Coastal Processes Study at Ocean Beach, San Francisco, 

CA: Summary of Data Collection 2004-2006 

By Patrick L. Barnard, Jodi Eshleman, Li Erikson and Daniel M. Hanes 

Open-File Report 2007–1217 

U.S. Department of the Interior 

U.S. Geological Survey 
U.S. Department of the Interior 

DIRK KEMPTHORNE, Secretary 

U.S. Geological Survey 

Mark D. Myers, Director 

U.S. Geological Survey, Reston, Virginia 2007 

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Barnard, P.L.., Eshleman, J., Erikson, L., and Hanes, D.M., 2007, Coastal processes study at Ocean Beach, 

San Francisco, CA; summary of data collection 2004-2006: U. S. Geological Survey Open-File Report 2007-

1217, 171 p. [http://pubs.usgs.gov/of/2007/1217/]. 

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endorsement by the U.S. Government. 

Although this report is in the public domain, permission must be secured from the individual 

copyright owners to reproduce any copyrighted material contained within this report. 

ii
Contents

Executive Summary of Major Findings..................................................................................................................................1

Chapter 2 - Beach Topographic Mapping..............................................................................................................1

Chapter 3 – Nearshore Surveys with Coastal Profiling System .........................................................................1

Chapter 4 – Image Monitoring..................................................................................................................................2

Chapter 5 – Offshore Instrument Deployments .....................................................................................................2

Chapter 6 – Surf Zone Instrument Deployments ...................................................................................................3

Chapter 7 – Multibeam Mapping..............................................................................................................................3

Chapter 8 – Grain Size Mapping...............................................................................................................................3

Chapter 9 – High-resolution Subbottom Profiles...................................................................................................4

Chapter 10 – Numerical Modeling ...........................................................................................................................4

Chapter 1- Introduction..........................................................................................................................................................5

Project Summary ............................................................................................................................................................5

Objectives.........................................................................................................................................................................5

Background .....................................................................................................................................................................5

Preliminary Findings.......................................................................................................................................................6

Prior Work........................................................................................................................................................................7

Future Work .....................................................................................................................................................................7

Report Outline..................................................................................................................................................................8

Project Support and Collaboration ..............................................................................................................................8

Chapter 2- Beach Topographic Mapping ............................................................................................................................12

Introduction ...................................................................................................................................................................12

Methodology..................................................................................................................................................................12

Results ............................................................................................................................................................................13

Seasonal Change ......................................................................................................................................................13

Storm-related Change..............................................................................................................................................13

Long-term Change ....................................................................................................................................................14

Beach Profile Analysis.............................................................................................................................................14

Dredge Disposal Monitoring...................................................................................................................................15

Empirical Model Development ...............................................................................................................................15

Discussion......................................................................................................................................................................15

Conclusions ...................................................................................................................................................................16

Chapter 3- Nearshore Surveys with Coastal Profiling System...........................................................................................29

Introduction ...................................................................................................................................................................29

Methodology..................................................................................................................................................................29

Results ............................................................................................................................................................................30

Seasonal Change ......................................................................................................................................................30

Range of Elevation Change .....................................................................................................................................31

Nearshore Bar Growth and Trough Erosion ........................................................................................................31

Discussion......................................................................................................................................................................32

Conclusions ...................................................................................................................................................................32

Chapter 4- Image Monitoring ..............................................................................................................................................45

Introduction ...................................................................................................................................................................45

Methods..........................................................................................................................................................................45

iii
Results ............................................................................................................................................................................46

Time-averaged Images............................................................................................................................................46

Sandbars ....................................................................................................................................................................46

Rip Currents ...............................................................................................................................................................47

Time-stack Images ...................................................................................................................................................47

Discussion......................................................................................................................................................................49

Conclusions ...................................................................................................................................................................49

Chapter 5-Offshore Instrument Deployments .....................................................................................................................57

Introduction ...................................................................................................................................................................57

Methodology..................................................................................................................................................................57

Results ............................................................................................................................................................................58

Currents ......................................................................................................................................................................58

Waves .........................................................................................................................................................................59

Discussion......................................................................................................................................................................60

Conclusions ...................................................................................................................................................................61

Chapter 6-Surf Zone Instrument Deployments ...................................................................................................................85

Introduction ...................................................................................................................................................................85

Methods..........................................................................................................................................................................85

Currents ......................................................................................................................................................................85

Waves .........................................................................................................................................................................86

Results ............................................................................................................................................................................86

Discussion......................................................................................................................................................................87

Conclusions ...................................................................................................................................................................88

Chapter 7-Multibeam Mapping.........................................................................................................................................100

Introduction .................................................................................................................................................................100

Methodology................................................................................................................................................................100

Results ..........................................................................................................................................................................101

Overview...................................................................................................................................................................101

Massive Sand Waves of the Golden Gate..........................................................................................................101

Offshore Ocean Beach ..........................................................................................................................................102

Dredge Disposal Monitoring.................................................................................................................................102

Discussion....................................................................................................................................................................103

Future Work .................................................................................................................................................................103

Conclusions .................................................................................................................................................................104

Chapter 8-Grain Size Mapping ..........................................................................................................................................116

Introduction .................................................................................................................................................................116

Methodology................................................................................................................................................................116

Results ..........................................................................................................................................................................116

Discussion....................................................................................................................................................................117

Conclusions .................................................................................................................................................................117

Chapter 9-Other Field Data Collection ..............................................................................................................................121

High-resolution Subbottom Profiles of Active Faults and Sediment on the Golden Gate Platform.............121

Chapter 10-Numerical Modeling.......................................................................................................................................126

Introduction .................................................................................................................................................................126

Methods........................................................................................................................................................................126

iv
Model Overview ......................................................................................................................................................127

Grid and Boundary Conditions..............................................................................................................................127

Time Step..................................................................................................................................................................129

Bathymetry...............................................................................................................................................................129

Calibrations and Parameter Settings ..................................................................................................................129

Tide Constituent Calibrations............................................................................................................................129

Constant Parameters..........................................................................................................................................130

Comparison of Model Results with Field Data...................................................................................................130

Water Levels and Wave Parameters ..............................................................................................................131

Longshore Currents ............................................................................................................................................131

Cross-shore Currents .........................................................................................................................................131

Results ..........................................................................................................................................................................132

Flow Patterns at the North End of Ocean Beach ..............................................................................................132

Variable Wave Impact Along the Beach ............................................................................................................132

Influence of Offshore Wave Direction ................................................................................................................133

Dredge Disposal Modeling....................................................................................................................................134

Conclusions .................................................................................................................................................................134

Acknowledgements ...........................................................................................................................................................152

References Cited ...............................................................................................................................................................153

Appendix ............................................................................................................................................................................158

Publications and Other Resources..........................................................................................................................158

Publications .............................................................................................................................................................158

Online Resources....................................................................................................................................................159

Research Featured in the News...........................................................................................................................159

Field Activity IDs and Web Links..............................................................................................................................161

v
Figures 

Figure 1.1. Map of the study area included in the San Francisco Bight Coastal Processes 

Study, and the focus site for the Ocean Beach Coastal Processes Study (green box). .....10

Figure 1.2. Map showing the Ocean Beach Coastal Processes study area, including the 

locations of the existing dredge disposal site (SF-8) and test dredge disposal site (Ocean 

Beach Disposal Site)........................................................................................................................11

Figure 1.3. Erosion south of Sloat Blvd. at Ocean Beach during 1997-98 El Niño winter (image 

courtesy of Surfrider). The Great Highway is to the left............................................................11

Figure 2.1. ATV set up for conducting topographic beach surveys using Differential GPS........16

Figure 2.2. Typical data coverage (middle panel) and resulting grid (right panel) at the northern 

end (Reach 1) of Ocean Beach, from the November 15, 2004 survey.....................................17

Figure 2.3. Map of the reach locations referenced in the analysis of beach topographic data. 

The area of chronic erosion is labeled. ........................................................................................18

Figure 2.4. Beach volumetric fluctuations above 0.5 m (NAVD88) from 

April 2004 to June 2006. ...................................................................................................................18

Figure 2.5. Cumulative beach change above 0.5 m (NAVD88) from April 2004 to June 2006. .....19

Figure 2.6. Winter change (MHW line) during the 1997-98 El Niño compared to the winters of 

2004-05. Profiles are spaced 50 m apart and numbering increases from north to south....19

Figure 2.7. Beach change in the Sloat Blvd. (main east-west street pictured) region between 

December 2004 and January 2005.................................................................................................20

Figure 2.8. Short-term beach change associated with a significant wave event (offshore wave 

heights reached six meters) at Ocean Beach in March 2005 as compared to the month 

prior. A) Northern Ocean Beach (Reach 1). B) Southern Ocean Beach (Reach 7)..............21

Figure 2.9. Alongshore shoreline change from two storms in 2005. Gaps in the data indicate no 

data and/or no MHW shoreline accessible.................................................................................23

Figure 2.10. Shoreline change since LIDAR data was collected in 1997-98. The red line 

represents the rate as determined from the fall beach (October 1997 - October 2004). The 

blue line represents the rate as determined from the spring beach 

(April 1997 - April 2006). ...................................................................................................................23

Figure 2.11. Average values of a) swash beach width, m b) swash sediment storage m2 and c) 

swash beach slope averaged over the profile for each individual profile and also by reach 

plotted on local bathymetry. ...........................................................................................................24

Figure 2.12. Seasonal averages of beach slope for each profile at Ocean Beach.......................25

Figure 2.13. Beach change during the dredge disposal monitoring period, as compared to 

2004. A) Northern Ocean Beach (Reaches 1-2. B) Southern Ocean Beach (Reaches 5-7) 

and average vertical change totals for entire beach study area. ...........................................26

Figure 2.14. Empirical relationship between the wave direction (Dp) and beach volume change 

at Reach five during the storm surveys of winter 2005-06. The blue line represents a 

horizontal line that goes through the mean of the mean volume change data. The solid red 

line is the best fit to the data based on the multiple regression equation. The dashed red 

curves are the 95% confidence interval curves. The correlation variance r2

=0.687............28

Figure 3.1. Third generation Coastal Profiling System in action. ....................................................33

Figure 3.2. Ocean Beach CPS survey profiles. ...................................................................................34

Figure 3.3. Ocean Beach cross-shore profiles 1- 4. ..........................................................................36

vi
Figure 3.4. Ocean Beach cross-shore profiles 5 - 8. .........................................................................37

Figure 3.5. Ocean Beach cross-shore profiles 9 - 12. .......................................................................38

Figure 3.6. Ocean Beach cross-shore profiles 13 - 16. .....................................................................39

Figure 3.7. Ocean Beach cross-shore profiles 17 - 18. .....................................................................40

Figure 3.8. Grid difference plots showing elevation change between surveys a) February, 

2006- November, 2005 b) May, 2006 – February, 2006 c) November, 2006 – May, 2006 d) 

December, 2006 – November, 2006. ..............................................................................................41

Figure 3.9. Calculations from all survey data available of a) standard deviation of elevation 

with mean elevation contours b) mean elevation (dredge disposal site and erosion 

hotspot in magenta)..........................................................................................................................42

Figure 3.10. Definition sketch for volume of bar growth and trough erosion calculations using 

profile five. The blue section shows the calculated volume of bar growth and the red 

section shows the volume of trough erosion. .............................................................................43

Figure 3.11. Variation in a) volume of bar growth and trough erosion and b) volume of bar 

growth and trough erosion per meter profile length for profiles 1-16, 18 along Ocean 

Beach..................................................................................................................................................44

Figure 4.1. Digital camera and video system on the top of the Cliff House Restaurant...............50

Figure 4.2. Aerial image showing camera’s field of view, in situ instrument locations (ADCP as 

a red square and Aquadopps as circles), CPS survey profiles (blue east-west oriented 

lines), and time-stack transects (yellow lines). Aerial image pt_bonita_se.tif, 08/25/1993.51

Figure 4.3 Typical images used for analysis: (a) unrectified time-averaged image, (b) rectified 

time-averaged image, and (c) time-stack image. .......................................................................52

Figure 4.4. Break points observed in time-averaged images plotted on cross-shore profile 

measured with the CPS. ..................................................................................................................52

Figure 4.5. Locations of dominant rip currents at the north end of Ocean Beach.......................53

Figure 4.6. Seasonal distribution of observed rip current occurrence at any of the four 

locations at the north end of Ocean Beach.................................................................................54

Figure 4.7. Typical 17 min tide detrended time-series illustrating the dominant infragravity 

component (transect T3 on 06/24/05, 10:09 to 10:23 am)............................................................54

Figure 4.8. Total energy density, averaged over ten subsequent 17 minute time-periods, 

measured at each cross-shore transect. The heavy solid line is the best linear fit through 

T3 over 0.03 to 0.1 Hz. Dashed vertical line is cutoff between infragravity and sea swell 

frequencies........................................................................................................................................55

Figure 4.9. Measured runup statistics versus (a) Hunt’s significant runup formula (1959), and 

(b) 2% exceedance using Ruggiero and others (2004) formulation. Both are shown 

with T=Tmo2. .........................................................................................................................................56

Figure 5.1. Instrument deployment sites at Ocean Beach................................................................64

Figure 5.2. Photographs of typical instrumented tripods deployed at a) Sites 1-3 and b) 

Sites 4-5. .............................................................................................................................................65

Figure 5.3. Water density calculated for Site 3 during winter 2006 deployment..........................65

Figure 5.4. Principal axis calculations for depth-averaged current measurements at a) Site 1 

summer 2005 b) Site 2 summer 2005 c) Site 3 summer 2005 d) Site 4 summer 2005 e) Site 3 

winter 2006 f) Site 5 winter 2006.....................................................................................................66

vii
Figure 5.5. Flow patterns measured at Ocean Beach throughout a tidal cycle on 06/25/05 

during the summer 2005 deployment. Plot a) shows the measured tide at Site 1; points 

and text refer to measured currents in plots b) through i). Depth values are shown by 

colored contours and currents at different vertical locations have colored arrows. .........69

Figure 5.6. Flow patterns measured at Ocean Beach throughout a tidal cycle on 01/28/06 

during the winter 2006 deployment. Plot a) shows the measured tide at Site 3; points and 

text refer to measured currents in plots b) through i). Depth values are shown by colored 

contours and currents at different vertical locations have colored arrows. ........................72

Figure 5.7. Current profile plots through time for summer deployment at Site 1 a) eastward 

velocity b) northward velocity. (Note that this is a different time period than the other 

plots and only 4 days since the instrument was buried.) ..........................................................73

Figure 5.8. Current profile plots through time for summer deployment at Site 2 a) eastward 

velocity b) northward velocity........................................................................................................74

Figure 5.9. Current profile plots through time for summer deployment at Site 3 a) eastward 

velocity b) northward velocity........................................................................................................75

Figure 5.10 Current profile plots through time for summer deployment at Site 4 a) eastward 

velocity b) northward velocity. (Note the different scale on both axes from previous plots 

because of more onshore directed flow at Site 4). ....................................................................76

Figure 5.11. Current profile plots through time for winter deployment at Site 3 a) eastward 

velocity b) northward velocity........................................................................................................77

Figure 5.12. Current profile plots through time for winter deployment at Site 5 a) eastward 

velocity b) northward velocity (Note the different scale on both axes from previous plots 

because of more onshore directed flow at Site 5). ....................................................................78

Figure 5.13. Direction histograms for Point Reyes CDIP buoy #029 by month for all available 

wave data measured from 1996 through 2006 (N is number of observations out of a total 

156,828, the percentage is for the total data that occurred in that month, and hm is the 

maximum wave height for the month which came from a direction marked by the solid 

black line) (SCRIPPS Institution of Oceanography, 2006). ........................................................79

Figure 5.14. Wave parameters calculated from measurements during summer 2005 

deployment at Sites 1 – 4 a) significant wave height b) peak wave period c) peak wave 

direction..............................................................................................................................................80

Figure 5.15. Wave parameters calculated from measurements during winter 2006 deployment 

at Sites 3 and 5 a) significant wave height b) peak wave period c) peak wave direction. .81

Figure 5.16. Polar plots of wave direction and height for the a) summer 2005 deployment and 

b) the winter 2006 deployment. (Note the different radial axis due to larger wave heights 

in the winter)......................................................................................................................................82

Figure 5.17. 1-D Spectral evolution through time from measurements during summer 2005 

deployment for a) Site 1 b) Site 2 c) Site 3 d) Site 4....................................................................83

Figure 5.18. Spectral evolution through time from measurements during winter 2006 

deployment for a) Site 3 b) Site 5. ..................................................................................................84

Figure 5.19. Estimated longshore transport (Q) from CERC equation for Sites 1-3 along Ocean 

Beach (Note the difference in units along the y-axis)...............................................................84

Figure 6.1. Overview of Aquadopp instrument deployments (01/23/06- 01/27/06). Data was not 

recorded at sz9 and the northern ADCP (Site1). .........................................................................90

viii
Figure 6.2. Aquadopp frame setup and surf zone deployment scheme: (a) deployment 

schematic, and (b) photo of instrument and frame. ...................................................................91

Figure 6.3. Measured water depth and vertical current structure measured with Nortek 

Aquadopps during the surf zone field study. Data shown are for complete tide cycles 

(depending on data availability) for measurement sites from north to south (sz1 through 

sz8); u-directed: east-west with east positive, v-directed: north-south, with 

north positive.....................................................................................................................................97

Figure 6.4 Maximum depth averaged currents measured in the surf zone at the north end of 

Ocean Beach during a complete tide cycle (Jan 24-25, 2006). ................................................98

Figure 6.5. Variations of the breaking parameter with tide level at the north end of Ocean 

Beach. Upper plot (a) shows concurrently measured offshore wave conditions at ADCP 

Site 5. Lower plot (b) shows calculated breaking parameters for surf zone measurements 

at sz1 through sz4 and measured water depth at sz1. Dashed horizontal line is the 0.78 

breaking ratio. ...................................................................................................................................99

Figure 7.1. Shaded relief image showing the multibeam coverage area from the 2004-2005 

survey and the location of sand wave migration surveys in the Golden Gate. ...................105

Figure 7.2. Change between bathymetric surveys conducted in 1956 and 2005.........................106

Figure 7.3. A) Bedform orientation based on sand wave orientation, and B) dominant sediment 

transport direction as inferred from bedform shape asymmetry...........................................107

Figure 7.4. Map of bedform A) wavelength and B) height, gridded to 50 m cell resolution. .....109

Figure 7.5. View of the giant sand waves at the mouth of San Francisco Bay (from Barnard and 

others, 2006a). View is to the east toward San Francisco Bay. The Golden Gate Bridge is 

approximately 2 km (1.2 mi) long. Shaded relief image created with a 2-m grid, 4x vertical 

exaggeration, sun azimuth of 240 degrees, and sun angle of 66 degrees. The land 

topography was generated by overlaying digital orthophoto quadrangles (DOQs) on USGS 

digital elevation models (DEMs), with a 2x vertical exaggeration. Bathymetry data inside 

the Bay (that is east of Golden Gate Bridge) is from Dartnell and Gardner (1999). Golden 

Gate Bridge model courtesy of Interactive Visualization Systems. ......................................111

Figure 7.6. Oblique view of the giant sand waves at the mouth of San Francisco Bay (from 

Barnard and others, 2006a). View is south across the Golden Gate toward Baker Beach 

and the city of San Francisco. See Figure 7.5 for more image information. ........................112

Figure 7.7. Diverse sand waves at the mouth of San Francisco Bay, seaward of the Golden 

Gate Bridge. Shaded relief image created with 5x vertical exaggeration, sun elevation of 

45 degrees, and sun azimuth of 45 degrees. (A) Irregular sand waves seaward of the main 

sand wave field. (B) Ebb-dominated sand waves with wavelengths as great as 150 m with 

superimposed sand waves of 5 m to 10 m wavelength. (C) Linguoid sand waves, 20 m to 30 

m in wavelength. (D) Flood-dominated sand waves, 15 m to 20 m in wavelength, just 

offshore of Baker Beach. ..............................................................................................................113

Figure 7.8. Overview of large sand wave field and high resolution difference map of two 

surveys approximately 21 hours apart illustrating both large-scale and small-scale sand 

wave migration and orientation. Migration is from right to left. ...........................................114

Figure 7.9. Multibeam survey from 2004 showing A) alongshore migrating bedforms, B) 

onshore-directed bedform morphologies north of the disposal site, and C) intense scour 

associated with the outfall pipe, the approximate site of the June 2005 dredge disposal 

(from Barnard and others, 2006b). ...............................................................................................115

ix
Figure 8.1. Location of beach sediment samples along Ocean Beach, from the May 2004 

survey. The profile locations are labeled...................................................................................118

Figure 8.2. Sediment sample locations at the mouth of San Francisco Bay in summer 2005, 

along with Oceanside Biology Laboratory (OBL) sample stations. .......................................119

Figure 8.3. Median grain size of swash samples from 3 surveys along Ocean Beach..............119

Figure 8.4. Median grain size along five profiles from the May 2004 survey...............................120

Figure 8.5. Grid of grain size class at the mouth of San Francisco Bay, using the both OBL and 

USGS samples.................................................................................................................................120

Figure 9.1. Trackline map of subbottom data collected on the Lakota in late September 2006 

(for more cruise information: http://walrus.wr.usgs.gov/infobank/l/l106sf/html/l-1-06-

sf.meta.html). Thin black lines correspond to CHIRP profiles; wider gray lines to minisparker profiles. Locations of Figures 9.2 and 9.3 are shown by bold black line. BBolinas, GG – Golden Gate, FF – Fort Funston...........................................................................123

Figure 9.2. Mini-sparker profile GG-30 collected offshore of Fort Funston showing folded and 

disrupted reflectors associated with the San Andreas Fault (SAF). M - water bottom 

multiple; TWTT- two-way travel time..........................................................................................124

Figure 9.3. Mini-sparker profile GG-9b collected across a fault-bounded graben located 

southwest of Bolinas. The dots show the base of the graben, which contains over 50 m of 

sediment. M - water bottom multiple; TWTT- two-way travel time; SGF – San Gregorio 

Fault; SAF - San Andreas Fault; GGF – Golden Gate Fault. .....................................................124

Figure 9.4. Map of the Golden Gate platform that shows thicknesses of acoustically 

transparent sediment of inferred Holocene age. These sediments are interpreted to be 

primarily composed of ebb-tidal delta deposits. The contour lines delineate sediment 

thicknesses that are greater than 10 m. The red lines show offshore fault traces. The 

gray lines show the locations of profiles used to map the acoustically transparent unit.125

Figure 10.1. Curvilinear grids used for the FLOW and WAVE modules (a) and FLOW grid with 

boundaries (b). ................................................................................................................................136

Figure 10.2. Final gridded bathymetry (positive depth in meters relative to mean sea level)...137

Figure 10.3. Measured and modeled water levels: (a) Site 2; (b) Site 3. Blue circles are 

residuals (measured - modeled). .................................................................................................138

Figure 10.4. Comparison of measured and modeled significant wave heights (Hs

). Note the 

residual (blue diamonds) y-axis on the right. ............................................................................139

Figure 10.5. Comparison of measured and modeled longshore currents (a, b) and cross-shore 

currents (c, d) at Sites 2 and 3......................................................................................................140

Figure 10.6. Flow patterns at the north end of Ocean Beach. Plot (a) shows the measured tide 

at Site 2; points and text refer to snap shots of model results in plots (b) through (m). 

Open circle is Site 1 sampling station. Flow directions are shown with arrows while 

current speeds (m/s) are shown with the color scheme. White horizontal lines in plots 

g,h, and i indicate rip current observations from time-averaged images (Chapter 4).......143

x
Figure 10.7. Eddy position as a function to tide stage. Based on analysis of model simulation 

slightly shorter than one month, the southern most point of the eddies reach to about N 

4.179E6, which coincides with PWC transect 5 (a). Approximate eddy center locations 

are plotted against the tidal stage in (b) and (c) (note that the axis of the Eastings and 

Northings are switched ease of geographic considerations). Central Easting position only 

moves slightly with positive tide levels, while at negative tides (corresponding to the 

spring cycle), the position moves as much as 1 km in the east-west direction. With 

respect to the right-hand Figure, the eddies appear to move about 1 km in the north-south 

direction with the tide, such that the eddies appear further south with lower tide stage.

............................................................................................................................................................144

Figure 10.8. Evidence of rip currents at N4180.63 km, which coincides with ‘rip 3’ as seen with 

time-averaged images (see Chapter 4). Plot (a) shows model predicted flow patterns 

along Ocean Beach; plot (b) shows measured tide at Site 1 and, with the red circle, the 

time-step of (a). ...............................................................................................................................145

Variation in line density is due to grid cell spacing. ..............................................................146

Figure 10.11. Along-shore variation of estimated long-shore sediment transport (m3

/day per 

along-shore unit width). The thick red lines bound the erosion ‘hot spot’...........................148

Figure 10.12. Modeled significant wave height values at Ocean Beach with parameterized 

forcing of Hs

= 4m and a)Tp= 10 sec, Dp=330 deg b) Tp= 10 sec, Dp = 280 deg c)Tp= 20 sec, Dp= 

330 deg d)Tp= 20 sec, Dp= 280 deg................................................................................................149

Figure 10.13. Modeled peak wave direction values at Ocean Beach with parameterized 

forcing of Hs= 4m and a)Tp= 10 sec, Dp=330 deg b) Tp= 10 sec, Dp = 280 deg c)Tp= 20 sec, 

Dp= 330 deg d)Tp= 20 sec, Dp= 280 deg. ....................................................................................150

Figure 10.14. Residual transport of the dredge disposal mound with tidal forcing only (a) 

Residual transport of the dredge disposal mound with tidal and wave forcing, illustrating 

the importance of wave shoaling in the onshore migration of the 

disposal material(b)........................................................................................................................151

xi
1

 

Coastal Processes Study at Ocean Beach, San 

Francisco, CA: Summary of Data Collection 2004-

2006 

By Patrick L. Barnard1, Jodi Eshleman2, Li Erikson3, and Daniel M. Hanes4

Executive Summary of Major Findings 

Chapter 2 - Beach Topographic Mapping 

• Beach volume at Ocean Beach varies seasonally over a maximum envelope of 

400,000 m3

. 

