LONGSHORE AND SEASONAL VARIATIONS IN BEACH SAND,

HUMBOLDT COUNTY, CALIFORNIA: IMPLICATIONS FOR

BULK LONGSHORE TRANSPORT DIRECTION

by

Paul Bodin

A Thesis

Presented to

The Faculty of Humboldt State University

In Partial Fulfillment

of the Requirements for the Degree

Master of Science

March, 1982

LONGSHORE AND SEASONAL VARIATIONS IN BEACH SANDS

FROM HUMBOLDT COUNTY, CALIFORNIA: IMPLICATIONS FOR

BULK LONGSHORE TRANSPORT DIRECTION

by

Paul Bodin

Approved by the Master's Thesis Committee

Robert W. Thompson, Chairman

Steven Costa

Gary Carver

Natural Resources Graduate Program

Approved by the Dean of Graduate Studies

Alba M. Gillespie

What is that feeling when you're driving away from people and they recede on the plaint till you see their specks dispersing?--it's the too-huge world vaulting us, and it's good-by. But we lean forward to the next crazy venture beneath the skies.

Jack Kerouac (from On The Road)

ABSTRACT

Subaerial beach sediments were sampled at 80

stations along 62 kilometers of the central Humboldt County

shoreline. Samples were taken during winter and summer to

represent both the fully eroded and fully accreted

conditions of the beach. Beach samples were analyzed for

the grain size distribution parameters of mode, mean,

standard deviation, and skewness. The 1.75 phi to 2.75 phi

size fractions were recombined and analyzed for both heavy

mineral to light mineral ratios and for heavy mineralogy.

Three samples each from the Mad and Eel Rivers, which are

the chief sediment contributors to the study area, were

subjected to a similar petrographic analysis. Results of

the grain size analyses and of the analyses of the ratio of

heavy minerals to light minerals indicate that the net

annual longshore drift is generally northward, and that the

Eel River is the chief source of sediment in the study area.

The entrance channel to Humboldt Bay appears to be

selectively trapping coarse particles (>500 microns) as

sediments are passed through the channel system by longshore

drift.

Heavy/light ratios along the beach show strong

seasonal differences probably related to selective sorting

associated with cross-shore sand movements.

Heavy mineral comparisons indicate that river

i i i

iv

sediments undergo a selective sorting in transport to the

beach which obscures the provenance of beach materials.

ACKNOWLEDGEMENTS

While performing this research, I was supported

almost entirely by a University of California Sea Grant

College Program traineeship, for which I am very grateful.

Much technical support was given to my research by the

Sea-Grant funded project, "A Study of the Entrance Problems

at Humboldt Bay, California", and I would like to

acknowledge the principal investigators: the late professor

John D. Isaacs, Dr. Theodore Kerstetter, and Dr. Robert

W. Thompson. Drs. Steven L. Costa and James T. Stork of

the Sea-Grant project gave much of their time and of

material assistance throughout the period of data collection

and analysis. Mr. Phillip Buttolph enthusiastically

assisted in sample collection and processing above and

beyond the call of duty. Mr. Hugh Whelan, Ms. Seanna

Willit, and Ms. Edna Rodrigues assisted with the technical

analyses--thank you.

This thesis owes its present form and readability to

Dr. Robert W. Thompson, whose knowledge and experience

were relied upon throughout the entire undertaking. I am

grateful he was able to stick it out to the end.

The staff of the Fred Telonicher Memorial Marine

Laboratory were specially wonderful to work with. In

particular, I would like to acknowledge Ms. Carol Wardrip,

Mr. James Rusconi, Mr. Hal Genger, Mr. John Smith, and

vi

Mr. David Hoskins. Without their cheerful support I might

still be in prison.

For the ease of preparation of the final drafts of

the thesis, I am grateful to Dr. Richard J. Seymour and

Ms. Martha Rognon of the Nearshore Reasearch group at

Scripps Institution of Oceanography for the use of their

word-processor.

Finally, my morale through the more difficult times

was maintained only by the loving support of Joan and my

parents.

TABLE OF CONTENTS

page

ABSTRACT iii

ACKNOWLEDGEMENTS v

TABLE OF CONTENTS vii

LIST OF TABLES ix

LIST OF FIGURES x

INTRODUCTION 1

STUDY AREA DESCRIPTION 4

Physiographic Features 4

Sediment Input to the Beach System

Oceanographic Features 8

METHODS OF STUDY 12

Sample Collection and Processing 12

Grain Size Analysis 15

Mineralogical Analysis 16

Statistical Analysis 17

AERIAL DISTRIBUTION OF GRAIN SIZE PARAMETERS 19

Results 19

Discussion 31

Bulk Northwards Longshore Transport Hypothesis 31

Evidence for Selective Trapping in the Bay Mouth 33

Effects of Mad River Sediment on the Beach 34

Alongshore Wave Energy Gradient 36

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viii

TABLE OF CONTENTS (continued) page

HEAVY MINERAL-LIGHT MINERAL RATIOS 38

Results 38

Discussion 38

HEAVY MINERALOGY 44

Results 44

Discussion 46

CONCLUSIONS 53

Bulk Northward Transport 53

Suggestions for Further Work 55

REFERENCES CITED 57

APPENDICES

A. Numerical values of grain-size parameters--winter 60

B. Numerical values of grain-size parameters--summer 62

C. Numerical values of heavy mineral abundance 64

LIST OF TABLES

Table

1 Heavy mineral percentages--river samples...

page

45

2 Beach heavy mineral percentages--winter 47

3 Beach heavy mineral percentages--summer 48

ix

LIST OF FIGURES

Figure page

1 Location map of study area 5

2 Beach morphology and names; River sampling sites 7

3 Wave power roses for the study area 9

4 Beach sampling south of the harbor entrance 13

5 Beach sampling north of the harbor entrance 14

6 Most common size constituent (mode) of the beach samples--winter 20

7 Most common size constituent (mode) of the beach samples--summer 21

8 Modal difference between seasons 22

9 Mean grain size--winter 23

10 Mean grain size--summer 24

11 Standard deviation of the grain size distributions--winter 26

12 Standard deviation of the grain size distributions--summer 27

13 Skewness of the grain size distributions--winter 29

14 Skewness of the grain size distributions—summer 30

15 Heavy mineral abundance along beach 39

16 Glaucophane abundance along the beach--summer 49

INTRODUCTION

As a coastal area becomes economically developed,

anthropogenic stresses can alter bordering beaches, with

consequences varying from aesthetic irritation to

large-scale economic loss. Undesireable changes in beaches

are often the result of ignorance about local shore

dynamics. Due to rapid economic development of coastal

areas, scientific knowledge of shore processes tends to

accumulate after problems arise. The magnitude of

difficulties which may follow coastal development, and the

uniqueness of each beach system, indicate that knowledge of

beach dynamics at unstressed coastal localities is required

to forestall beach degradation related to coastal

development. The beaches of Humboldt County, California,

have not yet been subjected to the same degree of stress as

have beaches on other parts of the California coast. As

developmental pressures grow, however, these relatively

unscathed beaches will come under increasing stress.

Investigating the dynamics of Humboldt County beaches will

help isolate areas of potential problems and enhance our

knowledge of unaltered beach systems.

An important problem arising from earlier

investigations of the study area is a controversy over the

dominant direction of littoral drift. Previous

investigators have noted that the prevalent longshore

transport direction at any one time in the study area varied

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2

depending on the season, being northward during the winter

and southward at other times (Noble 1971, Ritter 1972,

DeGraca et al. 1974). However,no clear consensus was

reached about which, if any, longshore transport direction

dominated in the annual cycle. In order to avoid confusion,

I will refer to average longshore transport caused by a

particular wave train, an instantaneous rate varying

seasonally, as "net longshore transport". The overall sum

of net longshore transport effects over the entire course of

a year, which is the controversial value, will be referred

to as "bulk longshore transport".

Elucidation of the bulk longshore sediment transport

direction is related to the question of which of the waves

arriving obliquely at the study area, when refracted to

shore, concentrates the largest longshore component of wave

power on mobile beach sediments. A mathematical model of

this process was used by DeGraca and Eckar (1974) to

determine the potential bulk longshore transport direction

north of the Humboldt Bay Jetties. Their results were

inconclusive and yielded patterns of convergence and

divergence of potential sediment transport for which there

is no physical evidence.

