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SANTA MONICA BAY, CALIFORNIA SS

THE OCEANOGRAPHY OF

Voltme I

by
Robert E. Stevenson, Richard B. Tibby
and

Donn S. Gorsline

é A Final Report
submitted to the Hyperion Engineers,
by the Geology Department,
University of Southern California

September 18, 1956

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TABLE OF CONTENTS Yen
Page
BOW ESER CORDES 10, YIN encima ae a cle ye ewe pn nm a 1 A: H. 0 ,.
SliIMATE PORN SANTA\ MONICA BAY scoewcmcccuo see secceeeeee 4
Sky Conditions------------~-----.-~---~-----=-- 9 WOODS
January qonn nen cen nnn ew en enn enn nnn 9 HOLE.
Pebruary cupeaee July--------------------- 12 MASS
Aurust through @Decembers=-==-—----2-—-—-—2— 14 .
HaZ@ wenn nae e wee we eee eee ee eee eee ee meen eee 15 Seal
Wind Direction and Velocity---~--------~-..... 16
Be ENN Ns PME Meet ee ome a fs ie 20
Wave Generation Areas=---------.-..-.---.----=~ 21
Southern Guif of Alaska Cyclones---------- 21
North Boundary of Pacific High----------~-- 24
Hawaiian LowS-<2<<e-20-cceen nnn nme neem enn e 24
Generation Areas in Southern Hemisphere--- 25
ivopi cel elurri canes ={———_—-=————————s———2oo5— 26
Cold Front Passagesoo2----<---- 2 - nee anne 28
Coastal LowS-<392-e2--020 ene ee ne mn mcm meee 29
Thermal Lows=-----<<---.5000c00—2 2202 <-e 29
DEW Beibers, Slee Sa Sioa Se ee Se See 30
Land and Sea Breeze Regime---------------~ 30
I gt Ro ePecE GR PAC ee es es eel ees eee ow ew mle 32
MethodS$-<<-.-~ee eee meee eee ee eon cee enemas Yn)
Thermoclines and Gradients-=---<-<ceeennnneua= 33
Classification of Water Masses and Types------ S77,
Annual Range in Temperaturej-----0ncccesenceone A2
Seasonal Character of Shelf Water Units------- 46
June 1955-ces2cencen meee eee ee em we nm eee owen 46 :
July 1955-~-2------ «62 ee ecw e wee ee eee wee 54
WuilvyaAOSGeeeneee tate ke ec oC eo 55
August 19552-22262 -ccwee eee e meen een ne 57
WiSuebigie LOS SaaS See se aoa eee ae eee 58
January 1956-2-222cceense cece ewes ew emo eecee 59
April 1956--cecnenaw emo eme wee eee seme ens 59
Heat Budge tqs=-—--2 n-ne we cee eee so om eeees 60
Source of Mixing Sea Water----=-=--.~..-=-~ 62

Suppression of Effluent Boil below Surface 63
AREAL DISTRIBUTION OF WATER TEMPERATURE AND RELATED

MOUTON = = nn ee ee eee eee eee meena 65
in tEsodUe th Of=—— eam eee nem aaa ae See eee ee a 65
Effect of a Thermal Gradient--2--=--~---.~--== 68

Some Conditions Causing Density Currents-= 76

Wind=——o ee emma eee 76

Tidai Currents==2<<.2.---s-2n~ concn new e 78

2 IbMeGianeel Wen o@cse asso SSeS eee 79

Temperature Distribution and Currents--e<c---= 79

Bieady Statel Condi tions--o<--co seamen es 79

iMenieil Wexler @ngaen ose ee 81

SUIS AG@ (WEsGre oe soe ae So ae ae ee 81

SOS MIErAee WA Gte see Seo Seo Seo aoa 83
Meteorological Relationship of the

Annwaley DiS tra but volta] ose ee alee ae = 34

ay

eae ew 1 et nk ty mart when een ee eo bee Wise ~ mie

bso tahauemnaraaates . Oe: ne ty Sheen oe in ee atid Add

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“pal pes ol a a i re oe me an Ly IIE uokeaie

ore 1 wee yea to woe eine dene none apt af Haste 3872
Kenic Kaas wth weed rigs eee ms ho eine LE Ek 8 LC “Reston }

A 218 ab Oh ON Oy ee Nk aE Ste eR TF ee cm gee Ew er) HS oe at me -~

Fy eI tent te ge Le ed oe OE Ee Pe we 8 wt 6s Oe ee _
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aiden Noha halon igh ew nay dell ed oh ly AN ieee eile ETC) o) | Caen
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' ‘9

287s woaled. tial Pali i wales 173
SHEATH GUA SSTAR IT BE TAW S00 Wb
ak Wen ee hal abe ere nats a We ne coer sare lene ma Or, San cae GP Ram Mm ty et ple Se ee ee ee a
Era a 0 te le fc tl ap a ech ca yg
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Cn ee a ee a
sh five oe slr pee 2a le
Nessa sh linn itleg ik ch salewcorsc"eeem arsine RD WRENN A ne a
Saneve cents bee mo bied eres aguteasqnat
AG Na PS ge ie Yep eo ae eae as ebin L IEEP et thao? ee LE haot4, ;
nr a engl eee em seen whnerchinin ow mame WS PEL pea¥ | panei
Oa), ab mae Ie Vile een Gy REP. Te aw ew oe SE oie Yave
vai a ma ng etn oe ge EE: j2sPepadae,
04 ho obtetattatet I a
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Page
Seasonal Distribution--<2<<e2--- nomen nn e ne 89
Winte fons ec enn ner eww meme meee ee eee ewe 89
Summe £f = 2-22 eee eee we en eww ee ew ee neem ne 117
WATER SALINITY AND NUTRIENTS----2-2-22e222eecenennns 140
MethodS=-~]<2cceeen nee e ence ewe eee eee ewe meee ewes 140
Equipment oon een anne een ce mw een een nee eena= 143
Additional Sources of Salinity Data----------- 143
Salinity Data of Shelf Water------------------ 143
Vertical Variation=---=--<-------2----22---= 143
Dilution from Salinity Data---------=--------= 148
Effect of Diffusers on Dilutione2-<2------= 148
Extent of Sewage Field-o-----n22--nn nee e enn n= 150
NutrientS-ceccm seme em ee eww ew ewe cee soem ee esas 150
Conditions at the Hyperion Outfall-------- 153
TRANS PARENCY oe ceceeecs em en se eee see ee ese eee seer eens 156
MethodS-ecnecwee ese nese ees ee esses eeecesewessaee 156
Transparency in Santa Monica Bayeoees-nn-<2--= 158
Compliance with State Standards-<<-<------- 162
The Relative Merits of Transparency Instruments164
Comparison of Hydrophotometer and Secchi
Disc Readings-s-22encesewn ew een wwe ee nen nan 165
THE CIRCULATION OF SANTA MONICA BAYece2eccenenenenne 169
Statement of the Problemesencsseceeneceena=e= 169
Current Meter ObservationS=<=«<<s<22==<sesseesce== 171
DrogueS~~----<9 2-22 mene ween cen ee een owen nese ne= 173
Drift Card ResultS-<220ececc scene ees eeesennene 175
Introductio0n-<2ceesccescc eee eee we eee ceeess LYS)
Explanation of Drift Cards--s2-seesccences 181
Cruise of September 8, 1955--2s--sesencce= = 183
Cruise of September 29, 1955-ceseesn--=-=- 186
Cruise of December 29, 1955-s2cecnseneeece 194
Cruise of January 18, 1956--s-encseneeecee 196
Cruise of February 16, 1956-ss<ces-esseces 198
Cruise of February 22, 1956s-ses--sssaccc= 198
Cruise of March 28, 1956s2-cescecsseecneee= 202
Cruise of April 25, 195 6e-scesesscoseocece= 204
Cruise of May 23-24, 1956--n-2-sen-seccenn 212
Cruise of June 19, 1956s---2ceccnecnnnscne 215
Cruise of June 29, 1956----2e-22s2secnen== 219
Cruise of July 26-27, 1956esesseccenessne 219
Cruise of August 9-10, 1956----ceceeencen= 221
Cruise of Anoust 20=21, 19562cccensnweesece 228
Drift Card Results from Sludge and Effiuent
Outfall Stations-c-------ccceee ewe eceeene= 228
Eddy Diffusi oneosc3ucescce coe meee cee eee escoeeees 247
Discussion and ConclusionS-<< =-2s02-sececneere 250
Surface Filme---2ce-n-cnn woes ewe eee eee ecee 251
Surface CurrentSe<3< -22-226eseee ee eee en ecee= 252
Deeper CurrentS$o-o2ccsse2eeecceeereneescses 256
SUMMARY 2-2 cece cw emcee eee sew ee eee eee eee ee eee eee eSees 257
Water Temperature =---s--cs cnc ec eee eee see eceee 259
Water Masses and UnitS=-<--2<-ceesseencmeeeeccee 260
Temperature and the Rising Effluent----------- 261

Water Temperature and Related Motion-<-<<seee> 262

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REFERENCES CITED

ity and Nutrients-------~---.--.-..

y 2 © © me © es me ow me oe ee ee os ws
of Santa Monica Bay---------------

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LIST OF ILLUSTRATIONS

FIGURE PAGE
1. Maximum and Minimum Air TemperaturesS-----~---------" 7
2. Maximum, Minimum, and Average Air

Temperatures, San Pedro Channel =--------<-----<---- 8
3. Average Air Temperature and Rainfall--------------- 10
4. Sky Conditions in the Los Angeles Area------------- 11
5. Average Yearly Winds at Los Angeles Harbor--------- ib
6. Monthly Wind Directions and Velocities
over the San Pedro Channel -----------=------ -—<————— 19
7. Frequency, Height, and Direction of Swell,
San Pedro Channel] -<=-<9<9 6-203 8 2 n= en nm 22
8. Monthiy Sea Conditions in San Pedro Channel-------- 31
9. Vertical Water Temperature Profile in
Santa Monica Bay Extending Seaward from
leyorormatteys) Lexayibs |fralye 2005 12) 5) 35
10. Detailed Water Temperature Profile,
July 20, 19552-99222 222222 22 cnn mee en wenn ee ese cree n= 36
11. Ranges of Water Temperature in 200 Feet
of Shelf Water-s-2<2= 92 2-2 ene en eee eee een ene ee eer e ne 38
12. Cumulative Temperature-Salinity Diagram
for the Waters of Santa Monica Bay----->---=---=-- sa Al
13. Limits of Temperature Range for Increments
of 10 feet of Depth in Santa Monica Bay~----------=- 43
14. Seasonal Range in Surface Water Temperature
in Santa Monica Bay=---e2=22-22= 222899 ee een cee ee enen= 44
15. Vertical Temperature Column for June 1955=--------- 47
16, Vertical Temperature Column for July 1955---------- 48
17. Vertical Temperature Column for July 1956--=2---=--=- 49
18. Vertical Temperature Column for August 1955------<-- 50
19. Vertical Temperature Column for October 1955------- 51
20. Vertical Temperature Column for January 1956=---=--- 52
21. Vertical Temperature Column for April 1956------<-=-- 58)
22. Vertical Temperature Profile, Seaward from
Playa del Rey, August 18, 1955=-<----<-2--<932-2-<-<-= 67
23. Depth to 55°F Isotherm and Drogue Track,
May (4, POS Cana i = ee = 70
24. Depth to 56°F Iostherm, May 4, 1956<-=---2---=---=-=-=- (fal
25. Depth to 66°F Tostherm, June 28, 1956----2----==-=<= 72
26. Depth to 65°F Isotherm and Drogue Track,
August 10, 1956====2<===<2 9s ss9eseecs wes aceon ae ees ea= 73
27. Depth to 58°F Isotherm and Drogue Track,
August 10, 1956-==2=-<2===<== Sosa aS Seca HSS QS SOS SSS 74
28. Surface Temperature, August 18, 1955-<-2=9-----2-=--= 86
29. Vertical Temperature Profile in North-South
Direction, August 18, 1955--2-2=<<29>c=s-es> eeseeeere= 87
30. Surface Temperature, August 24, 1955----22-2=<ss2s-=2 88
31. Depth to 58°F Isotherm, November 23, 1955---2---<-<= 90
32. Depth to 55°F Isotherm, November 23, 195$------=---= 92
33. Depth to 60°F Isotherm, May 23-24, 1956-<----<22=--== 93
34. Current Flow Between 20-80 Feet, May 23-24,

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LIST OF ILLUSTRATIONS

FIGURE PAGE
$5. Depth to 55°F Isotherm, May 23=24, 1956------------ 96
36. Current Flow Between 80-150 Feet,

May 25-24, 195 6 97
37. Depth to 54°F Isotherm, January 18, 1956----------- 98
38. Depth to 57°F Isotherm, December 29, 1955---------- 99
39. Current Flow Between 10-120 Feet,

Jjcnineray IRS IDS) SS 100
40. Current Flow Between 40-120 Feet,

December 29, 1955---------9 29922228 enn ee renee 101
41. Depth to 55°F Isotherm, December 29, 1955---------- 103
42. Depth to 520F Isotherm, January 18, 1956----------- 104
43. Current Flow Between 120-150 Feet,

January 18, 1956-292 --<2-299 or enna en ern er er ere 105
44, Current Flow Between 100-140 Feet,

December 29, 1955 2222-2 on= enn 28 oem enn een eee en ee an 106
45. Depth to 58°0F Isotherm, April 25, 1956----------=--- 107
46. Depth to 55°F Isotherm, February 22, 1956---------- 108
47. Current Flow Between 20-70 Feet, April 25, 1956---- 109
48. Current Flow Between 10-80 Feet,

February 22, 1956-93299 een 28 228 2m nn ean en eee 110
49. Depth to 53°F Isotherm, April 25, 1956-------=--=---- 112
50. Current Flow Between 70-150 Feet, April 25, 1956--=- 113
51. Depth to 52°F Isotherm, February 22, 1956-----=----- 114
52. Current Flow Between 100-150 Feet,

ISIE Ey B25 UD SSS 6 Se UES)
53. Depth to 56°F Isotherm, March 21, 1956------------- 116
34. Depth to 54°F Isotherm, March 21, 1956=------------- 118
39. Depth to 61°F Isotherm, July 6, 1955-----<-----<---=-- 120
56. Depth to 55°F Isotherm, July 6, 1955+---2--<----=--- 121
537. Depth to 620F Isotherm, August 10, 1955------------ 122
58. Depth to 53°F Isotherm, August 10, 1955------------ 123
59. Depth to 62°F Isotherm, August 18, 1955------------ 124
60. Depth to 60°F Isotherm, August 18, 1955-------<---=-- v2IS
61. Depth to 540F Isotherm, August 18, 1955------------ 126
62. Depth to 600F Isotherm, August 24, 1955------------ 127.
63. Depth to 540F Isotherm, August 24, 1955------------ 128
64. Depth to 60°F Isotherm, September 8, 1955---------- 130
65. Depth to 64°F Isotherm, September 16, 1955--------- 131
66. Depth to 55°F Isotherm, September 8, 1955---------- SS
67. Depth te 56°F Isotherm, September 16, 1955--------- 134
68. Depth to 61°F Isotherm, September 29, 1955--=----=- 135
69. Depth to 55°F Isotherm, September 29, 1955--------- 136
70. Depth to 60°F Isotherm, October 13, 1955-=---=-=------ 137
71. Depth to 55°F Isotherm, October 13, 1955------=-=--- 138
72. Vertical Salinity Distribution in Santa

Monica Bay, 1955-56-2--23= 2228 e828 288 en eer esr en reH= 145
73. Cumulative Percentage in Chlorinities,

Santa Monica Bay, 1955=-56--2=2-=---99 2-225 e--9------ 147
74. Salinity, June 20, 1955------9-2--2-<s9<s2e2-e-e--- shel
75. Surface Salinity, August 10, 1955----------=--=------ 1352

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LIST OF ILLUSTRATIONS

FIGURE PAGE
76. Average Transparency of Santa Monica Bay,
June 1955 to August 1956, Based on
Secchi DiSc ---------22-- <= 2-38 o-oo = $= = 157
77. Per Cent Light Transmitted at depth of
5 feet for Winter Months (1955-56) ----=--=--------- 159
78. North-South Profiles of Light Transmission
at Orange County Sewer Outfall, 7,000 feet
offshore, December 19-20, 1955 ---=--2----=---=----- 160
79. Comparison of Secchi Disc Readings with
Hydrophotometer Determinations of Percentage
Light Transmission at a Depth of 5 feet ----------- 167
80. Comparison of Secchi Disc Readings with
Average Light Transmission to Depth of
Secchi DiS --- ©-2=2- 9-2 <= 28 = 22 2 oe eee we oe 168
81. Drift Card Stations, September 8, 1955------------ 182
82. Drift Card Returns, September 8, 1955, Area I----- 184
83. Drift Card Returns, September 8, 1955, Area I----- 185
84. Drift Card Returns, September 8, 1955, Area II---- 187
85. Drift Card Returns, September 8, 1955, Area II---- 188
86. Drift Card Stations, September 29, 1955----------- 189
87. Drift Card Recoveries Outside Santa Monica
Bay, September 29, 1955, Areas I and II ----------- 191
88. Drift Card Recoveries, September 29, 1955,
Area I] 2-222 22222 22 665 ©2889 88 oe cee mee ees ere ererre= 192
89. Drift Card Recoveries, September 29, 1955,
Area I] --2229-28 62 22-682 s2 0 S28 e8 e ee ee eee eee cer ene 193
90. Drift Card Recoveries, December 29, 1955---------- 195
91. Drift Card Returns, January 18, 1956-------------- 197
92. Drift Card Returns, February 16, 1956------------- 199
93. Drift Card Stations, February 22, 1956------------ 200
94. Drift Card Returns, February 22, 1956, Area I----- 201
95. Drift Card Returns, February 22, 1956, Area II---- 203
96. Drift Card Returns, March 28, 1956 -2-=-=-<2--------- 205
97. Drift Card Returns, March 28, 1956 =---2--<---<------- 206
98. Drift Card Returns, March 28, 1956 -==----<---<+- ----- 207
99. Drift Card Returns, April 25, 1956 ------2---------- 209
100. Drift Card Returns, April 25, 1956 ---2-----=--<2---= 210
101. Drift Card Returns, May 23-24, 1956--------------- AS
102. Drift Card Returns, May 23-24, 1956-------=-<------- 214
103. Drift Card Returns, June 19, 1956----------------- 216
104, Drift Card Returns, June 19, 1956--------------=-- 217
105. Drift Card Returns, June 19, 1956----------------- 218
106. Drift Card Returns, June 29, 1956----------------- 221
107. Drift Card Returns, July 26-27, 1956-------------- 223
108. Drift Card Returns, July 26-27, 1956-------------- 224
109. Drift Card Returns, August 9-10, 1956-------=----- 225
110. Drift Card Returns, August 9-10, 1956 ------------- 226
111. Drift Card Returns, August 9-10, 1956------------- 227
112. Drift Card Returns, August 20-21, 1956------=-=----- 229
113. Drift Card Returns from Sludge and

Effluent Outfaill Stations, September 8, 1955------ 230

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122.
123.
124,
125.

LIST OF ILLUSTRATIONS

Drift Card Returns from Sludge and Effluent

Outfall Stations, September 29, 1955----------

Drift Card Returns from Sludge and Effluent

Outfall Stations, December 29, 1955-----------

Drift Card Returns from Sludge and Effluent

Outfall Stations, January 18, 1956------------

Drift Card Returns from Sludge and Effluent

Outfall Stations, February 16, 1956-----------

Drift Card Returns from Sludge and Effluent

Outfall Stations, February 22, 1956-----------

Drift Card Returns from Sludge and Effluent

Outfall Stations, March 28, 1956--------------

Drift Card Returns from Sludge and Effluent

Outfall Stations, April 25, 1956--------------

Drift Card Returns from Sludge and Effluent

Outfall Stations, May 23-24, 1956-------------

Drift Card Returns from Sludge and Effluent

Outfall Stations, June 19, 1956--------------=-

Drift Card Returns from Sludge and Effluent

Outfall Stations, July 26-27, 1956------------

Drift Card Returns from Sludge and Effluent

Outfall Stations, August 9-10, 1956-----------

Drift Card Returns from Sludge and Effluent

Outfall Stations, August 19-20, 1956----------

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PREFACE

In June 1955, when marine scientists at the University
of Southern California were called upon to conduct an
oceanographic survey of Santa Monica Bay, sanitary engineers
considered that by disposing sewage five miles from the
shore the effluent would be adequately diluted by the
great volume of sea water available, and that such dilutions
would eliminate any health hazard on the adjacent shores.
Within a few months, however, it was necessary to change
this philosophy, for by this time it had been determined
from numerous current measurements that the ocean in
Santa Monica Bay moved too slowly to give dilutions of
greater than 1:100 despite the method of mechanical
diffusion used.

It was essential, therefore, that the scientists
at the University initiate a program to investigate the
rate of disappearance of coliform bacteria from sea water,
and to determine the direction and net flow of the ocean
currents in the bay. These parts of the eventual over-
all program were begun in September 1955 and completed in
July 1956. New techniques were devised and used for the
first time at sea, and the results were believed to be
highly successful.

Nearly 1,500 stations were occuppied by the M/V
VELERO IV, the University's research vessel, during the
year. Some of the stations were occuppied for only a

Short period and for one purpose, while at other times,

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20 to 24 hours were spent making observations at one locality.
Work was conducted both during daylight hours and at night
in an attempt to eliminate inherent errors in investigations
limited to only one period of the day.

The results of this survey are embodied in six sepa-
rate reports covering bacteriology, marine biology, sub-
marine geology, oceanography, and the data in appendix
form.

The several fields of interest covered by the survey
required the capabilities of a number of experts who
specialize in the marine sciences, The following per-
sonnel at the University of Southern California contributed
either full or part time to the survey work:

Dr. K, O. Emery, Marine Geologist

Dr. Olga Hartman, Marine Biologist

Dr. Daniel Ivler, Bacteriologist

Dr. T. Mitwer, Bacteriologist

Dr. Sydney C. Rittenberg, Marine Bacteriologist

Dr. Robert E, Stevenson, Geological Oceanographer

Dr. Richard B. Tibby, Physical Oceanographer

Mr. D. Brostoff, Bacteriologist

Mr. John V, Byrne, Marine Geologist

Mr. Donn S. Gorsline, Marine Geologist

Mr. John R. Grady, Marine Geologist

Mr, L, Hoachstein, Bacteriologist

Mr. P, Kramer, Bacteriologist

Mr. R. MacGlasson, Laboratory Technician

that | RES 9 a)

whe ts OE Air, ROE ROW I At He

pac ae ie

# 1h 495 PHASE an Es oF incinae oe

a9 IO :

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iia

Mr. B. Mechalas, Bacteriologist

Mr. R. J. Martinez, Bacteriologist
Miss Sandy Lynagh, Technical Secretary
Miss Johanna Resig, Microbiologist

Mr. D. Scholl, Laboratory Technician
Mr. Richard D. Terry, Marine Geologist
Mr, Elazar Uchupi, Marine Geologist

Mr. E, Zalesny, Laboratory Technician

Respectfully submitted,

a

Robert E, Stevenson
September 18, 1956 Director, Inshore Research

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THE OCEANOGRAPHY OF SANTA MONICA BAY
INTRODUCTION

In the summer of 1955 the University of Southern California
was requested by Hyperion Engineers, Inc. to furnish infor-
mation on Santa Monica Bay which would assist in the design of
a proposed oceanic sewage outfall for the City of Los Angeles.
The existing Hyperion treatment plant, placed in operation in
1950, has an average design capacity of 245 million gallons of
sewage per day, which is treated by primary settling followed
by the high rate activated sludge process. The treatment is
supplemented by chlorination when necessary. The outfall from
this plant terminates one mile from shore. Because of the
unprecedented growth in the Los Angeles area this rate of flow
soon was reached and it was therefore necessary to provide for
the eventual disposal by the year 2000 of an average of 640
million gallons per day. A number of alternative schemes were
proposed for taking care of this enormous quantity of sewage.
However, the one which was considered to be most economical
recommended increasing the capacity of the present Hyperion
plant and disposing the sludge and primary-treated effluent
through separate ocean outfalls terminating at distances of
five to six miles from the shore of Santa Monica Bay.

