Dispersion and Flushing of Pollutants in Estuaries

The fate of a pollutant introduced into an estuary depends upon the relative density of the effluent and the receiving water, the vertical density structure of the estuary, the strength of the tidal currents, the nontidal circulation pattern, and the intensity of turbulent diffusion. Effluents having lower density than the receiving waters, and discharged from an outfall on the bottom, ascend to the surface as a buoyant plume, entraining diluting water en route. Tidal currents advect the polluted volume as an oscillating plume, and turbulent diffusion leads to further dilution of the pollutant. Numerical solutions to time dependent theoretical advection-diffusion equations can be used to depict the probable distribution of a pollutant in a tidal segment of the estuary centered on the outfall. Exchange of pollutant between tidal segments in the estuary and the ultimate flushing of the pollutant from the estuary are best treated using a two-dimensional segmented mathematical model of the estuary.