FEB2 1970

Field Measurement of the 

Initiation of Large Bed 

Particle Motion in Blue Creek 

Near Klamath, California

GEOLOGICAL SURVEY PROFESSIONAL PAPER 562-G

Prepared in cooperation 'with the California 

Department of Water Resources
Field Measurement of the 

Initiation of Large Bed 

Particle Motion in Blue Creek 

Near Klamath, California

By E. J. HELLEY

SEDIMENT TRANSPORT IN ALLUVIAL CHANNELS

GEOLOGICAL SURVEY PROFESSIONAL PAPER 562-G

Prepared in cooperation with the California 

Department of Water Resources

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1969
UNITED STATES DEPARTMENT OF THE INTERIOR 

WALTER J. HIGKEL, Secretary

GEOLOGICAL SURVEY 

William T. Pecora, Director

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

Washington, D.C. 20402 - Price 35 cents (paper cover)
CONTENTS

Page

Abstract.------_-----______________________________ Gl

Introduction.______________________________________ 1

Purpose.------------__________________________ 1

Location. ______________________________________ 2

Previous work__________________________________ 2

_____________.____________________________ 2

Turning moment- ______

Drag-force moment. 

Lift-force moment _.

Resisting moment____.

Conditions for motion,_.

Field measurements-______________--_---_

Test particles-_______-----__--------

Velocity measurements___-____-------

Distance of particle movement-_______

Comparison of field measurements to 

predictions. __ _________-_--------------

Channel changes___________---_-__-----

Cross-section surveys ______--_-----

Topographic surveys-_____________-_---__

Conclusions._____________--_-__---------

References cited.________-_____---_------

theoretical

Page 

G5

5

6

9

11

12

13

14

15

15

ILLUSTRATIONS

Page

FIGURE 1. Location map of Blue Creek._____________________________________--_---------------------------- G2

2. Diagram showing orientation of test particles placed on bed of Blue Creek.______________--___--------- 3

3. Graph showing relation between shape factor, SF, and drag coefficient CD and C'D for high Reynold's numbers,

>2,000____-_______--_________________.______________________________________-___-_-------- 4

4-6. Photographs showing 

4. View downstream of test reach at Blue Creek_____________________-_______-__---------------- 6

5. View upstream of Blue Creek showing the site at the downstream end of the test reach where particle

orientation was studied.___________-___________________----_-_--._-------------------- 7

6. Weight-mounted Pygmy current meter, standard A-reel, and counting device-____________------ 9

7-9. Graphs showing 

7. Dimensionless average velocity distribution for cross section at cableway-____________---------- 10

8. Relation between bed velocity at incipient motion and intermediate particle diameter for the range in

specific gravity, 0, and SF found in the test reach at Blue Creek as calculated from equation 3___ 11

9. Comparison of measured and calculated bed velocities at 0.6a for test particles------------------ 12

10-12. Graphs showing 

10. Comparison of previous studies relating bed velocity to particle size with present study _______-_-- 13

11. Low-water cross sections, Blue Creek gaging-station reach____________________---__----------- 14

12. Thalweg profiles of a reach of Blue Creek extending approximately one-fourth of a mile downstream

from the gaging station_____-______,._____________________-_-______---_-------------- 15

13-15. Maps of 

13. Cable-section reach of Blue Creek, 1966_____._______________-__---__-_---___.______-_-- 16

14. Cable-section reach of Blue Creek, 1967__________________________________-__------------- 17

15. Cable-section reach of Blue Creek, showing change of streambed topography, 1966-67 ________ 18

TABLES

Page 

TABLE 1. Summary of physical properties of test particles and theoretical threshold velocities___________-____--------- G8

2. Distance moved and measured threshold velocities of recovered test particles.------------------------------- H

SEDIMENT TRANSPORT IN ALLUVIAL CHANNELS

FIELD MEASUREMENT OF THE INITIATION OF LARGE BED PARTICLE MOTION IN

BLUE CREEK NEAR KLAMATH, CALIFORNIA

By E. J. HELLEY

ABSTRACT

More than two-thirds of the field measurements of bed velocity necessary to initiate motion of coarse natural particles whose 

size, shape, specific gravity, and orientation angle were known 

agree within 20 percent of those velocities predicted from theory. 

The theory is based on balancing turning moments of the fluid 

forces of drag and lift with the resisting moment of the submerged 

particle weight.

Initial motion seems to depend more on size and shape than 

on specific gravity or orientation angle. In fact, shape differences almost completely compensate for differences in specific 

gravity ranging from 2.65-3.00 and orientation angles ranging 

from 0°-25°.

Bed velocities necessary to initiate motion of coarse bed material in Blue Creek are equaled or exceeded about 5 percent of 

the time. This fact and changes in channel topography and 

cross-sectional area emphasize the ability of perennial mountain streams to transport coarse bed material frequently.

INTRODUCTION

A particle on a rough streambed begins to move when 

the force of the column of moving fluid intercepting it 

generates a moment equal to the oppositely directed 

moment of the immersed particle weight. This phenomenon may be viewed as a balance between fluid forces 

of drag and hydrodynamic lift, which tend to turn a 

particle, and resisting forces of immersed-particle 

weight, which tend to keep the particle at rest. When 

these two opposing forces are just in balance, the fluid 

is competent to move its bed particles and critical or 

threshold conditions exist. In this report, mean values 

of drag and lift are used, but it should be recognized 

that forces much larger than the mean exist.

Determination of critical or threshold conditions of 

sediment movement has long been a problem for hydraulic engineers as well as for those geomorphologists 

interested in fluvial processes. An excellent historical 

review of measuring threshold conditions for sediment 

motion is given by Leliavsky (1966), who stated that 

measurements of this type began as early as 1753.

