Numerical modelling of Macquarie Harbour

Tiris thesis is about the creation of a numerical model and its application to Macquarie Harbour (Tasmania, Australia). With the aim being to better understand the harbour and aid the management of its environment and industry. A numerical model was developed through the combination of an original two-dimensional laterally averaged river model and an existing three-dimensional ocean model. The existing three-dimensional model used is the Princeton Oceanographic Model (POM) by Blumberg and Mellor (1987), which is used for modelling the harbour. The author's river model is used for the two main rivers flowing into Macquarie Harbour, and part of the ocean surrounding the harbour. The river model is based on non-Boussinesq primitive equations, which include the density terms neglected in the commonly used Boussinesq approximation. These density terms are important where there are large salinity stratifications, which occur in the rivers flowing into Macquarie Harbour. The primitive equations for the model are derived in a rectangular Cartesian co-ordinate system and then transformed to a a co-ordinate system. The a coordinate system transformation, also used by POM, non-dimensionalises depth - resulting in a more accurate and efficient method for handling a varying bathymetry. The river model is solved with a finite difference implicit scheme, which is numerically centred in space and time. As the models' bathymetries vaiy from 1 to 90m, to get the required resolution in the deeper sections with the a co-ordinates, the resulting vertical spacing in the shallow sections is small. Hence, the finite difference equations are solved vertically, which avoids a restrictive Courant, Friedrichs and Lewy (CFL) time restraint with the explicit finite difference operators. The model successfully predicts the general circulation and pollution distribution in the harbour, agreeing to within 36% of peak velocities measured using a broad-band acoustic doppler current profiler (Koehnken, 1996). It also gives a reasonable representation of the salinity profile in the Gordon River compared to measurements taken by the Hydro-Electric Corporation (HEC), during the Lower Gordon River Scientific Survey (HEC, 1979). With an average depth of 25m, the harbour is sensitive to wind stresses and the large inflow from the Gordon River. fu the northern harbour, the polluted King River water is mixed by the tide and action of the Gordon River water. With no previously published numerical models of Macquarie Harbour, the model from this thesis has and will continue to be a useful management tool for the environmental instrumentalities and industry.