Sediment Transport 

and Turbidity in the 

Eel River Basin, 

California

GEOLOGICAL SURVEY WATER-SUPPLY PAPER 1986

Prepared in cooperation with the 

California Department of Water Resources
Sediment Transport 

and Turbidity in the 

Eel River Basin, 

California

By WILLIAM M. BROWN III and JOHN R. RITTER

GEOLOGICAL SURVEY WATER-SUPPLY PAPER 1986

Prepared in cooperation with the

California Department of Water Resources M

U. S. 6. S.

WATER RESOURCES DIVISION 

ROLUA. MO.

RECEIVED

APR 101972

AM PM

7|8l 9|10ill|12ll|2l 3|4t 5|6

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1971
UNITED STATES DEPARTMENT OF THE INTERIOR 

ROGERS C. B. MORTON, Secretary

GEOLOGICAL SURVEY 

W. A. Radlinski, Acting Director

Library of Congress catalog card No. 74-174753

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

Washington, D.C. 20402 - Price 50 cents (paper cover)

Stock Number 2401-1142
CONTENTS

Page

Abstract________________________________________________________ 1

Introduction._ ____________________________________________________ 2

Purpose and scope_____________________________________________ 3

Previous investigations.._______________________________________ 4

Personnel and acknowledgments_______________________-_________ 5

Physical setting.__________________________________________________ 5

Topography. _________________________________________________ 5

Climate ______________________________________________________ 7

Runoff. ______________________________________________________ 7

Geology._____________________________________________________ 9

Soils.________________________________________________________ 11

Vegetation..__________________________________________________ 11

Land use_____________________________________________________ 12

Hydrography.____________________________________________________ 13

Physical characteristics of streams.______________________________ 13

Eel River above confluence with Middle Fork Eel River__________ 13

Eel River below confluence with Middle Fork Eel River._________ 14

Middle Fork Eel River______________________________________-__ 15

Black Butte River___________________________________________ 15

South Fork Eel River__________________________________________ 15

Van Duzen River____________________________________________ 16

Hydraulic geometry______________________________________________ 16

Fluvial sediment._-_-__-_-_-__-__-_______________-___-______----_- 22

Definition of terms.___________________________________________ 22

Methods of computation.______________________________________ 23

Flood of December 1964______________________________________ 25

Eel River at Scotia.___________________________________________ 28

Middle Fork Eel River near Dos Rios__________________________ 36

Middle Fork Eel River below Black Butte River__________________ 40

Black Butte River______-____-____________________-___-__--_-_- 45

Eel River at Fort Seward_____________________________--___-_-__ 49

South Fork Eel River__________________________________________ 52

Quantity and distribution of fluvial sediment_____________-____--_- 56

Sedimentation in Lake Pillsbury_____--__-____-_-_-_--_--_------- 59

Turbidity_________________________________________________________ 60

Relation between turbidity and the concentration of suspended

sediment-__________________________________________________ 61

Selected references.________________________________________________ 66

Index.___________________________________________________________ 69

in
IV CONTENTS

ILLUSTRATIONS

FIGURES 1-3. Maps: Page

1. Study area, Eel River basin___________________ 6

2. Mean annual precipitation over the Eel River

basin, 1900-63. ____________________________ 8

3. General geology of the Eel River basin_________ 10

4-7. Graphs:

4. Longitudinal profiles of streams, Eel River basin__ 13

5. Relation of depth, width, and velocity to discharge, Eel River at Scotia, 1965-68. ________ 17

6. Downstream variations in the relation between 

water discharge and suspended-sediment discharge in the Eel River basin, October 1965- 

September 1967__________________________ 19

7. Relation of width, depth, and velocity to discharge, showing downstream variations in the 

hydraulic geometry of the Eel River, October 

1965-September 1967_______-_-_---__.__-_ 21

8-10. Photographs:

8. Remains of the devastated town of Pepperwood on 

the Eel River upstream from Scotia, Feb. 5, 

1965_____________________________________ 26

9. House engulfed by landslide associated with the 

December 1964 flood near the South Fork Eel 

River about 15 miles downstream from Garberville______________________________________ 27

10. Two views of the left bank of the Eel River just

upstream from the Scotia gage, Feb. 5, 1965. __ 28 

11-24. Graphs:

11. Sediment-transport curve for Eel River at Scotia,

October 1957-September 1967_______________ 31

12. Sediment-transport curves for Eel River at 

Scotia, showing the change in sedimenttransport characteristics after the December 

1964 flood___.____________________________ 32

13. Comparison of suspended-sediment loads of fix 

streams in the Eel River basin, showing typical 

seasonal variation in sediment discharge, 

October 1966-September 1967_ _____________ 33

14. Relation of streamflow to suspended-sediment

discharge by water years, Eel River at Scotia. 34

15. Particle size versus water discharge, Eel River

at Scotia, 1963-66_______________________ 35

16. Sediment-transport curve for Middle Fork Eel 

River near Dos Rios, October 1957-September 

1967_____________________________________ 37
CONTENTS V

FIGURES 11-24. Graphs Continued Page

17. Sediment-transport curves for Middle Fork Eel 

River near Dos Rios, showing the change in 

sediment-transport characteristics after the 

December 1964 flood__.___________________ 38

18. Particle size versus water discharge, Middle

Fork Eel River near Dos Rios, 1958-67____ 39

19. Changes in low-water streambed elevation, by

year, at four stations in the Eel River basin. _ 41

20. Cross sections at selected gaging stations in the 

Eel River basin, showing changes attributable 

to record-high flows during the 1965 water 

year_ ____________________________________ 42

21. Sediment-transport curve for Middle Fork Eel 

River below Black Butte River, near Covelo, 

October 1962-September 1967_ _____ __ _ _ _ _ 43

22. Particle size versus water discharge, Middle Fork 

Eel River below Black Butte River, near 

Covelo, 1962-67__________________________ 44

23. Sediment-transport curve for Black Butte River 

near Covelo, November 1965-April 1966 and 

December 1966-September 1967_ ___________ 46

24. Particle size versus water discharge, Black Butte

River near Covelo, 1966-67________________ 47

25. Photographs showing mass wasting adjacent to stream,

typical of many locations in the Eel River basin______ 48

26-33. Graphs:

26. Sediment-transport curve for Eel River at Fort

Seward, October 1965-September 1967_____ 50

27. Particle size versus water discharge, Eel River

at Fort Seward, 1966-67_-----_--_-__-__-__ 51

28. Sediment-transport curve for South Fork Eel 

River near Branscomb, October 1962-September 1967_----------____--------___--____- 53

29. Particle size versus water discharge, South Fork

Eel River near Miranda, 1958-62. __________ 54

30. Particle size versus water discharge, South Fork

Eel River near Branscomb, 1963-67.._______ 55

31. Plot of turbidity versus concentration, showing

trend typical of stations in the Eel River basin. 62

32. Regression curves of the approximate relation 

between concentration and turbidity for successive water years...______________________ 63

33. Regression curves of the station-by-station relations between concentration and turbidity, Eel 

River basin______________________________ 65
VI CONTENTS

TABLES

Page 

TABLE 1. Periods of operation of sediment-sampling stations in the

Eel River drainage basin__________________________ 4

2. Precipitation and runoff for hydrologic units of the Eel

River basin.. ____________________________________ 9

3. Rate of increase of width, velocity, and depth with discharge ____________________________________________ 18

4. Rate of increase of suspended-sediment discharge with 

water discharge at selected stations in the Eel River 

basin__________________________________________ 20

5. Downstream variations in sediment yield and hydraulic

geometry, Eel River basin.________________________ 20

6. Sample of computer output of program designed to compute an average relation between water discharge and 

suspended-sediment discharge._____________________ 24

7. Suspended-sediment yields of selected rivers of the world. 36

8. Summary of suspended-sediment and water discharge in

the Eel River basin, October 1957-September 1967. __ 57

9. Regression equations and selected related statistics for 

the relation between concentration and turbidity at 

various stations along the Eel River._______________ 64
SEDIMENT TRANSPORT AND

TURBIDITY IN THE EEL RIVER

BASIN, CALIFORNIA

By WILLIAM M. BROWN III and JOHN K. KITTER

ABSTRACT

The Eel River has the highest recorded average annual suspended-sediment 

yield per square mile of drainage area of any river of its size or larger in the 

United States. This yield, in tons per square mile, is more than 15 times that of 

the Mississippi River and more than four times that of the Colorado River. The 

erosion rate in the Eel River basin is a major watershed-management problem.

This study was made by the U.S. Geological Survey to determine the quantity 

of sediment transported by streams in several areas of the Eel River basin, 

California. Sediment-discharge data were collected at 22 locations within the 

basin for various periods between 1955 and 1967. The destruction of some stations 

by flooding and the establishment of new stations precluded continuous records 

for all stations for the 12-year period. Other characteristics of the streams and 

the basin pertinent to sedimentation have been employed to provide complementary information to the sediment records and to aid in the analysis of 

sedimentation.

The Eel River basin is underlain almost entirely by the sedimentary rocks of 

the Franciscan Formation. Regional uplifting and faulting of these rocks have 

produced a rugged topography characterized by steep slopes and narrow canyons 

which trend northwesterly parallel to the zones of weakness associated with the 

faulting. Weathering of the Franciscan Formation has produced moderately 

deep loamy soils which are highly erodible.

The climate of the basin is one of the wettest in the State of California. 

Throughout the winter months, heavy rains fall dluring intense storms of 

moderate duration and produce about 9 percent of the annual runoff in the 

State, although the basin occupies only 2 percent of the State's land area. The 

coastal region of the basin is generally cool and foggy, while farther inland, 

temperatures are more variable and average precipitation is lower. Snow falls 

in the higher elevations in the eastern part of the basin, but runoff from 

snowmelt is minor.

The combination of geology, soil types, steep slopes, and heavy precipitation 

produces slumps and landslides which contribute heavily to the sediment yield 

of the basin. In the places where landslides are adjacent to the stream channels, 

sediment production is consistently higher than in other areas. Landslides occur 

most frequently in the Middle Fork Eel River basin and along the slopes of the 

main stem of the Eel River in the central part of the basin.
2 SEDIMENT IN THE EEL RIVER BASIN, CALIFORNIA

Average annual rainfall in the basin is about 59 inches, and average annual 

runoff is about 35 inches. Most runoff occurs during and shortly after the late 

fall and winter storms. Because of the impermeability of the soil and mantle 

rock, base flow is poorly sustained. Precipitation during winter storms is 

generally extensive over the entire basin; thus, unit runoff is not extremely 

variable from point to point in the basin.

During the 10-year period beginning October 1957, the Eel River discharged 

an average suspended load of more than 31 million tons per year according 

to measurements made at Eel River at Scotia, the station farthest downstream 

on the main stem of the Eel River. An additional suspended-sediment discharge 

averaging more than 1% million tons per year during the same period was 

derived from the basin of the Van Duzen River, a tributary which enters the 

Eel River a few miles downstream from Scotia. All parts of the basin contributed 

to the suspended-sediment discharge at Scotia, although about two-thirds of the 

material came from the central one-third of the drainage area. The Eel River 

above its confluence with the Middle Fork Eel River contributed about 6 percent 

of the annual suspended load at Scotia, and the Middle Fork drainage added 

about 13 percent. An additional 13 percent came from the South Fork Eel River 

drainage. The remaining 68 percent of the annual suspended load was derived 

from the main stem of the Eel River between the South Fork and Middle Fork 

tributaries. In this vicinity, which includes the North Fork Eel River drainage, 

roughly equal portions of the computed load were discharged above and below 

Fort Seward. Most of the suspended sediment was moved by high flows, which 

occurred an average of 10 percent or less of the time. With few exceptions, 50 

percent or more of the annual suspended load at each station was carried in 

fewer than 6 days during the water year.

Emphasis is given to catastrophic flooding and record sediment discharges 

which occurred during the period of data collection. Floods in December 1964 

and January 1965 caused a suspended-sediment discharge of 160 million tons in a 

30-day period at Eel River at Scotia. This amount was about 51 percent of the 

suspended load computed for the entire 10-year period at that station. During 

this same flood period, record suspended-sediment discharges occurred at all 

sediment stations along the Eel River and its tributaries.

Turbidity and the concentration of suspended sediment at several stations 

in the Eel River basin follow a linear relation which persists throughout the 

range of measured values of these two variables. The trend in this relation was 

similar for each station during each year studied, and this indicated that 

turbidity may be a useful index for the estimation of sediment concentration at 

points within the basin.

INTRODUCTION

A Missouri physician, Dr. Josiah Gregg, named the Eel Kiver in 

1849 when his exploring party encountered a small group of Indians 

carrying "eels" (lampreys] which they had caught in the river. 

Settlement and development along the Eel River began within the 

next decade, and the basin has since become an area of forest-products 

industry, agriculture, and recreation. The basin, whose population is 

50,000, is noted for its natural resources, the most important of which
INTRODUCTION 6

are a vast supply of water and the spectacular California Redwood 

Forests, within which grow some of the tallest trees in the world. 

The Eel River basin is a potentially significant contributor to the 

water resources of California. Although the basin covers only 2 percent of the land area of the State, the average annual runoff from 

the basin is about 9 percent of the average annual runoff in the State. 

However, runoff from the basin is accompanied by a discharge of 

suspended sediment which is the highest per square mile of drainage 

basin of any river the size of the Eel River or larger in the United 

States.

PURPOSE AND SCOPE

The potential importance of the Eel River to the water-resources 

development of the State of California has led to a number of studies 

of the Eel River basin by State and Federal agencies. Primary water 

needs for human consumption, industry, wildlife, and recreation imply 

certain w^ater-quality requirements, and successful planning for establishing and maintaining a water supply meeting these requirements 

necessitates reliable information on sediment and turbidity. Part of 

a study aimed at creating an effective plan of development of the basin 

is a cooperative venture between the U.S. Geological Survey and the 

State of California to study sedimentation and the turbidity characteristics of the Eel River and its tributaries. Sediment yield is of great 

economic importance in the effective design of reservoirs and other 

construction on rivers, is significant in its relation to the frequent flooding along the Eel River, and has numerous attendant problems of 

importance to man.

The purposes of this project are to determine the quantity of sediment transported by streams in different areas of the Eel River basin, 

to compare sediment yields among selected regions of the basin, and 

to study the relation of turbidity to the concentration of suspended 

sediment. The data necessary for this project were obtained from 

sediment stations which were established at several locations in the 

basin (table 1). Even though many stations were discontinued or 

relocated as a result of the effects of the December 1964 flood, sufficient 

complementary records were obtained to provide a representative 

analysis of sedimentation. Turbidity samples were taken at several 

stations between 1964 and 1968 with simultaneous sediment samples 

and water-discharge measurements.

This report presents and interprets the data collected for this project, along with pertinent related information. Methods of analysis 

of these data are described in conjunction with computations, tables, 

and graphs.

427-150 O - 71 - 2
SEDIMENT IN THE EEL RIVER BASIN, CALIFORNIA

TABLE 1. Periods of operation of sediment-sampling stations in the Eel River

drainage 6 asm

Sampled daily Sampled periodically

Station Station name

Period of sampling

LD O LD 00 

Ol Ol 01 Ol

11-4700 LakePillsbury near Potter Valley. ................

4705 Eel River below Scott Dam. near Potter Valley. .........

4710 Potter Valley powerhouse tailrace, near

	Potter Valley ..... ..... ...............

