Historical Sedimentation in the San Francisco Estuary Bruce Jaffe 1, Theresa Fregoso 1, Amy Foxgrover 1, Shawn Higgins 2 1 United States Geological Survey 2 Kamman Hydrology and Engineering San Pablo Bay

Outline The Estuary in the past 150 years Sediment connectivity of sub-embaymentsSediment connectivity of sub-embayments Sediment delivery control on tidal flat changeSediment delivery control on tidal flat change

Outline The Estuary in the past 150 years Sediment connectivity of sub-embaymentsSediment connectivity of sub-embayments Sediment delivery control on tidal flat changeSediment delivery control on tidal flat change Jaffe et al., 1998; Capiella et al., 1999; Foxgrover et al., 2004; Jaffe and Foxgrover, 2006a; Jaffe and Foxgrover, 2006b; Jaffe et al., 2007; Fregoso et al., 2008; Jaffe, 2009

Outline The Estuary in the past 150 years Sediment connectivity of sub-embaymentsSediment connectivity of sub-embayments Sediment delivery control on tidal flat changeSediment delivery control on tidal flat change

The Data Image obtained from NOAA photo library (

Sample Data- South San Francisco Bay

Generation of Bathymetric Models Digitize soundings, contours, and marsh extent Georeference data Error checking Generate 25 or 50m bathymetric grid using TopoGrid

San Francisco Estuary in the 1980s Area: ~1200 km 2 Average depth: 7 m Median depth: m Deepest point: ~120 m (Golden Gate)

The morphology of the estuary has changed 1850s 1890s1920s 1950s1980s

Generation of Sedimentation Grids Correct to a common vertical datum Adjust for subsidence (as needed) Difference the grids

Difference Grids

Net sediment gain of ~250 million cubic meters from 1850s s Suisun Bay Loss 52 Mcm San Pablo Bay Gain 339 Mcm Central Bay Gain 71 Mcm ( loss of 48 Mcm from borrow areas) South Bay Loss 90 Mcm ( loss of 38 Mcm from borrow areas)

The patterns of sediment gain and loss are complex

1850s to 1890s1890s to 1920s1920s to 1950s1950s to 1980s 1850s to 1890s1890s to 1920s1920s to 1950s1950s to 1980s 1850s to 1890s1890s to 1920s1920s to 1950s1950s to 1980s 1850s to 1890s1890s to 1950s1950s to 1980s San Pablo Bay Suisun Bay South Bay Central Bay 300 Mcm Mcm Mcm Mcm s to 1890s- gain of ~290 Mcm Hydraulic mining

1850s to 1890s1890s to 1920s1920s to 1950s1950s to 1980s 1850s to 1890s1890s to 1920s1920s to 1950s1950s to 1980s 1850s to 1890s1890s to 1920s1920s to 1950s1950s to 1980s 1850s to 1890s1950s to 1980s San Pablo Bay Suisun Bay 1890s to 1950s South Bay Central Bay 300 Mcm Mcm Mcm Mcm After hydraulic mining 1890s to 1920s- loss of ~100 Mcm

1850s to 1890s1890s to 1920s1920s to 1950s1950s to 1980s 1850s to 1890s1890s to 1920s1920s to 1950s1950s to 1980s 1850s to 1890s1890s to 1920s1920s to 1950s1950s to 1980s 1850s to 1890s1950s to 1980s San Pablo Bay 1890s to 1950s Suisun Bay South Bay Central Bay 300 Mcm Mcm Mcm Mcm s to 1950s- gain of ~100 Mcm SF Bay Area population increase

1850s to 1890s1890s to 1920s1920s to 1950s1950s to 1980s 1850s to 1890s1890s to 1920s1920s to 1950s1950s to 1980s 1850s to 1890s1890s to 1920s1920s to 1950s1950s to 1980s 1850s to 1890s1950s to 1980s San Pablo Bay Suisun Bay 1890s to 1950s South Bay Central Bay 300 Mcm Mcm Mcm Mcm s to 1980s- loss of ~200 Mcm Water projects

From the 1850s-1980s Circular bays near the center of the Estuary bays (San Pablo and Central) had net deposition Elongate bays at ends of estuary (Suisun and South) had net erosion From 1950s-1980s All bays were erosional Net

Question: Will the bays continue to erode? ? ? ? ?

? ? ? Partial answer: Not necessarily…. South San Francisco Bay had net deposition from 1983 to 2005 No data for other bays

Outline The Estuary in the past 150 years Sediment connectivity of sub-embayments Sediment delivery control on tidal flat changeSediment delivery control on tidal flat change

Sediment Connectivity Sub-embayment #1 Sub-embayment #2 Sediment Exchange

Determining the degree of sediment connectivity Modeling studies Tracers (natural and anthropogenic) Patterns and quantities of erosion and deposition

Determining the degree of sediment connectivity Patterns and quantities of erosion and deposition –Similar behavior (erosion and deposition occur at sub- embayments at the same time) –Opposite behavior of subembayments with similar magnitude (sediment eroded from one sub- embayment transported and deposited in another embayment) –Quantity of deposition greater than local tributary supply (sediment coming from somewhere else)

Net South SF Bay example of similar behavior (inferred sediment connectivity)

Outline The Estuary in the past 150 years Sediment connectivity of sub-embaymentsSediment connectivity of sub-embayments Sediment delivery control on tidal flat change

Tidal flats of the estuary have changed 1850s 1890s1920s 1950s1980s

San Pablo Bay Central Bay Suisun Bay South Bay 1850s 1890s 1920s 1950s 1980s km km km km 2 Tidal flat area decrease >50%

Intertidal mudflat area responded to changes in sediment supply to San Pablo Bay

Mudflats widened where sediment was abundant Jaffe et al., 2007

Summary- Historical Sedimentation in the San Francisco Estuary The estuary in the past 150 years –The patterns of gain and loss of sediment are complex –There were periods with net gain (e.g., hydraulic mining in mid- 1800s) and periods with net loss (e.g., water projects in mid- to late 1900s) Sediment connectivity of sub-embayments –Patterns and quantities of erosion and deposition point towards a connected system Sediment supply controls on tidal flats –In San Pablo Bay, increased tidal flat area during the hydraulic mining period corresponded to increased sediment supply. Decrease in tidal flat area during the late 1900s corresponded with a decrease in sediment supply.

Sediment gains and losses- 1950s to 1980s

Sediment removal from 1950s to 1980s Areas outlined in green are where sediment was removed > 50 Mcm of sediment removed from the system ~60% of sediment loss from Central Bay was from human activities

1850s 1890s 1920s 1950s 1980s Central Bay South Bay km 2 Marsh area decrease >90%