The University was engaged by Hyperion Engineers, Inc. to
supply data on bottom topography, sediments, and hydrographic
features of Santa Monica Bay which were directly related to
the design and construction of the outfalls. However, within

a short time it became apparent that additional information on

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ocean currents, temperatures, and certain other characteristics
of the bay would be required. Shortly thereafter a study of
the types and distribution of bottom-dwelling animals was
included and finally, in October of 1955, the contract was
further extended to include an investigation of the rate of
disappearance of coliform bacteria in the sea from unchlori-
nated primary-treated effluent.

It has been the contractual responsibility of the University
of Southern California, after a period of one year's research in
the bay, to report to Hyperion Engineers, Inc. the scientific
results on the following specific topics:

1. The detailed bottom topography and sedimentary
characteristics of the sea floor.

2. The biology of bottom-dwelling animals.

3. The distribution and rate of disappearance of
coliform bacteria.

4, The temperature, salinity, turbidity, and other
properties of the water within the bay.

5. The directions and velocities of ocean currents.

The submarine topography and sediments, the biology of
bottom organisms, and the bacterial studies are contained in
separate sections of this report.

In addition to those items, a review of the climate, sea
and swell, and other meteorological conditions have been
included. Because both the data and the descriptive material
for this review were readily available, such a review could be
made without interfering with major research commi'ments.

Santa Monica Bay, California, is a crescent-shaped inden-

tation of the southern California coast, lying due west of the

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City of Los Angeles. The seaward boundary of the bay extends
from Point Dume on the north to Palos Verdes Point on the
south, a distance of 27 statute miles. The coast line of the
bay is approximately 38 miles in length. The eastern shore
is heavily populated and the cities of Santa Monica, Venice,
Playa del Rey, El Segundo, Manhattan Beach, Hermosa Beach,
and Redondo extend almost continuously for a distance of 15
miles from north to south. Along the northern border of the
bay the Santa Monica Mountains reach the shore and the main
access to this area is by a north-south highway. Only
relatively small and scattered communities have been built
along the northern shores, mostly in the vicinity of Malibu,
although the area is much used for recreational purposes.

The southern shore consists of 3 miles of precipitous cliffs
above a narrow, rocky beach, cut into the Palos Verdes Hills.
Like the alluvial Los Angeles plain to the east, the
bottom of the bay slopes gently from the shore to a depth of
300 feet, forming a sheif 3 to 6 miles wide. In the central
portion of the bay, between Playa del Rey and Hermosa Beach,
the shelf extends farther to sea and forms a submarine plain,

projecting to a distance of 10 miles from shore.

The shelf is incised by two major submarine canyons, one
to the north and one to the south of the central shelf extension.
The Santa Monica Canyon is wide and the wails are not steep
except at the head of the canyon at a distance of 43 miles from
shore. The Redondo Canyon is a well-defined physiographic
feature of the submarine landscape. It has relatively steep
Sides and its major head extends almost to shore at Redondo =

Beach.

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A number of offshore islands protect the area of Santa
Monica Bay from the effects of storms and high waves originating
in the open sea. From a hydrographic standpoint, the bay is
in open communication with the offshore region and the character
of its waters as well as its circulation, therefore, depend
upon events outside the bay. On the other hand, its shape and
orientation are such that waves, tides, and local winds deci-
sively modify the pattern of current flow, particularly in the
near-shore and littoral zones. Aithough the chemical and
physical structure of the waters in the bay are complicated,
the work of the past year has established certain general
features and patterns of flow that are the subject of this

report.
THE CLIMATE OF SANTA MONICA BAY

Los Angeles is situated in a region which has a
"Mediterranean" climate (Koppen, 1923). The characteristics
of this climate are hot summers, with the warmest month having
an average temperature higher than 71°F, mild winters with the
coolest month having average temperatures between 32°F and
64.4°F, and with at least three times as much rainfall in the
wettest month as in the dryest. The coastal regions of
southern California have all the prerequisites for such a
climate. Due to the concentration of rainfall in the winter
and early spring, plus the hot dry summers, the vegetation
imparts a brown color to the land area during most of the
year. Only in the late winter and early spring is the land-

scape green, and the duration of the green period is entirely

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dependent on the amount and spacing of rainfall for the parti-
cular year.

Chief among the meteorological factors influencing the
southern California climate is the prevalence in the vicinity
throughout most of the year of the eastern lobe of the Pacific
High. When it is strong and lies close to the shore, clear
skies and mild weather previal since it causes storms from
the North Pacific to be turned eastward before reaching this
latitude. As the strength of the high weakens, or if it
moves to the south or west, cold fronts may sweep in from the
northwest. During the summer when the high pressure belt has
moved northward, these rarely arrive. If they do, they are
quite weak. During the winter, however, the center of the
high is usually about a third of the distance between Hawaii
and the Aleutians. A col in the high pressure belt is
located over the eastern margin of the Pacific which resuits
in a strong northwesterly flow, and the southern parts of
cyclones are able to reach our coasts bringing fairly strong
winds and rain.

This northwesterly flow is apt to be as strong in summer
as in winter, but in the summer the trajectory of an air
particle would take it back to a position nearer the center
of the high pressure cell. Even though northwesterly winds
prevailytherefore, they do not originate in the North Pacific
and accordingly do not bring the cold fronts to the coast.

In the summer, the intensity of the northwesteriies may be
increased by the development of a deep thermal low over the

arid regions of the southwestern United States. It is not

a p

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dha te +jated. Haewiass Baas GO of 22 Voge

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wr wel °Sasmecwutl, 1 eth gh silat witch iat 94, we brat heal

aD *: iedterk, tanta ean Yong |

Pee sae er © von i. ” el eee

uncommon in late August and September for the pressure gradient
to become so steep over the water adjacent to Point Conception
that winds of Force 4, 5, and even 6 prevail for days on end
due to this influence.

Precipitation is usually light and steady when it occurs
and does not last more than two or three consecutive days,
except under unusual meterologic conditions. Cumulus clouds,
although rare over the Los Angeles area, frequently build to
considerable heights over the coastal mountains during the
fall and spring months. Thunderstorms occur less than three
times a year in Los Angeles and have never been recorded
over Santa Monica Bay. Most precipitation comes from cold
frontal activity, as warm fronts are normally not extensive
enough to reach this latitude with any intensity.

In Santa Monica Bay, climatic characteristics are even
milder than that of the bordering coastal areas. The highest,
lowest, and average temperatures are shown in Figure HiMEOr
coastal stations, and for the San Pedro Channel in Figure 2.
The annual range at the coast is a moderate 23.3°F, and the
mean minimum and maximum temperatures have a spread of only
18°F, The lowest temperature ever recorded along the Les
Angeles coastal region was 28.2°F at San Pedro on January 23,
1937. Temperatures higher than 87°F have been recorded for
every month of the year, and temperatures of 90°F or higher
have occurred at one time or another in 9 of the 12 months.

On the water temperatures are even milder. In nearly 30

years of operation, the Catalina Island Steamship Line has

7 rath big bis | sual

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Dy RE Ly, hake LY UW rr a a Aa OS hele uteciie 300

(—t

yrs eae M4 emk7) 3 - , ’ te aay wi’ (a2 egan? —

lee

fats ere TAA i J Tr) to vt, tH") ih 7 1'e ed hte Boom

at wan The * “1 aWik?2 » C45; ota .

eer ee) a ee ot s enlagnd ol 26 22h

LF ie? wa Neuss Tea ov , ry GA & a nee, atne

4 VE Hic'> © ty ha q ; i pee an , @F cen rae
; \
ye —

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L aki LL : Ae hae i ; J fy bs 4 Be ted *
, Pet Kiet Te “stg > ae au A
Pei ie sob ? a2 1) Jac? gee
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3 : rk’) sind vert] i? Sa) DOs aries & Pa Pie )
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nt iy ;

7 iii giten oh é r¢ no TM SroTr ap hay mewirew hoe cee
oe , roy RS ee wee IO | Pew en aid aE oat
* A ue Tekin an eee ae Fy Ae Ae, i pe ee ee Landi
hark Rese oue Rew) arial MAE ee (nkd pea ma DORs)
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PRMR RE Nl aN NF RE MD re omae ae is roa aago’

ae es ‘ Ds ¢) ty | Told . . i mee A: aan ta eg para walt . ft

Gh PANS A) Gree kek ae Gated wd BEE eran Laon sanalasege oe O'te.:

Figure 1. Maximum and minimum air temperatures.

OYGsd NWS ------

SYFLVM TWLSVOD YFIAO
HIVIG INOT ———

SITIINY SO7

WNLVAIdWIL LSIMO]

Gz WWCETES =

i=
:

ef

we “y
?

pei eon eves aa abhabts de wttiaud ai

4

Figure 2. Maximum, minimum, and average air temperatures,

San Pedro Channel.

/
Sem auc bar | tus th

tahnadd onthe aa’

/00—

S
i

boa)
i.

|

cy
‘L

PG RiES TT AND OW BE Sil,
PeMiPeRrAnUR ES Sh EGOrn DED

— MEAN TEMP.

MEAN MAX. ------ MEAN MIN.

-_—=

NUTT
UNIAN

\
\

ee CO | eee

\

4

eee "==

\

|

INAANAANHAUA AAU
DANA

TAA
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\
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\
IUUNAUAUNAUTTAUAT ATA

aaen
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moons

ry

7
a? s
'

i

BHO IH
IRUTAR SIME

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hens yar
4 earn’

never reported a freezing temperature nor one higher than
87°F aboard their ships.

Precipitation is less along the coast than in Los Angeles
and lower still over the waters of the continental shelf.
There are no continuous records of rainfall over the ocean,
but the figures for San Pedro probably give a close approxi=
mation (Fig. 3). At one time or another rain has fallen in
every month of the year, but the summer months are quite dry.
The average for June is 0.10 inch, for July, 0.01 inch, and
for August, 0.05 inch. Even in February, the rainiest month,
the average is less than 2.5 inches and the greatest preci-

pitation over a 24 hour period produced a mere 3.5 inches.
Sky Conditions

Data of the sky conditions on land are availabie from the
U. S. Weather Bureau station at the Los Angeies International
Airport and are shown in Figure 4. Even so, these do not
represent the conditions prevalent over the coastal waters of
Los Angeles. The sky and visibility conditions in Figure 4
were compiled from the logs of the Catalina Isiand steamers
and represent an observation period of ten years.
January

Fog is prevalent in January with 27% of the mornings
(9 days) having ceilings below 500 feet and visibilities less
than 3 mile. The fog usually changes to a low overcast or
broken clouds by 1100 hours. Siightly more than two days a
month have fog throughout a 24 hour period. However, in

January 1950, a continuous fog was recorded lasting 94 hours,

i

apaime a
: ais Omri ‘ian
i a meh
ide derd thet rene
so rOtH 39 Smi4 sim +A |
uz ath gad eaeny att te ae:
ALO
vf yeva
nik 2 yh ee

tae Ft pa |

1h Lewes
444 34 cok¥ate
Ma ened ex, Qwode
-aghiw ST] 250,
+ WIL DOA er bas
na ait 4g

ba bay Mmitavised> Ne |

L nb teolavesg ab pe

bom I4o) O82 wolfed geht bss werk wast Cave

nonmata ycinwes go) sat etn
somal oolL Xd abuolo ir

e tyortgworady aah ay

Figure 3,

Average air temperature and rainfall.

10

5
imeT ws
ES SUS

SYILVM WLSVOD YFIAO ——
OYUdId NWS ------

HIVFEF INOT ———

SFTIINY SOT ——

WHERE

eS hn 1
BENCH _
WAGES 2S

vs.
SA
owe
=

~
*
a,
oe
7
7
oc
~

ey

seis 5 amma saris say berm ie irene

Pie
/ .
4, .

a ee pee
4

Figure 4,

11

Sky conditions in the Los Angeles area.

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12

and it is not unknown in this month for fogs to last 3 to 6
days with only a 1 to 2 hour break near midday.

A low overcast with ceilings less than 1,000 feet but over
500 feet, and visibilities less than three miles is equally
common, An average of 23% of the mornings and 18% of the
afternoons have such an overcast. The stratus is continuous
throughout a 24 hour period 12% of the time. These overcasts
are seldom the result of fog lifting, but may precede a
heavy fog. Although alleday overcasts do occur, as noted,
the more common condition is for the stratus to "break" near
midday, resulting in broken or clear skies. Scattered clouds
are rare during any part of the year over waters of the
continental shelf.
February through July

February marks the beginning of a trend in the decrease
in the occurrence of fog. The decrease continues through
July,and in the months of March, June, and July the occurrence
of fog is negligible. April and May have a slight increase,
particularly in the morning hours, but the increase is minor
amounting to only two days. Fog during this part of the year
is primarily a morning condition and normally dissipates late
in the forenoon. In late April and early May, no fog has been
recorded in the afternoon and in the entire months of March,
June, and July no fog lasts throughout a 24 hour period. The
maximum fog conditions in this part of the year occur in
February and May when 12 and 9 per cent of the days, respec-

tively, have fog during the morning hours.

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PUNO: CLE pn oe ati teh be Mewad ;

13

Other overcast conditions also tend to decrease in
February and March from those noted in January. In February,
21% of the mornings and 21% of the afternoons (6 days) are
overcast and the stratus layer is continuous through 24 hours
12% of the month (4 days). Broken clouds show a marked «
decrease in occurrence in both months with none lasting 24
hours in February and only one recording in March.

Because of the decrease in overcasts there is a great
increase in the number of clear days in the first two months
of the period. In February, the sky is clear all day 62% of
the time (21 days), and in March, 66% of the month is clear
for 24 hours.

In April, the “summer sea fogs” begin to intrude the
southern California coast, although these low stratus layers
are more frequent in May, june, and August. The “sea fogs”
are actually low-lying stratus lavers of varying thickness
and are called “high fogs™ by the general public in the Los
Angeles Basin area. Usually the stratus dissipates or
“burns off** before noon, but there may be periods during which
a continuous overcast persists for a week or ten days. Aithough
it is uncommon, the morning cccurrence of stratus may be
remarkably regular. There have been summer months during which
an overcast occurred through most cf the forenoon for 21 of
the 30 days. In 1948, from the first of June to the first of
September, only 18 of 93 mornings were clear. in July 1948,
19 consecutive mornings were foggy or cloudy, and from the
lith of August through the 4th of September, every morning

was overcast, a total of 25 consecutive days. The ceilings of

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14

these stratus layers vary from 600 to 800 feet at dawn, rise
to 1,200 or 1,300 feet after sunrise, and are near 1,500 feet
at the time of dissipation.

Despite the increase in the number of cloudy mornings,
the summer months have a high percentage of clear days. If
the afternoon periods are considered along with the 24 hour
periods, it is noted that June has the least cloudiness and
August the most. An average of 27 afternoons are clear in
June and 14 all-day periods.

August through December

Fog conditions begin to increase in August and this trend
more or less continues through the end of January. The trend
is most obvious in 24-hour fogs. In August and September an
average of 7 mornings each month have low visibility due to
fog, a characteristic of these months. Whereas fog in the
early summer months is extremely irregular in occurrence, in
August and September regular sequences may occur. Records
show many periods when fog occurs each morning for 5 to 8
days. However, there is only one recording of fog persisting
throughout the day.

Afternoon fogs in these five months are irregular in
occurrence and are generaily the result of a noontime “lifting”
of the fog to be followed by a “lowering™ in the late after-
noon. Under such conditions, a fog bank persists throughout
the day 20 to 30 miles offshore and the “lifting” and “lowering”
is the result of morning land breezes and afternoon sea breezes.
During the midday break, the sky is hazy and visibility remains

less than 3 miles.

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LS

The occurrence of overcasts decreases regularly during
the period until in November and December, only 4 mornings a
month are overcast. The extent of summer sea fogs also dimi-
nishes rapidly after October and during the later months of
the year, most cloudy conditions are the result of infrequent
frontal storms. The number of days with a broken sky increases
slightly, the clouds being the remnants of the morning fogs.

The most striking climatic characteristic is the great
increase of days with clear skies in October, November, and
December. These conditions reach a maximum in November when
55% (21 days) of the month is clear all day long. This, with
the 67% of the clear afternoons in December, indicates the
fine weather to be expected in these two months.

Haze

An important and common deterrent to visibility over the
coastal waters is the haze which precedes and proceeds fog and
low stratus clouds. During the summer months in particular,
haze is prevalent and thick over the adjacent land mass. Its
occurrence cannot be missed due to the brownish tinge contri-
buted by the addition of smoke and fumes to the atmosphere.
Normally this “smog" does not cccur over the ocean, but
following several days of smog, a land breeze may carry it
seaward.

The haze results from the stable air conditions, the strong
temperature inversion, and the geography of the Los Angeies
region. Turbulent unstable air masses tend to disrupt the
inversion and allow the haze to dissipate. However, the nor-

mally stable marine air is held in check by the semi-circular

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(Aabesabo tne, comes Aveda: ink susie 7 7

16

ring of mountains and with the inversion acting as a "lid",
the haze may last for several weeks. Visibility in Santa
Monica Bay during these periods is normally greater than

3 miles and less than 12 miles.
Wind Direction and Velocity

The dominant winds occur in the afternoon, are westerly,
and are primarily the result of the land and sea breeze regime
active along the coast. Higher velocities normally occur in
the afternoons with the west winds, the land breezes at night
from the east or northeast are usually less than Beaufort
Force 2. Even Santanna wind conditions do not bring strong
northeasterlies to this area as the force is much reduced
after the air mass spreads out across the Los Angeles Plain.
The wind conditions at Venice are similar to those noted at
the Los Angeles International Airport and are known to be
somewhat different from those obtained aboard the VELERO IV
in Santa Monica Bay.

Wind conditions which are probably more representative
of nearshore ocean areas are shown in Figure 5. This is a
compilation from the monthly aerological records of the
U. S. Navy aircraft carriers LEXINGTON and SARATOGA from
April 1928 to July 1937. During this period the two ships
were at an anchorage two miles seaward from Long Beach for
a total time of 3.93 years. The winds were predominantly
light with velocities less than 13 mph, and blew the greatest
number of days from the southwest. For 60% of the year (219

days) the wind blew for more than 30 days, each from 5 different

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cred synzodons ns 1%

DAAwADe ae LE:
erway £2, ti te anke

gta tt ands sak natin thy )

17

Figure 5, Average yearly winds at Los Angeles Harbor.

wodoeH esloanA acl ta sbnkw Yiaesy SnzrevA ae @

18

directions. However, for 33% of the year (120 days) the wind
was from either the west or southwest, and from the duration
of wind in days and the wind movement in miles, a prevailing
wind from the southwest is indicated. These data do not show,
though, the land breeze which is the dominant air motion in
the morning hours throughout most of the year.

From information taken aboard the Catalina Island steamers,
the S. S. CATALINA and the S. S. AVALON, wind directions and
velocities have been compiled for morning and afternoon for
each month. Even though the reporting station is approximately
8 miles south of San Pedro, a check with the winds obtained
during 1955-56 aboard the VELERO IV in Santa Monica Bay show
there to be no detectable variations other than those to be
expected from year to year. These winds from the San Pedro
Channel are shown in Figure 6.

During the later fall and winter months the morning is
dominated by winds from the northeast and southeast while in
the afternoon, west and northwest breezes prevail. In the
spring, summer, and early fall, the morning northeast breeze
is almost nonexistent and although the southeast wind con-
tinues to occur, its velocity is much lower. This change in
the morning land breeze is due to the differential heating of
the land during the summer and winter seasons. Because of the
high temperatures over southern California in summer, a sea
breeze blows at nearly all hours and the night cooling effect
is shown mainly be a decrease in velocity of the sea breeze.
It may also cause the sea breeze to cease blowing in the

morning, this being indicated by the increase in calm mornings

in the summer.

“nokgaan ant ane bre teowrtanioe to teow ontt + aay

got traevesrq e ypotkm rk jrrsmeNo mite sd? bos avab RE

| eat aon 6b #tab deol ,boteogbri ai Saw iH e oat a
gi moitem tis iackmeb oa eb dokdw oego1d bewt ane :

. teoy sav to teom Swotiguara? aso |
senomasts betalel suiisyed sad ‘binode Weis? noitentotak te
hay eaoks: Sexkb botw -MOIAVA .@ 22 OA? bas RAL IATA o A

got moonisi in bas gekntom xot beliquon aeod ovat ae
yiotamixasqqu ak aoktate qotexzoger sat typed? novi pe
é {
bemtetdo ¢baiw wits dtiw Aosio s gorbel Ane ye cles ce

wots ys sotaok ains2 at VE OfS2aV odd bisods peaeeer

“ea al seads ante zedto anaktatiay sidstsa? ob on od of
Sibel ust ony wont wboiw seefl .agay of x897 mork oF
+4 arene nk mvode oe

ei yhtirrom ocd edécom rwstebw bas Sipt ast81 odt, pakie
at olffttw fesedttuoe boa tesentzon eft mori < bakw yd '
oat mt hevenq eesoetd famaitzen bas hate nookze?

ageanyd tzapottien suknzvom aff 44 ffi vitae (nae Rat: J

a”

~no5 biiw tegedtyor sit dwrodtin bss tootakxonon |
th opfalo prey =. tawol domm tf yttooiny ets IMD. ota +
Jo onkteot LakfaarsTiib af of, oth at asosu bret govkmxe on
ott Yo wausned ,enoaese sotdke hrs tome ome geiaubd baat
a62 4 + tammnes tt pinzothtsd frahtve2 19¥6 sewtasaceet |
Sostts gitk Loos tatnier ont. pte eipod its ytason te awold x
seseetd ace oat to exisetoy ak senoz0eb #) od ‘einkon awodte | a
ov? ci gokwold oases oF soon, eee oct ‘ouues oata va
ny

; sageteroe wind. oh seporoal ond yd! poteshbad pated aint .3a.
" + one, er

19

Figure 6. Monthly wind directions and velocities over

the San Pedro Channel.

xO¥O BOLYinolsy bug wzneigsezih Ontw yiritaom 40 ox me

sPsitesdD ogbst ane arti

=25 Knots

YSEWN3550

CA

9

YsAEWNs550

SUV JTBVINVA ® 0u3z 4O J9VIN3943d
Juv JSON GNIM 40 Y3LN3D NI SYIBWNN

SGNIM NOONY4ALAV

YSAENSAON YsgOL5D0 YsEW3ld3ss LSNONV

[= ———

N=
(%0l

XK

AYVNYE Ss 4 AYVOANVE

vi

ao

ONINYOW

YSAEWSAAON Y¥sdEOL50 YsEW3ld4as LSNONV

\

SS

~ 4 \LI
*SS Lh —=>

AYVNYess AYVANYE

: 5 Bs aseeaelen eee : : ; ' PY ase fi
aac : Fin Sand ng teenth ata alton eh com Helene ok thee arg ore em IE

wy

i w
: Hy Ca
am ¥ rd

MIMDe

wee
;
+
~
+

wy
'
| ;
: ” £
by Bs E
id NR fa E
\ Fe f
| ‘ | :
oe ee aR eT
peers Sit | et yi ee a

20

Not so dramatic a change occurs in the afternoon winds
between the summer and winter. The principle change is a
shift to the northwest of the dominant winds during the summer
accompanied by a slight increase in velocity. This is the
result of the northward displacement of the permanent east
Pacific high pressure area in the summer season and shifts
the prevailing winds more or less parallel to the coast.

