A multi-scale model of the hydrodynamics of the whole Great Barrier Reef

An unstructured-mesh parallel hydrodynamic model of the whole Great Barrier Reef is presented. This model simultaneously simulates most scales of motion. It allows interactions between small- and largescale processes. The depth-averaged equations of motion are discretized in space by means of a mixed finite element formulation while the time-marching procedure is based on a third order explicit Adams– Bashforth scheme. The mesh is made up of triangles. Their size and shape can be modified easily so as to resolve a wide range of scales of motion, from those of the regional flows to those of the eddies or tidal jets that develop in the vicinity of reefs and islands. The forcings are the surface wind stress, the tides and the inflow from the Coral Sea (East Australian Current, Coral Sea Coastal Current), the latter two forcings being applied along the open boundaries of the computational domain. The numerical results compare favourably with observations of both longshore currents and the local perturbations due to narrow reef passages. Comparisons are also performed with the simulations of a three-dimensional model applied to a small domain centered on Rattray Island, showing that both models produce similar horizontal flow fields. For a structured-mesh model to yield results of the same accuracy, there is no doubt that the computational cost would be much higher.