Sediment Deposition and Erosion in South San Francisco Bay, California from 1956 to 2005

Sediment deposition and erosion in South San Francisco Bay from 1956 to 2005
was studied by comparing bathymetric surveys made in 1956, 1983, and 2005. From
1956 to 1983, the region was erosional. In contrast, from 1983 to 2005, the
region was depositional. Analysis of subregions defined by depth, morphology
and location revealed similarities in behavior during both the erosional and
depositional periods. During the entire period of the study, there was net
erosion in the shallows (<1 m depth) on the eastern shore of the bay north of
the Dumbarton Bridge and net deposition in the region south of Dumbarton
Bridge. The rates, however, reflected the sediment regime of each time period.
Erosional areas were less erosional during the period with net deposition and
depositional zones were more depositional. The cause for the increase in
deposition from 1983 to 2005 is unknown, but could be related to an increase in
sediment supply from Central Bay. The patterns of deposition and erosion and
the change in rates are consistent with an increase in sediment supply from the
north, as would occur if the supply from Central Bay increased from 1956-1983
to 1983-2005. Additional research is needed to fully understand why South San
Francisco Bay became depositional from 1983 to 2005 and to determine the
implications of this change to the planned salt pond restoration in the region.

[Summary provided by the USGS.]