the S-foot flume Continu

59

60

61

71

72

70

63

6-1

65

66

80

81

62

67

79

84

69

68

98

100

99

97

1.535

1.699

1.722

1.673

1.588

1.515

1.535

1.601

1.506

1.526

1.594

1.584

1.647

1.620

1.355

1.640

1.430

1.738

1.440

1.561

1.492

1.597

1.50

1.48

1.55

1.61

1.56

1.63

1.54

1.56

1.49

1.56

1.46

1.66

1.48

1.55

1.48

1.53

1.58

1.58

1.57

1.51

1.60

1.66

0.237

.236

.240

.237

.234

.234

.236

.236

.237

.240

.238

.211

.243

.239

.236

.239

.241

.232

.218

.233

.233

0.234

.233

.234

.233

.228

.231

.233

.230

.230

.228

.227

.239

.229

.224

.232

.234

.188

.207

.228

7.50

2.43

3.43

3.43

3.44

3.34

3.36

4.40

4.00

3.90

3.60

3.73

4.00

3.10

4.04

3.38

.07

.12

.23

.20

.20

.20

.26

.04

.10

.08

.21

.26

.05

.24

.31

.16

0.72

 

 

 

 

 

 

 

 

 

0.54 mm sand in the 2-foot flume

[w computed on the basis of average median fall diameter (0.54 mm) and water temperatu

median fall diameter (0.54 mm) taking into account the effect of fine sediment 

1

3

4

5

6

1.585

1.526

1.640

1.53

1.55

1.67

.261

.264

.266

0.47

4.6

0.03

.10

.35

0. 0001

.0004

.0047

 
EFFECTS OF FINE SEDIMENT ON FLOW PHENOMENA Gil

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G12 STUDIES OF FLOW IN ALLUVIAL CHANNELS

For a series, data were first obtained for the water-sand run, and 

the run was continued with no changes made to the flow or system 

controls except that bentonite was added at the tail box until the 

desired concentration of fine sediment was attained. The desired 

concentration of fine sediment was maintained during the collection 

of data by adding more bentonite when necessary. The concentration 

of the fine sediment decreased with time owing to deposition of bentonite at the contact plane of the sand bed and the flume floor and 

to loss of some of the bentonite with the overflow from the tail box; 

because a constant concentration of fine material was able to be sustained only over a short period of time, data of the runs with bentonite 

were collected in a relatively short interval of time as compared with 

the runs without bentonite.

After completion of run series 15, run 16A was made by reversing 

run 15C. (See table 1.) Although some bentonite was conserved by 

this method, an undesirable bed condition resulted. The sand bed became partly stabilized with bentonite and difficult to move. Runs 16A, 

B, and C were completed with this anomalous bed condition and 

probably woul'd have been similar to run series 17, 17A, and 17B 

had the normal procedure of starting with clear water been followed.

BASIC DATA

The data obtained for each equilibrium run included water-surface 

slope, $; discharge, Q\ water temperature, J7 ; depth, Z>; average 

velocity, V ; velocity profiles; concentration of bed material transport, 

CT \ concentration of the fine sediment (bentonite) transport, 6"V; concentration of suspended sediment; characteristics of the bed material; 

bed configuration; and photographs of the water surface and corresponding bed configuration. The basic data are given in table 1.

The water-surface slope was determined by measuring the watersurface elevation with a mechanical point gage and also, in the 8-foot 

flume, with a differential bubble gage; both methods were in close 

agreement. The bubble gage continuously recorded the difference 

in elevation of the water surface, to within 0.001 foot, between two 

points on the flume at different cross sections. From the difference 

in the height of the water surface and the distance between the two 

cross sections, water-surface slope could be computed. The continuous bubble-gage record of the slope can be used to determine when 

equilibrium conditions are established, as equilibrium exists when the 

average slope does not change with time.

Typical records of the slope measured by the bubble gage for various forms of bed roughness are illustrated in figure 4. A study of 

figure 4 shows that the pattern of variation of slope with time is 

directly related to the form of bed roughness.
EFFECTS OF FINE SEDIMENT ON FLOW PHENOMENA G13 

0.000475

g- 0.000450 

CO

0.000425

Ripples 

Measured-^?

4 5 6 7 8 9 10

Time, in hours

0)

a. 

o

0.00275

0.00250

0.00225

0.00200

CO

0.000775

0.000750

0.000725

0.000700

0.000675 45678 9 10 II

Time, in hours

FIGURE 4. Measured and recorded water-surface slopes.

The discharges of the mixture of water and sediment were measured with calibrated orifice meters and water-air manometers.

The \vater temperature was measured in degrees centigrade to the 

nearest 0.1° wth a mercury thermometer. Water temperature was
G14 STUDIES OF FLOW IN ALLUVIAL CHANNELS

virtually constant for a particular run but ranged from 10.7°C to 

25.1°C during the study.

The average depth of flow was determined by measuring the difference in height between the water surface and the sand bed. Measurements were made every foot over a 100-foot length of the 8-foot flume 

and over a 35-foot length of the 2-foot flume. In the 8-foot flume the 

average depth ranged from 0.53 to 1.33 feet in the lower flow regime 

and from 0.30 to 0.89 feet in the upper flow regime. In the 2-foot 

flume the depths ranged from 0.59 to 0.82 feet. The measurements 

of average depth were accurate to within 0.02 feet.

The mean velocity was calculated by dividing the measured discharge by the area of the cross section of the water in the flume. 

Therefore, measurement of mean velocity accumulated the errors inherent in the depth and discharge measurements. In the study, mean 

velocity ranged from 0.89 to 2,96 feet per second in the lower flow 

regime and from 2.58 to 6.21 feet per second in the upper flow regime.

Velocity profiles for each run were obtained with a calibrated pitot 

tube and a tilting water-air manometer. They were obtained in three 

verticals in cross sections of the 8-foot flume and in one vertical in the 

2-foot flume.

The total sediment load was sampled with a width-depth integrating 

total-load sampler where the water discharged from the flume into the 

tail box. In the lower flow regime eight samples were collected over 

a 2-hour period, and in the upper flow regime four to six samples were 

collected over a 1-hour period. Each sample consisted of 70 to 110 

pounds of the mixture of water and sediment.

The total-load samples were separated into a fine-material fraction 

and a bed-material fraction. The fine-material concentration was 

measured by taking a sample of the mixture of water and sediment 

after it had been allowed to settle 1 minute. The bed material was 

the material retained after washing samples of the total load on a 270 

sieve for the 8-foot flume study and on a 200 sieve for the 2-foot flume 

study. The concentration of both fractions, which make up the total 

load, are given in table 1.

Part of the bed-material discharge for the bentonite runs could have 

been bentonite because 0.5 percent of the bentonite was coarser than 

the- number 200 sieve (0.074 mm opening) and 2.0 percent was 

coarser than the number 270 sieve (0.053 mm opening). (See 

figure 3.) For example, in run 8D the concentration of the bedmaterial discharge contributed by the bentonite could be 318 ppm (0.5 

percent of 63,700 ppm, which is 61 percent of the concentration of bed 

material Ct ). In run 17B the possible 230 ppm contributed by the 

bentonite is only 0.46 percent of the concentration of the bed material.

For a run series, the median fall diameter of the bed-material dis-
EFFECTS OF FINE SEDIMENT ON FLOW PHENOMENA G15

charge generally decreased with increasing concentration of bentonite. (See table, 1.) The decrease in median fall diameter was attributed to the finer particles contributed by the coarser portion of the 

bentonite, which was retained upon the sieves used for separating the 

bentonite from the bed-material load before analyzing for particle 

size distribution. The small median fall diameter of the total discharge of bed material for run 8D is certainly due to the relatively 

finer sediments contributed by the bentonite.