• The El Niño winter of 1997-98 caused double the average shoreline retreat than 

the more typical 2004-05 winter at Ocean Beach. 

• Shoreline retreat can exceed 20 m during severe winters, with localized retreat 

over 70 m. 

• Single storm events can cause an average shoreline retreat of over ten meters and 

remove over 100,000 m3

 of sediment from the beach. 

• Since the 1997-98 airborne LIDAR surveys, there has been a trend of accretion at 

the north end of Ocean Beach (Reach 1 shoreline change rate= +2.1 m/yr) and 

continued erosion at the south end (Reach 5-6 shoreline change rate= -1.1 m/yr). 

• Preliminary findings from storm response surveys indicate a potentially strong 

correlation between wave height and direction with beach response. 

• The shape of the ebb tidal delta exerts a first order control on decadal scale 

morphology changes at Ocean Beach. 

Chapter 3 – Nearshore Surveys with Coastal Profiling System 

• Comparisons of bathymetric profiles show patterns of seasonal bar migration 

onshore in the summer and offshore in the winter. Bars can be as high as two 

meters and move several hundred meters in the cross-shore. 

• A shorter-term survey after one month suggests that a few winter storms can force 

offshore bar migration on the order of 100 m. 

• Comparisons of elevation change throughout all surveys suggest a range in depth 

of closure from 15 m at the north end to a shallower 10 m at the south end. This 

1

 Research Geologist, Coastal and Marine Geology Team, Santa Cruz, CA, pbarnard@usgs.gov 

2

 Coastal Engineer, Coastal and Marine Geology Team, Santa Cruz, CA, jeshleman@usgs.gov 

3

 Coastal Engineer, Coastal and Marine Geology Team, Santa Cruz, CA, lerikson@usgs.gov 

4

 Research Oceanographer and Project Chief, Coastal and Marine Geology Team, Santa Cruz, CA, 

dhanes@usgs.gov 
analysis suggests that the dredge disposal site is too deep for significant crossshore transport of sand to occur. 

• An order of magnitude estimate of offshore bar growth from measured 

bathymetric profiles suggests 2 million m3 (2.6 million cubic yards) of sand is 

moving in the cross-shore to form nearshore bars. 

Chapter 4 – Image Monitoring 

• Wave-breaking locations deduced from time-averaged images agree with those 

from bathymetric data obtained with the CPS. 

• Time-averaged images show that multiple breaking locations are common along 

Ocean Beach. It is not clear if both of the breaker locations were associated with 

bars, or if the inner location was simply due to depth-limited breaking. 

• Four rip currents occurred seasonally at the north end of Ocean Beach with a 

spacing of 150 m to 200 m. 

• Analysis of time-stack runup data shows that the beach was dissipative under 

typical summer conditions with infragravity conditions dominating and swash 

periods on the order of a minute. 

Chapter 5 – Offshore Instrument Deployments 

• Current magnitudes are much greater along the northern portion of Ocean Beach 

due to the proximity of the mouth of the bay (root mean square values of depthaveraged currents were 50% greater at Site 1 than at Site 3), but wave energy is 

much greater along the southern portion (mean wave height was 15% greater at 

Site 3 than at Site 1) where erosion problems are greatest. 

• The gradients in current speed along Ocean Beach varied with the tide, where 

northern currents speeds were greater on the flooding and high tides and southern 

current speeds began to dominate on the ebbing and low tides. 

• Current directions along Ocean Beach were shore-parallel, whereas the offshore 

sites show principal axes shifted more east-west, with an increasing eastward 

magnitude of flow with increased northing and proximity to the mouth of the bay. 

• In the along-shore direction, vertical gradients in current magnitude of northsouth directed currents increased with increasing distance from the inlet; variation 

in current magnitude throughout the water column was greatest at Site 3. Eastwest currents show a relatively stronger vertical decay due to the influence of 

wave-induced currents. At the offshore sites (Sites 4 and 5) vertical gradients 

were apparent for both the north-south and east-west currents, and Site 4 had 

current reversal with a changing tide. 

• Refraction patterns across the delta oriented waves with an onshore direction 

around 270o in a more southwest direction as they propagated into shallower 

water. 

• Calculations of alongshore transport using wave measurements at Sites 1-3 and 

the CERC equation indicate the direction of transport was north in the winter at 

Site 3 and suggest that a nodal point existed somewhere between Site 2 and Site 3 

during the summer. 

2
Chapter 6 – Surf Zone Instrument Deployments 

• Analysis of surf-zone current data shows that instantaneous flows (O(50 cm/s)) 

occur in both the cross-shore and along-shore directions. 

• Simultaneous cross-shore current data show that flow direction and variation of 

relative speeds were correlated in time, suggesting that there was strong 

uniformity in cross-shore currents, but that the speeds were greater in the outer 

surf zone. 

• Simultaneous along-shore current data suggest that the maximum northward 

oriented tidal currents are stronger than southward currents but also that there is a 

cross-shore variation of the longshore currents such that the southward oriented 

currents are stronger further inshore. 

• There is little vertical current structure in the surf zone except near the bottom 

during high tide in east-west directed currents. 

• North-south currents within the surf zone reversed from a southerly directed 50 

cm/s flow during ebb-tide to an equally strong northward flow at low tide. Eastwest currents were also tidally driven but were slightly slower (35 cm/s to 45 

cm/s). 

• With varying tide levels and offshore wave conditions on the order of Hs

=1.5 m, 

the outer limit of the surf zone moved more than 40 m in the cross-shore direction 

with energy dissipation widths exceeding 20 m. 

Chapter 7 – Multibeam Mapping 

• The ebb-tidal delta at the mouth of San Francisco Bay has experienced a large 

scale erosion trend over the last 50 years. 

• Erosion of the shoals offshore of southern Ocean Beach has made the adjacent 

beach more susceptible to wave attack. 

• Large, dynamic sand waves are located in the Golden Gate and off Point Lobos. 

• Dominant sediment transport patterns outside the surf zone are controlled by tidal 

forcing, evident by the presence of alongshore migrating bedforms. 

• Bedload sediment transport is seaward through the center of the inlet and toward 

the bay adjacent to Baker Beach. 

Chapter 8 – Grain Size Mapping 

• Median grain size varies minimally along Ocean Beach during the summer with a 

d50= 0.28 mm. 

• Sediment placed in the nearshore disposal site (d50= 0.18 mm) is finer than swash 

samples (d50= 0.28 mm) collected at Ocean Beach, and thus it is not likely to be 

stable on the beach. 

• Large bodies of beach quality sand likely exist on the inner parts of the ebb-tidal 

delta at depths that could be dredged. Chapter 9 shows that a total volume of just 

over 1 km3 of acoustically transparent sediment is present. 

3
Chapter 9 – High-resolution Subbottom Profiles 

• The maximum sediment thickness of the ebb tidal delta is 16 m, with an overall 

volume of over 1 km3 of sediment. 

Chapter 10 – Numerical Modeling 

• Comparisons between measurements and model results show that the calibrated 

Delft3D model is capable of predicting hydrodynamics at Ocean Beach for 

summer conditions. 

• Model simulations predict that currents along Ocean Beach are strongest prior to 

flow reversal at both flood and ebb tides, and are strongly influenced by the 

Golden Gate entrance. 

• Along- and cross-shore currents are strongly modulated by the tide. The 

influence of the tidal inlet at the Golden Gate decreases significantly with distance 

such that the currents are about 30% stronger at the north end compared to the 

southern end of Ocean Beach. 

• The Pt. Lobos headland provides a shadow zone to the south so that nearshore 

tidal flows are weaker at ebb tide compared to areas further offshore. 

• Model results suggest that rip currents are related to tidal flows and occur near 

times of flow reversal (high and low tide). 

• Model results suggest that the longshore sediment transport is to the south during 

typical summer conditions and that the section stretching from the north part of 

Ocean Beach to immediately south of the erosion hot-spot undergoes strong 

longshore transport rates under high wave conditions (Hs>2.5m). Model results 

also suggest that the erosion hot-spot is directly impacted from shore-normal 

incident waves during storm conditions. Furthermore, the erosion hot-spot 

appears to be a result of wave focusing caused by the shape of the southern ebb 

tidal delta. 

• Long-period, shore-normal incident large waves at Ocean Beach will likely have 

the largest erosional capacity, as waves coming from the northwest tend to be 

dissipated by the northern lobe of the ebb tidal delta. Preliminary modeling 

suggests that offshore waves originating from the west undergo less energy loss 

compared to offshore waves originating from the northwest, whose wave height 

reduces by about 50% as a result of refraction over the northern lobe of the ebb 

tidal delta. 

• Numerical modeling suggests that despite the strong tidal currents in the region, 

wave forcing is the dominant factor moving the sediment slowly toward shore, 

and placing sediment at a depth of about 8 m will provide indirect beach 

nourishment. 

4
Chapter 1- Introduction 

Project Summary 

Ocean Beach in San Francisco, California, contains a persistent erosional section in 

the shadow of the San Francisco ebb tidal delta and south of Sloat Boulevard that threatens 

valuable public infrastructure as well as the safe recreational use of the beach. Coastal 

managers have been discussing potential mediation measures for over a decade, with little 

scientific research available to aid in decision making. The United States Geological Survey 

(USGS) initiated the Ocean Beach Coastal Processes Study in April 2004 to provide the 

scientific knowledge necessary for coastal managers to make informed management 

decisions. This study integrates a wide range of field data collection and numerical modeling 

techniques to document nearshore sediment transport processes at the mouth of San 

Francisco Bay, with emphasis on how these processes relate to erosion at Ocean Beach. The 

Ocean Beach Coastal Processes Study is the first comprehensive study of coastal processes at 

the mouth of San Francisco Bay. 

Objectives 

The objectives of this report are the following: 

• Provide a thorough summary of the data collection efforts conducted as part of 

the USGS Ocean Beach Coastal Processes Study, initiated in April 2004. 

• Present key findings, particularly as they may relate to pending management 

decisions. 

• Outline future research directions at the mouth of San Francisco Bay- the San 

Francisco Bight Coastal Processes Study. 

Background 

Ocean Beach is a seven kilometer long north-south trending sandy beach that 

stretches south from a rocky headland at Point Lobos to the bluffs at Fort Funston (Figures 

1.1-1.2). It is strongly affected by tidal currents from the adjacent Golden Gate, as well as 

wave refraction around the ebb-tidal delta. Ocean Beach has undergone numerous significant 

anthropogenic alterations since the late 19th century: highway construction, seawall 

construction, dune stabilization, dune removal, rip-rap emplacement, beach nourishment, 

inlet fill, etc. (United States Army Corps of Engineers, 1996). The most significant manmade feature is the 1.5 km long O’Shaughnessy Seawall at the northern end of the beach. It 

was built between 1915 and 1929 to protect the Great Highway and is arguably one of the 

more successful seawalls in the country (Wiegel, 2001). The beach has maintained a healthy 

volume of sand in front of the seawall and no significant end-around erosion has been noted. 

The seawall’s success can be attributed to several factors: it traps and prevents wind-blown 

sediment from leaving the beach system and Point Lobos acts as a natural jetty to trap the 

5
dominant northerly littoral drift, as well as return tidal flow from a strong eddy that spins off 

Pt. Lobos during the ebbing tide. 

Varying portions of the shoreline at Ocean Beach have experienced periods of erosion 

over the last century, with recent (since mid-1990) severe effects focused south of Sloat 

Blvd, in front of the San Francisco Zoo, which has destroyed and continues to threaten 

important local infrastructure (Figure 1.3). The greatest concern is the structural integrity of a 

3.6 m (12 ft) diameter sewage transport box that lies underneath the Great Highway. This 

approximately ten million dollar piece of infrastructure was exposed during the 1997-98 El 

Niño winter, and carries one third of the City of San Francisco’s treated sewage out to sea. 

Emergency rip-rap was placed in front the exposed pipe that winter, but that protection has 

steadily degraded. The City of San Francisco and the United States Army Corps of Engineers 

(USACE), San Francisco (SF) District have been formally investigating shoreline protection 

strategies since the mid-1990s (Moffatt and Nichol Engineers, 1995; United States Army 

Corps of Engineers, 1996). 

In 2004, the USGS instituted a state-of-the-art coastal monitoring program at Ocean 

Beach to provide coastal managers with scientific data to help mitigate the erosion problem. 

This program includes repeated topographic beach surveys using All-Terrain Vehicles 

(ATVs), cliff surveys using ground-based light detection and ranging (LIDAR), nearshore 

bathymetric surveys using the Coastal Profiling System (CPS), sediment surveys using a 

digital bed sediment “eyeball” camera, continuous video camera monitoring, and numerical 

modeling using Delft3D and the Nearshore Community Model (NearCoM). This program 

was further augmented by extensive field operations on the ebb-tidal delta culminating in 

winter 2006, that included over 50 days of bathymetric surveys using a multibeam side scan 

system, summer and winter physical process measurements of waves and tidal currents, and 

nearly 200 surface sediment samples. This project supports the long-term research goals of 

the USGS National Program priorities of understanding, modeling and forecasting coastal 

evolution and systems. 

Preliminary Findings 

Regular topographic beach surveys, sediment analysis, nearshore bathymetric 

surveys, and numerical modeling have begun to quantify the processes controlling this 

dynamic system. The fall 2004 multibeam survey (see Chapter 4) indicated that the ebb-tidal 

delta has been contracting since the 1950s and there has been extensive accretion on the 

southern lobe of the ebb-tidal delta at the existing dredge disposal site. Sediment dumped at 

this site has not been dispersing and may have become relatively immobile due to the steady 

reduction in tidal influence along the outer reaches of the ebb-tidal delta. This shoaling has 

made dredging operations increasingly dangerous in recent years. The constriction of the 

ebb-tidal delta is possibly due to a reduction in tidal prism from San Francisco Bay, and has 

resulted in new wave focusing patterns over the past few decades. The delta retreat has 

eroded shoals that once protected the Sloat region from direct wave attack from west and 

southwest swells. It may have also served to shift a littoral drift nodal point from Ft. Funston 

north to the Sloat Region. 

As a result of the new findings, the USACE implemented a new dredge disposal 

program in June 2005 to both reduce the strain on the existing disposal site and possibly feed 

sediment onto the eroding portion of Ocean Beach. Approximately 230,000 m3

 (300,000 yd3) 

of sediment was placed in a nearshore disposal site - numerical modeling suggests possible 

shoreward transport from this region (Figure 1.2; Barnard and Hanes, 2006). The California 

6
State University Monterey Bay Sea Floor Mapping Lab (SFML) and USGS are currently 

monitoring and modeling the fate of the dredge disposal to help USACE determine if this 

new dredge disposal practice should be implemented permanently. This technique is a lowimpact form of shoreline protection that has been a successful form of beach nourishment in 

The Netherlands for years (e.g. van Duin and others, 2004), but has rarely been implemented 

in the United States. The cost of dredge disposal at the offshore site is approximately $9/m3

($7/yd3

), whereas direct beach nourishment costs upwards of $33/m3 ($25/yd3). 

Prior Work 

Battalio and Trivedi (1996) estimated a sediment budget for Ocean Beach based on 

historical data summarized by Moffatt and Nichol Engineers (1994; 1995). The former 

estimated a net surplus of sediment between 1971 and 1992, which they believed to be 

caused by dredge material dumped on the southern lobe of the ebb-tidal delta migrating 

shoreward, and possibly, minor input from sea-cliff erosion to the south of Ocean Beach. 

Battalio and Trivedi (1996) estimated the potential shoreward transport of sediment from the 

ebb-tidal delta to range between 80,000 and 210,000 m3

/yr during this time. An average of 

403,000 m3

/yr of sediment was dredged from the San Francisco Ship Channel between 1931 

and 1994 (United States Army Corps of Engineers, 1996). Major losses of sediment to the 

Ocean Beach system are thought to occur as littoral transport moves sediment north past 

Point Lobos and by aeolian transport of sediment across the Great Highway driven by 

prevailing westerly and northwesterly winds (Domurat and others, 1979). A significant study 

was completed in 2000 on the ebb-tidal delta to identify a major potential borrow site for the 

San Francisco Airport Expansion (ADEC, 2000). The study focused primarily in the region 

located within and adjacent to the ship channel. Field work included 104 km (56 nautical 

miles) of geophysical surveys, 12 grab samples, and seven marine borings. A suite of other 

reference, while largely limited in scope, when taken as a whole provide a good knowledge 

base for the region (Battalio and Trivedi, 1996; Domurat and others, 1979; Galvin, 1980; 

Johnson, 1977; Moffatt and Nichol Engineers, 1995; Street and others, 1969; Trask, 1954; 

United States Army Corps of Engineers, 1996; Wiegel, 2001; Woodward-Clyde Consultants, 

1978). The USGS has published some summaries of work to date in this region (Barnard, 

2005; Barnard and Hanes, 2005, 2006; Barnard and others, 2006a; Barnard and others, 

2006b; Barnard and others, 2006c; Dartnell and others, 2006; Erikson and others, 2006). 

Future Work 

Beginning in Fiscal Year (FY) 2007, the Ocean Beach Coastal Processes Study 

officially transitioned to the San Francisco Bight Coastal Processes Study, in recognition of 

the impact of regional coastal processes within this massive interconnected coastal 

environment. This system includes the San Francisco littoral cell, extending 75 km from Pt. 

Reyes in the north to Pt. San Pedro in the south, and San Francisco Bay, covering an area of 

4100 km2

 and draining over 40% of the land of California (Figure 1.1; Chin and others, 2004; 

Friends of the Estuary, 1997). 

7
Report Outline 

This report is set up to provide a broad summary of each major data collection effort 

at the mouth of San Francisco Bay from 2004-2006: 

• Chapter 2-Beach Topographic Mapping 

• Chapter 3-Nearshore Surveys with Personal Watercraft 

• Chapter 4-Video Monitoring 

• Chapter 5-Offshore Instrument Deployments 

• Chapter 6-Surf Zone Instrument Deployments 

• Chapter 7-Multibeam Mapping 

• Chapter 8-Grain Size Mapping 

• Chapter 9-Numerical Modeling 

 Delft3d 

 NearCoM 

• Chapter 10-Other Data Collection 

At the end of each chapter there are bullet points to emphasize the key findings- these are 

also listed in the Executive summary at the beginning of this report. A comprehensive list of 

all field data collection efforts is contained in the appendix. 

Project Support and Collaboration 

The Ocean Beach Coastal Processes Study has benefited greatly from internal support 

at the USGS as well as its interactions with a number of other agencies and groups. A list of 

the primary collaborators is outlined below: 

• USGS Support: 

– Mendenhall Post-doctoral Fellowship (Patrick Barnard) 

– Coastal Evolution: Process-based, Multi-scale Modeling Project (Dan Hanes) 

– Delft Hydraulics Cooperative (Giles Lesser, Edwin Elias) 

– USGS Collaborators: Jeff List 

• Academic Partners 

– Cal State Monterey Bay (Rikk Kvitek, Seafloor Mapping Lab) 

– San Francisco State (Toby Garfield, Karen Grove, Jeffrey Hansen) 

– University of Delaware (Fengyan Shi) 

– University of California, Santa Cruz (Gary Griggs) 

– Oregon State University (Peter Ruggiero) 

• Government Agencies: 

– U.S. Army Corps of Engineers, San Francisco District (Peter Mull, Stephen 

Chesser, Tom Kendall) 

– City of San Francisco (Frank Filice) 

8
– California Department of Boating and Waterways (Kim Sterrett) 

– National Park Service, Golden Gate National Recreation (Tamara Williams, 

Steve Ortega, Daphne Hatch, Rebecca Beavers) 

• Private Sector: 

– Phillip Williams and Associates (Bob Battalio) 

– Moffatt & Nichol Engineers (Dilip Trivedi) 

9
Figure 1.1. Map of the study area included in the San Francisco Bight Coastal Processes 

Study, and the focus site for the Ocean Beach Coastal Processes Study (green box). 

10
Figure 1.2. Map showing the Ocean Beach Coastal Processes study area, including the 

locations of the existing dredge disposal site (SF-8) and test dredge disposal site (Ocean 

Beach Disposal Site). 

 

Figure 1.3. Erosion south of Sloat Blvd. at Ocean Beach during 1997-98 El Niño winter (image 

courtesy of Surfrider). The Great Highway is to the left.

11
Chapter 2- Beach Topographic Mapping 

By Patrick L. Barnard 

Introduction 

Forty-five topographic beach surveys have been conducted at Ocean Beach from 

April, 2004, through the end of 2006. The purpose of these surveys is to: 

• quantify seasonal changes in beach volume, shoreline position, and profile change 

• determine the impact of winter storms on beach morphology 

• determine beach response to nearshore dredge disposal 

• develop an empirical model for relating offshore wave conditions to beach response 

Methodology 

The surveys were conducted with all terrain vehicles (ATVs) that use Ashtech©

equipment to collect data with the Differential Global Positioning System (DGPS; Figure 

2.1). The data collected on the ATV was post-processed using data recorded at a base station, 

which was set up on a USGS benchmark at the Oceanside Water Pollution Control Plant, 

located at the southern end of Ocean Beach. All surveys were collected in the Universal 

Transverse Mercator (UTM) projection, using NAD83, Zone 10 as the horizontal coordinate 

system. All elevations are relative to NAVD 88, which is approximately 2 cm below MLLW 

at the Ft. Point Tide Station (National Oceanic and Atmospheric Association, 2006b), located 

just inside the Golden Gate in San Francisco Bay. Based on repeated surveys of the sidewalk 

behind the O’Shaugnessy Sea Wall before and after each topographic survey, the horizontal 

and vertical accuracy of this system is approximately +/- 3 cm. Each survey consisted of 

from 15,000 to 35,000 points covering the entire seven kilometer stretch of Ocean Beach, 

with coverage often reaching below the MLLW line. This is far more efficient than 

traditional land surveying techniques, where only approximately one percent of the number 

of survey points could be gathered in the same amount of time. Triangular irregular networks 

(TINs) are created from post-processed x-y-z data, and then gridded to 2 m cells to be 

analyzed in ArcGIS and MATLAB to identify seasonal trends, storm effects, areas of chronic 

erosion, shoreline position and beach volume changes (Figure 2.2). A list of the surveys to 

date is included in the appendix. Airborne light detection and ranging (LIDAR) data surveys 

collected by the National Oceanic and Atmospheric and Atmospheric Association (NOAA), 

USGS, and NASA in the Fall of 1997 and Spring of 1998 (National Oceanic and 

Atmospheric Association, 2007) is also used here to look at longer-term beach change and 

seasonal change during an El Niño winter. Of the 45 ATV topographic surveys performed 

thus far, 20 have been conducted in response to large winter storms. 

For analytical purposes, the beach has been divided into seven reaches based on 

beach morphology, observed morphologic response and physical structures. Shore normal 

profiles have been generated along Ocean Beach; 138 total with numbering increasing from 

north to south with 50 m alongshore spacing. The reaches and associated profiles have been 

assigned according to the profile ranges included in Table 2.1. 

12
Table 2.1 Reach designations at Ocean Beach. 

Profile Range

Length 

Name (m) Start End

Reach 1 North End/ O'Shougnessy Sea Wall 1477 1 30 

Reach 2 Dune Field- S of Lincoln 1282 31 56 

Reach 3 New Sea Wall 925 57 74 

Reach 4 Dune Field- N of Sloat 684 75 88 

Reach 5 North of pinch point (N Sloat) 574 89 100 

Reach 6 South of pinch point (S Sloat) 467 101 109 

Reach 7 Ft. Funston 1442 110 138 

See Fig. 2.3 for a map of these locations. Reaches 5 through 6 cover the erosion hot 

spot. Cross-sections were extracted along the profile lines for each of the processed 

topographic surveys to analyze beach parameters such as beach width, beach slope, and 

sediment storage. 

Results 

Seasonal Change 

Results from the ATV surveys show typical seasonal patterns of beach erosion during 

the winter months and accretion during the summer/early fall, with beach volume maximum 

in September/ October and beach minimum in January (Figures 2.4-2.5). Over the course of 

the surveys to date the beach volume has fluctuated within an envelope of approximately +/- 

200,000 m3

 of sediment on the subaerial beach (here defined as elevations above 0.5 m 

relative to NAVD88). Between October 2004 and May 2005, a fairly typical winter in terms 

of wave climate, the mean high water (MHW) shoreline position retreated an average of ten 

meters, with localized retreat up to 40 m (Figure 2.6). However, between October 1997 and 

April 1998, an intense El Niño winter with a more southerly wave approach, shoreline retreat 

was twice as great, with an average of 22 m of erosion for the entire beach, and localized 

pockets of shoreline retreat of over 70 m. The most vulnerable part of Ocean Beach (Reaches 

five and six) was significantly eroded during the1997-98 winter, with an already narrow 

beach eroding over 20 m on average. Reaches one and two both lost over 30 m of shoreline 

during this period, showing its vulnerability to more southerly swell. During the 1997-98 

winter, the northern end of most beaches in California accreted (Storlazzi and Griggs, 2000), 

due to the more southerly wave approach. However, due to the large ebb tidal delta at the 

mouth of San Francisco Bay, even waves from a more southerly direction will be refracted to 

near shore normal, and thus offshore transport dominates the beach morphology. 

