Lester J. McKee | Geology Reports

USGS2013

Sediment transport in the San Francisco Bay Coastal System: An overview

The papers in this special issue feature state-of-the-art approaches to understanding the physical processes related to sediment transport and geomorphology of complex coastal-estuarine systems. Here we focus on the San Francisco Bay Coastal System, extending from the lower San Joaquin-Sacramento Delta, through the Bay, and along the adjacent outer Pacific Coast. San Francisco Bay is an urbanized estuary that is impacted by numerous anthropogenic activities common to many large estuaries, including a mining legacy, channel dredging, aggregate mining, reservoirs, freshwater diversion, watershed modifications, urban run-off, ship traffic, exotic species introductions, land reclamation, and wetland restoration. The Golden Gate strait is the sole inlet connecting the Bay to the Pacific Ocean, and serves as the conduit for a tidal flow of ~ 8 x 109 m 3 /day, in addition to the transport of mud, sand, biogenic material, nutrients, and pollutants. Despite this physical, biological and chemical connection, resource management and prior research have often treated the Delta, Bay and adjacent ocean as separate entities, compartmentalized by artificial geographic or political boundaries. The body of work herein presents a comprehensive analysis of system-wide behavior, extending a rich heritage of sediment transport research that dates back to the groundbreaking hydraulic mining-impact research of G.K. Gilbert in the early 20th century.

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USGS2003

Sediment dynamics drive contaminant dynamics

Many contaminants of greatest concern in San Francisco Bay, including mercury and PCBs, are primarily associated with sediment particles rather than dissolved in water. Therefore, the movement and fate of sediment determines the movement and fate of many contaminants in the Bay. Because of this close association, the RMP monitors and seeks to understand the quantity and movement of sediment suspended in the water. Through study of suspended sediment dynamics, the RMP is developing a better understanding of trends and patterns of contaminants and how the Bay will respond to management actions during the next several decades. Recent RMP efforts to develop predictive models of contaminant fate in the Bay have highlighted the fundamental importance of understanding sediment dynamics. Sediment movement in the Bay is determined by tides, wind, and freshwater inflow. Tides flood and ebb twice a day, wind typically is strongest in the afternoon, and freshwater inflow is greatest during the winter rainy season (see sidebar on next page). To characterize these fluctuations, the U.S. Geological Survey (USGS) began continuous monitoring of suspended sediment concentration in 1991. Continuous suspended sediment concentration monitoring stations were established in each major region of San Francisco Bay (Figure 1), establishing a continuous monitoring network. The sensors at each station measure the amount of material in the water every 15 minutes. Results are available on the internet at . In addition to the network, sensors have been deployed at as many as 14 additional sites in the Bay for periods of several months as part of focused studies of sediment transport in Bay locales of special interest.

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