Unfortunately, the problem of measuring and predicting these threshold conditions is still largely unsolved. 

This is especially true with respect to bed materials 

larger than pebble size.

If the problem of measuring threshold conditions of 

sediment motion is viewed as a balance between the 

forces of fluid flow and resting particle, then the initiation of motion becomes one of the simpler problems 

involving threshold conditions (Vanoni, 1966) and one 

which hold promise of solution. This should be particularly true when dealing with coarse bed material, whose 

physical properties can be measured more accurately 

than those of sand or finer size particles. Attempts at 

measuring threshold conditions necessary to initiate 

motion of very large bed particles in this study are 

based on the use of "bed velocity" rather than on the 

depth-slope product ("critical tractive force"). Rubey 

(1938) in a review of Gilbert's (1914) flume data showed 

that "bed velocity" is more significant than the depthslope product, especially when measuring threshold conditions for particles larger than 2.5 mm (millimeters). 

In addition, the slope of the water surface of most 

natural streams needed to calculate tractive force is 

usually difficult to measure accurately especially at 

high stages. This is particularly evident in mountain 

streams, whose alinement and channel geometry change 

frequently and irregularly, a change that generates 

secondary currents and superelevations and gives rise 

to local and changing slopes. In this report, bed velocity 

is defined as the velocity measured at some finite 

distance close to the bed.

PURPOSE

The primary purpose of this study was to determine 

bed velocities necessary to initiate motion of very coarse 

bed material by direct measurement and, thereby, to 

extend existing size-versus-velocity relations. A secondGl
G2 SEDIMENT TRANSPORT IN ALLUVIAL CHANNELS

ary objective was to determine channel changes due 

to aggradation or degradation in the vicinity of the 

test reach during the period of study. This was done in 

an attempt to evaluate the geomorphic significance of 

threshold conditions of particle motion.

The study was made by the U.S. Geological Survey 

in cooperation with the California Department of Water 

Resources. The work was done under the immediate 

supervision of Loren E. Young, chief of the Menlo 

Park office of the Water Resourses Division of the Geological Survey. The author wishes to express gratitude 

to personnel of the U.S. Geological Survey, especially 

Gerald LaRue, for assistance in the field and Carl Goodwin and Winchell Smith for assistance in the theoretical 

calculations and computer programming. The manuscript benefited from critical review by Carl Nordin, 

Everett Richardson, and John Ritter.

LOCATION

Blue Creek, a small tributary to the Klamath River 

in northern California (fig. 1), was chosen as the study 

site for the following reasons. Discharge measurements 

at the U.S. Geological Survey gaging station at Blue 

Creek indicated that runoff from this small, 120-squaremile drainage basin had velocities ranging from less 

than 2 fps (feet per second) to as much as 13 fps but

FIGURE 1. Location map of Blue Creek near Klamath, Calif.

that the discharge was not flashy or large enough to 

be difficult to measure. Observations of the streambed 

during summer low-flow periods indicated that the bed 

material consisted of particles averaging about 0.5 foot 

but as much as 3 feet in median diameter. Shifts in 

the rating curve during periods of moderate to high 

discharges showed that the streambed at the gagingstation cableway was changing and, hence, that Blue 

Creek was actively transporting its coarse particles as 

bedload.

Blue Creek's drainage basin is underlain by a wide 

variety of rock types including shale, sandstone, and 

ultrabasic intrusive rock as well as minor amounts of 

granite (Irwin, 1960). Weathering characteristics of 

these rocks make available a wide variety of shapes 

and differences in mineralogy provide a large range in 

specific gravity from 2.60-3.10. Thus, the natural setting at Blue Creek was ideal for a study of the transport 

of coarse bed material. The gaging station and cableway also provided a means by which bed velocities 

could be measured.

PREVIOUS WORK

Previous attempts at measuring threshold conditions 

for sediment motion have been reviewed by Leliavsky 

(1966) and more recently by Raudkivi (1967). Most 

of their discussions concern smaller size particles and 

will not be discussed here. Mavis and Laushey (1949, 

p. 39) presented critical bed velocity-versus-size curves 

for particles up to 100 mm (0.3 ft). The coarsest 

material studied by direct measurement was that of 

Fahnestock (1963, p. 29), and his is probably the only 

data on particles greater than 1 foot in diameter. His 

measurements, however, were made under less than 

ideal conditions and on material in transport rather 

than at rest.

THEORY

The bed velocities necessary to initiate motion of 

coarse particles can be calculated by balancing turning 

moments of the fluid forces of drag and lift with the 

resisting moment of the submerged particle weight. The 

concept of balancing the turning and resisting moment 

is not new as shown by Leliavsky (1966, p. 36 and p. 

149). Although past workers have considered various 

aspects of the initiation of motion of bed material, 

none have considered all the physical characteristics 

of the particles, their orientation, or a lift force. The 

general physics of initial grain motion is summarized 

by Shepard (1963) who reviewed the work of Shields 

(1936), White (1940), and Bagnold (1942).

Consider, for example, a particle at rest on the 

streambed as shown in figure 2. The orientation of the 

three mutually perpendicular axes as shown places the
LARGE BED PARTICLE MOTION, BLUE CREEK, CALIFORNIA G3

Drag turning arm

0.1 a cos e+0/ 3/i6a^cose-0/4sine)

Weight-buoyancy *Lift turning arm

 sin0)

Where a=short axis

(8= intermediate axis 

7= long axis 

0=horizontal A/3

FIGURE 2. Orientation of test particles placed on bed of Blue Creek.

long axis, 7, normal to the flow direction. The angle, 0, 

between the intermediate axis, j8, and the horizontal 

is designated as the orientation angle. This neglects 

the bed slope, which is here considered insignificant. 

