Analysis of Ocean Current Meter Records Obtained from a 1975 Deployment· off the Farallon Islands, California


520/1-83-019

PB84-106475

Analysis of Ocean Current Meter Records
Obtained from a 1975 Deployment off the
Farallon Islands, California

Battelle Pacific Northwest Labs., Richland, WA
Prepared for

Office of Radiation Programs, Washington, DC
Aug 83



3

I

National Technical Information Service

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TECHNICAL REPORT DATA

(I'lease read Instructions on the reverse before completing)

1. REPORT NO.

EPA 520/1-83-019

2.

J. RECIPIENT'S ACCESSIQN.Nfi. gm

PBS A 106*7 5

4. TITLE AND SUBTITLE

Analysis of Ocean Current Meter Records
Obtained from p 1975 Deployment Off the
Farallon Islands, California

5. REPORT DATE

August 1983

6. PERFORMING ORGANIZATION CODE

7. AUTHOR(S)

David E. Crabbs

8. PERFORMING ORGANIZATION REPORT NO.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

Interstate Electronics Corporation



10. PROGRAM ELEMENT NO.

Anaheim, California 92803



11. CONTRACT/GRANT NO.

IAG No. AD-89-F-1-607-0
Subcontract No. B-C2076-A-X

12. SPONSORING AGENCY NAME AND ADDRESS

Office of Radiation Programs
U.S. Environmental Protection Agency
401 M Street., S.W.

Washington, D.C. 20460

13. TYPE OF REPORT AND PERIOD COVERED

Final

14. SPONSORING AGENCY CODE

ANR-461

15. SUPPLEMENTARY NOTES

16. ABSTRACT

\
i









'""Two bottom current records were obtained during August and September 1975
in the Farallon Islands low-level radioactive waste disposal area off San
Francisco, California. This report presents the results of the data
reduction and analysis ox the curent meter records,and interprets the
results with respect to additional data collected in 1977. An effort is
made to compare the patterns of current activity in the dumpsite area for
the time periods measured.^It is proposed that while the possibility of
transport of suspended material from within the dumpsite area cannot be
ignored, conditions which prevailed at the time and location of
measurements surest that there is little tendency for shoreward
transport of resuspended sediment. However, measurements taken
throughout the year and over a wider area would be helpful in verifying
this propositon.

17.

KEY WORDS AND DOCUMENT ANALYSIS



a. DESCRIPTORS

b. IDENTIFIERS/OPEN ENDED TERMS

c. COSAT1 Held/Group

Ocean Dumping

Ocean Disposal/Sea Disposal
Low-Level Radioactive Waste Disposal
Ocean Bottom Currents off California
Radioactivity Transport





1P. DISTRIBUTION STATEMENT



1U. SECURITY CLASS (This Report/
Unclassified

21. NO. OF PAGES

67

1 Unlimited Release

i



20. SECURITY CLASS (This pane)

Unclassified

22. PRICE

EPA F orm 2220—1 (Rev. 4—77) previous edition is obsolete i

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United States	Office of	EPA 520/1-83-019

Environmental Protection	Radiation Programs	August 1983

Agency	Washington DC 20460

						PB84-1Q6475

Radiation					

&EPA Analysis	20

of Ocean Current
Meter Records Obtained
from a 1975 Deployment
off the Farallon Islands,
California

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EPA REVIEW NOTICE

This report has been reviewed by the Office of Radiation Programs,
U.S. Environmental Protection Agency (EPA) and approved for publication.
Approval does not signify that the contents necessarily reflect the views
and policies of the EPA. Neither the United States Government nor the
EPA makes any warranty, expressed or implied, or assumes any legal
liability or responsibility for any information, apparatus, product or
process disclosed, or represents that its use would not infringe on
privately owned rights.

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EPA 520/1-83-019

ANALYSIS OF OCEAN CURRENT
METER RECORDS OBTAINED FROM A 1975 DEPLOYMENT
OFF THE FARALLON ISLANDS, CALIFORNIA

By

David E. Crabbs

Interstate Electronics Corporation
Anaheim, California 92803

August 1983

This report was prepared as an account of contract work sponsored by the
United States Environmental Protection Agency under Interagency Agreement
No. AD-89-F-1-607-0 with Battelle Pacific Northwest Laboratories

Project Officer

Robert S. Dyer

Office of Radiation Programs
U.S. Environmental Protection Agency
Washington, DC 20460

• i

ll

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FOREWORD

In response to the mandate of Public Law 92-532, the Marine
Protection, Research, and Sanctuaries Act of 1972, as amended, the
Environmental Protection Agency (EPA) has developed a program to
promulgate regulations and criteria to control the ocean disposal of
radioactive wastes. As part of that program, the EPA Office of Radiation
Programs initiated feasibility studies in 1974 to learn whether present
technologies could be used to determine the fate of radioactive wastes
dumped in the past.

After successfully locating radioactive waste drums in previously
used United States dumpsites, the Office of Radiation Programs developed
a program of dumpsite-specific studies to look at the biological,
chemical, and physical characteristics of the sites, and the presence and
distribution of radionuclides within these sites.

A primary mechanism for physically dispersing and redistributing
both soluble and particulate radioactive materials from a dumpsite is the
action of ocean bottom currents. Of particular interest is the magnitude
and direction of these currents. The present report discusses the
results of two sets of ocean bottom current measurements obtained from
the Farallon Islands 1700-meter low-level radioactive waste dumpsite area
off California. These data are then compared with additional information
collected two years later by EPA in an area east and slightly south of
the 1700-meter dumpsite. The report concludes with a discussion of the
velocity of the currents over the time period and area measured relative
to large-scale currents off the California coast; and the possibility of
shoreward transport of materials is examined.

The Agency invites all readers of this report to send any comments
or suggestions to Mr. David E. Janes, Director, Analysis and Support
Division, Office of Radiation Programs (ANR-461), Environmental
Protection Agency, Washington, D.C. 20460.

-4lea. L. SjoblomV' Director
Office of Radiation Programs

iii

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ABSTRACT

This report addresses the reduction, analysis and interpretation of ocean
current meter data records obtained during August and September 1975 in the
vicinity of the radioactive waste disposal area near the Farallon Islands, off
San Francisco, California. The data are interpreted in light of results from
a later study which involved data taken in the same vicinity in the fall and
winter months of 1977, and an effort is made to compare the two measurement
programs and draw inferences about the patterns of current activity for the
portions of the year for which satisfactory measurements were taken (i.e., late
summer and autumn). It is proposed that while the possibility of transport of
suspended material from within the dumpsite area cannot be ignored, for the
locations and time periods measured, conditions which prevailed at the time of
measurement in this report suggest that there is little tendency for shoreward
transport of resuspended sediment. Measurements taken throughout the year and
over a larger range, particularly closer to shore, would be helpful in verifying
this proposition.

