Wave processes on coral reef flats during storm and modal conditions: Implications for coral reef sediment dynamics

The transformation of swell waves from deep water across reef flats is the primary process regulating energy regimes in coral reef systems. The geomorphic evolution of a coral reef is dependent on this process, yet there have been comparatively few studies focusing on wave processes on coral reefs when compared to siliciclastic settings. Of these studies none have recorded storm wave propagation across reef flats. This is a significant oversight since major geomorphic change occurs during storm events with some studies considering coral reefs as event based systems that are primarily driven by high intensity stochastic events such as cyclones or storms. This study focuses on the transformation of swell waves generated by Tropical Cyclone Dylan (storm conditions, January 2014) across the windward reef flats in comparison to data collected during modal fair weather conditions (modal conditions). As such the data sets used in this study are novel due to the difficulty of accessing remote reef sites during storm events. Wave height on the reef flat was similar during modal and storm conditions with wave height primarily controlled by water depth. However, during storm conditions greater wave energy - particularly long period wave energy - and wave generated current velocity was observed despite the regulatory effects of water depth over the reef flat. The potential for sediment and coral rubble transport was much greater during storm conditions with limited sediment transport during modal conditions. This suggests that high frequency storm events are crucial processes driving sediment dynamics in coral reef systems.