The role of different approach directions of storm waves in the morphodynamics of sandy beaches (NW Portugal)

The impact of storm waves on the coastal zone can cause coastline retreat and, in extreme cases, the destruction of coastal properties and engineering structures within short periods of time. Understanding the coastal response to storms is essential for making effective management decisions. The main goal of the present work is to assess the morphodynamic response of sandy beaches to storm waves along a 50 km coastal stretch on the NW coast of Portugal. Eleven storm wave events were identified and characterized based on their weighted-mean storm direction, energy, duration and peak period. Fifteen pre- and post-storm dune-beach topographic profiles were analysed through several morphodynamic indicators, including shoreline position, sediment volume change and total water level. Results show that gains or losses in subaerial beach volume depend on the antecedent morphodynamic state, storm power and mean wave direction, which controls the intensity of longshore sediment transport. Storms also affected the dune system, with the collision-impact regime occurring in more than 50% of observed cases. Furthermore, the dune erosion and shoreline retreat were greater in the more anthropized northern sector than in the southern one, displaying beach scarps, which do not recover during low-energy wave conditions.