Science activity

USGS has conducted bathymetric analyses in San Francisco Bay, Suisun Bay, and the Delta intermittently since 1867 based on bathymetry data primarily collected by NOAA"s National Ocean Service (NOS) (formerly the United States Coast and Geodetic Survey (USCGS)). Since the days of hydraulic gold mining, sedimentation in San Francisco Bay has changed drastically. From the 1850's until at least the late 1800's, debris from hydraulic mining in the Sierra Nevada filled the Bay. As hydraulic mining practices ceased, the amount of sediment deposited decreased. In the latter half of the 20th century an increase in the implementation of flood control and water distribution projects in the Central Valley caused the Bay to be erosional due to the reduction of the frequency and duration of peak flow conditions, which in turn decreased sediment supply to the Bay. They have used this information to locate deposits of sediment-associated contaminants, restore wetland areas, and to provide the observable linkage between anthropogenic modifications of the landscape—such as evolving land use practices, flood control, and water diversions—and natural forces of climate-driven river flow, sea level change, tides, and wind. In 1999, USGS assessed how sedimentation in the Suisun Bay has changed between 1867 and 1990 (see info sources). They have also worked collaboratively with DWR, using their more recent bathymetry data to produce a high-resolution DEM of the Delta region (see info sources). It is not clear whether USGS will continue their bathymetry surveys. The latest survey is from 2005, and took place in the South of San Francisco Bay (outside the Delta study area).