Preceding page blank

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TABLE OF CONTENTS

Section



Page

1

INTRODUCTION

1

2

SUMMARY

2

3

METER DEPLOYMENT

5



3.1	Description of Deployment

3.2	Array Location and Relation to 1977 Deployment

5

6

4

DATA REDUCTION AND ANALYSIS

10



4.1	Data Calibration

4.2	Statistical Moments

4.3	Histograms and Scatter Diagrams

4.4	Time History Records

4.5	Progressive Vector Diagram and Stick Plot

for Current Meter #1028

4.6	Coherence and Correlation Studies

10
10
18
26

26
31

5

DATA INTERPRETATION

43



5.1 General Comments on Current Meter Hardware
¦5.2 Discussion of Relationships Observed between

the 1975 and 1977-1978 Data
5.3 Discussion of Current Field

43

44
48

6

RESULTS AND CONCLUSIONS

54



6.1	Overall Data Quality and Consistency

6.2	Results for Meters 1009 and 1028

6.3	Observations on the Local Current Field

6.4	Potential for Transport of Suspended Materials

54

55

55

56

7

REFERENCES

57

vii

Preceding page blank

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LIST OF FIGURES

Figure	Page

2.1	Local bathymetry chart showing meter arrays

and waste disposal area	3

3.1	Meter array locations for 1975 and 1977 deployments	8

4.1	Histogram of speed (cm/sec) for meter 1009	19

4.2	Histogram of speed (cm/sec) for meter 1028	20

4.3	East/west component histogram for meter 1028	21

4.4	North/south component histogram for meter 1028	22

4.5	Scatter diagram for meter 1028, speed versus direction	23

4.6	Scatter diagram for meter 1028, north/south

versus east/west component	24

4.7	Scatter diagram, speed for meter 1009

versus speed for meter 1028	25

4.8	Time history plot of speed for 1028	27

4.9	Time history plot of east speed component for 1028	28

4.10	Time history plot of north speed component for 1028	29

4.11	Time history plot of speed for 1009	30

4.12	Progressive vector plot for 1028 raw data record	32

4.13	Progressive vector plot for filtered 1028 record	33

4.14	Stick plot for filtered 1028 record	35

4.15	Power spectral density for east component for 1028	36

4.16	Power spectral density for north component for 1028	37

4.17	Power spectral density for speed for 1028	38

4.18	Power spectral density for speed for 1009	39

4.19	Coherence for speed for meters 1009 and 1028	41

5.1	Vector averaged long term currents	50

5.2	Semi-diurnal tidal ellipses	52

viii

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LIST OF TABLES

Table	^

3.1	Current meter deployments - 1975

3.2	Current meter deployments - 1977

4.1	Summary statistics for speed - current meter data from

1975 survey, daily moments for current meter #1009

4.2	Summary statistics for speed - current meter data from

1975 survey, daily moments for current meter #1028

4.3	Summary statistics for E/W component - current meter data

from 1975 survey, daily moments for current meter #1028

4.4	Summary statistics for N/S component - current meter data

from 1975 survey, daily moments for current meter #1028

4.5	Speed moments

4.6	Component moments

4.7	Vector averaged velocities

5.1	Long term averages

5.2	Energy components for meter 1028

ix

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SECTION 1

INTRODUCTION

This report has been produced by Interstate Electronics Corporation for
Battelle Pacific Northwest Laboratories of the Department of Energy in fulfill-
ment of Subcontract Number B-C2076-A-X. The prime contract is between the
U.S. Environmental Protection Agency, Office of Radiation Programs, and the
Department of Energy and is being carried out under Interagency Agreement
Number AD-89-F-607-0 by Battelle. The subject of this report consists of the
reduction, analysis, and interpretation of ocean current meter data records
obtained during August and September 1975 in the vicinity of the radioactive
waste disposal area near the Farallon Islands. Also included is a discussion
of the relationships between the 1975 measurements and the measurements taken
in the same vicinity in late 1977 and early 1978. The latter measurements have
been reported on by Interstate Electronics Corporation in "Farallon Islands
Oceanographic Data Analysis," Volumes I and II, prepared under EPA Contract
Number 68-01-0796, Modification Number 20, in May 1982. The intent of the
present report is to analyze and interpret the 1975 data in the context of how
it relates to the 1977-1978 measurement program, including the potential for
suspended particle transport away from the dumpsite.

The remainder of this report includes six sections, numbered 2 to 7.

Section 2 provides a summary of the work performed under this subcontract.
Section 3 describes the meter array deployment and includes information relating
to the 1977-1978 deployment program. Section 4 addresses the reduction and
analysis of the 1975 data record, Section 5 offers interpretive results in the
contexts mentioned above, and Section 6 presents results and conclusions.
Pertinent references are listed in Section 7.

1

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SECTION 2

SUMMARY

Four current meters were emplaced near the Farallon Islands low-level
radioactive waste dumpsite, in August 1975, by the Scripps Institution of
Oceanography of the University of California, San Diego. This study was under-
taken to assess the current regime present in the dumpsite. Figure 2.1 shows
the spatial relationship between the current meter locations, the dumpsite,
the Farallon Islands, and the California coastline off San Francisco. The
meter recovery operation took place approximately one month later and yielded
two usable data records. These records were for two meters located at
37°37'30"N, 123°18'0"W and 37o38'30"N, 123°18'0"W at depths of 1729 m and
1849 m, respectively, and spaced approximately 2.3 km (1.3 nautical miles)
apart. One of the records did not contain any directional information due to
a hardware fault in the recording device, but the other record was subsequently
analyzed by Dr. Richard Schwartzlose of Scripps. The analyses performed by
Dr. Schwartzlose (Ref. 7) included generation of calibrated time history records,
and the extraction of tidal currents for production of tidal ellipses and a
progressive vector diagram. His results are referenced and briefly summarized
in References 2 and 6.

The purpose of the present study is to extend the analyses performed by
Dr. Schwartzlose on the 1975 data and to relate the results of this measurement
program with a subsequent current measurement program performed in the same
vicinity in 1977 and 1978.

The 1977-1978 current measurements were taken beginning in October 1977
using several Aanderaa current meters and a Vector Averaging Current Meter
(VACM). The deployment period lasted for one year, and the results of five
current meter records were reported on by Interstate Electronics Corporation
(Reference 4).

2

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(ADAPTED FROM REFERENCE 8)

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The present study provides low-order statistical analysis of the 1975 data
records, including summaries of the statistical moments, graphical representation
of the time histories of the measured and derived parameters, histograms, and
scatter diagrams. Further analysis includes the derivation of filtered time
series of the orthogonal speed components, with tidal contributions removed,
and the production of a progressive vector diagram and stick plot for the vector
data. Power spectral density plots are also provided to allow resolution of
the relative energy distribution among periodic current processes (i.e., tides,
internal waves, inertial effects, etc.). The spectral analysis includes an
assessment of the coherence of the different parameters at the frequencies
associated with the major sources of periodic motion. Finally, the data from
the 1975 measurement program are compared with the data from the 1977-1978
program, and an attempt is made to integrate the results into a broader
characterization of ocean current activity in the vicinity of the Farallon
Islands low-level radioactive waste dumpsite area. The results and conclusions
from this effort are summarized in Section 6.

4

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SECTION 3

METER DEPLOYMENT

This section concerns the deployment of the meters during the 1975 survey,
and gives the operational scenario.

3.1 Description of Deployment

In August 1975, four Savonius-rotor current meters were deployed near the
1700 m Farallon Islands nuclear waste dumpsite. The meters were arranged in a
rectangle, with one meter deployed approximately 2 m off the bottom at each
corner. The distance between corners was approximately 1.6 kilometers and the
center was located near the intersection of the 37°38'N parallel and 123°18'W
meridian.

The meters, developed at the Scripps Institution of Oceanography, measured
current speed to a 0.5 cm/sec sensitivity, and obtained directional measurements
by means of a potentiometric compass. A strip chart recording medium was used,
with the direction measurement indicated as a function of time on a scale from
0° to 360° magnetic. The speed was recorded in terms of the number of revolu-
tions of the rotor in a given time period. Specifically, a mark was placed on
the edge of the strip chart for each 16 turns of the rotor. Thus, the speed
was a function of the number of marks per unit length of strip chart.

Two of the measurement records were successfully recovered 27 days after
deployment. One was found to have no record of the current direction, although
the speed record appeared to be properly recorded throughout the 27-day period.
However, no analysis was made at that time.: The other recovered record was
found to be complete, and was subsequently calibrated and analyzed to generate
tidal ellipses and a progressive vector diagram.

5

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The reported locations, depths and times of operation for the two recovered
meters are given in Table 3.1.

3.2 Array Location and Relation to 1977 Deployment

The reported locations, depths and times of operation for the five meters
recovered from the 1977-1978 deployment period appear in Table 3.2. Note that
only one of the five meters, the VACM, had data records covering the August-
September period. However, as noted in the report on these meters (Reference 4),
the recovered VACM time record was not preserved in its correct order, and
reconstruction efforts were only partly successful. Nevertheless, some
correspondence between the 1975 and 1977-1978 records should be observable by
comparing the October/November time period in 1977 with the 1975 August/September
record to see if a trend can be obtained. Published literature on surface
currents and general phenomena in the Farallon Islands area can be used to judge
the consistency of any observed trend with trends predicated by general knowledge
of the area.

The locations of the five meters of the 1977-1978 program and the two
meters deployed in 1975 (#1009 and #1028) are shown in Figure 3.1. Note that
the distance units on the axes are in minutes of arc longitude, equivalent to
1 nautical mile (nm) on both axes. The 1977-1978 meters were emplaced approx-
imately 0.8 kilometers south of the southern edge of the rectangle formed by
the 1975 meters, and form an east/west line approximately 14.4 kilometers in
length. Thus, the overall configuration of the seven meters from the two
surveys is 1L1 shape with 3 points defining an east/west reference and 3 points
defining a north/south reference. The east/west portion of the 1L1 is displaced
in time from the remaining part by about 2 years and one month, and the central
point on the north/south reference does not include directional information.

Figure 2.1 shows the configuration of the seven meters overlaid on a
bathymetric chart of the Farallon Islands Waste Disposal Area. Reference 3
discusses the local bathymetry readings obtained during a 1974 survey conducted
by IEC, while Reference 8 contains published bathymetry for the region.

6

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TABLE 3.1

CURRENT METER DEPLOYMENTS-1975

METER START END NORTH WEST SITE METER COMMENTS
NO. DATE/TIME DATE/TIME LAT LONG DEPTH DEPTH

Cm) Cm)

1009 8/21/75	9/17/75 37°37'30" 123°17'0" 1731 1729 NO DIRECTION
21:00 15:30	RECORD

1028 8/22/75	9/17/75 37°38'30" 123°18'0" 1851 1849
2:30 17:00

TABLE 3.2
CURRENT METER DEPLOYMENTS-1977

METER START END	NORTH WEST SITE METER

NO. DATE DATE	LAT	LONG DEPTH DEPTH

(m) (m)

COMMENTS

2920 10/25/77 3/15/78 37°36'36" 123°07'32" 914 911 ARRAY B

2830 10/25/77 2/06/78 37°36'52" 123°14'46" 1372 912 ARRAY C.

GAPS IN
RECORD

VACM 10/25/77 10/24/78 37°36'52" 123°14'46" 1372 911 ARRAY C.

TRANSPOSED
TIME RECORDS

2918 10/25/77 12/21/77 37°36'51" 123°17'27" 1829 1800 ARRAY D

2919 10/25/77 3/10/78 37°36'51" 123°17'27" 1829 1826 ARRAY D

7

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42.00

40.00

36.00

34.00

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Figure 2.1 is largely adapted from Reference 8 with minor local adjustments
resulting from data obtained in the 1974 survey. The meters cover an east/west
transect close to the edge of the continental shelf.

