Assessing the impacts of shoreline hardening on beach response to hurricanes: Saint-Barthélemy, Lesser Antilles

Abstract Based on an approach coupling geomatics (i.e. satellite imagery analysis) and fieldwork, this paper provides an in-depth analysis of the impacts of September 2017 hurricanes on the beaches of Saint-Barthelemy Island. First, it highlights the key role of low-frequency high-intensity events in driving high rates of changes on coastal systems. Importantly, all the studied beaches underwent shoreline retreat, detected along 47.73–100.00% of transects (mean shoreline movement ranging from −2.76 to −18.39 m). The stability line retreat was lower on highly-modified beaches because of the presence of longitudinal structures compared to natural beaches that mostly suffered severe vegetation destruction. Second, the methodology proposed here allowed attributing changes to specific anthropogenic drivers. Both natural (i.e. the hurricane's path and hurricane waves' direction) and anthropogenic (especially shoreline hardening and vegetation modification) drivers explain the high variability observed in the nature, intensity and spatial distribution of hurricanes' impacts on beaches. Based on the quantitative assessment of impacts, this paper advocates for the restoration of a 50 m-wide buffering area in front of human constructions, the exposure of which has considerably increased due to wave impact, which implies to establish new setback guidelines. So as to better assist decision-makers in disaster risk reduction on small islands, we therefore recommend the systematic inclusion, i.e. documentation and integration into GIS datasets, of human disturbances, as the latter highly influence shoreline and beach response. We propose a replicable methodology to address this challenge.