Optimising sediment resuspension processes for improved modelling of solid waste in coastal aquaculture

Modelling sediment resuspension in shallow and dynamic coastal marine environments requires a quantification of the combined shear stresses from waves and currents acting on the seabed. Predicting resuspension is essential when evaluating aquaculture-environment interactions from open-cage salmon pens. In this study, we used observations of waves, water currents and sediment properties from two coastal marine sites in southeast Tasmania, Australia, to assess the relative importance of currents and waves in driving resuspension based on two wave-current bottom shear stress models: a conventional linear superposition approach and an alternative formulation incorporating nonlinear wave-current interactions. Both models showed that wave-induced shear stress (${\tau }_w$) was the dominant driver of resuspension and the current-induced shear stress (${\tau }_c$) was comparatively unimportant. We then applied these shear stress estimates to parameterise a 1D sediment model Globosed and validated its predictions against in situ turbidity measurements. The results demonstrate that both linear and non-linear simulations captured resuspension trends observed in the field. The linear model, however, exhibited limited sensitivity to low suspended solid periods, whereas Globosed showed improved accuracy in silt-dominated environments. These results suggest that wave-induced shear stress should be considered in sediment transport models for wave-dominated coastal aquaculture environments like southeast Tasmania.