Wave effects on sediment dynamics in a macro-tidal estuary: Darwin Harbour, Australia during the monsoon season

Abstract

Darwin Harbour is a flood-dominated estuary with a large tidal range. Tides are considered to be the dominant factor influencing sediment resuspension and transport in the harbour during the dry season. However, the sediment dynamics during the wet or monsoon season have been little explored using either field data or numerical hydrodynamic modelling. This study focused on understanding the sediment dynamics during the monsoon and the dominant factors controlling the suspended-sediment concentration (SSC) in Darwin Harbour. Using the Finite Volume Coastal Ocean Model (FVCOM) coupled with the Simulating Waves Nearshore (SWAN) model, we investigated the effect of waves on the SSC during a particular wet season. SSC distributions modelled with tidal currents and wave in the outer harbour were significantly different to those only with tidal currents. Due to the narrow harbour entrance, strong monsoonal waves in the outer harbour barely propagated into the inner harbour; the SSC in the inner harbour was therefore almost hardly affected by waves. Numerical results show that the criterion of neglecting wave forcing in a macro-tidal environment when the tidal range is larger than 3 m is inaccurate, and that the effects of waves on the SSC can still be important in waters with a large tidal range such as Darwin Harbour.