Comments on Tidally Induced Residual Currents in Estuaries: Dynamics and Near-Bottom Flow Characteristics

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Abstract
The tidally induced Eulerian and Lagrangian residual currents in narrow tidal channels are interpreted in terms of the factors controlling their structure: the depth-integrated value (which is always seaward), the second-order velocity gradients at the bed and the surface, and the vertical structure of the driving terms in the time-averaged second-order momentum equations. The reasons for the relative complexity of the flow field in constricted channels are explained from this viewpoint. The conditions conducive to shoaling in the channel or to convergences in the near-bottom Lagrangian flow field are examined. It is shown that breadth and depth constrictions of 25% or greater lead to strong bottom-flow convergences. The surface boundary condition used in earlier studies is shown to be incorrect. This has some effect, generally slight, on previous solutions, and is shown to be most important in the upper part of the water column for the short-channel, constant-breadth-and-depth results.

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