The orientation shown in figure 2 is considered typical 

of the bed material found in the test reach.

TURNING MOMENT

The moment tending to turn the particle in figure 

2 must consist of two parts: first, the drag-force moment of the fluid parallel to the streambed, and second, 

a hydrodynamic-lift moment acting normal to the 

streambed (Einstein and El Samni, 1949, Vanoni, 1966, 

and Egiazaroff, 1967).

DRAG-FORCE MOMENT

The drag-force moment, neglecting fluid shear, may 

be expressed as the product of the average differential 

fluid pressure in the downsteam direction, the intercepted area of the particle, and the drag-force turning 

arm. Because the shapes of natural particles vary, the 

area intercepting the flow also varies, so that particles 

of the same size but of different shape exert a different 

form resistance to the flow. The Corey shape factor, 

SF = a/V7j8, (Schultz and others, 1954), quantitatively expresses shape and can be related to the familiar 

drag coefficient, CD- Because the Reynold's number 

in natural mountain streams like Blue Creek is extremely high, the drag coefficient (CD) will be constant 

for a given shape factor; hence, the drag coefficient

can be related to various shape factors. Figure 3 was 

constructed from the Reynold's number-versus-drag 

coefficient curve for various Corey shape factors, SF 

(U.S. Inter-Agency Committee on Water Resources 

Project Report No. 12, 1957, p. 20). The drag coefficient thus determined is for naturally worn sediments 

and was determined for free-falling bodies. Where particles are initially at rest on the streambed, not all the 

area described by the shape factor and drag coefficient 

exerts a form resistance to the flow. It is apparent 

that the drag coefficient for free-falling bodies must 

be modified before application to bodies at rest. An 

average drag coefficient used in this study is assumed 

to be Q.75CD and is designated as C' D. Egiazaroff (1967) 

has shown that the centroid of the drag force is 0.63 

particle diameter up from the bottom of the particle. 

For simplicity this is taken as 0.6a, where a is the 

short axis of the particle shown in figure 2. As shown 

in figure 2. the drag-force turning arm is dependent 

on the location of the pivot point. This point was 

determined from observations of the orientation of 

particles deposited on the bed of Blue Creek. The 

position of this point, as shown in figure 2, may be 

expressed in terms of the flow direction, X, and lift 

direction, Y. Assuming that the particle shape is an 

ellipse in cross section and that the centroid of the 

drag force is at 0.6a, the X location is on a normal

a

- from the intersection of the mutually perpendicular 

particle axes. In the Y or lift direction the pivot point
G4 SEDIMENT TRANSPORT IN ALLUVIAL CHANNELS

1.0

0.8

0.6

0.4

0.2

0.4 0.8 1.2 1.6 2.0 2.4 

DRAG COEFFICIENT (C0 and C')

2.8 3.2 3.6 4.0

FIGURE 3. Relation between shape factor, SF, and drag coefficient CD and C'D for high Reynold's numbers, >2000. CD from U.S. 

Inter-Agency Committee on Water Resources Report No. 12 (1957, p. 20).

may be located by solving the equation of an ellipse 

which yields

which reduces to

The coordinates which describe the location of the 

pivot in the drag and lift directions are

rj J / ^ 9 7 and -\/T^a2 , 4 \ 16

respectively.

The drag-turning arm shown in figure 2 is then

O.la cos cos 0 sn

and is here designated as MRD.

Using the symbols in figure 2 and expressing the 

particle shape in cross section as approximating an ellipse, the drag moment be written as

(CD) (drag force) (turning arm)

where

#= the bed velocity at 0.6a up from the bed

g=ihe acceleration due to gravity. 

It should be noted that the expression is applicable for 

angles of theta less than about 25°.

LIFT-FORCE MOMENT

The lift-force moment may be expressed in a manner 

similar to that of the drag-force moment; however, the 

lift moment turns about a different turning arm. 

Actually, very little data are presently available to 

calculate lift coefficients reliably except for those developed by the experimental work of Einstein and El Samni 

in 1949 (in Vanoni, 1966). Because the size of the particles used in their experimental work is relatively large 

(0.225 ft), the Einstein and El Samni lift coefficient, 

0.178, is applicable here. The lift force acting normal to 

the streambed turns about an arm of length

7 cos 4

where ft is the intermediate axis,

a is the short axis, and

8 is the orientation angle shown in figure 2. 

This turning arm is here designated as MRL. Again approximating the particle shape as an ellipse in cross 

section, the lift-force moment may be written
LARGE BED PARTICLE MOTION, BLUE CREEK, CALIFORNIA G5

(lift coefficient) (lift force) (turning arm) 

(0.178) (fg - 62.4) (

Combining the drag-force and lift-force moments into 

the turning moment (MET}, we have drag-force 

moment +lift-force moment

|- - 62.4) (^ (MRD)

and simplifying,

MET 62.4 -. [C'D ay(MRD)+0.l78 0y(MRL)]. 

zg 4

(1)

RESISTING MOMENT

The force which resists the turning of the particle 

consists of the immersed weight. This force may be expressed as the product of the submerged specific gravity, 

the specific weight of water, and the volume of the particle. Because the force of the immersed weight acts 

downward normal to the streambed, the turning arm 

needed to compute the resisting moment is the same as 

that for the lift-force moment. Approximating the volume with an ellipse rotated about its minor axis to form 

a prolate spheroid and using the symbols in figure 2 we 

may write the resisting moment (MEE) as :

(submerged specific weight) (volume) (turning arm)

-1) (62.4)

where sp gr is the specific gravity of the particle. 

Rearranging and simplifying :

gr-1) (41.6 rry) (2)

which holds for small angles of theta (less than 25°).

CONDITIONS FOB MOTION

At the instant when motion takes place, the sum 

of the turning and resisting moments is zero.

