Effects of Beach Nourishment Design Parameters on Typhoon-Induced Morphological Evolution Under Typhoon Conditions

Island beaches are key natural barriers against typhoons. Artificial nourishment is the main restoration method, yet how its design parameters affect typhoon-driven erosion–deposition remains unclear. Focusing on Xiaoshizui Beach on Wailingding Island outside the Pearl River Estuary, this study systematically examines how these parameters control beach morphological evolution under typhoon forcing. A MIKE 21 Hydrodynamics-wave spectrum-sediment transport (HD-SW-ST) coupled model was applied and validated against measured tidal levels, waves, and beach profile data during Typhoon Ragasa. Under consistent typhoon forcing conditions, different nourishment sediment grain sizes, beach-face slopes, berm heights, and berm widths were set to analyze wave propagation, sediment transport, and beach morphological responses. The results show that the effects of different design parameters on waves are mainly in the surf zone. These parameters control sediment activation and redistribution by altering wave breaking location, surf zone width, and energy dissipation range, producing distinct erosion–accretion responses. Coarser sediments produce steeper post-storm profiles, which shift nearshore breaking shoreward and intensify local transport and morphological activity, yet stronger retention capacity reduces net profile erosion. A gentler slope expands the surf zone and dissipation range, shifting erosion–accretion seaward and reducing net sediment loss. A higher berm suppresses overtopping, limiting backshore erosion while concentrating energy and sediment exchange at the crest. A wider berm extends the dissipation path, enhances redeposition within the active profile, and reduces net erosion. The findings clarify how nourishment design parameters govern artificial-beach morphological evolution under typhoons, providing theoretical support for optimized restoration design and disaster prevention.