9

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SECTION 4

DATA REDUCTION AND ANALYSIS

The topics covered in this section include all of the data reduction and
analysis performed on the two current meter records recovered in 1975. Compari-
sons with the 1977-1978 data are noted where pertinent.

4.1 Data Calibration

The two meter records recovered from the 1975 deployment required the speed
record to be calibrated and converted to metric units of measure. The speed
was recorded on a strip chart in terms of revolutions of the Savonius rotor.
A mark was made on the strip chart each time the rotor completed 16 revolutions.
Determining the velocity was thus a matter of counting the marks per unit length,
and then scaling and calibrating the result to give centimeters per second.
The scale factor used (i.e., 16) was multiplied by the number of marks per inch
at each half hour interval (1 inch = 1 hour), and the result was calibrated by
means of calibration curves provided by Scripps for the meters in question.

The direction record for meter number 1028 was read from the strip chart
in terms of magnetic north. The magnetic variation from true north was deter-
mined to be 14 degrees east at the deployment site, so 14 degrees was added to
each direction measurement to give the desired result in terms of true north.

4.2 Statistical Moments

The statistical moments (mean, standard deviation, skewness and kurtosis),
along with the minimum and maximum speeds are provided on a daily basis for
the speed record from meter number 1009 in Table 4.1. The summary statistics
for the full 27-day deployment period are also given at the bottom of the table.
The same statistical information is given for the speed record from meter
number 1028 in Table 4.2. Tables 4.3 and 4.4 give statistics for the east/west

10

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TABLE 4. 1

SUMMARY STATISTICS FOR SPEED

CURRENT METER DATA FROM 1975 SURVEY
DAILY MOMENTS FOR CURRENT METER #1009

DATE	MEAN MIN MAX STD. DEV. SKEWNESS KURTOSIS

8/21/75

10.81

9. 06

15. 16

2. 03

1.07

2.81

8/22/75

6. 75

1.38

17. 87

4. 29

.91

2. 86

8/23/75

5. 49

.00

16. 10

3. 53

. 86

3. 18

8/24/75

4. 24

.00

11.02

2. 36

.72

3. 26

8/25/75

3.51

.00

7. 64

1.74

.28

2. 58

8/26/75

3. 52

.00

7. 64

2. 00

.41

2. 53

8/27/75

3. 66

.00

8. 43

1.96

.51

2. 80

8/28/75

3. 84

.00

10. 23

2. 05

.62

3. 73

8/29/75

4. 18

.00

10. 23

2. 68

.65

2.51

8/30/75

5. 64

.00

17.31

3. 80

.84

3. 20

8/31/75

4. 11

1. 38

10. 23

2. 29

1.04

3. 15

9/01/75

5. 18

.00

17.31

3. 03

1.24

6. 27

9/02/75

4.31

.00

11. 58

2. 78

.63

2. 50

9/03/75

4. 49

.00

13. 98

2. 82

.91

4. 16

9/04/75

5. 49

.00

16. 75

4. 56

.96

2. 65

9/05/75

6. 60

1.38

20. 61

4. 15

1.29

4. 77

9/06/75

7. 26

1.38

13. 42

3. 02

.04

2. 38

9/07/75

4.61

.00

13. 42

2. 83

1.00

3. 73

9/08/75

3. 69

.00

6. 92

2. 04

.24

1.88

9/09/75

5. 55

.00

19. 87

4. 49

1.60

4. 90

9/10/75

7. 48

1.38

18. 44

4. 12

.84

3. 09

9/11/75

7. 95

1. 38

17. 87

4. 33

. 15

1.89

9/12/75

8. 12

.00

18. 44

4. 72

. 20

2. 19

9/13/75

8. 03

1.38

17.31

3. 89

.20

2. 09

9/14/75

6. 75

.00

12. 85

2. 92

-. 11

2. 24

9/15/75

5. 05

1.38

11.58

2. 70

.70

2. 62

9/16/75

5. 34

.00

11.58

3. 09

.32

2. 12

9/17/75

9. 05

1.38

16. 75

3.61

-. 24

2. 37

TOTAL PERIOD MOMENTS FOR CURRENT METER #1009
TOTAL DAYS MEAN MIN MAX STD.DEV. SKEWNESS KURTOSIS

27	5.54 .00 20.61 3.63 1.04 3.92

11

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TABLE 4.2

SUMMARY STATISTICS FOR SPEED

CURRENT METER DATA FROM 1975 SURVEY
DAILY MOMENTS FOR CURRENT METER #1028

DATE	MEAN MIN MAX STD.DEV. SKEWNESS KURTOSIS

8/22/75

3. 82

.80

8. 43

1.85

. 42

2. 48

8/23/75

4. 67

.00

10. 63

2. 93

.39

1. 94

8/24/75

4. 15

1.38

11.02

2. 27

1. 14

3. 99

8/25/75

4. 15

.80

9. 65

1.93

. 43

2. 82

8/26/75

3. 69

.80

9. 36

1. 92

. 88

3. 21

8/27/75

3. 28

.00

7. 64

1.58

.61

3. 10

8/28/75

4. 04

.80

11.58

2. 26

1.50

5.81

8/29/75

3. 71

1.38

11.02

2. 05

1.57

5. 72

8/30/75

6. 48

.80

13. 13

3. 67

. 17

1. 62

8/31/75

5. 97

1.88

13. 70

2. 94

. 53

2. 20

9/01/75

5. 87

.00

14. 83

3. 32

.92

3. 52

9/02/75

6. 38

.80

14. 26

3. 17

. 26

2. 23

9/03/75

6. 62

1.38

18. 15

3. 83

.92

3. 76

9/04/75

6. 67

1.38

13. 42

3. 22

.27

2. 01

9/05/75

6. 80

1.88

16. 47

3. 40

. 62

2. 95

9/06/75

5. 30

1.38

13. 13

3. 00

.99

3. 41

9/07/75

5. 34

1.38

12. 10

2. 41

.73

3. 24

9/08/75

4. 87

.80

11.02

2. 52

.70

2. 55

9/09/75

6. 41

1.88

11.34

2. 62

.06

1.98

9/10/75

5. 76

.00

17.31

3.71

1.00

3.91

9/11/75

4. 94

1.38

9. 06

2. 26

. 13

1. 75

9/12/75

5. 46

1.88

12. 85

2.81

.77

2. 67

9/13/75

4.21

.80

9. 06

2. 40

. 36

1.96

9/14/75

3. 43

.80

9. 36

1.83

.91

3. 74

9/15/75

3. 74

.00

10. 63

2. 22

1.28

4.31

9/16/75

8. 17

1.88

14. 55

3. 29

-. 20

2. 27

9/17/75

8. 95

3. 11

16. 75

3.41

. 46

2. 66

TOTAL PERIOD MOMENTS FOR CURRENT METER #1028
TOTAL DAYS MEAN MIN MAX STD. DEV. SKEWNESS KURTOSIS

26	5.26 .00 18.15 3.07 .93 3.62

12

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TABLE 4.3

SUMMARY STATISTICS FOR E/W COMPONENT

CURRENT METER DATA FROM 1975 SURVEY
DAILY MOMENTS FOR CURRENT METER #1028

DATE

MEAN

MIN

MAX STD.DEV.

SKEWNESS

KURTOSIS

8/22/75

.97

-5. 40

6. 22

2. 92

-. 40

2. 40

8/23/75

1.33

-10.60

8. 41

4. 48

-. 83

3. 20

8/24/75

18

-9. 88

10. 96

3. 92

.52

3. 84

8/25/75

.57

-7.21

6. 32

3. 52

-. 33

2.34

8/26/75

.23

-6. 98

8. 41

3. 46

.08

2. 60

8/27/75

.32

-7.34

4. 23

2. 72

-. 87

3. 03

8/28/75

.35

-7. 34

4. 90

3. 14

-. 75

2. 63

8/29/75

- 17

-11.00

6.01

3. 85

-.79

3. 15

8/30/75

43

-12. 62

9. 91

6. 55

-. 27

1. 89

8/31/75

10

-13.17

8.01

5. 80

~. 48

2. 07

9/01/75

25

-13.33

8. 41

6. 16

-. 45

2. 20

9/02/75

27

-14.19

9. 83

6. 31

-. 22

1. 96

9/03/75

. 12

-17. 62

9. 55

6. 35

83

3. 30

9/04/75

.31

-12.90

10. 19

6. 66

48

2. 00

9/05/75

81

-16. 38

9.55

7. 02

-. 44

1. 88

9/06/75

.26

-11.80

7. 21

4. 99

-. 99

3. 09

9/07/75

. 98

-10.20

10.87

4. 62

-. 06

2. 40

9/08/75

-. 06

-9.91

8.71

4. 36

-. 12

2. 46

9/09/75

.50

-10. 90

9. 55

5. 95

-. 37

1. 72

9/10/75

-. 93

-16. 64

7.33

5. 70

-. 83

3. 30

9/11/75

-. 13

-8. 41

7.08

4. 31

-. 33

1.96

9/12/75

. 15

-12.78

9. 83

5. 12

-. 72

2.72

9/13/75

06

-6. 99

6. 65

3. 57

-. 05

2. 45

9/14/75

. 03

-6. 32

7.57

2. 84

. 05

2. 80

9/15/75

-1. 21

-10. 57

4. 28

3. 26

-1. 00

3. 88

9/16/75

1. 10

-14. 47

10. 19

7.74

47

1.81

9/17/75

-. 19

-16. 66

10. 13

8. 55

41

1.77

TOTAL PERIOD MOMENTS FOR CURRENT METER #1028
TOTAL DAYS MEAN MIN MAX STD. DEV. SKEWNESS KURTOSIS

26

. 09

-17. 62

10. 96

5. 14

-. 55

3. 14

13

-------
TABLE 4.4

SUMMARY STATISTICS FOR N/S COMPONENT

CURRENT METER DATA FROM 1975 SURVEY
DAILY MOMENTS FOR CURRENT METER #1028

DATE

MEAN

MIN

MAX STD.DEV. SKEWNESS

; KURTO!

