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

robin@sfei.orgwww.sfei.org/HEP