LONGITUDINAL ESTUARINE DIFFUSION IN SAN FRANCISCO BAY CALIFORNIA

The concept of one-dimensional diffusion is discussed and applied to the San Francisco Bay, California, to evaluate the degree of mixing and dispersion existing within the estuarine system. The intensity of mixing and dispersion is expressed in terms of an overall, longitudinal diffusion coefficient E which can be varied throughout the system. A method for computing E from observations of water quality constituents in an estuary is presented and discussed. Concentration distributions of chlorosity and silica derived from field observations taken over four years of continuous sampling of the Bay waters are used to evaluate the diffusion coefficient within the two arms of the Bay system. The results derived from the two different concentration distributions are found to be comparable, giving at least a partial verification of the proposed procedures. The relationships between the observed coefficients and the hydrologic, hydrographic, and tidal wave characteristics of the Bay system are examined to ascertain if the diffusion coefficient can be predicted directly without making resourse to water quality observations. The only relationship investigated which appears to have merit is {A figure is presented} where u ̈ is the mean advective velocity in the estuary, u′m the mean tidal velocity, and D the hydraulic channel depth. The equation is applicable only to those regions of an estuary where the advective velocity is known to have a significant effect on the value of E. Procedures which may be used to predict the concentrations of a water quality constituent in the Bay system-once the diffusion coefficients are known-are discussed briefly. An example of a steady state computation is presented and discussed. © 1969.