Moment ( turning) = Moment (resisting) @ incipient 

motion combining equations (1) and (2); MRT=MRR.

 62.4 £ (C'D ay (MRD) +Q.1780y (MRL)]

= (sp gr-1) (41.6iry) 

Simplifying and solving for v at 0.6a

41.67T

16 (sp gr-1) 7 (MEL)

62.47T 

20 [C'D ay (MED) +0.178)87

(sp gr-1) (MRL)

7D ay (MRD) +0.178 187 (MEL)

(3)

or the bed velocity, vw.^ } at a distance 0.6a up 

from the streambed will be a constant at incipient 

motion if sp gr, 6, a, jS, 7, and C'D are known. Equation 

3 has the form of the familiar "Sixth-power law" 

(Rubey, 1938) except it attempts to consider particle 

shape, density, and orientation.

FIELD MEASUREMENTS

Field techniques for direct measurement of bed 

velocities were developed during topographic mapping 

of a test reach at Blue Creek in the summer low-flow 

period in 1967. At that time a 450-foot-long reach 

bisected by the Blue Creek gaging station cableway was 

selected as the test reach (fig. 4). During this initial 

survey, the streambed consisted of particles finer than 

those sizes desired for study; therefore, it was necessary to place particles of the desired size on the natural 

bed. Because natural gravel deposits often display a 

definite fabric or preferred particle orientation (Krumbein, 1940, 1942, Potter and Pettijohn, 1963), the 

particles placed for study on the streambed were 

oriented as others which had been naturally deposited 

by Blue Creek in the test reach. Measurement of 100 

large particles at the downstream end of the test reach 

showed a bimodal orientation which seemed to be 

mainly a function of shape (fig. 5). For example, rodlike particles tended to orient themselves such that the 

mean angle between their long axes and the flow direction was 39° ±24°. Platelike particles, on the other 

hand, tended to display an almost perpendicular 

orientation of their long axis to the flow direction; 

their mean angle between long axis and flow direction 

was 77° ±12°. In general, almost all particles were 

inclined upstream; those that were not, were horizontal. Platelike particles, generally, had lower inclinations than those less flat. The long axes of larger 

particles seemed to be oriented either normal or parallel to the flow direction more often than the long axes 

of the smaller particles. This was also true with those 

particles touching or making contact with others than 

isolated particles. The orientation angle 6, ranged from 

0°-30°, but most of the angles were less than 15°.

TEST PARTICLES

During the summer low-flow period of 1967, four 

plots of nine particles each were designed and placed 

just upstream from and parallel to the cableway at
G6 SEDIMENT TRANSPORT IN ALLUVIAL CHANNELS

FIGURE 4. View downstream of test reach at Blue Creek. (Note: man at left center is standing under cableway.)

the Blue Creek test reach. Each plot covered an area 

of 10 by 10 feet, and particles were spaced about 2 to 3 

diameters apart so that no one rock directly influenced 

the flow over other rocks. Thirty-six rocks of various 

sizes, shapes, and lithologies from a nearby gravel bar 

were selected as test particles. As each particle was 

removed from the gravel bar, its three mutually perpendicular axes, a, |8, and 7, were measured, and a small 

chip was removed for specific-gravity determination. 

Each particle was painted fluorescent red and numbered 

before placement on the streambed. The long axis was 

oriented normal to the flow direction. The angle 6, between the intermediate axis and the horizontal, was 

measured for each particle with the clinometer of a 

Brunton compass. As specific gravity and 6 had been 

measured and C'D calculated from measurement of a, ft, 

and 7, it was possible to calculate the theoretical bed 

velocity necessary to initiate motion using equation 3. 

The physical properties of the 36 test particles used in

this study and the calculated bed velocities necessary 

to initiate motion are summarized in table 1.

VELOCITY MEASUREMENTS

Attempts to test the theory of turning and resisting 

moments expressed in equation 3 were begun in the 

winter of 1966-67. At the outset it became readily 

apparent that turbid water made direct observation 

of bed-particle motion impossible. Large particles 

painted a bright fluorescent red could not be seen 

through depths exceeding 3 feet. Unfortunately, velocities at the test site did not initiate motion of the 

test particles until depths exceeded 4 feet. During 

the fieldwork in the winter of 1967-68, this problem 

was resolved by placing spherical styrofoam floats, 

numbered to correspond to the test particles, under 

each particle. These floats were also painted fluorescent 

colors a different color for each of the four test plots. 

In addition, each float was fixed with a 30-foot coil
LARGE BED PARTICLE MOTION, BLUE CREEK, CALIFORNIA G7

FIGURE 5. View upstream of Blue Creek showing the site at the downstream end of the test reach where particle orientation was

studied. (Note large size of bed material.)

of monofiliment which was tied to a ring in a steel 

reinforcing bar driven in the streambed. Testing this 

system during low-flow periods showed that turning 

of the test particles released the float. The monofilament uncoiled with the float coming to the surface 

under the cableway from which it could be seen and 

its corresponding number easily read. The 30-foot 

length of monofiliment would be necessary during 

higher stages and velocities.

