Numerical modelling of tide-induced residual circulation in Sydney Harbour

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 recirc ulating gyres that are due to the interaction of the tidal current with the complex coastal geometry and bathymetry of the harbour. Inclusion of the S -2 tide and homogeneous wind stress in the input forcing does not significa ntly change the residual circulation pattern. Residuals are produced mainly by the M-2 tide and there is no significant nonlinear interaction between the M-2 and the S-2 tide. Tracer simulations show that tidal mixing is limi ted in the vicinity of the entrance and the flushing rates of different seg ments of the harbour vary significantly. Lack of similarity between the Eul erian and Lagrangian residual fields demonstrates that the net displacement of material released during a particular phase of the tide has little conn ection with the mean current observed at fixed locations and is extremely s ensitive to the timing and location of release.