Extreme storm events drive beach connectivity through headland bypassing

Headland bypassing is a mainly wave-driven coastal process that interconnects sediment compartments and allows the continuity of longshore sediment transport. In turn, waves are subject to the variability of atmospheric patterns and climate drivers. This study focuses on identifying the atmospheric systems and associated hydrodynamic conditions that have triggered bypassing pulses in the study area, Fingal Head (New South Wales, Australia), over the last 33 years. For this, clustering techniques were applied 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 modeled including nearshore waves, currents, sediment transport and morphological changes around the headland. For each of those storms, it was identified the relevant weather type driving the development of the sand pulse and the characteristics of the bypassing mechanisms triggered. Results revealed that strong low-pressure systems (e.g., Tropical Cyclones and East Coast Lows) occurring off the Eastern Australian coast around 25-35°S are the dominant atmospheric patterns triggering bypassing events in the study area. The headland bypassing mechanism was observed to vary between a large sandbar system and sediment leaking around the headland according to changes in the sea states generated by the different storm tracks. Overall, atmospheric patterns showed control over when and how the bypassing pulse occurs, whereas sediment availability is the main factor driving long-term cycles of bypassing under the influence of large-scale climate drivers. Altogether, this study emphasized the intricacy between the multiple factors controlling headland bypassing, which has direct implications for predicting the future coastal interconnectivity and the planning of management actions.