Coastal Monitoring of the May 2005 Dredge Disposal 

Offshore of Ocean Beach, San Francisco, Calif. 

By Patrick L. Barnard and Daniel M. Hanes 

2006 

Open-File Report 2006–1140 

U.S. Department of the Interior 

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

P. Lynn Scarlett, Acting Secretary 

U.S. Geological Survey 

P. Patrick Leahy, Acting Director 

U.S. Geological Survey, Reston, Virginia 2006 

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Citation: 

Barnard, P.L., and Hanes, D.M., 2006, Coastal monitoring of the May 2005 dredge disposal offshore of Ocean 

Beach, San Francisco, Calif.: U.S. Geological Survey Open-File Report 2006-1140, 23 p. [available on the 

World Wide Web at URL http://pubs.usgs.gov/of/2006/1040/ ]. 

Any use of trade, product, or firm names is for descriptive purposes only and does not imply 

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 

Figures ................................................................................................................................. iii

Introduction .......................................................................................................................... 1

Background........................................................................................................................... 1

Mapping at the mouth of San Francisco Bay ............................................................................................................2

Beach and nearshore studies ......................................................................................................................................3

Methods ............................................................................................................................... 3

Results and Discussion ........................................................................................................ 3

Multibeam surveys .........................................................................................................................................................3

PWC nearshore surveys................................................................................................................................................4

Beach surveys.................................................................................................................................................................4

In situ instruments ..........................................................................................................................................................4

Grain size analysis..........................................................................................................................................................4

Conclusions .......................................................................................................................... 4

Future and ongoing related work......................................................................................... 5

Acknowledgements.............................................................................................................. 5

References Cited.................................................................................................................. 5

Appendix............................................................................................................................... 7

Field Activity IDs and Web Links..................................................................................................................................7

Figures 

Figure 1. Map of the study area showing the location of the existing dredge disposal site (SF-8) and the test 

dredge disposal site (Ocean Beach Disposal Site). Bathymetry is from a 1956 National Ocean Service 

(NOS) survey........................................................................................................................................................................9

Figure 2. Map of bathymetric change at the mouth of San Francisco Bay between the 1956 NOS survey and 

fall 2004-05 multibeam survey conducted by SFML. ..................................................................................................10

Figure 3. Shaded relief image of the bathymetry around the Southwest Ocean Outfall pipe offshore of 

Ocean Beach from the fall 2004 multibeam survey....................................................................................................11

Figure 4. Cross-sections over the outfall pipe from the May 2005 pre-dredge disposal survey, indicating > 1 

m of vertical scour adjacent to the exposed pipe. .....................................................................................................12

iii
Figure 5. Shaded relief image from the fall 2004 multibeam surveys showing bottom features along Ocean 

Beach..................................................................................................................................................................................13

Figure 6. Two transects from PWC surveys along Ocean Beach indicating seasonally high rates of cross 

shore sediment transport. The labels in the top panel are the survey lines numbers.........................................14

Figure 7. Short-term beach change associated with a significant wave event (offshore wave heights 

reached 6 m) at Ocean Beach in March 2005 as compared to the month prior. A) Northern Ocean Beach. B) 

Southern Ocean Beach. ..................................................................................................................................................15

Figure 8. Winter storm change in the location of the erosion hot spot. Note the narrow beach width- the 

Mean High Water (MHW) line no longer exists on the beach in January 2005 at the pinch point. ..................16

Figure 9. Location of instrument deployments and sediment sampling in summer 2005...................................17

Figure 10. Difference plot showing bathymetric change associated with the initial dredge disposal (June 

2005) and change 4 months after the dredge disposal (October 2005). All changes are measured relative to 

the pre-dredge disposal survey in May 2005. .............................................................................................................18

Figure 11. Cross sections over the outfall pipe immediately after dredge disposal. See Figs. 3-4 for predredge conditions.............................................................................................................................................................19

Figure 12. Detection of the dredge disposal mound in the November 2005 PWC survey along PWC survey 

line #16................................................................................................................................................................................20

Figure 13. Beach change during the dredge disposal monitoring period, as compared to 2004. A) Northern 

Ocean Beach. B) Southern Ocean Beach and average vertical change totals for entire beach study area. 22

Figure 14. Current and wave plots from site #3 (see Fig. 9) at the disposal site. Currents are more than 

adequate (peaking at 80 cm/sec) to move sediment from the disposal site. ........................................................23

iv
Coastal Monitoring of the May 2005 Dredge Disposal 

Offshore of Ocean Beach, San Francisco, Calif. 