Suspended sediment was sampled near the midpoint of the 8-foot 

flume with a specially designed depth-integrating sampler. The 

sampler consisted of a brass nozzle, 3 by ^ inches, attached to a wading rod. The nozzle was connected to a flexible tube. The sample 

was drawn through the tube to a container by a vacuum pump, which 

was adjusted to draw water at a velocity approximately equal to the 

velocity of the flow. To determine the suspended-sediment concentration, one 5-8 pound sample was collected from the flow along 

equally spaced verticals in the cross section. The transit rate for the 

sampler was approximately uniform throughout the collection period 

(no variation in transit rate between upward and downward trips at 

a. vertical or between verticals). Suspended sediment was not sampled in the 2-foot-flume study.

Concentration of suspended material, which included the clay fraction, ranged from 0 to 43,500 ppm in the lower flow regime and from 

3,046 t6 57,700 ppm in the upper flow regime. Some concentrations 

of suspended bed material discharge were larger than corresponding 

concentrations of total "bed-material discharge. This difference in 

concentration was due, in part, to the inadequate number of samples 

of suspended sediment and to the possibility that sampling was in a 

region of flow where local bed shear stress and turbulence were much 

larger than average and therefore local suspended loads were abnormally large.

The samples of the bed material were washed to remove all bentonite, 

dried, split, and analyzed in the visual accumulation tube (Colby and 

Christensen, 1956) to determine median fall diameter and gradation. The gradation of the material is indicated by o> which can be 

computed from the equation:

_I /'A _jA

 ^ i, °T 2\dl6 ^ d in which b

d the median fall diameter,

di6 =ihe size, by weight, for which 16 percent is finer, and 

£/84=the size for which 84 percent is finer.

In addition to the median fall diameter and the gradation coefficient, the fall velocity 10 of the median fall diameter at the tempera-
G16 STUDIES OF FLOW IN ALLUVIAL CHANNELS

ture of the run is given in table 1. Also when fine material was in 

the flow the fall velocity 10' is given that takes into account the effect 

of the concentration of fine sediment for that run.

The amplitude A,, length /, and velocity V* of the various bed configurations were evaluated by (1) direct measurement at the observation window, (2) direct measurement with a point gage and foot 

attachment, and (3) utilization of a sonic depth sounder (Richardson and others, 1961), a method which was only applicable when the 

form of bed roughnesss was ripples, dunes, or transition.

A comparison of the bed configurations as determined by the sonic 

depth sounder and the point gage is given in figure 5. The sonic 

depth sounder was in the developmental stage while collecting most of 

these data and was not available to measure the bed configuration of 

all the ripple and dune runs.

0.1

80 85 90 

DISTANCE ALONG FLUME, IN FEET

95 100

FIGURE 5. Comparison of bed-configuration, measurements.
EFFECTS OF FINE SEDIMENT ON FLOW PHENOMENA G17

The kinematic viscosity v for the water-sand runs was determined 

by using the viscosity of distilled water at the average water temperature for each run. For the water-sand runs with bentonite, the 

apparent viscosity v' of the aqueous dispersion of sediment was used.

EFFECT OF FINE SEDIMENT ON FLUID PROPERTIES

VISCOSITY

Aqueous dispersions of kaolin or bentonite are non-Newtonian; that 

i s, the shearing stress is not directly proportional to the rate of shear. 

Therefore, the coefficient relating the shearing stress to the rate of 

shear represents an apparent viscosity and is a function of the rate of 

shear. The modifier "apparent" is used to indicate that aqueous dispersions of bentonite or kaolin are non-Newtonian liquids. The apparent viscosities of aqueous dispersions of kaolin and bentonite were 

experimentally determined by using a Stormer viscosimeter and 

sodium hexametaphosphate as a dispersing agent. Viscosities of dispersions having 0.5,1, 2, 3, 5, and 10 percent bentonite and 3, 5, and 10 

percent kaolin by weight in distilled water were measured at temperatures ranging from 5 to 45° C. The dispersions tested after mixing 

at settling times of 0,10, and 60 minutes showed no changes in viscosity 

due to settling out of the coarser particles or to the formation of a 

gel. The apparent kinematic viscosity of the aqueous dispersions of 

bentonite is shown in figure 6, and the viscosity of the aqueous disper3.4 4.2 9 10 11 

5 , IN SQUARE FEET PER SECOND

FIGURE 6. -Apparent kinematic viscosity of aqueous dispersons of bentoaite. 

66S688 O 63 4
G18 STUDIES OF FLOW IN ALLUVIAL CHANNELS

sions of kaolin is shown in figure 7. For comparison, the kinematic 

viscosity of distilled water is also given in each figure.

These relations of apparent viscosity to concentration of clay are 

very similar to several that Bingham (1922) investigated by relating 

temperature and volume concentration of earth, china clay, and 

graphite to fluidity, the reciprocal of viscosity. On the basis of his 

studies, he concluded that at each temperature fluidity decreases rapidly and linearly with increasing concentration of solids.

I 1.2 1.4 1.6 1.8 2.0 2.2 

J-XlO 5 , IN SQUARE FEET PER SECOND

FIGURE 7. Apparent kinematic viscosity of aqueous dispersoms of kaolin.

Street (1958) related the viscosity of aqueous dispersions of clay to 

their behavior at different stages of neutralization. He showed experimentally that the viscosity increases with an increase of neutralizing agent to a maximum that occurs at the isoelectric point (approximately a pH of 7.5 for kaolin and about a pH of 4.5 for montmorillonite). After this maximum for the deflocculated state, the viscosity 

decreases rapidly with further addition of the neutralizing agent. He 

reasoned that the apparent viscosity at any stage of neutralization 

depends greatly on the type of flocculation present at that stage. He 

studied the effect of the zeta potential and hydration potential of the 

Ba, Ca, K, ISTa, and Li cations used for neutralization on the viscosity.

A study of the viscosity of dilute clay-mineral suspensions by Wood 

and others (1955) indicated that aqueous dispersions of bentonite 

from Wyoming, hectorite, and attapulgite exhibited non-Newtonian 

behavior at 0.5, 1, 2, 3, 4, and 5 percent concentrations. Their results 

show that the ratio of apparent viscosity of the liquids to the viscosity
EFFECTS OF FINE SEDIMENT ON FLOW PHENOMENA G19

of water at the same temperature is independent of the temperature. 

From this, they reasoned that the viscosity of dilute aqueous clay 

suspensions ( 5 percent concentration) is governed by the geometry 

of the particles rather than by the specific interactions between particle and suspending media or between particle and particle. Inspection 

of figures 6 and 7 indicates that at a specific temperature the ratio 

of the viscosity of the aqueous dispersions of kaolin and bentonite, for 

concentrations 5 percent, to the viscosity of water is relatively independent of temperature, which conforms with the findings of Wood 

and others (1955).

The ratio of the weight of dispersing agent (sodium hexametaphosphate) to weight of fine sediment was kept constant at 1/100 for 

the flume experiments, the viscosity determinations, and the fall velocity studies. This ratio resulted in a dispersion of approximately 

deflocculated bentonite in water but was probably too great to yield 

a dispersion of maximally deflocculated kaolin in water. The constant 

ratio was sufficient to allow study of the effect of change in fluid properties caused by addition of clays to water on flow phenomena and 

hydraulic properties of the bed material; however, a full study would 

necessarily include the effect of the amount and nature of adsorbed 

cations on the properties of the aqueous dispersions of clay. Figure 8 

was prepared from the literature and indicates in a general way that 

the viscosity of clay-water systems varies with amount and nature of 

adsorbed cations. Figure 8 is only the general shape of the relation

Monovalent ions 

such as Li, Na, K

Divalent ions 

such as Ca, Mg

Added base

FIGURE 8. General shape of the viscosity curves for clay-water 

systems with various amounts of added base.
G20 STUDIES OF FLOW IN ALLUVIAL CHANNELS

of viscosity to added base, and the relation varies with the type of 

clay and the amount of added base (Baver, 1959; Street^ 1958). The 

many investigators of viscosity of aqueous clay dispersions attribute 

the variation in viscosity with the amount of added base to the electric 

charge, the degree of ionization, the hydration of the ions, and the 

degree of flocculation. Apparently, the relation is more properly a 

function of all the foregoing physiochemical properties. The effect 

of fine sediments in a stream would depend upon the concentration, 

the size and type of the fine sediment, the amount and nature of the 

adsorbed ions, and the relatively uninvestigated role of turbulence in 

sustaining a dispersion of fine sediment.

