Headland sediment transport is dynamic and complex, but understanding the transport mechanisms is necessary for effective long-term management of downdrift beach compartments. In this study, we have develop a coastal process model using TUFLOWFV, that is used to calibrate an approximation tool for headland bypassing at the study site. The approximation tool is shown to reproduce sediment transport rates at the headland apexes accurately and efficiently. We have explored the headland sediment transport mechanism, the influence of wave height and direction, and the sensitivity in regional climate conditions. Headland sediment transport is shown to occur as ‘trickle’ bypassing under modal wave conditions or ‘sand slug’ migration under storm wave conditions that travel in either a headland-attached and a cross-embayment pathway. Bypassing during storm wave conditions produces 50% to 60% of total bypassing volume, despite only accounting for 6% of the recorded days. The results indicate that headland transport is sensitive to changes in wave direction and wave height, with the existing mean wave direction balancing sediment transport on the east and north faces of the headland. Seasonality is the most significant climatic control on headland transport, while ENSO phase is only significant for the headland apexes that are exposed to south-east wave conditions. The potential for anticlockwise rotation of the wave climate in future is explored, with greater erosion of the northern beaches of the headland likely due to a reduced supply of sediment around the eastern point of the headland and greater erosive wave power on the north side.

Changes in wave climate will impact coastal zones through changes in sediment supply via longshore sediment transport (LST). Estimating these changes is challenging as biases and uncertainty in wave climate projections lead to uncertainty in LST projections. This paper compared wave climate and LST projections derived from two iterations of the Coupled Model Intercomparison Project (CMIP), as well as the implications of using wave climate bias correction in these projections, for the end of the 21st century under high emission scenarios. LST was simulated in a process-based model calibrated against data from an artificial sand bypassing system. Bias correction improved the representation of the wave climate, including extremes, and reduced the uncertainty between CMIP iterations and climate models. While bias correction did not significantly change the projected mean LST, it reduced the spread of model ensembles by 20% and 10% for CMIP5 and CMIP6, respectively. Both CMIP5 and CMIP6 suggest a reduction of LST in the future for the study area. However, CMIP6-derived projections show: 1) 50% less uncertainty in wave forcing conditions; 2) greater consistency in LST projections between ensemble members; and 3) double the reduction in LST. This reduction is attributed to changes in the balance between modal and extreme waves and changes in wave direction. This contribution highlights the value of a bias-corrected model ensemble, and the improvement in CMIP iterations, in providing robust projections of future wave climate change and its impacts on regional coastal processes.

Headland Bypassing is mainly a wave-driven coastal process that interconnects sediment compartments and allows the continuity of the longshore sediment transport. Waves, in turn, are subject to atmospheric patterns and climate drivers. Hence, this study focuses on identifying the atmospheric systems and associated wave conditions that have triggered bypassing events in Fingal Head (New South Wales, Australia) over the last 33 years. For this, clustering techniques were used to identify 225 weather types that represent the daily atmospheric variability over the Coral-Tasman Seas. Four recent storm events that triggered headland bypassing were numerically simulated including waves, currents, sediment transport, and morphological evolution in order to identify the relevant weather types for the development of the sand pulse. Results revealed that strong low-pressure systems (e.g., Tropical Cyclones and East Coast Lows) occurring off the Eastern Australian coast around 30°S are the dominant patterns triggering bypassing events in the study area. The headland bypassing mechanism was observed to vary between large sandbar systems and sediment leaking around the headland according to slight changes in the sea states generated by these storm events. Overall, atmospheric patterns showed control over when and how the bypassing pulse occurs, whereas sediment availability is the main factor influencing long-term cycles of bypassing that are subject to the variability of El Niño – Southern Oscillation and Pacific Decadal Oscillation. Altogether, this study emphasized the intricacy between the multiple factors controlling headland bypassing events, which has direct implications on the potential for predicting the occurrence of this local coastal process.