By Patrick L. Barnard1 and Daniel M. Hanes2

Introduction 

Ocean Beach, California, contains an erosion hot spot in the shadow of the San Francisco 

ebb tidal delta south of Sloat Boulevard that threatens valuable public infrastructure as well as the 

safe recreational use of the beach. In an effort to reduce the erosion at this location 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 United States Army Corps of Engineers, San Francisco District 

(COE). The objective for COE was to perform a test dredge disposal of ~230,000 m3

 (300,000 yd3) 

of sand just offshore of the erosion hot spot, in depths between approximately 9 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 (Fig. 1). The onshore migration of 

sediment from the target disposal location might feed the primary longshore bar or the nearshore 

zone, and provide a buffer to erosion that peaks during winter months when large waves impact the 

region. The United States Geological Survey (USGS), in collaboration with the Sea Floor Mapping 

Lab (SFML) of California State University, Monterey Bay, monitored the initial bathymetric 

evolution of the test dredge disposal site and the adjacent coastal region from May 2005 to 

November 2005. This paper reports on this monitoring effort and assesses the short-term coastal 

response. 

Background 

The USGS has been conducting field research at the mouth of San Francisco Bay (Barnard, 

2005; Barnard and others, under review), with emphasis on Ocean Beach (Barnard and Hanes, in 

press) since April 2004. Much of this work complements the coastal monitoring research described 

in this report. The Ocean Beach Coastal Processes Study (website: http://walrus.wr.usgs.gov/ 

coastal_processes/) includes monthly topographic beach surveys, quarterly cross-shore bathymetric 

profiles, grain size analysis, numerical modeling, video monitoring, wave and current 

measurements, and a multibeam/side scan bathymetric survey in collaboration with SFML and 

COE. The goal of this project is to define the dominant sediment transport pathways at the mouth 

of San Francisco Bay and, in so doing, determine the cause of erosion at Ocean Beach. Our initial 

work describes a highly energetic coastal system that has evolved considerably over the last century 

and shows significant short-term fluctuations in the nearshore zone. 

 

1

 Research Geologist, Coastal and Marine Geology Team, Santa Cruz, CA, mailto:pbarnard@usgs.gov 2

 Research Oceanographer, Coastal and Marine Geology Team, Santa Cruz, CA, mailto:dhanes@usgs.gov

1
Mapping at the mouth of San Francisco Bay 

Fifty days of multibeam mapping were conducted during the fall of 2004/05 through a 

USGS-COE-SFML collaboration. One of the primary goals of this survey was to evaluate 

bathymetric change at the mouth of San Francisco Bay since the last comprehensive bathymetric 

survey was completed in 1956 by the National Ocean Service. Fig. 2 shows the change in depth 

from 1956 to 2005. The large scale morphological trend is ebb tidal delta constriction and sediment 

loss. The average depth change in the entire region was -70 cm (erosion), which amounts to ~105 

million m3

 of sediment loss in the region common to both surveys (Fig. 2). Even with a 

conservative vertical error bar of +/-30 cm this is a significant trend. The outer lobe of the ebb tidal 

delta is completely dominated by erosion. Several likely causes include a reduction in tidal 

prism/currents due to San Francisco Bay development and a decrease in sediment supply due to 

both removal by sand mining inside the bay (Chin and others, 1998; 2004) and reduced influx of 

hydraulic mining debris from the Sacramento River (Gilbert, 1917). There are two distinct 

accretionary mounds in the SF-8 disposal site, presumably the result of dredge disposal in this area 

that has totaled ~18 million m3

 since disposal commenced on this site in 1971 (United States Army 

Corps of Engineers, 1996). This accretion has increased navigational hazards for COE dredging 

operations. Note also the nearshore erosion seaward of the erosion hot spot at Ocean Beach near 

Sloat Boulevard (Fig. 2), leaving this reach of the beach more susceptible to wave attack. 