SPECIFIC WEIGHT

The specific weight of an aqueous dispersion of fine sediment depends on the concentration and specific gravity of the sediment. The 

specific weight of the aqueous dispersion of sediment is given by

Assume that

7«,= 62.4 Ib per cu ft, and 

7S =165.4 Ib per cuft,

then the equation becomes

10,021.8

160.6-

The importance of the increased specific weight of the fluid with 

increased concentration of fine sediment is shown when the specific 

weight of the fluid is related to the specific weight of the bed material 

particles. The unit weight of these particles submerged in the fluid 

is their specific weight ys minus the specific weight of the fluid y. 

The ys y represents the driving force causing downward motion, and 

in fall velocity studies the significance of this force is obvious.

EFFECT OF FINE SEDIMENT ON FALL VELOCITY

In a study of flow in alluvial channels, the properties of the bed 

material are significant. The mineral identification, density, shape, 

surface area, and volume of individual particles, and the size distribution of all the particles are usually used to describe the bed material. The fall velocity of the individual particles and the particlesize distribution based on fall velocity combine the properties of the 

bed material into one fundamental hydraulic principle. Because fall
EFFECTS OF FINE SEDIMENT ON FLOW PHENOMENA G21

velocity varies with changes in the fluid characteristics, it is also a 

means of directly relating the bed-material properties to the fluid 

characteristics. The effect of changes in the viscosity and specific 

weight of the fluid on the fall velocity of sand particles has been generally ignored in alluvial-channel research (Langbein, 1942). On 

pages Gl and G2 the appreciable effect of bentonite and kaolin on fluid 

properties was discussed. In this section the effect of the two fine 

sediments on fall velocity are discussed.

The particle-size distributions of samples of three different natural 

sands in aqueous dispersions of fine sediments were determined by the 

visual accumulation method. This method is described in detail in 

Inter-Agency Report 11, but, briefly, it is a calibrated system for determining the fall-diameter distribution of sand samples in distilled 

water. Naturally worn sand particles having specific gravities of 

about 2.65 were used in the calibration of the visual accumulation tube.

The settling velocities of particles in a sample of a mixture of 

water and sediment depend on the characteristics of the particles, the 

volume of the sample, the characteristics of the liquid, and the measuring apparatus. Test conditions were arranged so that the only 

variable in the particle-size analyses \vas the sedimentation media. 

A basic assumption was that the calibration of the visual accumulation 

tube was valid for the sedimentation media of fine sediments in water.

Samples of the three sands were analyzed in the visual accumulation tube for particle-size distribution in distilled water, in aqueous 

dispersions of 3, 5, and 10 percent kaolin and of 1, 5, and 10 percent 

bentonite. A graph of typical size distribution is shown in figure 9. 

The change in the fall velocities of the median fall diameters with 

the percentage of bentonite in water is shown in figure 10 and with 

the percentage of kaolin in water in figure 11. The fall velocities 

were computed from the relation of the fall diameter of naturally 

worn quartz particles to fall velocity given in Inter-Agency Report 12.

The variation of the gradation coefficient o>, with concentration of 

bentonite is summarized in table 2. The gradation coefficient varies 

because the coefficient of drag for any specific sand particle changes 

with viscosity, but the change is less for a large particle than a small 

particle.

A check was made on the accuracy of particle-size analyses in the 

visual accumulation tube when aqueous dispersions of fine sediment 

were used. The change in the fall velocity of a particle representing 

a single size, the median fall diameter of the sand sample, was computed for each of the fine-sediment media used in the visual accumulation tube. In the computations, the median fall diameter (converted 

to a nominal diameter), the apparent viscosity of the medium, the 

mass density of the medium and of the particle, and a particle shape
G22 STUDIES OF FLOW IN ALLUVIAL CHANNELS

TABLE 2. Variation of the measure of gradation with percentage of bentonite in water

Percent Bentonite

0_______. ________________________

1

5. _ ___ _ _

10__.__ _ ________ __

Measure of Gradation ar

Sand

Poudre River, 

Colo.

1. 

1.

1. 

1.

52 

53 

60

83

Elkhorn River, 

Nebr.

1.61 

1.59 

1.64 

1. 78

Loosely cemented 

sandstone 

Denver, Colo.

1. 32 

1. 32 

1. 37 

1. 39

factor of 0.7 were used. The empirically established relation between 

the drag coefficient CD for a particle falling at terminal velocity and 

the Reynolds number IR was then determinable and from these the fall 

velocity was computed. The CD versus IR relation for naturally worn 

sediment particles is given in figure 1 of Inter-Agency Report 12. 

The agreement between the computed fall velocities and those determined from the visual accumulation tube analyses is surprisingly 

good. (See figures 10 and 11.) Several of the many factors that 

might contribute to disagreement are: (1) the lack of a good definition

i.o

EXPLANATION

Percent 

.Symbol bentonite

Distilled water 

1 

5 

10

0.282

0.269

0.187

0.107

1.61 1.59- 

1.64 

1.78 /

Temperature, 24°C

0.1

12

0.05

10 20 30 40 50 60 70 80 90 95 

PERCENT OF PARTICLES FINER THAN INDICATED SIZE

98 99

FIGURE 9. The particle-size distribution of a sand sample from the Elkhorn River, Nebr., 

based on its fall velocity in various concentrations of bentonite dispersed in distilled 

water (analyzed in the visual accumulation tube).
EFFECTS OF FINE SEDIMENT ON FLOW PHENOMENA G23

(TEMPERATURE SECOND 24°C) IN CENTIMETERS PERw, 

OO3 

p^inooi-. i\j^o01 -4

t

Mi

h

1

X

<

^-~- .

» ^V^

^

X

Loose

- Co

C w\

^^

X^s

X

Denve 

ly ceme

mputed 

rom vis 

tub

- ^

\

X

jr, Colo. 

nted sar

ual accu 

e analys

^^(

i

\,

X

idstone

mulatto 

is

) P°l

i^x^^

. Elkh

X

X

n

idre Riv 

San

\

lorn Riv 

San

V

\

er, Colo 

J

\

V

er, Nebr 

J

X

\

\

N

\

v

\

\ <

\

(

\

Ni

<

\

i

>

i

)

\

)

\

4 6 

PERCENT BENTONITE BY WEIGHT

10

FIGURE 10. Variation of fall velocity with varying percentage of bentonite in water.

of the CD versus R relation for sediment particles; (2) errors in 

measuring the apparent viscosity of the fine sediment in water dispersions; (3) the shape factor of the sand particles that may differ 

appreciably from 0.7; and (4) the presence of the fine sediment particles in the visual accumulation tube that probably affects the fall 

velocity of the sand particles through interference, the currents and 

eddies generated by the falling fine sediment particles, and the possibility that the fine sediment was not uniformly distributed in the sedimentation column.

The variation of fall velocity of the three sands with water temperalure is given in figure 12. As the change in the specific weight of 

distilled water with temperature is relatively slight when compared 

with the change in the viscosity, the variation shown in figure 11 em-
G24 STUDIES OF FLOW IN ALLUVIAL CHANNELS

_Poudre River, Colo. 

Sand

 Computed w 

Owfrom visual accumulation 

tube analysis

Elkhorn River, Nebr. 

Sand

JD

Denver, Colo. 

Loosely cemented sandstone 

0 2 4 6 8 10 

PERCENT KAOLIN BY WEIGHT

FIGURE 11. Variation of fall velocity with varying percentage of kaolin in water.

phasizes the part that viscosity of the liquid has on the fall velocity 

without the complications introduced when considering a fine sediment dispersed in water.

Considering the determination of the actual fall velocity of bed 

materials in streams, two procedures can be used.
EFFECTS OF FINE SEDIMENT ON FLOW PHENOMENA G25

Poudre River, Colo. 