Winds from the north and south are rare and insignificant
during all months. They are most noticeable in the winter
when they result from frontal activity.

Winds of velocities greater than 30 knots are uncommon.
When they do occur, they are winter frontal winds or north-
west afternoon breezes of late summer and early fall. In
more than ten years of observations by the Catalina Island
steamers, only 4 days had winds with velocities greater than
Force 5 on the Beaufort scale. In each case they were north-

west winds.
SEA AND SWELL

Sea and swell are generated by winds and the difterences
between the two are determined by the proximity of the areas
of generation to the region under consideration. An adequate
understanding of the origin of local sea and swell can only
be gained through knowledge of the meteorology involved.

The northwesterly air flow and the southwestern thermal
low are the most important meteorological factors effecting
the formation of local wind waves. They control to a large

extent the movement of fronts and storm systems and are mainly

svg ont? aick-wh ebniw tenga ira ot to teowdt oR ont of f

“grevktingbet oak oxay ove divos bag dtiom od? motd aBeee

r xtsken ats bits: waned ara arco ke he: atnost: te: tuonevow oft

ahniw qocanat te git ak BIN 900 agneds: ofF wanes B

ona wanna, shadowing, en? .totelw seiianeis ti:

eit

oat ei e2aT .vtiooter ue Seeoronk sigila-2# wd 1
teas faoianes ott Yo tremaostueih brewdt ton sat Ye!
‘Sttine tite doesee seme edt mi core oweesrq digit 2

‘«Reeos ods of felietaq neal so s1om 2intw! pobtewe

\
‘s.

xeiniw suit na sidgsaiton t2om ssa yodT edtaoat ttm
¥tivitos Letaoxt mor rived §

,otmogay ota efonxd Of nadt t29tge95 eeistsoter tone
-titzvon wo ebetlw Letnow? setoiw ets yet a309 190 db |
yt sits? vines bee remme tal Yo eoxssrd rooHne$®
bttgi#t antietsD sif yd anokfavzsedo to «1859 nod aad
nedt Asteow e¢ithoolsy Atiw ehatw best evah + ¢inov mt

“ifvon S14w Yor? sess dose al -,efeoe taoivsel off no"

Ijewe Gua Az

noones thh en? Dns ebatw yd betererss ois I lowe 7
eesin ott utinkxond ‘ott vd bentarseteab siz owt ‘dt
etaupeie mA MoOkthrhianes isha aoizes od? oF epee
yy Lite ang Lowi hee #2 Laset to higtio ont 3¢ gdb bust
-boviovek ygolotoutom alt Yo egbs twond, davordt, bomk
Lanne? oreteewdtvee oft, bas woll 1% tliat gods zon. eat ~
'gaktoe? ts erorsar fastze Loimssdem tie? soqak- eon hoon ee

ey2nl « of Loxtaos yoat .gevew teriw isoot to okt sm0) 3 be

Me

ae a

21

responsible for the intensity and orientation of the “trade
winds" in the area just off the California coast.

The arrival of swell from distant storms is entirely
independent of the local weather, so in the discussion of
wave generation areas, only storms in the north and south
Pacific Oceans which are of sufficient strength and properly
situated to send waves to Santa Monica Bay are considered

Ghigo) 7)’.
Wave Generation Areas

Southern Gulf of Alaska Cyclones

Most cyclones in the North raciiic Ocean originate in the
vicinity of Japan and then move northeastwardly along the
Aleutian Island chain, where many die out in the Aleution low
pressure area. Most, however, succeed in reaching the Guif
of Alaska and some reach the North American continent. The
area of strong winds in these cyclones is usually located
in their southwest sectors so that heavy swell is sent out
in a southeast direction toward the United States. This
swell is unable to penetrate into Santa Monica Bay due to
the configuration of the California coast. Probably about
two-thirds of this moderate to heavy swell approaches from
between 290° and 3300, Thus, Santa Monica Bay is ideally
Situated behind Point Arguello and Point Dume to be protected
from swell of this origin.

If one of these storms takes an unusually scuthern route,
swell from it will reach Point Dume. Even when this cccurs,

the swell will be greatly reduced in height by refractior

around the point before entering the bay.

bes wth Ye sobiatest2o ete cthanstné one sot»
janem sittrotitsd odd Ve tent oe ott an

aiieetiad ef emote tasteth mort Piewe, to ieviwrs |

Ye Mokeauweth oot ac oe ,x>idtasw Lege ods Xe

hod ine «tron off alt enrote vino \eeeta soitts?

‘wlasqorg bis Atonesia taotoktive to Sin doiite eansod
bsisbietios o12 yaa soiseM sinae of Zovew bogs ot?

= 4
esoi1hk noitatented svaw ate

eenoLloy ) migetlh to ws

site mt otanigkvo. teased sf iboes draon srt ok esaolore

any naotle ylosawtansortzan evom age bon saqal, toe

wot cotwersA oadt st tuo oth yore o7edw entad> ‘bealal a

Vu) envy omrbiioset ft besoaue rovevon ,.i20M .8#9298

ast theuvbinon weapkxramA mPOA sit Hoan ome one

betesot vilavay 8 esnotoyn seett oi ebniw arowmeae

tua tnae uk Liewa yvgedt fate of etoyooe Pes imoam

siatT .esista betta sat brawot qorroestbh tesedine

fi , '
ot seh vat otinoM atane offer Sfartsusd of 2f Gay.

teods videdort st2eod Simi tad sift to noitawaph te
no2t eeddsonqas Dlows vyvaod ot sis yebom aids

wPitaa ek yee adenolt aanse .2uT ,SOfE bes COPS

ber ourouy et oF vomeG toret Gos nen tnkoT bas dai oe

: 0 .f'ntso eked to i

yoruers misitios et Leeds oe ‘ever gexete seedd to emo tL

Tae wise eat fore covet ..pmUt aaa ale itkiw tf mort
ms
Qn Ay? at Ne staat in oapa ber ehtaoey od cae. Brew

iia >)

22

Figure 7. Frequency, height, and direction of swell,

San Pedro Channel.

,ifews to toliseskh Sas ythytor ,foneupesl . Vv Saag
‘ie
7. .

,kenwaddD cribs c%

JANUARY

SEPTEMBER

FEBRUARY

AUGUST

OCTOBER

NUMBERS IN CENTER OF ROSE ARE

PERCENTAGE OF NO SWELL

4) * ¢
we

AC) eet Ha <> tym Gefen (309 yee

‘
4 a

TeyauA Yuk SAUL VAM

ASGOTIO ° sazenaTaae,

Mh Se0h % RITHID @ caw
lise GA . soetwgne es

23

A storm may also originate when the Polar Front trails
southwestward and approaches the high pressure belt. If
this occurs, warm maritime tropical air may be brought in
contact with cold polar maritime air resulting in cyclogenesis,
usually located about one third the distance between the
Hawaiian and Aleutian Islands. If the contrast of the air
masses is severe enough, cyclones may be formed which move
eastwardly and eastnortheastwardly toward North America.

These secondary cyclones usually have strong westerly
winds behind their cold fronts and heavy to moderate swell
is sent on its way toward the southern California coast and
may succeed in reaching the area by way of the Santa Barbara
Channel. Swell with a 280° source and a 13 second period is
representative from such an origin, and the direction and
period is believed to be applicable also to those North
Pacific storms which assume a southern track.

Storm tracks are farther south in the winter than in the
summer, so there is a greater frequency of significant swell
from these storms in the winter. Even in June and July,
however, conditions may be such that this type of generation
area is important.

The secondary cyclones mentioned above frequently occur
in families so that as many as six similar storms may march
across the ocean, all following a Similar path. On such
occasions, swell continues to arrive uninterrupted, but with
fluctuations depending on the vagaries of each storm. At
other times the secondary lows are diffuse and contain compli-

cated frontal systems. With these conditions the winds are

Abiaue $Hhos |
a 22 fed oinee org ae cae eouisnone ae be

ak sipvord ad Wan. nie Esai gor! amet iean ernew 28

ae ceisenegoloye at geet iitten aks ouktitae gekog bios atin #
a. ;

ee | ad} meowhed: Sons: +2b sits brkdy, ono treads botasol J
B tis aft tuo tasasioo edt aE, -abaetel ceitwolA nde
Ay syvom dobaw boo? sd-yae asozoys ePavoss osevenelll

B a
; ,eokxamA dtsoW Drswot yOREEetEeSATaenteee hes ba.
ie yizevezew guorde ovat viisvad 2eagloyo YX ncoose) ons

i ikow2 sisxstom of yvaed Die etno1t blo» nk ott bat

ae bon Yasoo etpractiled asstidgoe sae Daaswot yaw ooh ea
1 “7 i {

; Sasdqed AgnSe SAT Yo Yow YO oan Ott gnidonss at bseee

= :
4¢ fBokied bnooee EL # bite goboOt MOBS & diiw Liewe’ tai

a bee xoitosath od} tw ,WegkIo As dove wor) svidetm
bale

tit tev sent oF Wels aidact Iggn of Hi pevetied ae

7 Yours mredtios se smreae soitw sanekee
De =e

(‘odti wk a6) xstniw ond me ituce eedtxg) cu5 2toe8t mzo#
Ltowe tapohtingie bo yoneepeit 2uFe9TH © ot 190d Cig

;
¥lel bask sacl, ob asve . 2aIahw sit «i va 2oFe pe
Hobtorates io ayya? aii} Peat Mage od yam angat Eh
| » taet va
sryon ¢linsupsa? eveds beagk san #gm0 Layo crebnogee! ad
ores Yam enyote selinke Behe es Yet oe spat on Be ‘,
tone. AO toe 44 LKB & grniveliot tia -annpe Matt
Atbw tod betquaxatabay overt 6+ xounkinwe Liiie <a
ah ,MI0t2 Goss 6 eskungev ony ne gel baoge 4

: -# bhgnoa zaigoy bie sauttkh opelewoll Yasbionsa all

sow, uJ

ste abatw ee } gReE ORO saad aa A vt taye had:
A ei i ° .

24

apt to range considerably in direction and be fairly weak.
Only light and moderate swell will accordingly be generated
and dispatched toward Santa Monica Bay.

Two to three storms a month of this type occur on the
average during the winter which dispatch significant swell
to Santa Monica, and one a 8 in the summer.

North Boundary of the Pacific High

Whenever the Pacific High becomes elongated and migrates
to the south, westerly winds blowing along its north flank
generate waves which can reach the bay from bearings between
about 225° and 280°. This situation is most likely to occur
in the winter. Usually the winds are not greater than Force
4 in strength, and although the fetches and durations may be
great, the resulting swell is moderate. Swell arriving from
these areas may be expected to have periods of about 10 to 12
seconds and heights not exceeding three or four feet.

Since this generation area, and others associated with it,
contribute swell from nearly westerly directions which is low
and of only moderate length, it is of no great importance to
the bay shore. In addition, its low frequency of occurrence
should further bear this out, for it is estimated that it
occurs only about once a month during the winter and somewhat
less often in the summer.

Hawaiian Lows

The Hawaiian Lows originate in the expanse of ocean two
or three hundred miles north of the Hawaiian Islands. Such
lows are apt to remain stagnant for several days or even a

week before moving slowly to the northeast. Winds within

One ae

hea eiand?: ah ‘Ube ‘poktownth ak aa

padarensy od Ytgntbsosae, PCy
| ) | Hak a oR Rem ‘ape ane
MY Ro mODo py eit to stem # amrote mo
pt dwe eet h anes fotece eh « Aakiew- tetutw anh, gadaw
‘anme otto owt at ene tite

bets: gh tio05 ‘ots

oy

seterxuin bus botsghola somos dytt aitios* arit mewis
veel? Aozon 2th anole griwole Saaiw yiierssw ate |
neswpad sqatread ment you oft dpaga man softy

WEL Sé¢om ef ackteavae aide .°08S

BFL

ood med? asteesa tor ova shame 442 vitaveal

aft vem etottaygb brs eotofe? Bia ffevody le birs AS Bm

:

mont anivixysr liewe .siarahom sit ilowe yoitisas®

tf ot OL duode to ebobsad Sv¥ad OF) AeFteoixs 5¢

tse) “wuod 26 asia? nenbesexs® For ards. ad, bine
ad ue

te dhiw bornicosen) etodto ky yaoun nokisieonoa sith ey he
wot at daidw anokroerkh yie rst mew XA sa80 ato [lowe “-
oF snaatrodms Pasig Op to 2k @h 3 anol ster19bom ath

ee test noe yy vyornepee? wat eth .moltibds al oe
tk Fad, betawktes 22 HE fol -sNO arett asad redta

tegwanes bas eerie odd pntaeh fitmon « sono tueds bain’

; | oh. ene
be ’ : A , : - i . ae ; AS
Cos Kwada te ‘Sees eas we gtanigiro swol) mebbawel set
Pare. .eioel et Geb! wilt Yo Atron es thm: gas
# Aote yO syed lave ved) fod Sanpete nknaen of,

ee gor eee stanadiaom, ait ot ANOtiS

25

these depressions may, at times, dispatch swell to the
California coast, where it arrives with periods of 12 to 15
seconds from the westsouthwest, and with moderate heights
(usually less than 8 feet). This type of storm occurs most
frequently and with the greatest strength in the spring,
although examples have been known throughout the year. The
approximate frequency must give an annual average of about
one storm a month, but with an irregular season distribution
and from year to year.

Swell from these Hawaiian Lows arrives in Santa Monica
Bay from between 225° and 280° with a period between 11 and
iS pegonde
Generation Areas in the Southern Hemisphere

Wave observations at the Scripps Institution of Oceano-
graphy indicate that swell often arrives from a bearing
between south and southsoutheast and has an exceptionally
low period of from 13 to 20 seconds. It is believed that
this swell comes from generation areas in extratropical
cyclones moving from west to east across the South Pacific
Ocean between Australia and Chile. The lack of synoptic
weather observations in that part of the world eliminates
verification of this possibility (Nicholson, Grant, Shepard,
and Crowell, 1946). However, the direction of wave travel
leads either to an assumption of this source, or to consider
it as having been generated by tropical storms. This last
possibility is eliminated for the longer swell since the
observed period at the California coast indicates a travel

distance from 3,000 to 4,900 miies. The duration, fetches,

af oF Bb
atdgted

+ pooh es

14 ae is 2

hitate: 16

“OTH ALK)

i ha ke
ss
‘ PERS Y

~~ :
ME ek) |

Set Bite

ay i
e OD RYSTIS

scene i

{ i ie 63

1 om en,

MObindLits i

a,
aad gw west S3VEteR Hagia Itswe tad? otesi bak

FEEIORY

ie Te Oe aaa ee ol roy eae + COE

Od LO) SOS cu RAINES: ie etna i

mE AR eh. tA ae

J ahem at

e
>

ry ebb kieG ddiw asvearih: 2

Stews hoe Atiw bax (tesull tepntaos| ooo
ewe Fe LO oper ela

(emit ne ddgdevte t2stae7g ite athe bay

yen? Feorawondg sense nose oy itl

woes . Daria ns bik a) Fenny onaupeat |

Y nOwRee Te Les: Pe criw ted , dino) a

iA
ie
LF
‘
-s
~~
ol
b

ture Lt sevice 2wolaetiewah. seanty moaY) 4

wie Igk13¢ 6 aekRy 908s ies MESS

sosto2 kwh sy edtleo! Bid ak eaugh

nalgurrvedt s Vinee Sil) TH 2nuttaviasedan

1X8 @£6 240 Die bes sit? PORN ay 2
; ala 2! ‘
olod 28 91 .ehnense 0S of fF mor} toc

WGPIS AGLIRIIG | mer? 290d
aie sirae ny Sanna di ake OF venw mired nak vod
a aT rae hae pilasd aA te
fio binow edt Tol dtaq ted? ot enokpayay

‘ ee baa RP Sy 44 1

Met ae Meee eee)
ines, ynoatowotny yar bic heey. 2 bls ae

7

» RACLOMRS: baskgont) ye

Meda » bier?

cine gang th asta:

26

and wind velocities in tropical storms are not great enough
to develop such long periods.

The summer maximum in the frequency of occurrence of
this swell is quite reasonable, for the northern hemisphere
summer corresponds to the southern winter when the storms
there should be more intense and follow tracks farther to the
north. It would accordingly be expected that if this were
the source for these waves, the swell would be of greater
significance in the northern summer.

This swell probably arrives about two-thirds of the time,
but because it is usually low it is inconspicuous owing to
the existence at the same time of local wind waves or more
prominent swell from other generation areas. The presence
of this type of swell in the summer is particularly evident,
since during that season the contributions from other types is
at a minimum. The sea breeze, on the other hand, has a greater
frequency of occurrence and tends to have greater velocities
in summer than in winter. Thus, the wind waves caused by it
would tend to obscure the southern swell more often.

The Palos Verdes Hills lie in the path of the direction
of approach of southern hemisphere swell and only occasionally
is the swell of importance, even along the Malibu shore. Its
arrival along the Redondo-Santa Monica shoreline is negligible
and likely non-existent.

Tropical Hurricanes

In the summer and fall, tropical storms are apt to origi-

nate in the oceanic area off the coast of Costa Rica. Nine-

tenths of these storms travel northwest from their place of

a) Pesan n ays to. Poegrpes? oath: bik bic ommce

eranigeiawd sy ots tos ont 307 Ldaroesay othup ak
angers 2et eet rstnoe STATOR oss at ebnomeat
sy at Soatrsat etsert wolhet Pour seaotae axon odd :
egew ehilt NM dens
saresae to ad biswow, (Lowe ouit veorvaw sar meh

- tonne front inn ody mz 39

pemit od? to abridv~owt Teods gevizse vidsdo1d oa
of ghiwo arcwolqenao smi sk a wok vitswsy 22 tf -

; {
acon 4o a@evew botw Ceook v sunt? smna oft ts 22
“eangeesq aif vesete cobbesegeg aero a2 {iowa
aftwebkys viaaigortzaq &L Tome ont ai fiewe to oat?
ak sat} soto pert anobtadiantaeo otf godess Jett Eo ‘
$oteory & aa -bsed sete Ont Ae osnend soe ofT oie
2aitiogiey sedeoty ovat of meas ‘bees gone 21990 te
+i vo beawas eovew briw ont, ,eue?. .eetaiw at asit 3
dette stom ERtewe axemieee sft etuo2do ot ‘
noktowakh att. te dfsq 36s HE ak: 2i Li. eabre¥ aed
vitsnoteeosd vino hoe (tows saatgetaed ert SATE s

iia ..

ott, svone wok tal ot giote masve , eons tiogmk Ae how 9

‘ ait
SESE Ri igo es onk Leworte 89 Eels ainsZ-obnobes ot (quote 2

- aot kext tn hi

CHENG GT VIR SILO BOHTOPS teploods, (ites bie emi ents Pru

net

Sy! oS wAE WRAD he chews salt We, La ‘abaasber wear” ta

‘Ao “ope tee, xh aut} wean? feswad zon

27

origin, but have dissipated long before reaching southern
California. Nevertheless, some send swell toward the coast
with a period of 9 to 11 seconds. This swell differs from
the southern hemisphere swell in having a shorter period.

Data available indicate that the frequency of occurrence
of these storms is quite low. Six cyclones annually was the
average for 30 years determined by Nicholson, et al. (1946)
with an extreme of 14 for a single year. September is the
month when most of these occur. By the time the storms reach
the latitude of southern California they usually have utilized
a great deal of their initial energy and the surface winds are
not of the high velocities often associated with hurricanes.

Although data were incomplete, Nicholson, et al. hazarded
the following comments concerning this source of swell: “Over
a period of forty years only one typhoon, that of September
1939, entered southern California waters with high wind
velocities and caused significant damage due to wind waves.
Waves from a similar storm, if and when one arrives again,
will undoubtedly be the most severe affecting the area.
Unfortunately, the height of the typhoon waves, the direction
of their approach to the beach, and the strength and direction
of the longshore currents under such conditions cannot be
estimated."

Without additional data the estimate of one occurrence
every four or five years cannot be modified, but the possibility
should be entertained of a frequency as high as once a season.
There is no indication that these waves always arrive with

destructive heights. On the contrary, they will often be low.

povaloute ar pidoaey arate got

tendo wii? banat tewa: ‘bos, sno. .2aetsds Tate,

goth erethib Frege ike sebanoss Le are we wre
i

{Bokweq satsodens satel a Liewe eredqakmed mye

\ ee

asthe eihOSO Yo ‘Yorsoped bh pitt) ete Siar iss oid aL eye &
int

silt pow Vi Leese, neo Sov aeee eet oiep et sonore ph

(eee) .fn do woatotoey ye benkmiete® oxay ot a9 3
ine ‘

aly 4k xodmetise | ease SPARES B TOD Bs
osoy aniote oft sankey “ad ye | awene Geers 10 Yeom am

bexifits aved vliadesp, ysar sértotiLed axentuce jar

ave airhiw sosteee sid (bee yaqpoge S427 arek aisds to

Seesokainet ditw baetecomess tettea eoriboolsy ai

to: ~poalomonl “;sEelQMoone grew steb iia

>

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yodtisice2 to Tet .woadgy? Sap BIRO execv vr1¢ Daag

;, a

: fr ve t
dbtiw Asta Hskw Beetiw BEMZOPEERO avoir oe oe 191m

.mevex baiwoot evb siemaeb Peek Tipgte fowrso Gnas
i

» AE ate sovidtea. sow aot tie BE cotote tralian ge) ¢

pave 28% pottoo tts ereyee: Fane wee oc vlLiwrd

rots der hi oe) . 4508 qoonayy Bi To Paplart ety

HOdto eveD bee Pigeon? s Hy) So esa oa? oF ee
: Wiki

od) Ponies eke LP hey thee Vater By Here sncckagne ge,

mi '

hb

rei ‘ heoidtabh sauna

Ra Oe! “Pee ae peek hee ed fj

‘poze A: 8O00 26 OHFS) en (atioupon? 6 ie aax308 | cs nat
i

7; i Gee er see. Rew B Gide ny ae gag), souttt! ookveslabaie on ee wet

Wn was ne

Laie, re, aid 0 bbe nag streamed fi

28
Cold Front Passages

Two primary and three secondary meteorological patterns
result in bringing onshore wind waves to Santa Monica Bay.
These waves, characterized by their choppiness and short period,
are always accompanied by strong winds, and since they are
generated within the general area, the sheltering influence of
the points, headlands, and islands is not so well marked.
Because the height and period of the wind waves is a function
of the wind fetch as well as the wind velocity and duration,

a variation in size and period of the wind waves with the wind
direction is to be expected.

