Modeling the Variations of Freshwater Inflows and Tidal Mixing on Estuarine Circulation and Salt Flux

摘要

An idealized estuary model is employed to simulate the effects of freshwater inflows and tidal mixing on estuarine circulation and salt flux. The model is forced with idealized tides at the coastal ocean boundary, and constant freshwater inflows are imposed at the river end to allow steady state conditions to be achieved. The dependence of length scale L and diffusive fraction v is stronger with tidal mixing compared to inflows, and this indicates that estuarine circulation and salt flux have a stronger dependence with tidal mixing than inflows. L is proportional to inflows to the -1/3 power and is proportional to tidal mixing to the -2/3 power, while v is proportional to inflows to the -0.5 power and is directly proportional to tidal mixing. The importance of tidal mixing in estuarine circulation as a result of the coupling between vertical mixing and stratification is reinforced. This suggests that the assumption in classical estuarine theory of parameterizing the influence of tides in mixing coefficients and removing the direct effect of tidal motions by taking averages is insufficient. The relationships derived from the idealized model study may be applied to increase our understanding of estuaries with realistic coastlines and bathymetry and to improve our ability to protect and maintain the health of estuaries, many of which are highly dynamic and rapidly changing systems.