Numerical modelling of the physical response of coral reef Sandy island to sea level rise by considering seasonal patterns

Abstract

Sea level rise (SLR) can increase the bathymetry of coral reef platforms, thereby increasing the potential for island erosion and flooding to damage coastal buildings. However, SLR is a threat to the coastal buildings of islands not only in this way, but also in the destruction of coastal buildings due to island morphology changes caused by SLR. Based on sediment, offshore wave, and tidal data from Yongxing Island (sandy island), Xuande Atoll, South China Sea, a process-based morphodynamic model, XBeach-G, was used to predict the morphological evolution of coral reef sandy island under future SLR based on the RCP8.5 scenario. As waves and tides in the South China Sea are distinctly seasonal, the influence of seasonal patterns was considered in the model. Sensitivity analysis of the effects of water level on the reef, offshore significant wave height, sediment porosity and sediment size on the morphological evolution of the islands was conducted. Numerical simulations indicate that under SLR and extreme wave action, the sandy islands eventually retreat landward and the foreshore height increases and the slope steepens and as the SLR rate increases, the island retreats more towards land and the foreshore height rise decreases. While this natural adjustment of the coral reef island increases the island's potential to offset future flood events and support future physical persistence, there is a negative impact on the safety of coastal buildings. This paper highlights the need to develop reasonable conservation policies based on the island's specific environment and conditions. Excessive use of artificial shorelines to protect islands can damage their natural adjustment to resist disasters such as flooding, while artificial defenses are necessary in the case of threats to coastal buildings or the disappearance of certain islands.