Whenever the Pacific High has weakened or moved far enough
south, and northwesterly flow prevails over the eastern margin
of the Pacific Ocean, cold fronts originating in the Southern
Guif of Alaska may move to southern California. During the
winter season this may occur several times a month bringing
rain and moderate winds, in the main, first from the west and
then the northwest. At times, before the frontal crossing,
southwest winds may blow for a short period, generally less
than a day, causing a flat sea.

As the fronts approach California, the winds and fronts
move in about the same direction with the latter often
traveling at approximately the same speed as the group velocity
of the waves. Only rarely do the winds and waves follow a
bearing of less than 270°, This means that fairly high wind
waves of moderate period will enter Santa Monica Bay. Since
most of the wind waves will be traveling in a southeasterly
direction, they will be greatly modified along the Malibu

shore.

ne soxdt baa YoeMhag:

eae tat Laokyolor

7 U4

A ; ie y z i Fi Mei , ved

ene 2 Eavgtd aide “ot Borrem Boe saoet seat Sat RERE

. ef
Medcted) raede ters easniaagha #

Gin Yooh ainee bee ye bak

red besrotounady. gt

ing
y) mn

gitow 4a trey ks :qnoohe

te sore th wir tet. oae. sit an 2A Basen ay ote aha

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ee hae! %, TTI ea ie ROMER ae BOL SSE ok Cate don: ar ebas tab HAS .chea! on ft ota

»-

Le eee Se OF svatw Dobe ott Sas dean lars rdqzed of

otic Loe vrboa tow Gietw ay ap Irew eo dated be

&
=
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3
a
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ry co
sBeTvoyks 2 of. SE wae

Hgwons 3133 bevom vo banedaow Sah tek se Vioet odd 76¥ER

GQ asin oxetess ect tevo altey ean wal? vireteowdt10n |
Heoniwec wth AL Want od yhoo 54a Gioe ymaooO
saF Hen 0 Jserotiied qiedives ah ovor yor

ues wer o STA. 4 es te p> teas rye S720 ran eRe:
‘pits ee ow oft matt tetk) oeebad ane ‘ne eooary &
rk a hinw > tetnenrd ont 9 rind Veumke 1) ie aw tt rom:
as y yiilnseoned’ , batted 2 rast x boda wold vad alucukw ;

rere Ls, hae ji lemad te

denoch bem etw kot See. obi seit fhe Heactqus a tne? odt
aaa 4eneest ois ddiw ery. oeahh sane eng tyote.
: Rit

nino sew woth itt hat evan loere hath ’ 190 amine nae te

we walle?) Ze ante Ranta shihw ott ob 9ieiet y Let sesven

Rea hve 089 OT oe \ Sant, ish me ae ON ae wae Yo a xe

eons otal ea hae nite VAs LL ay poknon, atereton: to

Gaetesnttion 6 at 3

29

During the months of December, January, February, and
March, two to four cold front passages can be expected each
month, but it is estimated that only one of these is apt to
bring moderate onshore winds. In midsummer, owing to the
protective influence of the Pacific High, only the strongest
of these cold fronts reaches southern California, and then
with much reduced activity.

Coastal Lows

Depressions may originate off the coast of California
and then move northwestwardly to the continent under certain
meteorological conditions. These storms may contribute swell
when the low remains for a few days southwest of Los Angeles
before moving northwest or moves to the mainland without
crossing the bay. In either case the period will be moderate
or low, probably between 8 and 10 seconds. Coastal lows may
move across the area shortly after developing and before sweil
from the storm has had a chance to arrive. Under these con-
ditions wind waves are generated, but not always in an onshore
direction.

Thermal Lows

During the warmer months of the year an extensive interior
“heat low™ is situated over the arid regions of the southwestern
United States. On occasions this low expands northwestward,
especially if the high pressure belt moves northward, causing
southern California to come under the influence of the easterlies
and bringing westerly winds to Santa Monica Bay. Usually these
winds are weak and can be ignored in their influence on the

waves, except as they reinforce the sea breeze.

; eur teatwine: ath) boa vows ayit besbeeis anys oF niagOHd 199

fee yeamnadet Smal aeausost be eattaga als

rhodes ‘betasqx} oxf mo poasneed rnoxd Blog aig? of ont “

ao tes ‘eh seomy to: ‘So eine! bout betamts 29 ak. ‘gh
Sar ae yabwo “, xprietnm ir at .,ebalw srodene: ote
sgnonte. ant TLIO See okt: oo %o conse Dims, wit

wal ial

ed ie eine tk ha aetethoos geda~s 2tnort me

er

sv?ivetos bao baz

isl

ghurolilad to faeand at? 2706 sterigizo vam erokeaen
hiarre> rata fientkéaos off of Yldpawtesy ds 20n vet

iiewe atedisdnos vam amiote eeehf .teoitibaos fag |
&

2o(o8eA tay lo t2ewilnoe eveb wal 6 z0O!1 “nrames wot
te Lend

tuonréiw Seaketew of? of e89ou to Peéewls z0R qautve

a

rl ° P . : mer.
srereban ad ifiw bobisedt gid seen weutrs vi je odd
jt . ve
vam ewol Leteno -tbnoog2 Of bas 8 foowted + (dadomgm
tiew2s sie ted ben gaiacaleveb seeta. ¥it10 avrs
“non “2ed7 yeh eyiiwe oF sounio 4 het cost

pidvieta- din @) evawlio. Ton tod ,lieteionog 215 3%

sotuotes: ovbanstno na wee MEP Te edinvom sonra sil?
ast
Wiis lt -

nesreswitnor (adr te reer besa St xr9VO batsuthe ak wots
. exw s awh core abmayne woh Abt? evrokesooo os) vasmat?
Qet peas .. baewasTom eam, Shs, sanzasrd deta aly, u yin

he awe os kntld) MRS ph eto yisereom snisbad

i
ayant rail aae

CR sti: erent head | eee ab animist co aps tase ‘eine: “on

30

The prevailing northwesterly flow over the coast of
California is often strengthened by the coincident existence
of the thermal low and a strong lobe of the Pacific High
extending eastward, resulting in a steep pressure gradient.
Such a condition is quite conservative, and once established,
is apt to prevail with little modification for days, especi-
ally in September. Whenever this situation develops,offshore
winds blow.

Santanna Winds

Several times each winter a thick lens of continental
polar air moves southwestward toward southern California from
the interior of the continent. Strong isallobaric winds blow
from the northeast coming through the passes from the desert
when the air mass is dammed behind the mountains, But since
these winds, although at times strong, blow from the northeast,
they have little generative effect upon the waves in Santa
Monica Bay.

Hand and Sea Breeze Regime

‘Unequal heating of the earth's surface over land and

over the sea causes the development of the land and sea breeze
regime, which in southern California is especially well developed
in the summer months. At the coast, when these conditions exist,
a southwesterly wind prevails during the afternoon (the sea
breeze) and a northeasterly one during the early morning (the
land breeze) (Fig. 8). The sea breeze is stronger and more
persistent than the land breeze. It starts some miles at sea,
reaches shore about 0900 local time, and obtains its maximum

extension of approximately 70 miles inland at about 1300.

sonst axe lebeaite®
“gee othe? ont Ya dol, BAO ta % bk vol i

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fataont hos

/ Pe fi 7 J 7 W
ayy \ Mosk shoevothted asedtvoe biawot Hoewieewitwoe eovoms
aul wold aterty siaetolias: gpnesata. .Pienttinos 24% to rok
( figesh aa cont eeeecq ond Agaords gatmos rensitiowl

one tit .eatetoben af? Babtied homepb ct seem abe

t

Jamedtron ond ox) Wold ogitorme weinkt 14 Aquonray
eine nk eevsw oni soqr f00PTe ovitexonsy oDISRE

tat yj

es a gmbaoi osesnd 292 am
F ‘ ‘ Al ’

‘bia bast xevo saelauee *adsas edt to yadtaon taupe

" 7 7 } , ; is ain : Hi
aeognd gee bap baal sot to Mranigqelsye> sit sous weg

RSP as en wil
beqnisiah Dhow witeisaqes ef siaweodile) mrsdtwoe me) etal

teixe siatthibean evett aodw gtesos ent +4 -edvaom minum |
‘ait . obs edt) nodeaeny eat gibieb =tisvsiq ineekiw', ybro row

One) her won CESS ee eenrere ae vino reasata & “eee a

vammomas ae anne asad Bae vit

‘cul he ao Dm ona etrare on oem

31

Figure 8. Monthly sea conditons in San Pedro Channel.

wlenhet e1abel, ast ob asorgenos

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vas LHOI

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(NOONYSL IV)
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se ued apineer venenatis eens cide at et Re A Tag avehse recon ia eirmmamnefiams ee te

32

Experience indicates that waves generated by sea breezes
nave breaking heights averaging about 2 feet and periods of
about 5 seconds. They should reach their maximum development
at about 1500 or 1600 hours. Aithough some information can
be obtained on the fetches, durations, and velocities of sea
breeze situations, it is difficult and probably unwise to
interpret these data. In theory winds have to obtain an
average velocity of about 10 knots before they are able to
exert sufficient tractive force on the water surface to start
the growth of waves. Sea breezes, from observation, generally

have a velocity of about this order of magnitude.
WATER TEMPERATURE
Methods

Temperature data have been collected using two methods.
The first is surveys of the area accomplished by traversing
a network of stations at cruising speeds making bathythermo-
graph casts at short intervals along each traverse line. In
this way it is possible to obtain water temperatures to a
depth of 200 feet throughout the bay in six or seven hours.

The second method consisted of occupying a grid of hydro-
graphic stations and obtaining salinities as well as tempera-
tures at various depths in the water column using reversing
thermometers and Nansen bottles, or at the surface by bucket
samples.

The bathythermograph grid is best adapted to a detailed
study of temperature conditions. Hydrographic stations are

required to obtain data on the various water masses and types.

ee te dokdtnonate

‘bas agaom acaaay

ae aekhwaw tek sedoxd bela ‘Fipahiti ee Fh»
|e ekadda ot ornid : 3 baw upped mt a atah ow ot
‘et tds i pet t bia lad) whomtlOr ty od» to cha
“date. Of son tame LoTuW 3d no ‘Spnet avitoess ino fokM
by, ehieasats vita Eta seit not) «auisead aac s3ovew to |

.obutivgam ins xetae Edt Heods to ‘yt tookai
SAITARAS MET. AST AW <

shoghan

cabortt 4 im aw Saba batan tee Heed sve ata! outa
yntke eLtavreazt {d Bedad find 23m sna SES ry ay OvUB ak §
my i cee an ae at ahha oreo erie 7A HotList te,
2 ee xeyervely t thas ‘geoky etayieste | Poonte ra a

aor Heay | nape net nahin ob at OF Sidkezag uk 4

Bu ean wsvae 9 aie ma vad Sat Sueiignc ult tsa OOm

a,

rots to hh aa) 8 sedyayoos 0, bets fenos ere ‘boos -

)
i)

“wxqnes be fou bavot esi tadiee Binks rcp Dey en's

piash- aged age sie ‘on rh aa ‘seatdsor nie air na, esta

oie dod bo 0

Aug

33

Both methods are necessary parts of a complete survey.
Additional data were available from surf temperature

reports of the Los Angeles County Life Guard Station at Venice,

and from similar records of the U. S. Coast and Geodetic Survey

at Santa Monica Harbor. For adjacent offshore areas, tempera-

tures and salinities at various depths have been taken by the

Scripps Institution of Oceanography, but their stations in most

cases were located outside the area of the present investigation.

The staff of the Los Angeles City Bureau of Sanitation also

has collected data in the bay which are tabulated in the reports

of that organization.
Thermoclines and Gradients

For the purposes of this report, thermoclines and gradients
have been separated on the basis of their characteristic
appearance in bathythermograms. In general, if a temperature
curve changes abruptly in slope below a nearly isothermal sur-
face layer, thus forming a sharp discontinuity or boundary, and
the difference in temperature is relatively large, it has been
termed a thermocline. A smooth or even an intermittent change,
but without a marked break at any depth has been termed a
thermal gradient. While this is a rough, qualitative distinction,
it is adequate for the purpose at hand.

Thermoclines and gradients were best developed when the
surface waters were warmed in the spring and summer, They were
least prominent during the late fall and winter months when

surface temperatures were reduced.

cased ots a

‘oman Pages any tei}

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‘Ca tee B ik toe Sa ARAM okey seat achat

eb AS ety Bors B wanije V0) ‘toads be 404 oy ROU wa an
a ae el OE ae vad Rntyen)| suo Peay te. esk:
hi i ‘ a r ‘ : &

TE Bary Wt eae cr. ett hee Perel posed 1 A023 ORSEE
MPRA RA RET Set Thea AA Tee Se WE whi ‘ote ook aa
qeie pectatomhe To aoe PPR Beieed ook we

ApH ayo, Bt At botalodat sia HOLAwW eed att wi rte

Dupe ier me age Pee 47

‘ f : 7 ee Bs py tha ay 1D. &@ 4208 «He | '
=“ ‘ : siti! ye
j ie

Shite “Tuy Te ats ie Be ao ail) Ae: ieta SY AG 08 ae

‘a SOE TA SOGMS! a AE La BeRT R eR oMeTa ete eee
an We Lengettoe! vigeaak weted Sania at Vitqexda: :

Ss VT IRIO 2). wt Lunt emoeert 2S. 9 welirw) alt -

iy eso 4), fiir eee gb Pavel re Py Dax a2 STAD Oey»: a ie

Pike oP URS Beer lneiol on wee ee ‘neste 2A 6j end fon vent

s Bonita ay ra } ery hy \ime tp Rawr on tam a

me ay
EOE 4 MRM ERO SV EI CFL LEI sche my Ad ‘Ah ae ghee 4088 ba

i
;

can 2s Seeguing at to? spanpite!

ES ROB Geert Le Veh Sater? | stay adi wk fe 2 ci ‘sondtoqntent
ivi: RB ia TE any) e 3
ah vite iri brady 8? mia then sy Re autre fy ce 4 a (1a yee ¥e) a

the eatoist: ted be ber

34

Inversions were characteristically present in thermograms
from the outfall areas. Evidently the turbulent nature of the
boil is the primary cause of these thermal variations. As the
warm effluent leaves the pipe it mixes with bottom water and
moves toward the surface as a more or less fractured mass.

A bathythermograph lowered into the area of an outfall will
thus intercept alternate zones of poorly mixed, unstable water.
Typical inversions at the Hyperion outfall were present on
July 20, 1956. Figure 9 shows the vertical temperature pro-
file along a line extending from the boil to a distance of

6 miles from shore. Figure 10 is a detailed representation

of the area near the boil. The defiection of the 54° to 61°F
isotherms reflects the entrapment of cold bottom water by the
rising boil and its subsequent rise toward the surface.

Inversions were encountered frequently in the southern
reaches of the bay and in the offshore portions of the north
and north-central areas. Here the inversions appeared to be
due to a horizontal overlapping of different water types.
These warmer bodies of water must have had a sufficiently
high salinity to make them stable under such circumstances.

In ail cases the inversions were of small magnitude and the
level at which they occurred was well above the major boundary
between the warm surface layer and the colder subsurface water.

A peculiar inversion was encountered in only two or three
instances near the bottom of the central bay shelf. There is
no obvious explanation for such a warm layer in that area and
at that depth. In any event, it is not of major significance

in the thermal structure of the bay.

Remy ER eb Re eon ROE ee ee on a ee
Bet a

fates, Sic

t ; { :
Pa a Re a a ge a ey ee to } Ge £4 dLife augkvde

ntti

CW A PE oth hey | eet SOVigwd For

2D) 00 (270M #, 2h! Hor toye gag"

Mee RS Ode Da pgne) thet roe oe
id if pe

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. ea ih)

uy fepredg!)) sit jo wavtere werk .
_.)

6 SOY BE hoe vod pas
= 36)! a 24, ‘aytracelti

1 } ecme Deve ri SAS sag,
f a)
mn ati a ciao eee in,
j “5 Bo.
nu etches ite oan of webaae
it 4 9 eae AL PU? Sethu: a ee

* “i EAM oO | vay aa) ti te £
an, Tey wt Sac ae wa we “eit as ‘

a ee

poet) Bacay Aib3 ) fin haaael oa ea andag

ie ¥

ot) me yee hoagie eT,

lo ae ea oak: .

ACU fre [on Coe ae

35

Figure 9, Vertical water temperature profile in Santa
Monica Bay extending seaward from Hyperion

bord) July 20.) 1955.6

| q
SS6I AINE O2
(4 ul 2 anyesadua )
ATHAHS VOINOW VINVS

ATHOUd AANOLV AAI NOL

zal ws L
a 8
WOES) IODINE SIG)

Pee a ee! amr oY reves ey

aw

oy

4
&,
a
|

we

ee a

Siiiond FATTAAAG
WIiSHS ADIMOM fir AS
Bee a 2 +

(7 al siisraamel }

eee; YluL os

36

Figure 10. Detailed water temperature profile, July 20,
O56

YaAVT NOISYSANI Ee
cS.

S$S6] AINE Od

GWHOdd FTHOLV wad NAL
aw t1vLad

SS

fe)
@

@

0)
mM
“y
=|
it

SS) aN
+

(oe)
N

te L :
Soe N Nl SSO eS NOs Ss A2DN va2S/:a

rwaee

HAL E?O

Na
f
7
lf

37

The possible role of the thermocline as a density barrier
to the rise of effluent-sea water mixtures is discussed in the
section on dilution. It would appear from field observations
of bacteria, nutrients, and turbidity in the neighborhood of
outfalls that the main importance of these thermal and density
boundaries lies in their effect on the position of turbid
layers following the initial rise of the effluent discharge
toward the surface. Figure 11 shows the limiting ranges of
water temperature in 200 feet of shelf water at which sup-=

pression of the rising effluent may occur.
Classification of Water Masses and Types

It is convenient, when dealing with ocean water, to plot
temperature against salinity, the resulting curve being called
a T-S curve. A water mass is a body of water having certain
temperature and salinity relationships and is defined by a
T-S curve. The whole body of water lying over the Santa Monica
Bay shelf is an example of such a water mass. A water type, on
the other hand, is defined by a single temperature and a single
Salinity value. Within a restricted area the horizontal distri-
bution of water types can be represented by surfaces containing
all points in a water mass having these singular characteristics.
In the special case of the Santa Monica shelf where the sali-
nities are nearly uniform, such surfaces will approximately
correspond to isothermal surfaces. Ordinarily, water mass and
water type analyses are not made for waters near the surface
or in shallow areas. However, in this case they have proved

useful. In previous reports the two basic terms sometimes

iu wid pation ary vit

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pie i Ii va biel Wile

a anc! blew SE ened 9012 Ie

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y | x r ah re ey: : eemurestt mat i ee Ong m, nk 1) dt fade

7 a | SE 1 Be EBay as fo Pye Ts atau? ne “edt : - -
’ SRIMAOS i) dpe ita: «ity te wei Dees tet iy vero

., ane BO, Sn * a* t et biiaate | ii a wert 4 7a ont
ei : 7

Ai , 4 ee Le i7 ray Te Set ow iors ¥o rs isthe m sore aT

{malo Yee eRe Ys uehies-+. sc? oa

ye
& q byt Eye ! ‘ ia "O arate i t
7
T > 4 == :
Hino T57rw hi yy Oi J as) pw chy Toh —

nhs? 259 Ga) vat ce? bi vba 2 ‘ ,

me ||| BODNGM abn sat) reve yety tee de Whed olocy oft

: ‘ vty " te 8 A ; Ese A rt Dale Dal a («a a WE d ef ev AOR F, ’
; ;
Ry. DSR og Obes a tee bw sini? (ewe @ 0M Keats be ; hare ae
: erereti, Ly tee ee oid hee a lida aot piesa 2M wutew a

peo Ry & Pea Ee a eae eer’ Be wae if * 1h a in: ale. 2900 be
“ay fa Rk Sealy Sie TH a i & ve aft 9 6 r am aah iaW @ al ay |
a oat Mle A conse 09. Yo See Sa

a (Caton io wie. thew dtl ane vow w \ yea bored Qumaanees cre Pr

ray ives

mid Ea bath ital hy¥ * So LSA a) a LP tad & beara oie at ba eye

fe aa OR Ta eet (4 jee “pte ee Hod) phan (ie ome ‘ey Di says
Pelkey F re

Pa Vp aD) iy tay Ag

i it pee
be ie te) Ai

38

Figure 11, Maximum and minimum water temperatures at
200 feet, and maximum temperature differences
between surface and 200 feet, Santa Monica

Bay, 1955-56.

slo IN) > Eleiinti\/tsl Sle} e)AL

Ma)

HIGHE ST
TEMPERATURE AT 2009

x
fo}
fo)
N
=
<
WJ
a
=)
fs
<
a
uJ
a
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FE

Oo wn) v9)
at ae

sly IN] alON ers elelsil@ Eleliqdb\/ te] SlelAyelae

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=,
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39

have been used interchangeably. For this reason and also to
avoid confusion with the terms used in dealing with the open
ocean, the term water unit is introduced, better to describe
the detailed classification of the water in Santa Monica Bay.
Where further subdivision is necessary, the term sub-unit
will be used (Table I).

The principal body of water which overlies the Santa Monica
shelf has been named the Shelf Water Mass. Its characteristics
are an essentially uniform salinity of about 33.5 o/oo and
temperatures ranging from 48° to 73°F, depending on season and
depth. Its character and T-S relationships are shown in Figure
12, which is a cumulative temperature-salinity diagram for the
waters of Santa Monica Bay.

Below the Shelf Water Mass lies a layer of somewhat
different characteristics, here named the Slope Water Mass.
This water ranges in temperature from 46° to 50°F, and in
salinity from 33.6 o/oo to 34.3 o/oo.

The deepest water present in the vicinity is here termed
the Basin Water Mass. It exhibits an essentially uniform
Salinity below the depth of the sill of the Santa Monica Basin.
This water mass is characterized by an average temperature of
43°F and salinity of 34.3 o/oo.

