Tidal Modulation of Estuarine Plumes

Abstract

Off an estuary mouth, the nonlinear transfer of vorticity from the oscillating onshore-offshore tidal currents to the mean field generates a pair of counter-rotating eddies that flows seaward near the center axis of the inlet and landward on both sides. The Coriolis deflection strengthens the anticyclonic eddy but weakens the cyclonic one. A seaward sloping shelf enhances these eddies but a seaward sloping estuary weakens them. These tidal residual eddies strengthen and hasten the expansion of a river-forced plume off an estuary mouth, but weaken and retard the development of the coastal jet farther downcoast. To lowest order, this is the primary effect of tides on an estuarine plume in a coupled estuary-shelf system. Tidal effects on the subtidal river-forced circulation inside the estuary are secondary.