Modeling seasonal hydrodynamic regimes and their role in shaping mega cusps: insights from My Khe Beach, Vietnam

This study examines seasonal hydrodynamics shaping coastal morphology at My Khe Beach, Vietnam, with emphasis on mega cusp formation and evolution. A calibrated Delft3D model simulated wave fields, nearshore circulation, and processes using satellite, AUV, bathymetric, tidal, wave, and current data from field campaigns conducted in January and May 2024. The simulations reproduce the seasonal variability in coastal dynamics with reasonable accuracy. During the northeast monsoon, east-northeast (ENE) and northeast (NE) waves with significant heights (Hs) of 1.5–2.0 m generated strong nearshore currents that intensified beach erosion and promoted mega cusp formation. In contrast, during the southwest monsoon, ESE and SE waves with Hs around 1.0 m and oblique incidence angles reduced nearshore flow velocities (V < 0.2 m/s), mitigating erosional processes and contributing to beach profile stabilization. Results emphasize seasonal wave forcing as a key driver of coastal morphology and present a robust modeling framework to support management in monsoon-influenced regions.