Within the Shelf Water Mass are two distinct water units,
separated primarily by temperature discontinuities or thermo-
clines. The Surface Water Unit includes the layer in which
the greatest seasonal temperature changes occur. It lies
above the thermocline amd above such gradients in salinity

as do exist in the shelf water. The more uniform lower portion

Mm Poe et ig sito dee oe
PEA TW) realy

Shon es, SRA, NR RR te. ae ie fit, bgaty C617 5
Se raneteah wh yori <boaues at © we

' q ie " Nils ie ip
et) pe ogee Gta: wes tedele ‘ald he GE Re

ie, . Phair ine yok Se ae saliaeita oes or

Cheb whee’ tit hes ae OE cet le vied Dak one xt)

i) J see MU

Caner: HPO os BTS rl. Deh) ete. Thee id Soman 1 nae *
his Ph

be ais aC.) OF @ingiet to v¥inkinea stim ¥ii ii nega

ay i * 4 iW t \ "y J
\ ih ieee: Wer | D meer pet? Pi om a My ROR LOE ity eee

e Rerbrtas v E. Swi ‘ wes byt Ye Pa on tee 232 on tert

ae 3 cout i Vea Re ke Pan <a Ge Wg ‘re wit pale iW
. ieee Ge Ey ayers aed 26 WEE ani ag ibd
ake. TRU CONE!) GER GES ae att OTS VT yon : of

EG Rh Abe ime heoe dove, ave Tete ay 1 oma ait

Classification

Water Mass

Water

40

TABLE I

Classification System

Example

Shelf Water Mass

Water Unit Shelf Surface Water
| Shelf Subsurface Water
Water Subunits Sewage Field
Water Type Isothermal Temperature

Surface

i i
opener rata p

amar Cope py a Nhe ridh 14 mpl sy gc mi aa He ery
(niet em Smpne ropem 4 pee e P

De agiaee bt

ire | ¥

ata NB ey SR EL, Ge TR Te

} éeeh- satew |

ee aim tees ay

‘ese enetavednée Vod

ea Ee i Ee

i ete ase tae Wad

Siylnasgmel enisitor

deve ee

‘Ws

41

Figure 12, Temperature-salinity relationships in Santa

Monica Bay, 1955-56.

Mia i

Veil

oa = a - = = = T°)
ae Feownws © AN =A SBOE

"DI. 3uNLVYSdDWNI3L

i
| J the Me ; Xa! Wea
oe over cents tomes swipes eph rapid roy dol cero pemanetiiiehiy

a

eS a Ra SU 5 oe % ar ae
‘7 i my ce
me =o 4 i“

Boe ae ae ee ee

EW ot WERE ake

uiroiningyiere i Fe sow tegrirverrstni neem nape ire a SANE tp a dae ae aan
nu ° ‘ 1 “

42

of the Shelf Water Mass comprises the Subsurface Water Unit.
It is considered to be characteristic of the Shelf Water Mass
proper, and its upper boundary lies at the thermocline. At
this level more or less well-defined temperature discontinu-
ities are present throughout the year. Although they vary
greatly in the magnitude of the temperature change, there is
usually no difficulty in defining the boundary between the
Surface and Subsurface Water Units.

Within the Surface Water Unit, a Sewage Field Sub-unit
has been defined, characterized by high temperatures and low

salinities.
Annual Ranges in Temperature

The limits of the temperature range within the bay for
increments of ten feet of depth are shown in Figure 13. This
represents the yearly range at each of these depths over the
entire bay. It should be noted that in particular areas of
the bay the ranges are much smaller; for example, the tempera-
tures at particular localities, or at depths of 100 feet or
more, probably change less than 3°F,

The Surface Water Unit is the one of greatest tempera-
ture change because of seasonal variations in solar heating,
evaporation, and other factors (Fig. 14). During the summer
and early fail the inshore surface water may reach tempera-
tures of 72°F, In the winter the same area may have a surface
temperature of 58°F. In the central shelf area, summer tem-
peratures may approach 67°F and winter temperatures, 56°F.

For the bay as a whole, surface temperatures may range over

-oak ionieveth ie lay eel. unditagred a See ute bem
weiner h Pilgeite 8s ‘gerne danoe noqanst iit Sty | haw Sead. 20 sim ave
ven yor? rier sald al io, eat-twotiro wate tyoea ty

Od MST pyc weels ret eg ay a4? 26 stort ieee oe ee

Mt woowied ysabeiige aes Bakwh tals ot ¢itook 32beme

RR) were one Pwiedue beraysg

tiie O27 “paw ff CRE etch ene tre 7

\ = ee
Wol Dan ate epoine? (wh wd Gegedatas solic bon tae

‘et epeeney ai APR Lenina

Mit Yee edd mot tw Sonat o9GPaegest sir Ve at foal
wet} Weg Murr tf owesth oom, gh ko 7} set Ig >
wt 4a ettdel) Geet 1) Mae PS egkas vireo sy SMe ada
>» ¢2aae waloneprad nh 4adt tater 40 hiivoce Ff td _

oe ZHI WS ony ,>liimews ga? e2eiieee yore ots sonaeet AY
mony cn to nett 1% 20 peGL2 ther din’ © ti

OE Bats seel nyiete cisedas q

“SS Fe? CASTE Jf Cae Bat es Pov aedaw orate

(oa vS"ivoodk tetom oh enobtataaw LAmenee t+ onvapad |

Tid haieR, «Sa ee +m, woe? StOldss teutho! bn yak ae 3
PS: A np Nae ele a aie Pee oa sean aly Stat wim

HS
Oe ee My a ania! aia itd dank bw aie ay a gt a

ae ie eT Me teorike PADS. hat ites atte we <APek %0 eat fe: ah

ane 3, fal

iiss Peak aho cies edie

fi aks gp shartaxogiae
ree

YY AY

43

Figure 13, Limits of water temperature range for 10-foot

intervals of depth, Santa Monica Bay, 1955-56.

aA ae

VWEMPRERVSIURT TIN) oF

60

KE
LJ
uJ
Le
Z

OI Wal

JUNE 1955-JUNE 1956
MAXIMUM TEMPERATURE SPREADS
FROM BATHY THERMOGRAMS
FOR SANTA MONICA BAY
NOT REPRESENTATIVE OF
INDIVIDUAL STATIONS

is TN iain hones we ea) 1s OR aes RRR ees Se
mM. ;

pate emer eh ser Ne ERP AZE EE UR ON ee AD
‘tae

\ ee ny a i eee te

Sy eer rt aed tee

Cpe eae AS TIS a AI A a IR Sie

. : x \
‘ia jee Ne RS AAT OR te TE EO x

cocpan sp =t adeno: CLE eS OIG! tes EE ON

A NT CE mr maT MNES

er ee 1 oe rr yee

k

el ieeel + tera

" 7
; OBE LS SD

A GE
\ ee re a]

\ ee eS oe Re

\
1
a

BARS BAU TAC aT MUM
FROM DOK Shae YET . *
fA a&SIHOM: APUAE.
40 BVI TATY Se SA aA Tae
PH TATE HAUG IVIDI
a

J ! : + 5 oor) ie,
ae Fi Ph Ue Peay Mas Ook Bens Ser AS en oe oe BPEL a ‘s

44

Figure 14, Maximum and minimum surface water temperatures.

VINYOSJINVWD AVE VWOINOW VLNVS

SBYNLVYSIWSL 3BOVseNS

slo INI] Seni SeelnNiait

¥
|

ay
;
’ <

45

20°F, but as noted previously, the spread in temperature in
any given locality never approaches this extreme value. A
reasonable local figure for seasonal differences would be of
the order of 12° to 15°F,

As a thermal entity, the Sewage Field Sub-unit is clearly
defined on charts of surface temperature in the winter, and it
appears to occupy a relatively small area around the outfall.
In the summer, it is not as well defined because solar heating
has raised the temperature of the surrounding areas to nearly
that of the sewage field. In summer, therefore, surface tem=
perature charts may not be adequate to delineate the extent
and position of the field.

The Subsurface Water Unit is of relatively constant
temperature, the maximum range within the bay as a whole
being no more than 6°F. The most typical temperature seems to
be 53°F, and the greatest variations appear to be due to the
intrusion of water of slightly different thermal characteristics.

Figures 11 and 13 illustrate the differences in tempera-
ture between the surface and 200 feet in shelf water as a whole.
The maximum and minimum temperatures at 200 feet are also
indicated. The differences are greatest in those months when
the surface temperatures are highest. It is evident that
density distributions must follow the same seasonal pattern,
and that the greatest temperature drops at thermoclines or
gradients occur in the summer and early fall months coincident

with periods of greatest surface temperatures.

cl oo) ala ssceoest tit Rulbiaie a4 ceed aan at ni
ie Get os OSh Be

Untiteto #2 Phtw-dve btaka Seaweed aay . ¢tkdwe ain

(ge ‘ig Set ey sah Hi PUPPET RSs SoG rigeé ta otrsdo 4 fe

a

heet ra ead brevets woah Itama wreddaates « (Qe oo oa

“i paktaoe iwies «edeoed bemtiob Liew ae son ef 7s

An ak mh itt of Testa Ddbade TD 4% 16 aiwter opest odd tae

f

~ner siahens ,asotexedt cagmie GF blot? onawes ta
i

bietew wf? shagabions of atnypete Sd tan vam aise

~bL92) ons ta ‘wo £35
ity

todstynes vetevidates io 2: Panu ora soxd Lath

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io

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Sst mi Avex Ped ty: ets rteot hl Dt ima DE at

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nN ; : ;

hia. Pattie 2 te asattoh Ri ab ebdadiie v0'%

ater igvtnewed Sino ets wotna haba acol wdaabats tt

‘ Jeo

30 Bopelon ied t | eh tha sautanscites sears pate a

( Peiehtunkdo na woes rea, ePaws NS, ‘seine ant sb sHa90. *

ae ee Ree ne et aoe Pee Saoheote Ae ahok

46

The Seasonal Character of Shelf Water Units

The temperature characteristics of the various shelf water
elements from June 1955 to June 1956 are shown in Figures 15
to 21. Only the vertical relationships of the units and sub-
units have been scaled. Horizontal dimensions have been
ignored for simplicity. In the following discussion only a
few representative temperature distributions are described in
detail.

June 1955

In June 1955 a thermal boundary existed between the Sur-
face and Subsurface Water Units, consisting of successive
layers of nearly isothermal water and forming a series of
distinct steps. The Surface Unit had a temperature range of
from 60°F to 66°F inshore, and was subdivided into at least
two subunits (Fig. 15).

Subunit 1, which covered the greatest area, had a tem-
perature range of from 60° to 62° and an average thickness of
approximately 20 feet. It reached a maximum thickness of 50
feet in the central portions of the bay. This water was pro-
bably moved inshore by the prevailing winds where it mixed
partially with underlying water and partially with nearshore
water. Subsequently, it was overlapped by the warm nearshore
Surface Unit in the central shore margins of the bay.

The nearshore warm layer (Subunit 2) had a temperature
range of from 64° to 66°, which was apparently the resuit of
increased heating in shallow water and of heat contributed by

effluent and warm water discharge from the Edison Company Steam

Lies alae aaneiada Letezeo2 (Sat 9 id

ie chal ‘Vebna ailokaey ‘odd te GoiiebrotosrMto stutaxequet 8

Bill aorwpts nt (clas ous. ayn ® an], O23 Reel Set, moe:

n hig a toate! Be ait ait te weibitangst ale ieakizeav one iad

waad eas exo bears mk > iptmosi yok -balsoe ogad, Seam

x

a WING ‘Hebets Red fuerte? oid nl. .yitoliqure sod be
, : J ’ ; ; uae -

wht eiigoseh one snohtwcivtebh eymtearsai>! cvisetases Tae

awe sdf neswied betakke yasbeitod Lamsedt a Stel onnhl

evigesonus Yo ptkietiadad »22inU astew cos tsueadee ie

\ 8

to sehsen & ikune? ban setaw Lemzoi toss vixacn, 10°8

>

oa *7

Yo O#pekt Stwtersqie? « Dal Sin esate: ont .eqare Fe
«] hc

gaget te ofak bebivibdus sew tas , sxorlens 3° AR gf GE

on. (ei S54
-
rs
ee EOS BDSM ~ SITE FROTAILY eay Sereavoo March ,
hen “eaondeidy Sauxeve ma bas “SO oF “00 moxz).to $
wa ay
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‘ong Raw aotew aid syed OAS Ke anottiog (atiGe2 ant

tioke $k onsiw 2bitiw wakLisvend out yw s20tegk hevemg
Srotewnen aloe yiisntans bies ite goiytisobee ADEW YREae
Sot eA Se ORE ene wa Bbeagelkove eaw tx witn supaedut
ted ott Yn presen axode Ia2ias9 odt wk tea one

. ionlilalleds id r baa <S thoude2) weyal arew snodea moet ott :
We: betsy site: C1) ones iar dia fhe yO BM 98 OBA ost % 4
we petudiidmen $ x08 Ye bee STM we Lucie ak wank 3 pnch ‘

oh arene yarsqend noehis, aint ment synedoeh 8 sons Neha poy an

fe
‘ a) ett 4 ; 1) ‘ ‘ ee d pl fi

47

Figure 15.

A. Index map of temperature profiles in Santa

Monica Bay.

B, Vertical temperature distribution, June 20, 1955

Hov3e |,
OgNOoGgsaYy

OaGNnoO3s 13

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GS, aur O02 ———

SS

See

SE

ve

SS SS =,

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2 SR Se

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‘Sveey’,

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=
Al)

eas acai

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50

100

150

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100

150

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+150

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0820 0828 0832 084) 0846 0850

9
6/ 62|\

495 50

145 140

10.5

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SF
5/
49
$8 49 50
52
1130 25 1120 1109 06

1310

1300 1255 1248 1244 1240

50

20 JUNE Se

-
i
.:
=

Figure 16.

Vertical temperature distribution,

July 19, 1955

48

e"
ww.
: wo
1x3 +

0920 0926 seer 0935 0940 0945 0950 0955 1350 1340 1333 1330 1326 1324 1322 1320 1315 1313. 1309 1306 02 1300
0 fae Hae | — poe — Ta i AN , [ez] _ mali lca | ee id
s 66| |67| |67| |67
163 | e EN! 63 65) |65 60) |59 : Pea hel de el
ra 63| 160]
Bl ue 63! 55 eS VAwapca = Ame 6/| |6r| lez
a th al sa| |se| |s7| |s7| [6 58 57
55 = - ==
IE od 56 55 55 ie 55| |56
50 Z = Lj |55 == a ua)
55 SS Bee] 54|,
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50 50
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0 100. 1052 1040 1030 1020 1010 toos 1002 {ool 1000 0958 0957 oosais22 is24 1s26 1530 1540 1S49 1S51 1553 1855 1600 1604 1607 1609 1615
Pella 6a) jes |.2. JN [es_]-2- |] : [66 ||64 67| |66
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58 58 58
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0 1140 1150 1200 1210 1220 1230 1240 a
Jez ea? 62| |e3| \lez ? 68
a Nib Tol ool (I
+ .
57 \ 60 | INE 62
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59 EO Ne 57
57 |S
N 2 7 | 53
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52| |se| |53 50
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5/
[ede
i |
150 49 SI 50 | 85 Ties
||

19, SOENVALSS:

ies
she ep 3

Mi
ree

P Voyiy yar

Figure V7.5 Vertical temperature distribution,

July 26-27, 1956

49

¥ OF P af A Wy Vd
ma ee, aie ia) " 5 % Ae a Porn
St bal a .
A t b i r
h ; i pa ve
’ ‘ =
:
2 > ‘ ce a 7
MOV aL BivseseqneT
“peer VE
:
&
oh ay ‘

‘56

QBS 2 27, HUIL 7

Figure 18.

Vertical temperature distribution,

August 18, 1955

50

55

= wm
oll o| —
284 3[sb 3 3 | 3 a] = | 8 fo} 8

a
- N — S oO
Ae [os ie si[aisl| 8

18 AUGUST

1050

Oia

ect = a a

[Pip ete ee hese etna ERR Reed AOE RT ENTE CRD:
ay
‘ .
t

\
'
|
|
Suen

A
5
2

ee ee ee

<3! ine ag ae
\

5 pe a oe
= ; —— : . _ or —_
‘<i =) = | = > ; MEigr = i274 - } = pS ;

a ; = 7 ?
Aig —_ as a en nd BE 8 a

Figure 19,

Vertical temperature distribution,

October 13, 1955

S21

D

$2

L

0835 0830 0825 0820 O8I5 O8I0 0805 0757

50

N00 1055

WO 1105

20 Wis

N30

30

N35

1140

150 4s

158

50

—. ————— - —aT) “ r 3 : —
3 'y Pi 3 4 - Ps = a - a 2
e a : a - '
ac ’ s eS

_ enero
u : - :
——<- ss en a oe 5 be § Fr
ees —_ 4 = 1 ed : 2
~— >

7 = -
" - .— a 7 = —
ae _
Se et = ;
Los
' is | 4 _

Figure 20..

Vertical temperature distribution,

January 18, 1956

52

C if , rN ) An ‘ Ey man vit us i } 3
wie ALN 7 1, “AGT iN : A rd aah : 1 fier
al AL i i : i i ii
te : vi yy wy ae i Aas! ly
i i fea )
” by b
' om Ya ih dy)
i i
4
nobiodixte2rd ssutecsdiea? Banis.0¥
: 7¥ i NORMA TS L

fa

0 (617 1630 1635 1640 1645 1652 1655 1217 1220 225 1230 1235 1240 1245 1250 1255 1300

50

100

150

St
0 1600 1585 1550 1200 1555 1150 1145 1140 35

5 EMEA

50

100

150

50
0 1353 1345

50

100

150

18 JAN. ‘56

| Gemaele

Pos

Na sles EL tm talkers Malet

e = ; S
= , =
seat z 7 el : ~ <a =? 7 ca - - ? ;
E am ss

Ss i ~= ——- a

ter. .

Figure 21.

Vertical temperature distribution,

April 25, 1956

53

:
/

\

56

25 APRIL

54
Plant. Part of the increased temperature may also have been
due to the formation of slow moving gyrals in the southern
portion of the bay and a consequent increase in local water
temperature from solar heating alone.

Below these two subunits were several patches of water of
varying temperature that form an intermediate sane between the
Surface and Subsurface Units. These were sufficiently developed
to be treated as more than a transitional subunit.

The Subsurface Water Unit was composed of several broad
strata ranging downward in temperature from 53° to 48°F. The
main temperature differential between surface and subsurface
water amounted to about 10° at an average depth of 55 feet.
The subsurface water gave some indication of progressively
higher temperatures in an inshore direction, perhaps indi-
cating motion of water at most depths over the shelf toward
Shore. It is interesting to note that the coldest water and
the warmest water occurred together during the summer months.
This cool contribution may have been the result of several
processes including internal waves and upwelling offshore, both
of which would have introduced cooler water into the deeper
portions of the shelf water mass.

July 1955

The thermal characteristics of the various water units
and subunits in July 1955 were similar to those in June 1955,
except that surface temperatures reached 68°F (Fig. 16). Many
more patches of water appeared in the surface unit during this
month and the base lay at an average depth of 40 feet. The

surfaces were much distorted in their finer details, perhaps

abet st ve ti hw debsiognet bees pnd
pea att ie dtwnes e043 tone the Ba to “pptdnare

getew Yroet. ww wodeaaat easy secies Alene cad tt

bs 0h uaa tik sits hindi ean ae
; OS ce

“Se sitew or gadotey, LarwSe Binw as bredead ows ‘paenty

{-

| Wate) Wein ed WaHSE Ss KM SOrEeT Ak «re

s

7 4 :
AB RTS

a
me

Reigitin aes tol live ae ‘penty Share: os ede’ be
araucis Demesoenimeasr a as xo Mf "ag
Di oa sel

PER se) eeehRi sume? 7) tinscwal

esa tepadun bee soelate Reaw7ad faci nes ci ‘Dastyke

tows 2C Ve Gtah eonzere-aa fs ; da Qs

une wt ts «hPa etl aed “4 ie aw

q Cry pai

wb Yea

mnweok: thes oF vrowey ages Yoer 1) at we XS

indt oO OT teu one
ei iPad ae : gale. ge beep seg suc? ae ete - tan soon
Pave io dfwaon OOF Gee evar oro is 4 ue Lt aah: :
‘miodk} ty ool liewde Game cial Pnjeeeink ow » fuy Cath:
=

weyeen) edt opal <apne BRSGes tas

aime weiew tighe aed to ot
. bs,

2d a BA Dae y ie Yeo goklaiaet oon LOPee!

Oy Only Me oat on auctate Lommpbimiatlae fig i008

’

Siig ert vee ae eit ok be

ae ee Rao Bee shee

Qa ih nee Tt % aun Bi ha ae ¢

35

by internal waves, although the changes may also have been
caused by the irregular shifting of the various units in
response to short period fluctuations in the current system.

Generally, the Subsurface Unit ranged in temperature
from 48° to 53°, and the Surface Unit from 56° to 68°F,
including the intermediate subunit with the two surface units
discussed in the preceding section.

July 1956

For comparative purposes, the water unit structure for
July 1956 is shown in Figure 17.

Marked differences are seen in the patterns when compared
with the temperatures of the same month in the previous year.
While a warm surface unit lying above a cooler subsurface
unit was present in both years, the major differences existed
in the subsurface layer temperatures. Where the subsurface
water in July 1955 ranged from 48° to 53° over the shelf, in
July 1956, the range was from 53° to 56°F. The Surface Unit
is comparable to that of the previous year with a range,
including the intermediate subunit, of 58° to 70°F. However,
the Surface Unit was much thicker in 1956, reaching average
depths of 70 to 80 feet.

