Geometric-spatial parameterization of storm sandbars in post-storm beach profile self-recovery: Modulated by tide-wave-sandbar interplay

One of the most prominent modifications to beaches by storms is the formation of nearshore sandbars, which complicates processes in the surf and swash zones. However, the migration processes of these sandbars and their influence on the recovery of post-storm beaches remain unclear, especially under low-wave-energy conditions. This study, based on field campaign data, revealed that a storm-deposited sandbar formed after Typhoon Kompasu provided an essential sediment source for the eroded backshore, thereby boosting the self-recovery of the storm-altered profile. To further explore the hydrodynamic and morphological controls on the migration and dispersion of the storm-deposited sandbar, a state-of-the-art numerical model for coastal processes, XBeach, was employed. Simulation results are consistent with observational data, demonstrating that even in a micro-tidal regime, tides play a vital role in post-storm morphological evolution: by regulating wave asymmetry and wave breaking, tides prolong the duration of processes in the swash and surf zones. Specifically, rising tides facilitate sandbar overwash, while ebbing tides enhance sediment accretion on both the backshore and foreshore. In micro- to meso‑tidal environments, a berm can be more easily developed using sediment from storm-induced sandbars, whereas such berms rarely form in macro-tidal environments. Moreover, the initial configuration of sandbars controls the geometric features of equilibrium profiles in micro- to meso‑tidal environments, but this influence does not appear in macro-tidal settings. Notably, only when sandbars have a moderate width-to-height ratio (γsb≈20) and are positioned 0.1–0.3 times the incident wavelength from the dune toe can they effectively replenish the eroded backshore while preventing dune erosion. The findings of this study highlight the importance of incorporating tidal fluctuations into experimental setups and provide a scientific basis for formulating artificial intervention strategies for beach protection.