Storm-related Change 

Superimposed on the seasonal trends, there is a quasi-systematic alongshore 

alternating erosion/accretion trend at the same wavelengths as the rip spacing at Ocean 

Beach, approximately 200-400 m (Figure 2.7). In the vicinity of the erosion hot spot at Ocean 

13
Beach, winter storms cause dramatic and immediate beach response, with localized monthly 

shoreline retreat approaching as much 20 m. 

Looking at event-scale change, large storms can erode the beach at the same scale as 

the seasonal trends. A single storm in March 2005 removed over 40,000 m3

 of sediment from 

the beach and resulted in as much as 20 m of local shoreline retreat (Figures 2.8-2.9). A 

series of winter storms can result in more significant beach response, such as during the week 

of December 22-29, 2005, when over 100,000 m3

of sediment was removed from the beach, 

with an average shoreline retreat of ten meters, and localized retreat of over 22 m. 

Long-term Change 

Decadal scale change has been calculated using the LIDAR data collected in 1997-98, 

as the first datum based topographic survey, and recent USGS surveys (Figure 2.10). 

Although there are local anomalies based on large-scale horn and cusp location, there is a 

pronounced trend since 1997-98 of accretion in the northern and central portions of Ocean 

Beach (i.e. profiles 1-80) and erosion in the vicinity of Sloat in the southern portion of Ocean 

Beach (i.e. profiles 80-120). Overall, the entire beach Mean High Water (MHW) line 

accreted an average of 5.8 m (maximum erosion = 18.8 m, maximum accretion = 41.8 m) 

from October 1997 to October 2004, and 2.7 m from April 1998 to April 2006 (maximum 

erosion= 49.4 m, maximum accretion = 42.1 m). Reach five showed the highest amount of 

erosion along the entire beach, with 15.1 m of shoreline retreat since fall 1997. 

Rates of shoreline accretion at Reach one at the northern end of Ocean Beach average 

2.1 m/yr since the 1997-98 LIDAR surveys, and retreat at reaches five and six (erosion hot 

spot) average 1.1 m/yr. However, erosion along some profiles in Reach six has become so 

severe that the MHW line on the planar beach no longer exists with water reaching the 

shoreline protection structures, and therefore cannot be mapped with the ATV system, and no 

rate calculated. 

The USGS National Assessment study (Hapke and others, 2006) for the Ocean Beach 

area indicate that the long- (mid to late 1800’s - 1998) and short term (1950’s - 1998) rates of 

shoreline change are stable at the northern end (~ 0 m/yr), but become strongly erosional to 

the south (~ 1-2 m/yr). For the 56 km of coastline south of the Golden Gate, the long term 

average is -0.2 m/yr and the short term average is -0.5 m/yr. 

Beach Profile Analysis 

Beach profile calculations along the 138 profiles at Ocean Beach show significant 

spatial variation. Average values of beach width and sediment storage decrease with distance 

south along Ocean Beach (Figure 2.11). There is a sharp drop in both beach width and 

storage at reach 6. The slope is steeper in the southern portion of the beach and there is a 

distinct change in beach slope that corresponds precisely with the offshore location of the 

crest of the southern lobe of the ebb tidal delta. There is a sharp peak in maximum beach 

slope values at reach 4, however, this is approximately 1 kilometer north of the location 

where beach width and storage are at a minimum. There are also seasonal fluctuations in 

beach slope, although this also varies alongshore- during the winter the beach slope increases 

in the northern reaches and decreases in the southern reaches (Figure 2.12). 

14
Dredge Disposal Monitoring 

In May 2005 the USACE, placed 230,000 m3 of sediment dredged from the main 

shipping channel at a nearshore disposal site approximately 500 m offshore of the erosion hot 

spot at Ocean Beach (see Figure 1.2). A comparison of topographic beach surveys during the 

May-August period in both 2004 and 2005 indicate a higher rate of beach accretion, 

particularly along the northern half of Ocean Beach (Figure 2.13). However, this higher rate 

of accretion could be attributed to a number of variables (e.g. dominant wave direction), and 

without a longer term data set it is not possible to isolate the dredge disposal as the direct 

cause of this accretion (Barnard and Hanes, 2006). 

Empirical Model Development 

Preliminary analysis of the winter storm surveys indicates a strong correlation (r2 = 

0.65) between winter significant wave height (Hs

) and direction with beach response at Reach 

5 (Fig. 2.14). Large waves (HS> 5 m) from azimuths of less than 300o

 cause more erosion 

than from azimuths greater than 300o. This is likely due to the sheltering effects of the 

massive ebb tidal delta at the mouth of San Francisco Bay. Waves become increasingly less 

impeded as they approach Ocean Beach from more southerly directions. See Hansen (2007) 

for more information. 

Discussion 

The trend of erosion at the southern end of Ocean Beach has continued since the last 

airborne LIDAR surveys were conducted in the late 1990s, putting increased pressure on 

already threatened infrastructure. Conversely, the northern end of Ocean Beach has accreted 

significantly, with rates of over five meters per year measured at some profile locations. This 

accretion could be the result of onshore sediment transport from SF-8 (see Figure 1.2), as 

postulated by Battalio and Trivedi (1996). In 1971, the USACE began disposing of ship 

channel dredge material south of the Main Shipping Channel on the ebb tidal delta, as 

opposed to seaward of the ebb tidal delta. This beach accretion could represent transport 

from this disposal site. The rate of accretion at the northern end is much greater than that 

eroded from the southern end of Ocean Beach, and therefore a significant amount of 

sediment must be transported from offshore or from the north, potentially from the strong 

tidal currents carrying sediment around Point Lobos from the Golden Gate. This issue will be 

discussed further in upcoming chapters. 

The crest of the ebb tidal delta corresponds precisely with the location of increased 

beach slopes at Ocean Beach (Figure 2.11), as well as a shift from a decadal accretional to 

erosional trend (Figure 2.10). Therefore, it appears that the shape of the ebb tidal delta, and 

specifically the location of the crest of the ebb tidal delta, exerts a first order control on 

longer-term beach morphology changes at Ocean Beach. This control likely results due to 

wave focusing on the crest of the bar, which in turn produces variations in littoral drift 

magnitude and direction through this area (see Chapters 5 and 10). If the current trend of ebb 

tidal delta constriction continues (see Chapters 1 and 7), then it’s likely that the erosional 

trend in the southern portion of Ocean Beach will migrate further north. 

15
Conclusions 

• Beach volume at Ocean Beach varies seasonally over a maximum envelope of 

400,000 m3

. 

• The El Niño winter of 1997-98 caused double the average shoreline retreat 

than the more typical 2004-05 winter at Ocean Beach. 

• Shoreline retreat can exceed 20 m during severe winters, with localized retreat 

over 70 m. 

• Single storm events can cause an average shoreline retreat of over ten meters 

and remove over 100,000 m3

 of sediment from the beach. 

• Since the 1997-98 airborne LIDAR surveys, there has been a trend of 

accretion at the north end of Ocean Beach (Reach 1 shoreline change rate= 

+2.1 m/yr) and continued erosion at the south end (Reach 5-6 shoreline 

change rate= -1.1 m/yr). 

• Preliminary findings from storm response surveys indicate a potentially strong 

correlation between wave height and direction with beach response. 

• The shape of the ebb tidal delta exerts a first order control on decadal scale 

morphology changes at Ocean Beach. 

Figure 2.1. ATV set up for conducting topographic beach surveys using Differential GPS. 

16
Figure 2.2. Typical data coverage (middle panel) and resulting grid (right panel) at the 

northern end (Reach 1) of Ocean Beach, from the November 15, 2004 survey. 

17
Figure 2.3. Map of the reach locations referenced in the analysis of beach topographic data. 

The area of chronic erosion is labeled. 

Figure 2.4. Beach volumetric fluctuations above 0.5 m (NAVD88) from April 2004 to June 2006. 

18
Figure 2.5. Cumulative beach change above 0.5 m (NAVD88) from April 2004 to June 2006. 

Figure 2.6. Winter change (MHW line) during the 1997-98 El Niño compared to the winters of 

2004-05. Profiles are spaced 50 m apart and numbering increases from north to south. 

19
Figure 2.7. Beach change in the Sloat Blvd. (main east-west street pictured) region between 

December 2004 and January 2005. 

20
Figure 2.8. Short-term beach change associated with a significant wave event (offshore 

wave heights reached six meters) at Ocean Beach in March 2005 as compared to the month 

prior. A) Northern Ocean Beach (Reach 1). B) Southern Ocean Beach (Reach 7).

A 

21
B 

22
Figure 2.9. Alongshore shoreline change from two storms in 2005. Gaps in the data indicate no 

data and/or no MHW shoreline accessible. 

Figure 2.10. Shoreline change since LIDAR data was collected in 1997-98. The red line 

represents the rate as determined from the fall beach (October 1997 - October 2004). The blue 

line represents the rate as determined from the spring beach (April 1997 - April 2006). 

23
Figure 2.11. Average values of a) swash beach width, m b) swash sediment storage m2 and c) 

swash beach slope averaged over the profile for each individual profile and also by reach 

plotted on local bathymetry. 

24
Figure 2.12. Seasonal averages of beach slope for each profile at Ocean Beach. 

25
Figure 2.13. Beach change during the dredge disposal monitoring period, as compared to 

2004. A) Northern Ocean Beach (Reaches 1-2. B) Southern Ocean Beach (Reaches 5-7) and 

average vertical change totals for entire beach study area.

A

26
B 

27
-15

-10

-5

0

5

10

Reach 5 Vol. Diff. (m3/m) 

150 200 250 300 350

Dp During Max Hs (°)

Figure 2.14. Empirical relationship between the wave direction (Dp) and beach volume change 

at Reach five during the storm surveys of winter 2005-06. The blue line represents a horizontal 

line that goes through the mean of the mean volume change data. The solid red line is the 

best fit to the data based on the multiple regression equation. The dashed red curves are the 

95% confidence interval curves. The correlation variance r2=0.687.

 

28
Chapter 3- Nearshore Surveys with Coastal Profiling System 

By Jodi Eshleman 

Introduction 

In May, 2004, the USGS began a seasonal shallow-water bathymetric surveying 

campaign at Ocean Beach. Since then, bathymetric data has been collected bi-annually, with 

additional surveys scheduled to coincide with instrument deployments and to help capture 

inter-seasonal change. This nearshore mapping initiative provides data to monitor seasonal 

trends, identify areas of chronic erosion, and create detailed bathymetric grids for enhanced 

numerical modeling capabilities. Recent innovations in field techniques have made it 

possible to quickly collect high-quality survey data in an area where extreme conditions were 

prohibitive in the past. 

Methodology 

The Coastal Profiling System (CPS), a hydrographic surveying system mounted on a 

Personal Watercraft (PWC), is used to collect bathymetric data for a seven kilometer stretch 

within the Golden Gate National Recreation Area in San Francisco, CA (Figure 3.1). The 

CPS combines the high accuracy positioning of a DGPS and the mobility of a personal 

watercraft to collect rapid and precise bathymetric profiles. The CPS has traditionally been 

used to survey cross-shore profiles perpendicular to a shoreline from approximately 15 m 

depth to one meter depth (NAVD 88), depending on weather and tide conditions. The survey 

setup for this site consists of 18 cross-shore profiles running from 1.8 km offshore through 

the surf zone and two alongshore profiles parallel to the coastline (Figure 3.2). 

The bathymetric data has been collected using two different versions of the CPS. The 

first survey in May, 2004 was completed using the second generation CPS (CPS II), which 

was designed in cooperation with the University of Florida (MacMahan, 2001). All 

subsequent surveys were completed with the third generation CPS (CPS III), which is similar 

to the second generation version, but is mounted on a newer PWC model and includes 

updated hardware (Figure 3.2). A more complete discussion of specifics regarding the CPS 

can be found in Ruggiero and others (2005) and MacMahan (2001). This bathymetric 

surveying technique has been shown to achieve sub-decimeter accuracy (MacMahan, 2001); 

however reasonable variations in water temperature can affect depth estimates by as much as 

two percent of the total water depth. All data are corrected to adjust the vertical coordinate 

for the actual speed of sound in post-processing using the average of the surface water 

temperature measured at the San Francisco National Data Buoy Center (NDBC) Buoy, 

Station #46026 during the survey period (National Oceanic and Atmospheric Administration, 

2006a). 

There were two different types of GPS equipment used to collect bathymetric data. 

For all surveys completed after the fall of 2005, the Trimble® survey gear was replaced with 

Ashtech©. All survey data was collected in the UTM horizontal coordinate system, Zone 10 

and referenced to NAVD 88. Table 3.1 includes a list of the bathymetric surveys, which 

profiles were completed, and which survey equipment and CPS version was used. The CPS 

collects data at 5 Hz and while traveling at 3 m/s generates a depth sounding every 0.6 meters 

along the sea floor. All surveys were completed using Real Time Kinematic (RTK) GPS, 

29
where rovers receive information by radio signal from a base station while in the field, 

minimizing post-processing requirements. HYPACK® (Coastal Oceanographics, Inc.) 

hydrographic surveying software was the platform used for navigation and data collection in 

the field. 

Trimble® 4000 series receivers were used and have manufacturer reported root mean 

square (RMS) accuracies of approximately ±3 cm + 2ppm (parts per million) of baseline 

length (typically 10 km or less) in the horizontal and approximately ±5 cm + 2ppm in the 

vertical while operating in Real Time Kinematic surveying mode (Trimble Navigation 

Limited, 1998). Ashtech© Z-Extreme receivers were used for all subsequent surveys and 

have manufacturer reported accuracies of approximately ±1 cm + 1ppm in the horizontal and 

approximately ±2 cm + 2ppm in the vertical while operating in RTK surveying mode 

(Magellan Navigation, Inc., 2006). These reported accuracies are, however, additionally 

subject to multi-path, satellite obstructions, poor satellite geometry, and atmospheric 

conditions. While the horizontal uncertainty of individual data points is approximately 

0.05 m, the CPS operators cannot stay 'on line', in waves and currents, to this level of 

accuracy. Typically, mean offsets are less than 2.0 m from the preprogrammed track lines 

and maximum offsets along the approximately 2 km long transects are typically less than 

10.0 m. 

The geodetic benchmark used to set up a base station was located at the Oceanside 

Water Pollution Control Plant located on the opposite side of the Great Highway from Ocean 

Beach in the central portion of the survey area. The horizontal coordinates in NAD83 were 

37o 43’ 39.89423’’W and 122o 30’ 20.62585’’N, with an ellipsoid height of -10.902 m and 

NAVD88 elevation of 21.853 m. When necessary, a radio repeater was set up on the roof of 

the Cliff House restaurant to help extend radio coverage to southern portions of the beach 

where cliffs block the radio signal. 

Results 

Seasonal Change 

Figures 3.3 through 3.7 show cross-shore profiles at each of the 18 locations 

identified in Figure 3.2. Profiles 2-4 show a pronounced change in slope between the 10 and 

15 m depth contours, with a slightly shallower section beyond this break (Figure 3.3). For 

the rest of the profiles, the slope is much smoother and depth change flattens out offshore 

with little variation below 10 m depth. Figures 3.3 to 3.7 show cross-shore seasonal bar 

migration in all profiles over a profile section of approximately 300-600 m, with sand 

moving offshore in the winter and onshore in the summer. To allow for comparisons 

between individual surveys, alongshore profiles 19 and 20 were combined with the crossshore profile data to create 2-dimensional gridded surfaces in Matlab© using triangle-based, 

weighted linear interpolation. Figure 3.8 shows difference grids determined by subtracting 

the gridded surface of the more recent survey from the older survey to help identify trends in 

bar migration and beach volume change over time. The grid difference plots display offshore 

bar migration in the winter (Figure 3.3 a), and continued onshore bar migration over the 

summer and early fall (Figure 3.3 b, c). In Figure 3.3 d, a one month grid difference plot 

captures offshore bar migration resulting from a few winter storm events. 

30
Range of Elevation Change 

Figure 3.9 highlights the range of elevations that have been measured over the survey 

area throughout the entire sampling campaign. The mean and standard deviation of each grid 

cell were calculated by generating a grid over the same data range for each survey and then 

combining all grids for statistical analysis. Figure 3.9a shows that most changes in 

bathymetry offshore of Ocean Beach occurred in water depths less than 10 m. In the 

northern and central portions of the beach, two shallower sections exist. The shallow section 

in the center of the beach around northing 4178 km appears to be fairly stable, as the standard 

deviation in that region is very small, if not zero. The shallow section at the northern part of 

the beach (northing 4179-4181 km) is highly variable, with standard deviation values 

reaching 1.2 m in localized spots. Here, bathymetric change extended outside of the 15 m 

contour. 

Nearshore Bar Growth and Trough Erosion 

An estimation of the volume of bar growth and trough erosion at Ocean Beach using 

the measured bathymetric profiles was attempted. The goal of this analysis is to get an 

estimate of the amount of sand that moves in the cross-shore seasonally to form offshore 

bars. This was done using the surveys conducted in November, 2005, and February, 2006, 

because these surveys captured the winter offshore bar migration better than any other time. 

Unfortunately, beach topography data was not available for both of these surveys, so a total 

volume of profile change could not be calculated to determine if sediment was conserved in 

the cross-shore or evaluate the component from alongshore transport. For this analysis, a 

volume of bar growth was calculated for profiles one through eighteen by calculating a crossshore area for portions of the profile where the elevation in February, 2006 was greater than 

that in November, 2005. The trough erosion was estimated by calculating a similar crossshore area for sections when the November, 2005 elevation was greater than the February, 

2006 elevation. Both volumes were constrained between the two and ten meter depth 

contours to be consistent between different profiles, although there is change outside of this 

region. A schematic of this technique is presented in Figure 3.10. 

A value of volume change in m3

/m for each profile was computed since this was an 

areal difference at one location in the alongshore (Figure 3.11 a). These values were 

normalized by the profile length, which is the cross-shore distance over which we have data 

from both surveys. This quantity helps to facilitate comparisons between different profiles, 

giving a volume estimate of m3

/m/m (Figure 3.11 b). Profiles one and seventeen were 

removed from the analysis since the bar migration was not within the constrained depth 

contours. This simplified technique captures fluctuations in sand throughout the entire 

profile, but the assumption is that the volume of sand included in the bar is significantly 

larger, therefore it can give order of magnitude estimation. Another assumption here is that 

all sand accumulating in the offshore bar comes from offshore cross-shore transport, which is 

likely not the case at Ocean Beach where very strong shore-parallel tidal currents exist. By 

comparing winter and fall bathymetric surveys, an estimated volume of offshore bar growth 

of roughly 300 m3/m on and a trough erosion of 200 m3/m occurred on average for a single 

cross-shore profile (Figure 3.11 a). It is likely that the trough erosion is less than the bar 

growth because the sand moving off of the beach is not included in this calculation. When 

normalized by profile length, this results in approximately 0.6 m3

/m bar growth and 0.4 m3/m 

trough erosion on average. 

31
Discussion 

Comparisons of bathymetric survey data collected at Ocean Beach show seasonal 

patterns of bar migration. Figure 3.8 maps this movement in 2006. Figure 3.8a shows a very 

pronounced offshore bar migration in the winter of 2006, with a three meter trough 

developing in the northern portion of the beach. This was the largest change observed during 

the period of study, in part because it is very difficult to collect survey data in winter months 

due to the frequency and duration of storms. By May, 2006 the bar had partially migrated 

onshore and the deep trough had started to fill in (Figure 3.8 b). The onshore bar migration 

continued throughout the calm summer months, as shown in elevation difference plots from 

November 2006 (Figure 3.8 c). A survey completed one month later to look at shorter-term 

storm response identified offshore bar migration on the order of 100 m in the cross-shore 

(Figure 3.8 d, Figure 3.5) in response to a few storm events. During this one month period, 

there were six storm events (defined by periods when significant wave heights were greater 

than 2 m) based on measurements recorded at the Coastal Data Information Program (CDIP) 

Point Reyes buoy #029 (SCRIPPS Institution of Oceanography, 2006). 

Calculations of the range of elevations collected throughout the survey campaign at 

each grid cell suggest that the offshore extent of significant vertical profile change, or depth 

of closure (Hallermeier, 1978), varies alongshore at Ocean Beach. Using very small values 

of the standard deviation of elevation as a proxy for the depth of closure, Figure 3.9a 

suggests that this depth is much shallower in the southern and central sections than at the 

north end. The depth of closure ranges from 10 m in the central and southern portions of the 

beach to a depth of 15 m or greater at the northern end. Figure 3.9 also includes the dredge 

disposal site (magenta box), disposal mound peak (magenta star), and erosion hotspot 

(magenta box). The location of the disposal mound peak appears to be outside of the 

estimated depth of closure, suggesting that cross-shore transport of sand from this site is 

limited. Future attempts to dispose of this sand in shallower water may produce improved 

results. 

If the volume of bar growth estimate per profile of 300 m3

/m is multiplied by seven 

kilometers for the stretch of shoreline along Ocean Beach, the result is an approximate 

volume of 2.1 million m3

 (2.7 million cubic yards), giving a rough order of magnitude 

estimate of the amount of sand moving in the cross-shore to generate bars in this region. 

Conclusions 

• Comparisons of bathymetric profiles show patterns of seasonal bar migration 

onshore in the summer and offshore in the winter. Bars can be as high as two 

meters and move several hundred meters in the cross-shore. 

• A shorter-term survey after one month suggests that a few winter storms can 

force offshore bar migration on the order of 100 m. 

• Comparisons of elevation change throughout all surveys suggest a range in 

depth of closure from 15 m at the north end to a shallower 10 m at the south 

end. This analysis suggests that the dredge disposal site is too deep for 

significant cross-shore transport of sand to occur. 

• An order of magnitude estimate of offshore bar growth from measured 

bathymetric profiles suggests 2 million m3

 (2.6 million cubic yards) of sand is 

moving in the cross-shore to form nearshore bars. 

32
Figure 3.1. Third generation Coastal Profiling System in action. 

33
Figure 3.2. Ocean Beach CPS survey profiles. 

34
Table 3.1. Nearshore bathymetry survey coverage and equipment. 

Date Profiles Survey Equipment CPS System Notes 

5/4/2004 2-14 Trimble® CPS II 

7/20/2004 1-20 Trimble® CPS III 

11/12/2004 1-18 Trimble® CPS III 

5/3/2005 1,3,5,7-18 Trimble® CPS III *Survey completed just before 

summer instrument campaign. 

11/17/2005 1-18 Ashtech© CPS III 

2/10/2006 1-20 Ashtech© CPS III *Coincided with winter 

instrument campaign. 

5/23/2006 1-20 Ashtech© CPS III 

11/6/2006 1-20 Ashtech© CPS III 

12/5/2006 1-20 Ashtech© CPS III *inter-seasonal storm response 

survey. 

35
Figure 3.3. Ocean Beach cross-shore profiles 1- 4. 

36
Figure 3.4. Ocean Beach cross-shore profiles 5 - 8. 

37
Figure 3.5. Ocean Beach cross-shore profiles 9 - 12. 

38
Figure 3.6. Ocean Beach cross-shore profiles 13 - 16. 

39
Figure 3.7. Ocean Beach cross-shore profiles 17 - 18. 

40
Figure 3.8. Grid difference plots showing elevation change between surveys a) February, 

2006- November, 2005 b) May, 2006 – February, 2006 c) November, 2006 – May, 2006 d) 

December, 2006 – November, 2006. 

41
Figure 3.9. Calculations from all survey data available of a) standard deviation of elevation 

with mean elevation contours b) mean elevation (dredge disposal site and erosion hotspot in 

magenta). 

42
Figure 3.10. Definition sketch for volume of bar growth and trough erosion calculations using 

profile five. The blue section shows the calculated volume of bar growth and the red section 

shows the volume of trough erosion. 

43
Figure 3.11. Variation in a) volume of bar growth and trough erosion and b) volume of bar 

growth and trough erosion per meter profile length for profiles 1-16, 18 along Ocean Beach. 

44
Chapter 4- Image Monitoring 

By Li Erikson 

Introduction 

Digital still camera and video imagery provided continuous monitoring of the inshore 

region at the north end of Ocean Beach (http://www.evsboca.com/usgs/default.htm). Due to 

the shallow depth and the highly dynamic and energetic surf zone, the inshore region is 

typically off limits to traditional methods of measurement. The image monitoring system, on 

the other hand, supplemented the other field operations undertaken for this study in addition 

to providing continuous, long-term monitoring of coastal and shoreline dynamics. To this 

end, the main objectives of deploying the image monitoring system were to locate the 

shoreline and bathymetric features (e.g., bars and rip currents), and provide data on surf and 

swash hydrodynamics. 

