Study on the morphodynamic response of reef flat with moveable bed to monochromatic waves

Abstract

While carbonate sediment transport processes over coral reefs have been extensively investigated in the past decade，very few studies have focused on the morphodynamic response of sandy reef flats to wave action. In this study, a set of innovative wave-flume laboratory experiments was conducted for the first time to investigate the evolution of reef flat based on a barrier reef profile. Various monochromatic wave conditions (incident wave height, incident wave period and initial reef-flat water level) and sediment layer thicknesses were tested. A sand layer was paved on the reef flat to simulate a moveable bed and the reef surface roughness was replicated using an array of cylinders. Subsequently, a phase-resolving non-hydrostatic model (XBeach-NH) was adopted to simulate both the hydrodynamic and morphodynamic processes in the reef environment. A vegetation module was incorporated into Xbeach-NH to represent the rough reef surface. The adopted model was validated against the laboratory dataset for the first time as reported in this study. It was then used to examine the impacts of varying fore-reef slopes, sediment grain sizes and reef surface roughness on the morphodynamic response of sandy reef flats to monochromatic wave action. Model outputs suggested that projected sea-level rise, reduced reef surface roughness and increased storminess due to climate change have profound impacts on the morphodynamic processes on the reef flat thus may eventually contribute the geomorphological sustainability of reef islands.