Modelling the physical oceanography of the D'Entrecasteaux Channel and the Huon Estuary, south-eastern Tasmania

Abstract

A three-dimensional primitive-equation hydrodynamic model was applied to the Huon Estuary and D'Entrecasteaux Channel in south-eastern Tasmania to characterise the physical oceanography of the coupled system. Model results verify that the Huon Estuary behaves as a salt-wedge estuary, and can be considered the driver for residual circulation for the system; the bottom water enters the southern channel and is directed up-estuary in the form of a salt wedge, to be entrained into the surface layer along its length, whereas freshwater downstream flow is returned to the channel. The D'Entrecasteaux Channel behaves as a ROFI (Regions of Freshwater Influence) regime, where buoyancy owing to the freshwater inflow stabilises the water column, in competition with mixing processes. The ROFI is influenced by rotation, resulting in a flow predominantly directed northward in the channel, with only a small percentage exiting the southern boundary under the influence of northerly winds. The connectivity of the region is largely influenced by the residual circulation, where the northern channel exhibits poor connectivity with the rest of the system, whereas the southern channel and Huon are relatively well connected throughout. Flushing analysis and particle tracking show the flushing time for the whole region to be ~20–26 days.