The Southwest Ocean Outfall Pipe near the southern end of Ocean Beach carries 

approximately one-third of San Francisco’s treated sewage out to sea. It was constructed in the late 

1970’s (Woodward Clyde Consultants, 1978). The fall 2004-05 multibeam survey indicates 

extensive scour associated with the pipe (Figs. 3-4). 

The multibeam bathymetry shows the large-scale bedform morphology, primarily sand 

waves with wavelengths > 5-10 m, along Ocean Beach. The bedform orientation indicates 

dominance by tidal forcing outside the surf zone (Jordan, 1962; Bouma and others, 1977; 

Dalrypmple and others, 1978; Briggs and Southard, 1980; Ashley, 1990) (Fig. 5). Most bedforms in 

the northern half of Ocean Beach are oriented with their crests nearly perpendicular to the 

shoreline, while toward the middle of the beach, approximately 1 km north of the erosion hot spot, 

there are indications of onshore directed transport (Fig. 5, Inset A). 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 (Fig. 5, Inset B). Any bedforms < 5 m are not resolved with the 

multibeam system. 

 

In summary, three important management issues were highlighted by the multibeam survey: 

1. The SF-8 disposal site is accreting and a new site for disposing of ship channel sediment 

may soon be essential. 

2. The Southwest Ocean Outfall Pipe is exposed and is causing severe scour in the immediate 

vicinity. The ramifications for the structural integrity of the outfall pipe and the influence of 

this scour on the adjacent coastline are unknown. 

3. Most of the region offshore of the erosion hot spot at Ocean Beach has lost > 1m 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. 

2
Beach and nearshore studies

Work to date by the USGS suggests strong seasonal fluctuations in beach and nearshore 

sand volumes, high cross-shore sediment transport rates, and large short-term changes in beach 

morphology (Barnard and Hanes, in press). Intrannual shoreline positions can exceed 80 m, as 

measured during the 1997-98 El Niño period. USGS Personal Watercraft (PWC) surveys show 

seasonal cross-shore transport rates that can exceed 1000 m3

 per m of shoreline (Fig. 6). Monthly 

all terrain vehicle surveys have logged instances of dramatic changes in beach morphology, 

particularly during the winter months, when powerful storms can temporarily remove large 

volumes of beach sediment, leaving the beach and associated infrastructure more vulnerable to 

further wave attack (Fig. 7). The winter beach is typically narrower and flatter, while the summer 

beach is wider and steeper. The region of beach near Sloat Boulevard is the most vulnerable, 

historically narrow and often the first to lose significant sediment when the winter storm season 

begins (Fig. 8). Grain size surveys along Ocean Beach using both settling tube results and a digital 

bed sediment camera (Chezar and Rubin, 2004; Rubin, 2004) show that the grain size is quite 

consistent alongshore with a median grain size of 0.29 mm, with some coarser gravel lags 

occasionally occurring in the southern half of the beach. 

Methods 

The USGS monitored and evaluated the initial bathymetric evolution of the test dredge 

disposal site and the adjacent coastal region from May 2005 to November 2005. Four multibeam 

surveys (performed by SFML) were conducted: pre-dredge (May 2005), post dredge (June 2005), 1 

month post-dredge (July 2005) and 4 months post–dredge (October 2005). The USGS performed 

PWC surveys in May 2005 and November 2005. The beach was mapped using all-terrain vehicles 

in May, June, July, August and November, 2005. In June 2005, at the onset of the dredge disposal, 

the USGS deployed 4 tripods offshore of Ocean Beach, each equipped with a current profiler, to 

make calculations of the directional wave spectrum, water levels and tidal currents from in situ 

measurements (Fig. 9). The USGS conducted eight days of sediment sampling in June and July 

2005. A total of 191 stations were sampled by collecting grab samples or employing a digital bed 

sediment camera (eyeball) at the mouth of San Francisco Bay, with emphasis immediately on and 

around the Ocean Beach disposal site (Fig. 9). The subsequent sediment analysis will serve to track 

the dredge disposal (if the grain size is different from the surrounding sediment), to determine if the 

grain size of the dredge disposal is suitable for bed load transport under the prevailing 

hydrodynamic conditions of the area, and as input for use in future sediment transport models at 

Ocean Beach. 

