Non-uniform cumulative responses of beach sedimentary geomorphology to consecutive storms around a meso-macro tidal island

The response of beach sedimentary geomorphology to consecutive storms is a complex process, especially for beaches surrounding an island. Variations in coastal sedimentary landforms, dynamic environments and levels of development and utilization lead to non-uniformity in storm response, which may become more pronounced when influenced by continuous storms. This study focuses on the beaches around Weizhou Island to investigate this non-uniformity. Based on the topographic, surface sediment and hydrodynamic data collected on site before and after the consecutive typhoons (Typhoons Lionrock and Kompasu), the study examines the characteristics of beach geomorphology and surface sediment. The results show significant differences in the geomorphological responses between the four zones along the island. On the plane, the deposition degree of Zone I beach gradually weakened from west to east, and most areas of Zone III beach appeared in an alternating state of erosion and deposition. The beaches of Zone II and Zone IV showed the characteristics of dramatic changes in the northern and central beaches and relatively stable in the southern beaches. On the profile, the beach deformation area mainly occurs in the middle and upper parts of foreshore and berm. The response intensity of beaches in zone I is the weakest, the response intensity of beaches in zone III is the most intense, and the response intensity of beaches in zone II and zone IV is relatively close. However, the performance of beach sediments in different regions before and after continuous typhoons is less different. Except that the beach sediments in Zone I were mainly refined, the beach sediments in other zones of Weizhou Island were relatively coarse, and the sediments in the middle and upper parts of the foreshore were the coarsest, with the sorting being the worst. The different combinations of incident waves and storm surges during the typhoons are the primary factors that lead to various geomorphological responses in different zones. The antecedent beach status, distributions of rock and coral reefs, and anthropogenic activities further exacerbate these differences. This work can provide reference for island beach protection and management.