Sediment dynamics in Darwin Harbour, Northern Territory, Australia

The sediment dynamics of Darwin Harbour is studied by a sediment model (Wang, 2002) and a hydrodynamic model based on FVCOM. The sediment model bathymetry includes the high resolution Darwin Harbour coastal lines and sea surface area. The hydrodynamic model is forced by tides at the ocean open boundary with constant salinity and temperature. 20 sigma layers with 3/4 logarithmic layers near the surface/bottom and 13 evenly distributed layers in the middle are used in the model. The sediment model focuses on suspended fine sediment, and is initialized with limited bed thickness and one sediment type. The observed tidal elevation, currents and the suspended sediment concentration (SSC) data were used to calibrate the model. The simulation finds that the SSC in the harbour reaches its maximum at the bottom near Nightcliff Jetty and in the channel at spring and neap tide with a value of 10.0 and 0.1 g m-3, respectively. During spring tides, vertical averaged residual flux of SSC is mainly landward with a value of 0.8 g m-2s-1. During neap tide, vertical averaged residual flux of SSC is seaward with peak value of 0.05 g m-2s-1. Erosion happens near Darwin City and deposition appears near East Arm Wharf. An eddy in the East Arm found by David (2009) is also well reproduced by the model.