Influence of storm sequencing on breaker bar and shoreline evolution in large-scale experiments

Abstract

New large-scale experiments on the influence of storm sequencing on beach profile evolution are presented. The experiments comprised three sequences that commenced from the same initial beach profile. Each sequence consisted of two storms of different energy, with each storm followed by a recovery phase. A specific focus of the experiments was the influence of storm chronology as well as the influence of the recovery wave energy and duration on beach evolution. The breaker bar and the shoreline are studied as indicators for the beach response. Both evolve towards an equilibrium location for each wave condition where the breaker bar reaches its equilibrium much faster than the shoreline. Overall, no enhanced beach erosion due to storm sequencing is observed. Despite a similar cumulative wave power of the three sequences, the final beach configuration of each sequence seems to be determined by the last wave condition instead of previous storms. However, storm sequencing is important when the beach profile has not yet fully recovered before being disrupted by the subsequent storm. In this case, the second storm does not necessarily cause further erosion but can result in onshore sediment transport and hence, form part of the recovery. The bulk onshore sediment transport as well as the shoreline recovery rate vary depending on the wave condition and the profile disequilibrium and show a maximum value for a recovery condition with an intermediate wave energy. The very low energy condition that was performed for a long duration (24 hours) generated a near-stationary beach profile with typical features of a reflective beach.