Noble (1971) examined changes in beach shape

resulting from the emplacement of jetties at the entrance to

Humboldt Bay. He interpreted greater accretion in the lee

of North Jetty as evidence of the dominance of southward

transport.

3

Ritter (1972) performed grain-size analyses and

examined abundance of the accessory mineral garnet along the

study area. He concluded that northward sediment flow in

the winter was of sufficient magnitude to make the Eel River

the chief contributor to the beach as far north as the

Humboldt Bay Jetties.

Snow's (1962) survey of beach morphology and

grain-size along the Northern California coast included

several stations in the study area. Snow theorized that the

beach sediment south of the mouth of the Eel River was of

different origin than beach sediments north of the Eel, and

that the Eel's sediment may be the chief source of the

northern beach.

The purpose of my work was to investigate the

longshore variation of beach sediment grain size and

mineralogy, and to apply these to the question of the bulk

longshore transport direction. My investigation was carried

out as part of a Sea-Grant funded investigation of the

shoaling of the entrance channel system at Humboldt Bay,

California (Kerstetter 1980). My work was to be used in an

effort to determine the source of sediments which comprise

the entrance channel shoals.

Results and conclusions of this and future work

apply directly to several real-life problems in the study

area. These include: harbor shoaling, coastal erosion

problems, disposal of dredge spoils from Humboldt Bay, and

potential consequences of dams on the Eel and Mad Rivers.

STUDY AREA DESCRIPTION

Physlographic Features

The coast of central Humboldt County between 40°31'N

and 41° 02'N is a 62 kilometer sand beach bounded by rocky

headlands and containing the entrance to Humboldt Bay, a

major shipping and fishing port (Figure 1).

The beach is the seaward extension of two extensive

flood plains composed of recent sedimentary materials

(Evenson, 1959). The southern plain is the Eel River flood

plain, or delta. The northern plain contains both the

Humboldt Bay system, into which drain several small streams,

and the Mad River flood plain.

The tectonic framework which provides an underlying

"skeleton" for the shoreline of the study area is somewhat

unusual compared to that of many other California beaches.

The majority of the California coastline strikes

north-westerly and, typically, a rocky headland at the

northern end of a sand beach in California extends farther

west than does the southern boundary. In the study area,

however, the northern boundary (Trinidad Head) is east of

the southern bounding rocky promontories of False Cape

(Figure 1). The overall strike of the study area shoreline

is, therefore north-north-easterly.

The beach, and the nature of its landward backing,

4

5

Figure 1. Location map of study area. Stippled areas are areas of Holocene sedimentation.

6

change along the study area. South of the Humboldt Bay

jetties, the beach is generally steep and narrow, and is

backed by either: (1) cliffs which occasionally are eroded

actively by waves, or (2) a thin band of low dunes (Figure

2). North of the jetties, the beach tends to be broader and

flatter than it is to the south (Snow 1962), and is backed

by well developed dune systems. Where cliffs, eroded by

both wave and river action, occur in the northern part of

the study area, they are separated from the ocean by as much

as 0.75 kilometers of vegetated dune sand (Figure 2).

Sediment input, to the Beach System

There are two major sediment sources to the study

area at the present time, the Mad River in the north and the

Eel River in the south (Figures 1 and 2). These rivers

drain geologically similar terraines, and rocks of the same

formations (Bailey 1966). The Eel River contributes an

estimated average of 4.5X106 tons of sand per year; the Mad

approximately one tenth of this amount (Ritter 1972).

The Mad and Eel Rivers have the largest ratios of

sediment yields to drainage areas in .North America, and

carry extremely high sediment loads for their sizes (Judson

et al. 1964, Karlin 1980). Most of this sediment load is

carried at high flows attained in the winter months, and a

large portion of the overall total is moved during major

flood events with a long recurrence interval (Brown et al.

Wide, flat beach. Extensive dunes. "Abandoned" cliffs.

Intermediate-to-wide beach. Generally very low steepness. Extensive high backing dunes. Gravel on beach in some placesdunes.

Beach is seaward edge of Humboldt Bay barrier. Wide beach, low steepness. High backing dunes.

Beach is seaward edge of Humboldt Bay barrier. Steep & narrow in S. to broad & flat in N. Steep beach, stable cliffs?

Beach is seaward edge of Eel R. delta. Steep, narrow beach. Low backing dunes..

Verysteep, narrow beach. No dunes eroding cliffs.

7

Figure 2. Beach morphology and names; river sampling sites. Morphological character of the shoreline is shown for seven sections of beach. River samples from the Mad River were given the identification num-bers: m-20, m-30, and m-40. Eel River samples were numbered: e-20, e-30, and e-50.

8

1971, Kelsey 1980). The large amount of sediment input to

the beach system is another characteristic which

distinguishes the study area from other California coastal

locales.

Oceanographic Features

More wave power arrives at the study area (and to

the north) than at coastal localities to the south in

California (N.M.C. 1960, D.N.O.D. 1977). The incoming

wave power is distributed among three recognizable

"families" of waves, each with a particular season-of-effect

and average angle-of-approach (Johnson et al. 1971)(Figure

3):

1) From April through November, the dominant wave

energy component at the study area is the "prevailing

swell". These waves are generated by storms in the

north-central and northeastern Pacific. These waves are low

energy wave forms, generally not higher than three meters

and averaging under one meter high, and dominate the total

wave power as a result of their long season-of-effect. The

tectonic structure, and the high sediment input previously

discussed have allowed the beach to become oriented roughly

perpendicular to the direction from which the prevailing

swell arrives (another northern California beach exhibiting

these characteristics is discussed by I.E.E., 1968).

Therefore, these waves should not, on the average, cause net

9

Figure 3. Wave power roses for the study area. Values were obtained by averaging the results of calc-ulations by Johnson (1971) for two deep-water stations approximately 200 kilometers north and south of the study area.

10

longshore transport.

2) The winter months, November through March, are

characterized by very high energy "seas" which arrive from

the south (Figure 3) (Johnson et al. 1971). These

southerly waves average about three meters high and range

over eight meters high. They are associated with storm

fronts passing through the study area during winter. The

winter storms also contribute the bulk of the annual average

precipitation of about one meter (Rantz 1969). Therefore,

during this season the river runoff and stream sediment

contribution are high, coinciding with net northward

transport engendered by the high southerly waves of the

season.

3) A third group of waves arriving at the study area

are seas generated by NNW winds which occur most strongly in

the months of May to August. This family of waves has an

average deep-water approach direction of NW to NNW (Figure

3), and an average height of one to two meters with a

maximum height of five meters. Southward drift during the

late spring and summer months is a result of the arrival of

this group of waves. The total wave-power of this northerly

group is about equal to the total wave-power of the winter

southerly waves.

This description of wave power in the study area is

based on data hindcast for deep-water stations off the west

coast (N.M.C. 1960, D.N.O.D. 1977). These data can only

be used to generate a rough estimate of the actual wave

11

climate of the study area. It is hoped that wave data

collections underway at the present time will provide a more

detailed view of this important aspect of the local beach

processes (Seymour et al. 1980).

Tides in the study area are mixed semi-diurnal, with

a mean tide range of about 1.5 meters, and a maximum tide

range of about 3.4 meters (N.O.A.A. 1980).

METHODS OF STUDY

Sample Collection and Processing

River sediment samples were taken at the waterline

on the depositional (inside) bank of meanders. Three

locations from the floodplains of the Mad and Eel Rivers

were sampled (Figure 2). Samples consisted of about two

kilograms of sediment, scooped by hand to a depth of 10

centimeters.

Beach samples were selected from approximately one

thousand samples of beach sediment taken as part of the

Sea—Grant project on harbor entrance shoaling (Kerstetter

1980). Samples were taken monthly from stations located at

0.8 kilometer intervals along the beach except near the

Humboldt Bay jetties where the sampling interval was 0.2

kilometers (Figures 4 and 5). Mileage along the beach was

determined with the odometer of the sampling vehicle.

Sampling sites were marked with stakes placed on the first

line of permanent dunes, where permitted. Samples were

identified by numbers corresponding to their distance from

the Eel River mouth in kilometers, negative values being

south of the river mouth and positive values being north of

the river mouth.

Samples consisted of approximately 200 cm.3 of sand.

Each sample represented four sub—samples taken from the

12

13

Figure 4. Beach sampling south of the harbor entrance. Next to each sampling location there are symbols indicating which analyses were performed on that sample. See legend for meaning of symbols.