Bottom water temperatures (Table II) were normally quite
uniform, but changes did occur in a non-seasonal manner. An
examination of bathythermograms aiso shows that in water
deeper than 100 feet, the temperature remained essentially
stable over periods of several days. A 53°F subunit was
present in all seasons, and if this water represents the

normal for the basic shelf water unit, then it is apparent

aa wane oth we (esa enkx aah ches tay

oy) elo ‘atv ure “ ty tot Bt date 8 “ bp nah, 3
‘ i mt s ; He . : ‘ | | |
“ uta ai rt er f ine oF aes wa fpiok ty pea ee pier? Ree we tot rf on ia

ny ON Baud cs! VAR H bet! oe Tae “tum att etl
ai , eee eat ee y rage: SRR Seite F ‘nett ade a tz ‘ot i
AOR whl ee ook: et Witenes ot vite ert. Cae

oktoos en \ipteray pele mB

Tile page Momo fanw é@f 3 i 7aiyY Ve 168 T3322 23h 2 ty ry Sy + Pe

ce TOBY BHORtOnd 4) ah Afaom gage aie } ad ae

eon PeRedae T4olods ma eed aie oe Bh

) SIBeko Seanevoedvieh tote eh? Cexeey fod. ae ranean

Worl eddy, ate baa |e ePer eee corn! soe raat
| 4
Ame, Bete Dy: OF “SS mort Agytiar 22teLl ¥ coh

=
mse
=
ae

bit PAA: dee cre uf hae of “-Ele fare? 2c Pe |
OTe 4 ‘i iw Seay wpb ywge serft en
4 Le aS iY y OMe 1a ¥ +i musth a “> ¢ aay Sek

, | air
Spkrsve osiiokes OCR L GE CBRE AD Move aan DER ee

(Sten (eOEnst eto wk srbos hal) Seen eee |

sovow a FOF Mase we le Soe oe aN ee ee eS

past

(itt ieie Doan Stas hoes att, phase aOR Tae.
Hoe) kom AMER Oye eae Tel eee, ae

wh oe

pea? CSc ND eee ae Te baw Saag 98 tie

i HORS RE i, pet ee Het ay, ) toi

56

TABLE II

BOTTOM WATER TEMPERATURE RANGES OVER THE PERIOD
1955=56

June

July 49=53
August 50-53
September 53=56
October 53=55
November 51-53
December 51253
January 51-53
February 51253
March 51=53
April 51=53
May 51=53
June 51254
July 53=55
August 53=55

LY feat

aYeranee ga i yc = a hell | my ove abreast ps Pair base

} i
RS etary ee athe ame Oe pare shmeneayet Gy emeste

ve cae sont init a0 2a0MAR ‘BMT ARS TMA sec qe
‘i . BRA ERS ;

| eam valerie net: teen pen A renee Sekar +e enmpecemet paket a
be eee i. tho 58 gore

ao wansh orddetsqmel asteW uostod

tant hncege sree infaunal mpm Fmt hm cet a re i yah mca wit

i
io
as Ehwlk
ve
i oes Bal

Si,

that at some times its lower range is affected by the intro-
duction of deeper cooler water. For example, the lower tem-
peratures in July 1955 could represent an intrusion of slope
water over the edge of the shelf.

The subsurface water in October 1955 was similar to that
in July 1956, as was that representative of August 1956. On
the other hand, the Subsurface Water Unit in April 1956 was
more closely related to that in the summer of 1955.

August 1955

The water units and their temperatures for August 1955
are shown in Figure 18. As in the previous months, definite
surface and subsurface units were defined. The Surface Water
Unit was composed of an intermediate or transitional subunit,
and an offshore surface subunit. The latter was under the
inshore surface water in some places, and in others was
apparently missing either because of mixing, or because of
replacement by the inshore water unit.

In the inshore area of Redondo Canyon, the intermediate
water subunit was apparently absent and the Subsurface Water
Unit lay directly below the offshore surface subunit. This
may have been due to the exclusion of the intermediate water
nearshore followed by a subsequent flow of the upper surface
water directly over the deeper water in the canyon. The
sharp thermocline in this area may then have been the result
of shear between the surface and subsurface units.

The surface layer, including the intermediate or transi-
tional subunit, varied in temperature from 55° to 71°F. The

subsurface water varied from 51° to 54°F. The surface unit

ts ones ? iA
a ie
te er
1F
Neer i
¥ ee
* Rs
I hen:
io ;
‘
J

dy 4 ay eral

Via

‘ paok < te

Pe Nace ,
Y, iy we 1 vie eae Mini al) ia
o Td ny ml 7 : : ;
nat Ay) hae { fy : if
6 by AE Pall
4 \ Dyan c oly :
%
‘ i

si aa | bas ai

seo rt i

F f ul wil i mentee yp} be
, 7 hy) >

ik Sho eannt eul ebb \eomse Oey
ay, ; ss Ti a,

ic ore
alee TORK

PERS ee

Ree Bay Sah mir) stesags hia. st

et? 10 Syd

; deur oy TAT go 2 Beet oO Wi 9 Few aon tabadie (am
ah Beat Penumees ) vit avaseonges Fads esw we oem
pune meee j i of dee Satay! eye 3 yore th on? » tenet
ee a yet Se eR Pet of bat ebes
Meet’ teuweA Si be isyegmet whent ee “te ei =
waite Ve ay Taq \ vty Be f . suas b tek fs
“orn goa ree art - wr2ew B20. unde
ckhmiade Leogs tiated) 46 »inbbenseto : : bo AOC oa
ws Tee y te ; iv , Pr pusde esghive San “
ann § Lats 1 , 86244 BmHe a! row woe 1a: .

SO we AOR

a j hm 7 *evenod wel Atsee Fy wt
R
e rit pr? a v ; <7 vu T ie
, he
cavere alt Pewee 4 ete Dail 26 he otnek wae 4

Se
*

(oeeW woe kan dt tok Peed ire sol. me Te
4? othovdes scot geedeita ent + ant ottoorkl ie
mya eee bw ie tS oOHT ORO CORKS z wwe noodle
othe bane yeerepie rtd WOHT Seporwrgreader (ay bam LEQ
ant dn OES GR) TetRe. Tags 9 fh te 42) oor hig
a nage eyed. Melle” Awan eem Baa al voi toni aa a
ees cb a
; at cae én Ber att Hi PU wont tual sail poswisd ¥
fener? 33. of aspen wene “ate part pat one aeTE? baa yu oat
GOS HOLY oF PR monies dynepued thi rreawy «dinademy
ihe hoa Pane eat 4 ie. @ Be, u'r, Sadness

58

averaged 60 to 70 feet in depth, reaching its maximum develop-
ment in the central shelf area and thinning to the north and
south. This was likely due to superposition of the water by
current action over in situ water to the north and south,
brought about by the deflection of the main inshore flow.
October 1955

The characteristic temperatures for the various water
units during October 1955 are shown in Figure 19. In this
month the fall season began, as indicated by the decrease
in the temperature differences between the surface to the
bottom, from spreads of as much as 12° in the preceding
summer months. Also, the Surface Water Unit was then com-
posed of two main units, transitional and surface, rather
than three, and the nearshore warm subunit was markedly
decreased and was more restricted. Surface layer tempera-
tures, including the transitional subunit, ranged from 57°
to 63°F. The subsurface water ranged from 53° to 55° and
probably represented a different subsurface condition than
existed earlier in the year. The boundaries of the various
units are less distorted, probably because of the reduced
density differences. In addition, the summer months were
periods during which stronger density slopes were created
in the shelf water mass, adding to the complexity of the
boundaries. These were less dominant in the fall months as
the vertical water temperature spread decreased.

The profile in the Point Vicente region shows that
probably stronger currents were present as evidenced by the

abrupt changes in boundary slopes. This area was the site of

“sqoteysh mundane atk ree t “atgens nb isa OF
ea toa 6H ont or aiiaebdt hoe eots 3a: tastes

wd seen odd to Weettogn eae bg. airk ctouat au

iteoe bea dade am oF ator pb dae ave
wok) mages mine. ot
tetew necking of! so? eezedaueions

t+ OL sxwibd wh avaté ope ECPs

arte At ana. co2 ef wemetart Soon TS }
anbienaeig 809 nk Si On eve eA to bOoorge
mimo Aed® naw i sare ennaane ome , cel! sii taae
gulter ,Gondtve Keo fone eae =. a2 6 ctam
witedsat sow Ytanduk eiew eioraetaen ir DIES oy,
wapeyaqme } 1stal aoatie LAPSLWEGS) o107 2aW one
=
O°? mor? Leteat .)tavdos (Wwapresenes? +! ni pots
ima “Ct G Ei mas?) Sbenney TeTaw o>: iu edits ont
dt noliztnes eser2tueage ag44siikh 2 bot cae
~~

.

Hinktev dt Yo sobrshawed aal -. Rady oni ak sortie
‘pagubsr sti le saupese pidetesg «bol oneee aegk:
sow. enToom Tomas SAF uwergaihs «3 ¢€¢ onoasti eb ¥
betacrs ovew seyela Qeseend Tegra iss COZ ,
at? 36 Stieoldmo dr MO Battin .24an ror ow A Dede,

xe ectocnm I fet) oa te Sananineh rool ew gta :

: = bee ew etay Moire 92 1odnn wy ree

tees Swtate

Ss a

59

some inversions and rapid surface temperature changes at
other times of the year, so that it was likely an area of
interaction between several different water units.
January 1956

The temperature characteristics of the various water
subunits for the winter months is typified by those of
January 1956 (Fig. 20). Surface and subsurface water tem-
perature spreads were small, amounting to about 39°F. The
transitional subunit was weak and inshore water was nearly
isothermal. Diurnal heating is evidenced by small surface
warm layers which became mixed into the surface layer in the
afternoon by wind action.

Temperature differentials between distinct isothermal
layers were small and the thermograms showed temperature
gradients rather than thermoclines. Thus, water motion was
more or less uniform throughout the surface unit.

April 1956

The temperature relationships between the various units
for April 1956 bore marked resemblances to the generalized
picture in the fall temperature structure (Fig. 21). The
surface layer was beginning to develop a definite secondary
structure of subunits as the main mass of the Surface Unit
separated into surface warm subunits and a transitional zone.
The warm inshore subunit was well developed. The thickness
of the surface unit plus the transition zone averaged 100 to
110 feet which is the maximum depth of the surface layer for
the year.

,

ae! O84

His: vty ia eed: Bee Et

cca thin Hew 408: esRieL iayeves saenaie ae

F a » aeek

tetee euolwey cily' te ayibalsetos sds sani gsieqneee

. | Wy otoecr yd bob Yiqve ef esiteda sotekw ott 3o%

As
iy i _
- meet wxtew sos hades tip aoe tsue COs pb ote v4
Te ee _ ee
: : . St
- wat af tuodse of eabktageta . fins oxow BDPSTRES
Yianet caw votow syedaat tie Aaew eeu Jinudwe func
wi t a“) 7
; eoatsve [Lean ve feognhevs =? anitgod iearwan
im he,
a aft mk asynl oon duce. 02 Giak SeFtH Hen0sd doi hee
A
mot? Ss we
! tumpeddcat tontvalo novwred stabbesys i iit ewes
a '
eiutetsqHs > bewors enuatoom ey af? na iinan ate ‘
Sew mikfou astaw . st) :sormz isonaedg? aac solter ew
* ; "
-tton asstawe® S09 teodpiior!! mol ia, eee
: e
egkhaw tuokirey 2d? noowted agidemoticic: 5 1379 YOUwss
: at
batilexonsn s2 of eondgidtiadet hatnan orod ORR Re
oth) ALS. RET) saetgoeee Ret ete geo! Otel Saeiee
~ YIeoneoes Stinks mr n a0 Love by os meas. teint sect aaw Pra | mM
on fintl eparsne of) to pew nae aot eo APtoedes yo
fy i ee Z.
a: _stey Lacettiverst «beg Biieodes wise Sop eee aee es
a
iN

a sasnintdt sah abeqelevei: ise saw 2inedes vordant

oy a) ae SO 235VA S208 nokttens xt aif any: 7 hee oon ae ~~

ay j

‘te bireewd evettes end) Te drqob bein awk’ eh: mate ‘4

ie
‘ ial hte if a

1 eae

‘i

60

The Surface Unit, including the transitional subunit,
ranged from 56°F to 62°F. The subsurface water ranged from
51° to 53°. The water unit differential was, therefore, about

6°, and the maximum vertical temperature spread was about 10°.
Heat Budget

An analysis of the heat budget in the bay has been made
by Mr. C. G. Gunnerson, Bureau of Sanitation, Los Angeles.
This appears in that Bureau's publication, "Summary Report
on Oceanographic Investigations of Santa Monica Bay, July,
1956", The pertinent results of these calculations are
shown in Table III.

The important facts embodied in the calculated budget
are: (1) the surprisingly large potential heat contribution
from existing and future man-made sources, and (2) the
important effect that such heating may have on the nearshore
current system. This last is the result of the marked
density slope produced at the boundaries of the sewage field
as a result of its higher temperature and lower salinity as
compared with the shelf water. The foam lines, slicks, films,
and color changes are all visible evidence of the existence
of this boundary.

The total heat contributed by the existing outfall is
apparently embodied in a layer of slightly diluted sea water
varying in thickness from 5 to 20 feet, and covering an area
of from 10 to 20 square miles. This layer has probably been
formed as a result of the turbulent mixing of effluent and

bottom water at the outfall terminus and subsequent mixing

ya tae) i Y '
, ' 2
i 28 i? : if F Wi i t : ,
fh ‘a !
: he ti My
} t

U 4 ; Tan 8 5 v 7 i Ve ey i : LAY i i ; a ; My a.

i iu Rbk diaded tauak hangar Rr ie wabbel ok 02a soe tae
RiBD, | ins 2 re

awit i ava we ‘ihe S08 Nenad a a Ms ie age

+ Oheahe Bie p 3 uy

Picea m WORE Teast 4 é 28 hn : és Keats LS eee os ka OT. :

Re ‘ > a 5 {

Oey hiiedha Lae (ae nik aiaitened OP in te), Rom baw

i efegiant

™
~~
4,
“
-
nt
=
e

iy Teh a Oe
wee LEARIREIY (Bt Tre tive, » 1 what ef mors epaxines OR
Proms! en dotre”: et aon fue atuswoul tui? wh “— a
Mb dh Hl #928 gTaRE 20: asst weet yenvel onl
remand sung, we a :

itt Aste

x
@
-
-
~~
~
~
-
+
a
»
=e
i
—<-
=
4
-

Peers 47 ali i= i? tu : ahiunthy se ey a) 5 is roamed

ary, bir fiat 929 [alias ted swat 9LAO) wet UTS tht

wae we , enone Wheaten Siu’! Aas nakt
‘ , ie i ? 7
Ayre ne hwy Ai) jv si Ai ee, Sh effa Se) Ore rae raat 5
ff iat ia f ‘o, Plagesw (FhT ae rari j moar

Atenas ee Oe ite L seetn a Sey 3 9 en re eae
an Violen, Towel bee APRA F. SER ARS ie +t)
pies . pists sani 0 thal eee /iesaw ede pat or
sonadel * | ry y, wey ; vive’ win idtcy ile 2%4 syed “0

ee Siw’ ie ‘caskonod @

} ! ru
Re iia tte withers we 2 bet odit2ao9 Taee Lator “ 7
poten gue bebo lh Yliehte Tao gavel 4 mk hap herons tie
Bw y kW I ce pane? jaa Gk of mile nemeapadats. th

‘abe
ated Vitadaat cat Se DE | eee aiad ine wt (08) tacit

sith die | Veabonvtd & Hide) abe wii geet?

ta

61
TABLE III

HEAT BUDGET IN SANTA MONICA BAY

| Existin Proposed

Hyperion fam

Average flow, MGD 250 420

Ave. Temp. diff., sewage-ocean 16°F 10 16°F 16
Sensible heat to ocean, BIU/day | 3.3 X 10 5-6 X 10
Heat from oxidation sewage,

50% loss, BTU/day t.3 & 10° Ypexe K 10?

Heat equivalent of salinity

difference, BTU/day 21.7 X 1029 |34,.4 x 1010

Redondo Steam Plant

Installed capacity, megawatts
Assumed average output 65%
installed eae cooling
losses 3.33 X10° BTU/hr/nmw,
sensible heat to ocean BTU/day

638

10

2.4 X 10
E1 Segundo Steam Plant
Installed capacity, megawatts

Using same assumptions as at
Redondo, BTU/day

350

1.8 X 102°

Scattergood Steam Plant

Average operating capacity, mw
Using same assumptions as at

1212

Redondo, BTU/day 9.7 X 102°
Total sensible heat to ocean from 10
the above installations, BTU/day 29.6 X 1029 57.0 x 1010

Solar Heat Summer Winter
Average radiation, m-cal/cm2/min 0.3 0.1

BTU/mi2/day _ 4.4 x 1029 1.5 x 1010
Surface Equivalent Area

Sensible heat
Existing square miles
Proposed square miles

|
Total effective heat |
Existing square miles
Proposed square miles

epalrertei an perio Capa | ibtiy
a ek a= im rat

eee BEE SERENA

¥ lias teamed _" Senet
Kon ee ie ek aka jane Civtasas
;

Rib BQGAT

Sipe nae ee

vag potvom xiase Mi TeOduEL TARA Ras

ee . peneasas. ee aS
tee ose | oes | GOH jwok?
i “6 dk Sa WOR? | BResg-syewse (a TPED .Om
ep toy KX e.t haa | a fee aplure esne oF toon oF
i e “eaRewes awoltshixo mox
hi Soe ik als} “Gt F Bek | sb \UTE gee
wean . | tink ine ‘a Thelevia
et Olor x 4,00) O8or x his ab \ UTS eons
ere on brennahe ¥ ‘ . Set 7 ‘e- " nexentihsteosmualciperocmes toadieaietaa
aa
La ‘a - } ; ns - 4
m BES | czh | ethewagon . yi toages Fyre
nh S2e Taqiuo, sya tsvs
a i em eo" : y3 j9s8d82 be
* on | | Oty | uid Sore cf.0 aa
ny HE x Of OL x $5.4 qad\UTE Kasse of tra old)
oi e Fites4 er
- 1 ; 7
, 4 ! : ; ;
| One| eve | aes al yi tsaqss bette
Ml ot e : ta 28 tqnuuaza. SHS |
ee fs or «8.4 | *%0r K eo | cab \ OTE, i
ENN feat ORES ie ae) TO at ots
in AT ; ‘tnetd nae $2) D
by Sirs Ra | onon | we »ytioagso uckte29q0 aye
wi ; tg Be ano liqruers Saas
; Og: xN.e . “gab WTS) ge
- a a meeps ceca ie dnectiahbsatneentons “cree aad emcees isin emeeny—2 teen eae 5
wal | Row maaso of toed Stdh
by er x G74 Mfor. xX 8 esi gab TH Sadist:

ont eee lear

i?

serait || xemme |
'
£04 £.0 ita Bea\ i00- ee, , spobtaihan
Stee K2,t POL KBR, eo ba\ VES):

ALS | i astia S1RIDS Goose
e.t & eh es.tkim Da acon ic

eo) | taod evktootie:
Vagal 5.6 | gekke saanpe, gakteced |)
Os ae /

i sp ion oyna a a auily

28) i ems cae a oes seh: = hee

sae she Ve pn ea

peek ras iavupt 6
geen shezenel

mai a ene erates + orl aac enamine bane r= ees he eee

cca non giny

62

with surface water and nearshore water within the sewage field.
The sewage field is in steady state so that the loss of water
from it by diffusion and mixing at the edges is balanced by
the introduction of new effluent and of partly diluted shelf
water. A warm water field covers much of the inshore portions
of the bay in the summer and early fall, from the vicinity of
Venice south to Redondo, and seaward as far as three miles.

It also appears, from an examination of the thermograms,
that the boundary between the field and the shelf water is a
rather sharp one in the winter. This is borne out by obser-
vations which indicate that the field is bounded by slicks
and marked color changes. Thermally it is larger than sali-
nity differences indicate. This implies that the recognizable
thermal character of the field is maintained beyond the range
of dilutions observable from salinity, or to dilutions greater
than 200 to 1.
Source of Mixing Sea Water

Although evidence is limited, it is probable that the
initial mixing of the discharged effluent takes place partly
with the bottom water at the outfall terminus. This is
indicated by the fact that the average dilution does not
change appreciably during its rise to the surface, and also
by the action of a subsurface current cross which moved into
the boil area while a surface cross moved out with the field
during brief observations in May 1956. Therefore, the initial
dilutions of approximately 20 to 1 in the present discharge
boil represents initial mixing of the effluent with water at

the approximate depth of the pipe; the mixing water being

iota te ‘aan oa enue io mt Ede eet ‘nb ah, or

ier

ae: biomatsit 2k ‘Hep ing wie: cP ‘ge ake be wokaw?hie be

+ Poe Meduh he (id.1aG: diy! ith tthe fhe wen % nokioat

ae

*

ty ReIMLOLY wt? BOR +t aa vi Lind hie Voie ser ah” ei

i
b

SEO ETIOG Srotatr ot up dun iss2e re? ates wotew woah

ised Ey aon ae Vet OF Sewiuds Sis abner og Aree

i

Kawtvoks vit odd Yo me tiny eee ne cos} nandaqas onta | .

eae wotew Viete #2 ina Glatt ehh reo? sa (cabangdal
4

eraneday vd San ented 23 "aia unoeaw edi mk Ane \ a al

siotie vd. habawed #6 Diet) gbF eae? 24 yt bak dose

epige Kacy woRtel w: i village Seeness oO at)

—— 4

sideakepnoer of7 Fait? ¢« liqat etn @7ancrie:s ASO jhe

ogee it “i? teneod Oa aceyalaw eA tee wey io 299 ve ’ f
yohedty cao fey hes io er Lebin®g Bee? elds vines nak

| at

4 7

Bon 25% pik eka

ant tady eleaderd | @ betemks si ones hive Gees

; : =
vissad 4o0(a ¢o7e? Fase cys Ot a §S sa? tee inka
ce
ax abet . Ra 2? Jie One fn setew wah 3 tothe j
‘as . 5 | a ¢
Ti peed tie Pela) ope see See dads 72a) O8F vd |

wv

‘ . S . fi 7% v
Huth Bod .Soa 08 of? OF SeBRinee Orr ies videkso4 1)
Seep as

ork: baved \Mosdwy eros, 2s Ry eba’? sped te neko om!
HEei? ade dd he) red (\beveot eeege, FR v2 shuhaia! avery i

{ ’ ‘ hy ist?

feltink S42 yee) 2o0R2 ae 4h oooraresade: Yetad) £
‘pm sanoae tusavey o0t wi Foot Os viwtwmknanga ‘eo

thie Sadat tit hw pam itty: obs ¥9, ‘vata Keio bab) atioraaas

63

replenished by an inshore flow in the vicinity of the boil
at depth. After the mixed water spreads over the surface,
further mixing which takes place must be largely with water
in the surrounding sewage field and to a lesser extent by
vertical mixing with the underlying water.

A series of calculations using various assumed conditions
of temperature and salinity have been compiled in Table IV, in
order that some limiting conditions for the equilibrium posi-
tions of the rising effluent may be considered. The compu=
tations are based on various dilutions in the proposed boil,
an assumed depth of discharge of 200 feet, a normal shelf
water salinity of 33.50 o/oo, a mixed water temperature of
50° to 55°F in the rising column for each chosen dilution,
and various surface temperatures typical of each season of
the year in the approximate area of the proposed outfall.

It is also assumed that fresh sea water will be continually
available at the end of the outfall, so that no appreciable
change in the salinity or temperature of the rising column
will occur after initial dilution. It is evident that, as

a whole, the above criteria are the optimum conditions. It
is probable that the temperature of the rising effluent will
be close to those assumed, but its salinity may be higher.
It is also probable that the approach of new shelf water
will not be fast enough to prevent the mixing of previously
diluted sea water with the effluent, causing a lighter mass
than is here assumed. In any event, the calculations indicate

times at which suppression may possibly be expected.