Results and Discussion 

Multibeam surveys 

Fig. 10 shows the bathymetric change in June and October 2005, associated with the dredge 

disposal, relative to the bathymetry measured in May 2005. The peak of the asymmetric disposal 

mound in June is ~1.75 m high, with some secondary mounds scattered throughout the site. By 

October the peak location is largely unchanged, but the mound has greatly dissipated and the 

overall volume within the survey area (indicated by the survey extent in Fig. 10) has been reduced 

by ~50%. Much of this volume loss is likely attributed to the summer seasonal cross-shore 

sediment flux, that is, the natural cross-shore sediment transport trend toward the beach. A large 

portion of the dredge volume was placed in the vicinity of the exposed outfall pipe (Figs. 3-4), and 

3
cross sections show that some accretion has occurred around severely exposed portions of the pipe, 

reducing the exposure and thus the scour potential (Fig. 11). However, much of the pipe remains 

exposed. 

These repeated multibeam surveys confirm from the fall 2004/05 multibeam survey that no 

hard bottom exposure exists anywhere in the vicinity of the dredge disposal region. These surveys, 

coupled with the numerous grab samples and digital camera drops in this region, further confirm 

that the bottom is almost continuously sand covered, broken up only by occasional sand dollar 

colonies and coarse sand and gravel filled ripple scour depressions. Sand thickness is unknown. 

PWC nearshore surveys 

Between May and November 2005 the PWC surveys indicate a high rate of cross-shore 

sediment transport. The dredge disposal mound is identifiable along survey line #16 (Fig. 12). 

PWC surveys at Ocean Beach indicate that wave-induced cross-shore sediment transport (i.e. depth 

of closure) exists out to ~10 m of water depth, encompassing portions of the disposal area. 

Beach surveys 

 A comparison of topographic beach surveys during the May-August period in both 2004 

and 2005 indicate a higher rate of beach accretion during the initial disposal period in summer 

2005, particularly along the northern half of Ocean Beach (Fig. 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. 

In situ instruments 

Currents and waves measured at all sites (Fig. 9) are indicative of a highly dynamic coastal 

system, where waves and tidal currents both play important roles in sediment transport and the 

resulting morphology. Preliminary measurement analysis from the current profiler placed at the 

disposal site in June 2005 (Site 3) clearly show the potential for sand transport with summer waves 

approaching 2.5 m (offshore > 4 m) and currents peaking at 60 to 80 cm/s (Fig. 14). 

Grain size analysis 

Preliminary grain size analysis shows a highly spatially variable sedimentological character 

at the mouth of San Francisco Bay. Median grain size varies from coarse sand and gravel in the 

inlet throat to a massive ebb tidal delta dominated by fine to medium sand, with occasional sand 

dollar colonies and mud traces along the outer reaches. Intense sampling about the dredge disposal 

region confirms that the sediment offshore consists of fine to medium sand, broadly consistent with 

beach and dune sediment found along Ocean Beach. 

Conclusions 

The response of the beach and nearshore region to the June 2005 test dredge disposal thus 

far is largely inconclusive. The mound peak has not moved, but only ~50% of the initial increase in 

sediment volume associated with dredge disposal remained in the survey area after 4 months. 

Current measurements indicate the potential for high rates of sediment transport, and PWC profiles 

show very high rates of cross-shore sediment transport in this region. The beach did accrete at a 

higher rate during the dredge disposal monitoring period than it did during the prior year, but this 

4
correlation may be coincidental due to the common seasonal changes. The major directly 

observable benefit of the dredge disposal thus far is reducing the exposure of the outfall pipe, and 

thus the scour associated with the pipe exposure. It will likely take at least several more years of 

disposals of similar magnitude in this new location and careful monitoring to determine if the beach 

and nearshore region will benefit from the artificial increase in offshore sediment supply to this 

area.

Future and ongoing related work 

 In January 2006, a current profiler was also placed at SF-8 giving direct measurements of 

current velocities and wave conditions at the existing disposal site. Two additional profilers were 

deployed offshore and six Aquadopp profilers were deployed in the surf zone at Ocean Beach. 