Sand

Elkhorn River, Nebr. 

Sand

Denver, Colo. 

Loosely cemented sandstone

0 10 20 30 40 

WATER TEMPERATURE IN DEGREES CENTIGRADE

FIGURE 12. Variation of fall velocity with water temperature.

1- Direct computation of using the CD versus R relation. This entails determining or knowing the variation of the properties of 

the particles and of the characteristics of the stream liquid with
G26 STUDIES OF FLOW IN ALLUVIAL CHANNELS

time and temperature. However, a more exact definition of the 

CD versus IR relation for irregular shaped sediment particles is 

needed.

2. Determine the size distribution of the bad material in the stream 

liquid by dropping a representative sample in the visual accumulation tube using the stream liquid as the sedimentation 

medium. The size distribution can then be converted to a- fall 

velocity. However, the visual accumulation tube was calibrated 

for the range of temperatures from 20° centigrade to 30° C.; 

therefore, outside this range, the procudure reverts back to the 

method of direct computation. Extending the calibration of the 

visual accumulation tube to include temperatures normally found 

in streams appears to be desirable, and the reliability of particlesize distributions obtained from the visual accumulation tube 

analyses needs to be checked for sedimentation media other than 

distilled water.

OBSERVED FLOW PHENOMENA

REGIMES OF PLOW AND FORMS OF BED ROUGHNESS

The form of the bed roughness in alluvial channels is a function of 

the bed material, the fluid, and the shape, size, and slope of the channel. The bed configuration can be changed by changing discharge, 

slope, the median fall diameter of the bed material, the size distribution 

of the bed material, or the fall velocity of the bed-material particles.

The observed regimes of flow and the bed configurations and flow 

phenomena associated with them were described in detail by Simons 

and Richardson (1961). The classification resulted from combining 

laboratory results with information from field investigations by Colby 

(1960) and by Bawdy (1961). The regimes of flow and forms of 

bed roughness are as follows.

Lower flow regime: (1) plane bed without movement, '(2) ripples, 

(3) dunes with ripples superposed, and (4) Dunes;

Transition: transition from dunes to upper flow regime;

Upper flow regime: (1) Plane bed and water surface, (2) Standing 

sand and water waves which are in phase, and (3) Antidunes.

In this study these same major forms of bed roughness were observed 

in the 8-foot flume. However, in the 2-foot flume there were some 

differences. . The major difference was that the ripple form of bed 

roughness did not occur in the smaller flume. After the beginning 

of motion, ripples formed in the 8-foot flume (Simons and Richardson, 1960), but in the 2-foot flume the bed remained plane except for 

a few oblong shaped bed irregularities which occasionally formed 

and were randomly spaced in the flume.
EFFECTS OF FINE SEDIMENT ON FLOW PHENOMENA G27

The absence of ripples was investigated at depths varying from 0.2 

to 2.0 feet and at various water-surface slopes. Each investigation 

was started at the beginning of sediment motion. For each investigation, the depth was held constant, and the discharge and (or) the slope 

was increased until the shear on the bed and the bed material in transport increased sufficiently so that dunes developed. Artificially induced ripples were slowly erased back to a plane bed by the flow. Run 

3, where ripples were artificially produced that persisted throughout 

the run, was not considered representative of normal conditions. During run 3, insufficient time was allowed prior to collecting data for the 

flo\v to convert the artificially formed ripple bed back to a plane bed 

at the low transport rate of bed material, which was 0.6 ppm.

Ripples superposed on dunes were observed in the 8-foot flume but 

wTere not observed in the 2-foot flume. Owing to the narrower width, 

the flow and forms of bed roughness were more two dimensional in 

the smaller flume than in the larger flume. The dune fronts across the 

2-foot flume were continuous and virtually perpendicular to the flow, 

whereas in the 8-foot flume they were not. (See figures 13 and 14.) 

Also, in the 2-foot flume the standing waves and antidunes formed 

across the entire flume width. (See figures 15 and 16.)

With large concentrations of fine sediment, the spacing and shape of 

the ripples and dunes and the antidune activity were modified. For 

example, in run series 14, where flow conditions wrere not changed, the

FIGURE 13. Dune bed configuration in the 8-foot flume.
G28 STUDIES OF FLOW IN ALLUVIAL CHANNELS

FIGURE 14. Dune bed configuration in the 2-foot flume.

FIGURE 15. Antidunes in the 8-foot flume. Note the three-dimensional aspect of the two

lines of waves.

dunes increased in length from 4 feet to 5.8 feet, and eventually the bed 

became plane with increasing concentration of fine sediment. The 

changes that occurred in the bed form, the resistance to flow, and the 

sediment transport are elaborated on in subsequent paragraphs.
EFFECTS OF FINE SEDIMENT ON FLOW PHENOMENA G29

FIGURE 16. Antidunes in the 2-foot flume. Note the two-dimensional aspect of the waves.

LOWER FLOW REGIME 

RIPPLES

Runs 85-90, in the 8-foot flume, were made with ripple-bed configuration, holding Q and JS constant and varying the concentration of 

fine material. (See table 1.) This sequence of runs was made without stopping the flow. The fine material load was increased from 0 to 

11,400 ppm by portions added between runs. The addition of fine material that was in as small a concentration as 4,800 ppm affected sediment transport and resistance to flow. This amount of fine material 

was more than the turbulence of the flow could effectively keep in suspension. Consequently, the fine material was deposited on, and in, the 

bed. The fine material partly filled the voids in the bed and adhered 

to the sand particles causing a cohesive stable boundary to form. With 

the smaller concentrations of the fine material in runs 86 and 87, the 

stabilized patches of the bed were not as extensive in area as with the 

higher concentrations in runs 88 and 89, and the flow was able to break 

up the cohesive patches. However, new patches formed elsewhere on 

the sand bed. With the largest concentration (11,400 ppm), a major 

percentage of the surface of the ripple bed was stabilized, as a result of 

the presence of the clay binder, and the turbulence of the mixture of 

water and sediment was much greater than with the normal ripple 

bed. Run 90 had a larger percentage of the bed stabilized with the 

fine sediment than run 87, even though the concentration of fine material was less. This resulted from the residual effects of run 88.
G30 STUDIES OF FLOW IN ALLUVIAL CHANNELS

Where the bed was not bound by the fine material and the ripples 

were advancing, fine material was deposited in the ripple troughs. 

When the ripples moved over former troughs, lenses of fine material 

were trapped in the bed. (See figure 17.)

FIGURE 17. Lenses of fine material trapped in the bed. Note rounded crests.

The fine material decreased bed-material transport from 12 ppm 

to 2 ppm and increased O/\/g from 10.4 to 14.4. The decreased 

transport resulted from the cohering of the sand particles, which reduced the amount of bed material available to be transported. The 

depositing of fine material and the cohering of the sand particles 

changed the form of the ripples so that they were no longer angular 

but had rounded crests. The resultant change in form reduced 

the resistance to flow. The change in the shape of ripples is illustrated 

by comparing the ripples that are affected by the fine sediment (fig. 

17), with moving ripples (no fine sediment) (fig. 18).

In the last two runs of the sequence, 89 and 90, slope was increased 

to change the bed form to dunes, but the cohesive deposit of fine material on, and in, the bed resisted the change. However, the increase 

in slope did break up some of the areas stabilized by the fine sediment 

and increased total bed material transport from 2 to 37 ppm.

Although there was enough fine material deposited on the bed to 

stabilize large areas for a given condition of flow, the bed material 

sampled never contained more than 2 percent of material finer than 

53 microns.
EFFECTS OF FINE SEDIMENT ON FLOW PHENOMENA G31

FIGURE 18. Ripples during clearnwater run. Note angular crests. 

DTJNTJS, 8-FOOT FLTJME

As stated on pages G29 and G30, the change from the ripples to dunes 

was resisted by the somewhat cohesive nature of the bed resulting from 

the presence of the fine material deposited during the ripple runs. 

