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.

Nourishment grain size is a key parameter in beach nourishment projects, directly determining beach stability under extreme hydrodynamic environments. Taking Xiaoshizui Beach on Wailingding Island as the study area, this paper establishes a coupled typhoon storm surge–wave–sediment model based on the MIKE 21 HD-SW-ST coupled model. This model has been systematically verified through the measured data of tide levels, waves, and beach profiles, and the verification results are satisfactory. Four scenarios with nourishment grain sizes of 0.4, 0.6, 0.8, and 1.0 mm were established to quantify the morphological evolution patterns of the beach under strong typhoons. The results indicate that during the typhoon, the beach exhibits a cross-shore sediment transport pattern characterized by erosion of the backshore dune, accretion of the upper-middle foreshore, and erosion of the lower foreshore. The influence of nourishment grain size shows significant spatial variability: increasing grain size enhances the erosion resistance of the backshore and berm, reducing the erosion extent; however, within the breaker zone, coarse sand tends to form a steep profile, intensifying wave breaking, which increases the scour depth in this region. This study elucidates the regulatory mechanism of grain size under extreme conditions, providing scientific reference for grain size selection in beach restoration projects.