Methods 

Since September 2004, digital video and still cameras with high precision pan and tilt 

capabilities, encased in a protective housing, were mounted on the roof of the Cliff House 

Restaurant (Figure 4.1), approximately 30 m above MSL (Erdman Video Systems, Inc., 

1996-2006). The approximate region of the camera’s field of view is shown in Figure 4.2, 

along with locations of temporary in situ current meters (Chapters 5 and 6) and cross-shore 

bathymetric sampling transects (Chapter 3). Still images provide snapshots of the nearshore 

region, but the majority of the data analysis was done with images obtained by the video 

camera. Two variations of video images were generated: first, a series of video images 

averaged over ten minutes; and second, “time-stacks” along the five cross-shore transects (T1 

through T5, spaced ~50 m apart) shown in yellow in Figure 4.2. As of June 2005, timestacks were obtained between 10 am and 1 pm on a daily basis and time-averaged images 

were recorded at ten minute intervals during remaining daylight times. Due to increased 

capabilities of the monitoring hardware, the time-stack sampling scheme was increased to 

nine cross-shore and two along-shore transects in February 2006 (compared to five transects 

shown in Figure 4.2). 

Select time-averaged images have been analyzed for spatial determination of sandbar 

dynamics and the presence of rip currents. By averaging thousands of images over a ten 

minute time period, fluctuations due to incident waves breaking at different locations are 

averaged, yielding a more stable image of the wave breaking region, and thus illuminating 

shallows of offshore bars or shoaling regions. A typical time-averaged image is shown in 

Figure 4.3 a-b, where the bar location is evidenced by the lighter band in the image. 

In contrast to time-averaged images, time-stacks plot transects of image pixels 

(sampled at 1 Hz) and stack them in the vertical direction resulting in an image with time on 

the vertical axis and distance on the horizontal axis, as shown in Figure 4.3c. Time-stacks 

obtained during the surf zone experiment (January 2006) are shown in Figure 4.3 c for the 

five cross-shore transects (T1 through T5 in Figure 4.2). Select time-stack images have been 

analyzed for maximum runup height/length (i.e., maximum height/distance of the leading 

edge of the waves on the beach face) and swash period. 

45
Prior to extracting data from the images, rectification and geo-referencing were 

necessary to account for image distortion caused by the oblique field of view (other 

distortions such as those caused by lens irregularities are considered to be relatively small 

and have not been directly accounted for). Image rectification is the process of transforming 

a distorted image so that it is parallel to the baseline and so that a physical length unit 

anywhere on the image represents an equal real-world distance throughout the image (i.e., the 

image geometry is recovered). Geo-referencing is the process of assigning real-world 

coordinates to image pixels. Image rectification and geo-referencing were performed with 

transformation matrices determined from known ground control points, associated pixels, the 

assumption of a plane beach for the time-stack evaluations (Holland and others, 1997) and by 

constraining the vertical elevation to mean sea level, as was done by Lippman and Holman 

(1989) to determine bar and rip current positions. Based on comparisons with ground control 

points not used in the image rectification process, the error associated with bar and rip 

current positions was found to be 14 m ± 11 m in the north-south direction and 19 m ± 13 m 

in the east-west direction. 

Results 

Time-averaged Images 

Time-averaged images were evaluated for bar and rip current positions. This section 

begins with a comparison of bar positions observed with the images as compared to those 

measured with the CPS (Chapter 3). Time-averaged images were then used to infer which 

storms and wave energy levels caused an offshore bar to develop during the winter of 

2005/2006. 

Sandbars 

Although there are two CPS survey profiles that fell within the camera’s field of view 

(Figure 4.2), most of the northern one (profile 1) is lost during the image rectification 

process. Hence, image breaking locations were compared to CPS survey profile 2. Because 

the location of breaking is not only dependent on the bathymetry but also on wave 

conditions, the most noticeable bars in a cross-shore profile may not be visible in the timeaveraged images on a given day. The CPS surveys were intentionally completed on days 

with low wave energy (for safety and data quality requirements), while time-averaged images 

only show offshore bars on days with coincident low tide and relatively high wave 

conditions. As such, wave breaking positions were determined from time-averaged images 

taken within five days following the CPS surveys and when offshore significant wave heights 

measured at the CDIP buoy #029 (Scripps, 2006) exceeded 2.5 m. The breaking locations, as 

determined from the images, are shown with filled circles in Figure 4.4. These breaking 

locations concur with the inshore bar, near the depth-limited range of the CPS measurements. 

The second bar at about E542.55 km on 05/23/06 is not evident in the images because the 

wave conditions were too small. Not evidenced by the bathymetry however, is a second 

breaking location clearly evident in the images from 02/10/06 and 05/23/06 at 37 m and 64 m 

shoreward of the Eastern most CPS measurement, respectively (not shown in the Figure). 

The cross-shore profiles along profile 2 (Figure 4.4) show that a significant bar 

developed at a depth of approximately four meters sometime between 11/17/05 and 02/10/06. 

The depth at which the bar was situated suggests that it was generated by rather large wave 

events, with breaking wave heights on the order of 3+ m. There were nearly 20 Pacific 

46
storms whose swell (HS>2.5 m) reached the CDIP buoy and Ocean Beach between 11/17/05 

and 2/10/06. The offshore bar is not visible in the time-averaged images until the swell on 

12/21/05 (Hs>6.5m and TP=15s), as shown with the triangle in Figure 4.4. By 01/04/06, a 

storm swell of similar magnitude (Hs

=6.11m and Tp=16.7s) shows that the bar moved slightly 

further offshore (solid square in Figure 4.4). Following the swell of 01/04/06, large swell 

conditions were a meter or more lower than those measured at the CDIP buoy during the 

previous large swells. Time-averaged images from the remaining large swell events all 

showed breaking shoreward of the bar, indicating that the storms of 12/21/05 and 01/04/06 

generated the offshore bar. 

Rip Currents 

Rip current locations were manually digitized from time-averaged images spanning 

the entire data set from September 2004 through August 2006. The data showed that there 

were four primary rip current locations within the camera’s field of view (Figure 4.5). The 

rip currents were spaced on the order of 150 m to 200 m ( ± 41m). Based on available data, 

the rip current located furthest south of the Cliff House Restaurant (rip 4 in Figure 4.5) was 

most prevalent (37% of total number of observations) and appeared to occur at any time 

during the year, followed in decreasing frequency by rips 1, 3, and 2 (27%, 23%, and 13%). 

Rip current occurrence appeared to follow a cyclical seasonal distribution with the greatest 

number of observations occurring in April and August (Figure 4.6). The seasonal occurrence 

of rip currents is likely related to variations in wave conditions, bathymetry and beach 

topography. Previous studies suggest that rip currents most frequently occur when waves 

approach at near normal incidence, where there are alongshore variations in bathymetry and 

an alongshore sandbar is present. Variations in local bathymetry in the context of rip current 

generation have not yet been analyzed. However, a preliminary assessment suggests that the 

inshore bathymetric variance was not sufficient to fully describe the occurrence and location 

of rip currents. This suggests that refraction over varying offshore bathymetry and tidal 

currents affected by the inlet might provide a disturbance in the wave field resulting in 

alongshore wave height variation that could generate rip currents. This hypothesis could be 

tested with the numerical model described in Chapter 10 (e.g., Long and Ozkan-Haller, 

2005). 

Time-stack Images 

Swash hydrodynamics were investigated by closely analyzing time-stack images 

obtained along the five cross-shore transects (Figure 4.2) during a four hour sampling period 

on 06/24/05. Beach slopes were determined from topographic data collected with ATVs 

(Chapter 2) and were mild, ranging from 0.01 to 0.05. 

Neglecting set-up due to radiation stresses caused by breaking waves, total runup is 

often considered to consist of two components: first, incident waves producing runup and 

run-down (backwash) on a beach, and second, oscillations at infragravity frequencies, 

generating swash periods greater than 20 s, beyond the usual range of incident wave periods. 

In order to assess the relative contributions of each, the runup time-series were band-pass 

filtered to the sea and swell incident component, (Rinc, 05.0 < < 2.0 HzfHz ) and infragravity (Rig, 

< 05.0 Hzf ) component. The relative contribution of runup in the infragravity band to total 

47
runup ( RR ) ig was 0.83, similar to what Ruessink and others (1998) found ( RR = 85.0 ) ig , but 

less than the Oregon data set presented by Ruggiero and others (2001 and 2004). A typical 

time-series showing the dominant infragravity component is shown in Figure 4.7. 

Runup energy density spectra were calculated using Welch's averaging method and a 

bandwidth of 9E-4 Hz for each transect and are shown in Figure 4.8. The dashed vertical line 

depicts the cutoff between infragravity and incident runup frequencies, and it is clear that the 

peak energy lies within the infragravity band. The peak periods ( p 1 f ) range from 41 to 68 

s, with the longer periods (56 s - 68 s) observed at the three middle cross-shore transects. 

The steep drop-offs in Figure 4.8 suggest saturated surf and swash zones. Miche 

(1951) theorized that monochromatic incident waves consist of both a progressive and a 

standing wave component and that runup is proportional to the amount of shoreline reflection 

from the standing wave amplitude. The amplitude of the standing wave is depth-limited as 

an increase in incident wave heights causes the breaking to occur further offshore, allowing 

energy dissipation through wave breaking and less energy for swash. As such, saturation 

implies that the incident band runup height does not increase with increased offshore wave 

height. 

Swash hydrodynamics have many consequences, including defining the landward 

extent of shoreline change. Numerical process-based models are invaluable tools for 

simulating hydro- and morphodynamcis across large complex regions such as the San 

Francisco Bight and Ocean Beach, but are often limited in their ability to simulate detailed 

shoreline change. As a complement to the numerical modeling for shoreline evolution 

undertaken as part of this study, the use of analytical models to predict runup at Ocean Beach 

was assessed. Although numerous factors influence the extent of runup (e.g., grain size, 

friction, turbulence, swash interaction, and infiltration), three parameters are generally 

considered to be strongly linked to observed runup statistics: offshore wave height, 

deepwater wave length and beach slope. Various combinations of these three parameters 

have been proposed, and in particular, there have been some recent developments in the 

prediction of runup on dissipative beaches. 

Comparison of predicted runup values from six different semi-empirically-based 

analytical models showed that the significant runup, Rs

 (mean of the one-third highest runup 

elevations) is well predicted with the classic Hunt formula (R2=0.70, Figure 4.9a) and the 2% 

runup height (R2

, runup height that is exceeded 2% of the time) is well predicted with a 

recent formulation proposed by Ruggiero et al. (2001, R2=0.70, Figure 4.9b). Offshore wave 

heights employed in the models were measured with the offshore RD Instruments Acoustic 

Doppler Current Profiler (RDI ADCP) shown in Figure 4.2 (0.9m < Hs

 < 1.5m; 9s < Tp1 < 

13.5s). As mentioned previously, bimodal conditions dominated the wave spectra during the 

summer months, and as such the sensitivity of the models to the choice of bulk parameters 

obtained from the bimodal velocity spectra were compared using the two peak periods (Tp1

and Tp2) and mean representations (Tmo1 and Tmo2). Using peak wave periods increased the 

root-mean-square-error (rmse) in all cases, while the mean period, in particular Tmo2, which is 

theoretically similar to the wave period obtained through zero-down crossing, gave results 

with the smallest rmse. In all, the analytical runup formulations did quite well considering 

that Ocean Beach, and in particular the northern part of Ocean Beach, is strongly influenced 

by tidal currents (approximately 1 m/s during the field study) and associated wave-current 

interactions. The relatively mild conditions of the summer may be partially responsible for 

this positive performance. 

48
Discussion 

Although the time-averaged images can fill some of the time-series data gaps of 

locating the bars and break points in time and space, they are limited by daylight, tidal 

elevation, and weather and wave conditions (waves need to be large enough so that breaking 

occurs over the deeper situated bars). Even so, the analyses presented herein provide a 

means to determine multiple break points with a high resolution time-scale and a means to 

associate swell conditions with bar generation. As such, the images provided complementary 

information about the inner bar often not captured with the CPS surveys. 

A causal relationship between rip current occurrence and location was not 

determined. At this time it is thought that refraction over irregular bathymetry and complex 

flow patters associated with the tidal inlet may be the driving mechanism for rip currents at 

the north end of Ocean Beach. Implementation of the numerical model Delft3D might 

provide a means to test the hypothesis. 

Summer swash conditions were analyzed with time-stack images and were shown to 

be highly dissipative. Detailed analyses of winter runup conditions are expected to show a 

dominance of incident frequency swash oscillations, related to a steeper foreshore slope. 

This has yet to be determined with topographic data obtained with the ATV surveys and from 

validated profiles obtained with time-averaged images. Coupling between the surf and swash 

zones will need to be done with additional analysis of the time-stack images. Surf zone 

currents will be calibrated and validated with in situ measurements (Chapter 6) during the 

winter field campaign in 2006. This should provide additional data for the assessment of rip 

currents, as well as cross- and long-shore sediment transport. 

Conclusions 

• Wave-breaking locations deduced from time-averaged images agree with those from 

bathymetric data obtained with the CPS. 

• Time-averaged images show that multiple breaking locations are common along 

Ocean Beach. It is not clear if both of the breaker locations were associated with bars, 

or if the inner location was simply due to depth-limited breaking. 

• Four rip currents occurred seasonally at the north end of Ocean Beach with a spacing 

of 150 m to 200 m. 

• Analysis of time-stack runup data shows that the beach was dissipative under typical 

summer conditions with infragravity conditions dominating and swash periods on the 

order of a minute. 

49
High precision 

pan and tilt 

Window washer

tank 

Still and video 

camera housing

Figure 4.1. Digital camera and video system on the top of the Cliff House Restaurant. 

50
Figure 4.2. Aerial image showing camera’s field of view, in situ instrument locations (ADCP as 

a red square and Aquadopps as circles), CPS survey profiles (blue east-west oriented lines), 

and time-stack transects (yellow lines). Aerial image pt_bonita_se.tif, 08/25/1993. 

51
(c)

Figure 4.3 Typical images used for analysis: (a) unrectified time-averaged image, (b) rectified 

time-averaged image, and (c) time-stack image. 

Figure 4.4. Break points observed in time-averaged images plotted on cross-shore profile 

measured with the CPS. 

52
Figure 4.5. Locations of dominant rip currents at the north end of Ocean Beach. 

53
0

2

4

6

8

10

12

14

16

18

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

percent of total observations

Figure 4.6. Seasonal distribution of observed rip current occurrence at any of the four 

locations at the north end of Ocean Beach. 

Figure 4.7. Typical 17 min tide detrended time-series illustrating the dominant infragravity 

component (transect T3 on 06/24/05, 10:09 to 10:23 am). 

54
Figure 4.8. Total energy density, averaged over ten subsequent 17 minute time-periods, 

measured at each cross-shore transect. The heavy solid line is the best linear fit through T3 

over 0.03 to 0.1 Hz. Dashed vertical line is cutoff between infragravity and sea swell 

frequencies. 

55
(a) 

(b)

10 20 30 40 50

Rs (cm)

10

20

30

40

50

β LH oo (cm)

(cm)

10 20 30 40 50 60 70 80

R2% (cm)

10

20

30

40

50

60

70

80

27.0 β LH oo

Figure 4.9. Measured runup statistics versus (a) Hunt’s significant runup formula (1959), and 

(b) 2% exceedance using Ruggiero and others (2004) formulation. Both are shown with T=Tmo2. 

56
Chapter 5-Offshore Instrument Deployments 

By Jodi Eshleman 

Introduction 

Two oceanographic instrument deployment campaigns were conducted between June 

21, 2005 and February 11, 2006. The instrument deployment campaigns were designed to 

achieve two goals: 1) to provide data to calibrate a numerical model for the region, and 2) to 

characterize the wave and current climate in the surf zone and offshore of Ocean Beach. 

These goals are essential to aid in understanding coastal change in the area and in generation 

of a predictive numerical model to help coastal managers make more informed decisions to 

preserve and maintain local infrastructure and resources. 

Methodology 

In summer, 2005, current profilers were deployed at four locations offshore of Ocean 

Beach (Figure 5.1). RD Instruments Acoustic Doppler Current Profilers (RDI ADCP) were 

placed at Sites 1-3, which were located in the nearshore region in water depths ranging from 

seven to 15 m and were spread out in the alongshore to highlight spatial differences in wave 

and current patterns (Figure 5.1). The fourth instrument was a Nortek Acoustic Wave and 

Current Meter (AWAC), which was deployed offshore in 20 m of water to help understand 

wave transformation across the ebb-tidal delta. Pictures of typical instrumented frames 

deployed at these sites are shown in Figure 5.2. This deployment was designed for a two 

month duration, therefore sampling intervals for waves and currents were chosen to 

maximize battery life (Table 5.1). 

For the winter, 2006 deployment, several sites were revisited to help quantify 

seasonal changes in wave and current patterns. RDI ADCPs were deployed at Sites 1 and 3 

and the Nortek AWAC was moved to a new location offshore in 12 m of water on the outer 

ebb-tidal delta (Site 5). In this campaign, a Seabird SBE-37 Microcat was included on the 

frames deployed at Sites 3 and 5 to gain some insight into changes in temperature, density, 

and salinity values. The instrument included on the frame at Site 3 (S/N 2538) measured 

conductivity, temperature and pressure with a range of 0-350 m on the pressure sensor. The 

instrument included on the frame at Site 5 (S/N 3013) measured conductivity and 

temperature with an internal pump, but did not include pressure. The sampling setup for the 

winter deployment was identical to that of the summer (Table 5.1), except the AWAC at Site 

5 collected data at 2 Hz and had a wave bin size of 1.56 m and the blanking distance on the 

ADCP at Site 3 was changed to 0.20 m. 

Table 5.2 includes descriptions of locations and instrumentation for both the summer 

and winter deployments. The instrument located at Site 1 for the summer 2005 campaign 

(S/N 2054) was buried by 2.5 ft of sediment upon recovery and measurements show that data 

collection at this site stopped after six days. The ADCP deployed at this same site for the 

winter 2006 deployment (S/N 6363) was not recovered, likely because burial prevented the 

dive pinger required to locate the frame from working properly. The head of the ADCP from 

Site 3 during the winter deployment (S/N 2054) was cracked upon recovery, but this did not 

appear to affect the saved data files in any way. The Microcat at Site 3 (S/N 2538) also 

logged pressure, which is used as a backup to validate pressure measurements from the 

ADCP. The sampling tube on the Microcat that was deployed at Site 5 (S/N 3013) filled 

57
with sand after nine days and did not collect valid conductivity data after that time; the 

temperature sensor still logged data. Water density was calculated from measurements of 

salinity, temperature, and pressure and the average water density of 1025 kg/m3 was used to 

calculate water depths from pressure measured by the current profilers (Figure 5.3). 

The current profilers deployed at all sites provided detailed measurements of current 

magnitude and direction throughout the water column. In addition, this current data was used 

with an array processing technique to determine directional wave information. The details of 

these calculations are different for both the ADCP and the AWAC. The Wavesmon software 

package from RD Instruments and Quickwave from Nortek were used to generate power and 

directional spectra from pressure, surface track, and current profile measurements at each site 

and determine bulk statistics. The RDI ADCP current data was processed using the ADCP 

Data Processing System, a Matlab© toolbox developed at the USGS Woods Hole Field 

Center and detailed information about this toolbox can be found in the ADCP Data 

Processing System Manual (Cote, 2003). Measurements were compared at all sites, but since 

there were two types of instrumentation and software packages used, spectral output and 

wave parameters were not all determined using the same algorithm. It is possible that some 

differences in output could be a result of different methods used to measure waves by the 

different systems. 

Results 

Waves and currents were measured at five sites in the nearshore region off of Ocean 

Beach. These measurements show spatial gradients in current magnitude and direction and 

wave height and direction along the seven kilometer stretch of Ocean Beach, as well as 

across the ebb-tidal delta. 

Currents 

Table 5.3 includes basic statistics for depth-averaged current measurements. The 

principal axis was calculated for each site based on the covariance between the measured u 

and v depth-averaged velocities. Figure 5.4 includes plots of the principal axis and depthaveraged current data for each site. This highlights the differences in current magnitude and 

principal direction at different sites. Current magnitudes at the north end of the Ocean Beach 

(Sites 1 and 2) are almost twice as strong as those measured at the southern end (Site 3) or 

offshore (Sites 4 and 5). For the sites located in shallower water (7-13 m) just off the beach, 

the principal current axis follows the shoreline, with northward velocities dominating. At 

offshore sites, the eastward component becomes more important, especially at Site 4 where 

the greater influence of the mouth of San Francisco Bay becomes apparent. 

Figures 5.5 and 5.6 show the variation in measured currents throughout a tidal cycle 

for the summer and winter deployments. These include vectors of currents measured at the 

surface, middle, and bottom bin at each site to help identify vertical stratification as well as 

spatial differences in current speed and direction. During a summer tidal cycle, current 

speeds decay with distance from the inlet during the flooding and slack high tides (Figure 5.5 

d, e, h, i). However, currents measured at Site 3 (especially on the bottom) can be as great or 

greater than Site 1 on the ebbing and low slack tides (Figure 5.5 b, c, f, g). In addition, Site 3 

seems to have a stronger onshore component throughout the entire tidal cycle than Sites 1 

and 2, which are located further north along Ocean Beach. During a winter tidal cycle 

58
(Figure 5.6), Site 3 has less of an onshore component of flow and less stratification. Currents 

measured at Site 5 are often on the same order of magnitude as Site 3. 

Plots of eastward and northward current velocity variation with depth are shown in 

Figures 5.7 through 5.12 for all sites for both the summer and winter deployments. These 

plots show only one week of data at each site so trends corresponding to tidal cycles and 

daily changes are visible, and they suggest that comparing depth averages of current velocity 

is not always a good representation of the data. At all sites gradients of current magnitude 

throughout the water column were observed, commonly on the order of 50 to 100 cm/s. Sites 

2 and 3 had very strong surface currents, which decay with depth, especially in the eastward 

velocity component for the summer and the northward velocity component for the winter 

(Figures 5.8, 5.9, and 5.11). At Site 4, there are not only gradients in current magnitude, but 

reversal throughout the water column (Figure 5.10). For the eastward velocity component 

this occurred on the ebbing tide and for the northward component, on the flooding tide. 

Waves 

Valuable information about wave forcing for this region is available by reviewing 

historical data from the Point Reyes Coastal Data Information Program (CDIP) buoy #029 

located approximately 20 miles west of Point Reyes in 550 m water depth (SCRIPPS 

Institution of Oceanography, 2006). Figure 5.13 displays wave direction histograms 

calculated by month from the time series of bulk wave parameters calculated from data 

measured at the CDIP buoy. Of particular interest is the strong dominance of waves coming 

from the northwest direction. From April through October, most waves come from 

directions ranging from 300 to 330 degrees. During the winter months, a much greater 

occurrence of waves are directed more onshore, from directions ranging from 270 to 300 

degrees. Figure 5.13 shows the maximum wave height and direction measured in each 

month, and during the winter (October through January) these maximum wave heights come 

from an onshore directed angle. Figure 5.13 also shows a greater occurrence of waves in the 

four to six meter range from November through March, as would be expected during winter 

storms. 

Bulk wave statistics determined from wave spectra show similar trends at all sites, 

lending some confidence to the wave output determined from multiple algorithms. Table 5.4 

includes basic statistics of these bulk parameters. Significant wave heights at Site 3 are 

larger than at Sites 1 and 2 in the northern stretch along Ocean Beach (Figure 5.14). For the 

component of waves coming from onshore directed angles, directions measured for the 

summer at Site 4 had a higher angle by approximately 30 degrees than directions measured at 

the inshore sites during the summer (Figure 5.14, 5.16). Similarly, wave directions 

determined for the winter deployment show approximately a 40 degree difference from Site 3 

in the same direction, originating more from the west than southwest (Figure 5.15, 5.16). 

Measurements at Site 3 for the winter show longer peak periods than offshore at Site 5, 

encompassing a ten degree spread rather than five degree spread, but similar trends are 

evident in both time series. 

 Figures 5.17 and 5.18 show the full 1-D spectrum at each site through time. Figure 

5.17 indicates that there were bi-modal spectra most of the time during the summer, so bulk 

wave statistics of peak period and peak direction would not do a very good job of describing 

the wave climate. It is evident in Figure 5.17 that Site 3 has the most energy in the summer 

months. Some tidal modulation of waves is reflected in these plots for both winter and 

59
summer conditions by the streaky energy in the spectral plots. Note that the winter plots 

have a different scale, and these plots show much more energy in the winter at both sites. 

Discussion 

Current and wave measurements spanning different seasonal conditions show spatial 

gradients in wave power and current magnitude in the region offshore of Ocean Beach, likely 

due to the proximity of the mouth of San Francisco Bay. The northern and central sections of 

the beach experienced very strong tidal currents on the order of 1 m/s, whereas the southern 

stretch had current magnitudes that were almost half as strong. However, plots throughout a 

tidal cycle showed that this relationship occurs on the flooding tide, but on the ebbing tide 

current speeds at Site 3 can equal or exceed those measured in the northern section of the 

beach. These currents flowed in an axis along the coast, were dominated by tidal forcing, 

and had a very small eastward component of flow. The strongest currents were at the 

surface, and vertical gradients in current magnitude showed velocities varying by as much as 

1 m/s throughout the water column, with an average range of velocities on the order of 25 

cm/s. At the outer sites, the influence of the mouth of the bay skewed the principal axis to be 

angled further east and the eastward component of flow began to dominate at Site 4 on the 

ebb-tidal delta. Measurements of current profiles on the delta also showed flow reversal 

within the water column, which occurred on the ebbing tide for eastward flow and on the 

flooding tide for northward flow. 

