Dredge Spoil Placement Stability Study, Mermaid Sound

RPS assessed the potential sediment mobilisation for the proposed maintenance dredging and disposal activities in Mermaid Sound, Western Australia.

The study examined the degree of sediment mobilisation and related effects from several placement strategies at two potential spoil grounds under cyclonic conditions. Inputting expected sediment distribution data provided by Rio Tinto Iron Ore and Woodside Energy, an integrated sediment transport model – including sub-models for the hydrodynamics, waves and sediment fields – was developed using the Delft3D model suite. Wave and wind data were derived from calibrated models of three tropical cyclone events, and the hydrodynamic predictions were validated using measured data provided by Woodside.

The results showed that sediment mobility within the spoil grounds and beyond was likely to be low under ambient conditions and would quickly return to low levels following a cyclone event, and that use of a particular spoil ground and placement strategy was likely to minimise sediment mass loss.