14

Figure 5. Beach sampling north of the harbor entrance. Next to each sampling location there are symbols indicating which analyses were performed on that sample. See legend for meaning of symbols.

15

corners of a two meter grid. Samples were taken from

approximately mid-beach face to a depth of three centimeters

to represent the most recent beach-face transport (Bascom

1951).

Samples from two of the monthly sampling sets were

analyzed for sedimentary properties. The set collected in

late January and early February of 1979 represents the

winter high-energy condition. The set taken in September of

1979 represents the prevailing low-energy summer swell

condition.

River samples were hand sieved to remove particles

larger than -1 phi (2000 microns) and finer than 4 phi (63

microns), then treated the same as beach samples. Beach

samples were rinsed in fresh water and dried for two days in

an oven. 158 samples (79 each from winter and summer) were

analyzed for grain size parameters (Figures 4 and 5). Of

the samples analyzed for size, 41 (20 from winter, 21 from

summer) were further analyzed for heavy mineral content.

Samples were selected for mineralogical examination to

obtain equal coverage of the study area at approximately 3.5

kilometer intervals (Figures 4 and 5).

Grain Size Analysis

A thirty to fifty gram subsample was obtained from

each sample for grain-size analysis using a soil splitter.

Samples were sieved to quarter-phi intervals by placing them

16

in a Ro—Tap mechanical sieve shaker for twelve minutes. The

fraction of sample retained on each sieve was weighed to a

precision of 0.005 grams. The mean, standard deviation,

skewness, and kurtosis values of the grain size

distributions (based on the weight percent of the sample in

each size class) were calculated using central moment

derived measures (Blatt et al. 1972). In addition the

mode, or the most prevalent size class of the distribution

by weight, was calculated. Details regarding derivation of

statistical descriptors of the grain size distributions are

given in Blatt et at. 1972.

Mineralogical Analysis

The heavy mineral fraction of the size interval

between 1.75 phi and 2.75 phi was separated by gravity

settling in tetrabromoethane (specific gravity=2.90). The

restricted grain size was used for two reasons: 1) to

facilitate petrographic grain identification by

standardizing the grain thicknesses observed through the

microscope, and 2) to make the results more indicative of

provenance differences rather than sorting effects. The

1.75 phi to 2.75 phi size fraction was used because

particles in this size range were found in nearly every

sample. A two to three gram split of the sample was used in

the separation. Heavy minerals were mounted on microscope

slides in Canada Balsam (refractive index=1.56).

17

Prior to examination, each slide was randomly

assigned a letter identification symbol in order to

eliminate bias in counting. Samples were counted using a

petrographic microscope which was arranged to allow

reflected light examination of the grains as well as

transmitted light observation. The slide counts were made

in two steps: 1) counting one hundred grains of all types

in order to determine the percentage of non-translucent

grains, and 2) counting at least one-hundred translucent

grains. Minerals were identified using standard

petrographic techniques, tables, and references (Krumbein et

al. 1941, Milner 1962). During mineralogical examination,

grain shape and surface texture (roundness) were observed

and compared to standard figures (Powers 1953).

Statistical Analyses

I have analyzed the data for grain size trends by

statistically treating the aerial distribution of modal

values. Modal values were used instead of mean values

because they have use in ascribing provenance (Curray 1960),

and because the mean values (since they are based on

logarithmically transformed weight percentage measures) have

been questioned by some authorities as a basis for

statistical comparison (Blatt et al. 1972).

Aerial trend analyses were performed on the modal

grain size values by performing linear regressions of the

18

size values on alongshore location. The coefficient of the

resulting regression' was tested for significance. Unless

otherwise stated, the significance level for all tests of

significance was 0.01. Seasonal differences in modal grain

size were tested for significance by comparing samples taken

in both seasons from identical (staked) sites, and applying

the paired sample t-test. In order to test for separable

regions in sorting and sqewness values during a single

month, regime boundaries were selected visually, and, in the

cases of both sorting and sqewness in winter, a two-sample

t-test was used. For summer sqewness values, aerial trends

were discerned by testing the significance of the regression

of sqewness on alongshore location.

Mineralogical results were not subjected to

statistical analysis because of low precision in the results

of the examination of about 100 translucent grains per

slide. The mineralogical results, however, can be viewed as

being indicative of major trends which may be deserving of

more thorough statistical treatment in the future.

The error involved in determining ratios of heavy

minerals to light minerals is unknown, depending to a great

extent upon the skill of the worker, the materials and

methods used (Twenhoffel et al. 1941). Error involved in

this phase of analysis may compound difficulties in

interpreting results of the final petrographic analysis, but

does so to an unknown extent.

AERIAL DISTRIBUTION OF GRAIN SIZE PARAMETERS

Results

The most common size constituent of the beach

sediments became significantly finer with distance northward

in the study area during both winter and summer. Modal

values ranged from 0.125 phi (875 microns) in the south to

2.625 phi (225 microns) in the north (Figures 6 and 7).

During the winter high river-flow season the coarsest beach

sediments were located at, or Just north of, the Eel River

mouth (kilometer 0). Average and modal grain size decreased

in both directions from this point. In the summer, the

coarsest sediments were 8.1 and 8.9 kilometers south of the

Eel River. Most of the modal values south of the Eel during

the summer clustered around 1.125 phi (450 microns), with

the gradual fining trend beginning Just north of the Eel

River.

There was more variance in modal grain size among

samples south of the jetties than among samples north of

them in both seasons. There was not a significant

difference overall in modal grain size between seasons

(Figure 8).

Mean size values calculated from central moment

statistics showed the same general trend of fining to the

north as in the mode (Figures 9 and 10). However in the

mean values, a region of lower phi values (coarser mean

10

Figure 6. Most common size constituent (mode) of the beach samples--winter. Best-fit line indicates trend of decreasing modal size toward north. Correlation is significant at the 0.01 level (correlation coefficient=0.8673, number of samples=79).

20

Figure 7. Most common size constituent (mode) of the beach samples--summer. Best-fit line indicates trend of decreasing modal size toward the north. Correlation is significat at the 0.01 level (correlation coefficient=0.8392, number of samples=79).

21

Figure 8. Modal difference between seasons. Open circles represent the summer value minus the winter value for sites marked with stakes. Line through data represents line of no seasonal difference. Points above the line were sites finer in summer, those below the line were sites coarser in summer.

22

Figure 9. Mean grain size--winter.

23

Figure 10. Mean grain size--summer.

24

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sizes) was observed Just south of the Mad River mouth,

between about kilometer 32 and kilometer 42 in the winter,

and between about kilometer 35 and kilometer 41 in the

summer. The excursion to lower mean values implies the

presence of a coarse "tail" or secondary modes on the beach

in this region. In the area noted by coarser mean values,

the beach was observed to include occasional patches of

gravel on the surface, or an underlying layer of

coarse-medium sand.

Sorting of beach sediments, as reflected by the

standard deviation of a sample's grain size distribution,

showed distinct seasonal differences in aerial distribution

(Figures 11 and 12). In the winter significantly lower

values of standard deviation were evident south of the

Jetties compared to north of them (Figure 11). North of the

jetties, along North Spit (from kilometer fifteen to about

kilometer thirty), during the winter there was generally

less variability in sorting than south of the jetties in the

same season, and values were low, indicating well-sorted

sediment. An exceptional point was found at kilometer 23.3,

which during the winter was much less sorted than other

samples from North Spit. This sample was taken from a

disposal site of dredge spoils materials of a generally

coarser nature than the surrounding beach, and is an

artifact of the active erosion of these materials onto the

beach at this point during the winter cut-back of the berm.

Adjacent to and south of the Mad River mouth (kilometer 32

Figure 11. Standard deviation of the grain size distributions--winter. South of the.Humboldt Bay mouth (kilometer 14.5), the samples are significantly less sorted than north of the bay mouth (significance level=0.05, t=2.83, degrees of freedom=77).

26

Figure 12. Standard deviation of the grain size - distributions—summer. South of the Humboldt Bay mouth, the samples are significantly less sorted than from the same area in winter (significance level=0.01, t=4.92, degrees of freedom=36).

27

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to kilometer 41), there were several poorly sorted samples.

North of the Mad River mouth the samples were very well

sorted.

