A numerical model of sediment transport applied to San Francisco Bay, California

A two dimensional depth-averaged sediment transport model is used to simulate field measurements of suspended sediment concentrations in northern San Francisco Bay. The model uses a semi-implicit finite difference method to solve the shallow water equations and incorporates standard empirical expressions for erosion and deposition of sediments into the transport equation as source/sink terms. The field measurements indicate that tidal scale variations (both diurnal and spring-neap) dominate the variations in suspended sediment concentration (SSC). Increases in SSC also correlated highly with large delta outflows following a storm in late winter. The sediment transport model reproduces the field measurements quite well during periods when the water column is relatively well-mixed vertically. However, the present model only includes one size class of sediment and does not perform well when spatial variability of sediment properties and multiple size classes are significant factors. Comparison of erosion and accretion patterns generated by the model with those obtained from historical bathymetric surveys indicate that the model captures several of the general features observed historically. A sensitivity analysis demonstrates that the model is very sensitive to the critical shear stress for erosion and moderately sensitive to the erosion rate constant, critical shear stress for deposition, and settling velocity.