More tightly spaced topographic beach surveys have been conducted since December 2005 in an 

effort to document the very short term changes in beach response to the winter storm season. A 

Deflt3D hydrodynamic and sediment transport model continues to be developed, benefiting greatly 

from this in situ instrumentation. Over 1.5 years of images taken from a web camera at the Cliff 

House (http://www.evsboca.com/usgs/default.htm) are being analyzed to track short term changes 

in shoreline position, run-up statistics, and nearshore rip and bar evolution.

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 PWC survey support and data 

analysis along with Jodi Eshleman, who also performed instrument data analysis. Thomas Reiss 

provide GPS support for PWC and beach surveys. Gerry Hatcher assisted with the sediment 

sampling. Joanne Ferreira directed instrument deployments and recovery. The entire Ocean Beach 

team is responsible for the success of this project, including Li Erikson, Ann Gibbs, Hal Williams, 

Kevin O’Toole, Walt Olson, Charlene Parsons, Liron Friedman, Jeff Hansen, Andrew Schwartz, 

Lindsey Doermann, Etienne Kingsley and Patrick Smith. 

References Cited 

Ashley, G.M., 1990, Classification of large-scale subaqueous bedforms: a new look at an old 

problem: Journal of Sedimentary Petrology, v. 60, no. 1, p. 160-172. 

Barnard, P.L., 2005, Modern processes at the mouth of San Francisco Bay: San Francisco, 

American Shore and Beach Preservation Association, 2005 ASBPA Field Trip Guide, 23 p. 

Barnard, P.L., and Hanes, D.M., in press, Integrating field research, modeling and remote sensing 

to quantify morphodynamics in a high-energy coastal setting, Ocean Beach, San Francisco, 

California, in 5th International Conference on Coastal Dynamics, Barcelona, Spain, 

American Society of Civil Engineers, 14 p. 

5
Barnard, P.L., Hanes, D.M., Rubin, D.M., and Kvitek, R., under review, Giant active sand waves at 

the entrance to San Francisco Bay: EOS Transactions, 13 p. 

Bouma, A.H., Hampton, M.A., and Orlando, R.C., 1977, Sand waves and other bedforms in Lower 

Cook Inlet, Alaska: Marine Geotechnology, v. 2, p. 291-308. 

Briggs, S.R., and Southard, J.B., 1980, Tidal-Current Sand Waves In Vineyard Sound, 

Massachusetts: AAPG Bulletin, v. 64, no. 5, p. 681-681. 

Chezar, H., and Rubin, D.M., 2004, Underwater Microscope System: United States Patent 

#6,680,795 B2, The United States of America as represented by the Secretary of the 

Interior, 9 p. 

Chin, J.L., Carlson, P.R., Wong, F.L., and Cacchione, D.A., 1998, Multibeam data and socioeconomic issues in west-central San Francisco Bay (CA): United States Geological Survey, 

Open File Report 98-139. 

Chin, J.L., Wong, F.L., and Carlson, P.R., 2004, Shifting shoals and shattered rocks- how man has 

transformed the floor of West-central San Francisco Bay: United States Geological Survey, 

Circular 1259, 30 p. [available on the World Wide Web at URL 

http://pubs.usgs.gov/circ/2004/c1259/ ]. 

Dalrypmple, R.W., Knight, R.J., and Lambiase, J.J., 1978, Bedforms and their hydraulic stability 

relationships in a tidal environment, Bay of Fundy, Canada: Nature, v. 275, p. 100-104. 

Gilbert, G.K., 1917, Hydraulic-mining debris in the Sierra Nevada: United States Geological 

Survey, Professional Paper 105, 154 p. 

Jordan, G.F., 1962, Large submarine sand waves: Science, v. 136, p. 839-848. 

Rubin, D.M., 2004, A simple autocorrelation algorithm for determining grain size from digital 

images of sediment: Journal of Sedimentary Research, v. 74, no. 1, p. 160-165. 

United States Army Corps of Engineers, 1996, Ocean Beach Storm Damage Reduction Feasibility 

Study: USACE San Francisco District, Final Feasibility Study for the City and County of 

San Francisco, . 

Woodward Clyde Consultants, 1978, Coastal Engineering Evaluation - Southwest Ocean Outfall 

Project. 