In the summer set, the same general regions of poor

and well sorted sediments were observed. However,

differences in the boundaries of, and values within, the

regions of elevated values were evident (Figure 12). South

of the Jetties during summer there was more variation among

samples than during winter, with significantly higher values

of standard deviation. In summer, the zone of poor sorting

south of the Mad River mouth extended southward only to

Kilometer 35.

Skewness values in winter appear to be divided into

two regimes north and south of kilometer 31 (Figure 13).

For samples south of kilometer 31, the average sqewness

value was a near-symmetrical -0.003, while north of this

point the average sqewness value was -0.833. Significantly

smaller (more negative) sqewness values from north of

kilometer 31 than from south of this point showed either the

presence of a coarse tail or loss of fines north of

kilometer 31 compared to samples to the south.

In summer a two-regime pattern was also displayed by

the sqewness values. However in summer the break between

the two regimes was located at the Humboldt Bay jetties

(Figure 14). North of the Jetties there was a significant

correlation of increasingly negative sqewness with distance

northward. There was a visually observed offset between

Figure 13. Skewness of the grain size distributions--winter. Skewness values south of kilometer 31 average 0.003, significantly different than values north of kilometer 31, which average -.0833 (significance level=0.01, t=9.922, degrees of freedom=77).

29

Figure 14. Skewness of the grain size distributions--summer. Best-fit lines through points were tested for significance. Significant regressions of values from alongshore locations north of the bay mouth (significance

level=0.01, correlation coefficient=0.735, degrees of freedom35) indi-cates northward trend to smaller skewness values. Offset between lines at the bay mouth is such that higher values are from just north of the jetties than just south of them.

30

31

south and north of the Jetties, with larger skewness values

Just north of the Jetties than just south of them.

A trend to smaller values of skewness may indicate

the gradual loss of the finest part of the size distribution

(Inman 1949). An abrupt increase in values may represent a

sudden loss of coarse or gain of fine particles and a sudden

decline in skewness may represent the opposite.

Discussion

Northward Longshore

A hypothesis of northward bulk longshore transport

is supported by the grain size data. The general fining of

the beach to the north may reflect sorting accomplished

during longshore transport. Specifically, fine grains may

travel alongshore

more rapidly than coarse grains,

establishing a larger proportion of fines on the beach with

increasing distance from the source. The literature is

divided on the issue of which grain size is most readily and

rapidly advected downcurrent. Inman (1949) argues on both

theoretical and empirical grounds that the 2.6 phi (170

micron) size fraction is most rapidly transported in a

variety of environments. Also, Ingle (1966) has assembled

data which show that the 2.5 to 2.75 phi (180 to 200 micron)

sizes take the least energy to move alongshore (see also:

32

Raudkivi 1967). However, in measurements obtained on a low

energy beach, Komar (1977) found that the -0.25 phi (1200

micron) grain size fraction moved alongshore most rapidly,

with finer grains traveling more slowly. Komar's (1977)

results probably indicate the importance of rolling and

saltation grain transport modes in his low energy study

area. In a high energy beach, such as the present study

area, suspension load becomes more important, and rolling

may be only a minor mode of transport. Finer grains become

suspended in the water column more easily than coarse

grains, and spend more time exposed to longshore currents.

Therefore, fines would probably be transported more rapidly

alongshore in the study area than coarse grains because of

the high wave energy level.

The general improvement in sorting for samples from

North Spit compared to samples from south of the Jetties

indicates that the beach sediments undergo sorting with

northward drift. The existence of poorly sorted samples

north of kilometer 32 in winter and north of kilometer 35 in

summer may indicate the addition of relatively poorly sorted

Mad River materials.

The rather abrupt sqewness decrease at the

31-kilometer mark in the winter distribution is indicative

of a coarse tail being added to the grain size distribution

north of this point, presumably by Mad River derived

materials. During summer, the regions both south and north

of the Humboldt Bay jetties show trends of northward

33

decrease in sqewness, which is consistent with net northward

transport of material (Inman 1949).

The northward bulk longshore transport hypothesis

implies that the Eel River is the chief sediment supplier to

the entire study area.

Evidence for Selective Trapping in the Bay Mouth

In addition to selective longshore transport rates,

another mechanism which may produce alongshore trends in

grain size parameters is selective removal of particular

grain sizes by size-selective trapping. Some aspects of the

grain size data indicate that the entrance to Humboldt Bay

represents a size-selective littoral trap. Patchiness in

grain size from south of the Humboldt Bay Jetties, as

indicated by variability in modal, mean, and sorting values,

is in sharp contrast to the finer and better sorted

sediments along North Spit. The entrance channel may act as

a "littoral sediment filter", reducing the range of grain

sizes present as longshore movement passes sediment through

the channel system from south to north. Since the beach is

generally finer north of the harbor mouth, and since

sqewness values in summer indicate a sudden loss of coarse

particles at the Jetties, it must be coarse particles which

are preferentially removed from littoral transport at the

channel. The sediments north of the Jetties may be viewed

as a fine, relatively homogeneous differentiate of a more

34

heterogeneous and generally coarser "lag" sediment from

south of the harbor mouth.

Effects of Mad. River Sediment on the Beach

The occurrence of coarser, poorly sorted samples

(presumed to be the effect of the input of Mad River

materials) at about kilometer 32 to 35, Just south of the

Mad River mouth appears to contradict the bulk northward

drift hypothesis. However, these observations may be

explained by other processes.

Part of the solution to this problem may involve the

northward migration of the Mad River outlet. During the

two-year period November 1978 to November 1980 the mouth of

the Mad River migrated 500 meters north, an average rate of

0.25 kilometers per year. This migration is apparently

cyclic, with the mouth opening as far south as about

kilometer 36, then migrating northward for a period of

years, and finally re-opening at the southernmost point

again. The observed coarse underlying sediment could

represent materials deposited in the Mad River mouth when it

was both farther south and at flood stages with the

competence to move a coarse sand and gravel load. The

coarse materials deposited under high-flow conditions might

remain on the beach as a sluggish lag deposit at the site

where the Mad River outlet deposited them.

The lag of gravel and very coarse sand is subject to

35

seasonal burial by the onshore movement of finer particles

from the surf-zone during the relatively lower energy

non-winter months. The coarsening of the beach extends

farther southward, and is greater in magnitude, during

winter when the beach is in an eroded condition. The coarse

deposits are buried during beach accretion in the southern

part of the disturbed zone. However, in the northern part

of the disturbed zone, beach accretion is apparently not as

efficient in covering up the lag.

A possible additional process in maintaining coarse

particles south of the Mad River mouth is size selective

trapping of littoral materials by the lower Mad River

channel analagous to that proposed for Humboldt Bay. Such a

littoral sediment filter would explain the nearly uniform

fineness of the beach north of the Mad.

Lower wave energy north of the Mad than south of it

may also be a contributing factor to the maintenance of

coarser samples south of the mouth than north of it.

Refractive and diffractive wave energy losses in the lee of

Trinidad Head, and wave energy dissipation over the

generally shallower offshore waters north of the Mad River

may cause the beaches north of the Mad to have a lower wave

energy level. This is a complicated region which will

require more detailed examination.

The grain size data generally support the model of

Eel River dominance of the beach sediment system and of a

bulk northward longshore transport. The Mad River may only

36

become an important contributor during extremely high flows.

Alongshore Wave Energy Gradient

An alternative hypothesis to that of bulk northward

drift as an explanation for the general northward fining

-trend in the grain size data is that a wave energy gradient

exists alongshore in the study area. DeGraca and Eckar

(1974) suggested that a zone of wave convergence may exist

in the southern half of the study area due to refraction by

the Eel River delta offshore.. Convergence would cause the

southern half of the study area to have a higher wave energy

level than the northern sector. This suggestion has not

been tested, but could lead to the observed gradation in

average particle size observed in the study area because,

all else being equal, beaches with low energy waves tend to

be finer-grained than beaches with high energy waves (Bascom

1951).

While the northward bulk longshore transport

hypothesis suggests that much of the relatively unsorted

material arriving at the shoreline from the rivers remains

in the littoral zone and is subjected to size-sorting by

longshore currents, the wave gradient hypothesis suggests

that the relatively unsorted materials from the river may be

immediately size-sorted by wave action upon arrival at the

shore. In order to create the observed northward fining by

an alongshore wave gradient mechanism, fines would have to

37

be lost (presumably to offshore) in the southern half of the

study area, while fine and coarse particles would both be

retained in the northern half.

