Ocean Outfall Dilution: Effects of Currents

Analyses of data for the City of San Francisco, Calif., obtained from continuously recording current meters showed the most energetic current component, the first principal component, to be strongly tidal and to lie along an axis pointing approximately to the Golden Gate. The difusers were placed perpendicular to this component, where possible, to obtain the maximum beneficial effect of the currents on dilution. A mathematical model was applied to the proposed diffusers to predict dilution in the presence of currents, using measured oceanic conditions. Results show the dilution and wastefield rise height to vary widely due to the varying oceanic and discharge conditions. The median dilutions are found to depend on season and to be increased substantially over those predicted by neglecting the dynamic effect of currents on dilution. The effect of diffuser orientation was also investigated with the model, and it was found that suitable orientation to the prevailing currents can significantly affect the initial dilution.