8/22/75



64

-4.

51

8. 17

2.

90

.76

2.

81

8/23/75

1.

85

-3.

12

8. 48

2.

33

. 52

3.

08

8/24/75

1.

34

-4.

28

6. 32

2.

34

26

2.

73

8/25/75

1.

44

-6.

94

6. 65

2.

54

75

4.

44

8/26/75

1.

32

-2.

83

6. 72

1.

95

.04

3.

15

8/27/75

1.

43

-2.

34

6. 32

1.

94

.39

2.

91

8/28/75

1.

02

-5.

26

10.41

3.

28

. 49

3.

43

8/29/75

1.

09

-2.

50

3. 72

1.

48

49

2.

76

8/30/75

1.

52

-4.

97

9. 24

3.

31

.27

2.

46

8/31/75

1.

65

-4.

97

8. 00

2.

94

-. 07

2.

58

9/01/75

•

65

-6.

50

4. 95

2.

79

-. 75

2.

89

9/02/75

1.

01

-4.

97

8. 00

3.

28

.05

2.

18

9/03/75

2.

14

-4.

48

13. 29

3.

80

.73

3.

33

9/04/75

1.

91

-3.

97

8. 24

2.

77

-. 32

2.

76

9/05/75

1.

17

-5.

50

6. 48

2.

73

-. 49

2.

52

9/06/75

a

95

-6.

80

7.71

3.

44

-. 50

2.

55

9/07/75

1.

18

-5.

71

6.51

3.

34

-. 38

2.

13

9/08/75

1.

46

-4.

95

8. 92

3.

06

-. 06

2.

86

9/09/75

1.

81

-4.

83

9. 36

3.

14

-. 10

2.

88

9/10/75

1.

79

-4.

77

8. 38

3.

32

-. 19

2.

26

9/11/75

•

80

-4.

95

6. 38

3.

29

-. 09

1.

78

9/12/75

•

91

-5.

18

7. 99

3.

36

-. 06

2.

25

9/13/75

1.

33

-4.

77

8. 27

3.

06

. 24

2.

30

9/14/75

1.

55

-2.

75

6. 38

2.

20

. 25

2.

61

9/15/75

1.

10

-5.

13

6.01

2.

42

-. 41

2.

80

9/16/75

1.

48

-6.

65

7. 36

3.

94

-. 28

1.

80

9/17/75

1.

27

-8.

55

8. 10

4.

39

-. 59

2.

49

TOTAL PERIOD MOMENTS FOR CURRENT METER #1028
TOTAL DAYS MEAN MIN MAX STD. DEV. SKEWNESS KURTOSIS

26	1.33 -8.55 13.29 2.98 -.07 3.17

14

-------
component and the north/south component, respectively, for meter number 1028.
The components could not be resolved for meter number 1009 since it did not
record direction.

Examination of the statistics for the speed record for the two meters
shows them to be comparable, with their means differing from each other by only
about 5%. Meter number 1009 had the higher mean, and was found to also have
slightly higher moments and a slightly higher maximum. The distributions for
both meters had positive skewnesses of around 1.0, and were both slightly more
kurtotic than the normal distribution (which has a kurtosis of 3.0). Positive
skewness indicates that the distributions tail off towards higher speeds, and
the kurtosis indicates that the distributions are slightly peaked.

Table 4.5 gives statistics for the five meters deployed in 1977-1978 for
thfi last week of October 1977 and month of November 1977 (the first full month
of deployment). With the exception of meter number 2920 and the October portion
of the record for 2918, all of the meters have somewhat greater mean speeds
than those measured by 1009 and 1028. However, meter number 2920 was located
in the shallowest part of the deployment site fairly close to the edge of the
continental shelf, and was moored just off the bottom, measuring bottom currents
at a depth of about 900-meters. The observed trends suggest a reduction in
bottom current speed with progression up the continental shelf. Regarding the
other four meters, numbers 2918 and 2919 measured deep bottom currents at
around 1800 meters, and number 2830 and the VACM measured mid-water column
currents at the 900 meter level in a 1400 meter depth location.

The component statistics for the five 1977-1978 meters are given for the
last week of October and the month of November in Table 4.6. The component
statistics for meter number 1028 are closest in character to those of meter
number 2919. Both meters indicate a substantial mean northward flow, with
some additional average flow eastward. Both are located near the deeper
western edge of the dumpsite study area.

15

-------
TABLE 4.5: SPEED MOMENTS

METER MEAN MINIMUM MAXIMUM STANDARD SKEWNESS KURTOSIS
NO. (cm/sec)	DEVIATION

2920-0CT	4. 16	0.	14.

2920-N0V	4.77	0.	28.

2830-0CT	6.46	0.	20.

2830-N0V	6.07	0.	18.

VACM-OCT	6. 18	2.	17.

VACM-NOV	6.73	2.	21.

2918-OCT	5.25	2.	15.

2918-NOV	6.35	2.	25.

2919-OCT	5.74	0.	17.
2919-NOV	6.58	0.	25.

1009-'75	5.54	0.	21.
(AUG/SEP)

1028-'75	5.26	0.	18.
(AUG/SEP)

2.49	.93	4.40

2.82	.76	3.90

3.51	.36	3.38

3.60	.34	2.84

2.81	.70	3.18

3. 11	.57	2.95

2.84	.55	2.80

3.83	1.15	4.89

2.94	.83	3.66

3.71	1.12	4.91

3.63	1.04	3.92

3.07	.93	3.62

16

-------
TABLE 4.6: COMPONENT MOMENTS

METER MEAN MINIMUM MAXIMUM STANDARD SKEWNESS KURTOSIS

NO. (cm/sec) DEVIATION

2920-0CT CE/W) -.25 -12. 13. 3.81 -.02 3.89

2920-NOV -.13 -19. 17. 4.21 -.04 3.37

2920-0CT CN/S) .48 -9. 10. 3.02 -.19 3.14

2920-N0V .19 -12. 28. 3.56 .61 6.63

2830-0CT CE/W) -.55 -16. 12. 5.05 .19 2.52

2830-NOV -.20 -13. 16. 4.65 .05 2.81

2830-0CT
-------
4.3 Histograms and Scatter Diagrams

Histograms are provided for the speed records for both meter 1009
(Figure 4.1) and meter 1028 (Figure 4.2). Both histograms have peaks in the

2 cm/sec to 3 cm/sec class interval, indicating that the most likely speed
measurement for both meters is in this vicinity. The histograms both display
the positive skewness predicted by the summary statistics.

Histograms for the east/west and north/south components for meter number
1028 are shown in Figures 4.3 and 4.4, respectively. The east/west component
has virtually a zero mean, with a modal peak in the 0 cm/sec to 2 cm/sec range.
The distribution is visibly skewed in the western direction (i.e., negatively).
The north/south component, on the other hand, is not visibly skewed, but shows
a northward mean current, again with a modal peak in the 0 cm/sec to 2 cm/sec
region. The distribution is considerably more confined than the one for the
east/west component, indicating that the flow is generally less variable in
the north/south direction. This is also evidenced by the standard deviations
for the two distributions.

Scatter diagrams have been generated relating the east/west and north/south
speed components and the speed and direction for meter number 1028. The speed
versus direction scatter diagram shows significant correlation and indicates
that the greatest speeds occurred in conjunction with direction readings of
about 250° to 270° true (Figure 4.5). However, a modal peak occurs at about
4 cm/sec and 45° true. Almost 25% of the observed direction records fell
between 22.5° and 45° true. The scatter diagram for the speed components
(Figure 4.6) also shows the extreme velocity events tailing off to the west
and indicates a modal peak in the northeast quadrant. The relatively greater
magnitude of variance along the east/west axis is readily apparent.

An additional scatter diagram (Figure 4.7) was calculated to compare the
speed records for meters 1009 and 1028 with each other. The two records are
not highly correlated, especially with regard to joint high velocity events.
However, a modal peak exists in the region of 4 cm/sec for meter 1028 and

3 cm/sec for meter 1009.