Attempts to measure bed velocities with a standard 

Price current meter failed to reach the desired distances 

above the bed, 0.6a, which in two cases was less than 

0.2 foot (table 1). In order to measure velocities closer 

to the bed, a Pygmy current meter was mounted on the 

nose of a 75-pound sounding weight upstream from the 

point of flow stagnation at 0.2 foot above the base of 

the weight. A foot plate was attached to the base of 

the weight extending under the Pygmy meter to protect

the meter, and the area of the tail fin of the weight was 

doubled to increase stability. Because the revolutions 

of a Pygmy meter could not be counted manually at 

high velocities, a mechanical counter and an electrical 

relay mechanism were designed and added to the meter 

system. This allowed counting rates of 12.5 impulses 

per second or velocities of approximately 12.5 fps. The 

weight-mounted Pygmy meter and counting device 

are shown in figure 6. The Pygmy meter and standard 

Price meters used in this study are described and their 

limitations discussed by Corbett and others (1962). In 

normal practice the Pygmy meter is not designed for 

high-velocity measurements (Corbett and others, 1962, 

p. 180); therefore, it was necessary to compare velocities measured with the weight-mounted Pygmy system 

with those of a standard Price current meter. This was 

done by making simultaneous velocity measurements 

with both meters at the same height above the bed and
G8 SEDIMENT TRANSPORT IN ALLUVIAL CHANNELS 

TABLE 1. Summary of physical properties of test particles and theoretical threshold velocities

Rock No --. -- .

24_ _._.___.._..____._

26____-_--_-__________

14____________________

8

25 __________________

10 _________________

23 __ _

9

15---__ _____-___ 

16

27____________________

29_

35

36 _________________

22

7

31

21 _________________

34

19-____________-_-___-

20

2

28 _____-_____-___-__.

11 _____ ____ __ __

3

12

13 __________________

4

1 _____ __ __ _

30

17____________________

6 ___________________

18 __ _--___-___-__-___.

33

32____________________

37__ _________________

1 Measured.

2 Computed.

...... ........ a (ft)

----____- 0.55

Of)

. .____ .60

_---.____ .60

_________ .70

_________ .55

65

Of)

_________ .55

_________ .55

_________ .95

_________ .65

_________ .45

_________ 1.20

_________ .80

_________ .60

_________ .80

Of)

_________ .50

_________ .80

_________ .60

.--_-____ .35

_________ .65

_________ .45

_________ .30

_________ .75

_________ .75

_________ .50

_________ .70

_________ .40

_________ .50

_________ .60

Cf)

_________ .60

_________ .50

_________ .30

(5 (ft)

1.30

1. 10

1. 00

.85

1.45

1.25

.90

QD

. 65

1. 10

1.35

1. 00

Q 1!

1. 50

1. 10

an

1. 70

. 95

1. 00

.95

1. 40

1. 10

1. 00

. 80

1. 05

7^

7^.

.70

.85~ft

cc

OK

.60

. 70

.75

. 70

 y(ft)

1. 55

1. 70

1.60

1.70

1. 70

1.65

1. 65

1.95

1.25

i fjft

1. 70

1. 20

1. 25

2. 00

1. 15

1. 60

1 QO

1.40

1. 20

1 A.t\

1. 55

1. 20

1 QO

1. 45

1.40 i ^J~

QC

1.30

1. 30

1 9ft

oc

1 9ft

1.00

1 nc

1.40

.85

0.6a(ft) ,5

0.33

.54

. 36

.36

. 42

. 36

.39

. 54

. 33

.33

.57

.39

.27

. 72

.48

.36

.48

.54

. 30

.48

.36

. 21

. 39

. 27

. 18

.45

.45

. 30

. 42

94

.30

. 36

. 30

.36

. 30

. 18

if-Fa/V^T

0.38

. 66

.47

. 50

.45

.37

. 53

. 68

. 61

.39

.62

. 59

. 41

. 69

.72

.50

. 44

. 78

.45

.68

. 56

.26

.47

.42

.25

.75

CO

.53

.67

. 51

.73

. 56

.64

.70

.49

.39

C'D

1. 73

Q8

1. 44

1. 35

1. 51

1.80

1. 29

.96

1. 12

1. 70

1. 10

1. 16

1.65

.95

.89

1. 35

1. 56

.76

1.51

.96

1. 22

2. 36

1.46

1.62

2.40

. 82

.56

1.29

QQ

1.34

.86

1. 22

1. 05

Q9

1.39

1.71

e°

0

4

16

0

2

15

0

0

0

0

0

8

10

0

5

0

0

0

0

14

0

0

0

11

0

0

0

14

12

0

0

0

0

0

0

0

Spgri

2.85

2.65

2.85

2. 72

2.65

2. 70

2. 72

2. 71

2.85

2. 70

2.85

2.65

2.85

2. 85

2.85

2.85

2.65

2. 72

2. 72

2.85

2. 85

2. 72

2. 72

2.72

2.85

3. 10

2.65

2. 74

2. 64

2. 72

2. 70

2. 72

2. 70

2. 72

2. 72

2. 74

Volume (ft s) 2

0.46

. 70

.40

.36

. 72

.47

.40

.56

. 19

. 38

.91

.33

.23

1. 50

.42

.36

1.08

.50

.25

.46

.54

. 19

.51

.22

. 18

.32

.22

. 19

.32

. 10

. 10

.29

.13

. 19

.22

.07

Weight

(Ibs) 2

120.9

147.2

94.3

84.9

170.3

117.9

88.3

140.4

42. 7

89.3

215.2

69. 5

56.9

343.2

99.6

83.6

94.3

108. 6

59.4

103.1

144. 1

56.0

113.7

49.2

58.7

75.4

48.0

41.0

67. 5

22. 1

20. 2

64. 5

28.6

40. 7

47. 5

30.8

_c_lc fo.ea

(fps)

