Sand Transport in the San Francisco Sand Transport in the San Francisco Bay Coastal SystemBay Coastal System

Patrick BarnardPatrick Barnard11, Daniel Hanes, Daniel Hanes11, Li Erikson, Li Erikson11, , Jeff HansenJeff Hansen22 and Kate Dallas and Kate Dallas22

11U.S. Geological Survey, Coastal and Marine Geology Program, Santa Cruz, CAU.S. Geological Survey, Coastal and Marine Geology Program, Santa Cruz, CA22University of California, Santa Cruz, Department of Earth and Planetary SciencesUniversity of California, Santa Cruz, Department of Earth and Planetary Sciences

Recent USGS ResearchRecent 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 siteOcean Beach, incl. nearshore disposal site

– West-central BayWest-central Bay

– Crissy FieldCrissy Field

– Golden Gate and Angel Island sand wave fieldsGolden Gate and Angel Island sand wave fields

• Detailed process studiesDetailed process studies

– Ocean BeachOcean Beach

– SF BarSF Bar

– Golden GateGolden Gate

– Crissy FieldCrissy Field

– Bedform analysis adjacent to Golden GateBedform analysis adjacent to Golden Gate

– Angel Island sand wavesAngel Island sand waves

• Sediment sampling and multibeam mappingSediment sampling and multibeam mapping

1873 1873 toto 1900 1900 1900 1900 toto 1956 1956 1956 1956 toto 2005 2005

SF Bar Bathymetric ChangeSF Bar Bathymetric Change

K. DallasK. Dallas

SF Bar Bathymetric ChangeSF Bar Bathymetric Change

•Crest contracted radially 1 kmCrest contracted radially 1 km•Bar eroded vertically 80 cmBar eroded vertically 80 cm•From 1900-1956 changes consistent with a reduction in tidal prism and From 1900-1956 changes consistent with a reduction in tidal prism and increased sediment supplyincreased sediment supply•From 1956-2005 changes reflect reduced sediment supply and/or tidal From 1956-2005 changes reflect reduced sediment supply and/or tidal prismprism•Survey of the SF Bar was recently completed in 2009 for the California Survey of the SF Bar was recently completed in 2009 for the California State Waters Mapping ProjectState Waters Mapping Project

K. DallasK. Dallas

Recent ChangesRecent Changes

SF Bar (1956-2005) SF Bar (1956-2005)

-92 million m-92 million m33 (-1.9 mcm/yr)(-1.9 mcm/yr)

San Pablo Bay (1951-1983) San Pablo Bay (1951-1983)

-22 million m-22 million m33 (-0.7 mcm/yr)(-0.7 mcm/yr)

Suisun Bay (1942-1990) Suisun Bay (1942-1990)

-53 million m-53 million m33 (-1.1 mcm/yr)(-1.1 mcm/yr)

Central Bay (1947-1979) Central Bay (1947-1979)

-51 million m-51 million m33 (-1.6 mcm/yr)(-1.6 mcm/yr)

South Bay (1983-2005) South Bay (1983-2005)

+11 million m+11 million m33 (+0.5 mcm/yr)(+0.5 mcm/yr)

Estimated sediment loss in last 50 years =Estimated sediment loss in last 50 years =240 million m240 million m33

Ship channel dredge disposal nearshore Ship channel dredge disposal nearshore (1971 - present) = + 18 million m(1971 - present) = + 18 million m33

Dredging, borrow Dredging, borrow pit mining, and pit mining, and

aggregate mining aggregate mining (1900 - present) = (1900 - present) =

- 200 million m- 200 million m33

Bay development Bay development (last century) = reduction (last century) = reduction in tidal prism of ~ 30%in tidal prism of ~ 30%

Delta modifications = ~ 50% Delta modifications = ~ 50% reduction in suspended sediment reduction in suspended sediment

flux 1957-2001 (Wright and flux 1957-2001 (Wright and Schoellhamer, 2004)Schoellhamer, 2004)Ship channel dredge disposal offshore Ship channel dredge disposal offshore

(1931 - 1971) = - 21 million m(1931 - 1971) = - 21 million m33

Major Anthropogenic ActivitiesMajor Anthropogenic ActivitiesSan Francisco Bay System sediment loss = San Francisco Bay System sediment loss =

240 million m240 million m33 (est. last 50 years) (est. last 50 years)

Assessing the ImpactAssessing 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 analysisHistorical shoreline and bathymetric change analysis

– Bedform morphologyBedform morphology

– Numerical modelingNumerical modeling

– Physical process studiesPhysical process studies

– Sediment core analysisSediment core analysis

– Sediment provenanceSediment provenance

Sediment RemovalSediment Removal

•200 million m200 million m33 of sediment removed from system of sediment removed from system•113 million113 million33 from Central Bay from Central Bay•75 million75 million33 identified as sand (50 million identified as sand (50 million33 from Central Bay) 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. DallasK. Dallas

