Morphological response and recovery of a headland-bay beach under sequential typhoon impacts

Climate change is increasing the frequency and severity of coastal hazards, with rising sea levels and intensifying typhoons accelerating coastal erosion worldwide. Although headland-bay beaches are widely regarded as topographically protected, they are not immune to substantial erosion during intense typhoons. However, their morphodynamic responses to extreme events—particularly sequential typhoon impacts—remain poorly quantified and mechanistically understood, largely due to the lack of high-resolution monitoring. Here we examine Dasha Beach in Zhejiang Province, China, using high-resolution UAV-derived topography to quantify morphological changes associated with two sequential typhoons, Hinnamnor and Muifa, in September 2022. Hinnamnor generated 9827 m³ of net erosion concentrated in the central beach, and Muifa caused an additional 6370 m³ of erosion, completely removing the remaining beach berm. Post-typhoon recovery deposited 7352 m³ of sediment, predominately reconstructing the northern beach berm, and restoring volumes to pre-Muifa but not pre-Hinnamnor levels. Hydrodynamic analyses reveal pronounced cross-bay gradients in wave energy, with stronger forcing in the northern sector producing enhanced erosion during the typhoons and greater accretion during recovery. During typhoons, waves primarily drove cross-shore sediment transport. In the recovery phase dominated by obliquely incident waves, however, waves facilitated both cross-shore and longshore sediment transport. Swash processes (uprush and backwash) dominated sediment transport, while water-level variations controlled its spatial extent. Specifically, Muifa-induced high water levels combined with energetic waves led to severe berm erosion. The stable berm sediments, derived from well-sorted backshore and dune areas, exhibited minimal grain-size change under typhoon impact. The coarser sediments indicate that the depositional material during the recovery phase originated from the submarine seabed. Although Dasha Beach currently exhibits substantial short-term resilience, increasingly frequent and intense typhoons will pose escalating challenges. Therefore, the assessment of the need for human intervention on the beach and the design of appropriate beach nourishment schemes are among the key focuses for future research. Overall, these findings refine the process-based understanding of storm-driven morphodynamics, and provide a basis for safeguarding headland-bay beach stability.