-------
FIGURE 4.1: HISTOGRAM OF SPEED (CM/SEC) FOR METER 1009

40. 00 , 1 1 1 1 1 I I

30. 00

M
VO

10. 00

. GOOOE-'-OO

1 l

CM/SEC

-------
FIGURE 4. 2.1 HISTOGRAM OF SPEED (CM/SEC) FOR METER 1028

30. 00

10. 00

.OOOOE+OO

o
o
o

o
to

CM/SEC

-------
FIGURE.4. 3; EAST/WEST COMPONENT HISTOGRAM FOR METER 1028

40. 00

30. 00

10. 00

.OOOCE+OO

o
o

CM/SEC

-------
40. 00

FIGURE 4.4= NORTH/SDUTH COMPONENT HISTOGRAM FOR METER 1028

30.00

UJ
l_>

ci-

10. 00

.OOOOE+OO

CM/SEC

-------
FIGURE 4.5i SCATTER DIAGRAM FOR METER 1028
SPEED VERSUS DIRECTION

y erAi p. DIRECTION CDEG TRUE) FROM 0.0 TO 360.0 WITH 22.5 DEC. PER CLASS INTERVAL
Y IcAlI! SPEED (CM>SEC) FROM o! 0 TO 19.00 WITH 1.0 CM/SEC PER CLASS INTERVAL

19 0 0000000000000

18.0 oooooooooooio

17.0 0000000000003

16.0 0000000000011

1S-8 8 8 8 8 8 8 8 S 3 S 5 j f

14* 0 1 000000000041

13* 0 0 1 30000000052

HIS 0 0 4 0 0 0 0 0 0 0 7 3

11.0 0 1 14 1 0 0 0 0 0 0 1 11 8

11.0 0 1 14 1 U u u u u u j w -

10 0 1 4 17 60000001 5 5

a' n 0 4 29 8 0 0 0 0 0 1 .Z

1:8 2 0 1 6 2 0 0 0 o 0 4 19 10

7a-8 5 ig i 2? ? 8 ? 8 8 S i S I

5'° 8 15 32 27 I i n ? 7 0 6 17 11 *

4.0 7 10 41 12 7 3 0 1 7 0 6 17 11

IS M ii * 25 ll I I >f ? 5 § | J :

¦;8 'J I S 1 ? 8 8 1 i j I j 8

135.0 180.0 225.0 270.0

22.5 67.5 112.5 157.5 202.5 247.5 292

TOTAL NUMBER OF POINTS. 1275.0

-------
FIGURE 4.61 SCATTER DIAGRAM FOR METER 1028
NORTH/SOUTH VERSUS EAST/WEST COMPONENT

X SCALEt EAST/WEST COMPONENT (CM/SEC) FROM -19.00 TO 19.00 WITH 2.0 CM/SEC PER CLASS INTERVAL
Y SCALEi NORTH/SOUTH COMPONENT (CM/SEC) FROM -19.00 TO 19.00 WITH 2.0 CM/SEC PER CLASS INTERVAL

ig.O 00000000000000000000

17.0 00000000000000000000

15. o oooooooooooooooooooo

13.0 00000000000 1 1 0000000

11.0 00000001000010000000

9.0 0000002 1 3 1 0533200000

7.0 000000345611858840000

5 0 1 0 0 0 0 2 3 8 10 17 17 24 25 28 24 10 0 0 0 0

K> 3.0 o 0 0 1 1 3 2 5 37 49 64 51 42 27 IB 3 0 0 0 0

-P- 1 0 0 1 0 1 4 3 10 19 35 34 87 73 46 20 0 1 0 0 0 0

-10 o 3 3 4 9 14 11 33 28 15 19 36 15 4 1 0 0 0 0 0

-3.0 0 0 0 8 9 14 19 17 11 13 23 2 3 0 0 0 0 0 0 0

-5.0 014011978675200000000

-7.0 00 1 40 1 1 10 1 0000000000

-g] o 00000 1 0 1 000000000000

-11.0 OOOOOOOOOOOOOOOOOOOO

-13. o OOOOOOOOOOOOOOOOOOOO

-15 o OOOOOOOOOOOOOOOOOOOO

-17.0 OOOOOOOOOOOOOOOOOOOO

-ig] o OOOOOOOOOOOOOOOOOOOO

-19.0 -15.0 -11.0 -7.0 -3.0 1.0 5.0 9.0 13.0 17.0

-17.0 -13.0 -9.0 -5.0 -1.0 3.0 7.0 11.0 15.0 19.0

TOTAL NUMBER OF POI NTSi 1275.0

-------
FIGURE 4.7i SCATTER DIAGRAM
SPEED FOR METER 1009 VERSUS SPEED FOR METER 1028

N>
Ul

X SCALEi SPEED-1028 (CM/SEO FROM 0.0 TO 19.00 WITH 1.0 CM/SEC PER CLASS INTERVAL
Y SCALEi SPEED-1009 (CM/SEC) FROM 0.0 TO 19.00 WITH 1.0 CM/SEC PER CLASS INTERVAL

19.0

18.0

17.0

16.0

15.0

14.0

13.0

12.0

11. 0

10.0

9.0

8.0

7.0

6.0

5.0

4.0

3. 0

2.0

1.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

17.0

18.0

19.0

1.0

3.0

5.0

7.0

9.0

11.0

13.0

15.0

TOTAL NUMBER OF POINTSi 1275.0

-------
4.4 Time History Records

Time history plots were produced for the speed records for both meters, and
for the two speed component records for meter 1028. The time history for meter
1009 included 1286 half-hour samples, while the histories associated with meter
1028 consisted of 1278 samples. 1275 time points were common to both meters.

The speed record for meter 1028 essentially reproduces the information
previously given by Schwartz!ose, except that the format is changed to allow
presentation of the entire record on one plot (Figure 4.8). The envelope of
the speed record shows peak events occurring toward the middle of the record
(around 9/3-9/6 and 9/10/75) and at the end (9/16-9/17). Periods of relatively
lower activity occur around 8/25-8/29 and 9/11-9/14. Most of the changes in
the envelope are associated with changes in the east/west current speed, as
shown by the east/west speed plot in Figure 4.9. The envelope peaks and lows
are readily visible in Figure 4.9, but the north/south time history in
Figure 4.10 is virtually stationary. The skewing of the east/west speed
distribution to the west is very apparent in the time history plot, as it is
in the corresponding histogram and moments summary. Also, the north/south
time history shows a fairly visible northward bias, as previously noted from
the histogram and moment summary associated with it.

The speed time history plot for meter 1009 (Figure 4.11) differs somewhat
from the speed time history plot for 1028. The envelope shows peaks around
8/22-8/23, 8/31-9/2, 9/5-9/6, 9/9-9/13 and 9/17. Envelope lows are around
8/25-8/27 and 9/8. Comparing the envelope peaks and lows for the two meters
indicates that the two records are in greatest contrast around 9/11 through
9/13, where meter 1009 shows peak activity while meter 1028 is recording
relative lows. These differences are at least in part attributable to local
topographical differences. Figure 3.1 shows meter 1028 to be located on the
north side of a depression while 1009 is shown to be on the opposite slope.

4.5 Progressive Vector Diagram and Stick Plot for Current Meter No. 1028

Schwartzlose presented a progressive vector diagram for the speed and
direction data taken from meter 1028 (Ref. 2). A separate vector plot was

-------
20. 00

15. 00

Li
UJ
If)
\
s:
u

5. 000

.0000E+00 I

PLOT OF SPEED FOjR 1028

-------
20.00

10.00

ho
00

x
o

-10. 00

FIGURE 4. 9: TIME HISTORY PLOT

-20. 00

OF EAST SPEED COMPONENT FOR 1028

1 1 1 1 i i

DAYS

-------
20.00

FIGURE 4.10: TIME HISTORY PLOT OF NORTH SPEED COMPONENT FOR 1028

10. 00

ho
vo

LU
CO
\
X
LJ

-10. 00

-20. 00

DAYS

-------
20.00

15.00

5. 000

. 0000E+00

-------
generated here (Figure 4.12) using the raw speed record, and was found to be
the same as Schwartz!ose's. The plot indicates a definite northward trend,
with a mean speed of 1.33 cm/sec and a mean direction of 4° true. The tidal
excursions are apparent in the plot, and were characterized by speeds of
4-8 cm/sec and excursion distances of about one kilometer.

The progressive vector plot was generated again for Figure 4.13, this time
using digitally filtered speed component records in order to remove the tidal
frequencies. The filter used was a cosine tapered symmetric finite impulse
response filter with a cutoff frequency corresponding to a 50 hour period.

This was the same filter used in the development of the progressive vector
diagrams for the five meters in the 1977-1978 survey (Reference 4).

The vector-averaged current velocities for the 1977-1978 study and for
meter 1028 are tabulated in Table 4.7. The similarity between 2919 and 1028
is readily apparent.

The stick plot for the filtered speed components for meter 1028 is given
in Figure 4.14. This plot for the 27-day measurement period has been scaled
to maximize the resolution of the velocity vectors, and clearly illustrates
the predominance of northward flow during this measurement period. To convert
the vectors shown in the plot to filtered speeds in cm/sec, multiply the length
of the vector by the scaling factor of 4.63.

