Factors Influencing the Entrapment of Suspended Material in the San Francisco Bay-Delta Estuary
James F. Arthur, U.S. Bureau of Reclamation
Melvin D. Ball, U.S. Bureau of Reclamation

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ABSTRACT:

Inorganic suspended particulate matter, turbidity, particulate nutrients, phytoplankton, Neomysis mercedis (Holmes), certain other zooplankton, and juvenile striped bass (young-of-the-year) accumulate in an entrapment zone located in the upper San Francisco Bay-Delta estuary (Sacramento-San Joaquin River System). The location of this entrapment zone is regulated by the magnitude and the pattern of river inflow, as well as the tidal excursion. At Delta outflow indices of 20 m ³·s^-1, the zone was located 40-45 km upstream of its location at 1,800 m³·s^-1; tidal movement of the zone is from 3 to 10 km, depending on tidal phase and height. The location of the zone is related to, and can be approximated from, specific conductance values of 2 to 10 millimho·cm^-1 (1-6 ‰ salinity). The concentration of constituents in the zone varied directly with Delta outflow, water depth, and tidal velocity. Depending on the constituent and environmental conditions at the time of measurement, the suspended-material concentration varied from as little as twice to as much as several hundred times the upstream or downstream concentration. The most significant environmental aspect of the entrapment zone may be that the quantity of phytoplankton and certain other estuarine biota appear to be enhanced when the zone is located in upper Suisun Bay.

 

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