With discharge constant, the slope was double that measured for 

ripples before the flow was able to break up the stabilized areas and 

form a typical dune bed (run 91). There was a noticeable difference 

in the appearance of the water surfaced before the flow was able to 

break up the stabilized areas and form dunes. The water surface 

over the stabilized areas was choppy, as if the flow were over cobbles. 

A water surface typical of sand-bed streams with dunes was restored 

after the dune-bed configuration had formed.

With the dune-bed configuration, the turbulence of the flow was 

large enough to suspend the fine material even at the maximum concentration introduced into the flow, 28,300 ppm. This does not mean 

that fine material was not in the bed material. The turbulence exchange theory for sediment transport would predict that fine material 

would be in the bed, and direct measurement proved that some fine 

material was in the bed.

However, the fine material did not settle and coat the bed, never 

to go into suspension again, as with the ripples; instead, there was a 

constant exchange between the fine material in suspension and in the 

bed.

The maximum amount of fine material in the bed was about 2 percent, as determined from the size analysis of bed material samples.
G32 STUDIES OF FLOW IN ALLUVIAL CHANNELS

This fine material was fairly well distributed throughout the bed material. The presence of the fine material in the bed did not appear 

to reduce the mobility of the bed material, and the bed was as soft 

and mobile as when the fine material was not present. The flow of 

clear water removed the fine material from the bed in a few hours.

The presence of fine material in the flow in concentrations greater 

than 5,000 ppm (0.5 percent) decreased resistance to flow. The increase in C/\/ff was as large as 40 percent (run 96) when the concentration was 25,000 ppm. There may have been a decrease in resistance at concentrations lower than 5,000 ppm, but if so, it was not large 

enough to distinguish from the natural fluctuations in resistance. The 

decrease in resistance to flow as the fine sediment concentration was 

increased resulted from the reduction in the fall velocity of the bed 

material and the change in the shape of the dunes.

The data indicate that transport of bed material increased slightly 

with the addition of fine material. However, part of the increase in 

bed-material load transported may have resulted from bentonite retained on the 2TO sieve (0.053 mm), on which the fine-material discharge was separated from the bed-material discharge. About 2 

percent of the bentonite was retained on the sieve (fig. 3) ; this bentonite, which became added to the flow as fine material, could account 

for some of the increase in bed-material transport.

DUNES, 2-FOOT FL.UME

When bentonite was being added to the flow, it entered the bed 

with the pore water, and the accumulations in the bed were visible 

through the plastic sides. While the bentonite was being added, the 

dunes increased in length and decreased in amplitude until, in the 

extreme case, a plane bed formed throughout most of the flume. The 

initial bed configuration was quickly broken up by the flow after the 

desired concentration of fine sediment was reached and the addition 

of bentonite was stopped. Except for the buildup of a bentonite 

layer near the flume floor, the accumulations of bentonite in the bed 

were added to the material in suspension when exposed by a dune 

front moving through the flume. Only the normal exchange between 

bentonite in suspension and bentonite in the bed occurred after equilibrium was established.

Concentrations of less than 25,000 ppm of fine sediment had little 

or no effect on the resistance to flow or bed-material transport.

The form of bed roughness, and therefore the resistance to flow 

and the bed-material transport, was considerably modified when the 

concentration of fine sediment was increased over 25,000 ppm. As 

additional bentonite was added to the flow, the dunes increased in 

length and decreased in height until the bed configuration became
EFFECTS OF FINE SEDIMENT ON FLOW PHENOMENA G33

rounded sand waves of small amplitude at a concentration of 63,700 

ppm of fine sediment (run 8B). This amount of fine sediment was 

more than the turbulence of the flow was able to keep in suspension, 

and fine sediment was deposited on the bed in the dune troughs. The 

dunes moved over the deposited sediment and trapped it in the bed 

in lenses and layers, which were visible through the plastic flume 

walls; however, no stabilizing of the bed was discernible, and it remained soft and mobile. The resistance to flow decreased, and the 

bed-material transport was reduced.

After the completion of data collection for run 8D, the concentration of fine sediment in the flow was decreased with time by losses due 

to some bentonite entering the bed and to some being washed away 

with the overflow water. Five hours after the end of run 8D, the bed 

configuration was partly long dunes of very small amplitudes and 

partly plane bed. Sixteen hours after run 8D, the concentration of 

fine sediment had decreased from 63,700 to 14,500 ppm, and data for 

run 8E were collected. The bed configuration was dunes of the same 

length but of smaller height and slower velocity than the dunes for the 

water-sand run 8. Eesistance to flow was the same as that of runs 8, 

8A, 8B, and 8C, but the concentration of bed-material in the discharge 

was less. The decrease in bed-material transport may have resulted 

from either stabilization of the bed by the bentonite or a change in 

the shear-transport relation by the addition of the bentonite.

TRANSITION 

SHEABED-OUT DUNES, 8-FOOT FLUME

Fine sediment wy as added in amounts from 9,580 to 44,100 ppm 

in the sequence of runs number 14 through 14C, and these runs represented the effect of adding fine sediments to the sheared-out-dune form 

of bed roughness. Bentonite entered the bed, and a layer of sand adjacent to the flume floor became saturated with bentonite. Fine sediment did not coat the bed and accumulate in the troughs of the transition type dunes but remained in suspension once the dune action 

removed the bentonite that had entered the bed during the initial addition of bentonite.

The bed-material transport increased, and resistance to flow decreased for concentrations as small as 9,580 ppm of fine sediment. The 

amplitude of the sand waves remained nearly constant, but their length 

and velocity of movement increased. As the concentration of fine sediment was increased to amounts greater than 22,000 ppm the lengths 

of transition dunes increased to 10 to 20 feet, compared with transition 

dunes 4 to 6 % feet long at concentrations less than 22,000 ppm. The 

form of bed roughness changed from the long sheared-out dunes to a 

plane bed at about 30,000 ppm bentonite when the concentration of fine
G34 STUDIES OF FLOW IN ALLUVIAL CHANNELS

sediment was being increased; bed roughness changed from a plane 

back to transition dunes at approximately the same concentration of 

fine sediment, 30,000 ppm, when the concentration of bentonite was 

being decreased.

UPPER FLOW REGIME 

STANDING WAVES, 8-FOOT FLUME

Sand beds are firm and consolidated for the standing-wave form of 

bed roughness. When bentonite was added to the flow, the bed surface 

became very firm and felt slightly crusty; however, when the bed was 

thoroughly disturbed by raking several times during the sequence of 

runs, no differences in flow were observed or were detected in the 

measurements.

The form of bed roughness did not change for the sequence of runs 

15,15A, 15B, and 15C. The length of the standing sand waves, measured from crest to crest, changed very little, but their height decreased 

as the concentration of fine sediment was increased. The resistance to 

flow was unchanged for concentrations of fine sediment less than 41,000 

ppm, but increased slightly at the largest concentrations of fine material. The data in table 1 show that for each fine sediment run the 

amount of bed material in transport increased over the amount of bed 

material transported by the water-sand flow without bentonite.

There was a more noticeable effect as fine sediment was added to the 

standing-wave runs in the series 16, 16A, and 16B, and 18, 18A, 18B, 

and 18C. When the fine material concentration was increased, antidunes developed. The larger the concentration of fine material the 

greater the antidune activity. This activity was reversible. With the 

increase in concentration of fine material, there was an increase in resistance to flow and transport of bed material. The increase in resistance to flow and to the transport of bed material was due primarily to 

the change of the standing waves to the antidunes that resulted from 

the increase in concentration of fine sediment. The resistance to flow 

and the amount of bed material in transport are both greater with 

antidunes than with standing waves.