4721.5 Eel River near Dos Rios ......................

4722 Outlet Creek near Longvale. ...................

4725 Eel River above Dos Rios .....................

4729 Black Butte River near Covelo ..................

4730 Middle Fork Eel River below Black Butte River,

	near Covelo ...........................

4731 Williams Creek near Covelo. ...................

4736 Short Creek near Covelo .....................

4737 Mill Creek near Covelo ......................

4738 Elk Creek near Hearst. ......................

4739 Middle Fork Eel River at Dos Rios ................ C

4740 Eel River below Dos Rios .....................

4744 Hulls Creek near Covelo .....................

4745 North Fork Eel River near Mina . .................

4750 Eel River at Fort Seward .....................

4755 South Fork Eel River near Branscomb . .............

4765 South Fork Eel River near Miranda. ...............

4766 Bull Creek near Weott. ......................

4770 Eel River at Scotia . ........................

4785 Van Duzen River near Bridgeville ................

PREVIOUS INVESTIGATIONS

Studies of erosion and sedimentation in the Eel Eiver basin have 

been a part of investigations of the northern coastal area of California since July 1958 (California Department of Water Resources, 

1966, p. 2). The investigations include many aspects of development, 

control, and conveyance of water supplies; however, the studies of 

sediment within the program are more general than detailed. A report 

by the U.S. Department of Agriculture River Basin Planning Staff, 

Soil Conservation Service and Forest Service (1970), discusses recent 

detailed studies of soil types and erosion processes throughout the
PHYSICAL SETTING 5

Eel River basin. Detailed investigations of sedimentation were begun 

in 1957 by the U.S. Geological Survey in cooperation with the California Department of Water Resources, and information gained from 

these investigations has been analyzed as part of a report on the sediment yield of streams in northern coastal California (Hawley and 

Jones, 1969). A detailed report on many aspects of sedimentation in 

the Middle Fork Eel River basin is currently being prepared by 

J. M. Knott of the Geological Survey and will include analysis of 

sediment data collected since October 1957.

PERSONNEL AND ACKNOWLEDGMENTS

This report was prepared by the U.S. Geological Survey, Water 

Resources Division, in cooperation with the State of California Department of Water Resources as part of an investigation of the water 

resources of the State of California. This project was conducted under 

the general supervision of R. Stanley Lord, district ehief in charge of 

water-resources investigations in California, and under the immediate 

supervision of L. E. Young, chief of the Menlo Park subdistrict office.

The writers wish to express their gratitude to the following individuals: C. E. Stearns, for consultation and the supply of data on 

soils and erosion collected by the Soil Conservation Service; G. Porterfield, J. P. Akers, B. L. Jones, and S. G. Heidel, for critical review 

and constructive commentary; and J. M. Knott, for providing information and computations on sediment transport in the Middle Fork 

Eel River, and for his review and helpful criticism of this report.

PHYSICAL SETTING 

TOPOGRAPHY

The Eel River drains an area of about 3,600 square miles in the 

Coast Ranges of northern California and empties into the Pacific 

Ocean some 280 miles north of San Francisco (fig. 1). The basin is 

about 120 miles long, averages 30 miles in width, and is oriented in a 

northwesterly direction almost parallel to the Pacific coast. Regional 

folding and faulting have created a series of northwest-trending ridges 

and valleys, and a trellis drainage and erosional pattern characterizes 

the surface features which have formed. Elevations in the generally 

rugged terrain range from sea level to 7,000 feet, and the Eel River 

and its tributaries descend rapidly from the higher elevations in 

narrow, steep-walled canyons. In the coastal region south of Eureka, 

however, the Eel River near its delta flows in a gently sloping valley 

about 11 miles long that expands ocean ward from 1 to 9 miles in 

width. Round Valley and Little Lake Valley in the southern part of
6

SEDIMENT IN THE EEL RIVER BASIN, CALIFORNIA

A 

EXPLANATION

Sampling 

station and number

draii

FIGURE 1. Study area, Eel River basin. Base from U.S. Geological Survey, 1955,

scale 1:500,000.
PHYSICAL SETTING 7

the basin constitute the only noteworthy areas of regular topography 

besides the delta area. The only major surface-water features other 

than the rivers are Lake Pillsbury, a 2,280-acre reservior impounded 

behind Scott Dam on the Eel River in the southern tip of the basin, 

and Van Arsdale Reservoir which is just downstream of Lake Pillsbury. Cities and other manmade features constitute but a small part 

of the basin topography, and along with highways and railroads are 

confined to the lowlands along the river valleys.

CLIMATE

The climate of the Eel River basin is one of the wettest in the 

State of California. The average annual precipitation ranges from 

about 35 inches along the Pacific coast south of Humboldt Bay to 

more than 110 inches in the mountains southeast of Scotia (fig. 2). 

This precipitation is generally the result of large storms which move 

into California from the northwest during the late autumn and winter 

months. These storms produce brief, intense rains which contribute as 

much as 80 percent of the annual precipitation in the basin. Snow 

falls at higher elevations, but its quantity and contribution to runoff 

are usually insignificant.

The climate of the coastal region of the basin is predominantly 

influenced by the moist airmass over the ocean which produces onshore 

winds, cool foggy summers, and mild wet winters. Temperatures near 

the coast are moderate, ranging from 0.6°C (33°F) to 29°C (85°F) 

and averaging about 11 °C (52°F); rainfall averages about 40 inches 

per year. Farther inland, the changing topography and increased 

distance from the ocean bring about wider temperature ranges and 

increased precipitation. Temperature extremes range from about 

-18°C (0°F) to about 43°C (110°F), and the mean annual rainfall 

approaches 80 inches. Because of a decrease in the amount of fog, 

however, the general climate of the inland part of the basin is less 

moist than that along the coast.

RUNOFF

The average annual runoff in the Eel River basin is approximately 

35 inches on the basis of streamflow records and synthesized information for the 60-year period 1900-59 (Rantz, 1964, p. 3). The runoff 

has been adjusted for evaporation and change in reservoir contents of 

Lake Pillsbury and for diversion into the Russian River basin at the 

Van Arsdale Reservoir. Average annual runoff is highest in the 

western part of the basin and lowest in the central part; however, 

variations from the average are not great within each of the larger 

hydrologic units of the basin listed in table 2.
8 SEDIMENT IN THE EEL RIVER BASIN, CALIFORNIA

Line of equal mean 

annual precipication

FIGURE 2. Mean annual precipitation over the Eel River basin, 

1900-63. (Rantz, 1968.)
PHYSICAL SETTING 9

TABLE 2. Precipitation and runoff for hydrologic units of the Eel River basin 

(adjusted to base period 1900-59)

[From Rantz, 1964, table 1]

Hydrologic unit

Drainage 

area 

(sq. mi.)

......-..- 709

._.__._._. 753

....-. . 282

..-..-..- 689

........... 3,113

..-.-.-..- 429

.___.._.__. 3,625

Average 

annual

tation 

(inches)

52 

54 

59 

71 

59 

64 

59

Average annual 

runoff

1,000's of 

acre-feet

1,140 

1,170 

425 

1,738 

5,720 

995 

6,808

Inches

30.2 

29.1 

28.3 

47.3 

34.4 

43 

35

The runoff throughout the basin is sustained almost entirely by 

overland runoff and base flow. Although snow does fall in the higher 

elevations of the eastern part of the basin, the runoff from snowmelt 

is generally insignificant. Most runoff is the result of large, general 

storms which affect the entire basin, and the unit frequency distribution of runoff is therefore similar for most individual streams. The 

ratio of precipitation to runoff varies with each storm depending 

upon the storm intensity and the amount of antecedent saturation of 

the soil. High flows diminish quickly in the absence of sustaining 

rainfall, and discharges drop well below their average annual values 

during the dry summer months, when there may be more than 200 

days without significant precipitation.

Annual runoff extremes for the basin above Scotia during the period of sediment record were 20 inches in the 1964 water year and 67 

inches during the 1958 water year. It is noteworthy that neither of 

these extremes was accompanied by the lowest or highest annual 

sediment discharge for the same period of record. A detailed study of 

the relations between runoff and sediment discharge is discussed in 

a subsequent section of this report (p. 22).

GEOLOGY

The rocks underlying most of the Eel Eiver basin are a part of the 

Franciscan Formation, which extends over much of the northern 

Coast Ranges geomorphic province. This formation was described in 

some detail by Bailey, Irwin, and Jones (1964) and was described in 

general by Page (1966, p. 258) as a complex assemblage of sedimentary rocks of deep-water origin and mafic marine volcanic material, accompanied locally by masses of serpentine. Sandstone, chiefly 

graywacke, is the prevalent rock type in the part of the Franciscan 

assemblage that underlies the Eel River basin.
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PHYSICAL, SETTING 11

luvial deposits are found in scattered regions of the basin, notably 

along the main stem of the Eel Kiver (fig. 3).

Major structural features are formed by a complex pattern of 

strike-slip faulting generally oriented southeast-northwest, and the 

drainage patterns of the Eel Kiver and its tributaries reflect this 

orientation. Topographic changes in this region are still in progress 

as regional uplifting and faulting, which began in the late Miocene 

period, continue to influence the landforms throughout the northern 

Coast Ranges.

Widespread areas of the Eel River basin are subject to landslides 

and earth flows. Combinations of uplifting topography, steep hillslopes, and the saturation of soils by rainfall contribute to massmovement processes which are commonly augmented by the erosive 

action of streams along the base of the slopes. Because of their past 

and potential contributions of large quantities of sediment to stream 

channels, landslides and earth flows are of special interest in this 

report. For example, sediment yield is greatest in the central part of 

the basin along the main stem of the Eel River where large-scale 

sliding is common along both sides of the river for many miles.

SOILS

Although many soil types are present within the Eel River basin, 

the general character of soils throughout the basin is similar because 

the parent rocks are much the same over the entire basin. With minor 

variations, nearly all the soils are loamy in texture and generally 

range from 20 to 60 inches in depth (C. E. Stearns, written commun., 

1968). These soils are generally stable with good infiltration rates 

and water-holding capacities, and the natural vegetal cover of the 

basin helps to reinforce. this stability. However, the basin is often 

subject to a combination of conditions which tends to render these 

soils unstable. Soils resting on steep slopes become quickly saturated 

during periods of intense rainfall that follow extended periods of 

moderate precipitation, and severe erosion may thus occur in a very 

short period of time. In areas which have been subjected to heavy 

grazing or to deforestation by fires or lumbering practices, soils may 

become unstable and erosion may be severe even under normal runoff 

conditions.

VEGETATION

The vegetal cover of the Eel River basin includes a variety of 

forms, but the greater part of the basin is moderately to heavily 

forested with redwood and other conifers. The remaining part is covered by varying proportions of hardwood trees, chaparral, and grass.

427-150 O - 71 - 3
12 SEDIMENT IN THE EEL RIVER BASIN, CALIFORNIA

The distribution of these vegetation types forms four roughly 

denned and discontinuous belts which trend in a northwesterly direction parallel to the long axis of the basin. Along the western side grow 

forests of California redwoods (Sequoia sempervirens) , the valuable 

and spectacular trees which are the basis of the lumber and recreation 

industries of the basin. The redwoods are concentrated in a large area 

surrounding the lower reaches of the Van Duzen and Eel Rivers, and 

they occupy most of the western drainage of the South Fork of the 

Eel River from Weott to Branscomb. The forest belt directly east 

of the redwood forests is predominately Douglas Fir but includes 

grasslands and scattered stands of pine. This belt, extending roughly 

from Kneeland south through Willits, reflects a change from the 

coastal climate to one of lower rainfall and less fog. A third zone of 

vegetation is less readily denned but includes a variety of hardwoods, 

mixed conifers, and chaparral in the central and southern parts of 

the basin. A woodland typified by oak, maple, and madrone extends 

somewhat discontinuously from Fort Seward to Potter Valley. Chaparral covers the drier areas of the southern part of the basin, especially in the vicinity of Lake Pillsbury and along Elk Creek. The 

fourth forest type, which consists of pines and Douglas Fir, covers the 

higher elevations of the eastern and southern parts of the basin. It 

extends over the headwaters of all the eastern drainage and constitutes 

commercial timberland typical of national forests.

LAND USE

Surveys of land use by the California Department of Water Resources (1965) divide land development within the Eel River basin 

into four major categories. Irrigated lands compose approximately 

14,500 acres and include properties receiving water artificially. Dryfarmed lands are those on which farming practices are dependent 

upon the natural moisture supplied by ground water and precipitation. These lands cover some 32,000 acres part concentrated in the 

delta area of the Eel and the remainder widely scattered throughout 

the basin. Urban lands compose 11,000 acres, less than 1 percent of the 

basin area, and are confined generally to the towns along the Eel 

River valley. Recreational lands make up approximately 28,200 acres 

of commercial and residential property, campsites, and parks. The 

remaining 2,272,300 acres of basin area is undeveloped and is used 

primarily for grazing livestock, various recreational activities, and 

commercial timber production.
SEDIMENT IN THE EEL RIVER BASIN, CALIFORNIA 13

HYDROGRAPHY 

PHYSICAL CHARACTERISTICS OF STREAMS

A variety of factors influences the form and processes of natural 

streams, among which the most significant are precipitation and subsequent channel flow, the composition of the material forming the 

channel bed and banks, and the topography through which the stream 

flows. The following discussion describes the general and noteworthy 

features of the streams in the Eel River basin, and emphasizes those 

features that significantly affect sedimentation processes.

EEL RIVER ABOVE CONFLUENCE WITH MIDDLE FORK EEL RIVER

The upper Eel River emanates from the slopes of Bald Mountain 

in western Meiidocino County, Calif., and flows in a southerly direction 

for 23 miles before turning westward and flowing into Lake Pillsbury. 

In this initial reach, the Eel drops through rugged, forested canyons 

at an average rate of 200 feet per mile (fig. 4). Several minor tributaries drain the 6,500-foot mountains which form the basin above Lake 

Pillsbury, and the Rice Fork of the Eel drains the chaparral-covered 

slopes of the southern tip of the basin, entering Lake Pillsbury from 

the south.

Soils through which these streams flow are primarily the deep forest 

soils which tend to be moderately erodible under dense forest vegeta7000

6000

5000

4000

0 20 40 60 80 100 120 140 160 180 200 

DISTANCE, IN MILES UPSTREAM FROM MOUTH OF EEL RIVER

FIGURE 4. Longitudinal profiles of streams, Eel River basin.
14 SEDIMENT IN THE EEL RIVER BASIN, CALIFORNIA

tion. However, a large area of highly erodible material extends south 

and east of Lake Pillsbury through the Rice Fork basin where the 

vegetal cover is predominantly chaparral. Below Lake Pillsbury, the 

water released at Scott Dam continues its westward flow 10 miles to 

Van Arsdale Reservoir where a portion of it is diverted into the Russian River basin. This diversion is a part of Pacific Gas and Electric's 

Potter Valley Project to supply water and power for local areas in 

Lake, Sonoma, and Mendocino Counties. About one-third of the average flow of the Eel River at this point is diverted into Potter Valley. 

Downstream from Van Arsdale Reservoir, the Eel River turns northwestward, dropping with an average slope of 16 feet per mile to its 

confluence with the Middle Fork of the Eel River, 55 miles downstream. Landslides and bank slumping are common 'along this reach, 

and the slopes adjacent to the river are generally composed of moderately to highly erodible soils.

Outlet Creek is the major tributary of the Eel above its confluence 

with Middle Fork Eel River. Outlet Creek has its source in the 

vicinity of Little Lake Valley and flows into the Eel from the west. 