While the northern portion of the beach experienced stronger currents overall, wave 

energy was much greater in the southern portion near the erosion hotspot. This is reflected in 

the larger energy spectrum values for Site 3 and increased estimates of significant wave 

height at that location compared to Sites 1 and 2. The summer months were dominated by 

bimodal spectra with two peaks in energy representing local seas (8 second range) and swell 

(15 second range). For this reason, the peak direction jumps between the two values at 

different frequencies, and bulk parameters do not do a good job of representing the direction 

and frequency of energy, because they only include information for one peak. During the 

winter months, there was a more consistent dominant wave direction because the spectrum 

was usually unimodal, and dominated by long period energy. For both seasons, waves 

measured around 270o offshore have lower measured angles at the inshore sites (Figure 5.16). 

This suggests that complicated refraction patterns over the ebb-tidal delta caused the waves 

to be oriented more from the southwest as they propagated into shallower water. In addition, 

Figure 5.14 displays more southerly dominant wave angles at Site 2 than 3 during the 

summer, and a closer look at the spectral plot (Figure 5.17) shows that the lower frequency 

peak dominated more often at Site 2 than at Site 3. In reality, both sites were seeing two 

different peaks in energy coming from different directions, but the bulk parameter plot is 

misleading. 

Figure 5.19 shows calculated magnitudes of alongshore transport (Q) using the CERC 

formula (ERDC, 1984) and a gamma value of 0.78, K of 0.60, n of 0.4, and a breaking wave 

height at the instrument location determined through conservation of energy. This 

formulation is very dependent on wave direction, and shows increased wave energy at Site 3 

during the winter (Figure 5.17) and more southwest directions at Site 2 in the summer 

(Figure 5.14). This longshore transport calculation is based on wave parameters and 

shoreline angle, and therefore does not include a lot of important components at Ocean 

Beach, where tidally-forced currents are very strong. Figure 5.19 does not identify a clear 

nodal point, although Figure 5.19 a shows times when the direction of transport was to the 

60
north at Site 2 and to the south at Site 3 (07/5/05-7/10/05, 07/17/05-07/20/05, 07/25/05-

07/30/05). Most of the beach change occurred during the winter months, and magnitudes of 

transport were greater in Figure 5.19 b due to increased wave energy. For the summer, most 

transport was south at Site 3, but in the winter the direction of transport was almost always 

directed north due to the more onshore directed wave climate. As a result of instrument loss 

at Site 1, there is no data from the northern portion of the beach to compare this transport 

direction with for the winter deployment, when magnitudes of sediment transport are likely 

highest. 

Conclusions 

• Current magnitudes are much greater along the northern portion of Ocean Beach 

due to the proximity of the mouth of the bay (root mean square values of depthaveraged currents were 50% greater at Site 1 than at Site 3), but wave energy is 

much greater along the southern portion (mean wave height was 15% greater at 

Site 3 than at Site 1) where erosion problems are greatest. 

• The gradients in current speed along Ocean Beach varied with the tide, where 

northern currents speeds were greater on the flooding and high tides and southern 

current speeds began to dominate on the ebbing and low tides. 

• Current directions along Ocean Beach were shore-parallel, whereas the offshore 

sites show principal axes shifted more east-west, with an increasing eastward 

magnitude of flow with increased northing and proximity to the mouth of the bay. 

• In the along-shore direction, vertical gradients in current magnitude of northsouth directed currents increased with increasing distance from the inlet; variation 

in current magnitude throughout the water column was greatest at Site 3. Eastwest currents show a relatively stronger vertical decay due to the influence of 

wave-induced currents. At the offshore sites (Sites 4 and 5) vertical gradients 

were apparent for both the north-south and east-west currents, and Site 4 had 

current reversal with a changing tide. 

• Refraction patterns across the delta oriented waves with an onshore direction 

around 270o in a more southwest direction as they propagated into shallower 

water. 

• Calculations of alongshore transport using wave measurements at Sites 1-3 and 

the CERC equation indicate the direction of transport was north in the winter at 

Site 3 and suggest that a nodal point existed somewhere between Site 2 and Site 3 

during the summer. 

61
Table 5.1. Summer 2005 current profiler sampling design. 

Parameters Site 1 Site 2 Site 3 Site 4 

Instrument Type RDI ADCP RDI ADCP RDI ADCP Nortek AWAC 

Instrument Serial Number 2054 5620 3796 WAV 5179 

Frequency (kHz) 1200 1200 1200 1000 

Coordinate System BEAM BEAM BEAM ENU 

Blanking distance (m) 0.44 0.44 0.44 0.50 

Current Sampling: 

Cell size (m) 1 1 1 1 

Ensemble interval (min) 10 10 10 20 

Ensemble Averaging Length 

(min) 1 1 1 1.5 

Sampling Rate (Hz) 1 1 1 61

Wave Sampling: 

Cell size (m) 1 1 1 2.52 

Burst interval (min) 120 120 120 20 

Sampling rate (Hz) 2 2 2 1 

Samples per burst 8192 8192 8192 1024 

1

 Internal sampling rate is 6 Hz but the fastest the instrument can write out data is 1 Hz (Nortek 2004). 

Table 5.2. Instrumented Frames Deployed at Ocean Beach in 2005 / 2006. 

Deployment 

Campaign Location Deployment Dates Latitude Longitude Instruments 

Summer 2005 Site 1 06/21/05 – 

08/16/05 

37.775 

N 122.519 W RD I 1200 kHz ADCP S/N 2054 

Site 2 06/21/05 – 

08/16/05 

37.756 

N 122.520 W RD I 1200 kHz ADCP S/N 5620 

Site 3 06/21/05 – 

08/16/05 

37.726 

N 122.518 W RD I 1200 kHz ADCP S/N 3796 

Site 4 06/21/05 – 

07/26/05 

37.789 

N 122.643 W Nortek AWAC S/N WAV 5179 

Winter 2006 Site 1 01/12/06 -

present 

37.775 

N 122.520 W RD I 1200 kHz ADCP S/N 6363 

Site 3 01/12/06-

02/10/06 

37.726 

N 122.518 W RD I 1200 kHz ADCP S/N 2054, Microcat CTD S/N 2538 

Site 5 01/12/06-

02/11/06 

37.747 

N 122.609 W Nortek AWAC S/N WAV 5179, Microcat CTD S/N 3013 

62
Table 5.3. Basic Statistics for Depth-Averaged Currents. 

Eastward Velocity (m/s) Northward Velocity (m/s) 

Deployment Location mean min max rms mean min max rms 

Summer 

2005 Site 1 -0.05 -0.44 0.21 0.09 0.29 -0.94 1.35 0.60 

Site 2 -0.00 -0.23 0.33 0.07 0.14 -1.02 1.09 0.48 

Site 3 0.01 -0.11 0.16 0.04 0.07 -0.86 0.70 0.31 

Site 4 -0.07 -0.44 0.28 0.16 0.04 -0.47 0.56 0.15 

Winter 

2006 Site 3 -0.03 -0.43 0.17 0.06 0.04 -0.79 0.74 0.31 

Site 5 -0.03 -0.56 0.43 0.18 -0.07 -0.78 0.67 0.31 

Table 5.4. Basic Statistics for Wave Parameters. 

Hs Tp Dp 

Deployment Location mean min max mean min max mean min max 

Summer 

2005 Site 1 1.2 0.9 1.7 15.5 8.5 18.2 238 206 290 

Site 2 1.1 0.6 2.0 12.6 4.1 21.3 252 198 309 

Site 3 1.4 0.7 2.4 10.1 3.3 18.2 270 178 324 

Site 4 1.2 0.6 2.2 10.1 4.5 16.6 273 224 304 

Winter 

2006 Site 3 2.1 0.8 4.1 14.6 9.8 21.3 245 226 306 

Site 5 2.6 1.1 5.6 12.0 9.1 18.3 276 256 294 

63
Figure 5.1. Instrument deployment sites at Ocean Beach. 

a) 

64
b) 

Figure 5.2. Photographs of typical instrumented tripods deployed at a) Sites 1-3 and b) Sites 

4-5.

Figure 5.3. Water density calculated for Site 3 during winter 2006 deployment. 

65
Figure 5.4. Principal axis calculations for depth-averaged current measurements at a) Site 1 

summer 2005 b) Site 2 summer 2005 c) Site 3 summer 2005 d) Site 4 summer 2005 e) Site 3 

winter 2006 f) Site 5 winter 2006. 

66
67
68
Figure 5.5. Flow patterns measured at Ocean Beach throughout a tidal cycle on 06/25/05 

during the summer 2005 deployment. Plot a) shows the measured tide at Site 1; points and 

text refer to measured currents in plots b) through i). Depth values are shown by colored 

contours and currents at different vertical locations have colored arrows. 

69
70
71
Figure 5.6. Flow patterns measured at Ocean Beach throughout a tidal cycle on 01/28/06 

during the winter 2006 deployment. Plot a) shows the measured tide at Site 3; points and text 

refer to measured currents in plots b) through i). Depth values are shown by colored contours 

and currents at different vertical locations have colored arrows. 

72
Figure 5.7. Current profile plots through time for summer deployment at Site 1 a) eastward 

velocity b) northward velocity. (Note that this is a different time period than the other plots 

and only 4 days since the instrument was buried.) 

73
Figure 5.8. Current profile plots through time for summer deployment at Site 2 a) eastward 

velocity b) northward velocity. 

74
Figure 5.9. Current profile plots through time for summer deployment at Site 3 a) eastward 

velocity b) northward velocity. 

75
Figure 5.10 Current profile plots through time for summer deployment at Site 4 a) eastward 

velocity b) northward velocity. (Note the different scale on both axes from previous plots 

because of more onshore directed flow at Site 4). 

76
Figure 5.11. Current profile plots through time for winter deployment at Site 3 a) eastward 

velocity b) northward velocity. 

77
Figure 5.12. Current profile plots through time for winter deployment at Site 5 a) eastward 

velocity b) northward velocity (Note the different scale on both axes from previous plots 

because of more onshore directed flow at Site 5). 

78
Figure 5.13. Direction histograms for Point Reyes CDIP buoy #029 by month for all available 

wave data measured from 1996 through 2006 (N is number of observations out of a total 

156,828, the percentage is for the total data that occurred in that month, and hm is the 

maximum wave height for the month which came from a direction marked by the solid black 

line) (SCRIPPS Institution of Oceanography, 2006). 

79
Figure 5.14. Wave parameters calculated from measurements during summer 2005 

deployment at Sites 1 – 4 a) significant wave height b) peak wave period c) peak wave 

direction. 

80
Figure 5.15. Wave parameters calculated from measurements during winter 2006 deployment 

at Sites 3 and 5 a) significant wave height b) peak wave period c) peak wave direction. 

81
Figure 5.16. Polar plots of wave direction and height for the a) summer 2005 deployment and 

b) the winter 2006 deployment. (Note the different radial axis due to larger wave heights in 

the winter). 

82
Figure 5.17. 1-D Spectral evolution through time from measurements during summer 2005 

deployment for a) Site 1 b) Site 2 c) Site 3 d) Site 4. 

83
Figure 5.18. Spectral evolution through time from measurements during winter 2006 

deployment for a) Site 3 b) Site 5. 

Figure 5.19. Estimated longshore transport (Q) from CERC equation for Sites 1-3 along Ocean 

Beach (Note the difference in units along the y-axis). 

84
Chapter 6-Surf Zone Instrument Deployments 

By Li Erikson and Jodi Eshleman 

Introduction 

A surf zone study was conducted over five days (1/23/2006 – 1/27/2006) approaching 

spring tides (maximum measured tide range was 2.2 meters). A total of five upward looking 

2 MHz Nortek AquadoppTM (http://www.nortek-as.com/) current profilers were deployed at 

nine select locations along Ocean Beach (Figure 6.1, Table 6.1). The measurements were 

used to investigate surf zone hydrodynamics and sediment transport in the breaking region 

along the beach, calibrate and validate the numerical models Delft3D and NearCoM, and 

support the development and validation of models describing swash hydrodynamics and 

runup statistics at Ocean Beach. Concurrent with the Aquadopp measurements, time-stack 

and time-averaged images of the surf zone were collected (see Chapter 4), as well as 

sediment grain size, beach topography, and bathymetric profiles (Chapter 3). At the time of 

writing this report, the beach topography and bathymetry data have not been post-processed 

and so are not included in the Figures. 

The Aquadopp profilers were mounted on aluminum frames that were deployed at 

low tide, and secured with sand anchors. Total water depths ranged from 2.7 m to complete 

exposure during times of negative tide. Due to the fluctuating tide and relatively constant 

wave climate (1.19 < Hs

 < 1.87 m), the break points moved so that the instruments were well 

within or outside the surf zone at different times during the measurement period. The frames 

were partially buried in the sand and stabilized with weights and two sand anchors on either 

side of the frame along the direction of breaking waves (Figure 6.2) so as to keep the 

instruments in place on the seabed and within the high-energy surf zone. 

The Aquadopps measured depth (pressure), heading, pitch, and roll and recorded 

velocity data in east, north and up coordinates in 40 ten centimeter vertical bins. Data was 

collected continuously at 1 Hz (Table 6.2), which allowed for flexibility in post-processing. 

This setup was chosen over added deployment length because the dynamic surf zone 

environment contains air bubbles and turbulence that make data-screening and manipulation 

more challenging than in deeper areas. By maximizing the amount of data saved, it was 

possible to assess a variety of averaging intervals and data screening techniques to get the 

best possible characterization of surf zone activity from the measurements. 

Methods 

Currents 

Data was saved internally in the Aquadopp profilers and extracted to binary format 

using the Nortek proprietary AquaPro software and subsequently converted to Matlab binary 

format. In order to eliminate ‘bad’ velocity data and account for times when the instruments 

were out of the water, several steps were undertaken as part of data post-processing, Timeseries endpoints associated with before and after instrument deployments were removed as 

were data spikes, defined as data values equal to three times the standard deviation of the 

entire time-series. Measurement points with low signal-to-noise ratio (SNR<120 counts) 

were removed (Nortek AS, TN-020), as were date in upper bins where sidelobe interference 

85
was predicted to occur. Lastly, the current data was time-averaged with a running mean over 

six wave cycles (estimated to be 6x15=90 s) to remove additional noise. 

Waves 

Bulk wave parameters were calculated with the well known PUV technique where pressure 

(P) was used to estimate wave heights and peak periods 

(http://www.nortekusa.com/software/QuickWave.html, 2006). Although less reliable in the 

surf zone, the east-west and north-south velocities (UV) in the bin closest to the bed were 

used to estimate wave directions. Significant wave heights were calculated with the classical 

approach of s = 4 CH ηηp where is the surface elevation energy spectra after 

accounting for non-linear transfer from the near bottom to the surface. Measurements were 

binned to 17 minute segments (1024 sampling points at 1Hz) with a low frequency cutoff set 

at 0.035 Hz. A series of ‘reality checks’, such as the maximum wave steepness and 

maximum ratio of wave height to water depth, were used to infer erroneous wave height 

estimates. 

Cηηp

Results 

Figure 6.3 presents 24 hour time-series of post-processed depth and current 

measurements obtained at sz1 through sz6 at the north end of Ocean Beach, and at sz8 at the 

south end of Ocean Beach. No data was recorded at sz9, just south of sz8 (Fig. 6.1) due to 

instrument failure. Plots 6.3a through 6.3d and 6.3h show concurrent measurements at sites 

sz1 through sz4 at the north end of Ocean Beach and at sz8 at the south end of the beach. 

The remaining plots span subsequent full tide cycles. The measurements shown here are 

only a subset of the available dataset; the total length of the experiment was more than three 

days. 

Sampling sites sz1 and sz2 were aligned in the cross-shore direction with sz2 located 

closer to the shore. The instrument at sz2 was out of the water during low tide as evidenced 

by the pressure signal at the beginning of the time-series (Fig. 6.3b). A second cross-shore 

array, slightly further south, was also deployed during the same time-interval. A comparison 

of plots 6.3ai with 6.3bi and 6.3ci with 6.3di show that the flow direction and variation of 

relative magnitude are correlated in time, suggesting that there was strong uniformity in 

cross-shore currents. However, the magnitude was greater and more complex at the offshore 

sites as compared to the inshore sites. 

Disregarding the lack of data near the bed due to instrument blanking distance, there 

does not appear to be much vertical structure except during high tide. This was particularly 

noticeable at sz4 (Fig. 6.4di) where the velocities decayed from 40 cm/s to near zero at 25 cm 

above the bed. Also, at sz4, the cross-shore flow direction switched drastically from about 

35 cm/s shoreward to 45 cm/s seaward halfway through ebbing tide. Flow reversal is 

apparent at all the sites along the north end of Ocean Beach and may be at least partially 

related to the eddies that form from tidally driven flows around Pt. Lobos just to the north 

(see the modeling chapter for further discussion). The intermittent pattern of very low flow 

velocities to rather strong currents during the flood at sz1 and sz2 are likely related to the 

complex hydrodynamics such as reflection and diffraction around the outcrop at the north 

end of Ocean Beach. 

86
With respect to the north-south direction (v-directed velocities), the currents were 

quite strong reversing from a southerly directed average 50 cm/s current during ebb-tide to an 

equally strong current northward near low tide. In Figure 6.4, the measurements have been 

rotated to the along- and cross-shore directions, and the maximum measured depth-averaged 

currents over the same tide cycle shown with vectors for sites sz1 through sz4. Maximum 

currents were on the order of 0.63 m/s in the cross-shore direction and 0.73 m/s in the alongshore direction. The along-shore currents were greater when heading north, except at 

sampling station sz2, located furthest inshore (~85) where the southward directed alongshore currents were 10 cm/s greater than the northward bound currents. This apparent crossshore distribution of the along-shore current can have a significant impact on longshore 

sediment transport patterns. 

Time-series of breaking parameters (Hs/h) are shown for sites sz1 through sz4 at the 

north end of Ocean Beach in Figure 6.5b. The horizontal dashed line at Hs/h=0.78 is the 

proxy to breaking conditions. Recalling that sz1/sz2 and sz3/sz4 were in cross-shore arrays, 

it is clear that the instruments along the northern array at sz1/sz2 were under changing surf 

zone conditions, while the array formed by sz3/sz4 was situated either at the inner or outer 

part of the surf zone. The fact that little shoaling occurred at sz3/sz4, even during the lower 

stages of the tide, suggests that the instruments were in the inner part of the surf zone and 

that the shoal associated with the ebb-tidal delta caused the waves to break offshore of 

sz3/sz4. For the sz2/sz3 array, it is apparent that breaking occurred at the offshore 

instrument, sz1, at the beginning of the time series during lower tide and higher offshore 

wave conditions. Offshore wave conditions measured with an ADCP at Site5 (see chapter on 

‘offshore instrument deployments’) are shown in the upper plot of Figure 6.4. Although an 

ADCP was placed just outside the surf zone (Site 1, square in Fig. 6.1) specifically for this 

study, data was not retrievable and hence Site 5 is used to assess the offshore conditions. 

Following the start of the shown time-series (Fig. 6.4), the offshore wave heights decreased 

and remained fairly constant with the exception of similar conditions around 06:00 hrs. The 

increased signal is apparent in the breaking parameter at sz1/sz2. During the lower high tide 

and higher low tide (between 03:00 and 09:00 hours), the break point moved shoreward from 

sz1 toward sz2. At high tide there was a drop-off of the breaking parameter, and breaking 

appears to have occurred landward of sz2 but then back out to sz2 during ebbing tide. This 

cycle is expected to repeat itself with the tide cycle and vary depending on offshore 

conditions. With these few select point measurements, the entire surf zone, and variations 

along shore, were measured and are expected to be of great value in furthering the 

understanding of surf zone processes at Ocean Beach. 

 

Discussion 

Assessment of the data suggests that the measurements obtained with the Aquadopps 

in the surf zone are reasonable and representative of the conditions at the time of the field 

study. A series of checks and evaluations of the pressure and velocity spectra, vertical 

current structure, predicted breaking, wave steepness, and correlation between offshore wave 

parameters and surf zone conditions indicate that the resulting current measurements and 

calculated wave parameters are within reason. Air bubbles during breaking and stronger than 

normal pressure attenuation due to highly non-linear effects of near breaking waves may 

have introduced errors in the measurements that were not explicitly accounted for however. 

In shallow water, nonlinearly forced high frequency components are strongly amplified and 

87
significantly change the local wave kinematics. Constantian (1999) and Herbers and others 

(2002) showed that the observed vertical attenuation of horizontal velocity spectra at high 

frequencies in eight and four meter depths was much weaker than predicted using linear 

theory, whereas at two meter depths there was little difference. To resolve this issue, they 

suggest to include a Boussinesq term in the transfer function. Because the measurements 

obtained for this study were all in water depths less than 3 m, the Boussinesq term was not 

included in the calculations, but may provide increased accuracy if accounted for. 

Conclusions 

• Analysis of surf-zone current data shows that instantaneous flows (O(50 cm/s)) occur 

in both the cross-shore and along-shore directions. 

• Simultaneous cross-shore current data show that flow direction and variation of 

relative speeds were correlated in time, suggesting that there was strong uniformity in 

cross-shore currents, but that the speeds were greater in the outer surf zone. 

• Simultaneous along-shore current data suggest that the maximum northward oriented 

tidal currents are stronger than southward currents but also that there is a cross-shore 

variation of the longshore currents such that the southward oriented currents are 

stronger further inshore. 

• There is little vertical current structure in the surf zone except near the bottom during 

high tide in east-west directed currents. 

• North-south currents within the surf zone reversed from a southerly directed 50 cm/s 

flow during ebb-tide to an equally strong northward flow at low tide. East-west 

currents were also tidally driven but were slightly slower (35 cm/s to 45 cm/s). 

• With varying tide levels and offshore wave conditions on the order of Hs=1.5 m, the 

outer limit of the surf zone moved more than 40 m in the cross-shore direction with 

energy dissipation widths exceeding 20 m. 

88
Table 6.1 Nortek Aquadopp profiler locations and sampling times at Ocean Beach. 

Site Dates Lat Long Distance to 

shore (m) 

Instrument 

ID 

sz1 01/23/06-01/25/06 37.777 N 122.514 W 104 S/N Y06 

sz2 01/23/06-01/25/06 37.777 N 122.514 W 85 S/N W5 

sz3 01/22/06-01/25/06 37.775 N 122.514 W 120 S/N Y4 

sz4 01/23/06-01/27/06 37.775 N 122.514 W 139 S/N BY3 

sz5 01/25/06-01/28/06 37.775 N 122.515 W 180 S/N Y4 

sz6 01/26/06-01/27/06 37.774 N 122.514 W 111 S/N Y06 

sz7 01/25/06-01/28/06 37.774 N 122.515 W 210 S/N W5 

sz8 01/24/06-01/26/06 37.736 N 122.509 W 95 S/N O2 

sz9 01/24/06-01/26/06 37.735 N 122.509 W 86 S/N B1 

Table 6.2 Aquadopp profiler setup. 

Parameters Value 

Instrument Type Nortek Aquadopp 

Profiler 

Corrected Magnetic Declination +14.77 

Cell size – Currents (m) 0.1 

Number of Cells 40 

Sampling Rate (Hz) 1 

Blanking distance (m) 0.1 

89
Figure 6.1. Overview of Aquadopp instrument deployments (01/23/06- 01/27/06). Data was not 

recorded at sz9 and the northern ADCP (Site1). 

90
(a) 

(b) 

Figure 6.2. Aquadopp frame setup and surf zone deployment scheme: (a) deployment 

schematic, and (b) photo of instrument and frame. 

91
92
93
94
95
96
Figure 6.3. Measured water depth and vertical current structure measured with Nortek 

Aquadopps during the surf zone field study. Data shown are for complete tide cycles 

(depending on data availability) for measurement sites from north to south (sz1 through sz8); 

u-directed: east-west with east positive, v-directed: north-south, with north positive. 

97
Figure 6.4 Maximum depth averaged currents measured in the surf zone at the north end of 

Ocean Beach during a complete tide cycle (Jan 24-25, 2006). 

98
(a)

(b) 

Figure 6.5. Variations of the breaking parameter with tide level at the north end of Ocean 

Beach. Upper plot (a) shows concurrently measured offshore wave conditions at ADCP Site 

5. Lower plot (b) shows calculated breaking parameters for surf zone measurements at sz1 

through sz4 and measured water depth at sz1. Dashed horizontal line is the 0.78 breaking 

ratio. 

99
Chapter 7-Multibeam Mapping 

By Patrick L. Barnard 

Introduction 

Forty-four days of multibeam mapping were conducted at the mouth of San Francisco 

Bay (Figure 7.1) during the fall of 2004 and 2005 through a USGS-USACE-California State 

University, Monterey Bay Seafloor Mapping Lab (SFML) collaboration (Barnard and others, 

2006a; Barnard and others, 2006c). The primary goals of this survey were to: 

• evaluate bathymetric change at the mouth of San Francisco Bay since the last 

comprehensive bathymetric survey was completed in 1956 

• document dominant sediment transport pathways 

• estimate bedload transport via multiple surveys of a transect through an active 

bedform field 

An additional 7 surveys of the Ocean Beach Disposal Site were completed in the 

summer of 2005 and 2006 (Barnard and Hanes, 2006). These surveys documented the 

morphological evolution of a nearshore disposal site. 

