Surfside Beach, located in the inner bay of Batemans Bay, New South Wales, Australia, has experienced persistent shoreline erosion in the recent decade. To mitigate this problem, Transport for NSW initiated a dredging and dumping operation between 17 October and 1 November 2025, in which sediment accumulated near the Clyde River entrance was dredged and dumped offshore of Surfside Beach with the intention that sediment transport would redistribute the dredged materials landward and enhance shoreline stability. However, the hydrodynamic effectiveness of this intervention and its impact on local suspended sediment dynamics remain uncertain. In this study, we deployed a monitoring system equipped with nephelometer, wave gauges, and Acoustic Doppler Current Profilers near the dumping area to assess the short-term response of the inner bay. We further applied a coupled FVCOM-SWAN-Sediment model to investigate the spatial evolution of wave, current, and SSC fields across the broader Batemans Bay system.
The results show that variations in significant wave height can substantially modify the circulation in the outer bay of this semi-enclosed embayment. The outer-bay circulation then interacts with the pre-existing inner-bay circulation, altering the inner-bay flow structure during the dumping period. In particular, this interaction can shift the more common clockwise circulation pattern to an anticlockwise mode in the inner bay, leading to marked changes in local current speed and triggering anomalous SSC extremes near the dumping region. These findings demonstrate that the fate of dredged sand in Batemans Bay is strongly controlled by wave-driven circulation connecting the outer and inner bay. This highlights the importance of integrating field observations with wave-current-sediment coupled modelling when evaluating the effectiveness of coastal nourishment strategies.