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Continuous Monitoring in the San Francisco Bay and Delta
D.Schoellhamer and P.Buchanan
Background
Freshwater from rivers mixes with saltwater from the Pacific Ocean in San Francisco Bay.  Salinity indicates the relative mixing of freshwater and saltwater and, along with water temperature, affects circulation and ecology. Rivers also transport sediment to the Bay.  Within the San Francisco Bay and Delta, sediment carries toxic substances, provides habitat for benthic organisms, reduces light and limits photosynthesis, and deposits on the bottom of channels, subembayments, and wetlands.  Tides move water in and out of the Bay and affect water level, salinity, water temperature, and suspended-solids concentration (SSC).  The U.S. Geological Survey continuously monitors water level, salinity, water temperature, and SSC in San Francisco Bay to improve our knowledge of how the Bay works.
Purpose and Scope
The purpose of this web page is to make time series data of salinity, temperature, water level, and SSC in San Francisco Bay available to scientists, resource managers, educators, and the general public.  Data are collected every 15 minutes at many sites in the Bay and usually at two elevations in the water column at each site.  Salinity, water temperature, and water level time series began in 1989 and SSC time series begin in the 1990s.  All data have been reviewed, edited, and approved for release.
Study Area
Map of SF BayIn San Francisco Bay (fig. 1), tides are semidiurnal (two high and low tides per day) with a range from about 5.5 ft in Suisun Bay, to 6.5 ft at the Golden Gate and Central San Francisco Bay (Central Bay), to about 10 ft in South San Francisco Bay (South Bay). The tides also have a 14-day spring-neap cycle. Typical tidal currents range from 0.6 ft/s in shallow water to more than 3 ft/s in deep channels (Smith, 1987). Winds are typically strongest during the summer when there is an afternoon onshore sea breeze. Most precipitation occurs from late autumn to early spring, and freshwater discharge into the bay is greatest in the spring as a result of runoff from snowmelt. About 90 percent of the discharge is from the Sacramento ­San Joaquin River Delta, which drains the Central Valley of California (Smith, 1987). Freshwater inflow from the Central Valley typically first encounters saltwater in northern San Francisco Bay.

Discharge from the delta contains 83 to 86 percent of the fluvial sediments that enter the bay (Porterfield, 1980). During wet winters, turbid plumes of water from the delta have extended into South Bay (Carlson and McCulloch, 1974). Local maxima of SSC, called estuarine turbidity maxima, are located in Suisun Bay (Schoellhamer and Burau, 1998). The bottom sediments are composed mostly of silts and clays in South Bay and in the shallow water (about 12 ft or less) of Central, San Pablo, and Suisun Bays. Silts and sands are present in the deeper parts of Central, San Pablo, and Suisun Bays and in Carquinez Strait (Conomos and Peterson, 1977). Large tidal velocities, spring tides, and wind waves in shallow water all are capable of resuspending bottom sediments (Powell and others, 1989; Schoellhamer, 1996).

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Acknowledgements

We gratefully acknowledge the U.S. Coast Guard, California Department of Transportation, California Department of Water Resources, San Francisco Port Authority, San Francisco Regional Water Quality Control Board, the EAI International, the Port of Richmond and the Golden Gate Bridge, Highway and Transportation District, for their permission and assistance in establishing the monitoring sites used in this study.  Collection of the time-series data were supported by the Interagency Ecological Program, the San Francisco Regional Water Quality Control Board, U.S. Army Corps of Engineers as part of the Regional Monitoring Program for Trace Substances, and by the U.S. Geological Survey Federal/State Cooperative and Place Based Studies Programs.

References

Buchanan, P.A., and Schoellhamer, D.H., 1995, Summary of suspended-solids concentration data, Central and South San Francisco Bays, California, water years 1992 and 1993: U.S. Geological Survey Open-File Report 94-543, 15 p.

Buchanan, P.A., and Schoellhamer, D.H., 1996, Summary of suspended-solids concentration data, Central and South San Francisco Bays, California, water year 1995: U.S. Geological Survey Open-File Report 96-591, 40 p.

Buchanan, P.A., Schoellhamer, D.H., and Sheipline, R.C., 1996, Summary of suspended-solids concentration data, Central and South San Francisco Bays, California, water year 1994: U.S. Geological Survey Open-File Report 95-776, 48 p.

Campbell Scientific, Inc., 1997, Model 107 Temperature Probe Instruction Manual, p. 5.

Carlson, P.R., and McCulloch, D.S., 1974, Aerial observations of suspended-sediment plumes in San Francisco Bay and adjacent Pacific Ocean: U.S. Geological Survey Water-Resources Research, v. 2, no. 5, p. 519­526.

Conomos, T.J., and Peterson, D.H., 1977, Suspended-particle transport and circulation in San Francisco Bay, an overview: New York, Academic Press. Estuarine Processes, v. 2, p. 82­97.

Downing, J.P., 1983, An optical instrument for monitoring suspended particulates in ocean and laboratory: in OCEANS 1983 San Francisco, California, August 29-September 1, 1983, Proceedings: p. 199-202.

Downing, J.P., Sternburg, R.W., and Lister, C.R.B., 1981, New instrumentation for the investigation of sediment suspension processes in the shallow marine environment: Marine Geology, v. 42, p. 19-34.

Fishman, M.J. and Friedman, L.C., 1989, Methods for determination of inorganic substances in water and fluvial sediments: U.S. Geological Survey Techniques of Water-Resources Investigations, book 5, chap. A1, 545 p.

Foxboro, 1991, Instruction Book 2573, 871EC Electrodeless Conductivity Sensors and Accessories, 38 p.

Levesque, V.A., and Schoellhamer, D.H., 1995, Summary of sediment resuspension monitoring, Old Tampa Bay and Hillsborough Bay, Florida, 1988-1991: U.S. Geological Survey Water-Resources Investigations Report 94-4081, 31 p.

Porterfield, George, 1980, Sediment transport of streams tributary to San Francisco, San Pablo, and Suisun Bays, California, 1909­1966: U.S. Geological Survey Water-Resources Investigations Report 80-64, 91 p.

Powell, T.M., Cloern, J.E., and Huzzey, L.M., 1989, Spatial and temporal variability in South San Francisco Bay (U.S.A.). I. Horizontal distributions of salinity, suspended sediments, and phytoplankton biomass and productivity: Estuarine, Coastal and Shelf Science, v. 28, p. 583­597.

Schemel, L.E., 1995, Measurements of salinity, temperature, and tides in South San Francisco Bay, California, at Dumbarton Bridge: 1990-1993 water years:  U.S. Geological Survey Open-File Report 95-326.

Schoellhamer, D. H., 1996, Factors affecting suspended-solids concentrations in South San Francisco Bay, California: Journal of Geophysical Research, v. 101, no. C5, p. 12087-12095.

Schoellhamer, D.H., and Burau, J.R., 1998, Summary of findings about circulation and the estuarine
turbidity maximum in Suisun Bay, California, U.S. Geological Survey Fact Sheet FS-047-98, 6 p.
 
Smith, L.H., 1987, A review of circulation and mixing studies of San Francisco Bay, California: U.S. Geological Survey Circular 1015, 38 p.

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