Tide induced mass-flux in shallow estuaries

Aimed at resolving the 3-D structure of subtidal currents caused by tidal wave motion in estuaries, this paper presents an analytic solution and a numerical solution for a 3-D hydrodynamic model of a tidal channel with transverse depth variation. The study indicates that, under the influence of nonlinearity and significant depth variation across a shallow coastal plain estuary, the tidally induced subtidal flow is seaward in the channel with a core of high velocity centered between surface and mid- depth of the channel. The landward subtidal flow occurs over the shoals, with a maximum at the surface. When vertically averaged, the results are consistent with those from 2-D models. Data obtained in the lower James River Estuary in the fall of 1996 are analyzed to separate the tidally induced subtidal flow from density-driven estuarine flows. Observed subtidal flows show patterns consistent with theoretical model results.