‘thed: oar, ie + ite

liga ebagaat

Ws

Ae ea

pore re

; LI Ye

eee hes Shaeey ;

00

cae

iy Sere

nen) ee

‘gids sage
me hy

in gh matt
watt M
+)

Puvaee

rs La

im ‘i
ORR IO AT DEE
Ae we Sheek

tik ight

lebiisd

Fatty

a a)

wo RY ea

"

+

¥

eutwt doy nix

id a
inetd 4 ry 7 weeid
ayia

, ns a fi« :4 nuawee, and baa

an a)

‘etew’ axils eta!) ote

baat Ate |o0

G0 ave Wilet ; he

@WOlr> Lua:

vom funn t

f

“jm?

eer 4 65 157

é e1ava

“Jar

Go’ ls
Se enon
town. ee)

iwea

Lmptis? 7
waLTHwe th

mele oa

a + ae Se Oe Tits oti

+ ' ’
Le ee

‘inksee 22 oon an Sead? it *

gata OTe HAD ‘ei idtadarg conta .

evct witht ky roar toh Agito its tte #2 t

KCAR Xa gute ATL

a ae wer
pany: wit ud

nee ae tithing <a mabe
uh at Pe

Para a oe ag

64

TABLE IV

CALCULATED DENSITIES OF VARIOUS MIXED WATER COLUMNS
COMPARED TO SEVERAL SURFACE WATER DENSITY CONDITIONS

Mixed Water (Assuming effluent chlorinity of 0.25°/oo)

Dilution 20:1 | 9031 100:1 200:1
50°R 1.02459; 1.02530 1.02556! 1.02569
55°F 1.02409 | 1.02480 1.02505 1.02518

Shelf Surface Water Unit .

Temperature 55°F | 58°F — 61°R 64°R | 66°F
| |

Density 1.02529 1.02497 1.02459 1.02419 1.02392

Maximum Temperatures for Suppressing Effluent-sea water Mixture

Dilution 20:1 50:1 LOO21s = | 9920021

Mixed water at
50°F, Surface T | |
less than- 61 -F | 55°R 52°F 50°F

Mixed water at
55°F, Surface T |
less than- 65°F | 58°R 56°F dee

nny Yann i at Ht ‘
£ 1001 “ExOR i:o0s

e2ego. L ens.
at2G0.2 20880, OBA8O.E '@0aso,t

£008

— Roe SO.L

“~ ~ oes — — = yee Ve tna se | pina a ett wp i vt cay eee . as

tial votsl s
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a { \ ees § 2
40 2 Oo Wee

ied WEESOES

KeESO, £ athe Preenery

soberly rime “ en eno fs ante ees sre eh

saunas aeten g2e-in9el; 18 3 agteseraye x

Lonoke Pree

LPOG

+ MOOR ae aR at I

Hee

65

It is evident from the tabulated data that the higher
the dilution at the diffuser, the greater the possibility
that the field will tend to attain a subsurface level of
equilibrium. Also, the warmer the mixed effluent-shelf
water, the more likely the tendency for the column to pene-
trate through to the surface. The best conditions for
suppression should occur during the summer and this is the
season for which such an event would be most welcome from a
publicity and health point of view. However, the differ-
ential in all cases is a delicate one, It is quite certain
that the column will tend to rise above its level of equili-
brium initially due to is momentum. Thus, a large differ=
ential in density must be present to insure the subsurface
spread of the mixed water. The critical factors would appear
to be the dilution achieved in the diffusers and the temper-

ature of the mixed water.

THE AREAL DISTRIBUTION OF WATER TEMPERATURE
AND RELATED WATER MOTION

Introduction

The areal distribution of temperature in coastal waters
is of interest in many phases of the marine sciences, but in
this study its main value is in the interpretation of water
motion in Santa Monica Bay. The flow of ocean currents in
the bay ami the distribution of the various water units derive
their importance from the necessity of determining with some
degree of accuracy the motion of the proposed sewage field.

Because of this importance and the fact that any decision as

4 ie aa) por oh ftir win be dauiinns ae “naa 3
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Li

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a
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ae, mena 1 rate path tom) WF barn @ yah

66

whether or not the proposed outfall should be constructed must
be based on the current patterns, empirical methods for the
measurement of direction and velocity were employed. Neither
current meters nor drogues give more than an instantaneous
trace of the water motion in a restricted locality, and drift
cards represent merely the upper mixed layer and its net
motion. Furthermore, the distribution of surface and sub-
surface water units and their impression on the water structure
of the bay as a whole can in only a casual way be interpreted
by these methods of measurement.

On the other hand, there is no theoretical or mathematical
method by which density patterns can be used to compute current
flow in shallow water overlying continental shelves. Deter-
minations of ocean currents from the slopes of isobaric sur-
faces assume level surfaces at some depth along which no hori-
zontal component of gravity is active. Such level surfaces
are usually taken at depths of 500 meters or more. Thus, the
preparation of ammemtic height anomalies and the subsequent
construction of the geopotential topography of isobaric sur-
faces by conventional methods is not possible in shallow
water.

However, it is believed that density currents can exist
in shelf water and the basic problem becomes one of determining,
at least in a qualitative way, their directions if not their
velocities. It is only logical to assume that the larger scale
differences in temperature in Santa Monica Bay are related to
the character of circulation. A temperature profile, such as

that obtained on August 18, 1955 (Fig. 22), is an example of

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if &) ?
ms

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nyt

67

Figure 22. Vertical temperature profile, seaward from

Playa del Rey, August 18, 1955.

; Rae
SS6l “Bl LSNONV
(4 ul 2unyesaduia )
ATHHS VOINOW VINVS
ATWAOUd ANNOLV Tadd WAL

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Aad 190 VWAv1d WOds OeVMVS3S

NOILS3SS

68

temperature gradients that might be associated with currents
in the bay. The initial assumption which can be made is that
the density of water near the surface of the sea generally

is more dependent upon the temperature than upon the salinity.
Since vertical profiles show that the salinities in these
coastal waters are nearly constant with depth and with dis-
tance from shore, examination of temperature conditions alone
May permit first approximations as to the directions of the
currents. Under such a theme of utilization, the term
“lighter”, as used with density slopes, may be replaced by
“warmer", and “denser™ by “colder™. Bearing these conditions
in mind and for an understanding of the following discussion,

one has then the simple rule: Im the northern hemishpere the

the left hand.

The Effect of a Temperature Gradient

A change in water temperature per unit distance is called
a temperature gradient. The term may be used to describe a
change in temperature with depth (vertical temperature gradient),
or it may refer to a change per unit distance along a level
surface (horizontal gradient). The following discussion deals
entirely with horizontal temperature gradients which are most
conveniently represented by charts showing the topography of
selected isothermal surfaces.

The gradients associated with slopes of isothermal sur-

faces are directly related to currents only under four

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at
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<tenatiae ae

69

conditions: (1) the water is uniformly stratified with respect
to salinity, (2) the horizontal temperature gradient becomes
zero at the bottom, (3) the topography of an isothermal layer
is not distorted by other factors, and (4) the effect of
friction is negligible. The first condition is approximately
fulfilled in Santa Monica Bay. The second is not, for from
the great number of temperature measurements taken over the
San Pedro and Santa Monica shelves, it is quite apparent that
no such level surfaces exist in these waters. The third con-
dition also is not fulfilled, although its relative importance
is difficult to assess, as is the effect of friction.

In spite of these limitations, it can be demonstrated that
there is a general correspondence between the current directions
as deduced from temperature distribution and those obtained
from empirical measurements.

The paths of the surface and subsurface drogues used in
May, June, and July 1956, and the corresponding temperature
surfaces are shown im Figures 23, 24, 25, 26, and 27. The
paths of the drogues in the surface layers followed closely
the thermal gradients. However, the subsurface drogues were
not as closely aligned with the isothermal lines as one might
have suspected. It is believed that three possible uncon-
trollable situations may have resulted in the non-conformity.
First, since the contours were drawn free-hand with no attempt
to correct the bathythermograph traces, a slight variation
or correction could easily superimpose the contours and the
drogue path. Second, the positions of the bathythermograph

casts were taken while the ship was underway, so that a

=

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wert ie | shop tacts one yaad “it4 tons roe

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70

Figure 23, Depth to 55°F isotherm and drogue track,
May 4, 1956.

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71

Figure 24. Depth to 56°F isotherm and track of deep

drogue, May 4, 1956.

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72

Figure 25. Depth to 66°F isotherm and drogue track,
June 28, 1956

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13

Figure 26. Depth to 65°F isotherm and drogue track,

August 10, 1956

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74

Figure 27, Depth to 58°F isotherm and drogue track,

August 10, 1956

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75

slight error in navigation could displace the contoured sur-
face the 500 or 600 feet necessary to bring the isothermal
lines into agreement. Third, the surface float used for
identification of the subsurface drogue cross was a 12"x12"x24"
block of wood which presented a large surface area. The move-
ment of the upper water layer may have been such that the

track of the subsurface drogue was not the one it might have
followed had it been able to move freely. Even with these
possible sources of error, there is a remarkable correlation
between the drogue paths and the associated thermal gradients.

It is because of this correlation that the effects of
temperature gradients are discussed below and that certain
conclusions regarding the circulation in Santa Monica Bay
are drawn from temperature distribution.

Assuming now that water motion is related to a horizontal
temperature gradient, the rate of movement of the water
increases as the gradient becomes larger. If the gradient
were to act alone, the water would flow in the direction of
the gradient. Movement of water in the ocean, however, is
profoundly modified by an effect due to the rotation of the
earth (Coriolis force) and the result is a flow perpendicular
to the gradient, that is, parallel to the isotherms. This is
the reason, therefore, for the statement made above, for we
find that as a particle of water begins to flow down the
gradient, it is deflected to the right in the northern hemis-
phere so that the net result is a flow along isothermal lines
rather than across them. This deflecting reaction (force) is

a function of the sine of the latitude, acts at right angles

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76

to the horizontal motion of the water, and is directly pro-
portional to the horizontal velocity.

The current velocity is inversely proportional to Coriolis
force, but in qualitatively comparing the velocities associated
with varying slopes of isothermal surfaces within a restricted
range in latitude (Santa Monica Bay), Coriolis force can be
considered as contant and the relative velocities are therefore
directly proportional to the slopes.

Centrifugal and deflective forces always act perpendicular
to the instantaneous direction of a wind in the atmosphere and
the same is true of water motion in the sea. It can be shown,
mathematically, that when the three forces (gradient, centri-
fugal, and deflective), are in balance, a steady state is
reached. The resultant wind (or current, in the case of water)
is called a gradient wind. Such a gradient flow occurs after
the gradient has initiated the movement, although the gradient
itself may be formed by a current driven by some external force
(the wind, for example). If a gradient current is present which
flows along isolines that are parallel and straight, it is called
a geostrophic current. Currents of this nature are know to
exist in the open sea, and undoubtedly they also occur in shelf
waters. However, in the shelf area, where many conditions tend
to disrupt water motion, it is unlikely that a “steady state™
of more than a few hours duration ever occurs.

Some Conditions Causing Density Currents

Wind. In the open ocean the stress that the wind exerts

on the sea surface leads directly to the development of a

Shallow wind drift, and the transport of water by the wind

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drift leads to an altered distribution of density and the
development of corresponding currents. In the northern hemis-
phere, the wind drift at the surface is directed 45° to the
right of the wind and with increasing depth, the angle between
the wind and the current increases while the velocity decreases.
If the current at equal depths is represented by an arrow of

the correct direction and a length corresponding to the velocity,
these arrows will form a spiral “staircase™", the steps of which
become shorter as the depth increases. Thus, a depth can
theoretically be found at which the current flows in a direction
opposite to that of the surface current. However, at that

depth the velocity approaches zero. Such a theoretical condi-=
tion can only develop, however, in the open ocean in regions
where the wind blows with a constant velocity and direction

over wide areas. No such simple application can be used in
shallow coastal waters where wind velocities and directions
change continuously throughout the day and where there are
countless modifying features caused by the shoreline, shoal
water, tidal effects, and unequal heating in the nearshore

zone.

Near coasts the secondary effect of the wind becomes impor-
tant and dominant. A wind blowing parallel to the coast, with
the land on the right hand side looking downwind, leads to the
transport of light and warm surface water toward the coast.

The coast acts as a barrier so that the light and warmer water
piles up against it, and at some distance denser and colder
subsurface water must rise to replace that carried to the coast.

The distribution of density is altered and a current develops

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evaaersob V?tseley s8? oftty assgenoni idoiuie oud 7

| ty wors 1g vd betneastges ek asinqo Leyps tn Ymorath |
koe ley att of astbnogsestoo bbuaes $ bak nots oorkb to

, aaa 7
Hotdw. te agess 369 “sansthate" Dexkge « ariok Lit bee ewe, 2
geo.tedeb 2 sud? lesaentoas diqeb ett ex sotuente
gotdsouih 6 at ewott tnorano $0? dokdw de basot od yi s 74
todd te ,tevewo! daasi9p Spadace ‘sat %6 vedt ot 3

‘ ; ont
~towou fLeatretoadts « dow ,omaR eettonexqts (sisolewr.

wl da
enckas? Mi wasoe oeqo oct a peevewod ,gelovad cis ‘ems
noitooxskh bas ythootov Sxeheaed oe dkiw eold Duke
ak been od am: aotiaotiaqs eigmia dove of .é@se%m SBE
eneipoonib bits eudt ingen lbubw 9totw e19taw al BO
ate 220d? sietw bos tab sat teodguo7c? yLavousksaoa
tweodesakivieds at xa peauyd 201d 07? Joly Tkbom 289

stotereasa ofc at gakiaed Isepote tas Letootie Labbe

~raqink zomooad bathe oft Gs faetie ernbaooss. ad% aturod
etiw, *na09 sdf of falisaeg qakwotd bans A -omnstkaot |
ai? of abeel’ )Dokwnmeb yitADo! ehie bust bight eat, 0b
8860 of3 Deewot wetaw gee tawe unxew | hens tight to. 4298

Iota terew bow piu kl oats $eaS oa xotreed ama etoe ,
Awhies has 332 ish comes ee) tide ts UR? ya Aeoksas

genop kt oF imea sen tant omtans oF: Rial sae matan

U
i)

Jame Deveb ensysho 6 bea! beast ia ok

78

that flows in the direction of the wind, according to the
rule that the lighter water shall be on the right-hand side
of the current. Warm water placed adjacent to the coast by
other means, such as that developed by the outfalls in Santa
Monica Bay, also results in currents of this nature.

Now consider a wind with the coastline on the left of
the direction of travel. Light and warm water is necessarily
transported away from the coast and is replaced by denser
and colder subsurface water. This process, which is know as
upwelling, also leads to an altered distribution of density
to which a current flowing in the direction of the wind
corresponds.

Each of these wind effects occurs in Santa Monica Bay
and is instrumental in developing water motion which can be
readily identified by horizontal temperature patterns. In
Many instances, it can be shown that the flows along isotherms
are directly related to wind directions, but modifications
occur which are not so easily interpreted. Other factors,
therefore, must be effective in modifying the density flows.

Tidal Currents. Tidal currents do not bring about the
transport of water over large distances. They vary from one
locality to another, depending upon the character of the tide,
the depth to the bottom, and the configuration of the coast,
but in any given locality they repeat themselves as regularly
as the tides to which they are related. The most important
aspect of the tidal currents in coastal areas is that they
contribute greatly toward the stirring of water layers. Be-

- cause of their minor effect on net water motion, they frequently

are obscured by the forces of density slopes.

ont et gatineson ibniw oat Me 0: 0 | ;
obhe: baad 8dgta ‘ant Cael ‘Lie asta “7

Sa seaoo’ ont: “ie tinboet be beoeigq 2od awe wat

jo Steh oft wo onkibrands reed ike bakw ry abbas
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sevb vd Deon gee ek bag teaod “oat nom ame

as wort ok Hdokdw ,etenosg @bAT s2etew Son tovadeat
a 7 / yiiaensh te woktodiareib bevetta ae ot abaol oaks a.

' ixiw ett 2o noisoexkh ont ni yatwel i riox sea a

3 ¥ a
ie

ey ee
vad sokao atua® wi atns00 efootia batw seodt to de

ad aso totdw mottom x9tew gnigafeveb ah 'aisemrag

at janen tied esutgzomre? isiaesihxed xc bob thtnshie

‘ eesedtieatr seole 2wolt ott tepid gwode ad cae +t zonal
enotiantiihom tud ,enobsoe ved bakw od dota lon YLeem
paxetont s9d70 . bodtenqwerme vitesse os tow one “
,twolh vy? haash. odz quky tibestob eviteostis sd sanm. 43
eat trodes gaixd ton ob afearieo fehcT gipesasd
ang) aos yaav yes! .aeonatehh Spiral 190 aetew bl
obit, ott Yo todersada off (nogir g2t hregah rodttomare
Reod sit, Tey nodoetekbmos: eat tag ,nodtod okt of
vivetoQer) as eowl oeumaly. teoqen yodt vi dceood ayee

. daatrogek Pnor oat, a bets tsa its cas did et

o6 .eneved, retaw te gairsite, eas nurwo vite

eitneepe yan? Miciminan as: Tar Rw: tea ot fon

is ARE Se: tne Me

79

Internal Waves. Internal waves that may develop currents
are generally of tidal period. In an internal wave, one or
more density surfaces at intermediate depths remain level,
however, and the slopes that result above or below a level
surface are in opposite directions. The corresponding currents
are in opposite directions and if internal waves of different
periods are present simultaneously, a complicated pattern of
currents results. This is especially true in shelf waters
where shoaling conditions may cause the breaking and re-
development of a multitude of internal waves with several
differing periods. It is recognized that temperature patterns
in Santa Monica Bay may be frequently complicated by this

feature of the subsurface water motion.
The Temperature Distribution and Currents

Steady State Conditions

Along the Malibu coast and in the southern part of the
bay adjacent to the Palos Verdes Hills, cool water units are
nearly always present. The temperature differential between
the water nearshore at Malibu and that offshore is generally
not great and the occurrence here of this water pattern is
attributed to upwelling. At the present state of knowledge
concerning the existence of cooler water nearshore, it is
impossible to determine whether the occurrence along Malibu
represents an upward displacement of subsurface water, or a
continuously rising flow associated with upwelling or diver-
gence. Either is possible, but because of the wind patterns

in the area, it is more likely that an intermittent upward

staan olson wa Naess ae td taavsty, ips wait s

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itera: en betas hail Staibunay tek hie

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a

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“oe ie oe Edasvd ont Sanka YSe GHP coAas ankle
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knot tag TIDSHIIGHH Teed Destegooasy ef +1 abo E08 i

eins ved botsailqnos eidebyees? ef van vcd pknOM

oe Po 449 ew
efaqxiwO’ baa qobpede ey een Stet ax oqueT

OLTE tira 32

ot te Sey nretsiade, add am ben hebe> wd biel odd
mas ethow rehew Loos (eae gobiov Sole ait. OF ons
costed Lettaoasd3ip ora retest site sabesag ay
vs iszago ab. rade S18 teas beat ncbtsn ta, sxodeansn :
Ok U9) Tay Adee BLT an ened ‘ggnertus Sou" wits bac, °}
4 Doge, sided Yo ta a. dries ort. 7A gat i owger my

F ; ib T BR
phe ite 920 dineen staal Fo toe9 to, some relies ont aa

HIE Reig) fodnaaepee ‘auth tedtodw oniaréitet of ‘oldie

0 Smw 6 Ls youd Mo ) tasmboataetn a Ha

i eg huss ey

80

flow occurs. Whatever the action, the mechanism is unimpor-
tant to this discussion.

The cold water unit in the southern part of the bay is
usually most intense along the western shore of the Palos
Verdes Hills. Frequently its extent is minor and the tempera-
ture differential between it and adjacent water units is great.
At’ such times it is close to shore with a steep thermal gradient
separating it from the offshore water. At other times, the
unit spreads into the bay and along the coast as far north as
Redondo. Both temperature differentials and gradients are
small during such an expansion.

The existence of these cold water units almost contin-
uously throughout the year establishes thermal conditions which
do not occur in any other parts of the bay. The occurrence
along the Malibu coast is easily explained by the dominant
westerly winds with resultant upwelling action. That along
the Palos Verdes shore is not likely due to wind action because
the orientation of the coast to the winds is such that surface
water should be eae toward the shore rather than away.

There appear to be two possible explanations for this
cooler Hes. It is known that unusually rugged topography
on the sea floor in'’shallow water areas can result in the
projection of subsurface water to the surface (Stevenson and
Gorsline, in press). The region of cold water in this part
of the bay fluctuates across Redondo Canyon, the shelf pro-
jection south of the canyon, and the narrow shelf adjacent to
the Palos Verdes Hills. It is not unreasonable to assume,

therefore, that tidal currents and internal waves flowing over

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: | liad soo keeusedty

tae 2h a bee v8rew taeonl be ‘baw $f weawt ocd 1skanoei
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1 ‘

‘Ae

taan tet add wd be atelqae Vik eR? zk P2K00 ode Lem
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Seveoed mohton baiw of ovb vindtl toa at ssote zobre¥ |

Soe tiee tent dows eh ber bee odh OF tegos ont 3
eaniee msl? rodtex exoge out bréwod beroovth sd bt
Stan uo? anak nan tex Sfdratog ows od of teeqie ‘oa0m
i) ydqs tyaqot ORAS x vilasavme teds nwo BL! Fa wae .

att mi tisgou wad eeete tetew wolleds nt ‘yool? weer

ae
if
brs OAs te) Con Tae) ae ood catew ane teddy a; Fo 08:

tay whey nh Reta tik 26) Botgen sft > (aeerq. mz aa
“ray Rete eet woes WODMODOR: Baer oi) Sota our "vad
of teesnt bs Pepi o'rxsn aes baw eee ah oat Yo roe

ePRiit 9B bis oidunoe horny son at sith -eLRit

81

these extreme variations on the sea floor could cause the
surface projection of cooler water. On the other hand, it
might be unreasonable to assume steady state conditions, for
certainly variations in the periods of tides and internal
waves would be sufficient to cause marked differences in the
occurrence of the water unit. Such variations may be why the
varying intensities as noted do occur.