Lower elevations, mild slopes, and generally less erodible materials 

characterize its drainage basin. Tomki Creek provides additional 

drainage for the steeper, forested area between Van Arsdale Dam and 

Little Lake Valley.

EEL RIVER BELOW CONFLUENCE WITH MIDDLE FORK EEL RIVER

From Dos Rios to its mouth at the Pacific Ocean, the Eel continues 

its northwesterly course at a generally regular slope of 8 feet per mile. 

The Eel River canyon retains its narrow, boxlike proportions throughout most of this reach until the valley begins to widen below Scotia. 

The North Fork Eel River and the Van Duzen River are the major 

tributaries entering the Eel from the east along this reach, and the 

South Fork Eel River provides the principal drainage from the west. 

The Van Duzen and South Fork Eel Rivers are discussed in separate 

sections within this report.

The Eel River canyon from Van Arsdale Reservoir north to Eel 

Rock is characterized by large-scale landsliding, and sediment records 

indicate that the major part of suspended-sediment discharge from 

the basin originates in this reach. In addition to the direct contribution 

of landslides to the main channel, at least 20 short steeply sloping 

tributaries drain two parallel ridges between which the Eel River 

flows from Dos Rios to the South Fork, and these streams may be major 

contributors of fluvial sediment by their combined effects. These 

smaller streams contribute sediment from side canyons, transport 

slide material to the main stream, and erode deposits along the 

channel of the Eel River as it recedes after flooding.
HYDROGRAPHY 15 

MIDDLE FORK EEL RIVER

The headwaters of the Middle Fork Eel Kiver drain the forested 

high country of the eastern Eel Kiver basin divide. Stream slopes of 

these waters are very steep, averaging approximately 140 feet per 

mile above the mouth of the Black Butte Kiver. Below the Black Butte 

Kiver to its confluence with the Eel near Dos Rios, the Middle Fork has 

a more gentle slope of about 21 feet per mile.

The headwater streams of the Middle Fork flow through areas underlain by the metamorphosed sedimentary rocks of the Franciscan Formation, but Elk Creek and the streams in the vicinity of Covelo flow 

through a complex structure of Quaternary alluvium, marine terrace 

deposits, and intrusive ultramafic material. Soils formed on the 

rocks of the central basin lie on gently sloping ground and are more 

erosion resistant than those in the upper basin. Between the mouth 

of Elk Creek and Dos Rios, the Middle Fork flows through a narrow 

canyon where it transects the ridge between adjacent fault-formed 

valleys.

BLACK BUTTB RIVER

The Black Butte River drains 162 square miles of steep mountain 

slopes and enters the Middle Fork from the south. The river has a slope 

of 163 feet per mile along its straight northwesterly course, and the 

orientation and formation of its valley are probably related to a fault 

which parallels the river throughout most its length. Deposits of 

Quaternary landslide material on the slopes along the east side of the 

river provide a ready source of sediment (fig. 3). The Black Butte 

River basin is otherwise underlain by the Franciscan sandstones, 

shales, and conglomerates typical of most of the rest of the Eel River 

basin.

SOUTH FORK EEL RIVER

The drainage of the South Fork is unique among the tributaries 

of the Eel, differing in form, climate, vegetation types, and underlying rock. The South Fork has an average slope of 24 feet per mile 

for its 92-mile length. It flows northwest parallel to the main stem 

of the Eel through the redwood forests which cover most of its western drainage. Underlying materials are marine sands of Cretaceous 

age similar to those of the Franciscan Formation but distinctive to 

the South Fork and lower Eel drainages (fig. 3). The soils that form 

on this formation are highly erodible, especially along the steeply 

sloping western side of the basin. The landslide topography found in 

many areas throughout the Eel River basin does not exist along the 

South Fork except in a small region north of Garberville.
16 SEDIMENT IN THE EEL RIVER BASIN, CALIFORNIA

VAN DUZEN RIVER

The Van Duzen River drains the northern reaches of the Eel River 

basin and flows out into the flat delta region of the Eel about 11 miles 

inland from the ocean. The river has an average slope of 59 feet per 

mile over its 67-mile length. Its headwaters drop quickly from the 

4,000-foot elevations near the eastern boundary of the basin at a rate 

of 110 feet per mile over the first 15 miles, but the stream gradient 

decreases to less than 30 feet per mile below Bridgeville.

The Van Duzen River and its principal tributary, Yager Creek, 

flow through moderately sloping grassland in the central part of the 

drainage basin and through redwood forests in their lower reaches. 

Many of these grassland areas are underlain by unstable soils and are 

subject to erosion by gullying. The lower reaches of the basin areunderlain by Quaternary terrace deposits and alluvium, and the bedrock of the upper basin contains the sandstone and conglomerate of 

the Franciscan Formation (fig. 3). Bank cutting and sliding are common along Yager Creek north of Carlotta and along the Van Duzen 

River between Carlotta and Bridgeville.

HYDRAULIC GEOMETRY

The physical characteristics of streams include the hydraulic geometry of stream channels, which is defined by the relations among 

certain hydraulic characteristics of the stream (Leopold and Maddock, 1953). At a given cross section, depth, width, velocity, and 

suspended load vary as power functions of the discharge according 

to equations of the following form:

w=aQ* (1)

d=cQf (2)

v=kQm (3)

L=pQ* (±)

wheie

w=width

<Z=mean depth=area divided by width

#=mean velocity

L=suspended-sediment load

Q= water discharge

a, c, k, p, b, f, m, and j are numerical constants.

These equations may be determined empirically by plotting data 

obtained from current-meter and other measurements at river cross 

sections. When width, depth, velocity, and suspended load are plotted 

against discharge on logarithmic paper, their relations to discharge 

are expressed by nearly straight lines.
HYDRAULIC GEOMETRY 17

The graphs of figure 5 illustrate the changes of width, depth, and 

velocity with discharge of the Eel River at Scotia. The values shown 

for the exponents &, /, and m are consistent with the nature of the 

channel. The steep-walled canyon restricts the channel width while 

the depth and velocity increase rapidly with increasing discharge. 

The graphs shown are for the period following the December 1964 

flood; however, a comparison of these data with preflood data shows 

that there has been no appreciable change in the hydraulic geometry 

at Scotia from preflood conditions.

Table 3 lists the parameters of the hydraulic geometry at Scotia 

and four other stations in the Eel River basin. The data used to de30

10

0 5

I I I I

I I I "_

1000 10,000 100,000

WATER DISCHARGE. IN CUBIC FEET PER SECOND

1,000,000

FIGURE 5. Relation of depth, width, and velocity to discharge, 

Eel River at Scotia, 1965-68.
18 SEDIMENT IN THE EEL RIVER BASEST, CALIFORNIA

rive these parameters were collected during the period 1965-68, and 

the values shown typify the hydraulic geometry of these stations for 

this period. Although these values may not provide a visual picture 

of the channel conditions along the Eel River, they may be used for 

comparison with those of the other rivers listed.

TABLE 3. Rate of increase of width, velocity, and depth with discharge 

[Exponents 6, m, and/are defined by equations 1-3 (p. 16)]

Rate of increase with discharge ( Q)

Station and location b m f Q more 

(width) (velocity) (depth) than 

(cfs)

Black Butte River near Covelo, Calif

Middle Fork Eel River below Black Butte River, near 

Covelo, Calif........ ..____.___.________ .......

Middle Fork Eel River near Dos Rios, Calif .. ..... ... _ Eel River at Fort Seward, Calif

Eel River at Scotia, Calif...

Rio Grande at San Felipe, N. Mex.i _ . .

Rio Grande near Bernalillo, N. Mex.i . - . .

Middle Loup River at Arcadia, Nebr.i . . . _ _ _ Moreau River near Faith, S. Dak. 1

Rio Puerco at Rio Puerco, N. Mex.i. .............

Bighorn River at Thermopolis, Wyo. 1

Powder River at Arvada, Wyo. 1

0.06

.10 

.14 

.10 

.10 

.22 

.03 

.13 

.10 

.43 

.14 

.10 

.37

0.26

.32

.27 

.54 

.40 

.30 

.51 

.35 

.34 

.41 

.55 

.31 

.25

0.68

.58 

.59 

.35 

.50 

.48 -.-

.46

.52 ...

.56

.16 ...

.31 ...

.59 

.38 .-_

750

500 

1,000 

1,000 

1,000

1,000

400

200

1 Leopold and Maddock (1953).

At each station on the Eel River, the velocity and depth increase 

with increasing discharge more rapidly than the width. Velocity increases most rapidly at Eel River at Fort Seward and does so at a 

rate greater than the rate of increase of the depth. Among the selected 

stations along the Eel River, this characteristic prevails only at Eel 

River at Fort Seward, perhaps because the channel is somewhat constricted at that site.

Leopold and Maddock (1953, p. 21) stated that it is typical at a 

given cross section of an alluvial stream for the suspended-sediment 

load to increase with increase in discharge, and at a more rapid rate 

than discharge. That is, the concentration of suspended sediment increases with discharge. At the stations in the Eel River basin, the 

daily suspended-sediment discharge increases as a power (j, 4) of water 

discharge ranging from about 1.8 in the upper parts of the sedimenttransport curves to about 2.6 in the lower parts (table 4). These values 

are consistent with those postulated by Leopold and Maddock.

The downstream variation in suspended-sediment discharge at a 

given frequency of water discharge provides useful information about 

the nature of sediment transport in the Eel River basin. Concurrent 

records of suspended-sediment discharge were collected at five stations 

in downstream order from Black Butte River near Covelo to Eel 

River at Scotia for the period October 1965-September 1967. After
HYDRAULIC GEOMETRY 19

a sediment-transport curve was plotted for each station for this 

period, the suspended-sediment discharge corresponding to the mean 

annual water discharge, Qmea.n, at each station was taken from the 

curve. These values were used to plot the first graph in figure 6. The 

second graph in figure 6 was plotted in a similar manner; however, 

the water discharge used was that discharge equaled or exceeded 1 percent of the time at each station (Q01 ). It is shown later in this report 

that Q01 produced about 50 percent of the suspended-sediment discharge for the period of record for most stations in the Eel River basin. 

The graphs indicate that the concentration of suspended sediment increased in a downstream direction at a given frequency of discharge

1000 10,000

10,000 

EXPLANATION 

Station Symbol

1000 

 1.000,000

 100,000

1000 10.000 100,000 

WATER, DISCHARGE, IN CUBIC FEET PER SECOND

10,000

FIGURE 6. Downstream variations in the relation between water discharge and 

suspended-sediment discharge in the Eel River basin, October 1965-September 1967. Qmean is the mean annual discharge, and Qoi is the discharge equaled 

or exceeded 1 percent of the time for each station shown. The stations and 

their corresponding numbers are given in table 5.

427-150 O - 71 - 4
20 SEDIMENT IN THE EEL RIVER BASIN, CALIFORNIA

TABLE 4. Rate of increase of suspended-sediment discharge with water discharge at 

selected stations in the Eel River basin

Station and period of record (water years)

Range of Approximate

water discharge value of j in

(cfs) equation 4

Black Butte River near Covelo, 1966-67. .............. 

Middle Fork Eel River below Black Butte River near Covelo, 1963-67. _ Middle Fork Eel River near Dos Rios 1958-67. . . 

Eel River at Fort Seward 1966-67.. ...... __ - ---. 

Eel River at Scotia, 1958-67 

100- 1,000

1, 000- 10, 000 

500- 5,000

5, 000- 50, 000 . 

1, 000- 10, 000

10, 000-100, 000 

4, 000- 40. 000

40, 000-700, 000 

200- 2,000

2, 000- 20, 000

2.6

2.2 

2.2

1.8 

2.5

2.0 

2.3

2.4 

2.5

1.8

and that concentrations increased at about the same rate for discharges 

between $me an and Q01 . (The latter observation was tested, and there 

was no appreciable change in j for other values of Q between $me an and 

$oi') These phenomena are supported by the observation that the 

average annual yield of suspended sediment per square mile of drainage 

area increased with increasing drainage area (table 5). Although these 

empirical observations show conditions atypical of other rivers 

(Leopold and Maddock, 1953, p. 22), they give some insight into the 

unusually high capacity for sediment transport of the Eel Kiver and 

its tributaries. These observations help to verify that there was less 

sediment-free inflow, such as ground-water inflow, than sedimentproducing runoff as the drainage area increased downstream. It is 

possible that the credibility of the basin changes in a downstream 

direction because of changing geology below Fort Seward (fig. 3), 

although data are insufficient to support this contention adequately.

TABLE 5. Downstream variations in sediment yield and hydraulic geometry,

Eel River basin

[Upper values, at Qmeanl lower values, at Qoi]

Station and No.

Black Butte River, near 

Covelo 11-4729. 

Middle Fork Eel River, 

below Black Butte 

River, near Covelo, 

11-4730. 

Middle Fork Eel River 

near Dos Rios, 11-4739. 

ifiel River at Fort Seward, 

11-4750. 

Eel River at Scotia, 11-4770.

Average 

sediment 

yield, 

1966-67 

(tons per 

sq. mi) '

4,330

4,210

6,181 

6,932 

8,311

Average 

sediment 

yield, 

1963-67 

(tons per 

sqmi) '

8,127 

12, 027

15,829

Variation in hydraulic geometry at Qmei 

Qoi (1966-67)

Q

(cfs)

338 

4,050 

914 

8,500

1,726 

19,100 

4,472 

50,000 

7,853 

93,400

W

(feet)

160

250

275

350

600

d 

(feet)

1.0 

3.3

1.1 

3.9

1.8 

7.7 

7.2 

18 

5.5 

18

V

(ft per 

sec)

4.0 

7.6 

4.2 

8.6

4.6 

8.8 

2.4 

8.8 

2.8 

9.0

L

(tons per 

day)

300 

55,000 

1,000 

120,000

3,000 

300,000 

5,000 

1,000,000 

13,000 

2,000,000

m and

Concentration 

(mg/1)

330 

5,040 

400 

5,220

640 

5,810 

410 

7,410 

610 

7,930

1 Values computed from data shown in table 8.
HYDRAULIC GEOMETRY 21

The Eel River accommodated high sediment-producing discharges 

in 1966 and 1967 principally by a downstream increase in depth of 

flow (fig. 7). At $01, depth of flow increased downstream at about 

twice the rate of increase in width, while the downstream rate of increase in velocity was almost negligible.

Further analysis of the hydraulic geometry of the Eel River basin 

is somewhat hampered by insufficient data and is generally beyond 

the scope of this report. However, the material presented in this 

section when viewed in connection with other information presented 

in this report and with other findings (Carlston, 1969) may be useful 

in future and more detailed studies of the Eel and similar rivers.

1000

x G

I L±J 

Q- LJ_ 

LJ

Q Z

300

100

10

10,000 100.000 

WATER DISCHARGE, IN CUBIC FEET PER SECOND

FIGURE 7. Relation of width, depth, and velocity to discharge, showing downstream variations in the hydraulic geometry of the Bel River, October 1965- 

September 1967. The discharge from which the points are plotted is that 

discharge, Qoi, equaled or exceeded 1 percent of the time for each station 

shown.
22 SEDIMENT IN THE EEL RIVER BASIN, CALIFORNIA

FLUVIAL SEDIMENT 

DEFINITION OF TERMS

Many terms relating to fluvial sediment are not completely standardized ; the terminology used in this report is based on the following 

definitions:

Fluvial sediment or sediment is fragmental material that originates 

from weathering of rocks and is transported by, suspended in, or 

deposited by streams.

