Persistence of storm-induced morphology on a modal low-energy beach: A case study from NW-Iberian Peninsula

The morphology of low-energy beaches is inherited from high-energy events showing a non equilibrium state with the prevailing conditions. An example of a sheltered, low-energy beach (Rodas Beach, NW-Iberian Peninsula) is examined in this paper. The evolution of six beach profiles was analysed during three years in order to investigate the response of this beach under fair-weather and storm conditions. The beach presented significant morphological differences alongshore due to its geographical location with respect to the wave approach. These differences determined the sediment transfer pattern (longshore or cross-shore sediment transport) from the emerged beach towards the adjacent inner shoreface zone. Significant morphological changes at each profile seem to be related to the incidence of sea waves along the beach superimposed on persistent swell during winter. Morphological changes were recorded under high-energy storms, during winter, whereas the recovery to prestorm conditions occurred under prevailing fair weather conditions, during summer. The traditional beach classification parameter Relative Tidal Range (RTR), which takes into account the effect of the tide range, was found unsuitable to properly classify such a mesotidal low-energy beach. Therefore, a new parameter, the Relative Tidal Range Maximum (RTRmax) was introduced, which is a modification of the commonly used RTR. RTRmax uses the highest wave breaking height, observed during high-energy storm conditions, instead of the modal wave breaking height. By using this parameter, the studied beach could be properly classified into the traditional beach classification models taking into account the tide range. Since low-energy beaches generally show a morphology that is inherited from higher energy conditions than the prevailing conditions, it is expected that the RTRmax will be applicable for the classification of other low-energy sheltered beaches.