Methodology 

The mouth of San Francisco Bay was mapped using a Reson 8101 multibeam sonar 

system aboard the R/V VenTresca operated by the Sea Floor Mapping Lab (SFML) at the 

California State University of Monterey Bay, between 9/15/2004–10/31/2004, and between 

9/17/2005-10/30/2005. Passes over a large bedform field in the Golden Gate were completed 

October 17, 18, 25 and 30, 2004, and September 17, 18, and October 30, 2005, to measure 

sand wave migration rates. The 8101 operates at 240 kHz and measures relative water depths 

within a 150° swath consisting of 101 1.5° x 1.5° beams. This transducer geometry makes 

the 8101 capable of taking up to 3,000 soundings per second with swath coverage of up to 

7.4 times the water depth. A Trimble® 4700 GPS receiver logged position and attitude data 

with differential corrections provided by a Trimble® ProBeacon receiver. Horizontal 

positional accuracy of this system is typically +/- 1-2 m. Attitude (pitch, roll, yaw, and 

heave) data were recorded at 200 Hz by a TSS Position and Orientation System, Marine 

Vessel (POS-MV). Attitude accuracy for the POS/MV pitch, roll and yaw measurements 

averaged +/-0.03°, while heave accuracy was maintained at +/-5% or 5 cm. Sonar, position, 

and attitude data were logged in XTF format using a Triton Elics Isis data acquisition system 

running Isis Sonar software. Multibeam data were monitored in real-time using the 8101 

Sonar Processor control interface and 2-D and 3-D display windows in the Isis Sonar and 

DelphMap software. Survey planning and navigation were performed using Coastal 

Oceanographics Hypack Max software. Surface-to-seafloor profiles of the speed of sound 

through the water were collected periodically during the surveys with an Applied 

Microsystems Limited (AML) SV+ sound velocity profiler. These profiles were used to 

correct for variations in sound velocity due to salinity and temperature changes throughout 

the water column. 

Shipboard data were post-processed using CARIS Hydrographic Information 

Processing System (HIPS) 5.4 software. Tide and SVP (sound velocity profile) corrections 

100
were applied, and the sounding data were cleaned to remove erroneous soundings. The HIPS 

refraction coefficient editor was used where necessary to reduce artifacts due to inadequate 

sound velocity compensation. The 1138 survey lines yielded a total of 1,108,456,315 

soundings. 

For the mouth of San Francisco Bay the tides were obtained from the NOAA 

(2006b). Verified tides from the tide gauge at San Francisco-Fort Point using a six-minute 

interval at MLLW were applied. For the rest of the area that was surveyed, verified tides 

were taken from the NOAA website and subtracted the difference of predicted tides from the 

Golden Gate minus the predicted tides at the San Francisco ebb-tidal delta. The predicted 

tides from the Golden Gate and SF Bar were taken from the program Tides and Currents 

Lite. The vertical error arising from the tide corrections and GPS positioning combined is 

estimated at +/- 12 cm. 

Grids for the entire survey as well as each of the sand wave migration surveys were 

created from the cleaned x-y-z files using a weighted moving average method. Measurements 

of sand wave position, slope, wavelength and height were determined using tools in ArcGIS©, 

Fledermaus©

 and Matlab©. Analysis of bedform characteristics from the individual surveys 

was performed to quantify wavelength, orientation, amplitude, and slope. Difference maps 

between surveys were generated to quantify the spatial offset through time of the bedform 

field, migration rates, and bedform morphology evolution. 

Results 

Overview 

The bathymetry at the mouth of San Francisco Bay has changed considerably since 

the last complete survey was conducted by the National Ocean Service (NOS) in 1956. The 

large-scale trend is sediment loss (Figure 7.2). The average depth change in the region was 

-60 cm (-2.0 ft, erosion), which amounts to approximately 92 million m3 (120 million yd3) of 

sediment loss in the common survey area in 50 years. The outer lobe of the ebb-tidal delta is 

dominated by erosion, with the exception of two distinct accretionary mounds in the vicinity 

of SF-8, the USACE disposal location for ship channel dredging since 1971 (United States 

Army Corps of Engineers, 1996). Most of the region offshore of the erosion hot spot at 

Ocean Beach has lost more than 1 m of sediment since 1956, reducing the wave protection 

these shoals formerly provided to the adjacent beach, and indicating a general reduction in 

sediment supply to this reach of the ebb tidal delta. 

Mapping of bedform orientations throughout the study area shows that most bedforms 

are controlled by the dominant tidal current directions associated with flux in and out of San 

Francisco Bay (Figure 7.3). The lone exception is an area of divergence along the peak of the 

southern lobe of the ebb tidal delta, along the bar that intersects central Ocean Beach. The 

largest bedforms (maximum height= 10 m, wavelength = 317 m) can be found in the inlet 

throat (Figure 7.4), near the Golden Gate, where tidal power is focused to produce currents 

greater than 2.5 m/s during ebb and flood tide. 

Massive Sand Waves of the Golden Gate 

Some of the largest sand waves in the world are located just west of the Golden Gate 

Bridge- these waves have been formed by abundant sediment and extremely powerful tidal 

currents (Figures 7.5-7.6). This massive sand wave field covers an area of approximately 4 

101
km2

 (1.5 mi2) in water depths ranging from 30 m (98 ft) to 106 m (348 ft). More than 40 

distinct sand waves were identified; the waves have an average wavelength of 82 m (269 ft) 

and an average height of 6 m (20 ft). The maximum wavelength and height are 317 m (1040 

ft) and 10 m (33 ft), respectively. Sand wave crests can be traced continuously for as far as 2 

km across the mouth of this energetic tidal inlet, where each tide forces 2 billion m3

 (528 

billion gallons) of water through the Golden Gate. The resulting strong currents sweep large 

volumes of sediment between the narrow rocky headlands, spanned by the Golden Gate 

Bridge, into the Bay during the flooding tide and toward the Pacific Ocean during the ebbing 

tide. 

The complex temporal and spatial variations in wave and tidal current interactions at 

the mouth of San Francisco Bay result in a diverse array of bedform morphologies, scales, 

and orientations (Figure 7.7; Barnard and others, 2006). Strong tidal currents peak at over 2.5 

m/s (5.6 mi/hr) and rocky headlands and embayments help to create strong eddies and 

reverse flows, all of which combine to form highly variable bottom features. 

Multiple surveys of a 2.5 km (1.6 mi) track line through the center of the massive 

sand wave field were completed in 2004 and 2005. Analysis of these surveys enables the 

calculation of short- (daily) and long-term (annual) rates of bedform migration and sediment 

transport. In 2004, surveys repeated as frequently as 24 hours (Figure 7.8) showed that crests 

shifted as much as 3 m (10 ft), whereas over the entire 13-day sampling period the average 

migration of each sand wave was just 1.4 m (4.4 ft), or 11 cm/day (4.3 in/day). However, the 

2005 surveys indicate that the net migration rate, when averaged over an entire year, is just 7 

m (23 ft), or less than 2 cm/day (0.7 in/day) seaward. These data show that strong tidal 

fluctuations cause daily sand wave oscillations that are a significant percentage of annual 

migration rates, but flow reversals result in a relatively low rate of net sand wave migration 

annually (Barnard and others, 2006). 

Offshore Ocean Beach 

Offshore of Ocean Beach, the bedform orientation indicates dominance by tidal 

forcing outside of the surf zone (Figure 7.3; Jordan, 1962). Most bedforms in the northern 

half of Ocean Beach are oriented with their crests nearly perpendicular to the shoreline 

(Figure 7.9 a, Inset A), while toward the middle of the beach, approximately 1.5 km north of 

the erosion hot spot, there are onshore-directed bedforms, an indication of onshore-directed 

transport (Figure 7.9, Inset B). The Southwest Ocean Outfall Pipe, constructed in the late 

1970’s (Woodward Clyde Consultants, 1978), is located in the southern end of Ocean Beach 

and carries approximately one-third of San Francisco’s treated sewage out to sea. The only 

bedforms observable offshore of the erosion hot spot are scour ripples associated with the 

Outfall Pipe and ripple scour depressions oriented east-west. The Southwest Ocean Outfall 

Pipe is exposed and is causing severe scour in the immediate vicinity (Figure 7.10). The 

ramifications for the structural integrity of the outfall pipe and the influence of this scour on 

the adjacent coastline are unknown. 

Dredge Disposal Monitoring 

In an effort to reduce the erosion south of Sloat Blvd. at Ocean Beach and avoid 

hazardous navigation conditions at the current disposal site (SF-8), a new plan for the 

management of sediment dredged annually from the main shipping channel at the mouth of 

Francisco Bay was implemented in May 2005 by the USACE, San Francisco District. The 

102
objective for USCAE was to perform a test dredge disposal of approximately 230,000 m3

(300,000 yd3) of sand just offshore of the erosion hot spot, in depths between approximately 

9 m and 14 m. This disposal site was chosen because it is in a location where the strong tidal 

currents associated with the mouth of San Francisco Bay and waves can potentially feed 

sediment toward the littoral zone in the reach of the beach that is experiencing critical 

erosion. The onshore migration of sediment from the target disposal location might feed the 

primary longshore bar or the nearshore zone, and thus provide a buffer to erosion that peaks 

during winter months when large waves impact the region. The USGS, in collaboration with 

SFML, monitored the initial bathymetric evolution of the test dredge disposal site and the 

adjacent coastal region from May 2005 to November 2005. Multibeam surveys of the region 

were able to track the evolution of the disposal mound for one year. After the initial dispersal 

of the disposal mound by approximately 50%, the volume remained fairly steady and slowly 

migrated toward shore. As of May 2006, one year after initial disposal, the mound had 

migrated 100 m toward shore. Complete results of this preliminary monitoring effort can be 

found in (Barnard and Hanes, 2006; Barnard and others, 2006b) 

Discussion 

Several likely causes for the observed erosion trend at the mouth of San Francisco 

Bay include the reduction in tidal prism of approximately 30 percent due to development and 

loss of wetlands in San Francisco Bay, a decrease in sediment supply due to removal by sand 

mining inside the bay of approximately 50 million m3 (65 million yd3) since the middle of 

20th Century (Chin and others, 1998; 2004), and a reduced influx of hydraulic mining debris 

from the Sacramento River (Gilbert, 1917). There are two distinct accretionary mounds just 

south of the main shipping channel, presumably the result of the annual dredge disposal of 

shipping channel sediments in this area, that have totaled about 18 million m3

 (24 million yd3) 

since disposal commenced on this site (SF-8) in 1971 (USACE, 1996). The dredging of the 

ship channel and the shrinking of the ebb tidal delta has led to filling in the of the peripheral 

secondary tidal channels offshore of Ocean Beach and Point Bonita, and therefore may also 

be at least partially responsible for the observed accretion trend at the northern end of Ocean 

Beach (see Chapter 2). 

The presence of large, alongshore migrating bedforms suggests that tidal currents 

dominate sediment transport patterns offshore of Ocean Beach despite a robust wave climate. 

However, erosion of the shoals offshore of the Sloat region over the last 50 years is likely a 

major cause of the chronic erosion along this stretch of coastline, due to increased 

susceptibility to wave attack. 

Future Work 

The California Coastal Conservancy has commissioned a nearshore multibeam survey 

within the 3 mile limit extending from Año Nuevo to Bolinas that began in fall 2006 and will 

fill in the entire inner shelf of the San Francisco Bight not covered in the USGS study. 

Dredge disposal monitoring continues, as do annual surveys of the sand wave field in the 

Golden Gate. 

103
Conclusions 

• The ebb-tidal delta at the mouth of San Francisco Bay has experienced a large 

scale erosion trend over the last 50 years. 

• Erosion of the shoals offshore of southern Ocean Beach has made the adjacent 

beach more susceptible to wave attack. 

• Large, dynamic sand waves are located in the Golden Gate and off Point 

Lobos. 

• Dominant sediment transport patterns outside the surf zone are controlled by 

tidal forcing, evident by the presence of alongshore migrating bedforms. 

• Bedload sediment transport is seaward through the center of the inlet and 

toward the bay adjacent to Baker Beach. 

104
Figure 7.1. Shaded relief image showing the multibeam coverage area from the 2004-2005 

survey and the location of sand wave migration surveys in the Golden Gate. 

105
Figure 7.2. Change between bathymetric surveys conducted in 1956 and 2005. 

106
Figure 7.3. A) Bedform orientation based on sand wave orientation, and B) dominant sediment 

transport direction as inferred from bedform shape asymmetry. 

A 

107
B 

108
Figure 7.4. Map of bedform A) wavelength and B) height, gridded to 50 m cell resolution. 

A 

109
B 

110
Figure 7.5. View of the giant sand waves at the mouth of San Francisco Bay (from Barnard 

and others, 2006a). View is to the east toward San Francisco Bay. The Golden Gate Bridge is 

approximately 2 km (1.2 mi) long. Shaded relief image created with a 2-m grid, 4x vertical 

exaggeration, sun azimuth of 240 degrees, and sun angle of 66 degrees. The land topography 

was generated by overlaying digital orthophoto quadrangles (DOQs) on USGS digital elevation 

models (DEMs), with a 2x vertical exaggeration. Bathymetry data inside the Bay (that is east 

of Golden Gate Bridge) is from Dartnell and Gardner (1999). Golden Gate Bridge model 

courtesy of Interactive Visualization Systems.

111
Figure 7.6. Oblique view of the giant sand waves at the mouth of San Francisco Bay (from 

Barnard and others, 2006a). View is south across the Golden Gate toward Baker Beach and 

the city of San Francisco. See Figure 7.5 for more image information. 

112
Figure 7.7. Diverse sand waves at the mouth of San Francisco Bay, seaward of the Golden 

Gate Bridge. Shaded relief image created with 5x vertical exaggeration, sun elevation of 45 

degrees, and sun azimuth of 45 degrees. (A) Irregular sand waves seaward of the main sand 

wave field. (B) Ebb-dominated sand waves with wavelengths as great as 150 m with 

superimposed sand waves of 5 m to 10 m wavelength. (C) Linguoid sand waves, 20 m to 30 m 

in wavelength. (D) Flood-dominated sand waves, 15 m to 20 m in wavelength, just offshore of 

Baker Beach.

113
Figure 7.8. Overview of large sand wave field and high resolution difference map of two 

surveys approximately 21 hours apart illustrating both large-scale and small-scale sand wave 

migration and orientation. Migration is from right to left. 

114
Figure 7.9. Multibeam survey from 2004 showing A) alongshore migrating bedforms, B) 

onshore-directed bedform morphologies north of the disposal site, and C) intense scour 

associated with the outfall pipe, the approximate site of the June 2005 dredge disposal (from 

Barnard and others, 2006b). 

115
Chapter 8-Grain Size Mapping 

By Patrick L Barnard 

Introduction 

The USGS has conducted periodic sediment sampling along Ocean Beach to quantify 

grain size variation alongshore and seasonally. Further, in summer 2005, the USGS 

performed a regional sediment sampling survey of the mouth of San Francisco Bay, 

including the region offshore of Ocean Beach, to document large-scale grain size patterns, 

sediment and sources, and to track the grain size at the Ocean Beach Disposal Site (see 

Figure 1.2). 

Methodology 

Using a digital bed-sediment camera, grain size surveys have been conducted 

periodically at Ocean Beach as a proxy for tracking variations in the physical energy 

transporting sediment along the beach. Using an autocorrelation technique developed by 

Rubin (2004), the grain size of the sample in a digital image can be extracted by statistical 

analysis of the autocorrelation of pixel intensities. The efficiency of this technique allows us 

to process over 300 images/samples in less than a day, whereas traditional sieving could take 

several months of work. Seven Ocean Beach grain size surveys have been completed since 

April 2004. Swash samples were taken at each of 18 profiles along the shoreward extension 

of the PWC lines (see Figures 3.2, 8.1). At five of these lines, samples were taken every ten 

meters along a cross-shore transect. Ocean Beach grain size samples were analyzed with both 

the settling tube and using the digital camera technique in May 2005 to test the accuracy of 

the new technique. Results of each method are well correlated with r2 values = ~ 0.70 for 

both median and mean grain size (Barnard and others, 2007) 

The USGS conducted eight days of sediment sampling in June and July 2005 at 

mouth of San Francisco Bay. A total of 191 stations were sampled by collecting grab samples 

or employing a digital bed sediment ‘eyeball’ camera (Chezar, 2001) at the mouth of San 

Francisco Bay, with emphasis immediately on and around the Ocean Beach disposal site 

(Figure 8.2). 

The City of San Francisco’s Oceanside Biology Laboratory (OBL) has also 

conducted extensive sediment sampling at the mouth of San Francisco Bay, with emphasis 

offshore of Ocean Beach. The OBL data set includes over 40 samples stations where 

thorough sediment, biological and chemical analysis have been performed each year from 

1997 to the present. 

Results 

Median grain size in the swash along Ocean Beach averages 0.28 mm, with no 

significant alongshore variation except for localized coarse lags where median grain size can 

exceed 0.5 mm (Figure 8.3). Seasonal variation is inconclusive, with several surveys 

awaiting processing, but at the southern part of Ocean Beach the heavy mineral content 

noticeably increases during the winter months. Cross-shore surveys of median grain size 

show only moderate variance, except along the longer profiles where the backbeach is 

supratidal (e.g. profile 2; Figure 8.4). 

116
Sediment at the mouth of San Francisco Bay is highly variable, ranging from very 

fine sand on the outer reaches of the ebb tidal delta, to coarse sand and gravel in the inlet 

throat, in the heart of the massive bedform field (Figure 8.5). The distribution of sediment 

grain size is linked to tidal current strength, with the coarsest sediment associated with the 

strongest currents, as in the inlet throat. Sediment sampling at the nearshore disposal site 

after the June 2005 disposal indicates a median grain size of 0.18 mm in that location.

Discussion 

Detailed sampling in the nearshore dredge disposal region indicates that surficial 

sediments consist of fine sand (median grain size (d50)= 0.18 mm), broadly consistent with 

nearshore bar and dune sediment found at Ocean Beach, but finer than beach sand (d50= 0.28 

mm). This sediment is therefore not ideally compatible to stay on the beach, but could build 

up the nearshore bars and help protect the beach from direct wave attack. However, Figure 

8.5 shows that there is an abundance of beach compatible sand on the inner part of the ebb 

tidal delta that ranges from d50= 0.25 to 0.50 mm. If the surficial grain size is consistent with 

sediment several meters below the surface in these ‘optimal’ locations, then there exists an 

enormous amount (on the order of 100’s of millions of m3

) of sediment that could be used for 

future beach nourishment efforts. 

Conclusions 

• Median grain size varies minimally along Ocean Beach during the summer with a 

d50= 0.28 mm. 

• Sediment placed in the nearshore disposal site (d50= 0.18 mm) is finer than swash 

samples (d50= 0.28 mm) collected at Ocean Beach, and thus it is not likely to be stable 

on the beach. 

• Large bodies of beach quality sand likely exist on the inner parts of the ebb-tidal delta 

at depths that could be dredged. Chapter 9 shows that a total volume of just over 1 

km3

 of acoustically transparent sediment is present. 

117
Figure 8.1. Location of beach sediment samples along Ocean Beach, from the May 2004 

survey. The profile locations are labeled. 

118
Figure 8.2. Sediment sample locations at the mouth of San Francisco Bay in summer 2005, 

along with Oceanside Biology Laboratory (OBL) sample stations. 

Figure 8.3. Median grain size of swash samples from 3 surveys along Ocean Beach. 

119
Figure 8.4. Median grain size along five profiles from the May 2004 survey. 

Figure 8.5. Grid of grain size class at the mouth of San Francisco Bay, using the both OBL and 

USGS samples. 

120
Chapter 9-Other Field Data Collection 

 This includes data collected that is somewhat peripheral to the Ocean Beach Coastal 

Processes Study, but can provide useful information to understanding the coastal system. 

High-resolution Subbottom Profiles of Active Faults and Sediment on the Golden Gate 

Platform 

By Holly Ryan 

The USGS collected high-resolution seismic reflection profiles for 10 days in 

September 2006 in support of tectonic and coastal erosion studies in the area near the 

epicenter of the Great San Francisco Earthquake of 1906. Data were collected from Fort 

Funston, south of the Golden Gate, to as far north as Bolinas to image several faults 

considered capable of producing damaging earthquakes, including the San Gregorio and San 

Andreas Faults. Another part of the mission was to determine the subsurface structure of 

gigantic sand waves located immediately west of the Golden Gate and to provide shelfsediment information for the USGS coastal-erosion study off Ocean Beach. This effort 

included collecting data to calculate the volume of sediment in the ebb-tide delta seaward of 

the Golden Gate and in Holocene deposits on the continental shelf. 

The 54-foot boat Lakota was used as the research vessel with Captain Tim Fleming at 

the helm. Over 400 km of high-resolution seismic profiles were collected (Figure 9.1). For 

studies of fault geometry and Holocene sediment, a 50-tip mini-sparker was used as the 

sound source and a short, single-channel hydrophone streamer as receiver. The minisparker is 

towed just beneath the water 5 to 10 m behind the vessel, where, at regular intervals, it 

produces an electric spark that vaporizes a small volume of water. Rapid expansion of the 

vapor bubble generates a sharp pulse of sound that radiates outward through the water. To 

image the sand waves, an Edgetech 512i subbottom-profiling system composed of a highfrequency Chirp source was used, towed three to five meters below the sea surface and a 

small hydrophone array. Chirp frequencies were typically swept over the range of 500 to 

7200 Hz during a 30 ms period. The mini-sparker system provided deeper imaging 

penetration below the sea floor but less resolution than the CHIRP system. Data for both 

systems were digitally recorded for post-cruise processing and interpretation. Several profiles 

were collected with both systems for data comparison. 

Results of the seismic-reflection surveys were mixed. In some areas, gas from natural 

seeps scattered the sound energy, making it difficult to map the subsurface. Evidence of gas 

in the seismic-reflection data included bright spots caused by pockets of trapped gas, and 

data “washouts” caused by gas dispersed through the sediment. In addition, over parts of the 

ebb-tide delta, where thick, sandy deposits are present, sub-bottom penetration was minimal. 

In many areas, however, especially away from the ebb-tide delta, the data were excellent 

with subbottom penetration ranging from 75 ms (about 60 m; Figure 9.2) to as much as 120 

ms (about 100 m; Figure 9.3). These data allowed a more accurate mapping of the San 

Andreas and San Gregorio fault zones, which are the main faults that deform the Golden 

Gate platform (e.g. Figure 9.2 and 9.3). 

Many of the subbottom mini-sparker profiles show an acoustically transparent unit 

above a layered unit. This transparent unit is interpreted to be comprised primarily of ebbtide delta deposits, but also may include recent sediment deposited in a fault-bounded graben 

121
(shown in Figure 9.2). To calculate the thickness of the transparent unit, we subtracted the 

depth to the water bottom from the depth to the top of the layered reflectors in two-way 

travel time (TWTT), and converted from TWTT to meters by using a velocity of 1.6 km/s. A 

velocity of 1.6 km/s is probably reasonable if the deposits are composed of coarser, sandier 

sediment. If finer grained, the thicknesses may be overestimated. These thicknesses were 

gridded onto a 20 m grid to create an isopach map (Figure 9.4). The maximum thickness of 

the transparent unit was 16 m, with the greatest thicknesses occurring between the San 

Andreas and San Gregorio faults (Figure 9.4). A total volume of just over 1 km3

 of 

acoustically transparent sediment was calculated. 

122
Figure 9.1. Trackline map of subbottom data collected on the Lakota in late September 2006 

(for more cruise information: http://walrus.wr.usgs.gov/infobank/l/l106sf/html/l-1-06-

sf.meta.html). Thin black lines correspond to CHIRP profiles; wider gray lines to mini-sparker 

profiles. Locations of Figures 9.2 and 9.3 are shown by bold black line. B- Bolinas, GG – 

Golden Gate, FF – Fort Funston. 

123
Figure 9.2. Mini-sparker profile GG-30 collected offshore of Fort Funston showing folded and 

disrupted reflectors associated with the San Andreas Fault (SAF). M - water bottom multiple; 

TWTT- two-way travel time. 

Figure 9.3. Mini-sparker profile GG-9b collected across a fault-bounded graben located 

southwest of Bolinas. The dots show the base of the graben, which contains over 50 m of 

sediment. M - water bottom multiple; TWTT- two-way travel time; SGF – San Gregorio Fault; 

SAF - San Andreas Fault; GGF – Golden Gate Fault. 

124
Figure 9.4. Map of the Golden Gate platform that shows thicknesses of acoustically 

transparent sediment of inferred Holocene age. These sediments are interpreted to be 

primarily composed of ebb-tidal delta deposits. The contour lines delineate sediment 

thicknesses that are greater than 10 m. The red lines show offshore fault traces. The gray 

lines show the locations of profiles used to map the acoustically transparent unit.