This process may occur to some extent, but it is

difficult to perceive it as a controlling process in

producing the grain size trend in the study area. Skewness

values do not show truncation of the fine tail of the grain

size distributions in the area of high energy hypothesized

by DeGraca and Eckar (1974). Also, sorting does not become

markedly and gradually poorer toward the north, which would

be expected if a wider range of grain sizes were generally

being maintained on the beach in the north than in the

south. Instead, poor sorting is restricted to an area

immediately adjacent to the Mad River mouth, as previously

discussed, which indicates that the input of Mad River

materials. causes a very localized disturbance unrelated to

the major fining trend throughout the study area. In

addition, the relative smootheness of the northward fining,

showing no area in the south which appears to be the focus

of wave energy by having elevated modal sizes, argues

against the wave energy difference hypothesis.

HEAVY MINERAL-LIGHT MINERAL RATIOS

Results

The ratio of heavy minerals to light minerals in the

1.75 to 2.75 phi size range, expressed as the percentage of

heavy minerals in that size range, varied both seasonally

and spatially in the study area (Figure 15). The winter

values ranged from 1.53 percent to 5.07 percent, with a mean

of 2.58 percent. There were no regular longshore trends

during winter. During summer, however, a three-region

pattern emerged. South of the Humboldt Bay jetties, for

fifteen kilometers on either side of the Eel River mouth

there were somewhat variable values with an average of 1.82

percent, and no value below one percent. From the jetties

north to kilometer 32 the values were all low; none of the

six adjacent samples from North Spit contain even one

percent heavy minerals. From kilometer 35 to the northern

end of the study area, the values were again elevated to

about two percent, with the exception of a single point at

kilometer 41. The anomalous sample was taken in part from a

beach placer deposit and was influenced by this sampling

error.

Discussion

Alongshore patterns in heavy mineral abundance may

38

Figure 15. Heavy mineral abundance along the beach. The curves display the weight-percentage of the 1.75 phi to 2.75 phi size fraction which is contributed by heavy minerals (specific gravity= 2.9). 39

40

express the effects not only of sedimentary source

(provenance), but of sorting related to sediment movement

subsequent to arrival at the shoreline (White et al. 1967).

Lowright et al. (1972) noted that heavy minerals were found

in higher proportion to lights near source areas. DuBois

(1972) showed that cross shore movements may also be

important in determining the heavy-light ratio expressed on

the beach face.

The relatively high concentration of heavy minerals

on the beach near both the Eel and Mad River mouths during

summer are probably an expression of the overall longshore

spreading of sand in both directions from both sources.

Within a restricted grain size such as I examined, the

heavies may be less easily entrained than the lights and

thus tend to lag behind them in transport. This would form

a region near the source which is enriched in heavies. In

addition, heavies have been found to become preferentially

buried in the beach sediments, and may become removed from

transport this way (Clifton 1969), also leading to decreased

heavy-light mineral ratios downcurrent from the source.

The elevated heavy mineral content throughout the

area south of Jetties implies that the Eel River is the

primary source and that heavy minerals must be transported

northward from the Eel river to at least the Humboldt Bay

Jetties. If lights outstrip heavies in transport, then Eel

River materials must be transported north of the Jetties and

along North Spit. This evidence supports the bulk northward

41

drift hypothesis proposed to explain the grain size data.

The rather sudden drop off of heavy minerals during

the summer north of the jetties compared to the south may be

explained by the existence of a selective trap in the

entrance channel system. The heavies in the analyzed sizes

would be filtered out along with coarser light grains in

accordance with the principle of hydraulic equivalence

(Rubey 1933; Blatt et al. 1972). This selective removal

process would augment the selective transport process

described above in creating the observed small heavy-light

mineral ratios from along North Spit.

The occurrence of elevated quantities of heavy

minerals south of the Mad River mouth (north of kilometer

35) coincides with the region of coarser grain sizes caused

by the introduction of Mad River materials. The same

processes (chiefly northward river mouth migration)

responsible for the coarser grain sizes may be responsible

for the elevated heavies. In the heavy mineral fraction

abundance, however, unlike in the coarse grain sizes, the

elevation of values extends north of the Mad River to the

northern end of the study area. This elevation may

represent northward mixing of Mad River materials with

sorted Eel River sand. Alternatively it may be an

expression of the proclivity of heavies to be concentrated

in the finer sand grain sizes (Pettijohn et al. 1972).

Since these fine sizes are the major sedimentary

constituents north of the Mad, the elevation of heavies may

42

be an artifact of this association. More detailed analyses

are needed to resolve these possibilities.

The larger area of elevation in heavy mineral

content around the Eel than around the Mad may be evidence

of the dominance of the southern sediment source. It could,

however, be the expression of more rapid transport in the

southern sector, as proposed by DeGraca and Eckar (1974). I

believe that it is a combination of more sediment and faster

transport.

The generally higher abundance of heavy minerals in

the winter samples compared with summer samples reflects the

seasonal effects of beach cutback in winter. Light grains

have been found to move offshore more readily than heavy

grains during episodes of beach cutback (Rao 1957). This

process allows the beach face to become enriched in heavy

mineral particles during winter. Simultaneously, the winter

surf-zone becomes enriched in light particles which have

been preferentially moved off of the beach face. During

spring and summer, onshore movements, which build the broad

summer berm, "swamp" the beach face with particles which had

resided in the surf zone during winter. Therefore the

summer samples are depleted in heavy minerals relative to

the winter samples.

The locations discussed previously which display

either enrichment or depletion of heavy minerals in the

summer samples, then, reflect to some extent either the

enriching or the depleting .effects of sorting associated

43

with winter movement in the surf zone.. The summer samples

should therefore not be interpereted as indicating the

effects of longshore movement taking place during the summer

months.

HEAVY MINERALOGY

Results

The translucent fraction of the heavy mineral suite

of Eel and Mad River samples was dominated by amphibole

minerals including hornblende, glaucophane, and members of

the tremolite-actinolite series. In both rivers, pyroxenes

comprised the second most numerous class of minerals. The

metamorphic mineral epidote was the next most abundant

mineral in both rivers, followed by the accessory minerals

sphene, garnet, and sillimanite (Table 1).

Differences between the two rivers were observed in

the amount of hornblende and glaucophane, which comprised a

greater proportion of the translucent fraction of the Mad

River (54 percent) than of the Eel (40 percent). The

increase of amphiboles in the Mad relative to the Eel was

apparently at the expense of garnet and sphene--both of

which occured in relatively elevated percentages in the Eel

samples.

Substantial variations in relative percentages of

some minerals occured among samples from the same river.

Examples of this variation could be seen in the amount of

hornblende, garnet, clino-pyroxenes, and opaques from the

Eel River, and in the opaques and garnet content of the Mad

River samples.

The beach samples displayed mineral suites similar

44

45

Table 1. Heavy mineral percentages--river samples. Measured for one hundred grain count. T-A= tremolite-actinolite; HO=hornblende; GL=glaucophane; CPX=clinopyroxenes (augite-diopside); OPX=orthopyroxenes (enstatite-hypersthene); EP=epidote; GA=garnet; Sl=sillimanite; SPH=sphene; AP=apatite; OTH=other translucents; TNT=total non-translucents; LF=lithie fragments; OPQ=opaques.; Values given are percentage of translucent fraction, except for 0TH, LF, and OPQ, which values indicate percentage of total heavy mineral fraction. np=not present.

46

to both of the rivers sampled (Tables 2 and 3), however the

data showed that important differences existed between river

and beach samples. Beach samples typically contained more

hornblende and less sphene and opaques than either of the

stream sources. The only alongshore trend apparent in the

mineralogical data was the glaucophane abundance, which

showed an irregular decrease to the north (Figure 16)..

South of the Jetties, summer glaucophane abundance varied

around an average of about fifteen percent. North of the

Jetties there was an overall decrease except for elevated

values between kilometer 32 and the mouth of the Mad River

at kilometer 41.

Discussion

Similarities between the suite of heavy minerals

found in a typical beach sample during either season and the

suites displayed by 'both the Mad and Eel Rivers strongly

suggest that the active beach sediments are wholly

contributed by these streams. Only minor contributions can

be expected from sources which might have differing

mineralogical character, such as material contributed by

cliff erosion and by "leakage" around headlands.

