Placement Stability Study

RPS undertook a study to assess potential sediment mobilisation for the proposed maintenance dredging and disposal activities in Mermaid Sound.

The study examined the degree of sediment mobilisation and related effects from several placement strategies at two potential spoil grounds under cyclonic conditions. Using expected sediment distribution data provided by Rio Tinto Iron Ore and Woodside Energy as an input, 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 was 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 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.