Persistence of residual currents in the James River estuary and its implication to mass transport

Abstract

The distribution and persistence of Eulerian and Lagrangian residual velocity in a cross sectional transect of the James River estuary, Virginia are analyzed. The Eulerian residual velocity has the characteristic two-layered estuarine circulation in the northern half of the transect, however, the net flow is directed downriver at all depths in the shallower southern half of the transect. In the deep channel, the two-layered Eulerian residual circulation is highly persistent over the six month study duration, with disruptions occurring less than 10% of the time when meteorological forcings are intense. No spring-neap tidal cycle variation is apparent. The magnitude of the long-term advective mass transport (calculated as the lowest order approximation to the Lagrangian residual velocity) is approximately twice that of the Eulerian residual velocity and in the same direction in the deep channel. The Stokes drift velocity contribution to the Lagrangian residual velocity enhances the upriver Eulerian residual velocity transport on the north side of the transect and only slightly increases the downriver transport on the south side.