7.90

6. 78

7.78

5.32

8.00

8. 74

5.53

5.45

4.83

6.45

7.62

6.93

7.40

8.09

7.95

5.84

8. 44

6.38

6. 50

7. 65

9. 30

7. 16

5. 80

6. 17

7. 61

5.92

6.22

5.98

6. 60

3.86

4.65

6. 20

4.61

5.25

5.07

5.61

comparing the measurements. A rectangular concretelined channel was used for comparison. Depths were 

about 2 feet, but velocities exceeded 12 fps. It was found 

that the Pygmy system differed from the standard 

Price meter by a maximum of only ±4.5 percent in 

velocities in excess of 8 fps. and only ±2 percent for 

lower velocities. Even though the thickness of the standard Price meter bucket wheel is at least twice that of 

a Pygmy meter and integrates velocities over a wider 

range in the vertical, the agreement is good. When the 

weight-mounted Pygmy meter was compared with other 

Pygmy meters which were rod mounted, velocity measurements differed by less than ±2 percent. Some difficulties were discovered when lowering the weightmounted Pygmy meter into the flow. If lowered into 

the flow slowly, the entire system was twisted, thrown 

about, and almost impossible to handle. When, however the weight was -immersed quickly, it remained

fairly stable and was as easy to handle as a standard 

meter and weight. In actual practice at the Blue Creek 

cableway, either the redesigned Pygmy system or the 

standard Price meter was used, the choice depending 

on the surface roughness of the flow and the amount 

of floating debris.

Under field conditions during storm periods, it was 

practically impossible to maintain the suspended weight 

and attached meter, either Pygmy or standard Price, 

at the desired height above the bed, 0.6a. Most of the 

difficulties resulted from vertical motion of the cableway 

due to movement of the cablecar and water drag on 

the meter system. It was then necessary to determine 

the velocity distribution over each test-particle location. 

An average velocity distribution at each of the 36 testparticle locations was determined from measurements 

made by wading for flows from 125-700 cfs (cubic feet 

per second) and from the cableway for 24 particle
LARGE BED PARTICLE MOTION, BLUE CREEK, CALIFORNIA G9

FIGUBE 6. Weight-mounted Pygmy current meter, standard A-reel, and counting device. (Note enlarged tail-fin assembly and

foot-plate modifications on sounding weight.)

locations for flows ranging from 700-5,500 cfs. These 

data were combined into a dimensionless average velocity distribution for the entire cross section as shown in 

figure 7. The plotting data are also shown where Y is 

the height above the bed, V is the point velocity measured at Y, Vmean is the velocity at six-tenths the depth, 

and Fmax is the total depth.

The range of velocity measurements covered from 

12-80 percent of the total depths (F/Fmax) observed. 

By using the curve in figure 7, it is possible to determine 

the bed velocities at any 0.6a above the bed from the 

maximum depth and mean velocity in each vertical. 

For example, it is desired to find the threshold velocity 

at 0.6a for a rock with an a. dimension of 1 foot. At the 

time of initial motion, the depth, Fmax, was 4.0 feet; 

and the mean velocity was 5.0 fps. By entering figure

7 on the ordinate with F/Fmax= (0'6) (1 '0) =0.15,

which intersects the curve at a F/Fmean of 0.77, then 

with a mean velocity of 5.0 fps, the velocity at 0.6a is 

3.85 fps.

DISTANCE OF PARTICLE MOVEMENT

Although only 15 painted test particles were recovered, it was possible to measure the distance each had 

moved during a single runoff event. The particle numbers, distance moved, and measured velocities necessary 

to initiate motion are given in table 2. In general, no 

clear relation between the physical properties of the 

test particles and distance moved could be ascertained. 

Undoubtedly, the interaction between particles and 

bed roughness is an important factor but beyond the 

scope of this study. Interaction and abrasion must 

certainly influence the distance moved as most of the 

fluorescent red paint was removed from those test 

particles which had moved more than 50 feet. Because 

the distances moved are for only one runoff event, they 

emphasize the ability of a mountain stream to transport 

coarse material easily. The threshold bed velocities 

necessary to move the test particles were generated from 

discharge equal to or greater than 2,500 cfs, at least 

for the present channel geometry. Correlating this discharge with mean monthly discharges at the nearby 

gaging station and transposing flow duration from other
G10 SEDIMENT TRANSPORT IN ALLUVIAL CHANNELS

1.0

0.1

PLOTTING DATA

V/ V mean Number of 

Measurements

0.2 

0.5 

1.0 

1.5 

2.0 

2.5 

4.4

0.12±0.06 

0.25 ±0.15 

0.40 ±0.02 

0.51 ±0.18 

0.56±0.18 

0.47 ±0.04 

0.80±0.02

0.72±0.11 

0.85±0.15 

0.96±0.09 

1.03±0.09 

1.05 ±0.06 

1.03±0.01 

1.08±0.02

64

88

105

90

64

18

20

0.01

0.1 1.0 

V/ V mean

10.0

FIGURE 7. Dimensionless average velocity distribution for cross section at cableway.

older gaging stations in the same area indicate that 

2,500 cfs is equalled or exceeded about 5 percent of the 

time. This not only emphasizes the streams ability to 

transport coarse debris, but to do so for a significant 

amount of time.

Three runoff events in late December and January of 

1967-68 moved all but two of the test particles. Sixteen 

particles moved during the first event, seven moved 

during the second, and 11 moved during the third. In 

general, the styrofoam floats behaved satisfactorily

during the first runoff event, but behaved less satisfactorily for the second and third. Apparently, local 

scour around the test particle caused several floats to be 

released before the particles actually moved. It was 

necessary then, during the second and third events, to 

make velocity observations on the rising stage up to 

and including the peak discharge. The peak discharge 

lasted for only about 15 minutes during the second 

event. Assuming then that the particles moved at or 

near the peak discharge, the field measurements of
LARGE BED PARTICLE MOTION, BLUE CREEK, CALIFORNIA Gil

TABLE 2. Distance moved and measured threshold velocities of 

recovered test particles

Particle No.

8

10 . 

9 . 

16 

22

34 

2 ......