125
Chapter 10-Numerical Modeling 

By Li Erikson and Patrick L. Barnard 

Introduction 

An understanding and capability to predict the hydro-and morphodynamics at Ocean 

Beach is essential to the management and protection of infrastructure and human health and 

safety along this high-use beach on the west side of San Francisco. These issues are 

particularly evidenced by chronic erosion encroaching on the wastewater treatment plant at 

the south end of Ocean Beach, while human health and safety are frequently threatened by 

shifting sands and strong currents (in the form of along-shore currents and rip-tides). The 

physical processes at Ocean Beach are a function of several inter-related mechanisms such as 

offshore wave and wind climate, tidal processes, delta discharge, and sediment management 

practices (e.g. channel dredging and sand mining). Due to the inter-related nature of these 

processes, it is essential to include the San Francisco Bight and offshore areas within the 

model domain in order to understand and predict the hydro- and morphodynamics at Ocean 

Beach. 

In order to analyze a coastal region with high spatial and temporal gradients in wave, 

wind and tidal energy, it was desirable to employ a process-based numerical model. This 

allowed the expansion of localized physical process measurements to an enormous study 

area, analyze gradients in tidal currents and wave focusing patterns, and assess the impact of 

variable physical forcing conditions (e.g. storms, high discharge events, varying swell 

direction, high winds, etc.). With a cooperative agreement in place between the USGS and 

Delft Hydraulics, it was a logical step to set up a process-based numerical model using 

Delft3D (Delft3D, 2006) to analyze coastal processes in the San Francisco Bight and, once 

validated, use the model as a predictive tool for coastal change. 

Delft3D is capable of providing wave, current and sediment transport estimates on 

varying spatial- and time-scales. The Delft3D software package consists of a number of 

modules including those to simulate wave transformation, current flows, and sediment 

transport. The modules may be coupled according to the needs of the modeling project. 

The overall goal of implementing Delft3D is to provide a means to understand and 

predict hydrodynamics and morphodynamic evolution along Ocean Beach. Specific goals 

were to 

1) assess the return flow of currents at the north end of Ocean Beach, 

2) determine the cause of chronic erosion at the south end of Ocean Beach near Sloat 

Blvd., and 

3) provide coastal managers with scientific data necessary to make informed sediment 

management decisions for mitigating chronic erosion. 

Methods 

In this section, a brief description of model calibration, validation, and 

implementation are presented. For further details on model specifics, the reader is referred to 

the USGS Open File Report (OFR) entitled ‘Toward a validated 2-D hydrodynamic model 

for the mouth of San Francisco Bay’, currently under preparation (Barnard, et al, 2008). 

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Model Overview 

The Delft3D model consists of a set of modules which together constitute a system 

capable of modeling various coastal and estuarine processes including wave propagation, 

currents, sediment transport, and morphological evolution (Roelvink and van Banning, 

1994). The Delft3D model is applied to Ocean Beach and its surrounding region for the 

purpose of assessing both the hydrodynamics and, in the future, the morphodynamics of the 

region. However, only a brief description of simulated hydrodynamics is presented herein 

with a more detailed description in Barnard et al. (2008). 

Delft3D can be run in 2 or 3 dimensions, the latter being much more computationally 

expensive. A 2D mode is often deemed sufficient for situations where a well-mixed water 

column with little density stratification can be assumed. Ocean Beach is well removed from 

areas inside the bay where shear and density stratification might be commonplace, and 

although there may still be some density stratification along Ocean Beach particularly during 

winter and spring months during high freshwater inputs, up to this point the model has been 

run in 2D mode. In addition to ignoring density stratification, running the model in 2D 

eliminates undertow as a physical process in the surf zone and therefore, modeling 

phenomena such as surf zone bar migration cannot be conducted with the model in its present 

state. Following this present study on hydrodynamics and shoreline impacts, the model will 

be implemented in 3D mode to better predict surf zone and shoreline evolution. 

Hydrodynamics at Ocean Beach have been simulated employing the WAVE and 

FLOW modules of Delft3D. The WAVE module is a numerical scheme for estimating the 

propagation of wave parameters from input wind, bathymetry, and offshore wave conditions. 

The WAVE module is a direct implementation of the SWAN model that accounts for 

refraction, propagation, wind-induced wave growth, wave-wave interaction, bottom 

dissipation, depth induced wave breaking, and current dissipation. Wave blocking by 

currents is also explicitly accounted for in the model. Although the WAVE module can 

handle either bulk wave parameters or spectral wave conditions as boundary inputs, Delft3D 

is not yet capable of outputting spectral wave parameters at various times. As a result, all 

simulations thus far have been run with bulk parameter wave inputs even though the wave 

conditions are strongly bimodal during the summer (see Chapter 5). The FLOW module is 

the hydrodynamic routine that accounts for tidal and meteorological forcing. 

Grid and Boundary Conditions 

Two separate computational curvilinear grids were generated and employed for the 

WAVE and FLOW modules (Figure 10.1). The WAVE grid is shown in blue and the FLOW 

grid is shown in red in Fig. 10.1a. The open boundaries of the curvilinear WAVE grid 

extend beyond the open boundaries of the FLOW grid by approximately 20 km at the 

northern boundary, ten kilometers at the southern boundary, and 70 km offshore. The wave 

grid extends beyond the lateral boundaries of the FLOW grid to allow for instabilities in the 

wave field, due to uniform forcing along all open boundaries, to dissipate prior to entering 

into the domain of the flow field. If the instabilities were to propagate into the flow domain, 

unrealistic flows would be forced and would potentially alter the predicted hydrodynamics in 

areas of interest. The eastern edge of the WAVE grid terminates inside San Francisco Bay 

just east of the Golden Gate, and therefore does not simulate local wind-generated waves 

within San Francisco Bay. The primary purpose of the wave model is to propagate swell 

waves from deep water over the continental shelf and into the study area. 

127
The application of a curvilinear grid with variable spacing allows for cells aligned 

with the major direction of wave propagation (to avoid energy losses) and shorter 

computation time, as only the area of interest along Ocean Beach has a finer meshed grid. 

Further refinement of the grid is a goal for future morphological simulations. The grid sizes 

are on the order of 300 m in each direction at the offshore cells and 20 m in both directions 

along Ocean Beach. In all, the WAVE and FLOW grids each consist of ~32,000 and 

~19,000 grid cells, respectively. 

The model consists of three primary boundaries (Figure 10.1 b): 

1. Closed- no flow across boundary (i.e. land-sea interface) 

2. Discharge- two point sources for time-varying San Joaquin-Sacramento River delta 

discharge 

3. Open- primary driving force of model, populated with time varying physical forcing 

(i.e. waves and tidal harmonics) along open Pacific Ocean 

 

While considered negligible in terms of large-scale hydrodynamics, time-varying 

discharge rates from the San Joaquin and Sacramento Rivers into the Bay (Figure 10.1 b) 

were included in the model. The freshwater discharge to the bay is largely modulated by 

dams and agricultural use, and thus during even the largest winter storms, freshwater 

discharge to the bay only accounts for ~ 3% of tidal flow. This may however, result in 

stronger density stratification during winter months, with higher freshwater flows in the 

upper portion of the water column. 

Measured wave conditions at offshore buoys were used to force the model at the open 

boundaries. The measured wave conditions were collected primarily by the CDIP Pt. Reyes 

buoy (SCRIPPS Institution of Oceanography, 2006) and secondarily by the NDBC Monterey 

buoy (National Oceanic and Atmospheric Association, 2006a). The CDIP Pt Reyes buoy, 

029, is located at 37.946oN and 123.470oW in 550 m of water depth, about 20 km offshore. 

Bulk wave statistics were used to force the wave model. These statistics included significant 

wave height (Hs

), peak period (Tp), and mean wave direction (Dirp). The conditions observed 

at these buoys were applied to all open boundaries, including lateral boundaries, of the 

model. Our assumption is that because these buoys are located off of the edge of the shelf, 

deep-water swell observed at these buoys does not vary significantly across the boundaries of 

the model domain. Because the model was forced with parameterized wave conditions, the 

potential effects of bimodal wave spectra were not captured. Bimodal wave spectra with one 

swell and one sea peak are common during the summer months. Two swell peaks, on the 

other hand, are not common at Ocean Beach, but can occur during the summer months when 

moderate, bimodal long period swell originating from the southern and northern parts of the 

Pacific Ocean move into the region. 

Bulk atmospheric parameters, collected by the NDBC San Francisco buoy, were used 

to force the wave and flow models (National Oceanic and Atmospheric Association, 2006a). 

The San Francisco buoy (Station 46026) is located at 37.759oN and 122.833oW in 

approximately 52 m of water. The anemometer is located five meters above sea level and the 

barometer elevation is at sea level. The parameters utilized in this study were wind speed, 

wind direction, and atmospheric pressure, which were all applied uniformly over the domain. 

128
Time Step 

Since the choice of a model time-step is related to the grid size and flow dynamics, an 

analysis of simulated currents along Ocean Beach with varying time-steps applied to the 

given grid was completed. Based on several model runs, a model time-step of 0.5 minutes 

(30 seconds) was deemed to yield an acceptable numerical error (<5% in phase and 

magnitude compared to a six second time step; Courant numbers <10). 

Bathymetry 

Bathymetry used in the model originates from various sources. In the nearshore 

region off of Ocean Beach, ATV, multibeam, and PWC surveys were conducted as part of 

this study. This data was gridded and combined to create a single grid with 25 m horizontal 

spacing. Multibeam data obtained by the USGS in 1997, and 1991 NOAA soundings were 

used to complete the bathymetry of the remaining grid. Depth samples were added to the 

model domain using simple grid cell averaging and interpolation with the RFGrid tool 

included in the Delft3D package. Where necessary, a built in smoothing algorithm was 

applied to reduce inconsistencies between adjacent data sets. The final gridded bathymetry is 

shown in Figure 10.2 and referenced to NAVD88 in meters. 

Calibrations and Parameter Settings 

Tide Constituent Calibrations 

Calibration of primary tidal constituents was done via harmonic analysis (T-tide, 

Pawlocicz and others, 2002) and several model iterations, employing only the FLOW 

module, until the amplitude ratios and phase differences were less than 0.5% between 

predicted and observed water levels. Simulated water levels were compared to measurements 

obtained at the San Francisco (Ft. Point) Co-Ops water level station (National Oceanic and 

Atmospheric Association, 2006b), located west of the Golden Gate Bridge for a 64 day 

contiguous time-series (06/19/05 through 08/07/05). Resulting calibrated major constituents 

are listed in Table 10.1. 

Table 10.1. Calibrated tidal constituent amplitudes and phases. 

Northern boundary Southern boundary 

Constituent Amp (m) Phase (o) Amp (m) Phase (o) 

M2 0.545 191.5 0.523 187.9 

K1 0.365 216.8 0.359 216.6 

O1 0.221 201.4 0.219 201.0 

S2 0.132 199.9 0.130 194.0 

P1 0.441 213.7 0.110 213.1 

N2 0.145 168.1 0.141 164.6 

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Constant Parameters 

Constants used throughout the simulations are listed in Table 10.2. With the 

exception of the eddy viscosity and bed roughness which were calibrated via numerous 

simulations, the parameters are default values or derived values based on field surveys. 

Calibrations of the eddy viscosity and bed roughness were done using the first 28 days 

(06/19/05 through 07/19/05, including spin-up time) of measurements obtained during the 

summer field study. The remaining measurement times were used to validate the model. 

Table 10.2. FLOW and WAVE module constants employed. 

WAVE module

Battjes and Janssen (1978) bore based 

model for depth induced breaking α γ

1 / 0.73 

Spectral peak enhancement factor 

(Jonswap) 

3.3 

min/max/number bins in freq. space 0.05 / 1.0 / 36

Non-linear triad wave-wave interactions 

α / β

0.1 / 2.2 

Bottom friction (Jonswap) 0.067 

Water density 1025 

Temperature 15oC 

FLOW module

Water/air density (kg/m3) 1025 / 1 

Salinity 31 

Horizontal eddy viscosity (m2/s) 10 

Threshold depth (m) 0.1 

bottom stress formulation due to wave 

forces 

Fredsoe, 

1984 

bottom roughness (Chezy coeff) 78 

Comparison of Model Results with Field Data 

In this section, hydrodynamic model results are compared to field data measured at 

Sites 2 and 3 (see Chapter 5 for instrument and sampling descriptions). Site 1, also located 

along-shore of Ocean Beach, was used in the calibration but is not included in this 

comparison as it was buried 6 days into the validation measurement period. The latter part of 

the instrument sampling period (from 07/18/05 to 07/30/05) is used for validation while the 

first 30 days were used for calibration. 

The comparisons presented herein include an overview of model performance and 

residuals between modeled and measured parameters. In an attempt towards a more 

systematic way of evaluating the model, a set of model performance statistics have been 

calculated (e.g., Sutherland and others, 2004) and are summarized in Barnard et al (2008).. 

Note that sampling frequencies and time-averaging periods are not identical between the 

model and measurement data sets. Whereas the model results represent stationary 

conditions at half minute time-steps, measured water levels and currents are time-averages 

over ten minutes and wave parameters are spectral representations of 70 minute sampling 

periods. For statistical analysis and comparison between the data sets, the model results were 

down-sampled to the instrument sampling frequencies. 

130
Water Levels and Wave Parameters 

Predicted and measured water levels are compared in Figures 10.3 a and 10.3 b for 

Site 2 and Site 3, respectively. The semi-diurnal tidal signal is clearly evident and varies 

between +/-1.4 m, as would be expected for this time period (maximum reported tide range 

for Ocean Beach is from -0.6m to +2.2 m (mean 0.97m) from MLLW). The residuals 

(measured – predicted) are plotted as blue points, and, considering the fact that they represent 

errors of both phase and magnitude, are quite small (mean -0.07m, maximum 0.09m, 

R2=0.96). 

Significant wave heights are compared in Figure 10.4. Note that the residuals are 

plotted on the right-hand scale. Model predictions follow the general trend of measured 

wave heights but tend to slightly under-predict during low wave conditions (Hs

<1m) at Site 2 

and for most of the time at Site 3. Residuals suggest a good fit at Site 2 during the storm 

event from 07/23/05 through 07/28/05, as evidenced by the random error about zero. 

Overall, the mean random error is about -0.2m. 

Model results are expected to improve with the use of spectral forcing. The forcing 

conditions employed in the model thus far have been with bulk parameters. It is clear from 

field measurements that offshore wave spectra are strongly bimodal, particularly during the 

summer (with two peaks on the order of T=8s (sea) and T=15s (swell)). At the present time, 

work is currently underway to enable Delft3D to provide time-dependent spectral outputs. 

When this capability is included, the model will be run with spectral forcing conditions that 

are expected to improve the results with respect to measurements. 

Longshore Currents 

Modeled longshore currents are compared to depth-averaged measurements at Sites 2 

and 3 in Figures 10.5 a and 10.5 b, respectively. Longshore velocities are tidally dominated 

and strongly influenced by the proximity of the Golden Gate. Peak longshore velocities, only 

accounting for the larger of the two diurnal cycles, are equal and opposite of the flood 

(southward) and ebb (northward) tides and are predicted to be ~0.7 m/s at Site 2. At Site 3, 

southward directed along-shore currents are predicted to be slightly greater (0.46 m/s) than 

northward directed currents (0.38 m/s). 

Overall, the model seemed to do well at simulating the longshore currents. Residuals 

are not plotted as there is a large amount of scatter due to slight phase differences (R2

=0.55 

and coherence = 0.97). Model to measurement comparisons for the phase and magnitude are 

discussed separately in Barnard, et al. (2008) In short, the model does well with the 

exception of a few instances when it under-predicts longshore currents by about 5 cm/s to 10 

cm/s. 

Cross-shore Currents 

Modeled cross-shore currents are compared to depth-averaged measurements at Sites 

2 and 3 in Figures 10.5 c and 10.5 d, respectively. Similar to the longshore currents, the 

cross-shore currents are also tidally dominated with peak velocities associated with the ebb 

tide of the higher tide and with the flood tide of the lower high tide (Fig. 10.5 c and 10.5 d). 

The relative magnitudes are also similar to the longshore currents in that stronger velocities 

were measured and modeled at Site 2 near the tidal inlet at the Golden Gate as compared to 

131
Site 3 further south. Peak onshore and offshore velocities were 0.18 m/s and 0.14 m/s, 

respectively at Site 2 and about half as strong at Site 3 with 0.07 m/s in both the on- and 

offshore directions. 

Results 

Flow Patterns at the North End of Ocean Beach 

Modeled flow patterns at the north end of Ocean Beach are shown for a complete tide 

cycle (the full moon was on 07/21/05) in Figure 10.6. The top panel (Figure 10.6 a) shows 

the measured tide at Site 2, about halfway down the coast at Ocean Beach. Figures 10.6 b 

through 10.6 m show modeled flow patterns (arrows) and velocity currents (colored scale, 

m/s) at the times indicated in Figure 10.6 a. Close inspection of the Figures indicate that the 

flow directions are primarily oriented in the north-south direction and are tidally dominated. 

Currents are strongest prior to flow reversal at both ebb and flood tides (Figures 10.6d, 10.6g, 

10.6h, and 10.6k). At ebb tide, before flow reversal, the currents are oriented southwest at 

the very north end of Ocean Beach and a shadow zone of lower flow velocities forms along 

the beach (shown with blue in Figures 10.6g and 10.6h, velocities approximately 0.2 m/s). 

During flood tides, the currents flow northward, Pt. Lobos headland does not offer any 

protection, and higher flow velocities extend further shoreward (Figures 10.6d, 10.6j, and 

10.6k). 

Immediately following the flow reversal after ebb tide (Figure 10.6i), the model 

predicts that eddies with flow velocities on the order of 0.4 m/s will form. An eddy is 

apparent at about N4180.5 km and a smaller one near the shore at N4181.1 km. Based on 

analysis of model simulation slightly shorter than one month, the southern most point of 

eddies reach to about N 4.179E6 as shown in Figure 10.7a. In all cases, eddies only form 

during low tide. Approximate eddy center locations are plotted against the tidal stage in 

Figures 10.7b and 10.7c. Eddy locations only move slightly in the east-west direction with 

positive tide levels, while during negative tides (corresponding to the spring cycle), they 

migrate as much as 1 km in the east-west direction (Fig. 10.7b). With respect to the northsouth direction (Fig. 10.7c), central eddy locations are within a 1 km stretch with the furthest 

southern position with the lower tides. 

A consequence of these eddies appears to be rip currents as seen with seaward 

oriented velocity vectors at about the same locations as observed in the time-averaged images 

(Chapter 4). Observed rip current locations from the time-averaged images are shown in 

white on the sub-plots corresponding to low tide in Figure 10.6. The formation of rip 

currents can also be seen in Figures 10.6b and 10.6h, both of which are associated with low 

tide. Based on the present model results, rip currents appear to be at least partly related to 

tidal flows, and in particular near times of flow reversal associated with either low (Figures 

10.6b,g,h and i) or high tide (Figure 10.8). 

Variable Wave Impact Along the Beach 

Model simulated wave heights along Ocean Beach for four time periods, each with 

different forcing conditions during the model validation period are shown in Figure 10.9. 

Conditions measured at Pt. Reyes buoy and used to drive the model are shown for each case 

and were chosen based on the greatest frequency of occurrence during the summer validation 

period. The top panel shows the along shore section of Ocean Beach in plan view and with 

north pointing to the left. The thick red line indicates the erosion hot-spot just south of Sloat 

132
Blvd. The four panels beneath depict model predicted significant wave height magnitude and 

direction for four cases with offshore wave heights ranging from 4 m to 2.3 m. The 

significant wave heights shown are those output by the model immediately seaward of the 

predicted breaking line as depicted with the ⊗ symbol in Figure 10.10. 

Predicted wave heights vary along the shore (Figure 10.10) with a consistent pattern 

such that greater heights are observed near the hot-spot erosion area than at the far south end 

of Ocean Beach. The angle of incidence is consistently shore-normal near the hot-spot area, 

while it deviates southward to a maximum of about 20 degrees from shore-normal at the 

south end of the beach. Due to the similar offshore wave directions (323o

 to 334o), there is 

little change in approach angle at a given site near the shore; variations in wave height near 

the shore, as a function of varying offshore wave angles, are further assessed in the next 

section for a set of hypothetical situations. 

Figure 10.10 shows predicted significant wave heights along Ocean Beach and 

immediate offshore region for the same time steps as in Figure 10.9. The Figure suggests 

that the focus of increased wave heights near the hot-spot are related to the southern lobe of 

the ebb tidal shoal. Waves at the north end of the beach, north of the shoal and erosion hotspot, appear to have undergone more refraction as they propagated across the northern ebb 

tidal shoal, losing energy and decreasing wave height. The lower wave heights immediately 

to the south of the shoal might be the effect of a shadow zone present during northwest 

incident waves. 

Along-shore variation of longshore sediment transport (Figure 10.11) was estimated 

with the ‘CERC formula’ (ERDC, 1984) for the same four time periods as in Figure 10.10. 

The formula is a function of breaking wave height and angle of incidence and an empirical 

coefficient related to the grain size (Komar, 1988). It does not account for tidal currents, 

which are known to be strong in this area, and as such, the estimates should be considered as 

very crude. Because the incident wave angle of the selected validation time-series is from 

the northwest with little variation, all the longshore transport is predicted to go south (as was 

also shown with ADCP measurements in Chapter 5). The estimates suggest high rates of 

longshore transport from the very north end (approximately 350 m3/m/day with offshore 

Hs=4m) of the beach past the south end of the erosion hot-spot (approximately 200 

m3/m/day). A greater rate is predicted just south of the hot-spot than at the hot-spot itself. 

This is because the Delft model predicted shore-normal incident waves at the hot-spot while 

the incidence angle is slightly skewed north just south of the hot-spot. Under these types of 

conditions, it would be expected that erosion at the hot-spot would be due to both variations 

in longshore sediment transport and direct wave impact from shore-normal incident waves. 

Influence of Offshore Wave Direction 

The offshore direction of wave approach has a very large impact on resulting wave 

heights at Ocean Beach. To help illustrate this, several SWAN runs were completed using 

the same grid that was coupled with the previous Delft3D simulations, but running SWAN in 

a stand-alone, stationary, mode. These runs are simplified, and include parameterized wave 

forcing but do not include wind, tidal currents, or wave-wave interaction. Figure 10.12 

includes maps of significant wave heights output from SWAN for wave forcing with varied 

peak period and peak direction input. Figure 10.13 a, and c represent waves coming from a 

direction of 330o, which is characteristic of a large majority of waves seen in this region, 

especially in summer months. There is a drastic difference of almost 2 m in wave height at 

Ocean Beach when the same conditions come from a more westerly direction of 280o (Figure 

133
10.13 b, d), which is more common in winter months (Figure 5.11). This suggests that longperiod, large waves coming directly onshore at Ocean Beach will likely have the largest 

erosional capability, as waves coming from the northwest tend to dissipate over the ebb tidal 

delta. Figure 10.13b, and d show that waves coming from 280o are oriented shore-normal 

along the southern half of Ocean Beach, and coming slightly from the south in northern 

sections near the erosion hot spot. The waves coming from 330o still have a northward 

component in wave direction close to shore along some sections along northern Ocean 

Beach. 

Dredge Disposal Modeling 

 

Model runs were done to assess the potential of indirectly providing material for 

beach nourishment by placing dredged material immediately offshore of the erosion hot-spot. 

In June, 2005, 225,000 m3 of sand were dredged from the Main Shipping Channel at the 

mouth of San Francisco Bay and placed in depths ranging from 9-14 m approximately 500 m 

offshore from the hot-spot. The aim of applying the Delft3D model package was to assess 

the potential for the strong tidal currents and onshore directed asymmetric wave orbital 

velocities to potentially feed sediment into the littoral zone, thus providing a buffer to the 

erosion. 

A plot of residual sediment transport based on the tidal forcing alone indicates only 

minimal transport from the disposal site (Figure 10.14 a), with net transport predominately 

north-south. However, once waves were incorporated in the model, the residual transport 

increased substantially in shallower depths (Figure 10.14 b), where wave-induced bottom 

currents due to wave shoaling produced net-onshore directed transport. 

Conclusions 

• Comparisons between measurements and model results show that the calibrated 

Delft3D model is capable of predicting hydrodynamics at Ocean Beach for summer 

conditions. 

• Model simulations predict that currents along Ocean Beach are strongest prior to flow 

reversal at both flood and ebb tides, and are strongly influenced by the Golden Gate 

entrance. 

• Along- and cross-shore currents are strongly modulated by the tide. The influence of 

the tidal inlet at the Golden Gate decreases significantly with distance such that the 

currents are about 30% stronger at the north end compared to the southern end of 

Ocean Beach. 

• The Pt. Lobos headland provides a shadow zone to the south so that nearshore tidal 

flows are weaker at ebb tide compared to areas further offshore. 

• Model results suggest that rip currents are related to tidal flows and occur near times 

of flow reversal (high and low tide). 

• Model results suggest that the longshore sediment transport is to the south during 

typical summer conditions and that the section stretching from the north part of 

Ocean Beach to immediately south of the erosion hot-spot undergoes strong 

longshore transport rates under high wave conditions (Hs

>2.5m). Model results also 

suggest that the erosion hot-spot is directly impacted from shore-normal incident 

134
waves during storm conditions. Furthermore, the erosion hot-spot appears to be a 

result of wave focusing caused by the shape of the southern ebb tidal delta. 

• Long-period, shore-normal incident large waves at Ocean Beach will likely have the 

largest erosional capacity, as waves coming from the northwest tend to be dissipated 

by the northern lobe of the ebb tidal delta. Preliminary modeling suggests that 

offshore waves originating from the west undergo less energy loss compared to 

offshore waves originating from the northwest, whose wave height reduces by about 

50% as a result of refraction over the northern lobe of the ebb tidal delta. 

