Tidal straining, density currents, and stirring in the control of estuarine stratification

摘要: Buoyancy input as fresh water exerts a stratifying influence in estuaries and adjacent coastal waters. Predicting the development breakdown of such stratification is an inherently more difficult problem than that involved analogous case induced by surface heating because buoyancy originates at lateral boundaries. In approach adopted here, we have adapted energy considerations used to describe competition between stabilizing effect vertical mixing brought about tidal wind stirring. Freshwater induces horizontal gradients which drive estuarine circulation lighter fluid moved seaward over heavier moving landward below. This contribution expected vary time level turbulence varies cycle. The density gradient also interacts directly with shear current induce periodic positive on ebb phase tide. Comparison this available stirring leads simple criterion for existence strain-induced stratification. Observations region Liverpool Bay satisfying confirm occurrence strong semidiurnal variation complete apparent around high except neap tides when permanent may develop. A simulation monthly cycle based model including straining, stirring, qualitative agreement main features observations.