Mechanisms of Headland Bypassing During Modal and Storm Wave Conditions.

The transport of sediment around headlands is a complex and dynamic process. Gaining a comprehensive understanding of the underlying mechanisms is crucial for effective long-term management of downdrift beach compartments. This study presents research investigating the mechanisms behind headland bypassing using remote sensing, coastal process modelling (TUFLOW FV) and a specifically developed Headland Bypassing Approximation Tool at Noosa Headland, Australia. The study explored the migration of sand around the headland under varying wave conditions and identified the key wave and climatic conditions that impact headland sediment bypassing. The research suggests that headland bypassing occurs through two mechanisms: "trickle" bypassing under modal wave conditions, and through the migration of large sand slugs during storm conditions. The results indicate that storm waves account for 60% to 70% of total bypassing, despite representing only 6% of the recorded days. Both mechanisms were shown to be sensitive to wave direction, which is presently finely balanced between southeast wave conditions and east to northeast wave conditions. Results reveal that sand supply to protected down-drift beaches can be insufficient during periods where storm wave conditions did not occur from the correct sequence of wave directions. Bypassing was significantly modulated by seasonality, however, no significant relationship between ENSO phase and bypassing volumes was discovered, with successful bypassing during storm conditions dependent on the specific characteristics of each individual or sequence of storms that generated waves at the target site. A sensitivity assessment illuminated that a shift in mean wave direction of between 10 and 15 degrees, as is forecasted by several global climate models, would result in insufficient headland bypassing and sand starvation of the protected down-drift beaches. Overall, the research provides valuable insights into the mechanisms behind headland bypassing and highlights and has implications for coastal management of down-drift headland protected beaches. [ABSTRACT FROM AUTHOR]