Another contributing agency to the cold water area may
be from the more or less constant flow of water out of the
bay to the south. Flushing of the shelf water occurs normally
by this current, which is established by water conditions with-
in the bay rather than by those that may exist along the
southern border. A constantly moving current here would of
necessity require the existence of cooler water on the left
of its course, i.e., adjacent to the shore. Because the
current originates in the bay, as an overflow condition, for
example, the temperature slopes noted would be developed as
a consequence of the flow. Thus, varying conditions within
the bay, causing varying current flows to the south, would
result in considerable variation in the cold water unit.
Annual Variations

Surface Water. There is a seasonal cycle in the distri-
bution of water units, but it is more indicative of two rather
than four seasons. The major distinction between the two
seasons is the location of cold water units with respect to
the Santa Monica-Redondo coast. In the colder months of the
year, November through May, the water three miles or more from

shore iS warmer than that inshore. The reverse is true in the

y agjencs8 ity es aetaw ystooo, to es
4 otdsnol

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beam: ‘oxeed ot dent ok tie: ge

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tine agtew ott 0:

oe safe ard vy gittt ‘anokd oe OF sini
+ wIOIe ‘ob toto: 28 eskhhens

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sotuwAbede sat te ankden lt aan

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“phtanzon StI RO .

withw eaokiihnes +otew yd bede
xo vam tant etods we watt xedtex! rat

ont geole 7@
me wail

. io ayen, Tas iar gakvow qitie3 2no> A

bignw
whet od? no 2otaw salo0o te gnasteixe ont oxkupe

‘enoda sd? od tassatbr ..o-8 oem

add, gaused
oo woltxevo me ep tad oft ai -ovanbaks

‘ok Sete k a
gveab, od biwow betos aaqote surt sx sqnet out

F ae bagot
yeuret ‘ieee LY ont tov ®

mths M8 gaorikbaoo geneiey |
a add oF ewo i? tievauo vatvisy Bekewes

o\de2ebkeae

biuow gMteo
sti sodaw hoo oat ani @oktat/s2*

6 ant af) PLOTS Lamoee oe @ ok waa, satel 938
vane vstaw |

nkided®
*t owt to) ovisaok hak anon #h th ted
crt ec apowtad: aobronis nk neler itt
debe’ afin. aehew bor to , sutnaeh et

29S 8

Aa TIahss sin
Site: bo ahtane; soho: one me.
ne 2o hha goat natee oat

‘ aoe ane

~ patty euik aah: eb Mee vIe) ete

82

warmer months, June through October. Exceptions to this
general distribution do occur, as in March when the water was
cooler offshore, and in June when it was cool nearshore. These
differences can be ascribed to particular weather conditions
that existed at the time of the temperature survey. Obviously,
digressions from the general patterns may have occurred during
other times of the year, but were not sampled during this sur-
vey. These differences that occur from time to time through-
out the year indicate the close relationship between the water
distribution and the immediate meteorologic conditions, in
addition to the annual cycle. Nevertheless, the biannual
patterns are too regular to dismiss lightly and it is certain
that the two-season distribution is real.

The location of the major portion of warm and cold water
determines the basic direction of water motion that is con-
sequently established. This is especially true within three
miles of shore where temperature slopes are better developed
than farther offshore. Thus, a general southerly flow exists
in the winter and a northerly flow in the summer. The tempera-
tures from the data taken in April, May, and September indicate
no north or south component, and such periods could well have
occurred in other months. However, during most of the year a
water motion parallel to the eastern shore of the bay is present
and material carried shoreward must necessarily follow a devious
path, either to the north or south.

In all months there are parts of the bay where no iso-
thermal slopes are developed. There is no apparent regular

distribution of these flat thermal surfaces, except that they

vu a

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“apenas eveviué onwixegn #0) Xo outs oe: te |
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he ay eis? pabieth be tones ton oxaw tod ,xs0% ot, eile
| eiigvenitt omit 64 anes moet 10930 tant erousso tthe

nvewied gifonolteles saute od? |
t eRaet te bre: chyole m4 hee net nnn

Lgiaaeid> O07 ,ensloddrevew Vetoes fares odd)

celts ef th bow ylrdgi l webmake OF Jalogex:ootigs

Levey O£0D tae ise ie ee...
“Has eh hee moLtom totew W moktseiih otesd oat an
sort aid?iw ovat yilelaeqes ai nial “a i tdaaaen
baqolovel ated #25 aoqole piste xegus? osottw ‘snot
atetxs woLt viusdvoe Leatedag ie, en - 930s Fe
“areqms. itt smn e sult ob won? Yaaits ron & bee) ot
e¥nod herd Iwiastqee ote al + LEGA, act meat stab ont |
svam I bow Balas yer aboé ang Rane: ica atosroqaag: ftwoe 30
2 eae eey ey $e bean yak: ery eRerowol ald Cra ite vorzo’ ai)
TAneotg BE yet ods de teste mtedens OH. ws fol tareq ae
avot veh 4 wo Dhan cela is denw Sasiwotcte bobwana ta
| ek ; ae oiewos 9 ST IOg) ‘ont of
saad DOS teas TH Ua rad with he | ataeg, ny ote aatdiaom
th huge dota et wie! eee +s bege898 ot,

eat tails Myons saunenaite. Asano

83

occur offshore more frequently than inshore. There were no
instances when the entire Surface Water Unit was "flat™ through-
out the whole bay. Every month showed temperature slopes of
sufficient magnitude to be associated with water motion some-
where. In areas where the surface layer exhibits no gradients,
the wind is the dominant force contributing to water motion.
Since these surfaces occur almost exclusively seaward of a
line about three miles from shore, and since the winds here
are almost prevailing westerlies, the surface drift must be
toward shore with a slight southerly component. The angle
between the wind direction and the water motion will not be

as great as is known to occur in the open ocean, but from
experience is closer to 20°. Therefore, an average condition
in any given month would allow surface water in the outer
portion of the bay to move shoreward to the southwest until it
reached a point two to three miles from the coast where it
would be carried either to the north or to the south prior to
reaching the beach.

It is of interest to note that when flat surfaces exist
nearshore, there are always gradients offshore which rarely
indicate an easterly flow. Thus, even though drift may be
to the east inshore, the initial travel from the offshore area
will be north or south. Only a rare coincidence of water
temperature conditions result in a continuous flow to the east
of water originating farther than three miles from the coast.

Subsurface Water. The Subsurface Water Units do not show

the biannual distribution to the same degree as the surface

layers. Except for two months, June and October, colder water

oe oxw gael. oxeitvn ‘ agi? tv etait: oom

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ee

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sians ef? i gonognos Yinedsoee tosife « idiw

od jon firw cine 4 ms 29700: one fos Holtoote b hank a

most tuwd .wasoe mag 62 ah Yasou od owort re ae

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12feo off at a9fow Sonteve wollte blvow “tno nevi
ti Liver teowdtwoe off of trawesoile avon 0:
si Sredw teso>s oft mos) Balke wage? el.

at sxoinzg Atuoe sit oF 70 iyaoe sett ov

téhes sone tues told wedte Jeee A¥on ot feavwedak Fo:

Viote’ taidw soda) ho \etwolbets avew!a oun sxetlt,

nef Yat Phish dpsodd Gere yeudT 9 .wol’ rf29tem9 am

SLs Oot The) wats sgt} hea Lets beak. out .srofand sh

to4 ave te hee Rete eee & VIO. Aeon Re

Seay alt. oy Mott ehouaitae 5 mt tees ano td kbmos)
{Paes ct hort eat am ooat ited node uwitantgtae’ 3
wore, ton ob et het sensi) Bop! vara aT 2246 sons
eaten Sey ei sale ahr ea. 4d) et ef mokdadé iB

. rooaie eptos, « tada.ta bas: at

84

lay next to the shore with sufficiently strong temperature
Slopes to establish a southerly drift. However, during the
summer period, there were two months during which cold water
was nearshore in part of the bay and offshore along the rest

of the coastline. Thus, during the months when the surface
layers next to shore were consistently warm, the Subsurface
Water Unit did show marked variations from its constant pattern
in the other months.

The flat surfaces which occurred in the upper water in the
offshore area were not present in the lower layers. Only in
October were the thermal surfaces of the entire outer shelf
flat, although in all but two of the remaining months there
were low gradients in portions of the offshore area. The
inshore subsurface unit had flat topography over the entire
bay during three months, February, May, and September, and no
slopes in portions of the area in seven of the remaining nine
months. Taken as a whole, therefore, the Subsurface Water Unit
is more complex throughout the year than the surface layer, but
the annual cycle is less extreme.

Meteorologic Relationship of the Annual Distribution. The
shift in the major cold and warm water units is probably asso-
Ciated with the oscillation of the dominant winds along the
southern California coast. A dominant, but not prevailing,
northwest wind blows during the winter and even though it may
be frequently modified by frontal winds, its constancy over the
ocean is remarkable. The Santa Monica Mountains diminish the
force of these winds along the Malibu shore, but this effect

does not extend beyond the city of Santa Monica. South to about

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85

Redondo, therefore, the northwest wind causes the surface
water to be driven eicenere resulting in mild upwelling along
the coast. The upwelling action is intense because of the
broad shelf opposite the shore, so the thermal gradient is
usually gentle, the surface water nearshore rising from only
about 20 or 30 feet. Thus, the seaward flow, when it occurs,
is not strong and does not cancel water motion to the east,
although certainly it must reduce its velocity to some extent.
Under some wind conditions the surface water is driven from
the bay along the western shores of the Palos Verdes Hills.
More commonly, though, it is caught’ between Redondo and Palos
Verdes Point until a wind shift or a varying current condi-
tion causes it to be redistributed.

In the late spring the dominant wind pattern along the
southern California coast shifts to the west and southwest.
The resulting surface water flow causes warmer and lighter
water to pile up along the bay shoreline, particularly in the
southern part near Redondo (Figs. 28 and 29). The temperature
of the water is further increased by heating in the shallow
nearshore zone and the addition of heat from man-made sources
(Fig. 30). This deepens the warm surface unit and causes an
expansion seaward resulting in a gradient current flowing to
the north. Many variations in the size, temperature, location,
and intensity of the nearshore warm water obviously result
from the varying winds and the magnitude of solar insolation.
Even so, the consistency of this summer characteristic is

readily apparent.

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Figure 28.

86

Surface temperatures, August 18, 1955.

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Figure 29, Vertical temperature profile in a north-
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Point, August 18, 1955.

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88

Surface temperatures, August24, 1955.

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Seasonal Distribution

Winter. The winter season, i.e., those months when cold
water is characteristic of the nearshpre area, begins in
November and ends in May. Within three miles of the Santa
Monica=Redondo shoreline the gradient current is toward the
south, although its velocity and direction along any part of
the coast varies considerably. The nearshore area, where the
least motion results from thermal gradients, is in the central
part of the bay between Playa del Rey and Manhattan Beach.
Here flat isothermal surfaces are common and when thermal
slopes occur, they are gentile. Thus, currents due to winds
and tides are more effective and the semi-diurnal tidal
oscillations are frequently the dominant motion in a north and
south direction. There are also conditions when the extent
of the upwelling along the Malibu shore may be so great that
a cold tongue of water projects to the south causing an
easterly flowing current opposite the Santa Monica~Venice
shoreline.

The spatial distribution of the Surface Unit on November
23, 1955 exemplifies many of the conditions characteristic of
this season (Fig. 31). The 58°F temperature surface inter-
sects sea level nearshore north of Malibu and is within 15
feet of the sea surface off Palos Verdes. Offshore it deepens
to a maximum depth of 96 feet over the edge of the shelf. Any
currents generated by the isothermal slopes must be toward
shore off Santa Monica, Playa del Rey, and Redondo, and south
out of the bay opposite the Palos Verdes Hills. Southerly

drift is likely negligible or non-existent due to the gently

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Figure 31, Depth to the 58°F isotherm, November 23, 1955.

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91

sloping gradient to the east. Thus, net motion in the upper
surface layers opposite Venice and Manhattan Beach would be
strictly due to wind drift.

The topography of the subsurface water unit was similar
to the upper layer in November with temperature slopes oriented
so as to develop landward flows off Santa Monica and Manhattan
Beach, and a southerly flow out of the bay opposite Redondo
(Fig. 32). A gyral of cold water was prominent about four
miles offshore from Playa del Rey and a gyral of warm water
elongated parallel to the shore occurred over the shelf south
of Redondo Canyon. The northern gyral may have aided in
producing a seaward flow of water opposite Hyperion, but the
gradient is gentle and in that area the currents were probably
the result of minor fluctuations with tidal periods.

The least complex pattern noted during the winter period
occurred on May 23-24, 1956 (Fig. 33). That this pattern was
drawn from temperatures taken at night in the absence of wind
and solar heating may indicate a rather rapid change in the
conditions of the mixed layer from the more complex slope
systems developed in the daytime. There was no horizontal
gradient over the entire inshore area on those days and the
only semblance of slopes occurred offshore and off the Palos
Verdes Hills; both trending in a southerly direction. Water
motion in the upper layers under such conditons is controlled
by tides and winds (Fig. 34).

As with the surface unit topography, the subsurface water
had a relatively simple temperature distribution. There was

a general rise of the isotherms toward shore, but for the most

eee 1 ott ptao oe eet ote wet ot | at

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Figure 32. Depth to the 55°F isotherm, November 23, 1955.

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part the gradient was quite gentle over the entire bay (Fig.
35). Closely packed isotherms near the Palos Verdes Hills
may have been associated with a current to the south, but
the irregularity of the water adjacent to the shore from
Redondo south perhaps is more indicative of no gradient
motion (Fig. 36).

Different degrees and locations of upwelling in the
north, cold water in the south, and the magnitude of iso-
thermal slopes occured on January 18, 1956, and December 29,
1955 (Figs. 37 and 38). In January, the central and southern
pattern nearshore was similar to that in November. In the
northern part of the bay, closely packed isotherms indicated
a rather rapid flow to the south without the subsequent flow
to the east noted in November. The slight gradients in the
central part of the bay would result in slow or non-flow
conditions, with an increased southerly drift in the southern
part of the bay. Offshore, small gyrals indicative of minor
convergences and divergences occurred, but they were likely
too insignificant to be visually represented (Fig. 39). The
isothermal pattern in the north and south part of the bay in
December compared closely with that in November. However, the
isothermal slope nearshore in the center of the bay was
straight and constant for more than 10 miles, and must have
resulted in a dominant flow to the south (Fig. 40).

The subsurface water in December and January showed
dissimilarities as did the surface layers, but not to the
Same degree. Also, some of the temperature features were much

the same in the two months. For example, in both December

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and January, a subsurface convergence is indicated offshore
from Redondo (Figs. 41 and 42). In January the shoreward
moving water appeared to be dominant (Fig. 43), and in
December it was that part of the subsurface unit moving to
the south along shore which must have had the higher velocity
(Fig. 44). In each case, however, there was no reflection of
this action in the surface layers. In January, offshore
gyrals and a steep thermal slope in the northern part of the
bay matched conditions in the surface layers. The December
subsurface temperature topography corresponded to that of the
surface unit in the nearshore area amd in the north where
slopes were indicative of southerly flow along shore and a
flow towards the east from offshore.

The temperature patterns for April 25, 1956, and February
22, 1956, show two differing conditions in which water may be
brought in and out of the bay (Figs. 45 and 46). Om April 25,
water should have flowed rather gently into the bay in the
north toward Santa Monica followed by a swing to the south to
Playa del Rey, and then seaward in a southwesterly direction
opposite Hyperion. As this flow entered the area of flat
gradients in the south, any current flow should have been
due to wind drift, which in this case would have been shore-
ward (Fig. 47). In February, a similar cold water area
existed in the north, but in this instance, the isotherms were
closely packed in the central part of the bay opposite Hyperion.
Water motion should have been rather strong toward the central
shore of Santa Monica Bay followed by a turn to the south with-

in one or two miles of shore (Fig. 48). In each case, the flow

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Figure 41, Depth to the 55°F isotherm, December 29, 1955,

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Figure 45. Depth to 58°F isotherm, April 25, 1956.

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Figure 46, Depth to the 55°F isotherm, February 22, 1956.

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simulates a large gyral, but the introduction and removal of
water is restricted to only part of the bay.

The April subsurface temperature distribution was more
indicative of water motion than that in the upper layers (Fig.
49). In this month there was an indication of a divergence
opposite Playa del Rey where the isotherms showed a flow
entering from the west to within three miles of shore and
then diverging to the north and south (Fig. 50). Both of
the slopes parallel to the shore were strong and continuous,
and likely developed dominant flows out of the bay in the two
directions. The subsurface topography in February showed an
almost completely different pattern from the surface water
(Fig. 51). There was a similar packing of the isotherms in
the central part of the bay which may have resulted in a
shoreward transport, but the general motion was then to the
north following the warmer mass of water near shore (Fig. 52).
This is not an uncommon feature of the water in the bay, and
certainly must indicate the immediate reaction of the upper-
most water layers to specific meteorologic conditions.

The thermal pattern for March 21, 1956 shows the only
temperature distribution that departs from that normal to
the winter (Fig. 53). This is also ne only clear cut case
where any data show the introduction of water from the south
into the bay and the escape of water to the north. The flat
gradient offshore would allow drift toward the east to with-
in two miles of shore where the strong northerly flow was
present. Drift cards released on this day all landed to the

north of their point of origin, confirming this pattern. This

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Figure 49, Depth to 53°F isotherm, April 25, 1956.

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Figure 50. Current flow between 70-150 feet, April 25,1956.

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Figure 51. Depth to 52°F isotherm, February 22, 1956.

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Figure 52. Current flow between 100-150 feet,

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Figure 53. Depth to 56°F isotherm, March 21, 1956

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is one of the simplest thermal patterns occurring and yet is
the one showing the most striking effects of flow resulting
from thermal slopes.

Again in March there was a marked dissimilarity between
the surface and subsurface temperature topographies. Whereas
_in the upper mixed zone there was warm water offshore and
adjacent to the coast, with a cooler mass lying between, the
subsurface water was more complex in its temperature distri-
bution and the cool water was next to the coast (Fig. 54).

In this case, the water motion must have been into the bay
through the northern portion and out of the bay to the south,
almost in complete opposition to the motion in the Surface
Water Unit. As noted previously, such a condition is not
unique and is to be expected when ocean and meteorological
Situations combine to give strong thermociines and definite
wind drift patterns in the upper water layers.

Summer. The summer season, i.e., the months when the
nearshore waters of Santa Monica Bay are warmer than those
offshore, begins in June and extends through October. These
are also the months when greater differences are noted between
the surface and subsurface water units. The upper layers
during this season have dominant flows to the north with a
varying degree of fluctuation due to man-made contribution,
solar insolation, and wind. The subsurface patterns, on the
other hand, indicate northerly drift in two months, southerly
drift during another, and drifts in different directions in
the other two months. More convergences and divergences occur

in the bay waters during these months, and on the whole, the

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118

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119

temperature topographies are more complex than in the colder
months of the year. This, of course, is to be expected due
to greater density differences between the surface and sub-
surface water in the warmer season.

A typical surface is shown in Figure 55, which depicts
the 61°F isothermal surface on July 6, 1955. The normal up-
welling pattern occurred in the northern part of the bay,
indicating a flow into the area off Santa Monica. A conver-
gence was found off Venice coupled with a divergence to the
south opposite El Segundo. Water was obviously leaving the
bay to the south, and the flat gradient offshore was indicative
of wind dominance over the drift of the water. The subsurface
topography on this day had a nearly identical pattern which
shows the stability of water motion over the continental
shelf following extended periods of stable meteorological
conditions (Fig. 56).

The constant nature of the cold water along the Malibu
shore, and the variation from simple to highly complex tem-
perature surfaces that occur over short periods of time are
shown in Figures 57, 58, 59, 60, 61, 62, and 63, which show
thermal topographies for August 10, 18, and 24, 1955. On
each day, the colder units discussed previously as being in
a more or less steady state condition in the north and south
borders of the bay were dominantly present. On August 18,
the upwelling water from the north extended into the bay as
far south as Manhattan Beach; a temperature pattern which
repeated itself in March 1956. On each occasion, winds stronger

than Force 4 had blown quite steadily for the two to three pre-

- ceding days.

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129

A rather exceptional pattern occurred on the 10th of
August; a pattern which was never repeated during the remainder
of the survey. A large flat-surfaced gyral of warm water ex-
tended over the northern shelf with rather steep thermal slopes
along the east and southern borders. A similar flat gyral,
but of cold water extended over the southern shelf. Water
motion generated by this pattern would be out the center of
the bay directly opposite Hyperion. Wind drift would, of
course, be dominant over most of the bay and with a strong
west wind, the flow in the central portion would likely be
negligible.

The upper temperature topography on August 24 had no
thermal slopes of any magnitude. Nevertheless, upwelling is
still present in the north and isolated but definitive warm
areas occurred in the nearshore zone. In contrast, the sub-
surface topography was more complex and showed a definite
trend of water motion to the south. There was a pattern
directly seaward from Hyperion similar to that noted on
August 18. In this pattern, however, the thermal slopes were
more pronounced, although not as continuous; and in the absence
of movement by the wind, it is more likely that a seaward flow
existed.

The Surface Water Unit topography was similar on September
8 and 16, 1955, in that any water motion that did occur from
temperature slopes was from the southwest into the Bay (Figs.
64 and 65). The thermal slope in the offshore area on the 8th
was more pronounced than on the 16th, so it is presumed that

wind drift was less a factor of importance on the earlier date.

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Figure 64, Depth to 60°F isotherm, September 8, 1955

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132

The subsurface distribution on these two days was similar over
the outer shelf where again a flow to the northeast was indi-
cated (Figs. 66 and 67). However, over the rest of the bay
the two patterns were different; there being an irregular
gradient on the 8th and a fairly smooth slope developing a
southerly flow on the 16th. Similar conditions occurred on
September 29, 1955 (Figs. 68 and 69).

The most complex pattern of temperature distribution
gained from the data obtained during this survey is shown in
Figures 70 and 71 of the surface and subsurface topographies
on October 13, 1955. Even though it is conceivable and pro-
bable that temperature structures such as these exist, and
perhaps more frequently than is supposed, it is believed that
there were two outside contributing factors. First, the
traverse lines and the bathythermograph stations were closer
together than on any other survey. Minor variations in tem-
perature, which normally would have gone unrecorded, were there-
fore observed, particularly in the nearshore area. Secondly,
this cruise was a joint effort by the University of Southern
California and the Bureau of Sanitation. Both bathythermo-
graphs were carefully checked and all temperatures reduced to
the constant error between the surface temperature from bucket
Samples and that from the bathythermograph. Nevertheless, there
ap the distinct possibility that depth errors that are inherent
to these instruments were enough different in the two bathy-
thermographs to result in an unnatural depiction of the tem-

perature topographies. -

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Figure 66. Depth to 55°F isotherm, September 8, 1955

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However, since the northern part of the bay from the
Hyperion plant was covered by the Bureau of Sanitation, and
the southern part by the University, and since the patterns
resulting from the data in each section are continuous from
one area to the other, it appears definitely reasonable to
assume that the data as recorded are compatible and the
patterns as shown are real. Furthermore, it is believed that
had there been more opportunities when the two organizations
could have conducted other joint surveys of this nature, that
patterns of equivalent complexity would have been noted.

It is immediately apparent that the surface and subsurface
topographies were almost identical on the 13th, with the nor-
mal departures expectable from, the submarine topography and
the variations in the external forces acting on the flow of
ocean water. The center of the cold dome of water is dis-
placed to the north in the subsurface water, for example,
and the thermal slope along its eastern boumdary is more con-
tinuous and pronounced. The temperature slope indicating a
southerly flow nearshore in the surface layers is absent in
the subsurface layer chosen because the 55 F isotherm inter-
sected the sea floor seaward of the zone. Any flow estab-
lished by thermal slopes was, of course, south and out of the
bay in the offshore and southern areas. The indication of a
northerly flow in the lower layers in the central part of the
bay is not as well defined in the surface water, but the
tendency is still present. That such patterns and consequent
current Aeon can and do exist is confirmed by data from the

log of the VELERO IV on this and other days. Course corrections

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