6
Appendix 

Field Activity IDs and Web Links 

ATV Survey List 

Survey # FACS ID

Survey 

Date

1 OB104CA 4/7/2004 

2 OB204CA 5/7/2004 

3 OB304CA 6/7/2004 

4 OB404CA 7/6/2004 

5 OB504CA 10/13/2004 

6 OB604CA 11/15/2004 

7 OB704CA 12/10/2004 

8 OB105CA 1/11/2005 

9 OB205CA 2/7/2005 

10 OB305CA 3/8/2005 

11 OB405CA 3/11/2005 

12 OB505CA 5/2/2005 

13 OB605CA 6/10/2005 

14 OB705CA 6/27/2005 

15 OB805CA 7/12/2005 

16 OB905CA 7/22/2005 

17 OBA05CA 8/22/2005 

18 OBB05CA 11/17/2005 

PWC Survey List 

Survey # FACS ID

Survey 

Date

1 OB204CA 5/4/2004 

2 OB404CA 7/20/2004 

3 OB604CA 11/12/2004 

4 OB505CA 5/5/2005 

5 OB805CA 7/5/2005 

6 OBB05CA 11/17/2005 

Beach Eyeball Survey List 

Survey # FACS ID

Survey 

Date

1 OB104CA 4/7/2004 

2 OB204CA 5/7/2004 

3 OB404CA 8/3/2004 

4 OB305CA 3/7/2005 

7
5 OBB05CA 11/17/2005 

Sediment Sampling Offshore 

Survey # FACS ID

Survey 

Date

1 S105NC 6/21/2005 

2 S105NC 6/22/2005 

3 S105NC 6/23/2005 

4 S205NC 7/25/2005 

5 S205NC 7/27/2005 

Instrument 

Deployments/Recovery 

Survey # FACS ID

Survey 

Date

1 S105NC 6/21/2005 

2 S205NC 7/26/2005 

 

 

 

 

 

 

 

 

 

 

 

 

8
Figure 1. Map of the study area showing the location of the existing dredge disposal site (SF-8) and 

the test dredge disposal site (Ocean Beach Disposal Site). Bathymetry is from a 1956 National 

Ocean Service (NOS) survey. 

 

9
Figure 2. Map of bathymetric change at the mouth of San Francisco Bay between the 1956 NOS 

survey and fall 2004-05 multibeam survey conducted by SFML. 

10
Figure 3. Shaded relief image of the bathymetry around the Southwest Ocean Outfall pipe offshore 

of Ocean Beach from the fall 2004 multibeam survey. 

11
Figure 4. Cross-sections over the outfall pipe from the May 2005 pre-dredge disposal survey, 

indicating > 1 m of vertical scour adjacent to the exposed pipe. 

12
Figure 5. Shaded relief image from the fall 2004 multibeam surveys showing bottom features along 

Ocean Beach.

13
Figure 6. Two transects from PWC surveys along Ocean Beach indicating seasonally high rates of 

cross shore sediment transport. The labels in the top panel are the survey lines numbers.

14
A 

B 

Figure 7. Short-term beach change associated with a significant wave event (offshore wave 

heights reached 6 m) at Ocean Beach in March 2005 as compared to the month prior. A) Northern 

Ocean Beach. B) Southern Ocean Beach.

15
Figure 8. Winter storm change in the location of the erosion hot spot. Note the narrow beach widththe Mean High Water (MHW) line no longer exists on the beach in January 2005 at the pinch point. 

16
Figure 9. Location of instrument deployments and sediment sampling in summer 2005. 

17
Figure 10. Difference plot showing bathymetric change associated with the initial dredge disposal 

(June 2005) and change 4 months after the dredge disposal (October 2005). All changes are 

measured relative to the pre-dredge disposal survey in May 2005. 

18
Figure 11. Cross sections over the outfall pipe immediately after dredge disposal. See Figs. 3-4 for 

pre-dredge conditions. 

19
Figure 12. Detection of the dredge disposal mound in the November 2005 PWC survey along PWC 

survey line #16.

20
A

21
B 

Figure 13. Beach change during the dredge disposal monitoring period, as compared to 2004. A) 

Northern Ocean Beach. B) Southern Ocean Beach and average vertical change totals for entire 

beach study area.

22
Figure 14. Current and wave plots from site #3 (see Fig. 9) at the disposal site. Currents are more 

than adequate (peaking at 80 cm/sec) to move sediment from the disposal site.

23