Sand Transport in the San Francisco Bay Coastal System Patrick Barnard 1, Daniel Hanes 1, Li Erikson 1, Sand Transport in the San Francisco Bay Coastal System Patrick Barnard 1, Daniel Hanes 1, Li Erikson 1, Jeff Hansen 2 and Kate Dallas 2 1 U.S. Geological Survey, Coastal and Marine Geology Program, Santa Cruz, CA 2 University of California, Santa Cruz, Department of Earth and Planetary Sciences

Recent USGS Research San Francisco Bay Coastal System historical changesSan Francisco Bay Coastal System historical changes Recent morphological changesRecent morphological changes –Ocean Beach, incl. nearshore disposal site –West-central Bay –Crissy Field –Golden Gate and Angel Island sand wave fields Detailed process studiesDetailed process studies –Ocean Beach –SF Bar –Golden Gate –Crissy Field –Bedform analysis adjacent to Golden Gate –Angel Island sand waves Sediment sampling and multibeam mappingSediment sampling and multibeam mapping

1873 to to to 2005 SF Bar Bathymetric Change K. Dallas

SF Bar Bathymetric Change Crest contracted radially 1 kmCrest contracted radially 1 km Bar eroded vertically 80 cmBar eroded vertically 80 cm From changes consistent with a reduction in tidal prism and increased sediment supplyFrom changes consistent with a reduction in tidal prism and increased sediment supply From changes reflect reduced sediment supply and/or tidal prismFrom changes reflect reduced sediment supply and/or tidal prism Survey of the SF Bar was recently completed in 2009 for the California State Waters Mapping ProjectSurvey of the SF Bar was recently completed in 2009 for the California State Waters Mapping Project K. Dallas

Recent Changes SF Bar ( ) -92 million m 3 (-1.9 mcm/yr) San Pablo Bay ( ) -22 million m 3 (-0.7 mcm/yr) Suisun Bay ( ) -53 million m 3 (-1.1 mcm/yr) Central Bay ( ) -51 million m 3 (-1.6 mcm/yr) South Bay ( ) +11 million m 3 (+0.5 mcm/yr) Estimated sediment loss in last 50 years = 240 million m 3

Ship channel dredge disposal nearshore Ship channel dredge disposal nearshore ( present) = + 18 million m 3 ( present) = + 18 million m 3 Dredging, borrow pit mining, and aggregate mining ( present) = million m 3 Bay development Bay development (last century) = reduction in tidal prism of ~ 30% in tidal prism of ~ 30% Delta modifications = ~ 50% reduction in suspended sediment flux (Wright and Schoellhamer, 2004) reduction in suspended sediment flux (Wright and Schoellhamer, 2004) Ship channel dredge disposal offshore ( ) = - 21 million m 3 ( ) = - 21 million m 3 Major Anthropogenic Activities San Francisco Bay System sediment loss = 240 million m 3 (est. last 50 years)

Assessing the Impact Tally up sediment removed from systemTally up sediment removed from system Identify sediment transport pathways, patterns and sourcesIdentify sediment transport pathways, patterns and sources –Historical shoreline and bathymetric change analysis –Bedform morphology –Numerical modeling –Physical process studies –Sediment core analysis –Sediment provenance

Sediment Removal 200 million m 3 of sediment removed from system200 million m 3 of sediment removed from system 113 million 3 from Central Bay113 million 3 from Central Bay 75 million 3 identified as sand (50 million 3 from Central Bay)75 million 3 identified as sand (50 million 3 from Central Bay) Records incompleteRecords incomplete Missing many borrow pit mining recordsMissing many borrow pit mining records No aggregate mining records pre-1974 (began in 1930’s)No aggregate mining records pre-1974 (began in 1930’s) K. Dallas

Bathymetric Change ~3-fold increase in rate of erosion~3-fold increase in rate of erosion (-3.2 cm/yr) from change analysis (Fregoso et al., 2008) Lease sites lost sediment at a rate 5 times higher than rest of study areaLease sites lost sediment at a rate 5 times higher than rest of study area 10.8 million m 3 of sediment was removed by aggregate mining from million m 3 of sediment was removed by aggregate mining from No borrow pit mining or dredging was performed in this area from No borrow pit mining or dredging was performed in this area from % of sediment removed was not naturally replenished85% of sediment removed was not naturally replenished

2008 Multibeam Survey

Bedform Morphology

- 443 transects - 3,386 bedforms

Inferred Bedload Transport

FLOW grid High res grid Low res grid # cells44,14818,063 OB min size (m)3070 Offshore max size (km) Inlet40140 dt (min) # cells44,148 cell size30 m to 1.3 km dt (min)1.0 and 0.5 Delft3D Modeling

SF Bay Coastal System Model 4 domain 3D model 10 layers Grid cell size in region of GG ~50 (ac) x 70 (cc) Sacramento river inputs San Joaquin river inputs water level boundaries defined by tidal constituents Neumann boundary sea.grd cbay.grd nbay.grd sbay.grd L. Erikson

Predicted sediment transport - ‘hydrodynamic tide’ L. Erikson

Net Sediment Flux L. Erikson

In January 2008, we collected sediment samples, ADCP data, and CTD-LISST profiles along two transects across the Gate Golden Gate Sediment Flux L. Erikson

Golden Gate Model-Data Results L. Erikson

Coastal Erosion

Coastal Impacts

Ocean Beach Changes J. Hansen

South Ocean Beach Erosion J. Hansen

Change in Nearshore Wave Heights K. Dallas

Change in Nearshore Wave Heights K. Dallas

Regional Shoreline Changes In SF Region, rate of accretion increased 4- fold from long (~ last 100 years) to short term (~ last 20 years)In SF Region, rate of accretion increased 4- fold from long (~ last 100 years) to short term (~ last 20 years) Shift to erosion where SF Bar attaches at Ocean BeachShift to erosion where SF Bar attaches at Ocean Beach San Mateo region strongly erosional in long-term (93%) and short-term (98%)San Mateo region strongly erosional in long-term (93%) and short-term (98%) In SM region rate of erosion increased by 50% from long to short termIn SM region rate of erosion increased by 50% from long to short term K. Dallas

Objective: Apply multiple approaches to identify the source and pathways of beach-sized material in the San Francisco Bay Coastal System Funding: USGS and California Sediment Management Workgroup (CSMW) Remote techniquesRemote techniques –Bedform asymmetry –Numerical modeling Direct sampling and physical characteristicsDirect sampling and physical characteristics –Morphometric analyses (grain size, shape, sorting, etc) –Foraminiferal analysis (McGann) Geochemical analysisGeochemical analysis –Isotopes, 143 Nd/ 144 Nd and 87 Sr/ 86 Sr (Hein) –X-ray diffraction (Hein) –Heavy minerals (Woodrow and Wong) –Rare earth elements (Rosenbauer) Provenance Study Approach

Sediment Sampling

Provenance Study

Summary What we knowWhat we know –Historical changes –Short-term changes/patterns/processes –Semi-quantitative information on transport pathways What we are working on (What we know we don’t know)What we are working on (What we know we don’t know) –Golden Gate sediment flux –Sand provenance Questions/Comments? (What we don’t know that we don’t know?)Questions/Comments? (What we don’t know that we don’t know?)