Although no unique tracers were detected, it is

possible that the relative proportions of certain minerals

in the heavy mineral suite may be different for each river.

The present mineralogical data are not adequate for

47

Table 2. Beach heavy mineral percentages--winter. Measured for one hundred grain count. T-A= tremolite-actinolite; HO=hornblende; GL=glaucophane; CPX=clinopyroxenes (augite-diopside); OPX=orthopyroxenes (enstatite-hypersthene); EP=epidote; GA=garnet; Sl=sillimanite; SPH=sphene; AP=apatite; OTH=other translucents; TNT=total non-translucents; LF=lithic fragments; OPQ=opaques.; Values given are percentage of translucent fraction, except for 0TH, LF, and OPQ, which values indicate percentage of total heavy mineral fraction. np=not present.

48

Table 3. Beach heavy mineral percentages--summer. Measured for one hundred grain count. T-A= tremolite-actinolite; HO=hornblende; GL=glaucophane; CPX=clinopyroxenes (augite-diopside); OPX=orthopyroxenes (enstatite-hypersthene); EP=epidote; GA=garnet; Sl=sillimanite; SPH=sphene; AP=apatite; OTH=other translucents; TNT=total non-translucents; LF=lithic fragments; OPQ=opaques.; Values given are percentage of translucent fraction, except for 0TH, LF, and OPQ, which values indicate percentage of total heavy mineral fraction. np=not present, *=data unavailable.

Figure 16. Glaucophane abundance along the beach--summer.

49

50

statistical analysis, but variations between the two rivers

in the content of hornblende, garnet, and sphene may

ultimately prove distinctive for each river. Variations in

hydraulic properties between different locations in a river

leads to variations in relative mineral abundances at the

different sites, and indicates that the problem of

separating the rivers mineralogically is very complex and

would require extensive investigation.

Differences between either river's heavy mineral

suite and that of any beach sample suggests that sorting

occurs between the river environment and the beach

environment. The sorting acts to enrich primarily the

hornblende component of the beach sediment in the analyzed

size fraction while depleting the opaques and sphene.

Clearly, this implies that simple mixing of the two sediment

sources is not the only process operating to create the

heavy mineral suite of the beaches. Sorting between river

and beach environments is an important and unknown

intervening step. As all mineral suites from along the

beach were very similar and there were no trends or

disturbances alongshore, even close to the river outlets,

and as there are no trends leading away from the river

mouths (with the exception of glaucophane), this initial

sorting must occur prior to the arrival of sediments to the

shoreline. Since all river sampling sites were located

upstream of the region of tidal action in the rivers, I

propose that the sorting takes place in the lower reaches,

51

or "estuary", of the rivers under the action of oscillating

tidal currents. Despite differences in the relative amounts

of certain minerals between the two rivers, therefore, it is

not possible to ascribe absolute provenance to any beach

sample.

The alongshore density sorting observed in the

heavy-light ratios were not, apparently, carried out to any

appreciable degree among the heavy minerals themselves.

This implies that the density sorting process associated

with longshore transport is fairly gross and is not

sensitive to small density differences between minerals.

Because both rivers contained substantial amounts of

glaucophane, and since the Mad river displayed if anything

more glaucophane than the Eel River, the apparent general

northward decrease of glaucophane is surprising. The

decrease of glaucophane from near riverine abundances in the

south to lower than riverine values in the north implies

that glaucophane is somehow preferentially lost to the beach

transport system with bulk transport northward.

A plausible explanation of the trend is the

restriction of glaucophane to the coarser of the analyzed

sizes. Then glaucophane would- occur in lower abundances

away from the source as it lags behind in transport with the

rest of the coarse grains. If in the source rocks

glaucophane crystals were larger than the other heavies were

in their source rocks, then a size restriction might

ultimately result on the beaches (Briggs 1963).

52

Restriction of glaucophane to the coarse fractions

would also explain its paucity in the uniformly fine grained

beach north of the Mad River. The peak in values south of

the Mad may be generally associated with the coarse

components which occur there.

Another, although less plausible, explanation for

the trend in glaucophane is its possible loss to the

littoral transport system as a result of its mineral

character. For example, glaucophane could conceivably be

more friable, or less stable, than other minerals and be

gradually removed from transport by eroding away as it

spends time on the beach. The problem with this explanation

is that glaucophane shares many mineralogical properties

with other minerals in the heavy suite, yet no similar trend

in abundance is observed for any other mineral.

CONCLUSIONS

Bulk Northward Transport

The grain size and heavy/light mineral ratio data

suggest that bulk longshore transport direction in the study

area is northward. This is a response to wave energy

arriving from the south during winter, at the same time that

the majority of fresh sediment is mobilized to the beach by

the river outflow. Apparently there is a very rapid sorting

of grains by size during winter by longshore drift

mechanisms in which the finer grains advect rapidly

northward from the Eel River, which is the major source of

beach sand to the study area. Sediments near the mouth of

the Eel River represent a heterogenous lag deposit. The

entrance channel to Humboldt Bay appears to filter the

coarser, heavier grains out of the beach sediments,

resulting in a more uniform beach along North Spit.

The Mad River probably is not a very important

sediment source except to the fine beach north of the Mad

River mouth. Also, at extremely high flows coarse sand and

gravel are deposited. These coarse deposits remain to some

extent, as markers of previous river mouth locations, while

the active river mouth migrates northward. Mixing of Eel

River and Mad River sediments takes place near the Mad River

outlet. North of the Mad River mouth, it appears that

refractive, diffractive, and dissipative wave energy

53

54

losses--perhaps in concert with size selective trapping of

beach sand by the lower reaches of the Mad--maintain a

relatively homogeneous fine-grained beach.

The bulk northward transport in the study area, in

contrast to the southward transport exhibited by most other

California beaches, results from differences in wave climate

and shoreline orientation between the study area and other

locales in California. The coastal tectonic orientation of

the study area, in concert with the extremely high sediment

yields of the provenance areas for the local coastal

sediments, has allowed the shoreline to orient facing

approximately WNW, the direction from which the greatest

proportion of the wave power comes. A very high southerly

component of wave power arriving during winter, the season

of the largest sediment input, effects an efficient drifting

of the beach sediment northward. Then, apparently, the

onshore movements. associated with wave power arriving from

directions more normal to the strike of the beach, moves

material which was in the surf zone during winter onto the

subaerial beach, with little southward drift.

By contrast, the majority of California beaches to

the south of the study area are forced by their tectonic

skeleton to face WSW. This orientation causes a major

proportion of the total annual wave power, that from west to

northwest, to impinge onto the surf zone at a northerly

oblique angle to the beach normal, engendering southward

bulk drift. Also, on beaches to the south there is a

55

smaller proportion of southerly wave energy in the total

wave climate, and these waves tend to arrive in summer, when

beach sediments are less mobile (Komar 1976).

The likelihood that the majority of the longshore

drifting of sand takes place during winter and is directed

northward should be taken into account by designers of

coastal engineering projects. Disposal sites of dredge

spoils, for example, might be located in such a way that

they do not immediately shoal channels again. Coastal

projects which would interfere with longshore drift should

not be located to the south of regions which have but little

beach sediment to protect the backshore from destructive

wave energy. The possible starvation of already sand-poor

areas should be considered prior to interfering with the

downstream sediment transport of the Eel River. Projects to

improve the entrance conditions at Humboldt Bay should be

aware of the mechanisms which give rise to shoaling.

Suggestions for Further Work

This study should be regarded as preliminary. Much

more knowledge is needed before a satisfactory level of

assurance about beach processes in the study area can be

reached.

Surely the accumulation of high quality, shallow

water wave data is fundamental to our further knowledge of

the system. I believe that such information from at least

56

two widely-spaced stations within the study area is

necessary to adequately respond to questions about

alongshore wave energy variation. In addition, the

acquisition of reliable and detailed bathymetry in the

shallow nearshore would allow for the elaboration of a

mathematical transport model including the entire study

area.

Sediments must be sampled from difficult surf zone

locations, because we need a better understanding of the

structure and composition of such a high energy surf zone.

Samples from offshore of the breakers might allow for a

satisfactory assessment of offshore losses. Closely spaced

observations should be made of beach processes at the mouth

of the Mad River, where curious things are apparently

happening. Finally, carefully planned tracer studies may be

used to confirm predictions about beach response in the

study area.

