The effects of storm clustering on beach profile variability

Impacts of storms in reshaping coastlines are well known. Also, the far greater impact of clusters of storms, where storms occur at close succession, has been noted in a number of previous studies. In this paper, we analyse and discuss the storm wave climate and the beach profile response to clusters of storms at Narrabeen Beach, New South Wales, Australia. Narrabeen Beach is subjected to frequent storms all year round and the beach undergoes substantial variability as a result. The impact of storm clusters with closely spaced individual storms reaching the beach is investigated by combining historic measurements of beach profile surveys and numerical modelling of storm induced beach change. Our analysis of storm power index of storm clusters and its correlation with the change in beach width reveals that the strengths of single storms in a storm cluster alone are not the reason for beach change, but time interval between successive storms and the post-storm recovery speed of the beach concerned also play important roles. We have quantified and compared beach erosion return levels resulting from single storms and storm clusters. It was found that beach erosion volumes resulting from storm clusters with two or more storms resemble potential beach erosion volumes induced by single storms of far higher return periods.