Numerical simulation of the coastal boundary layer off Perth, Western Australia

Circulation and mixing processes within the coastal boundary layer off Perth, Western Australia were examined numerically. This region is characterised by low tides and a topography consisting of discontinuous submerged barrier reefs. An integral mixed-layer model was embedded into an existing three-dimensional hydrostatic finite difference model and the combined model was used to quantify: (1) the response of daily vertical structure to meteorological forcing, (2) the relative importance of wind and alongshore pressure gradient on the velocity field in the study area, and (3) the advection characteristics between the lagoonal waters (onshore of the reefs) and the adjacent shelf waters. The results indicated that the daily vertical structure in the lagoonal waters was completely mixed when the wind was 6 ms(-1) or greater over the afternoon and evening. For winds less than 5 ms(-1) the alongshore pressure gradient of 1.75 x 10(-7) dominated the shelf waters, but in the lagoonal waters, wind, even at low speeds, remained the dominant force. Cross-shore mass exchange across the reef system was found to be about 25% of the total mass exchange of the lagoonal area.