Suspended sediment or suspended load is sediment that moves in 

suspension in water and is maintained in suspension by the upward 

components of turbulent currents or by colloidal suspension.

Bedload or sediment discharged as bedload includes both the sediment that moves along in continuous contact with the streambed 

(contact load) and the material that bounces along the bed in 

short skips or leaps (saltation load).

Sediment sample is a quantity of water-sediment mixture that is 

collected to determine the concentration of suspended sediment, the 

size distribution of suspended or deposited sediment, or the specific 

weight of deposited sediment.

Sediment discharge is (a) rate at which dry weight of sediment 

passes a section of a stream or (b) quantity of sediment, as measured 

by dry weight or by volume, that is discharged in a given time.

Sediment-transport curve is a curve of relation between water discharge and sediment discharge. Usually the relation is between 

water discharge and suspended-sediment discharge, but it can be 

between water discharge and bedload discharge or between water 

discharge and total sediment discharge (sum of sediment discharge 

in suspension and as bedload).

Water discharge or discharge is the amount of water flowing in a 

channel expressed as volume per unit of time. The water contains 

both dissolved solids and suspended sediment.

The general principles of sediment-discharged measurement as well 

as the practical aspects of selecting sampling points and determining 

the frequency of sampling are discussed in several reports. A suitable 

reference on methods of measurement and analysis of sediment loads 

is Keport 14 of the U.S. Inter-Agency Committee on Water Resources 

(1963). The procedure for the measurement of water discharge was 

described in detail in Corbett and others (1943}.
SEDIMENT IN THE EEL RIVER BASIN, CALIFORNIA 23 

METHODS OF COMPUTATION

Basic data which were interpreted for use in graphs and tables 

in this report were prepared according to standard procedures of the 

U.S. Geological Survey, Water Eesources Division, California District. 

However, it is instructive to comment further on certain of these 

procedures and the methods of data interpretation in this report 

because of the record values of some of the sediment-discharge data.

The sediment yield of the Eel Eiver basin and its subunits is determined in this report primarily from measured, computed, and estimated rates of transport of suspended sediment. These rates correspond 

to certain significant time periods within the years during which sediment samples were taken, and the rates can be extrapolated to other 

periods of time, given certain complementary information (Miller, 

1951). However, an extreme flood event which occurred during the 

period of sediment record produced sediment-transport rates of such 

magnitude that their correspondence to time periods other than the 

period during and after the flood is somewhat obscure. Thus, the 

analyses here are presented on the basis of preflood and postflood sediment transport rates, with the emphasis that the characteristics of 

these rates are probably dissimilar. Extrapolation is performed using 

both preflood rates and rates for the entire period of record so that the 

bias of the flood effects is apparent.

Sediment-transport curves shown in this report were plotted from 

suspended-sediment data according to standard procedures with the 

following exception: The coordinates of each of the points used to 

define the curves represent an average value for a selected interval of 

water discharge and the corresponding average sediment discharge 

computed for that interval. These computations were performed as a 

part of a computer program written for this purpose, and a sample of 

the output of this program is shown in table 6. The data show that the 

upper end of the curve is defined by only a few points, and the water 

and sediment discharges defining some of these points are estimated or 

computed rather than measured directly. However, the value used to 

define the upper ends of curves shown in this report have not been revised to fit an assumed pattern. Only values previously computed and 

published have been used to maintain consistency in reports on this 

subject and to allow for the fact that some sediment-discharge values 

are affected by unusual hydrologic events. Obviously, there are 

limitations on the accuracy of the sediment-transport curves and 

the accuracy of extreme values estimated from these curves. However, 

the adequacy of these values cannot be intelligently evaluated until 

additional information is obtained on the probable accuracy of mea-
24 SEDIMENT IN THE EEL RIVER BASEST, CALIFORNIA

sured sediment discharge (Colby, 1956, p. 167). It should be sufficient 

to say that interpolation of the curves and use of the extreme values 

presented in this report should be done with caution and with the 

previous comments in mind. Extrapolation of curves shown in this report, especially at the upper end, is too likely to be in error to be useful 

because there are too few measured values, and many of the estimated 

values were the result of an extremely infrequent flood event (Helley 

and LaMarche, 1968).

TABLE 6. Sample of computer output of program designed to compute an average 

relation between water discharge and suspended-sediment discharge

[A plot of Q w versus 08 may accompany this output at the option of the user] 

11-4770. Eel River at Scotia, Calif.

[Period of daily record: October 1957-September 1967]

Range of water discharge,

Q w , in cubic feet per

second

0. 0- 10. 0

10.0- 100.0.....

100.0- 200.0... ______

200. 0- 300. 0 ..

300.0- 500.0...__ _ .

500.0- 750.0...._ _ _

750.0- 1000.0... ______

1000.0- 1500. 0.........

1500. 0- 2000. 0-

2000. 0- 3000. 0

3000. 0- 4000. 0. .

4000. 0- 5000. 0.. .

5000.0- 6000.0... _ . .

6000.0- 7000.0..... _..

7000. 0- 8000. 0

8000.0- 9000.0... .

9000.0- 10000.0... .

10000.0- 11000.0- .

11000.0- 12000.0.

12000.0- 13000.0... _

13000.0- 14000. 0....... .

14000.0- 15000. 0.........

15000.0- 20000.0-

20000.0- 25000.0... _ .

25000.0- 30000. 0...__ _

30000.0- 40000.0-

40000.0- 50000.0. _

50000.0- 60000.0.. .__..

60000.0- 70000.0... __....

70000. 0- 80000. 0 .

80000.0- 90000.0.. ..

90000.0- 100000.0........

100000.0- 150000.0........

150000. 0- 200000. 0

200000. 0- 250000. 0.. .

250000.0- 300000.0. ____..

300000.0- 400000.0........

400000. 0- 500000. 0 . .

500000.0- 600000.0.. __...

600000.0- 700000. 0........

700000.0- 800000.0.. ..

800000.0- 900000. 0........

900000.0-1000000.0-

Total... ...........

Average of discharges within

range listed in

column 1, in cubic

feet per second

78.2

146. 0

243. 5

378. 2

622. 4

861. 6

1256. 3

1718. 7

2511. 5

3464. 2

4478. 9

5478. 2

6507. 4

7486. 9

8490. 5

9496. 3

10452. 6

11461. 5

12360. 6

13380. 0

14346. 4

17406. 7

22135. 1

26837. 2

34716. 2

43915. 2

54757. 1

65317. 4

72438. 4

83707. 1

94130. 8

119473. 6

184250. 0

206500. 0

261000. 0

311000. 0

521000. 0

648000. 0

Average suspendedsediment discharge,

() in tons per day,

corresponding to

value of <?«, in column 2

0.52

0.94

2.14

5.82

11.23

35.95

54.25

111.60

241.29

793.04

1621. 74

2772. 40

4969. 24

5855. 47

8170. 84

14156. 20

14736. 31

20726. 73

25039. 09

26781. 66

32095. 36

51303. 33

80425. 62

126637. 19

199858. 06

295276. 06

447514. 25

495434. 75

615384. 56

906428. 56

1273538. 00

1904052. 00

6262500. 00

3540000. 00

5995000. 00

19000000.00

40000000. 00

57000000. 00

Number of days 

during period of

record when Q w

within range

listed in

column 1

0

104

759

243

192

141

102

187

164

282

200

174

121

92

95

59

71

38

52

33

30

28

120

74

43

74

46

35

23

13

14

13

19

4

2

2

1

0

1

1

0

0

0

3.652

Percent of

time Qw

equaled or

exceeded

100. 00

100.00

97.15

76.37

69.72

64.46

60.60

57.80

52.68

48.19

40.47

34.99

30.23

26.92

24.40

21.80

20.18

18.24

17.20

15.77

14.87

14.05

13.28

9.99

7.97

6.79

4.76

3.50

2.55

1.92

1.56

1.18

0.82

0.30

0.19

0.14

0.08

0.05

0.05

0.03

0.0

0.0

0.0
SEDIMENT IN THE EEL RIVER BASIN, CALIFORNIA 25 

FLOOD OF DECEMBER 1964

In December 1964, rainfall of historically unprecedented intensity 

coupled with conditions favorable for heavy runoff produced record 

flooding in the Eel River basin, as well as in a large area of the Western 

United States (Rantz and Moore, 1965). Rainfall which in places 

exceeded 20 inches in a 48-hour period produced runoff that sent 

river stages 5-15 feet above previous record stages and caused severe 

damage in river valleys in all parts of the Eel River basin. Highvelocity flow and high stages accelerated erosional processes so much 

that an enormous volume of soil and rock was stripped from the 

land and deposited downstream or carried to the sea.

Bank slumping, landslides, and channel scouring in upstream reaches 

contributed a record sediment load to streams throughout the basin, 

and the downstream deposition of this material added to the damage 

caused by the rampaging waters. Sediment and debris clogged bridges 

and culverts, forcing floodwater to overtop the structures or to seek 

alternative channels. In the flood plains and other areas of the lower 

valleys where the flow velocity decreased, sediment commonly was deposited to depths of several feet. Houses, stores, and automobiles 

abandoned before the rising waters were left filled with sediment and 

debris when the water receded (figs. 8 and 9).

The quantity and distribution of material transported during the 

course of the flood are best determined from the suspended-sediment 

discharge measurements made at gaging stations at that time. That 

ideal could not be realized at various stations during the 1964 flood. 

At every station for which sediment records were available or could 

be calculated, the volume of suspended sediment and the rate at which 

it moved exceeded all previous records. For example, a suspendedsediment discharge of 116 million tons was computed for Eel River 

at Scotia for a 3-day period beginning December 22, 1964. The total 

suspended-sediment load at this station for the previous 8 years 

amounted to 94 million tons.

Erosion was most severe in the eastern section of the Eel River 

basin where the North and Middle Forks of the Eel River were fed 

by runoff from the steep westward-facing slopes. These slopes, saturated by antecedent precipitation and somewhat unstable even under 

normal conditions, were badly eroded by landslides, slumps, and 

gullying in areas of sparse vegetal cover. Material derived from 

this type of erosion, added to the contributions from banks and channels, provided the sediment load for the steeply sloping tributaries 

of these two rivers.

Farther downstream in the vicinity of the confluence of the Middle 

Fork Eel and Black Butte Rivers, enough sediment was deposited
26 SEDIMENT IN THE EEL RIVER BASIN, CALIFORNIA

FIGURE 8. Remains of the devasted town of Pepperwood on the Eel River 

upstream from Scotia, Feb. 5, 1965. Pepperwood was destroyed by flooding 

during December 1955. It was subsequently rebuilt, only to be destroyed again 

by the flood of December 1964.
FLOOD OF DECEMBER 1|964 27

FIGURE 9. House engulfed by landslide associated with the December 1964 flood 

near the South Fork Eel River about 15 miles downstream from Garberville. 

A small stream is flowing over the top of a fence which once bridged the 

stream near where the man is standing.

as a result of the flood to raise the streambeds 6-8 feet (Hickey, 

1968, p. E8). Hickey noted that in this area, channel fill continued 

during the following water year, probably as a result of continued 

erosion of material brought into upstream reaches during the 1964 

flood period.

On the upper main stem of the Eel, 2 feet of sediment was deposited 

just above the confluence with the Middle Fork. Sediment transport 

and deposition from this point upstream is partly influenced by the 

operations of Lake Pillsbury and Van Arsdale Reservoir.

During the period December 21-30, 1964, the suspended-sediment 

discharge computed for Eel River at Scotia was about 145 million 

tons. A suspended-sediment load of about ?!/£> million tons was computed during this same period at Eel River above Dos Rios compared 

with a load of approximately 8^ million tons at Middle Fork Eel 

River near Dos Rios. Although measurements of sediment discharge 

for the flood period are not available for points along the Eel River 

between Dos Rios and Scotia, the difference between sediment discharges computed at these two points equals the suspended-sediment 

yield for the central part of the basin less material deposited along 

the channel. If the sediment discharge of the South Fork is taken to 

be approximately 19 million tons, the computed value for the sediment 

load derived from the central part of the basin and the North Fork

427-150 O - 71 - 5
28 SEDIMENT IN THE EE1. RIVER BASEST, CALIFORNIA

drainage is 110 million tons, or 76 percent of the sediment load at 

Scotia. The sediment load estimated for the South Fork Eel River was 

taken as 13 percent of the load computed at Scotia on the basis of 

relations between past records at the two stations; however, the accuracy of this value is of minor significance in this particular example. 

The large sediment yield between Dos Rios and Scotia emphasizes the 

need for additional sediment data from along this reach.

EEL RIVER AT SCOTIA

Sediment studies began at Eel River at Scotia in September 1955. 

Periodic observations were made during the 1956 and 1957 water 

years, and a program of daily sampling was begun in October 1957. 

Suspended-sediment measurements are made from the bridge on U.S. 

Highway 101, 0.5 mile north of Scotia and 6 miles upstream from the 

mouth of the Van Duzen River. The Eel River channel along this 

reach is straight for a distance of 1,000 feet above and 1,000 feet below the bridge and has steep wooded banks which are not subject to 

overflow. The channel is fairly stable and the annual changes in 

streambed elevation are minor. The streambed is a shallow layer of 

gravel resting on bedrock, and the bottom topography generally 

consists of shifting gravel bars and exposed bedrock. Bank slumping 

occurs at higher stages of flow (fig. 10).

FIGTJEE 10. Two views (above and facing page) of the left bank of the Eel River 

just upstream from the Scotia gage, Feb. 5, 1965. A fallen tree, undermined 

by erosion during the December 1964 flood, rests on a shelf at the transition 

from alluvial material to bedrock. Flow in picture above is from left to right
EEL RIVER AT SCOTIA 29
30 SEDIMENT IN THE EEL RIVER BASIN, CALIFORNIA

During the 10-year period of daily sediment record, large variations 

in both runoff and sediment discharge occurred at the Scotia station. 

Precipitation and runoff were greatest during the 1958 water year 

when the total runoff was the highest for the 55-year period of record 

for the station. A large number of rainy days resulted from storms 

occurring during each month from October through April, and days 

of high sediment transport were more evenly distributed than in the 

following 9 years. Runoff was lowest in the 1964 water year, and high 

flows occurred only in November and January. Annual discharges 

within 15 percent of the mean annual flow at Scotia were measured 

during 3 of the 10 years of sediment record.

Suspended-sediment discharge of Eel Eiver at Scotia was 313,900,000 

tons from October 1957 through September 1967. Maximum yearly discharge was 167,800,000 tons for the 1965 water year, and the minimum 

yearly discharge was 4,758,000 tons during the 1962 water year. The 

monthly maximum suspended-sediment load was 145,700,000 tons in 

December 1964, and the minimum was 12.3 tons in October 1958. The. 

maximum daily load was an estimated 57 million tons on December 23, 

1964, and minimum discharge of less than 0.5 ton per day was 

measured nearly every year during September and October.

The relation between water discharge and suspended-sediment discharge for Eel Eiver at Scotia is shown in figure 11. This curve 

represents the 10-year period of sediment record at this station and 

is biased by the record sediment discharges observed during the 1965 

water year. The points through which the curve is drawn are plotted 

from the data sfiown in table 6.

To demonstrate the effect of the December 1964 flood on the relation 

between water discharge and suspended-sediment discharge at Scotia, 

similar computations were made for the preflood and postflood data, 

an the resulting curves are shown in figure 12. These data must be 

supplemented by additional data from the years following 1967 in 

order that apparent trends may be established as conclusive; however, 

the curves of figure 12 indicate at least a temporary change in trend. 