4.6 Coherence and Correlation Studies

In order to provide some initial insight into the periodic phenomena
involved in the time records for meters 1009 and 1028, spectral density func-
tions were obtained. The power spectral densities for the east/west and
north/south current components for meter 1028 are shown in Figure 4.15 and 4.16,
respectively. Power spectral densities were also obtained for the velocity
for both 1028 (Figure 4.17) and 1009 (Figure 4.18). These plots provide an
indication of the amount of current flow associated with the tides and other
periodic current components. Spectral density estimates are not normally
obtained for speed magnitude measurements since the result is biased due to
the necessarily positive nature of the record. Also, harmonics are introduced

-------
35.00

FIGURE 4.12: PROGRESSIVE VECTOR PLOT FOR 1028 RAW DATA RECORD

25. 00

5. 000

-5.000

(T)

o
o

E/W (KM)

o
o

-------
FIGURE 4. 13: PROGRESSIVE VECTOR PLOT FOR FILTERED 1028 RECORD

35.00

25. 00

5. 000

-5.000

o o

7 7 7 E/W (KM)

o
o

-------
TABLE 4.7: VECTOR AVERAGED VELOCITIES

METER NOV'77 NOV'77 DEC'77 DEC'77 TOTAL TOTAL

NO. SPEED DIRECTION SPEED DIRECTION PERIOD PERIOD

(cm/sec)
-------
12.00

FIGURE 4.14: STICK PLOT FOR FILTERED 1028 RECORD

6. 000

CJ
Ui
>

-6. 000

-12.00

o
o
+
LU
O

o
o

o
o
o

0AYS

-------
FIGURE 4.15: POWER SPECTRAL DENSITY FOR EAST COMPONENT FOR 1028

-------
FIGURE 4. 16= POWER SPECTRAL DENSITY FOR NORTH COMPONENT FOR 1028

CYC/HR

-------
-------
FIGURE 4.18: POWER SPECTRAL DENSITY FOR SPEED FOR 1009

CYC/HR

-------
into the spectrum. However, since no directional information was available
for meter 1009, this provided the only means of identifying spectral peaks for
this meter. The spectral estimates obtained are useful for comparison.

The east/west component spectrum for 1028 is dominated by a sharp peak at
the 12 hour semi-diurnal tidal frequency. Smaller peaks are apparent at the
24 hour diurnal frequency and at the 6 hour frequency. The north/south component
reveals the same three peaks, but the semi-diurnal peak is not nearly so dominat-
ing, and the diurnal frequency is proportionally larger.

The spectrum of speed for meter 1028 (Figure 4.17) shows a bias component
at zero frequency and four main spectral peaks. Ranked in decreasing order of
size, these are the semi-diurnal tide, diurnal tide, a 6-hour peak, and a 4-hour
peak. Since the 4-hour peak is not observed in either of the component spectra,
it is probably just a numerical artifact at the second harmonic of the semi-diurnal
tide. In addition, the 6-hour peak contains some energy from the first harmonic.

The speed magnitude spectrum for meter 1009 (Figure 4.18) also contains
the bias peak, and peaks at the four frequencies noted above, with the size
decreasing in the same order. However, the semi-diurnal tide is relatively
much larger. This suggests that currents recorded at this meter were more
influenced by tidal phenomena than those measured by 1028.

A magnitude squared coherence function was produced for the velocity
spectra for the two meters, and is given in Figure 4.19. The plot indicates
relatively low coherence except at the low-frequency end of the spectrum. This,
however, is mostly due to the presence of bias in the spectra caused by using
the velocity magnitudes instead of orthogonal components. The other coherence
peaks occur in the regions of the diurnal tides (and inertial frequency) and
around the semi-diurnal tides. Neither of these peaks suggest strong coherences
between the two meters, but there is some measure of consistency.

Since the two meters discussed above, 1009 and 1028, were displaced in
time by more than 2 years (as well as having been deployed at different depths
and having had different local bathymetric conditions) from the meters of the
1977-1978 deployment, no major coherences would be anticipated between the two

-------
FIGURE 4.19: COHERENCE FOR SPEED FOR METERS 1009 AND 1028

-------
measurement programs. In fact, even within the 1977-1978 deployment very little
coherence could be discerned between any of the five meters, except in very
narrow bandwidths around the tidal energies, and except for the meters which
were deployed on the same arrays. However, general lower-order statistical
relationships are observable between all seven meters, and these relationships
are discussed in the next section.

-------
SECTION 5

DATA INTERPRETATION

This section attempts to integrate the results of the analyses performed
in the previous section with (1) the results of the analyses performed on the
data collected with the five meters deployed in 1977-1978, and (2) general
information on oceanographic phenomena within the Farallon Islands area. The
current field in the area is characterized based on these results.

5.1 General Comments on Current Meter Hardware

Three types of current meters were used during the two measurement programs:
Aanderaa meters, a Vector Averaging Current Meter, and the Scripps meters used
in the 1975 deployment. All three meters are based on a Savonius rotor with
directional readings recorded relative to magnetic north by means of a poten-
tiometric compass. Consequently all three meter types produced speed records
in terms of some digital revolution count of the rotor. The main physical
differences in the meters relate to the means of determining current direction.
The Aanderaa and Scripps meters used a large vane mounted behind the rotor
which causes the rotor to always be pivoted into the oncoming current. The
VACM uses a separate magnetically-coupled vane mounted above the rotor. Also,
the VACM performs inter-sample vector averaging on the record, a process which
is believed to help filter out high-frequency oscillations caused by mooring
motions.

As for the records themselves, the major differences resulted from
different sample rates. The VACM sampled at 4 samples/hour, the five Aanderaa
meters each sampled at 3 samples/hour, and the two Scripps meters at 2 samples/
hour. It should be noted, however, that the Scripps meters actually returned a
continuous direction record since the recording medium was a strip chart. The
velocity record was a quantized record by nature of the measurement mechanism.
The sampling interval of one-half hour was chosen by the Scripps analysts when

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initial data reduction was performed by Dr. Schwartz!ose on meter 1028. The
nyquist rate of one sample/hour (i.e., the minimum sampling rate that must be
used to avoid introducing aliasing errors) associated with the half-hour
sampling interval (the slowest of the seven meters) was significantly higher
than any energetic frequencies observed in any of the seven records.

5.2 Discussion of Relationships Observed between the 1975 and 1977-1978 Data

Some preliminary remarks may be made regarding the general nature of the
currents near the Farallon Islands. The surface currents in the region are
principally characterized by the California and the Davidson currents
(Reference 5). These two currents flow counter to each other, the California
current flowing southward with an average speed of approximately 25 cm/sec,
and the Davidson current traveling northward either beneath the California
current or at the surface closer to the shore. This second condition, when
the Davidson current forms a wedge between the California current and the shore,
occurs between mid-November and February. For the remainder of the year, the
Davidson current runs at depths of greater than 200 meters at speeds of 10 to
40 cm/sec. Between mid-February and September, the California current carries
surface water offshore and upwelling of deeper water occurs. The transition
period, September to mid-November, following this upwelling period is charac-
terized by ocean current patterns that are not well defined. This transition
period occurs roughly during the period corresponding to the 1975 meter
deployment. The 1977-1978 meter deployment began near the end of the transition
period and continued into the surface period for the Davidson current, starting
in mid-November. It is therefore evident that the two measurement programs
obtained records of different phases of the current dynamics for two different
years, a situation which severely limits the probability of finding specific
correlations. For this reason, this discussion will be limited to observations
on general relationships and general trends.

One apparent inconsistency observed regarding the 1975 deployment relates
to the reported deployment locations and depths for -.ha meters. The depths to
which the meters were deployed were reported as being approximately 1849 m and
1729 m (both about 2 m above the bottom) for 1028 and 1009, respectively. In
addition, 1009 was reported to be further west than any of the meters deployed

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in 1977-1978. The array which contained meters 2918 and 2919 was reported to
be in water over 1800 m deep. This array was located fairly close to 1009 and,
if anything, should have been in slightly shallower water. Thus it would appear
that the discrepancy may be in the locations and/or depths reported in 1975.

It is possible that these two meters were actually slightly east of the loca-
tions given, but if so, the discrepancy is not a large one. In any event,

1009 and 1028 were reportedly measuring currents just off the bottom, and this
relationship will be assumed for the remainder of this discussion.

It is instructive to compare these two meters with the near-bottom meters
2919 and 2920. 2918 was also close to the bottom, having been approximately
26 m above 2919 on the same array. It was noted earlier, in Section 4.2, that
the component statistical moments for 1028 and 2919 were notably close in
character, both indicating mainly northward flow with a lesser shoreward compo-
nent. The mean speeds for 1028 and 1009 were both within 20% of the mean speed
for 2919 for the month of November, and this difference was diminished to less
than 10% if the comparison was made using the first 6 days of the record
(i.e., the final days of October) for 2919.

Meter 2918 was even closer in speed to 1009 and 1028 but the direction,
although still in the northeast quadrant, was substantially different. In.fact,
the directional measurements for 2918 and 2919 appear to be inconsistent with
each other, especially since they were only 26 m apart. However, the component
minima, maxima and standard deviations were in close agreement. The discrepancy
may have been due to a possible compass calibration error for 2918.