ANTIDUNES, 8-FOOT FLUME

The most obvious effects of the fine-material load on flow phenomena 

in the upper flow regime was the increase in antidune activity with the 

increase in concentration of fine material. With the increase in antidune activity, the transport of bed material and the resistance to flow 

increased. With fine material present, antidunes occurred, at smaller 

Froude numbers than without the presence of fine material. In one 

set of runs, the concentration of fine sediment was reduced from 

26,900 (run 99) to 106 ppm (run 100) by adding clear water and dis-
EFFECTS OF FINE SEDIMENT ON FLOW PHENOMENA G35

carding the excess mixture of water and sediment. When concentration of fine material was large, antidune activity was intense, and the 

concentration of bed material in transport was 16,100 ppm. Antidune 

activity decreased with the decrease in concentration of fine material 

until, during run 100, the water surface and bed were plane, and the 

bed-material concentration was 8,440 ppm. The only other changes 

in flow condition during runs 99 and 100 were a slight decrease in 

water temperature and possibly a slight coarsening of the bed material, which resulted from the wastage of the mixture of water and 

fine sediment. The increase in antidune activity with increasing concentration of fine sediment was the result of the reduction of the fall 

velocity of the bed material and, hence, the increase in the mobility of 

the bed material.

In the upper flow regime, fine sediment was not deposited on the 

bed, however, the fine material built up with time on the rigid floor 

of the flume under the sand bed, as with the dunes. The rate of increase or decrease of concentration of fine material in the bed was 

smaller than for dunes owing to the increased compaction and reduced 

porosity of the bed. Also, only about 0.05 feet of the top surface of 

the bed material was moving, whereas large dunes turn over the full 

depth of the alluvial bed.

In runs in the 8-foot flume, the antidune water-surface patterns 

generally formed in two parallel lines of waves (fig. 15). This 

pattern is different from the antidune water-surface patterns observed 

during the first 45 runs (Simons and others, 1961), when only a single 

train of antidune waves generally formed.

ANTIDTJNES, 2-FOOT FLUME

Antidune activity increased with increasing concentration of fine 

sediment. The antidunes occupied more of the flume length; the sand 

and water waves broke more frequently; and the breaking lasted 

longer and was more violent with the larger concentration of fine 

sediment. Consequently, the resistance to flow and concentration of 

the total discharge of bed material increased with increasing concentration of fine sediment.

The decrease in fall velocity of the bed material was evident by 

observing the sand suspended during the antidune runs with bentonite. 

The suspended bed-material load was composed of dark-colored 

particles which contrasted sharply with the white aqueous dispersion 

of bentonite. The particles of bed material suspended in the aqueous 

dispersions of bentonite stayed in suspension much longer and were 

carried a greater distance by the flow than were the particles suspended 

in the flow containing only sand. This could account for a substantial 

part of the increase in the total bed material in transport.
G36 STUDIES OF FLOW IN ALLUVIAL CHANNELS

EFFECT OF FINE SEDIMENT ON RESISTANCE TO FLOW

The influence of fine sediment on resistance to flow is illustrated in 

figures 19 and 20. The magnitude of the change in C/\/g depends on 

the concentration of fine sediment, the form of bed roughness, and 

whether the addition of the fine sediment causes only a modification 

of the existing roughness or causes a complete change in form of bed 

roughness, as from dunes to plane bed.

With a dune-bed form, an increase in the concentration of fine sediment decreased resistance to flow. The decrease resulted from the 

increase in length of the dunes. In the extreme, the bed changed 

from dunes in the low flow regime to plane bed in the upper flow 

regime. With standing waves and antidunes, an increase in fine 

sediment concentration increased resistance to flow. The increase 

resulted from the increase in size of the standing waves and from the 

violence of the antidune activity. In some runs the addition of fine 

sediment changed standing waves to antidunes.

EFFECT OF FINE SEDIMENT ON BED-MATERIAL 

TRANSPORT

The effect of fine sediment on bed material transport is difficult to 

determine by analysis of the flume data because the coarser fraction 

of the fine-material load may have been included in the bed-material 

load owing to the method used to separate the two loads. However, 

if it is remembered that the concentration of bed material in the discharge, given in table 1, may be greater than the true value by some 

percentage of the concentration of fine material (2 percent for the 

8-foot flume data and 0.5 percent for the 2-foot flume data approximately), some generalizations can be made.

With relatively low concentrations of fine material and with a 

ripple-bed form, the bed was partly stabilized, and bed-material 

transport was reduced. With larger concentrations of fine material, 

larger areas of the bed were stabilized.

The effect of concentrations of less than 10,000 ppm of fine material 

was relatively small on bed-material transport in flows with a dune 

bed configuration. With concentrations greater than 10,000 ppm of 

fine sediment bed-material transport in the 2-foot flume decreased 

(fig. 21). The decrease may have been greater because the concentration of bed material in transport may have contained some finematerial load. Data for the 8-foot flume show either no change or an 

increase in bed-material transport with an increase in fine material 

load. However, the increase could have resulted from fine sediment 

in the bed-material transport. The decrease in the transport of bed 

material when the concentration of fine sediment was increased probably resulted from the decrease in resistance to flow that occurred and
14

12

10

11

9

7

II

9

7

18

16

14

1

> 

<?* 7.0 :fs

«

90 T~ 

J9

^

89

-088

Q* 8.2 cfs

m « 

-*i

. _,

73 

7^

76.

W

9^

>75

G>« 15.3

 

cfs

1

54^

r 56

R*v

57

J

^

Q* 15.5 cfs

-=i63

"^N,

^

 *^ 

f

t 

/

>« 

,6

65

k

10 10' 10°

Cf, IN PARTS PER MILLION

10' 

FIGURE 19. Variation of resistance coefficient, G/\/g, with concentration o
13 

It 

9

7

12

10

8

14

12

16

14

12

13

II 

13

a

Run s

 Run s

_______

1 Run s

sries

H

sries

k-l

8, 0=3.8cf?

14, Q~*

 \

.8c

H

eries 15, 0~7.0c1

 

Dun < 

 . - eries 18, 0«7

^

.6 c

s 

 

0

_ c

-0-Q&-

___ ^ 

©

s

s

Fs 

-,

- 

-- -^

 ^-^

X

i i i 

Run series 16, Q~ 7.8

eries 17, Q~~i J

* ^1

\

^*

10

10' 10°

Ct, IN PARTS PER MILLION

FIGURE 20. Variation of resistance coefficient, O/^/g, with concentration o
EFFECTS OF FINE SEDIMENT ON FLOW PHENOMENA G39

Form of bed roughness

Dune 

O Modified dunes

Transition

Plane

Standing waves

Antidunes

Violent anti dunes

"4XIQ2

FIGUEB 21. Variation of bed-material transport with varying concentration of fine

material.

from the decrease in the shear that resulted when depth and slope 

adjusted to the smaller resistance to flow. In some dune runs in the 

2-foot flume the bed was partly stabilized, and bed material transport 

decreased; however, the decrease in bed-material transport also occurred when the bed was known to be not stabilized.

With the bed forms of the upper flow regime, a large concentration 

of fine sediment increased bed-material transport (fig. 21). This increase existed even if the values for the amount of bed-material load 

were adjusted for the possibility that some of the load was fine sediment. The increase in bed-material load occurred because the fine 

sediment increased the viscosity and the specific weight of the fluid, 

decreased the fall velocity of the bed material, and increased the resistance to flow and fluid shear. With shear constant, bed-material 

transport increased with a decrease in sand size or a decrease in fall 

velocity. When fine sediment was added to the flow, shear increased 

in the upper flow regime.

The total discharge of sediment by a stream when fine sediment is 

in the flow cannot be predicted from knowledge of fluid, sediment, and 

channel characteristics, unless the concentration of fine sediment is 

measured and the effects of the concentration on the fluid properties
G40 STUDIES OF FLOW IN ALLUVIAL CHANNELS

of the stream and, in turn, the effect of the fluid properties on the fall 

velocity of the bed-material particles are considered that is, equations, 

such as Einstein's (1950) and Bagnold's (1956), cannot predict total 

transport when fine sediment is included in the load. It has long 

been known that total load cannot be predicted when fine sediment is 

in the flow (Einstein and Chien, 1953a, b). To illustrate this, 

Bagnold's equations are used. His dimensionless transport and shear 

parameters are defined respectively as:

A_<£^_____M____

(2) 0 cos 0

and

«,=[(^-0,)eT, (3) 

in which

M=the mass of sediment transport passing a fixed plane per unit

width of channel per unit time.

i8=the angle the channel bed makes with the horizontal. 