28 

11 

3

13.... -.- 

4. ___ __ 

1

17...,-- 

18

Distance 

moved (ft)

 _ 5

 35

... ... 235

 -. 9

 30

 - - 6

 40

 1.5

... . ... 65

 6

---------- 4

---------- 45

 . 100

 7.5

 ... 65

Velocity at 

0.6« (fps)

4.79 

5.83 

5.47 

5.06 

5.76 

5.49 

5.04 

5.67 

7.62 

4.67 

6.77 

5.41 

6.65 

5.28 

5.18

velocities used to determine V at 0.6a are considered 

the best estimate of Fmean and Fmax for the time of 

actual movement.

COMPARISON OF FIELD MEASUREMENTS TO 

THEORETICAL PREDICTIONS

Using equation 3, and the range in physical characteristics found in the test reach at Blue Creek (table 1), 

a relation between the intermediate diameter, /3, and 

bed velocity, y0.6a , may be drawn. Figure 8 shows a 

family of four curves for the range in specific gravity 

from 2.65-3.00, 6 from 0°-25°, and for shapes of SF=

100

0.1

5^=0.25^

EXPLANATION

Field measurements 

at Blue Creek

Specific gravity=3.00 0 = 25° 

Specific gravity = 2.65 0=0"

SF=1.00

-.»

001 0.1 1 

INTERMEDIATE DIAMETER (/3), IN FEET

10

FIGURE 8. Relation between bed velocity at incipient motion and intermediate particle diameter for the range in specific 

gravity, 6, and SF found in the test reach at Blue Creek as calculated from equation 3.
G12 SEDIMENT TRANSPORT IN ALLUVIAL CHANNELS

0.25-1.00. It should be readily noted that shape is a 

dominant factor in the determination of the bed velocity 

at incipient motion. In fact, changes in shape of particles 

of the same size (j8 axis) almost completely compensate 

specific gravity differences from 2.65-3.00. The angle 

of orientation 0, does not seem to be as important as 

shape or density and is one of the most difficult parameters to measure accurately.

Field measurements of bed velocities necessary to 

initiate motion of coarse particles made at Blue Creek, 

also plotted in figure 8, agree closely with the range 

in velocities predicted from theory. These theoretical 

bed velocities for the initition of motion calculated 

from equation 3 are plotted against the measured bed 

velocities in the test reach (fig. 9). This plot shows 

that approximately 70 percent of the data deviate by 

±20 percent of that predicted from theory. At least 

the field data are compatible with the theory of 

turning and resisting moments. When the difficulties 

of making such measurements and the assumptions in 

the theory are considered, the agreement is good. The 

curves shown in figure 8 may be represented as an 

envelope by using extreme values for purposes of com2 4 6 8 10 

MEASURED VELOCITY AT 0.6a , IN FEET PER SECOND

DISTRIBUTION OF ERROR

Number of 

Percent Error measurements Percent total

± 0-10 

±11-20 

±21-30

16

8

7

3

47.1

23.5

20.6

8.8

34 100.0

FIGURE 9. Comparison of measured and calculated bed velocities at 0.6a for test particles.

paring previous work relating bed velocity and particle size (fig. 10). It should be noted that all curves 

are extrapolations over two log cycles when, in fact, 

most measurements are actually made over a range 

of about one log cycle. The direct measurements by 

Fahnestock (1963) agree fairly well, but the curve of 

Mavis and Laushey (1949) fits better especially in 

the same size range as Fahnestock's. The major consideration in figure 10 is the fact that most differences 

in relations between velocity for the initition of motion 

and size result from differences in particle shape, density, and orientation. The envelope curves shown here 

are representative for the range in physical characteristics of particles in many natural streams with 

coarse beds and, therefore, should be applicable to 

other areas.

CHANNEL CHANGES

Channel changes, as shown by aggradation or 

degradation, were studied at Blue Creek for two 

purposes. First, it was desired to describe the general 

channel behavior during the study period. This was 

necessary to relate the measured bed velocities 

needed to initiate motion to either an aggrading, 

degrading, or stable streambed. The second objective 

was to measure the response of a mountain stream, 

such as Blue Creek, to the effects of the devastating 

floods of December 1964. Blue Creek, as many other 

rivers and streams in northern California, underwent 

considerable streambed changes during these floods 

(Hickey, 1967). According to the studies done on 

Coffee Creek, also in northern California (Stewart and 

La Marche, 1967), the catastrophic 1964 flooding 

largely determined the channel morphology and the 

location and character of the alluvial deposits. The 

general hydrologic character of the December 1964 

flood has been described by Rantz and Moore (1965); 

they showed that this event has been without precedent 

back to 1861 in northern California and in adjacent 

parts of Oregon, Idaho, and Nevada. In fact, geomorphic and botanical evidence indicate that a flood 

of the magnitude of the December 1964 flood had 

occurred only once in the last 400 years (Helley and 

La Marche, 1968). Fresh landslide scars, bank collapse, 

and uprooted trees give evidence to the fact that 

large volumes of colluvium and bank material were 

supplied to the channel" of Blue Creek during the 

1964 flood. Most of this material was deposited in 

the lower few miles of Blue Creek because of simultaneous high stages on the Klamath River. Narrow 

reaches in the lower course of Blue Creek commonly 

displayed boulder levees, and wide reaches contained 

large volumes of finer grained well-stratified deposits. 

Inspection of the Blue Creek channel from the gaging
LARGE BED PARTICLE MOTION, BLUE CREEK, CALIFORNIA G13

100

EXPLANATION

X

Field measurements from

0.01

INTERMEDIATE DIAMETER, IN FEET

FIGURE 10. Comparison of previous studies relating bed velocity to particle size with present study. In the present study,

particles are initially at resu

station downstream to its mouth (fig. 1) indicated 

that during the period of this study there was active 

erosion of the flood debris stored in the channel.