Meter 2920, which was located closest to shore of the seven meters,
recorded somewhat reduced speeds relative to the other meters. It also showed
very little consistency in average directional measurements, although there
was some northward tendency. This meter may have been measuring dynamics close
to the boundary of the surface California and Davidson currents, and consequently
the behavior of the measured phenomena was not as well defined. The records
from 1028 and 1009 were clearly more similar to those taken by 2919 and 2918
at the western end of the deployment region.

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The array with the VACM and meter 2830 was reportedly deployed in 1372 m
of water with the meters at a midwater depth of about 912 m. As noted in the
report on the 1977-1978 analyses (Reference 4), the current vector reversed to
a southeastward direction for these meters sometime around the end of November.
However, during the northward phase the vector had a westward component. The
average speeds, like the average speeds for 2918 and 2919, were a little larger
(by about 20-25%) than the average magnitudes for the two 1975 meters.

Table 5.1 summarizes the mean speeds and vector average speeds for the
seven meters.

Turning now to the periodic aspects of the data records, it was observed in
Section 4.6 that both the east/west and north/south components of the speed record
from 1028 are characterized by three major spectral peaks ~ the semi-diurnal,
diurnal, and a peak corresponding to roughly a 6-hour period. The semi-diurnal
peak predominates in both components, especially in the east/west spectrum.
The diurnal and 6-hour peaks are of about the same magnitude in the east/west
spectrum, but the 6-hour peak has almost twice the energy of the diurnal peak
in the north/south spectrum.

The November spectra for 2918 and 2919, provided in Reference 4 for these
meters, tend to confirm the observations noted above for 1028. The east/west
spectra for both of these meters show a dominant semi-diurnal peak followed by
a much smaller (i.e., by a factor of 5) diurnal peak. A 6-hour peak of similar
magnitude is observed in both spectra, and 2919 also contains a peak at about
8 hours. The north/south spectra are much less clearly defined, but in both
of them the energy around the 6-hour peak is close in magnitude to the energy
about the semi-diurnal tides. In the subsequent December, January and February
north/south spectra for 2919 and 2918, the 6-hour peak emerges to become the
dominating spectral energy. The emergence of this peak seems to be coincident
with the surface phase of the Davidson current, suggesting that internal wave
phenomena, connected with the interaction between the California and Davidson
currents, are present.

Table 5.2 summarizes the spectral energy sources in the north/south and
east/west current components of meter 1028.

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TABLE 5.1: LONG TERM AVERAGES

METER MEAN EAST/WEST NORTH/SOUTH VECTOR DIRECTION COMPASS

NO. SPEED COMPONENT COMPONENT AVERAGE (deg. true) POINT

(cm/sec) SPEED

2920-0CT
2920-N0V

4. 16
4. 77

.25
-. 13

.48
. 19

.54

.23

28.
-34.

NE
NW

2830-0CT
2830-N0V

6. 46
6. 07

-. 55
-. 20

.06
.52

.55
.56

-84.
-21.

NNW

VACM-OCT
VACM-NOV

6. 18
6. 73

-. 44

-. 26

.56
.95

.71
.98

-38.
-15.

NW
NNW

2918-OCT
2918-NOV

5. 25

6. 35

1.97
1.42

.61
.42

2. 06
1. 48

73.

74.

ENE
ENE

2919-OCT
2919-NOV

5. 74

6. 58

1.04
.43

1.75
1.77

2. 04
1.82

31.
14.

NE
NNE

1009-
AUG/SEP

5. 54

—

1028-
AUG/SEP

5. 26

.09

1.33

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TABLE 5.2: ENERGY COMPONENTS FOR METER 1028

EAST/WEST NORTH/SOUTH
PERIODIC FREQUENCY ENERGY ENERGY

ENERGY (cph) (cm/sec)2 (cm/sec)2

DIURNAL & .04-.05 1.6 0.5

INERTIAL CURRENTS

SEMIDIURNAL TIDES .08-.083 12.9 1.8

SIX-HOUR .16-.175 1.5 0.8

SPECTRAL PEAK

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5.3 Discussion of the Current Field

The seven current meter records discussed in the preceding section form
the basis for estimating the nature of the current field neighboring the
investigation area. The deployment geometry provides records at three points
on the bottom, defining a triangular region in the horizontal plane. A fourth
reference point is defined in the midwater column, located slightly south of
the centroid of the horizontal triangle.

Figure 5.1 depicts graphically the vector-averaged current information
given in Table 5.1. Note that no vectors are shown at the site of meter 1009
since this meter did not provide any directional record. The vectors shown at
the other sites are the vector averages for October and November in the case
of the 1977-1978 meters, and the vector average for the entire August to
September record for meter 1028.

All of the vectors depicted are in the northern half of the compass. Almost
all the vectors are predominantly northward, with the exceptions of the October
and November vectors for 2918 and the October vector for 2830. It was noted
earlier that meter 2918 seemed inconsistent regarding directional measurements,
especially in view of its close proximity to 2919, and a miscalibrated compass
was cited as a possible cause. The October vector for 2830 is not consistent
with the VACM readings for the same period, but only six days of data are
included in the October time period, and the measurements may contain some
start-up transients. In any case, it is reasonably safe to say that, based on
the measurements, the predominant flow through the area between August and
November is northward. It also appears that the vector magnitudes decrease
significantly as one proceeds up the continental shelf towards the shore. This
decrease in vector magnitudes occurs in conjunction with a decrease in average
current speeds, as indicated in Table 4.5. This suggests that the potential
for suspended sediment transport from the dumpsite area progressively diminishes
toward the eastern, or shoreward, end of the measurement site.

The prevailing surface currents through the region flow toward the south
throughout most of the measurement period discussed here, which is consistent
with the northward counterflows observed by the meters. However, some confusion

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42.00

FIGURE 5.1: VECTOR AVERAGED LONG TERM CURRENTS

40.00

LO
s
•z.

36.00

34.00

o
o

to
1

o
a

o
o

(M
I

O
o
o

E/W
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of direction occurs as the Davidson current surfaces toward the eastern part
of the area in the latter part of November. As noted in Reference 4, a current
direction reversal is observed in the midwater measurements at this time, and
the measurements at the eastern end of the site do not show a very pronounced
directional trend for any of the measurement period. The measurements taken
by the seven current meters are reasonably consistent with the trends predicated
by the hypothesis that they should observe flows counter to the surface currents.
Also, the slight shoreward upslope flow observed at the western end of the site
is reasonable in view of the shoreward direction of coriolis influences on the
northward deepwater flow.

As discussed in Reference 4, a possible sediment transport mechanism might
involve tidal and other periodic current components providing the impetus to
suspend finer~grained sediment particles, with long term average currents sweep-
ing the finer particles upslope and shoreward before they fall out of suspension.
Reference 1 provides background on the nature of the sediments sampled in the
dumpsite region. A hypothetical case was put forward in Reference 4 in which
a particle which was only able to become suspended about 3% of the time (using
20 cm/sec as the threshold) at meter 2919, nevertheless remained in suspension
about 85% of the time. The periodic current energy sources (particularly
semi-diurnal tides) become large enough to make this possible, but the shoreward
decay in vector averaged velocities noted above is matched by a shoreward decay
in spectral energy magnitudes, thereby reducing the effectiveness of this
mechanism with proximity to shore.

The major periodic energy sources, semi-diurnal tides, are depicted
graphically as tidal ellipses in Figure 5.2. The majority of the energy in
the deep western end of the site is east/west, as indicated by the shapes of
the ellipses for meters 2918, 2919, and 1028. The midwater meters, 2830 and
the VACM, have almost equal energies along the two orthogonal axes, with the
maximum energy occurring along the northwest/southeast diagonal. Meter 2920
has slightly more energy in the north/south direction, with the maximum along
the northeast/southwest diagonal. Meter 1028's ellipse more closely resembles
those of the western deepwater meters 2918 and 2919 in terms of magnitudes,
but it bears a closer resemblance in terms of orientation to the ellipse of
meter 2920. This may be due to the possible misreporting of the location of

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FIGURE 5.2: SEMI-DIURNAL TIDAL ELLIPSES

42.00 . _

4a oo

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meter 1028, a possibility noted earlier in conjunction with an apparent incon-
sistency between the reported geographical coordinates and the reported depth.
If this is the case, it seems likely that meter 1028 was actually located
somewhat shoreward of the location shown in Figures 5.1 and 5.2.

Nevertheless, the major energy components are observed to be greatest
toward the western end of the site, decreasing in magnitude toward the shore.
Consequently, the potential for shoreward transport of suspended material
appears to decrease significantly in the shoreward portion of the investigated
region at least during the meter deployment periods. This decrease in transport
potential is also supported by the observed velocity magnitudes and vector
averages for the seven meters. It is therefore concluded that suspended transport
from the dumpsite area during the months of August through November is a small
but existent possibility, although additional measurements closer to shore and
at other times of the year (particularly during upwelling) would be helpful in
verifying this assessment.

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SECTION 6

RESULTS AND CONCLUSIONS

The results and conclusions fall into four major categories: a) Overall
Data Quality and Consistency, b) Specific Results for Meters 1009 and 1028, c)
General Observations on the Local Current Field, and d) General Assessment of
the Potential for Suspended Load Sediment Transport. Each of these categories
is discussed below.

