Influence of wave direction sequencing and regional climate drivers on sediment headland bypassing

Abstract

Headland sediment bypassing is a critical component in understanding the sediment budgets of headland protected beaches, yet the bypassing is often sporadic and complex. In this study we have completed shoreline change analysis from aerial imagery spanning >60 years for all the beaches within the Noosa Headland (Queensland, Australia) region to better understand how sediment moves between compartments. Shoreline change of each compartment was evaluated in conjunction with local wave data and regional climate indices. Headland bypassing may only occur following a specific sequence of wave events, with a moderate (Hs > 2.5 m) downdrift oblique wave event being followed by a moderate shore-normal/updrift oblique wave event. Long term beach accretion of 0.56 m/year (± 0.17), primarily due to intervention, was observed at headland adjacent beaches, with negligible change for the headland embayed beaches. Volume calculations from the headland sheltered Noosa Main Beach indicate a natural sediment budget of negative 8900 m3/year over an 11-year span, with sand backpassing used to recover these losses. The change to sediment bypassing as a result in forecasted global warming induced wave direction changes is discussed, with the expectation that fewer bypassing events, with more erosive events, will occur in future. This research has implications for the management of beach compartments adjacent to large headlands.