1997-2008 Bathymetric Change1997-2008 Bathymetric Change

•~3-fold increase in rate of erosion ~3-fold increase in rate of erosion

(-3.2 cm/yr) from 1947-1979 change (-3.2 cm/yr) from 1947-1979 change analysis (Fregoso et al., 2008) analysis (Fregoso et al., 2008)

•Lease sites lost sediment at a rate Lease sites lost sediment at a rate 5 times higher than rest of study 5 times higher than rest of study areaarea

•10.8 million m10.8 million m33 of sediment was of sediment was removed by aggregate mining from removed by aggregate mining from 1997-2008 1997-2008

•No borrow pit mining or dredging No borrow pit mining or dredging was performed in this area from was performed in this area from 1997-20081997-2008

•85% of sediment removed was not 85% of sediment removed was not naturally replenishednaturally replenished

2008 Multibeam Survey2008 Multibeam Survey

Bedform MorphologyBedform Morphology

- 443 transects- 443 transects

- 3,386 bedforms- 3,386 bedforms

Inferred Bedload TransportInferred Bedload Transport

Inferred Bedload TransportInferred Bedload Transport

FLOW grid

 

High res grid

Low res grid

# cells 44,148 18,063

OB min size (m) 30 70

Offshore max size (km)

1.3 1.8

Inlet 40 140

dt (min) 0.5 2.0

# cells 44,148

cell size 30 m to 1.3 km

dt (min) 1.0 and 0.5

Delft3D ModelingDelft3D Modeling

SF Bay Coastal System ModelSF 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

Neumann boundary

sea.grd

cbay.grd

nbay.grd

sbay.grd

L. EriksonL. Erikson

Predicted sediment transport - ‘hydrodynamic tide’Predicted sediment transport - ‘hydrodynamic tide’

L. EriksonL. Erikson

Net Sediment Flux Net Sediment Flux

L. EriksonL. Erikson

In January 2008, we collected sediment samples, ADCP data, and In January 2008, we collected sediment samples, ADCP data, and CTD-LISST profiles along two transects across the GateCTD-LISST profiles along two transects across the Gate

Golden Gate Sediment Flux Golden Gate Sediment Flux

L. EriksonL. Erikson

Golden Gate Model-Data ResultsGolden Gate Model-Data Results

L. EriksonL. Erikson

Coastal ErosionCoastal Erosion

Coastal ImpactsCoastal Impacts

Ocean Beach ChangesOcean Beach Changes

J. HansenJ. Hansen

South Ocean Beach ErosionSouth Ocean Beach Erosion

J. HansenJ. Hansen

Change in Nearshore Wave HeightsChange in Nearshore Wave Heights

K. DallasK. Dallas

Change in Nearshore Wave HeightsChange in Nearshore Wave Heights

K. DallasK. Dallas

Regional Shoreline ChangesRegional Shoreline Changes

•In SF Region, rate of In SF Region, rate of accretion increased 4-accretion increased 4-fold from long (~ last 100 fold from long (~ last 100 years) to short term (~ years) to short term (~ last 20 years)last 20 years)

•Shift to erosion where Shift to erosion where SF Bar attaches at Ocean SF Bar attaches at Ocean BeachBeach

•San Mateo region San Mateo region strongly erosional in strongly erosional in long-term (93%) and long-term (93%) and short-term (98%)short-term (98%)

•In SM region rate of In SM region rate of erosion increased by erosion increased by 50% from long to short 50% from long to short termterm

K. DallasK. Dallas

Objective: Apply multiple approaches to identify the source and pathways of beach-sized material Objective: Apply multiple approaches to identify the source and pathways of beach-sized material in the San Francisco Bay Coastal Systemin the San Francisco Bay Coastal System

Funding: USGS and California Sediment Management Workgroup (CSMW)Funding: USGS and California Sediment Management Workgroup (CSMW)

• Remote techniquesRemote techniques– Bedform asymmetryBedform asymmetry– Numerical modelingNumerical modeling

• Direct sampling and physical characteristicsDirect sampling and physical characteristics– Morphometric analyses (grain size, shape, sorting, etc)Morphometric analyses (grain size, shape, sorting, etc)– Foraminiferal analysis (McGann)Foraminiferal analysis (McGann)

• Geochemical analysisGeochemical analysis– Isotopes, Isotopes, 143143Nd/Nd/144144Nd and Nd and 8787Sr/Sr/8686Sr (Hein)Sr (Hein)– X-ray diffraction (Hein)X-ray diffraction (Hein)– Heavy minerals (Woodrow and Wong)Heavy minerals (Woodrow and Wong)– Rare earth elements (Rosenbauer)Rare earth elements (Rosenbauer)

Provenance Study ApproachProvenance Study Approach

Sediment SamplingSediment Sampling

Provenance StudyProvenance Study

SummarySummary•What we knowWhat we know

–Historical changesHistorical changes–Short-term changes/patterns/processesShort-term changes/patterns/processes–Semi-quantitative information on transport pathwaysSemi-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 fluxGolden Gate sediment flux–Sand provenanceSand 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?)

http://walrus.wr.usgs.gov/coastal_processes/http://walrus.wr.usgs.gov/coastal_processes/