A similar change may have been associated with the large-scale 

flooding of 1955; however, this cannot be substantiated. Sufficient information is not available to determine the duration of these effects; 

thus, it is not known if the 1965-67 trend will persist for more than 

a short period.

The seasonal variability of sediment yield for the Eel River at 

Scotia and other stations is illustrated by figure 13. In every year, 

increased sediment yield is an immediate result of winter storms, and 

the greater part of the total annual load is moved during the days of 

maximum runoff in these storm periods. The effects of snowmelt,
EEL RIVER AT SCOTIA 31

100,000,000

10,000,000

1,000,000

100,000

10,000

1000

1000 10.000 100,000 1,000,000

AVERAGE DAILY WATER DISCHARGE, 

IN CUBIC FEET PER SECOND

FIGUBE 11. Sediment-transport curve for Eel River at Scotia, 

October 1957-September 1967.

frozen ground, and runoff from ground-water inflow are usually 

insignificant in the movement of sediment during periods between 

storms. Sediment transport during the summer months is negligible. 

Figure 14 indicates an approximate relation between yearly water 

discharge and sediment load. Because the relation between sediment 

discharge and streamflow is not constant throughout the year, the 

use of this curve for estimating periods shorter than a year would 

be misleading. The data are so scattered that even the estimation of 

annual sediment discharges is questionable, and several additional data 

points will be needed to define a more usable curve. Estimates or 

interpolation of sediment discharge may be done more accurately 

on a daily basis using the curves of figure 12.
32 SEDIMENT IN THE EEL RIVER BASIN, CALIFORNIA

100,000,000

c/5 10.000.000

1,000,000

100,000

10,000

1000

1000 10.000 100,000 1,000,000

AVERAGE DAILY WATER DISCHARGE, 

IN CUBIC FEET PER SECOND

FIGURE 12. Sediment-transport curves for Eel River at Scotia, 

showing the change in sediment-transport characteristics 

after the December 1964 flood.

The variation in particle-size distribution with water discharge 

for sediment carried as suspended load is shown in figure 15. The 

scatter of the data points renders the graph somewhat inconclusive; 

however, certain properties of the relations shown are noteworthy. 

The most obvious characteristic of the graph is the change in the 

amount of coarser material transported before and after the December 

1964 flood at discharges above 40,000 cfs. Apparently, about 10 percent more sand and silt was carried in suspension in the period after 

the flood than in the period preceding it. The graph also shows that as 

much as 50 percent of the suspended load has been of sand size, a size
EEL RIVER AT SCOTIA 33

FIGURE 13. Comparison of suspended-sediment loads of six streams in the Eel 

River basin, showing typical seasonal variation in sediment discharge, 

October 1966-September 1967.

that is usually a part of the bed material. Coarse material transported 

is primarily a function of flow and the availability of coarse material. Hence, the curves indicate that the quantity of coarse material 

available for transport increased during and after the 1965 water 

year.

Long-term average suspended-sediment discharges at Scotia were 

computed by combining the flow-duration characteristics of 

the water discharge for a long period of streamflow record with 

sediment-discharge figures taken from appropriate sedimenttransport curves, according to procedures discussed by Colby (1956, 

p. 24). Using the curve of figure 11, the computed average suspendedsediment discharge was 23 million tons per year for the period of 

streamflow record 1911-14 and 1917-67 water years. Using the
34 SEDIMENT IN THE EEL RIVER BASEST, CALIFORNIA

300

100

Q 10

UJ 

Q

1 10 30 

WATER DISCHARGE, IN MILLIONS OF ACRE-FEET

FIGUKE 14. Relation of streamflow to suspended-sediment 

discharge by water years, Bel River at Scotia.

sediment-transport curve shown in figure 12 for the preflood period, 

an average suspended-sediment discharge of 13 million tons per year 

was computed for the 1911-14 and 1917-64: water years.

Suspended-sediment yield for the basin above Scotia was 10,080 

tons per square mile per year for the 1958-67 water years, and the 

yield for the preflood period, 1958-64, was 4,330 tons per square mile 

per year. The lower figure very nearly represents the long-term yield, 

which is based on preflood sediment records, and is highly significant 

even though it is considerably less than the flood-affected higher 

value. It must be emphasized that preflood sediment discharges and 

yields were many times greater than those for similar basins throughout the United States (Judson and Bitter, 1964). The flood effects 

only increased formerly excessive values.1

1 Preflood yields for other stations where data are available may be computed from 

figures given in table 8.
EEL RIVER AT SCOTlX 35

400,000

100.000

10.000

7000

j;- >x Silt

0.004-0.062 mm

20 40 60 80 

PERCENTAGE OF PARTICLES FINER THAN INDICATED SIZE

100

FIGURE 15. Particle size versus water discharge, Eel River at Scotia, 1968-66.

A comparison of the sediment yield of the Eel River with other 

rivers of the world is shown in table 7. The figure of 10,000 tons per 

square mile per year for the Eel River is computed only for the period 

of sediment record at Eel River at Scotia. The validity of this comparison is somewhat questionable because of short periods of record 

and differences in methods of sampling; however, the general magnitude of the average annual suspended load figures is indicative of the 

extremely high sediment production of the Eel River basin.
36 SEDIMENT IN THE EEL RIVER BASIN, CALIFORNIA

TABLE 7. Suspended-sediment yields of selected rivers of the world 

[Holeman (1968)]

River and location

Ching Changchiashan, China. . . .

Eel California, U.S.A...... .......

Yellow Shenhsien, China. ....... __

Ganges delta East Pakistan. _ ......

Colorado Arizona, U.S.A _ ............

Brazos Texas, U.S.A. ...................

Arno San Giovanni Alia Vena, Italy _ .

Pecos New Mexico. U.S.A...... ...........

Mississippi Louisiana, U.S.A........ ......

Nile Egypt............................... .

Drainage 

area 

(sqmi)

....... 22,000

....... 2,040

....... 3.113

....... 276,000

....... 409,200

--.-. 137,800

....... 34,800

..... .. 3,160

....... 3,970

....... 1,244,000

....... 1,150,000

Average 

annual 

suspended 

load (tons 

per sq mi)

20,500

11,844 .

110,000

7,545

4,000

1,082

1,000

770 .

685

277

100

Average 

water 

discharge 

at mouth 

(105 cfs)

2

7

53

498

5.5

5.2

.6

630

100

Period 

of 

sediment 

record

1932-45

1961-63

1 1957-67

1934-42

1874-79

1925-57

1924-50

1936-42

1954-64 

1948-57

1951-65

1958-64

1 Figures from this report; not shown by Holeman (1968).

MIDDLE FORK EEL RIVER NEAR DOS RIOS

Sediment studies began at Middle Fork Eel Eiver near Dos Kios 

in January 1956 with periodic sampling which continued through 

September 1957. Daily sampling was started in October of the 1958 

water year and has been continued since that time.

Sediment samples are taken at the highway bridge approximately 

0.5 mile upstream from the mouth of the Middle Fork. The stream 

channel at this point has steep rocky banks and a gravel bed. The 

channel curves slightly just upstream from the bridge, and is straight 

for about 1,500 feet downstream of that point. The stream flows in 

one channel at most stages, and the steep banks are not subject to 

overflow. 'Streamflow at higher stages is characterized by high velocities and standing waves. The channel is somewhat contracted in the 

vicinity of the bridge, and flood stages are so high that streambed 

elevation changes are small relative to the depth of water. High water 

during the December 1964 flood reached the base of the bridge, about 

68 feet above the streambed at that time. The streambed material that 

moves past the sediment-sampling site ranges from sand to cobbles 

with varying types of flow. Bank slumping is minimal in the vicinity 

of the bridge, and the channel geometry has remained basically unchanged over the past several years.

Runoff of the Middle Fork near Dos Rlos prior to the 1966 water 

year was computed as the difference in runoff between stations on the 

Eel River downstream and upstream of the mouth of the Middle 

Fork. However, a streamflow gaging station was established on the 

Middle Fork in August 1965, and the runoff has been determined at 

the gage since that time. Total runoff since sediment studies began in
MIDDLE FORK EEL RIVER NEAR DOS RIOS 37

1957 has been about 13,620,000 acre-feet with a corresponding suspended-sediment load of 42,450,000 tons. Both the maximum annual 

water discharge and the maximum annual suspended-sediment discharge occurred in the 1965 water year when a load of 18,700,000 tons 

was moved past the gaging site by a flow of 2,768,000 acre-feet.

A sediment-transport curve for Middle Fork Eel Kiver near Dos 

Bios is shown in figure 16. The curve represents 10 years of sediment 

data, and restrictions on its application are similar to those discussed 

for Eel Kiver at Scotia. The data used to define this curve are taken 

from unpublished records of the U.S. Geological Survey. Figure 17 

illustrates the change in the sediment-transport relation at the station 

due to the effects of the December 1964 flood.

10,000,000

1,000,000

100,000

10,000

1000

100

v/

1000 10,000 100,000 1,000,000

AVERAGE DAILY WATER DISCHARGE, 

IN CUBIC FEET PER SECOND

FIGURE 16. Sediment-transport curve for Middle Fork Eel River near Dos Bios, 

October 1957-September 1967.
38 SEDIMENT IN THE EEL RIVER BASEST, CALIFORNIA

10,000,000

1,000,000

100.000

10,000

1000

100

1000 10,000 100,000 1,000,000

AVERAGE DAILY WATER DISCHARGE, 

IN CUBIC FEET PER SECOND

FIGURE 17. Sediment-transport curves for Middle Fork Eel River near Dos 

Bios, showing the change in sediment-transport characteristics after the 

December 1964 flood.

Kesults of particle-size analyses of samples taken at Middle Fork 

Eel River near Dos Kios are plotted in figure 18. Two points are 

plotted for each sample taken to show the breakdown of percentages 

of sand, silt, and clay carried in suspension at different discharges, 

The two points chosen define the break in each sample between sand 

and silt and between silt and clay. The lines on this and subsequent 

particle-size plots in this report serve only to define general boundaries 

and indicate possible trends. At Middle Fork Eel Kiver near Dos 

Kios, the particle-size distribution is similar for most values of water 

discharge, and there was no apparent change in the distribution after 

the flood of December 1964.
MIDDLE FORK EEL RIVER NEAR DOS RIOS 39

100,000

EXPLANATION

October 1957-November 1964 

December 1964-September 1967

Clay-silt Silt-sand 

break break

y 10,000

CD

Z3 

O

1000

O 

o ooo,

Clay § 

<0.004 mm o o

o

Silt 

0.004-0.062 mm

20 40 60 80 

PERCENTAGE OF PARTICLES FINER THAN INDICATED SIZE

100

FIGURE 18. Particle size versus water discharge, Middle Fork Eel River near 

Dos Bios, 1958-67. Prior to October 1965 the water discharge was estimated 

by the method described on page 36.
40 SEDIMENT IN THE EEL RIVER BASEST, CALIFORNIA

MIDDLE FORK EEL RIVER BELOW BLACK BUTTE RIVER

Upstream from Middle Fork Eel River near Dos Rios, daily sediment sampling was carried on for a 5-year period just below the 

confluence of the Middle Fork Eel and Black Butte Rivers. Sampling 

was begun in October 1962 and discontinued on September 30, 1967. 

The station was destroyed in the December 1964 flood, then replaced, 

and again destroyed by a flood in January 1967. No suitable site was 

found to replace the station below the Black Butte River after the 

1967 event, and the station was relocated above the Black Butte River. 

The nature of records obtained at the new station after relocation is, 

of course, not equivalent to the nature of records from the previous 

location. Although the available data do not cover an extensive time 

period, they are of high value when viewed in connection with the 

general runoff patterns of the Middle Fork basin and the data obtained 

from studies near Dos Rios.

The stream channel of the Middle Fork below the Black Butte 

River has a shifting gravel bed and steep banks lined with boulders 

and brush. The stream has one channel at high stages and two at low 

stages. At high stages, standing waves form in the swift flow. Lowwater streambed elevations remained fairly constant for the 10 years 

preceding the December 1964 flood, but considerable deposition has 

taken place since that time (figs. 19 and 20).

Extreme flows of 89,100 and 132,000 cfs occurred in December 1955 

and December 1964, respectively. Daily suspended-sediment loads 

ranged from negligible traces on many days throughout the period 

of record to an estimated maximum of 21/£ million tons on December 22, 

1964. The smallest and largest annual loads were recorded in consecutive years. In the 1964 water year 105,300 tons of suspended sediment was discharged, whereas 10,100,000 tons was discharged during 

the 1965 water year.

Sediment discharge per square mile of drainage area is higher at 

this station than at any other station in the Eel River basin except 

Eel River at Scotia. An average rate of more than 8,000 tons per square 

mile of suspended-sediment discharge has been computed for the upper 

Middle Fork Eel River drainage basin for the 5-year period beginning 

October 1963. Storm runoff transports most of this load; 50 percent 

of the suspended load is transported during an average of 4 days per 

year. The sediment-transport curve for Middle Fork Eel River below 

Black Butte River is shown in figure 21, and the relation between 

particle size and water discharge is shown in figure 22.
MIDDLE FORK EEL RIVER BELOW BLACK BUTTE RIVER 41

15

o 10

<

o

1955

I I

Gage datum = 

1450ft above 

mean sea 

level

1960 1965

YEAR

Black Butte River 

near Covelo, Calif

1970

20

15

10

r~

Gage datum = 

950ft above 

mean sea 

level

1950 1955 1960 1965 1970

YEAR

Eel River above 

Dos Rios, Calif.

2°

10

Gage datum = 

1434ft above 

mean sea 

level

 

1955 1960 1965 1970

YEAR

Middle Fork Eel River 

below Black Butte 

River, near Covelo, 

Calif.

20

15

10

0

 I

Gage datum = 

800 ft above 

mean sea 

level

1950 1955 1960 1965 1970

YEAR

Eel River below 

Dos Rios. Calif.

FIGURE 19. Changes in low-water streambed elevation, by year, at four stations 

in the Eel River basin. From Hiekey (1968).
42 SEDIMENT IN THE EEL RIVER BASEST, CALIFORNIA

25

20

15

10

LJ 0

i i r i i i i i

January 3. 1966 _

\Februaryl.l963 .. 

 -v."~--V 

I I I

0 20 40 60 80 100 120 140 160 180 200 220 240

CHANNEL WIDTH, IN FEET 

Black Butte River near Covelo, Calif.

20

15

10

0 25 50 75 100 125 150 175 200 225 250 275 300

CHANNEL WIDTH, IN FEET

Middle Fork Eel River below Black Butte River near 

Covelo, Calif.

FIGURE 20. Cross sections at selected gaging stations in the Bel River basin, 

showing changes attributable to record-high flows during the 1965 water 

year. From Hickey (1968).
MIDDLE FORK EEL RIVER BELOW BLACK BUTTE RIVER

10,000,000

43

1,000,000

100,000

10,000

1000

100

1000 10,000 100,000 1,000,000

AVERAGE DAILY WATER DISCHARGE, 

IN CUBIC FEET PER SECOND

FIGURE 21. Sediment-transport curve for Middle Fork Eel 

River below Black Butte River, near Covelo, 1963-67 water 

years.
44 SEDIMENT IN THE EEL RIVER BASIN, CALIFORNIA

EXPLANATION

Clay-silt Silt-sand 

break break

October 1962-November 1964 

December 1964-January 1967 o

100,000

1000

Clay -0.004 mm

Silt 0.004-0.062 mm

Sand >0.062 mm

-e-

-e20 40 60 80 

PERCENTAGE OF PARTICLES FINER THAN INDICATED SIZE

100

FIGURE 22. Particle size versus water discharge, Middle Fork Eel River below 

Black Butte River, near Covelo, 1963-67 water years.
SEDIMENT IN THE EEL RIVER BASIN, CALIFORNIA 45 

BLACK BUTTE RIVER

Sediment studies in the Black Butte Kiver basin are based on suspended-sediment samples collected daily from November to April of 

the 1966 water year and December to September of the 1967 water 

year. During these periods, daily measurements of suspended load were 

made at the gaging station 0.5 mile upstream from the confluence of 

the Black Butte and Middle Fork Eel Kivers. Because of the short 

sampling period, only *a limited amount of information is available 

from which to evaluate fluvial sediment characteristics. However, information from other sources, together with interstation correlation 

and field observations, offers alternatives in evaluating the basin 

sediment yield.

