A MODEL STUDY OF ESTUARY AND SHELF TIDALLY DRIVEN CIRCULATION

We develop a three-dimensional numerical model for barotropic tidal ho ws in the coastal ocean useful in a weakly nonlinear regime. The flow field can then be split into a first;order linear, harmonic tidal flow and a second-order, nonlinearly induced mean or residual flow. First we test the model against two different, but well-established, tidal m odels, that of Leendertse and that of Ianniello. The model is successf ul in nearly replicating these earlier model results for an estuarine setting. We then apply the model first to an isolated, straight contin ental shelf. The mean flow generated then flows primarily alongshelf. We name this the Tee Current after Tee's (1980) discovery of this curr ent with a two-dimensional model that neglected all alongshelf variati ons. The Tee current appears to be ubiquitous on shelves as well as pe rsistent and to have alongshelf transport that is an appreciable fract ion of that produced by buoyancy forcing, for example. Its dynamics is analogous to that of alongshore currents in the surf zone. For a long , straight shelf the Tee Current is directed alongshelf opposite the s ense of the first order tidal current offshore major axis. For the cas es we analyzed, this current direction was upshelf, i.e., opposite the direction of coastally trapped wave propagation. The model results sh ow that the presence of a large, adjacent estuary alters the flow fiel ds of both the first and second order tides significantly. Eulerian me an transport leaving the estuary turns cyclonically to join and reinfo rce the Tee Current on the inner shelf. From an application to the Del aware Estuary and adjacent shelf we find excellent agreement between m odeled and observed first-order tidal currents, but only modest agreem ent between second-order mean currents. (C) 1998 Elsevier Science Ltd. All rights reserved.