Historical San Francisco Bay Historical San Francisco Bay ShorelineShoreline
Perspectives on the Past and FuturePerspectives on the Past and Future
Predicting the future of San Francisco Bay: learning from history
UC Museum of Paleontology Short CourseFebruary 6, 2010
Robin GrossingerHistorical Ecology ProgramSan Francisco Estuary Institute
I. Historical Bayscape
1800
1800
Watkins 1861
Tidal marsh habitat and plan form geometry at the local scale
► Tidal marshes are more than pickleweed Tidal marshes are more than pickleweed plainsplains
► Extent of tidal channelsExtent of tidal channels► Frequency of marsh pannes, salinasFrequency of marsh pannes, salinas► Prevalence of sandy beachesPrevalence of sandy beaches► Upland ecotoneUpland ecotone
II. Shoreline Change
1800
2000
Acres x 1000
Open Bay (<MLLW)
Intertidal (tidal flat and marsh)
Ca 18501800
Acres x 1000
Open Bay (<MLLW)
Intertidal (tidal flat and marsh)
20002000
formed since ~1900
~1920
Salt ponds and remnant marsh at Ravenswood (San Mateo County), 1993
Shoreline change
1857 versus 1993
erosionaccretion
Shoreline change
415 feet
III. Our Response
The historical practice of using stream-borne sediment to raise marsh elevations:
• “warping”
•common in South Bay 75-100 years ago
•diverted local streams into contained baylands areas
“Advantage is taken of this rapid
sedimentation both here [San Francisquito
Creek] and on Alameda Creek for reclaiming
the saltmarsh. The reclamation work is
accomplished by building a levee around a
certain portion and allowing the flood waters
to spread over it and thus drop the sediment
at the desired place.”Clark 1924
Thank youThank you