Tide and Fair-Weather Wind Effects in a Bar-Built Louisiana Estuary.

摘要

An in-depth, fair-weather field study in July 1972 provided information about the response of the water level of Caminada Bay, an extremely shallow bar-built Louisiana estuary. The water surface elevation was recorded at three locations in the bay along the other parameters, an equipotential surface was established, and the time-dependent variations of a slope vector along the surface gradient were computed. It was found that the instantaneous fair-weather wind stress induced a slowly oscillating set-up around a time-averaged slope magnitude of 1,500,000 rad. This constituted less than 50% of the measured time-averaged slope. The remaining time-averaged slope is accounted for by tidal nonlinearities. The instantaneous slope vector was found to rotate or oscillate in the horizontal plane with a diurnal period. Tidal input through two entrances governed this behavior, while the wind stress and atmospheric pressure gradients served only to modify the direction of the surface slope. In general, on the diurnal scale, tidal rather than wind effects dominate the dynamics of Caminada Bay. However, the mean water level responded to the wind direction on a time-scale longer than one day. Winds parallel rather than normal to the coast controlled the water elevation, indicating an Ekman effect. (Author)