The channel of the Black Butte River in the vicinity of the gaging 

station is straight, and has steep sparsely wooded banks and a gravel 

bed. For the 2-year period of suspended-sediment observations, sediment deposition has occurred in this section. During the December 

1964 flood, the channel bed aggraded approximately 8 feet (fig. 19), 

and deposition occurred subsequently as material deposited upstream 

in 1964 was transported downstream by high water in the 1966 and 

1967 water years (Hickey, 1968). Deposition of this type is not likely 

to continue indefinitely; however, the time necessary for the stream 

to readjust itself to a configuration consistent with the changes which 

resulted from the flood is unknown.

The general relation between water discharge and suspended-sediment discharge is shown in figure 23 and can be considered representative only of the short term from which the data are taken. Extension of these data over past or projected flows presents many uncertainties because of the presently changing channel conditions. The 

relation between particle size and water discharge (fig. 24) shows 

a pattern similar to other stations in the Middle Fork Eel River basin; 

however, the number of samples is insufficient to show more than a 

comparison with other stations.

Runoff in the Black Butte River basin ranged from a minimum of 1.2 

cfs in September 1959 to a maximum of 29,000 cfs in December 1964, 

during a 9-year period of record beginning in October 1956. Total 

runoff for the period of sediment record was 473,800 acre-feet, and 

the corresponding sediment discharge was calculated to be 1,405,000 

tons. Maximum monthly suspended-sediment discharge was 496,200 

tons in January 1967, and the maximum daily suspended-sediment 

discharge was 143,000 tons on January 4, 1966. Minimum loads of 

less than 0.1 ton were measured for many days during the summer 

months in 1967.
46 SEDIMENT IN THE EEL RIVER BASIN, CALIFORNIA

1.000,000

co 100,000

10,000

1000

100

100 1000 10,000

AVERAGE DAILY WATER DISCHARGE, 

IN CUBIC FEET PER SECOND

FIGURE 23. Sediment-transport curve for Black Butte River 

near Covelo, November 1965-April 1966 and December 

1966-September 1967.

Fluvial sediment in the Black Butte River basin is derived primarily 

from a large area of landslides covering the eastern slopes of the basin 

(fig. 3). Although the sediment removed from this slide region is not 

measured directly, observations of the mechanisms by which it moves 

show that large volumes of soil and rock will enter the stream channel 

under the influence of bank cutting by the stream. The already precarious stability of an earthflow is readily disturbed as the lower supporting material is removed, and residual uphill material becomes 

immediately susceptible to downslope movement (fig. 25).
2, N o »

DISCHARGE, IN CUBIC FEET PER SECOND

TJ >

33 >

(6 &1. (8 | *

M W

w
48 SEDIMENT IN THE EEL RIVER BASIN, CALIFORNIA.

FIGURE 25. Mass wasting adjacent to stream, typical of many locations in the 

Eel River basin. Comparative photographs show slide activity along the Middle 

Fork Eel River. Top, Photograph taken Apr. 23, 1968. Recent and older landsliding along the Middle Fork Eel River above the mouth of the Black Butte 

River. Note gullying along the older slide (at right) and the seeps at the bases 

of both, slides. Bottom, Photograph taken Apr. 30, 1969. Slide in left of picture 

has moved several feet, toppling a tree (indicated by arrow in each photograph) which was undisturbed the previous year. Note the crack in the older 

slide which does not appear in the earlier picture.
SEDIMENT IN THE EEL RIVER BASIN, CALIFORNIA 49 

EEL RIVER AT FORT SEWARD

A sediment station was established on the Eel Kiver at Fort Seward 

in October 1965. Sediment samples have been collected daily at the 

highway bridge about 0.25 mile east of Fort Seward since that time. 

Information about the nature of fluvial sediment at this station is 

minimal because of the short period of sampling; however, sediment 

studies at this station do give some indication of the contribution of 

sediment of that part of the basin between Dos Kios and Scotia. 

Because of the magnitude of the sediment yield in this area, future 

sediment programs should emphasize the reach of the Eel River 

between Dos Rios and Scotia.

Varying proportions of sand and gravel make up the streambed 

at the gaging site. The river banks are steep and rocky and not subject 

to overflow. The flow is in one channel at all stages, and at higher 

stages the flow is swift and turbulent. At a gage height of approximately 30 feet, the flow begins to override a sharp bend in the river 

about 600 feet upstream of the gage and approaches the bridge at a 

slight angle.

Suspended-sediment discharge was 29,210,000 tons during the 2-year 

period of record at Fort Seward, and this discharge was about 56 

percent of that recorded during the same period at Scotia. The South 

Fork Eel River annually contributes about 13 percent of the sediment 

discharge at Scotia (table 9) ; thus, the South Fork and the Eel River 

above Fort Seward had a combined suspended-sediment discharge 

which was about 69 percent of that at Scotia. The remaining drainage 

area below Fort Seward and above Scotia excluding the South Fork 

apparently contributed about 31 percent of the discharge at Scotia 

during the 2-year period, or about 17,000 tons per square mile per 

year from a 35-mile stretch of river draining 469 square miles. Similarly, the suspended-sediment yield between Dos Rios and Fort 

Seward, a reach draining 657 square miles, was about 15,000 tons per 

square mile per year. These yields are about twice the yield of the 

entire basin above Scotia during this period. This again emphasizes 

the importance of sediment studies in the drainage area between Dos 

Rios and Scotia, which includes the North Fork Eel River and 

Larabee Creek drainages.

A sediment-transport curve for a 2-year period of sediment record 

at Eel River at Fort Seward is shown in figure 26. The variation in 

particle-size distribution with flow is shown by figure 27.
50 SEDIMENT IN THE EEL RIVER BASIN, CALIFORNIA

10,000,000

1,000,000

100,000

10,000

1000

100

1000 10.000 100,000 1,000,000

AVERAGE DAILY WATER DISCHARGE, 

IN CUBIC FEET PER SECOND

FIGURE 26. Sediment-transport curve for Eel River at Fort 

Seward, 1966-67 water years.
EEL RIVER AT FORT SEWARD 51

200,000

100,000

Q 10.000

2000

Silt 

0.004-0 062 mm

EXPLANATION

Silt-sand 

break

1966 water year

1967 water year

0 20 40 60 80

PERCENTAGE OF PARTICLES FINER THAN INDICATED SIZE

100

FIGURE 27. Particle size versus water discharge, Eel River at Fork Seward.

1966-67 water years.
52 SEDIMENT IN THE EEL RIVER BASIN, CALIFORNIA 

SOUTH FORK EEL RIVER

Sediment studies along the South Fork Eel Eiver are based primarily on data collected at samplings stations near Branscomb and 

Miranda. Periodic sediment sampling was begun at South Fork Eel 

River near Miranda in October 1955 and continued through September 1962. South Fork Eel Eiver near Branscomb was sampled periodically from August 1957 until a daily sampling program began in 

October 1962. Daily sediment sampling has been continuous at the 

Branscomb station since that time.

The channel bed at South Fork Eel Kiver near Miranda is composed 

of gravel. The left bank of the river is wooded, and is fairly stable 

at all stages. The right bank is sandy up to medium stages and wooded 

at high stages, and the river overflows the right bank at a gage height 

of about 30 feet. The channel is straight for a distance of 600 feet 

upstream and 600 feet downstream from the measuring cableway, 

and flow in the channel is swift at high stages.

Computations by Hawley and Jones (1969, p. 13) from the periodic 

records collected at the Miranda station indicate that sediment discharge from October 1957 through September 1962 was 8,870,000 

tons, or about 13 percent of the suspended-sediment discharge measured downstream at Scotia during the same period. The maximum 

annual load was 3,900,000 tons, which accompanied a water discharge 

of 2,444,000 acre-feet in the 1958 water year. Sediment data are not 

available subsequent to September 1962; thus, the effect of the December 1964 flood on the sediment transport at the Miranda station is 

unmeasured.

Upstream, at South Fork Eel Kiver near Branscomb, the streambed 

consists of gravel and bedrock, and the channel has steep banks covered 

with undergrowth. The flow is confined to one channel at all stages.

Hawley and Jones (1969, p. 13) computed a sediment discharge of 

446,000 tons at the Branscomb station for the 5-year period beginning 

October 1957. Suspended-sediment discharge from October 1962 

through September 1967 was 800,700 tons, of which 502,800 tons was 

measured during the 1965 water year. Average runoff over the 10-year 

period was 125,200 acre-feet per year, and the maximum annual runoff was 219,200 acre-feet in the 1958 water year. The patterns of runoff 

and sediment discharge at the Branscomb station are similar to the 

patterns observed elsewhere in the basin. Maximum annual suspended-sediment discharge did not accompany the maximum annual 

water discharge which occurred in 1958, and the 1966 and 1967 water 

years exhibited comparatively high sediment discharges because of continuing adjustments of the stream to the December 1964 flood effects.
^ 

g AVERAGE DAILY SUSPENDED-SEDIMENT DISC

^ 

t

1

g s

3 c

" f

1 

0 ~ 

f. >- o 

w '-' ° o 

,-0 0 0 

c °

> 1

(T K98 g

>-S (D >

w g. <

^ P o 

o P ( mo

o ^ "

O' * 

M

3 ro 0 S

"" ^ < m ^

5O o m «=

05 a H §

CO h1 >

1 < Tl H

O5 CD mm 1 3D 3D

^ o" co o o

1" 80 § 

>-s 02 " i °

3 § °5

^5 ^

yi

? o r m

O

W o 

o

.

^^^ 

^"^^

^\^

"^
54 SEDIMENT IN THE EEL RIVER BASIN, CALIFORNIA

60,000

CL

uJ 10,000

1000

Sand 

-0.062 mm

Silt 

0.004-0.062 mm

20 40 60 80 

PERCENTAGE OF PARTICLES FINER THAN INDICATED SIZE

100

FIGURE 29. Particle size versus water discharge, South Fork Bel River near 

Miranda, 1958-62 water years.
SOUTH FORK EEL RIVER 55

EXPLANATION

October 1962-November 1964 

December 1964-September 1967

Clay-silt Silt-sand

break break

o -e20,000

10,000

1000

200

Silt 

0.004-0.062 mm

Sand 

>0.062 mm

20 40 60 80 100 

PERCENTAGE OF PARTICLES FINER THAN INDICATED SIZE

FIGURE 30. Particle size versus water discharge, South Fork Eel River near 

Branscomb, 1963-67 water years.
56 SEDIMENT IN THE EEL RIVER BASEST, CALIFORNIA

QUANTITY AND DISTRIBUTION OF FLUVIAL SEDIMENT

The suspended-sediment discharge determined at Eel Eiver at Scotia 

was 313,900,000 tons for the 10-year period beginning October 1957. 

By use of this figure and the data presented in table 8, the quantity 

and distribution of suspended-sediment discharge throughout the basin 

may be computed. A lack of data concurrent with the 10-year record 

at Scotia precludes an exact analysis of sediment sources in some areas 

of the basin; however, reasonable estimates and computations can be 

made where significant trends exist in the concurrent records of shorter 

periods.

The Middle Fork Eel Eiver, which drains 24 percent of the Eel 

Eiver basin above Scotia, discharged 'about 42 million tons, or 13.4 percent, of the suspended load at Scotia during the 10-year period of 

record. The suspended-sediment discharges of other subunits of the 

Eel Eiver basin were not determined for a comparable period; thus, an 

approximation of the yields of these basins must be made by using the 

average percentages shown in the last column in table 9. On this basis, 

the Eel Eiver above its confluence with the Middle Fork Eel Eiver contributes about 6 percent of the annual suspended load at Scotia, 

although sedimentation along the upper Eel Eiver is influenced by 

Lake Pillsbury, Van Arsdale Eeservoir, and the diversion of water 

into Potter Valley. Thus, the suspended sediment derived from the 

upper Eel Eiver was about 19 million tons during the period cited 

above.

The South Fork Eel Eiver drains 17 percent of the basin above 

Scotia, and the suspended-sediment discharge of the South Fork 

constituted 13 percent of the discharge at Scotia from the 1958 water 

year through the 1962 water year. Projection of the 13 percent figure 

through the 1967 water year would show that the suspended sediment 

carried by the South Fork was about the same as that of the Middle 

Fork for the 10-year period. Data from South Fork Eel Eiver near 

Branscomb do not show a significant change in the percentage of suspended sediment delivered downstream to Scotia in the 5 years following the discontinuation of sampling at South Fork Eel Eiver 

near Miranda. Thus, a reasonable estimate of the suspended-sediment 

discharge of the South Fork Eel Eiver is about 13 percent of the discharge at Scotia, which is 41 million tons for the 10-year period beginning October 1957, or about 7,600 tons per square mile per year. 

This figure is consistent with the figures derived for stations in the 

basin where preflood sediment yields were considerably less than 

the 10-year 'average sediment yield which included the 1964-65 flood 

period. For example, the average sediment yield at Middle Fork
QUANTITY AND DISTRIBUTION OF FLUVIAL SEDIMENT 57

TABLE 8. Summary of suspended-sediment and water discharge in the Eel River 

basin, October 1957-September 1967

Water 

Water year discharge 

(acre-feet)

Suspended- Suspended- Days per year 

sediment sediment required for 

discharge, yield (tons transport of - 

Q, (tons) per sq mi) 50 percent Q,

Percent of discharge 

at Scotia

Water Suspendedsediment, Q,

11-4725. Eel River above Dos Rios

[Drainage area, 705 sq mi]

1958.. _-_-_-.

1959. ........

1960. ........

1961... _.__..

1962. ........

1963. _____._.

1964. ...... ..

1965. ........

...-- 2,051,000

.-..- 479,000

...-. 943,700

.... . 757,200

.... - 630,500

.-.-.- 1,105,000

.--__ 376,000

.--_.. 1,822,000

.-. . 1,021,000

2, 062, 000 2, 925 

332, 103 471 

1, 803, 000 2, 557 

412, 900 586 

430, 800 611 

1, 715, 000 2, 433 

240, 500 341 

9, 571, 000 13, 580

2,071,000 2,938 .... .....

9 

4 

2 

5 

4 

2 

2 

2

17.9 

12.0 

20.8 

14.6 

16.8 

16.0 

11.3 

19.7

16.9

7.0 

3.3 

11.9 

5.0 

9.0 

8.1 

4.2 

5.7

6.3

11-4729. Black Butte River near Covelo

[Drainage area, 162 sq mi]

19661. _._._..

19671-----.-.

._._ _ 169,600

.-.-. 304,200

.__.__ 236,900

474,300 .._-......-...

930,800 ______ _ .....

3702,100 4,330 ..........