• Numerical modeling suggests that despite the strong tidal currents in the region, wave 

forcing is the dominant factor moving the sediment slowly toward shore, and placing 

sediment at a depth of about 8 m will provide indirect beach nourishment. 

135
(b) 

(a) 

Figure 10.1. Curvilinear grids used for the FLOW and WAVE modules (a) and FLOW grid with 

boundaries (b). 

136
Figure 10.2. Final gridded bathymetry (positive depth in meters relative to mean sea level).

137
07/19 07/21 07/23 07/25 07/27 07/29

-1.5

-1

-0.5

0

0.5

1

1.5

eta (m)

Site 2

modeled

measured

residual

(a)

 

07/19 07/21 07/23 07/25 07/27 07/29

-1.5

-1

-0.5

0

0.5

1

1.5

eta (m)

Site 3

(b)

Figure 10.3. Measured and modeled water levels: (a) Site 2; (b) Site 3. Blue circles are 

residuals (measured - modeled).

138
Figure 10.4. Comparison of measured and modeled significant wave heights (Hs

). Note the 

residual (blue diamonds) y-axis on the right. 

139
Figure 10.5. Comparison of measured and modeled longshore currents (a, b) and cross-shore 

currents (c, d) at Sites 2 and 3. 

140
00:00 06:00 12:00 18:00 00:00

-2

-1

0

1

2

7/21/05

Water level (m)

Measured at Site 2

(b)

(c)

(d) (e)

(f)

(g)

(h)

(i)

(j)

(k)

(l) (m)

(a)

141
(j) 

142
Figure 10.6. Flow patterns at the north end of Ocean Beach. Plot (a) shows the measured tide 

at Site 2; points and text refer to snap shots of model results in plots (b) through (m). Open 

circle is Site 1 sampling station. Flow directions are shown with arrows while current speeds 

(m/s) are shown with the color scheme. White horizontal lines in plots g,h, and i indicate rip 

current observations from time-averaged images (Chapter 4). 

143
Figure 10.7. Eddy position as a function to tide stage. Based on analysis of model simulation 

slightly shorter than one month, the southern most point of the eddies reach to about N 

4.179E6, which coincides with PWC transect 5 (a). Approximate eddy center locations are 

plotted against the tidal stage in (b) and (c) (note that the axis of the Eastings and Northings 

are switched ease of geographic considerations). Central Easting position only moves slightly 

with positive tide levels, while at negative tides (corresponding to the spring cycle), the 

position moves as much as 1 km in the east-west direction. With respect to the right-hand 

Figure, the eddies appear to move about 1 km in the north-south direction with the tide, such 

that the eddies appear further south with lower tide stage. 

144
(b) (a) 

Pt. Lobos

‘rip 3’ 

Figure 10.8. Evidence of rip currents at N4180.63 km, which coincides with ‘rip 3’ as seen with 

time-averaged images (see Chapter 4). Plot (a) shows model predicted flow patterns along 

Ocean Beach; plot (b) shows measured tide at Site 1 and, with the red circle, the time-step of 

(a). 

145
Pt. Lobos

Figure 10.9. Along-shore variation of model predicted wave height and direction at Ocean 

Beach. The thick red lines indicate area of erosion ‘hot spot’. 

Variation in line density is due to grid cell spacing.

146
Hso=3.6 

m 

Tp=8.6s

Hso=4 m 

Tp=9.1s 

Dir=325o

Figure 10.10. Model predicted significant wave heights for four offshore conditions during the 

summer of 2005. Contour lines are bathymetry as measured with multi-beam surveys. 

Hso=2.3 

m 

Tp=8.3s

Hso=2.4 

m 

Tp=9.2s 

147
Pt. Lobos 

Figure 10.11. Along-shore variation of estimated long-shore sediment transport (m3/day per alongshore unit width). The thick red lines bound the erosion ‘hot spot’. 

148
Figure 10.12. Modeled significant wave height values at Ocean Beach with parameterized forcing of 

Hs

= 4m and a)Tp= 10 sec, Dp=330 deg b) Tp= 10 sec, Dp = 280 deg c)Tp= 20 sec, Dp= 330 deg d)Tp= 20 

sec, Dp= 280 deg. 

149
Figure 10.13. Modeled peak wave direction values at Ocean Beach with parameterized forcing of 

Hs= 4m and a)Tp= 10 sec, Dp=330 deg b) Tp= 10 sec, Dp = 280 deg c)Tp= 20 sec, Dp= 330 deg d)Tp= 

20 sec, Dp= 280 deg.

150
Figure 10.14. Residual transport of the dredge disposal mound with tidal forcing only (a) Residual 

transport of the dredge disposal mound with tidal and wave forcing, illustrating the importance of 

wave shoaling in the onshore migration of the disposal material(b).

151
Acknowledgements 

Thanks to the USGS Coastal and Marine Geology Team, particularly the Coastal Evolution: 

Process-based, Multi-scale Modeling Project for the generous support of this project. The United 

States Army Crops of Engineers, San Francisco District, funded a portion of this study. Peter Mull, 

in particular, has been extremely supportive. The National Park Service provided site permits and 

other logistical support. The San Francisco Public Utilities Commission generously granted us 

access to their secure Oceanside Water Pollution Control Plant to establish a permanent base station 

for our survey work at Ocean Beach. Peter Ruggiero provided CPS survey support. Thomas Reiss 

provide GPS support for CPS and beach surveys. Gerry Hatcher assisted with the sediment 

sampling. Joanne Ferreira directed instrument deployments and recovery. Ann Gibbs maintained 

the video monitoring system. Jeff Hansen conducted many of the beach surveys. The entire Ocean 

Beach team is responsible for the success of this project, including Hal Williams, Kevin O’Toole, 

Walt Olson, Charlene Parsons, Liron Friedman, Andrew Schwartz, Lindsey Doermann, Etienne 

Kingsley and Patrick Smith. Many thanks to Curt Storlazzi and Ann Gibbs for their through 

internal reviews. 

152
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157
Appendix

Publications and Other Resources 

Below is a list of resources released to date and other links related to the Ocean Beach 

Coastal Processes Study: 

Publications 

Barnard, P.L. and Hanes, D.M., 2006. Coastal monitoring of the May 2005 dredge disposal 

offshore of Ocean Beach, San Francisco, California. U.S. Geological Survey, Open-File Report, 

Report Series 2006-1140, 27 pp., http://pubs.usgs.gov/of/2006/1140/

Barnard, P.L., Hanes, D.M., Kvitek, R.G, and Iampietro, P.J., 2006. Sand waves at the mouth of 

San Francisco Bay, California. U.S. Geological Survey, Scientific Investigations Map 2006-2944, 

5 map sheets, http://pubs.usgs.gov/sim/2006/2944/ 

Barnard, P.L., Hanes, D.M., Lescinski, J. and Elias, E., 2007. Monitoring and modeling nearshore 

dredge disposal for indirect beach nourishment, Ocean Beach, San Francisco. In: Smith, J.M. 

(ed.), Coastal Engineering 2006, Proceedings of the 30th International Conference, Conference 

Proceedings, San Diego, CA, USA, 3-8 September 2006, Volume 4, p. 4192-4204 (for PDF go 

to: http://walrus.wr.usgs.gov/coastal_processes/pubs.html) 

Barnard, P.L., Hanes, D.M, Rubin, D.M. and Kvitek, R.G., 2006. Giant sand waves at the mouth of 

San Francisco Bay. EOS Transactions, Volume 87, Number 29, p. 285, 289 (for PDF go to: 

http://walrus.wr.usgs.gov/coastal_processes/pubs.html) 

Dartnell, P., Barnard, P.L., Chin, J.L., Hanes, D.M., Kvitek, R.G, Iampietro, P.J. and Gardner, J.V., 

2006. Under the Golden Gate Bridge-views of the seafloor near the entrance to San Francisco 

Bay, California. United States Geological Survey, Scientific Investigations Map 2917. 1 map 

sheet http://pubs.usgs.gov/sim/2006/2917/

Erikson, L., Hanes, D.M., Barnard, P.L. and Gibbs, A.E., 2007. Swash zone characteristics at 

Ocean Beach. In: Smith, J.M. (ed.), Coastal Engineering 2006, Proceedings of the 30th 

International Conference, Conference Proceedings, San Diego, CA, USA, 3-8 September 2006, 

Volume 1, p. 909-921 (for PDF go to: http://walrus.wr.usgs.gov/coastal_processes/pubs.html) 

Barnard, P.L., 2005. Modern processes at the mouth of San Francisco Bay. American Shore and 

Beach Preservation Association, 2005 Conference Field Trip Guide, 21 pp. (for PDF go to: 

http://walrus.wr.usgs.gov/coastal_processes/pubs.html) 

Barnard, P.L., Hanes, D.M., 2005. Integrating field research, modeling and remote sensing to 

quantify morphodynamics in a high-energy coastal setting, Ocean Beach, San Francisco, 

California. 5th International Conference on Coastal Dynamics 2005 Conference Proceedings, 

Barcelona, Spain, American Society of Civil Engineers, CD-Rom, 14 pp. (for PDF go to: 

http://walrus.wr.usgs.gov/coastal_processes/pubs.html) 

158
Online Resources 

• San Francisco Bight Coastal Processes Study Project Website: 

http://walrus.wr.usgs.gov/coastal_processes/

• Coastal Evolution Modeling Project Website: 

http://walrus.wr.usgs.gov/research/projects/CEM.html

• Ocean Beach webcam: 

http://www.evsboca.com/usgs/default.htm

• USGS Online Reports 

o Dredge Disposal Monitoring 

http://pubs.usgs.gov/of/2006/1140/

o Sand Wave Maps 

http://pubs.usgs.gov/sim/2006/2944/

• Multibeam Data: 

http://seafloor.csumb.edu/SFMLwebDATA.htm

Research Featured in the News 

• Sand Waves 

 “City’s beautiful but hidden sand dunes” by Glen Martin 

San Francisco Chronicle, July 20, 2006 

http://www.sfgate.com/cgibin/article.cgi?file=/c/a/2006/07/20/MNGU1K2AV91.DTL

 “Sand dunes by the dock of the bay” 

News.Com, July 20, 2006 

http://news.com.com/2300-11395_3-6096457-1.html?tag=ne.gall.pg

 “Scientists map miles of underwater dunes” by Associated Press 

Appeared in ABC News, CBS News, Boston Globe, San Jose Mercury New, 

etc., on July 20 and 21, 2006 

http://abcnews.go.com/Technology/wireStory?id=2218566&CMP=OTCRSSFeeds0312

http://www.cbsnews.com/stories/2006/07/21/ap/tech/mainD8J0DUF00.shtml

http://www.boston.com/news/science/articles/2006/07/20/scientists_map_sub

merged_sand_dunes_off_sf/

http://www.mercurynews.com/mld/mercurynews/living/health/15092078.htm

 “Giant Underwater Sand Waves Seaward of the Golden Gate Bridge” by 

Patrick Barnard Soundwaves, United States Geological Survey, Monthly 

Newsletter, 2 pp., http://soundwaves.usgs.gov/2006/09/research.html

159
• Coastal Erosion 

“Beach study hopes to unlock mystery of erosion” by Ryder W. Miller 

Richmond Review, March 2005 

http://www.sunsetbeacon.com/archives/richmondreview/2005editions/Mar05/beachstudy.html

• Dredging 

“New tack to hold back Ocean Beach erosion: 300,000-ton gift from dredge could curb 

erosion” by Kelly Hill 

San Francisco Chronicle, June 20, 2005 

http://www.sfgate.com/cgibin/article.cgi?f=/c/a/2005/06/10/BAG93D6K5J1.DTL&hw=Ocean+Beach&sn=003&sc=

646

• Winter 2006 Surf Zone Experiment 

“USGS Scientists Investigate Surf-Zone Hydrodynamics at San Francisco's Ocean Beach” 

by Li Erikson, Patrick Barnard and Dan Hanes 

USGS Sound Waves, April 2006 

http://soundwaves.usgs.gov/2006/04/

160
Field Activity IDs and Web Links 

ATV Survey List 

Survey #

Field Activity

ID

Survey 

Date

URL For Field Activity ID

1 O-B1-04-CA 04/07/04 

http://walrus.wr.usgs.gov/infobank/o/ob104ca

/html/o-b1-04-ca.meta.html 

2 O-B2-04-CA 05/07/04 

http://walrus.wr.usgs.gov/infobank/o/ob204ca

/html/o-b2-04-ca.meta.html 

3 O-B3-04-CA 06/07/04 

http://walrus.wr.usgs.gov/infobank/o/ob304ca

/html/o-b3-04-ca.meta.html 

4 O-B4-04-CA 07/06/04 

http://walrus.wr.usgs.gov/infobank/o/ob404ca

/html/o-b4-04-ca.meta.html 

5 O-B5-04-CA 10/13/04 

http://walrus.wr.usgs.gov/infobank/o/ob504ca

/html/o-b5-04-ca.meta.html 

6 O-B6-04-CA 11/15/04 

http://walrus.wr.usgs.gov/infobank/o/ob604ca

/html/o-b6-04-ca.meta.html 

7 O-B7-04-CA 12/10/04 

http://walrus.wr.usgs.gov/infobank/o/ob704ca

/html/o-b7-04-ca.meta.html 

8 O-B1-05-CA 01/11/05 

http://walrus.wr.usgs.gov/infobank/o/ob105ca

/html/o-b1-05-ca.meta.html 

9 O-B2-05-CA 02/07/05 

http://walrus.wr.usgs.gov/infobank/o/ob205ca

/html/o-b2-05-ca.meta.html 

10 O-B3-05-CA 03/08/05 

http://walrus.wr.usgs.gov/infobank/o/ob305ca

/html/o-b3-05-ca.meta.html 

11 O-B4-05-CA 03/11/05 

http://walrus.wr.usgs.gov/infobank/o/ob405ca

/html/o-b4-05-ca.meta.html 

12 O-B5-05-CA 05/02/05 

http://walrus.wr.usgs.gov/infobank/o/ob505ca

/html/o-b5-05-ca.meta.html 

13 O-B6-05-CA 06/10/05 

http://walrus.wr.usgs.gov/infobank/o/ob605ca

/html/o-b6-05-ca.meta.html 

14 O-B7-05-CA 06/27/05 

http://walrus.wr.usgs.gov/infobank/o/ob705ca

/html/o-b7-05-ca.meta.html 

15 O-B8-05-CA 07/12/05 

http://walrus.wr.usgs.gov/infobank/o/ob805ca

/html/o-b8-05-ca.meta.html 

16 O-B9-05-CA 07/22/05 

http://walrus.wr.usgs.gov/infobank/o/ob905ca

/html/o-b9-05-ca.meta.html 

17 O-BA-05-CA 08/22/05 

http://walrus.wr.usgs.gov/infobank/o/oba05ca

/html/o-ba-05-ca.meta.html 

18 O-BB-05-CA 11/17/05 

http://walrus.wr.usgs.gov/infobank/o/obb05ca

/html/o-bb-05-ca.meta.html 

19 O-BC-05-CA 12/15/05 

http://walrus.wr.usgs.gov/infobank/o/obc05ca

/html/o-bc-05-ca.meta.html 

20 O-BD-05-CA 12/22/05 

http://walrus.wr.usgs.gov/infobank/o/obd05ca

/html/o-bd-05-ca.meta.html 

21 O-BE-05-CA 12/29/05 

http://walrus.wr.usgs.gov/infobank/o/obe05ca

/html/o-be-05-ca.meta.html 

161
22 O-B1-06-CA 01/16/06 

http://walrus.wr.usgs.gov/infobank/o/ob106ca

/html/o-b1-06-ca.meta.html 

23 O-B2-06-CA 01/24/06 

http://walrus.wr.usgs.gov/infobank/o/ob206ca

/html/o-b2-06-ca.meta.html 

24 O-B3-06-CA 01/26/06 

http://walrus.wr.usgs.gov/infobank/o/ob306ca

/html/o-b3-06-ca.meta.html 

25 O-B4-06-CA 01/30/06 

http://walrus.wr.usgs.gov/infobank/o/ob406ca

/html/o-b4-06-ca.meta.html 

26 O-B5-06-CA 02/10/06 

http://walrus.wr.usgs.gov/infobank/o/ob506ca

/html/o-b5-06-ca.meta.html 

27 O-B6-06-CA 02/13/06 

http://walrus.wr.usgs.gov/infobank/o/ob606ca

/html/o-b6-06-ca.meta.html 

28 O-B7-06-CA 02/21/06 

http://walrus.wr.usgs.gov/infobank/o/ob706ca

/html/o-b7-06-ca.meta.html 

29 O-B8-06-CA 02/26/06 

http://walrus.wr.usgs.gov/infobank/o/ob806ca

/html/o-b8-06-ca.meta.html 

30 O-B9-06-CA 03/05/05 

http://walrus.wr.usgs.gov/infobank/o/ob906ca

/html/o-b9-06-ca.meta.html 

31 O-10-06-CA 03/23/06 

http://walrus.wr.usgs.gov/infobank/o/o1006ca

/html/o-10-06-ca.meta.html 

32 O-11-06-CA 04/06/06 

http://walrus.wr.usgs.gov/infobank/o/o1106ca

/html/o-11-06-ca.meta.html 

33 O-12-06-CA 04/21/06 

http://walrus.wr.usgs.gov/infobank/o/o1206ca

/html/o-12-06-ca.meta.html 

34 O-13-06-CA 05/08/06 

http://walrus.wr.usgs.gov/infobank/o/o1306ca

/html/o-13-06-ca.meta.html 

35 O-14-06-CA 05/22/06 

http://walrus.wr.usgs.gov/infobank/o/o1406ca

/html/o-14-06-ca.meta.html 

36 O-15-06-CA 06/19/06 

http://walrus.wr.usgs.gov/infobank/o/o1506ca

/html/o-15-06-ca.meta.html 

37 O-16-06-CA 06/30/06 

http://walrus.wr.usgs.gov/infobank/o/o1606ca

/html/o-16-06-ca.meta.html 

38 O-17-06-CA 08/13/06 

http://walrus.wr.usgs.gov/infobank/o/o1706ca

/html/o-17-06-ca.meta.html 

39 O-18-06-CA 10/23/06 

http://walrus.wr.usgs.gov/infobank/o/o1806ca

/html/o-18-06-ca.meta.html 

40 O-19-06-CA 11/06/06 

http://walrus.wr.usgs.gov/infobank/o/o1906ca

/html/o-19-06-ca.meta.html 

41 O-20-06-CA 11/20/06 

http://walrus.wr.usgs.gov/infobank/o/o2006ca

/html/o-20-06-ca.meta.html 

42 O-21-06-CA 11/24/06 

http://walrus.wr.usgs.gov/infobank/o/o2106ca

/html/o-21-06-ca.meta.html 

43 O-22-06-CA 12/05/06 

http://walrus.wr.usgs.gov/infobank/o/o2206ca

/html/o-22-06-ca.meta.html 

44 O-23-06-CA 12/10/06 

http://walrus.wr.usgs.gov/infobank/o/o2306ca

/html/o-23-06-ca.meta.html 

45 O-24-06-CA 12/29/06 

http://walrus.wr.usgs.gov/infobank/o/o2406ca

/html/o-24-06-ca.meta.html 

162
PWC Survey List 

Survey #

Field Activity

ID

Survey 

Date

1 O-B2-04-CA 05/04/04 

http://walrus.wr.usgs.gov/infobank/o/ob204ca

/html/o-b2-04-ca.meta.html 

2 O-B4-04-CA 07/20/04 

http://walrus.wr.usgs.gov/infobank/o/ob404ca

/html/o-b4-04-ca.meta.html 

3 O-B6-O4-CA 11/12/04 

http://walrus.wr.usgs.gov/infobank/o/ob604ca

/html/o-b6-04-ca.meta.html 

4 O-B5-05-CA 05/05/05 

http://walrus.wr.usgs.gov/infobank/o/ob505ca

/html/o-b5-05-ca.meta.html 

5 O-B8-05-CA 07/05/05 

http://walrus.wr.usgs.gov/infobank/o/ob805ca

/html/o-b8-05-ca.meta.html 

6 O-BB-05-CA 11/17/05 

http://walrus.wr.usgs.gov/infobank/o/obb05ca

/html/o-bb-05-ca.meta.html 

7 O-BA-06-CA 02/01/06 

http://walrus.wr.usgs.gov/infobank/o/oba06ca

/html/o-ba-06-ca.meta.html 

8 O-BB-06-CA 02/10/06 

http://walrus.wr.usgs.gov/infobank/o/obb06ca

/html/o-bb-06-ca.meta.html 

9 O-BC-06-CA 05/23/06 

http://walrus.wr.usgs.gov/infobank/o/obc06ca

/html/o-bc-06-ca.meta.html 

10 O-BD-06-CA 05/23/06 

http://walrus.wr.usgs.gov/infobank/o/obd06ca

/html/o-bd-06-ca.meta.html 

11 O-BD-06_CA 11/06/06 

http://walrus.wr.usgs.gov/infobank/o/obd06ca

/html/o-bd-06-ca.meta.html 

12 O-22-06-CA 11/21/06 

http://walrus.wr.usgs.gov/infobank/o/o2206ca

/html/o-22-06-ca.meta.html 

13 O-B2-04-CA 12/05/06 

http://walrus.wr.usgs.gov/infobank/o/ob204ca

/html/o-b2-04-ca.meta.html 

Beach Eyeball 

Survey List 

Survey #

Field Activity

ID

Survey 

Date

1 O-B1-04-CA 04/07/04 

http://walrus.wr.usgs.gov/infobank/o/ob104ca

/html/o-b1-04-ca.meta.html 

2 O-B2-04-CA 05/07/04 

http://walrus.wr.usgs.gov/infobank/o/ob204ca

/html/o-b2-04-ca.meta.html 

3 O-B4-04-CA 08/03/04 

http://walrus.wr.usgs.gov/infobank/o/ob404ca

/html/o-b4-04-ca.meta.html 

4 O-B3-05-CA 03/07/05 

http://walrus.wr.usgs.gov/infobank/o/ob305ca

/html/o-b3-05-ca.meta.html 

5 O-BB-05-CA 11/17/05 

http://walrus.wr.usgs.gov/infobank/o/obb05ca

/html/o-bb-05-ca.meta.html 

6 O-B3-06-CA 01/26/06 

http://walrus.wr.usgs.gov/infobank/o/ob306ca

/html/o-b3-06-ca.meta.html 

7 O-19-06-CA 11/06/06 http://walrus.wr.usgs.gov/infobank/o/o1906ca

163
/html/o-19-06-ca.meta.html 

Sediment Sampling 

Offshore 

Survey #

Field Activity

ID

Survey 

Date

1 S-1-05-NC 06/21/05 

http://walrus.wr.usgs.gov/infobank/s/s105nc/h

tml/s-1-05-nc.meta.html 

2 S-1-05-NC 06/22/05 

http://walrus.wr.usgs.gov/infobank/s/s105nc/h

tml/s-1-05-nc.meta.html 

3 S-1-05-NC 06/23/05 

http://walrus.wr.usgs.gov/infobank/s/s105nc/h

tml/s-1-05-nc.meta.html 

4 S-2-05-NC 07/25/05 

http://walrus.wr.usgs.gov/infobank/s/s205nc/h

tml/s-2-05-nc.meta.html 

5 S-2-05-NC 07/27/05 

http://walrus.wr.usgs.gov/infobank/s/s205nc/h

tml/s-2-05-nc.meta.html 

Instrument 

Deployments/ 

Recovery 

Survey #

Field Activity

ID

Survey 

Date

1 S-1-05-NC 06/21/05 

http://walrus.wr.usgs.gov/infobank/s/s105nc/h

tml/s-1-05-nc.meta.html 

2 S-2-05-NC 07/26/05 

http://walrus.wr.usgs.gov/infobank/s/s205nc/h

tml/s-2-05-nc.meta.html 

3 none 07/28/05 

4 none 08/16/05 

5 S-1-06-NC 01/12/06 

http://walrus.wr.usgs.gov/infobank/s/s106nc/h

tml/s-1-06-nc.meta.html 

6 D-1-06-NC 01/23/06 

http://walrus.wr.usgs.gov/infobank/d/d106nc/

html/d-1-06-nc.meta.html 

7 none 01/27/06 

8 none 02/01/06 

9 S-1-05-NC 07/28/05 

http://walrus.wr.usgs.gov/infobank/s/s105nc/h

tml/s-1-05-nc.meta.html 

10 S-2-05-NC 08/16/05 

http://walrus.wr.usgs.gov/infobank/s/s205nc/h

tml/s-2-05-nc.meta.html 

Multibeam Surveys 

Field Activity

ID

Survey 

Date

Survey

Mouth of SF Bay #1 V-2-04-NC 09/15/04 

http://walrus.wr.usgs.gov/infobank/v/v204nc/

html/v-2-04-nc.meta.html 

Mouth of SF Bay #2 none 09/17/05 

Dredge Monitoring #1 none 05/16/05 

164
165

Dredge Monitoring #2 none 06/07/05 

Dredge Monitoring #3 none 07/09/05 

Dredge Monitoring #4 none 10/19/05 

Dredge Monitoring #5 none 05/13/06 

Dredge Monitoring #6 none 06/02/06 

Dredge Monitoring #7 none 11/30/06