B a constant for a given bed material which can be related to

the grain diameter of the bed material. 

d=the median diameter of the bed material. 

00 =the dimensionless shear stress, T0/&yd. 

0(=the critical shear stress, Tc /kyd, at beginning of motion. 

p=the mass density of the water. 

Aps =the difference in mass density of the water and the sediment.

The two groups of values shown on figure 22 were computed using 

equations 2 and 3. In the group of values on the right, only bed-material transport has been considered in computing <£. In the group of 

values on the left, total load (including fine sediment) was used to 

compute the respective values of <£ for each run. In the group of 

values using total load, the scatter is so great when fine sediment transport is included that the relation between </> and 0% has no significance. 

In fact, an infinite number of possible values for </> exist for the 0.47 

millimeter bed material when fine sediment is included in the computation. This illustrates that the transport parameter should not include the concentration of fine sediment. Although total load cannot 

be predicted from a knowledge of hydraulic and bed-material characteristics unless the concentration of fine sediment and its effects are 

known, approximate methods have been formulated that estimate total 

load including fine sediment (Colby and Hembree, 1955), but these 

methods do not account for the effects of fine sediment on the flow 

phenomena.

A change exists in the sediment-transport relation of Bagnold at the 

point where the form of bed roughness changes from dunes through
EFFECTS OF FINE SEDIMENT ON FLOW PHENOMENA G41

I03

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FIGURE 22. Variation of sediment transport parameter 0 with shear parameter 6 t 

8-foot flume data. 

transition to standing waves. This change in relation, which can be a 

discontinuity that also exists when the equations of Einstein (1950) 

are used, is caused by the large .reduction in resistance to flow that takes 

place as the form of bed roughness changes. Because of this change in 

the relation, it ultimately may be desirable to break the theory of flow 

in alluvial channels into two parts: one which treats the ripple, dune, 

and transition forms of bed roughness and another which treats the 

plane bed, standing wave, and antidune forms of bed roughness.
G42 STUDIES OF FLOW IN ALLUVIAL CHANNELS

FINE SEDIMENT TRANSPORT

Fine material as defined in this report is that part of the total load 

composed of sediment sizes not found in appreciable quantities in the 

bed material. From a practical viewpoint fine sediment includes all 

material finer than 0.062 mm when investigating sand channel streams.

Another comparable definition of fine-material load used by others 

is wash load. This definition has the connotation that the fine material 

is not present in the bed, but logic indicates and experimental evidence 

proves that the fine material is present in the bed. Einstein and 

Chien (1953a,b) also concluded that fine sediment (wash load) would 

be present in the bed; however, they found that the fine material always managed to stay at the top of the bed whereas the fine material 

in our experiments was distributed throughout the bed material. The 

different observations probably resulted from the fact that the fine 

material used by Einstein and Chien was much coarser than the fine 

material used in our experiments.

In our series of runs, the concentration of fine material in the interstitial water in the bed increased rapidly with time until it was equal 

to the concentration of fine material in the stream. This amount of 

fine material changed the size-distribution curve of the finer bed material, but this change had very little effect on the median fall diameter. 

Whether or not this small amount of fine material in the bed affects 

the relation between sand properties, fluid properties, resistance to 

flow, or total load depends largely on the form of bed roughness. 

Surprisingly enough, when clear water was added to the flow and the 

excess mixture of water and sediment was discarded, the fine material 

in the bed was removed along with that in the water in a relatively 

short time.

In both flume studies, the concentration of fine material in the flow 

for each run decreased with time logarithmically from its peak value. 

The rate of decrease was determined by periodic measurements of 

concentration with a hydrometer. The decrease in concentration of 

fine material in the flow resulted from the increase in concentration 

of fine material in the bed and from the deposition of some of the fine 

material at the contact plane between the sand bed and flume floor. 

This deposition, over a period of several runs, built up a layer of clayimpregnated sand about 0.1 foot thick (fig. 23).

In a natural stream what may happen to the fine material in transport will depend to some extent on the position of the water table. A 

high water table, which contributes water to the flow in the stream, 

would probably help keep the bed material free of the fine material. 

With a low water table, the concentration of fine material in the interstitial water in the bed would vary with time depending on the
EFFECTS OF FINE SEDIMENT ON FLOW PHENOMENA G43

il

FIGCRE 23. Layer of bed material adjacent to the flume floor impregnated with

fine sediment.

concentration of fine sediment in the stream and on the concentration 

gradient. The concentration in the bed will increase if it is smaller 

than the stream concentration or will decrease if it is larger. This 

fact may account for a small part of the lag of the sediment hydrograph behind the water hydrograph as a flood peak travels downstream 

(Heidel, 1956). A layer of fine material such as observed on the floor 

of the flume (fig. 21), may build up in a natural streambed if:

1. The ground water is not flowing into the stream.

2. The ground water is considerably lower than the streambed, and 

a filter layer or hard pan exists within a foot or so of the channel 

bed.

3. The ground water is slightly lower than the streambed. In this 

example, the layer of fine material may form at the contact between the static ground water and the water flowing in the 

streambed or at some higher elevation where a layer of material 

has a smaller coefficient of permeability. This zone of deposition 

would probably be slightly lower than the deepest pothole which 

developed with the dune form of bed roughness.
G44 STUDIES or FLOW IN ALLUVIAL CHANNELS

CONCLUSIONS AND RECOMMENDATIONS

The specific weight and apparent viscosity of aqueous dispersions of 

fine sediment are different than those of pure water. The apparent 

viscosity of an aqueous dispersion of fine sediment depends on the concentration of the fine sediment, the chemical and physical properties 

of the fine sediment, the amount and type of any base added as a dispersing agent, and, with some fine sediments at certain concentrations, 

the temperature of the fluid.

The ratio of the apparent viscosity of aqueous dispersions of bentonite, as measured with a Stormer viscosimeter, to the viscosity of 

water was independent of the temperature at concentrations of less 

than about 5 percent by weight but was dependent on the temperature 

at concentrations greater than about 5 percent. The ratio of the apparent viscosity of aqueous dispersions of kaolin to the viscosity of 

water, however, wras independent of the temperature at concentrations 

less than 10 percent. The apparent viscosities of aqueous dispersions 

of bentonite were much greater than those of aqueous dispersions of 

kaolin. At 40°C the difference between the viscosity of water and the 

apparent viscosity of an aqueous dispersion of bentonite, 10 percent 

by weight, was 1,100 percent, and the difference with an aqueous dispersion of kaolin under the same conditions was 45 percent.

The specific weight of the aqueous dispersions of fine sediment increased in accordance with the amount and density of the fine material 

that was added.

The change in fluid properties that results from the presence of fine 

sediment has a definite effect on the fall velocity of the bed material. 

For example, at 24°C the fall velocity of a 0.47-mm median falldiameter sand in aqueous dispersions of bentonite and of kaolin, 10 

percent by weight, is decreased by 65 and 20 percent, respectively. 

This decrease of fall velocity in aqueous dispersions of bentonite is 

equivalent to the difference between the fall velocities of a 0.47-mm 

and of a 0.24-mm sand particle in water of 24°C.

The resistance to flow and bed-material transport are decreased in 

the lowT er flow regime and increased in the upper flow regime when 

fine sediment is added to the flow. When there are ripples, fine sediment, even in moderate concentrations, stabilizes the bed, streamlines 

bed forms, reduces resistance to flow, and reduces bed-material transport. When there are dunes, fine sediment, in relatively large concentrations, may stabilize the bed, reduce resistance to flow, and 

reduce bed-material transport; however, resistance to flow and bedmaterial transport are reduced even when the bed is not stabilized. 

The reduction in resistance to flow when the bed is not stabilized 

results from increases in dune length and from the changes in dune 

shape that occur when the fall velocity of the bed material decreases.
EFFECTS OF FINE SEDIMENT ON FLOW PHENOMENA G45

With very large concentrations of fine material, the dune bed may 

become plane. The reduction in the transport of bed material results from a decrease in shear that occurs when the resistance to flow 

decreases.