REFERENCES CITED

Bailey, E.H., ed. 1966, "Geology of Northern California", Cal. Div. Min. Geol. Bull. 190.

Bascom, W.H., 1951, "The relationship between sand size and beach face slope", Trans. Am. Geophys. Union., 32:866-874.

Blatt, H., G. Middleton, and R. Murray, 1972, The _Origin Of Sedimentary Rocks, Prentice Hall, New Jersey, 624

P.P.

Briggs, L.I., 1965, "Heavy mineral correlations and provenances", J. Sed. Pet., 35:935-955.

Brown, W.B.III, and J.R. Ritter, 1971, "Sediment transport and turbidity in the Eel River basin, California", U.S. Geol. Surv.., Water-Supply Paper 1986.

Clifton, H.E., 1969, "Beach lamination: nature and origin", Mar.. Geol., 7:553-559.

Curray, J.R., 1960, "Tracing sediment masses by grain size modes", International _Geological Congress, Report of the 21st Session Norden, Copenhagen.

DeGraca, H.M., and R.M. Eckar,1974, "Sediment transport, coast of Northern California", Am. Soc. Civ, Engin., National meeting, Los Angeles, California.

D.N.O.D., 1977, (Department of Navigation and Ocean Development), Deep-Water. Wave. Statistics for _the

California Coast-Station 1, D.N.O.D., Sacramento.

DuBois, R.N., 1972, "Inverse relation between foreshore slope and mean grain size as a. function of heavy mineral content", 83:871-876.

Evenson, R.E., 1959, "Geology and ground-water features of the Eureka area, Humboldt County, California", U.S. Geol. Surv., Water-Supply Paper 1470.

Ingle, J.C., 1966, The Movement of Beach Sand, Elsevier, Amsterdam, 221 pp.

Inman, D.L., 1949, "Sorting of sediments in the light of fluid mechanics", J. Sed. Pet., 19/2:51-70

I.E.E., 1968, (Interstate Electronics and Engineering), Preliminary Investigation of Littoral Drift

57

58

Characteristics Bolinas , Lagoon California, IEC-Oceanics Report 445-027, prepared for Bolinas Harbor District, Bolinas, California.

Johnson, J.W., J.T. Moore, and E.B. Orret, 1971, "Summary of annual wave power for ten deep water stations along the California, Oregon, and Washington coasts", Univ.

Tech. Report. HEL-24-9.

Judson, S., and Ritter, D.F., 1964, "Rates of regional denudation in the United States", Jour. Geophys.. Res., 69, pp. 3395-3401.

Karlin, R., 1980, "Sediment sources and clay mineral distributions off the Oregon coast", J. Sed. Pet. 50/2:543-560.

Kelsey, H.M., 1980, "A Sediment budget and analysis of geomorphic process in the Van Duzen River basin, north coastal California, 1941-1975: a summary", Geol._ Soc. Am. Bull. part 1, 91:190-195.

Kerstetter, T.A., 1980, "A study of the entrance problems at Humboldt Bay", California Sea _Grant College Program, Final Report, R/CZ-47

Komar, P.D., 1976, Nearshore Processes. and Sedimentation, Prentice-Hall, New Jersey, 429 pp.

Komar, P.D., 1977, "Selective longshore transport rates of different grain-size fractions within a beach, J. Sed Pet„ 47/4:1444-1453.

Krumbein, W.C., and F.J. Pettijohn, 1941, Manual of Sedimentary Petrology, D. Appleton-Century Co., New

York, 549 pp.

Lowright, R., E.G. Williams, and F. Dachille, 1972, "An analysis of some factors controlling deviations in hydraulic equivalence in some modern sands", Sed. Pet., 42/3:635-645

Milner, H.B., 1962, ...Sedimentary Petrography, MacMillan Co., New York, Vol. I 643 pp., Vol. II 715 pp.

Murray, S.P., 1967, "Control of grain dispersal by particle size and wave state", J. Geol., 75:612-634.

N.M.C. (National Marine Consultants), 1960, Wave Statistics for Seven Deep Water Stations Along the California

Coast, Santa Barbara, California.

59

N.O.A.A., 1980, United_ States Coast Pilot 7 16th ed., National Ocean Survey, Washington, D.C.

Noble, R.M., 1971 "Shoreline changes, Humboldt Bay, California", Shore and Beach, 39:11-18.

Pettijohn, F.J., P.E. Potter, and R. Stever, 1972, Sand and Sandstone, Springer-Verlag, New York, 618 pp.

Powers, M.C., 1953, "A new roundness scale for sedimentary particles", J. Sed. _Pet., 23:117-119.

Rantz, S.E., 1969, "Mean annual precipitation in the California region", U.S. Geol. Surv., Open-File Maps.

Rao, C.B., 1957, "Beach erosion and concentration of heavy mineral sands", Sed. Pet., 27:143-147.

Raudkivi, A.J., 1967, Loose, Boundary Hydraulics, Pergamon Press, New York, 331 pp.

Ritter, J.R., 1972, "Sand transport by the Eel and its effect on nearby beaches",U.S. Geol. Surv., Open-File Report.

Rubey, W.W., 1933, "Settling velocities of gravel, sand, and silt", Amer. J. Sci., 25:325-338.

Seymour, R.J., J. O. Thomas, D. Castel, A.E. Woods, and M.H. Sessions, 1980, California Coastal Data CollectIon Program Annual Report, 1979, California Department of Boating and Waterways, Sacramento, California.

Snow, D.T., 1962, "Beaches in northwestern California", Hyd. _Eng.. Lab., Tech. Report series

14, issue 25, 74 pp.

Twenhoffel, W.H., and S.A. Tyler, 1941, Methods of Study of Sediments, McGraw-Hill, New York, 183 pp.

White, J.R., and E.G. Williams, 1967, "The nature of the fluvial process as defined by settling velocities of heavy and light minerals",J. Sed.. Pet., 37:530-539.

APPENDICES

A. Numerical values of grain-size parameters--winter.

Site Mean MSt. Dev.de St. Dev. Skewness Kurtosis 49.1 2.436 2.625 0.289 -0.984 6.549 48.3 2.427 2.625 0.292 -1.055 7.083 47.5 2.439 2.375 0.240 -0.372 3.706 46.7 2.399 2.375 0.259 -0.374 3.154 45.9 2.415 2.375 0.257 -0.494 3.444 45.1 2.446 2.625 0.249 -0.647 4.467 44.3 2.426 2.625 0.283 -0.651 4.811 43.5 2.462 2.625 0.258 -0.591 4.041 42.7 2.336 2.375 0.299 -0.658 4.057 41.9 2.295 2.375 0.299 -0.651 4.765 41.1 2.258 2.375 0.440 -1.234 5.358 40.9 2.017 2.375 0.506 -0.893 3.605 40.7 2.169 2.375 0.460 -0.985 4.994 39.9 1.809 2.375 1.019 -1.271 3.129 39.1 2.256 2.375 0.304 -0.675 4.666 38.3 2.160 2.375 0.380 -0.554 3.495 37.5 1.776 1.875 0.553 -0.376 2.675 36.7 1.704 2.375 0.767 -0.589 1.946 35.9 2.210 2.375 0.348 -0.522 3.985 35.1 2.288 2.375 0.355 -1.269 7.009 34.3 2.045 2.375 0.659 -2.309 9.325 33.5 2.027 2.125 0.407 -0.918 5.267 32.7 1.965 2.125 0.484 -0.820 3.444 31.9 1.948 2.375 0.637 -1.350 4.701 31.1 2.096 2.125 0.354 -0.909 6.026 30.3 2.061 2.125 0.340 -0.514 3.550 29.5 2.179 2.375 0.299 -0.244 3.095 28.7 2.068 2.125 0.304 -0.173 3.101 27.9 2.149 2.125 0.289 -0.078 2.877 27.0 2.187 2.125 0.287 -0.103 2.909 26.2 2.207 2.375 0.293 -0.119 2.929 25.4 1.982 1.875 0.339 -0.137 3.004 24.6 1.895 1.875 0.386 -0.037 2.878 23.8 1.853 1.875 0.360 0.174 3.385 23.3 1.475 1.625 0.575 -0.657 3.621 23.0 1.724 1.875 0.344 -0.033 3.405 22.2 2.044 1.875 0.306 0.129 2.976 21.4 1.775 1.875 0.369 -0.060 3.056 20.6 1.897 1.875 0.305 0.054 3.243 19.8 1.873 1.875 0.388 -0.118 3.167 19.0 1.845 1.875 0.312 0.163 3.215 18.2 1.886 1.875 0.291 0.080 3.224 17.4 1.764 1.875 0.343 0.042 2.909