11-4730. Middle Fork Eel River below Black Butte River,

[Drainage area, 367 sq mi]

1963..-..--.

1964. _.___...

1965. --------

1966........

1967--...--.

.... _ 829,100

.---.. 334,900

...... 1,339,000

...... 559,000

...... 798,700

.-... 772,100

1, 618, 000 4, 409 

105, 300 287 

10, 100, 000 27, 520 

1,116,000 3,041 

1, 974, 000 5, 379

2,983,000 8,041 ____ .....

3

5

3.5 

4.8

4.2

1.7 

4.0

2.7

near Covelo

2 

2 

4

5

7

12.0 

10.1 

14.4 

11.3 

12.5

12.5

7.6 

1.9 

6.0 

4.0 

8.4

6.0

11-4739. Middle Fork Eel River near Dos Rios

[Drainage area, 745 sq mi]

1958. ..----..

1959. ........

1960. . _.____.

1961. ....... .

1962. ........

1963. . .......

1964.-.---

1965-.---.-

1966--.----.

1967.. .......

....._ 32,498,000

... .- 3746900

._.... 3886,000

...... 31,110,000

...... 3857,600

.-- 3 1,614,000

.-.._ 3647,300

...... 32,768,000

.--- 1,062,000

.-._.- 1,434,000

----- 1,363,000

4,157,000 5,580 ___ . . _

841,900 1,130 _._. _ ...

2,649,000 3,556 ____ .....

847,900 1,138 ..........

579,000 777 .........

4,710,000 6,322 _

759,400 1,019 .........

18,700,000 25,100 ... ... .

4, 330, 000 5, 812 

4, 880, 000 6, 550

3

7

21.8 

18.9 

19.6 

21.5 

22.7 

23.4 

19.4 

30.2 

21.3 

22.3

22.8

14.1 

8.5 

17.5 

10.2 

12.2 

22.3 

13.4 

11.2 

15.4 

20.7

13.6

11-4750. Eel River at Fort Seward

[Drainage area, 2,107 sq mi]

1966..........

1967-.-...--

.---. 2,657,000

----- 3,818,000

...... 3,238,000

13, 210, 000 6, 270 

16, 000, 000 7, 594

14,600,000 6,872 ._.__._-.

2 

6

53.5 

59.6

57.0

46.8 

68.0

56.0

Footnotes at end of table.
58 SEDIMENT IN THE EEL RIVER BASIN, CALIFORNIA

TABLE 8. Summary of suspended-sediment and water discharge in the Eel River 

basin, October 1957-September 1967 Continued

Suspended- Suspended- Days per year 

Water sediment sediment required for 

Water year discharge discharge, yield (tons transport of - 

(acre-feet) Q, (tons) per sq mi) 50 percent Q,

Percent of discharge 

at Scotia

Water Suspendedsediment, Q,

11-4755. South Fork Eel River near Branscomb

[Drainage area, 43.9 sq mi]

1958..............

1959. -------------

1960__ 

1961-- --- -

1962--...-.-.-....

1963...-....---.-.

1964..... .........

1965..............

1966. ....-_..-.. ..

1967.-.-....-...-.

Avg, 1958-67. . 

Avg, 1963-67. .

219, 200 

81, 590 

110, 300 

116, 600 

77,480 

133, 200 

87, 550 

194, 300 

107, 400 

124, 300

125, 200 

129,400

4 88, 000 

4 10, 000 

4 330, 000 

* 10, 000 

48,000 

61, 760 

26, 330 

502, 800 

154, 500 

55, 340

125, 000 

160, 100

2,000 _---_-_---.

230 - .......

7,500 _..-. .....

230 ...........

180 --_____._

1,407 

600 

1,145 

3,519 

1,261

2,850 ...........

3,583 ...........

4 

1 

2 

1 

5

1.9

2.0 

2.4 

2.2 

2.1 

1.9 

2.6 

2.1 

2.2 

1.1

2.1

2.1

0.3 

.1 

2.2 

. 1 

.2 

.3 

.5 

.3 

.6 

.2

.4 

.3

11-4765. South Fork Eel River near Miranda

[Drainage area, 537 sq mi]

1958... . ------

1959.- ..---.-

I960.. ..... .-_--..

1961.. ..... _- ---.-

1962. .............

A Vcr

2, 444, 000 

970, 200 

1, 142, 000 

1, 299, 000 

847,000

1, 340, 000

4 3, 900, 000 

4 1, 300, 000 

4 2, 000, 000 

4 1, 200, 000 

4 470, 000

1, 774, 000

7,300 ......._--.

2,400 ._------.-_

3,700 ----------

2,200 .-...-.----

880 _._._-_ 

3,300 ._ _ __

21.3 

24.3 

25.2 

25.1 

22.5

23.2

13.3 

13.1 

13.2 

14.5 

9.9

13.0

11-4770. Eel River at Scotia

[Drainage area, 3,113 sq mi]

1958.......--.-.-.

1959 - ..

I960 _....--__.

1961 .

1962.. , .-.._ .

1963 .. -.-.--...

1964.. .. -.-.-.. .

1965 .- 

1966..... ... ------

1967 __-._-.__.

1958 .. ........ .

1959 ____-_. ...

I960 _._.-__-_

1961 -_.__.-_-_-

1962 --.- ....--.

1963 ...

1964 . - ..

1965...--.--...-..

1966. -

1967 . ..........

11,470,000 29,420,000 

3, 991, 000 9, 936, 000 

4, 532, 000 15, 120, 000 

5, 178, 000 8, 279, 000 

3, 764, 000 4, 758, 000 

6, 883, 000 21, 190, 000 

3,329,000 5,652,000 

9, 242, 000 167, 800, 000 

4, 963, 000 28, 220, 000 

6,407,000 23,530,000

5, 976, 000

11-4785

1, 006, 000 

491, 200 

467, 700 

586, 200 

417, 600 

770, 600 

455, 800 

791, 000 

538, 000 

617, 200

614, 100

31, 390, 000

9,450 

3,192 

4,857 

2,659 

1,528 

6,807 

1,816 

53, 900 

9,065 

7,558

10,080 ............

12 

5 

2 

9 

6 

6 

2 

2 

3 

7

100 

100 

100 

100 

100 

100 

100 

100 

100 

100

100

100 

100 

100 

100 

100 

100 

100 

100 

100 

100

100

. Van Duzen River near Bridgeville

[Drainage area, 216 sq mi]

4 2, 000, 000 

4 2, 600, 000 

4 2, 000, 000 

4 790, 000 

4 300, 000 

4 1, 000, 000 

4 800, 000 

2 3, 530, 000 

21,350,000 

2 1, 200, 000

1, 557, 000

9,260 -..._ ..

12,037 ...........

9,260 ......

3,657 ...........

1 3RQ

4,630 ...........

3,704 ...........

16,343 ........

6,250 ----------

5,555 . _.

7,208 -.-_---...

1 Figures based on partial records, from November to May, 1966 water year, and from November to September, 1967 water year.

2 Computed by flow-duration and sediment-ratmg-curve method (Miller, 1951).

3 Discharge computed as difference between discharges at Eel River above Dos Rios and Eel River below 

Dos Rios.

4 Hawley and Jones (1969).
SEDIMENTATION IN LAKE PILLSBURY 59

Eel Eiver near Dos Eios was 2,400 tons per square mile between October 1957 and September 1962 and was increased to 5,700 tons per 

square mile with the inclusion of subsequent data for the 1963-67 

water years.

The three basins discussed, which make up 64 percent of the Eel 

River basin above the Scotia gage, contributed annually an average 

of 32 percent of the suspended-sediment discharge computed 

a,t Scotia. The remaining suspended-sediment discharge, about 212 

million tons during the 10-year period, came from an area of 1,126 

square miles in the central part of the basin which includes the North 

Fork Eel River basin. Further division of this area to pinpoint local 

areas of high sediment yield cannot be done adequately using the 

existing data. However, records from the 1966 and 1967 water years 

at Eel River at Fort Seward show that during these 2 years the sediment yield was divided about equally between the parts of this central 

area above and below Fort Seward.

Sediment yield is greatest in those parts of the basin where earthflows and landslides are adjacent to the stream channels. According 

to Soil Conservation Service studies (file data, 1968), streambank 

erosion at higher flows produces between 60 and 65 percent of the 

sediment yield in the basin; however, the combined effects of the 

erosion of channels and landslide debris contribute about 90 percent 

of the fluvial sediment in the basin. Ephemeral runoff from watershed slopes and roads accounts for the remaining 10 percent.

SEDIMENTATION IN LAKE PILLSBURY

Lake Pillsbury on the upper Eel River is an important source of 

information concerning the effects of reservoirs on sedimentation. 

Few data on reservoir sedimentation are available for northern coastal 

California watersheds; thus, past and present studies of Lake Pillsbury provide the principal usable data for planning additional reservoir projects along the Eel River.

Lake Pillsbury is the larger of twT o reservoirs which make up a 

part of the Potter Valley Project, a multiple-use facility designed 

to provide for irrigation and recreation needs and power development 

in the vicinity of the upper Eel River and Russian River basins. The 

drainage area of the lake encompasses 288 square miles of steep 

rugged terrain in which the maximum basin relief is about 5,200 feet. 

The lake is fed principally by the Eel and Rice Fork Eel Rivers, 

both of which have slopes greater than 160 feet per mile above the 

lake. Most of the sediment supplied to Lake Pillsbury is derived from 

the erosion of stream channels and £he erosion of lands from which 

protective vegetal cover has been removed.
60 SEDIMENT IN THE EEL RIVER BASIN, CALIFORNIA

The accumulation and distribution of sediment in the reservoir 

were studied in some detail by Porterfield and Dunnam (1964) to 

evaluate changes which had taken place since water storage began 

in 1921. Data from their report show a sediment inflow between 

1921 and 1959 of about 343,000 tons per year, of which 94 percent 

was deposited within the reservoir. The sediment inflow was computed using sediment-accumulation figures and a specific weight 

for sediment of 73 pounds per cubic foot (Porterfield and Dunnam, 

1964, p. EE45). Thus, the average sediment load passing through 

the reservoir and carried downstream was about 21,000 tons per year 

and was composed primarily of sediment finer than sand. Most sediment of sand size and larger drops out of suspension in the lake.

Reservoir design in the Eel River basin should take into account 

the high trap efficiency observed at Lake Pillsbury as well as other 

factors which affect reservoir sedimentation such as bank slides, the 

effect of wa,ve action on bank erosion, and reservoir orientation with 

respect to inflowing streams. Discussion and computations provided 

in the report by Porterfield and Dunnam, combined with a knowledge 

of sedimentation rates, provide useful information for future reservoir studies.

TURBIDITY

Part of the studies aimed at the development of northern coastal 

California watersheds is a study of the causes and effects of turbidity 

in streams and reservoirs. Turbidity may limit the use of water for 

public consumption, and it may make water unsatisfactory for recreational uses such as fishing. Recognizing that turbidity could be a major 

problem in the development of northern coastal streams, State and 

Federal agencies have initiated various sampling programs and other 

studies to gain more information about turbidity. The U.S. Geological 

Survey in cooperation with the State of California has collected 

turbidity samples and has made field turbidity measurements at 

several stations in the Eel River watershed. Turbidity measurement 

was begun in the latter part of the 1964 water year and was continued 

through the 1968 water year at several stations. The 1964 data were 

collected after most of the runoff for that water year had already 

occurred; thus, those data are considered incomplete and are not used 

in this report.

Turbidity was defined by Rainwater and Thatcher (1960, p. 289) as 

"the optical property of a suspension with reference to the extent to 

which the penetration of light is inhibited by the presence of insoluble 

material." Turbidity may be defined less precisely as an unclear condition or cloudiness of water. During the drier months of the year when 

runoff is low, turbidity in the streams and reservoirs of the Eel River
TURBIDITY 61

basin is caused primarily by the presence of phytoplankton and other 

micro-organisms which proliferate in the presence of sunlight. During 

the rainy months when runoff is high, suspended sediment is the 

chief cause of turbidity. Phytoplankton, which usually is made up of 

diatoms and other algae, needs light to survive. The presence of suspended sediment in the winter months obstructs the passage of sunlight 

and precludes the reproduction of the phytoplankton. Thus, turbidity 

during periods of high suspended-sediment discharge may be attributed almost entirely to suspended sediment, and the effect of 

diatoms upon the turbidity during these periods may be considered 

negligible.

Turbidity measurements were made wT ith a Hellige turbidimeter 

prior to August 1966 and thereafter with a Hach turbidimeter model 

1860. Both of these instruments employ a, rtephelometric or lightscattering principle in which a light beam is reflected or scattered by 

particles in suspension, and the intensity of this reflected light is 

compared with a standard. In the Hellige turbidimeter, the slit width 

that controls the amount of light passing up through the solution is 

controlled by a knob on the side of the instrument. This knob is calibrated in arbitrary unite from standard solutions, and the readings 

from the knob are converted to milligrams per liter turbidity by 

means of appropriate curves developed in the laboratory. The transmitted light is viewed as a circle of light in a field of Tyndall light 

(Rainwater and Thatcher, 1960, p. 70-71). In the Hach instrument, 

the light scattered at right angles to the light beam is received by two 

photoelectric cells and converted into an electrical signal which is 

measured on a precalibrated meter to indicate turbidity units. The 

Hach turbidimeter, in contrast to the Hellige instrument, does not 

require operator judgment or interpretation; thus, the results obtained with the Hach turbidimeter are probably more consistent 

than those obtained with the Hellige turbidimeter. The Hach instrument measures turbidity in Jackson Turbidity Units (JTU's) 

as defined by Newell (1902) ; however, a calibration between JTU's 

and milligrams per liter silica from standard silica suspensions was 

made in the Geological Survey so that consistency might be maintained in the publication of turbidity data.

RELATION BETWEEN TURBIDITY AND THE CONCENTRATION 

OF SUSPENDED SEDIMENT

The turbidity, density, and other fluid properties of a water and 

sediment mixture are related to the concentration of suspended sediment. The relation between turbidity and concentration of suspended 

sediment for stations along the Eel River is typified by figure 21.
62 SEDIMENT IN THE EEL RIVER BASIN, CALIFORNIA

The data are taken from turbidity and concentration measurements 

made on individual samples, and an apparent trend exists when these 

data are plotted on full logarithmic paper. The scatter of points for 

the station used in figure 31 is characteristic of all the stations from 

which data were collected; however, with sufficient data, curves may be 

obtained which are usable approximations of the turbidity-concentration relation.

A rapid and simple method was used to obtain approximate curves 

for six stations along the Eel Kiver for a variety of different periods 

and conditions. Turbidity and concentration data were recorded on 

punched cards, and these data, were manipulated in appropriate computer programs for regression analyses and other studies. Linear

100,000

10,000

1000

100

10

10 100 

TURBIDITY, IN MILLIGRAMS PER LITER

1000

FIGURE 31. Plot of turbidity versus concentration, showing trend typical of 

stations in the Eel River basin. Data are taken from observations at Middle 

Fork Eel River near Dos Dios during the 1966 water year.
TURBIDITY 63

logarithmic equations for each water year of record for each station 

studied were computed by a least-squares regression analysis, and 

the graphs of these equations are shown in figure 32. Some of the 

statistical parameters of the regressions are tabulated in table 9 to

10,000

1000 -

Black Butte River near Covelo 

I________I______

Middle Fork Eel River 

below Black Butte River near Covelo 

_____I________|_______

100 1000 10,000 10 100 

TURBIDITY, IN MILLIGRAMS PER LITER

1000 10,000

FIGURE 32. Regression curves of the approximate relation between concentration 

and turbidity for successive water years.
64 SEDIMENT IN THE EEL RIVER BASIN, CALIFORNIA

TABLE 9. Regression equations and selected related statistics for the relation between 

concentration and turbidity at various stations along the Eel River

No.

