Modeling Tidal Circulation in an Island's Wake

Abstract

Details of a numerical model study to predict the tidal circulation observed and measured in the lee of Rattray Island, Australia are presented. The hydrodynamic model is of the two‐dimensional depth integrated type, with particular emphasis being placed on the modeling of the advective accelerations and the lateral mixing in the free shear layer in the island's wake. The component of free shear layer turbulence includes a constant eddy viscosity approach in the mixing zone and the use of a semi‐empirical lateral velocity distribution. The numerically predicted circulatory velocity fields have been compared with field measurements, taken at 26 sites, aerial observations and Landsat imagery. The comparisons between both predicted and measured results are encouraging, with the eddy dimensions and circulation strength being similar for all tidal phases. Various other simulations are described, which chiefly suggest that, for this study: (1) The eddy characteristics are reduced when the lateral shear stress is neglected; (2) no eddy is reproduced when the advective accelerations are excluded; (3) bathymetric effects are significant; and (4) geostrophic effects are important at water elevation boundaries.