6.1 Overall Data Quality and Consistency

Data quality for the time periods under discussion, August/September 1975
and October/November 1977, was suitable for analysis. The data records were
consistent and usable with the following qualifications:

The data record for meter 1009 (August/September 1975) lacked
directional reference due to a malfunction in the meter's compass.

The reported geographical coordinates and the reported deployment
depths for meters 1009 and 1028 were somewhat inconsistent with
published bathymetry and with the bathymetry determined for the
1977-1978 survey of the Farallon area dumpsites. It is possible
that the two meters were located somewhat shoreward of the reported
coordinates.

In the 1977 deployments within the same area (Reference 4), meter
2918 yielded vector-averaged velocities that were 60 to 70 degrees
offset to the east from those of meter 2919. These meters were
located on the same mooring only 26 m apart. It appears that the
direction measurements for 2918 may not have been properly calibrated.
Although a hydrographic station near the site of current meter 2918
and 2919 deployments was occupied in October 1977 (Reference 1), no

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anomalous water properties were observed in the near-bottom samples
that could suggest that different water masses were responsible for
the directional disparity within the 26 meter distance separating
the two instruments.

As noted in Reference 4, the record for meter 2830 had a dropout of
about 9 hours at the beginning of the October deployment period.
The VACM time sequence was jumbled, but the records of interest were
rectified by matching them with the 2830 records since these two
meters were located only 2 m apart on the same mooring.

6.2 Results for Meters 1009 and 1028

The speed for meter 1009 ranged between 0.0 and 20.61 cm/sec, with a mean
magnitude of 5.54 cm/sec. For meter 1028, the range was 0.0 to 18.15 cm/sec,
with a mean magnitude of 5.26 cm/sec. The majority of the spectral energy for
both meters was at the semi-diurnal tidal frequency. The semi-diurnal tidal
ellipse for 1028 had its major axis aligned in a northeast/southwest direction,
and it encompassed north/south and east/west excursions comparable in magnitude
to those of the deepwater meters 2918 and 2919. In addition to the diurnal
and inertial peaks, 1028 also exhibited a significant spectral peak at about
6 hours, similar to the 6-hour peaks observed in the spectra for 2918 and 2919,
which could be attributed to internal waves. Finally, the vector-averaged
currents for 1028 were very similar to those of meter 2919, i.e., mostly
northward, with an average vector magnitude of 1.33 cm/sec.

6.3 Observations on the Local Current Field

The general direction of flow for all seven current meter records from
the 1975 and 1977-1978 deployments was predominantly northward and slightly
upslope, with the greatest vector-averaged speeds occurring in the deeper water
to the western part of the dumpsite area which encompasses both the 900 m and
1700 m dumpsites. The arithmetic mean speeds also show a decay in magnitude
with proximity to the shore. Consequently, long term drift currents appear to
dwindle in magnitude as one proceeds shoreward up the continental slope.

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Semi-diurnal tidal energy also diminishes from the deeper western
locations toward the eastern, shoreward locations. The tidal ellipses decrease
in perimeter and change somewhat in orientation, from east/west in the deeper
water to northeast/southwest toward shore. The greatest periodic energy compo-
nents are observed along the east/west axes in the deeper water, and these
magnitudes appear to diminish rapidly upslope. The orientation of the midwater
ellipses, located partway upslope of the westernmost meters, is northwest/
southeast, suggesting that midwator energies are directed more parallel than
perpendicular to the shore.

6.4 Potential for Transport of Suspended Materials

On the basis of current speeds recorded during the two month period and
in considering the sediment properties present at the waste disposal site, it
may be concluded that resuspension of local sediments by bottom currents is
unlikely. Sediment transport experiments and direct observations of sediment
resuspension confirm thr theory that fine-grained sediment requires relatively
high (greater than 40 cm/sec) current speeds to place particles in motion (see
Reference 4 for discussion; also Reference 9). This so-called "threshold
velocity" and the factors influencing it are discussed in greater detail in a
companion report (Reference 4, in press) detailing the results of a 1977 survey
in this dumpsite area. Drift vectors obtained from the present study suggest
that current magnitude decreases toward shore and this aspect, plus the diminished
energies observed in shallower water, tend to reduce the net shoreward motion.

Due to the limited period during which the current meters were operational,
it is clear that the nature of water motion at the waste disposal site requires
further study which would include seasonal variables. Additional measurements
further inshore would be of particular value as there is a seasonal current
regime (the Davidson Current) which affects local circulation patterns.

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SECTION 7

REFERENCES

1. Dayal, R., I.W. Duedall, M. Fuhrmann, and M.G. Heaton. 1979. Sediment and
Water Column Properties at the Farallon Islands Radioactive Waste Dumpsites.
Final report to the Office of Radiation Programs. U.S. Environmental
Protection Agency, Washington, D.C.

2. Dyer, R.S. 1976. Environmental Surveys of Two Deep Sea Radioactive
Waste Disposal Sites Using Submersibles. Proceedings of an International
Symposium on Management of Radioactive Wastes from the Nuclear Fuel
Cycle, Vol. 2. International Atomic Energy Agency, Vienna, Austria.
IAEA-SM-207/65, p. 317-338.

3. Interstate Electronics Corporation. 1975. Operations Report: A Survey
of the Farallon Islands 500-Fathom Radioactive Waste Disposal Site.

U.S. Environmental Protection Agency, Office of Radiation Programs
Technical Note ORP-75-1, Washington, D.C.

4. Interstate Electronics Corporation. 1982. Farallon Islands Oceanographic
Data Analysis. Vol. I and II. Final Report to the Office of Radiation
Programs, U.S. Environmental Protection Agency, Washington, D.C.

5. NOAA, Office of Coastal Zone Management. 1980. Draft Environmental
Impact Statement on the Proposed Point Reyes-Farallon Islands Marine
Sanctuary, p. E4-E9.

6. Nosnkin, V.E., K.M. Wong, T.A. Jokela, R.J. Eagle, and J.L. Brunk. 1978.
Radionuclides in the marine environment near the Farallon Islands. Lawrence
Livermore Laboratory, University of California Report No. UCRL-52381,
Livermore, California.

7. Schwartzlose, R. Scripps Institution of Oceanography. La Jolla,

California. Unpublished materials received December 1980 and August
1982, including raw data records for meters 1009 and 1028, and subsequent
analysis.

8. Wilde, P. 1976. Oceanographic data off central California, 37° to 40°
north including the Delgada deep sea fan. Lawrence Berkeley Laboratory
Pub. No. 92, University of California, Berkeley, California.

9. Larsen, L.H., R. W. Sternberg, N.C. Shi, M.A.H. Marsden, and L. Thomas.
1981. Field investigations of the threshold of grain motion by ocean
waves and currents. In Sedimentary Dynamics of Continental Shelves.
Elsevier, Amsterdam, reprinted as Developments in Sedimentology, Vol. 32,
p. 105-132, C.A. Nittrouer, ed. 449 p.

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TECHNICAL REPORT DATA .

(Please read Instructions on the reverse before completing)

1. REPORT NO.

EPA 520/1-83-019

3. RECIPIENT'S ACCESSION NO.

4. TITLE AND SUBTITLE

Analysis of Ocean Current Meter Records
Obtained from a 1975 Deployment Off the
Farallon Islands, California

5. REPORT DATE

August 1983

6. PERFORMING ORGANIZATION CODE

7. AUTHOR(S)

David E. Crabbs

8. PERFORMING ORGANIZATION REPORT NO.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

Interstate Electronics Corporation

10. PROGRAM ELEMENT NO.

Anaheim, California 92803

11. CONTRACT/GRANT NO.

IAG No. AD-89-F-1-607-0
Subcontract No. 3-C2076-A-X

12. SPONSORING AGENCY NAME AND ADDRESS

Office of Radiation Programs
U.S. Environmental Protection Agency
401 M Street., S.W.

Washington, D.C. 20460

13. TYPE OF REPORT AND PERIOD COVERED

Final

14. SPONSORING AGENCY CODE

ANR-461

15. SUPPLEMENTARY NOTES

16. ABSTRACT

Two bottom current records were obtained during August and September 1975
in the Farallon Islands low-level radioactive waste disposal area off San
Francisco, California. This report presents the results of the data
reduction and analysis of the curent meter records,and interprets the
results with respect to additional data collected in 1977. An effort is
made to compare the patterns of current activity in the dumpsite area for
the time periods measured. It is proposed that while the possibility of
transport of suspended material from within the dumpsite area cannot be
ignored, conditions which prevailed at the time and location of
measurements suggest that there is little tendency for shoreward
transport of resuspended sediment. However, measurements taken
throughout the year and over a wider area would be helpful in verifying
this propositon.

17.

KEY WORDS AND DOCUMENT ANALYSIS

a. DESCRIPTORS

b. IDENTIFIERS/OPEN ENDED TERMS

c. COSATI Held/Group

Ocean Dumping

Ocean Disposal/Sea Disposal
Low-Level Radioactive Waste Disposal
Ocean Bottom Currents off California
Radioactivity Transport

18. DISTRIBUTION STATEMENT

19. SECURITY CLASS (This Report 1

Unclassified

21. NO. OF PAGES

Unlimited Release

20. SECURITY CLASS (This page)

Unclassified

22. PRICE

EPA Form 2220-1 (Rev. 4-77) PREVIOUS EDITION IS OBSOLETE

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