11-4729

11-4730

11-4739

11-4750

11-4755

11-4770

Station

Location

Black Butte River

near Covelo.

Middle Fork Eel

River below Black

Butte River near

Covelo.

Middle Fork Eel

River near Dos

Rios.

Eel River at Fort

Seward.

South Fork Eel River

near Branscomb.

Eel River at Scotia....

Water 

year

1966

1967

1968

1965

1966

1967

1965

1966

1967

1968

1966

1967

1968

1965

1966

1967

1968

1965

1966

1967

1968

Equation for Number 

concentration- of 

turbidity relation observa- 

(least-squares tions 

computation)

(7=1.220(7)1.108

1.255(7)1-13*

1.540(7)1-031

1.649(7)1-150

1.736(7)1-102

2.290(7)1-021

1.275(7)1-132

1.521(7)i-i«o

1.434(7)1-10°

2.351 (T)o. »«s

.863(7)i-i'i

.381(7)1-134

.818(7)i-iH

1.025(7)1-1"

.862(7)1-057

1.073(7)1-0"

.876(T)i-OM

.984(7)1-180

.837(7)1-203

1.554(7)1.081

2.327(7)1-005

102

125

116

187

162

124

198.

249

205

145

240

175

167

37

45

72

53

243

210

170

109

Standard 

Correla- Degrees error of 

tion co- of estimate 

efficient freedom (log units)

0.9706

.9758

.9792

.9764

.9717

.9765

.9784

.9820

.9754

.9736

.9505

.9826

.9761

.9662

.9672

.9700

.9582

.9593

.9739

.9727

.9723

99

122

113

184

159

121

195

246

202

142

237

172

164

34

42

69

50

240

207

167

106

0. 19462

.18608

. 19573

.23352

. 21897

.20034

.23477

. 21492

.17357

. 21175

. 31626

.19059

. 18126

.15615

. 18738

. 16146

.14491

. 26993

. 21311

. 24148

.23510

indicate the degree of correlation between turbidity and concentration, and a confidence interval for values which may be estimated 

from the equations.

The turbidity-concentration relation is very consistent for each 

station and throughout the basin. The slopes of the regression lines 

are much the same for all stations and for all the observed periods. 

However, there is an apparent trend for concentration to decrease 

slightly for a given value of turbidity with each succeeding year. In 

general, the computed slopes for the 1965 and 1966 water years are 

steeper than slopes computed for the 1967 and 1968 water years.2 

The regression lines not only have similar slopes, but they are also 

clustered about a common region of the graph. In virtually all the observed cases, the value of concentration is higher than the corresponding value of turbidity.

The year-by-year differences in the relations at each station are 

shown in figure 33. The graphs show that for a given value of turbidity, concentration is higher at stations on the Middle Fork Eel 

River and lower at South Fork Eel River near Branscomb than at the 

stations on the main stem of the Eel River.

The significance of the data presented in this section is apparent 

in the consistency of the form and correlation of the concentration2 This effect may be related to the percentage of sand carried in suspension, although 

data are too limited to verify this assumption. The authors have observed that turbidity 

is higher at a given concentration for a water and sediment mixture which contains only 

silt and clay than for a mixture containing mostly sand.
TURBIDITY 65

10.000

o

=1 100

1965 water year

/'/// Station Symbol

11-4730 

4739 -------

4755 

4770 

1968 water yea

'Station Symbol

11-4729 - - 

4730 

4739 -------

4755 - 

4770 

100 1000 10.000 10 100 

TURBIDITY, IN MILLIGRAMS PER LITER

1000 10,000

FIGURE 33. Regression curves of the station-by^station relations between concentration and turbidity, Eel River basin.

turbidity relation throughout the Eel River basin. In the absence 

of a sediment-measurement program in the future, or at certain key 

sites within the basin where sediment sampling is not done, turbidity 

data might be used to obtain at least an approximation of suspendedsediment discharge. However, the concentration-turbidity relations 

obtained for the Eel River basin should not be used as indices for 

studies in other similar basins. For example, studies on the Russian 

River basin, which is immediately south of the Eel River basin and 

in a similar geologic and climatological evironment, show that the 

value of turbidity is higher than the graphically corresponding value 

of concentration for many of the stations observed.

The relations between turbidity and other properties and characteristics of a water and sediment mixture were of some interest in the 

study leading to this report, and are of special interest in a more 

detailed study currently being made of turbidity and its relation to
66 SEDIMENT IN THE EEL RIVER BASIN, CALIFORNIA

suspended sediment. In the course of study of turbidity in the Eel 

River basin, many of these relations were explored, including the 

relations among turbidity, concentration and particle size of the suspended sediment, specific conductance of the water and sediment 

mixture, and depth of flow. Although certain trends existed among 

the relations developed, it was decided that the data were insufficient 

to provide conclusive information within the scope of this report other 

than the concentration-turbidity plots shown. More detailed aspects 

of turbidity are being studied, and a report in progress by the authors 

on turbidity in the Russian River basin will include comparisons of 

turbidity relations with several parameters in both the Russian and 

Eel River basins.

SELECTED REFERENCES

Bailey, B. H., Irwin, W. P., and Jones, D. L., 1964, Franciscan and related 

rocks, and their significance in the geology of western California: California Div. Mines and Geology Bull. 183,177 p.

California Department of Water Resources, 1965, Land and water use in Eel 

River Hydrographic Unit, Volume I: Dept. Water Resources Bull. 94-8,113 p.

 1966, Watershed management in the Eel River Basin, in North coastal 

area investigation: Dept. Water Resources Bull. 136, App. A, 143 p.

Carlston, C. W., 1969, Downstream variations in the hydraulic geometry of 

streams special emphasis on mean velocity : Am. Jour. Sci., v. 267, p. 499-509.

Colby, B. R., 1956, Relationship of sediment discharge to streamfiow: U.S. Geol. 

Survey open-file report, 170 p.

 1963, Fluvial sediments a summary of source, transportation deposition,

and measurement of sediment discharge: U.S. Geol. Survey Bull. 1181-A,

47 p. 

Colby, B. R., Hembree, C. H., and Rainwater, F. H., 1956, Sedimentation and

chemical quality of surface waters in the Wind River basin, Wyoming:

U.S. Geol. Survey Water-Supply Paper 1373, 336 p. 

Corbett, D. M., and others, 1943, Stream-gaging procedures, a manual describing

methods and practices of the Geological Survey: U.S. Geol. Survey WaterSupply Paper 888, 245 p. 

Hawley, N. L., and Jones, B. J., 1969, Sediment yield of coastal streams in

northern California, 1958-64: U.S. Geol. Survey open-file report, 19 p. 

Helley, E. J., and LaMarche, V. C., Jr., 1968, December 1964, a 400-year flood

in northern California: U.S. Geol. Survey Prof. Paper 600-D, p. D34-D37. 

Hickey, J. J., 1968, Variations in low-water streambed elevations at selected

stream-gaging stations in northwestern California : U.S. Geol. Survey Water

Supply Paper 1879-E, 33 p. 

Holeman, J. N., 1968, The sediment yield of major rivers of the world: Water

Resources Research, v. 4, p. 737-747. 

Irwin, W. P., 1960, Geologic reconnaissance of the northern Coast Ranges and

Kalmath Mountains, California : California Div. Mines and Geology Bull.

179,80 p.
SELECTED REFERENCES 67

Judson, Sheldon, and Hitter, D. F., 1964, Rates of regional denudation in the

United States: Jour. Geophys. Research, v. 69, no. 16, p. 3395-3401. 

Leopold, L. B., and Maddock, Thomas, 1953, The hydraulic geometry of stream

channels and some physiographic implications: U.S. Geol. Survey Prof.

Paper 252, 56 p. 

Leopold, L. B., Wolman, M. G., and Miller, J. P., 1964, Fluvial processes in geomorphology : San Francisco, Freeman, 522 p. 

Miller, C. R., 1951, Analysis of flow-duration, sediment-rating curve method of

computing sediment yield: U.S. Bur. Reclamation rept, 15 p. 

Newell, F. H., 1902, Measurement of turbidity and color: U.S. Geol. Survey Div.

Hydrography Circ. 8, 4 p. 

Page, B. M., 1966, Geology of the Coast Ranges of California, in Geology of

northern California : California Div. Mines and Geology Bull. 190, p. 253-321. 

Porterfleld, George, and Dunnam, C. A., 1964, Sedimentation of Lake Pillsbury,

Lake County, California: U.S. Geol. Survey Water-Supply Paper 1619-EE,

46 p. 

Rainwater, F. H., and Thatcher, L. L., 1960, Methods for collection and analysis

of water samples: U.S. Geol. Survey Water-Supply Paper 1454, 301 p. 

Rantz, S. E., 1964, Surface-water hydrology of coastal basins of northern

California: U.S. Geol. Survey Water-Supply Paper 1758, 77 p.

 1968, Average annual precipitation and runoff in north coastal California : 

U.S. Geol. Survey Hydrologic Inv. Atlas HA-298.

Rantz, S. E., and Moore, A. M., 1965, Floods of December 1964 in the far western 

States : U.S. Geol. Survey open-file report, 205 p.

Ritter, J. R., 1968, Changes in the channel morphology of Trinity River and 

eight tributaries, California, 1961-65: U.S. Geol. Survey open-file report, 

60 p.

U.S. Department of Agriculture River Basin Planning Staff, Soil Conservation 

Service and Forest Service, 1970, Appendix No. 1 Sediment yield and land 

treatment, Eel and Mad River basins, in North coastal area of California and 

portions of southern Oregon, in Water, land, and related resources: Portland, 

Oreg., U.S. Department of Agriculture Soil Conservation Service, 143 p.

U.S. Geological Survey, Water resources data for California Part 1, Surface 

water records, Volume 1, Colorado River basin, southern Great Basin, and 

Pacific slope basins excluding Central Valley: U.S. Geol. Survey (published 

annually).

 Water resources data for California Part 2, Water quality records:

U.S. Geol. Survey (publishedannually). 

U.S. Inter-Agency Committee on Water Resources, 1963, Determination of fluvial

sediment discharge, in A study of methods used in measurement and analysis

of sediment loads in streams : Reptor. 14,151 p.

U. S. GOVERNMENT PRINTING OFFICE : 1971 O - 427-150

INDEX

[Italic page numbers indicate major references]

Acknowledgments__________. 

Aggradation, Black Butte Elver bed. 

Algae_________________. 

Area, Eel Eiver drainage._-.---....

Page

5

45

61

5

Bald Mountain__________________ 13 

Black Butte Eiver-.--..---_..-_--____-._. 15,25,46 

near Covelo...__.___________ 18 

Branscomb________________ 12,52,56 

BridgeviUe................... ............. 16

California Eedwood Forests___._____ 3,12

Carlotta____________________ 16

Chaparral.....--.--..-..-......--.......--... 11,14

Climate...................................... 7,12

Coast Eanges_________________ 5,9,11

Computation methods____________ S3

Computer program_______________ 23

Conifers___________________.. 11

Covelo...___________________ 15

Cretaceous sands.__--.-.__.....__-... 15

Definition of terms. --..-. --......___...... 22

Diatoms_.__________________ 61 

Dos Eios ......................... 14,15,27,28,49

Douglas Fir................................. 12

Eel Eiver.... ....................... 13,49,59,64

above confluence with Middle Fork Eel

Eiver............................. IS

above Dos Rios______________ 27 

at Fort Seward........................ 18,45,59

at Scotia...................... 18,25,27,28,40,56

below confluence with Middle Fork Eel

Eiver............................. 14

canyon____________________ 14 

Eel Rock.................................._ 14

Elevations.................................. 5,14,16

Elk Creek.................................... 12,15

Erosion............................ 4,11, 13, 20,25,59

Eureka_.__________.____.. 5 

Evaporation__..________________ 7

Fanning____________________ 12 

Faulting.................................... 5,11,15

Flood, December 1964.........-.--...-.-..... 3,

17,23,25,32,37,40,45,52,56 

Fog.......................................... 7,12

Forests............................... 3,11,13,15,16

Fort Seward............................... 12,20,49

Franciscan Formation____________ 9,15,16

Geology. 

Grazing.

Page 

9 

12

Hardwoods...______--.----...-.--.--.-- 11

Humboldt Bay -.....--.-...-.-.-..--..--. 7

Hydraulic geometry_________.. 16

Hydrography_-. 18

Introduction...... .. 2

Investigations, previous..__ .... .. 4

Irrigation..................................... 12

Kneeland. 12

Lake County.. 14 

LakePillsbury.. ............... 7,12,13,27,56,59

Land use_____. ___ . 12

Landslides...................... 11,14,15,25,46,59

Larabee Creek___... .... 49

Little Lake VaUey....................- 5,14

Lumbering..________... -... 11,12

Madrone____-.-.--..-..._.-... . 12

Maple........... - - . 12

Measurement methods.._ 22 

Mendocino County. 13,14 

Middle Fork Eel Eiver............ 5, 16, 25,45,56,64

below Black Butte River........... ... 40

near Dos Eios......................... 27,36,59

upper. 40 

Miranda...................................... 52

North Fork Eel Eiver.............. . 14,25,49,59

Oak..........

Outlet Creek.

Particle-size distribution......... 32,38,40,49,53,66

Phytoplankton___ 61 

Pines..............-.......... ............ 12

Population__._.. 2 

Potter Valley.. - 12,14,56

Potter Valley Project 14,59

Precipitation, rain.............. . 7,12,25,30,61

snow.....__---.____---.---.-.--. 7,30

Purpose and scope.. ---- 3

Quaternary deposits 15,16

Recreation................................... 12,60

Eedwoods.............................. 11,15,16
70 INDEX

Page

Reservoirs.- . ..... . 7,14,27,56,59

Rice Fork Eel River.-- .. .___..___.. 13,14,59 

Round Valley _______. _________ 5 

Runoff 3,7,40,52,59,60

Black Butte River basin................. 45

December 1964 flood._.................. 25

Eel River at Scotia....................... 30

Middle Fork Eel River near Dos Rios.... 36

Russian River basin....-.-..-....... 7,14,59,65,66

San Francisco... ...._._________ 5

Scotia..................... 7,9,14,17,27, 88, 49,56,59

Scott Dam.........._....--....--...-...... 7,14

Sediment-- . 4,11,14,18, ££

concentration as related to turbidity..... 61

quantity and distribution ________ 56 

Soils. -.. -...................... 11, 13,15,16

Sonoma County.. . _... .. 14 

South Fork Eel River............... 14,15,49,52,56

nearBranscomb_._____.__._.. 52,64 

near Miranda. - -------------- 52,56

Streams, physical characteristics .

Page

IS

Temperatures..________________ 7

Tertiary sedimentary rocks.. ________ 10

Tomki Creek. ..^............................ 14

Topography_._........ . . 5,11

Turbidity_...-..-..--......---..-....-..-.. 60

relation to suspended-sediment concentration.. ... .,... >... 61

turbidimeters...___________._ 61

Upper Cretaceous sedimentary rocks. 10

Van Arsdale Reservoir.................. 7,14,27,56

Van Duzen River...................... 12,14,10,28

Vegetation................................... 11, 13

Weott. 

Willits.

Yager Creek................................. 16

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