HOW BEACH STATE INFLUENCES WAVE RUNUP ON A PERCHED BEACH IN SOUTHWESTERN AUSTRALIA

Approximately 20 to 30 percent of the world’s coastlines are fronted by shallowly buried or outcropping shore platforms overlain by perched beaches (Kirk, 1977; Marshall and Stephenson, 2011; Trenhaile, 2002). Seasonal erosion of perched sediment can shift the beach state from ‘accreted’ to ‘exposed’ (Gallop et al., 2011), and the effect this has on wave-induced flood risk (known as wave runup) is unknown. As sea levels rise and storm severity increases, understanding how beach state influences wave runup is crucial for minimising coastal hazard risk and managing perched beach coastlines. In this work, idealised numerical modelling and field observations along a perched beach in southwestern Australia were used to quantify the influence of beach state on wave runup, setup, and swash processes.