A 3-DIMENSIONAL MODEL OF THE WATER CIRCULATION AROUND AN ISLAND IN SHALLOW-WATER

A three-dimensional model is applied to the study of the tidal flow in the shallow waters around Rattray Island, Great Barrier Reef, Australia. The model uses the sigma-coordinate system and the numerical procedure is based on the finite volume approach. Two counter-rotating eddies develop in the wake of the island. The shearing and veering of the horizontal velocity is predicted to be small, hence the vertical motions are negligible almost everywhere, with the exception of some small regions. In the center of the eddies important upwelling is found, which is in qualitative agreement with theory and observations. The model exhibits strong downwelling along the upstream side of the island. Overall, the magnitude of the computed vertical motions may be too small and it is hypothesized that this may be due to a lack of resolution of the model. Further improvements to the model are outlined.