Hydrography and Circulation Processes of Gulf Estuaries

Abstract

Gulf estuaries (excluding the Mississippi) are lagoonal em-bayments, which, although possessing qualitative features common to most estuarine circulations, frequently exhibit these in extreme ranges or altered importance. These hydrographic features must be considered in developing or applying transport models (and hence water quality models) for these systems. In particular the following factors are generally the most important to bay hydrography: meteorological forcing, tides, freshwater inflow, and density currents. The bays are sensitive to meteorological forcing, especially relative to the feeble tidal effects. Among the important meteorological influences are windwaves, large-scale wind-driven gyres and flushing due to frontal passages. Freshwater inflows are highly transient and are important in establishing salinity gradients. Insofar as general water-quality considerations are concerned, the density current affects the large-scale circulation and transport within the bay, and is extremely important when the bay is transected by deepdraft ship channels (as are most of the Gulf estuaries). Mathematical water quality (including salinity) models usually parameterize the density-current transport by an inflated dispersion coefficient, however this approach is poorly founded theoretically, and for bays can lead to large errors in the water quality predictions. Examples are presented to display the characteristics and significance of each of these factors, and available modeling techniques (both physical and mathematical) are appraised with respect to each.