Geometry‐induced residual eddies in estuaries with curved channels: Observations and modeling studies

Abstract

Observations using a vessel‐based acoustic Doppler current profiler conducted in two tidal channels with significant curvatures have shown persistent residual eddies. The residual eddies are clearly related to the bend of the channel. For a channel bending toward the north, the residual eddy on the east side of the channel tends to be clockwise, and the residual eddy on the west side of the channel tends to be counterclockwise. Water in these tidal channels is mostly well mixed or weakly stratified. Motivated by these observations, an analytic model is developed to study tidally induced mean circulation in a curved channel with arbitrary depth variations. A sinusoidal channel is used to simulate the effect of curved channels. A series of experiments with different parameters have shown consistently that a pair of residual eddies around the curvature exists. By analyzing the model results, it is found that advection is a major contributor to the residual eddies. Although the pressure gradient and the nonlinear wave propagation may not be negligible, especially for long channels, it is the advection that generates the vorticity of the residual eddies. The conclusion is true for both short and long channels. Here the division between a short and long channel is 0.6 of a quarter of the tidal wavelength. In addition, we also analyzed results from a finite volume numerical model for Lake Pontchartrain, which has curved tidal channels. The results demonstrate similar residual eddies as shown by the analytical model and the observations.