CROSS-SECTION SURVEYS

Seven cross sections were surveyed annually for 3 

consecutive years (1965-67) at a reach extending about 

one-quarter of a mile downstream from the gaging station (fig. 1). Each cross section, spaced about 200 feet 

apart, was marked by steel reinforcing bars, which

made relocation from year to year accurate. A tag line 

was stretched from each section end, and elevations 

were measured with a level. Elevations were determined 

at intervals of 10 feet along each section. Figure 11 

shows these seven sections as viewed downstream. 

Most noticeable is an increase in cross-section area 

during the study period which was caused by an increase 

in depth. As expected, width changed only slightly because most of the side slopes are exposed bedrock of 

sandstone and shale. The thalweg profile of this reach
G14 SEDIMENT TRANSPORT IN ALLUVIAL CHANNELS

1966 1967

RIGHT BANK

FIGURE 11. Low-water cross sections, Blue Creek gaging-station reach.

shown in figure 12 clearly indicates that most of the 

increase in depth occurred during the rainy months 

of November through March of 1966-67, three seasons 

after the record flood of December 1964. Only one section shows a decrease in depth, a decrease that is very 

slight. Perennial streams with gravel beds commonly 

tend to scour over relatively long reaches (Leopold 

and others, 1964, p. 234). Although the net degradation over the gaging-station reach is not surprising, 

it is indicative of the ability of Blue Creek to move 

rapidly large volumes of coarse material supplied to 

the channel.

TOPOGRAPHIC SURVEYS

The cableway test reach half a mile downstream 

from the gaging station was surveyed in 1966 and again

in 1967. Both surveys were done during summer lowflow periods and were used to describe the net change 

in the 450-foot-long test reach during the study period. 

The areal distribution of bedrock and bed material of 

various sizes according to the Wentworth scale are 

shown (with the topography) in figures 13 and 14. 

The distribution of bed material is generalized and 

indicates that the areas mapped are overlain mainly by 

the indicated size. The most noticeable change from 

1966 to 1967 is in flow direction (shown by large arrows) 

which was caused by local scour of as much as 3 feet 

along the left bank. Lesser scour along the right bank 

has exposed additional bedrock underlying the channel. 

Particle size increased from pebbles to cobbles and 

boulders in the downstream portion of the test reach.
LARGE BED PARTICLE MOTION, BLUE CREEK, CALIFORNIA G15

100 

98 

96 

94 

92 

90J

\

-X

t / / / /

/ / /

t

1 1

1 t 1

1 1

f

1

1 1 1

1

~~ ^

r~

X

N^>

X

N\ \ \

X ,

\

. % 

\ \

\

\ \ \

V

X

EXPLANATION

X

Indicates location of 

surveyed cross section

October 26, 1965

September 26, 1966

September 26, 1967

^A.

rlH

X

k

"*-->..

X

) 200 400 600 800 1000 1200 14

DISTANCE DOWNSTREAM, IN FEET

FIGURE 12. Thalweg profiles of a reach of Blue Creek extending approximately one-fourth of a mile downstream from the gaging station.

Figure 15 shows the change in streambed topography 

and the net degradation that occurred during the study 

period. The volume removed from the test reach was 

determined by planimetry of an area bounded by the 

upper and lowermost cross sections. The removal of 

approximately 2,800 cubic yards resulted in an average 

bed-elevation decrease of 1.2 feet.

CONCLUSIONS

The bed velocities necessary to initiate motion of 

coarse bed material, as calculated from a theory which 

considers particle size, shape, specific gravity, and orientation angle agree well with those determined by field 

observation. The initial movement seems to depend 

more on particle size and shape than on specific gravity 

and orientation angle. In fact, difference in specific 

gravity from 2.65-3.10 is almost completely compensated by difference in shape.

Present data also suggest that threshold velocities 

necessary to move coarse material exists for at least 

5 percent of the time in Blue Creek.

Field data were collected on channel changes and 

were completed during a degradational phase of channel 

adjustment. Long reaches of the channel of Blue Creek 

have degraded considerably since the December 1964 

flood, and most of the degradation occurred during the 

rainy season of 1966-67 three seasons after the flood. 

Cross-sectional and topographic surveys indicated that 

approximately 2,800 cubic yards of material were 

scoured from a 450-foot-long reach of Blue Creek between September 29, 1966, and September 29, 1967. 

This demonstrates the ability of perennial mountain 

streams, such as Blue Creek, to transport very coarse 

debris.
G16 SEDIMENT TRANSPORT IN ALLUVIAL CHANNELS

0 20 40 60 80 100 FEET 

 I I I I I I

FIGURE 13. Cable-section reach of Blue Creek, 1966.
LARGE BED PARTICLE MOTION, BLUE CREEK, CALIFORNIA G17

130 

 129 

Contours

Dashed where approvimat 

Contour interval I fool.

20 40 60 80 100 FEET

FIGURE 14. Cable-section reach of Blue Creek, 1967.
G18 SEDIMENT TRANSPORT IN ALLUVIAL CHANNELS

EXPLANATION

Bedrock outcrops 

not surveyed

Lines of equal scour or fill. 

Numbers indicate fill or 

scour(-), in feet, between 

September 29,1966, through 

September 29,1967

® 

Surveyed ends of cross sections

TOTAL SCOUR -2835 cubic yards

TOTAL FILL -23 cubic yards 

NET CHANGE-2812 cubic yards scou 

BED CHANGE (-) 1.2 feet

0 20 40 6O 80 100 FEET 

I I I I I I

FIGURE 15. Cable-section reach of Blue Creek, showing change of streambed topography, 1966-67.
LARGE BED PARTICLE MOTION, BLUE CREEK, CALIFORNIA G19

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US. GOVERNMENT PRINTING OFFICE: 1969 O-359-778