In the upper flow regime, the reduction in fall velocity that results 

from the addition of fine sediment may change a plane-bed flow to a 

standing wave or antidune flow, change a standing wave flow to an 

antidune flow, or increase the activity and turbulence of an antidune 

flow. These changes increase resistance to flow and increase bedmaterial transport.

Total sediment transport can be predicted if, where fine sediment 

is involved, the concentration of fine sediment is determined by 

sampling and the effects of the fine sediment on the properties of the 

stream liquid are taken into account.

As fluid properties are affected differently by fine sediment having 

different physical and chemical properties, further study of the rheology of dispersions of fine sediment in water is needed. Also, the 

effects that different kinds of fine sediment have on the fall velocity 

of sand particles need to be studied. Furthermore, additional flume 

studies should be made with coarse bed materials and various concentrations and types of fine sediment.

LITERATURE CITED

Bagnold, R. A., 1956, The flow of cohesionless grains in fluids: Royal Soc. (London) Philos. Trans., v. 249, no. 964, p. 235-297.

Beaver, L. D., 1956, Soil physics, 3d ed.: New York, John Wiley and Sons, p. 

81-93.

Bingham, E. C., 1922, Fluidity and plasticity: New York, McGraw Hill Book Co.

Blench, T., 1957, Regime behavior of canals and rivers: London, Butterworths 

Scientific Publications.

Colby, B. D., and Christensen, R. P., 1956, Visual accumulation tube for size 

analysis of sand: Am. Soc. Civil Engineers Jour., v. 82, no. HY3, p. 1004- 

1-17.

Colby, B. R., and Hembree, C. H., 1955, Computations of total sediment discharge, Niobrara River near Cody, Nebraska: U.S. Geol. Survey WaterSupply Paper 1357.

Colby, B. R., 1960, Discontinuous rating curves for Pigeon Roost and Cuffawa 

Creeks in Northern Mississippi: U.S. Dept. of Agriculture, ARS 41-36.

Dawdy, D. R., 1961, Studies of flow in alluvial channels, depth-discharge relations of alluvial streams: U.S. Geol. Survey Water-Supply Paper 1498-C, 

16 p.

Einstein, H. A., 1950, The bed load function for sediment transportation in open 

channel flows: U.S. Dept. of Agriculture Tech. Bull. 1026, 70 p.

Einstein, H. A., and Chien, Ning, 1953a, Transport of sediment mixtures with 

large ranges of grain sizes: California Univ. Inst. Eng. Research, Missouri 

River Div. sediment series 2.

 , 1953b, Can the rate of wash load be predicted from the bed load function? : Am. Geophys. Union Trans., v. 34, p. 876-882.
G46 STUDIES OF FLOW IN ALLUVIAL CHANNELS

Heidel, S. G., 1956, The progressive lag of sediment concentration with flood 

waves: Am. Geophys. Union Trans., v. 37, no. 1, p. 56-66.

Langbein, W. B., 1942, Hydraulic criteria for sand waves: Am. Geophys. Union 

Trans., v. 23, p. 615-618.

Richardson, E. V., Simons, D. B., and Posakony, G. J., 1961, Sonic depth 

sounder for laboratory and field use: U.S. Geol. Survey Cir. 450.

House, Hunter, 1950, Engineering hydraulics: New York, John Wiley and Sons.

Simons, D. B., and Richardson ,E. V., 1960, Resistance to flow in alluvial channels : Am. Soc. Civil Engineers Jour., v. 86, no. HY5, p. 73-99.

 , 1961, Form of bed roughness in alluvial channels: Am. Soc. Civil Engineers Jour., v. 87, no. HY3.

Simons, D. B., Richardson, E. V., and Albertson, M. L., 1961, Studies of flow in 

alluvial channels, flume studies using medium sand (0.45 mm) : U.S. Geol. 

Survey Water-Supply Paper 1498-A, 76 p.

Street, Norman, 1958, Viscosity of clay suspensions: World Oil, no. 107, p. 151- 

156.

U.S. Inter-Agency Report No. 11, 1957, The development and calibration of the 

visual accumulation tube: U.S. Dept. Army, St. Paul, Minn.

U.S. Inter-Agency Report No. 12, 1957, Some fundamentals of particle size 

analysis: U.S. Dept. Army, St. Paul, Minn.

Wood, W. H, Granquuist, W. T., and Krieger, I. M., 1955, Viscosity studies on 

dilute clay mineral suspensions; clays and minerals: Nat'1 Research Council 

Publ., 456, p. 240-250.
INDEX

Page

Abstract -___________________ Gl 

Antidunes- __~_____ 26,27,34-35 

Apparent viscosity, general discussion____ 17-20 

Attapulgite, viscosity affected by_______ 18

Bagnold's equations_______________ 40 

Basic data, discussion of___________ 2,12-17 

Bed configurations, measurement of_ _____ 16 

Bed materials, general description ______ 3-4

sampling of _________________ 15-16 

Bed-material transport, fine sediment

affecting.,.________ 30,34,35,36-41 

Bed-roughness forms, modified by fine sediment ________ 27-28

stabilized by fine sediment.._______ 29,30

See also particular form. 

Bentonite, fall velocity affected by. _____ 21

general discussion of___________ 4

viscosity affected by.. _________ 17,18 

Bibliography......._._______.__.. 45-46

Cations, viscosity affected byConclusions _.----.

Denver, Colo., sandstone from________ 22 

Discharge, measurement of._________ 13 

Dunes- _ _ . 26,27,31-33 

See also Sheared-out dunes.

Elkhorn River, Nebr_____. 

Equipment, general discussion. 

See also Flumes.

Fall velocity, determination of. ______ 24-26 

fine sediment affecting__________ 20-26 

Fine materials, general description__..__ 4 

in strearnbeds._ _______ 43 

Fine-sediment transport, general discussion.. 42-43 

Flow depth, measurement of__________ 14 

Flow regimes. See Transition zone and particular flow regime.

Fluidity. ___ _ .. ... 18 

Flumes, general description______..__ 2-3

Gradation coefficient, variation in.

Hectorite, viscosity affected by.

21

18

Introduction__________________ 1-2 

Isoelectric point.. ______.__ 18

Page

Kaolin, fall velocity affected by________ G21

general discussion of 4

viscosity affected by 17

Kinematic viscosity, determination of. 17

Lenses of fine material in bed_____ 30,32 

Lower flow regime _________ 26,29-33,44-45

Mean velocity, calculation of. 14 

Median fall diameter...________.. 14-15 

Montmorillonite, viscosity affected by_ 18

Neutralization, viscosity affected by 18 

Non-Newtonian liquids.-. __ 17,18

Particle-size distribution, determination of. 21 

Plane bed ______. ____ __ 26,27 

Procedure, discussed_________ 2,4-12,27 

Poudre River, Colo...-_____-__ 22

Ripples___________________- 26,27,29-30 

Resistance to flow, fine material affecting 32,

33,34,35,36

Sand. See Bed materials.

Sediment load, sampling of _ 14,15 

Sheared-out dunes... . _ 26,33-34 

Sodium hexametaphosphate, as dispersing

agent. _. .. 17,19 

Specific weight, formula for 20 

Standing waves_____________ 26,27,34 

Stormer viscosimeter... 17 

Suspended sediment, sampling of_ 15

Temperature of water, fall velocity affected

by . 23-24

measurement of.... 13-14

viscosity affected by... . 18,19,44

Transition zone. ___________ 26,33-34

Turbulence, fine sediment sustained by 20,31

Upper flow regime_ 26,34-35,45

Velocity profiles, determination of. 14 

Viscosity. See Apparent viscosity; Bentonite; 

Kaolin; Kinematic viscosity.

Wash load, defined_______ . 1 

Water-surface forms.. 31,35 

Water-surface slope, computation of.. - 12 

Water table, fine-material concentration affected by.. _ 42-43

G47

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