Numerical modelling of tide-induced residual circulation in Sydney Harbour

Abstract

Tide-induced residual circulation and dispersion in Sydney Harbour has been studied with a vertically integrated, two-dimensional, primitive equation model. The tide-induced residual circulation consists of a series of recirculating gyres that are due to the interaction of the tidal current with the complex coastal geometry and bathymetry of the harbour. Inclusion of the S₂ tide and homogeneous wind stress in the input forcing does not significantly change the residual circulation pattern. Residuals are produced mainly by the M₂ tide and there is no significant nonlinear interaction between the M₂ and the S₂ tide. Tracer simulations show that tidal mixing is limited in the vicinity of the entrance and the flushing rates of different segments of the harbour vary significantly. Lack of similarity between the Eulerian and Lagrangian residual fields demonstrates that the net displacement of material released during a particular phase of the tide has little connection with the mean current observed at fixed locations and is extremely sensitive to the timing and location of release.