60

Values of grain-size parameters--winter (continued)

Site. Mean. _ Mde St.. Dev. Skewness Kurtosis 16.6 1.745 1.875 0.337 -0.139 3.204 16.3 1.996 1.875 0.287 0.011 3.084 16.2 1.996 1.875 0.287 0 011 3.084 15.8 1.694 1.625 0.338 -0.037 3.475 15.6 1.754 1.875 0.306 0.102 3.093 15.5 1.821 1.875 0.305 0.077 3.307 15.3 1.876 1.875 0.351 -0.367 3.471 15.1 1.949 1.875 0.343 -0.262 3.151 14.5 2.140 2.125 0.331 0.042 2.903 14.3 2.175 2.125 0.289 0.024 2.782 14.2 1.975 1.875 0.310 0.423 3.106 14.0 2.128 2.125 0.272 0.502 3.773 13.8 2.001 1.875 0.271 0.214 3.552 13.7 1.754 1.875 0.286 0.331 3.336 10.5 1.785 1.875 0.347 -0.062 3.533 9.7 2.052 1.875 0.289 0.321 3.275 8.9 1.697 1.875 0.389 -0.136 2.967 8.1 1.788 1.875 0.370 -0.204 3.518 7.2 1.302 1.375 0.376 -0.538 5.108 6.4 1.466 1.375 0.383 0.346 3.219 5.6 1.989 1.875 0.300 0.301 3.555 4.8 1.895 1.875 0.314 0.217 3.269 4.0 1.559 1.625 0.373 -0.081 2.937 3.2 1.554 1.375 0.349 0.077 3.484 2.4 1.364 1.375 0.399 0.077 2.970 1.6 1.350 1.375 0.483 -0.542 3.614 0.8 0.517 0.625 0.491 0.506 4.180 0.2 0.758 0.875 0.556 0.442 4.036 -1.6 1.100 1.125 0.391 -0.032 5.324 -4.8 1.744 1.625 0.344 0.149 3.432 -6.4 1.537 1.625 0.339 -0.225 3.444 -8.1 1.371 1.625 0.555 -1.273 5.371 -9.7 1.588 1.625 0.302 -0.055 3.644 -11.3 1.337 1.375 0.375 -0.061 3.016 -12.9 1.050 0.875 0.333 0.362 2.744 -13.4 1.118 1.125 0.282 0.440 5.016

61

62

B. Numerical values of grain-size parameters--summer.

Site Mean Mode St. Dev. Skewness. Kurtosis 48.9 2.551 2.625 0.274 -0.720 4.371 48.3 2.540 2.625 0.230 -0.480 3.689 47.5 2.453 2.625 0.288 -0.533 3.652 46.7 2.470 2.625 0.243 -0.432 3.245 45.9 2.448 2.375 0.251 -0.457 3.450 45.1 2.387 2.375 0.263 -0.362 2.957 44.3 2.457 2.625 0.254 -0.389 3.193 43.5 2.347 2.375 0.284 -0.426 3.175 42.7 2.453 2.375 0.251 -0.418 3.448 41.9 2.427 2.625 0.282 -0.437 3.106 41.1 2.458 2.625 0.290 -0.326 3.389 40.7 2.272 2.375 0.321 -0.349 2.905 40.7 1.991 2.375 0.715 -1.222 4.408 39.1 2.299 2.375 0.311 -0.359 3.025 37.5 0.908 2.375 1.091 0.064 1.733 35.1 1.235 2.375 1.139 -0.460 1.820 34.3 2.208 2.375 0.309 -0.171 2.692 33.5 2.348 2.375 0.269 -0.162 3.495 32.7 2.239 2.375 0.294 -0.241 2.860 32.3 2.226 2.375 0.309 -0.207 2.895 31.9 2.203 2.125 0.300 0.129 2.905 31.1 1.988 1.875 0.355 -0.101 2.984 30.3 2.130 2.125 0.297 0.014 2.831 29.5 1.927 1.875 0.298 0.312 3.020 27.9 1.840 1.875 0.314 0.032 2.982 26.2 2.045 1.875 0.255 0.321 3.102 24.6 1.838 1.875 0.311 0.101 3.525 23.3 1.693 1.625 0.335 0.288 3.353 23.0 1.979 1.875 0.353 -0.240 3.140 21.4 1.666 1.625 0.327 0.127 3.352 19.8 1.720 1.625 0.294 0.206 3.456 19.0 1.706 1.625 0.266 0.440 3.817 18.2 1.721 1.625 0.258 0.201 4.512 16.6 1.464 1.375 0.343 0.306 3.239 15.8 1.826 1.875 0.295 0.105 2.922 15.3 1.806 1.875 0.343 0.185 2.960 15.0 1.698 1.625 0.281 0.314 3.697 14.5 2.314 2.375 0.316 0.063 2.554 14.3 2.072 2.125 0.338 -0.222 3.334 14.2 1.979 1.875 0.379 -0.561 3.729 14.0 1.841 1.875 0.385 -0.506 3.553 13.8 2.083 2.125 0.298 -0.139 3.059

63

Values of grain-size parameters--summer (continued).

Site. Mean. Mode St. Dev. Skewness Kurtosis 13.7 1.688 1.625 0.337 0.470 3.307 12.9 1.751 1.875 0.356 -0.186 3.572 12.1 2.165 2.375 0.331 -0.120 2.873 11.3 1.738 1.875 0.390 -0.510 3.552 10.5 1.689 1.875 0.376 -0.533 3.991 9.7 1.677 1.875 0.382 -0.618 3.731 8.9 1.418 1.625 0.481 -0.991 4.813 8.1 1.422 1.625 0.538 -0.856 3.867 7.2 1.101 1.625 0.706 -0.592 2.897 6.4 1.743 1.875 8.341 -0.192 3.345 5.6 0.780 1.375 0.774 -0.335 2.250 4.8 1.885 1.875 0.358 -0.261 3.445 4.0 1.505 1.375 0.428 0.212 3.090 3.2 1.557 1.625 0.431 -0.900 5.605 2.4 1.620 1.625 0.374 -0.328 3.893 1.6 1.719 1.875 0.369 -0.058 3.150 0.0 1.652 1.625 0.393 -0.125 3.567 -0.8 0.724 0.875 0.747 -0.153 2.382 -1.6 1.372 1.375 0.396 0.095 3.366 -2.4 1.307 1.375 0.386 -0.347 3.627 -3.2 1.459 1.375 0.341 0.041 3.249 -4.0 1.047 1.375 0.547 -0.678 3.706 -4.8 0.893 0.875 0.588 -0.561 3.174 -5.6 0.930 1.375 0.651 -0.545 2.803 -6.4. 0.869 0.875 0.533 -0.446 3.050 -7.2 0.924 0.085 0.561 -0.603 3.132 -8.1 0.243 0.125 0.602 0.189 2.657 -8.9 0.415 0.125 0.645 0.029 2.382 -9.7 1.511 1.625 0.355 -0.310 3.368 -10.5 1.148 1.375 0.496 -0.253 2.724 -11.3 0.874 0.875 0.635 -0.412 2.602 -12.1 1.383 1.375 0.371 -0.028 3.044 -12.9 1.104 0.875 0.463 0.202 2.287 -13.7 1.290 1.375 0.388 0.018 2.725 -14.5 1.454 1.625 0.358 -0.172 3.127

C. Numerical values of heavy mineral abundances.

Site Summer Winter 47.5 1.59 1.38 44.3 2.10 3.16 41.1 13.4 2.54 40.7 2.03 37.5 0.77 34.3 2.00 1.72 31.1 0.96 1.35 27.9 0.42 27.8 1.74 24.6 0.61 5.07 21.4 0.74 1.38 18.2 1.93 13.7 0.89 1.06 10.5 1.22 3.15 7.3 2.79 3.83 4.0 1.19 1.75

.0.8 1.53 -1.6 2.97 2.96 -4.8 1.36 3.88 -8.0 4.23 -9.7 3.64

-11.3 1.14 4.93 -14.5 1.01

64