LAUSR

Using multi-date satellite imagery and field observations, this paper assesses the inferred impacts of September 2017 cyclones on the beaches of Saint-Martin Island. Twenty-two beaches out of 30 predominantly exhibited shoreline retreat, with the highest retreat value (−166.45 m) recorded on the north-eastern coast. While erosion predominated on beaches and at the sand dune front, inner areas generally exhibited accretion, with sand sheets (up to 135 m from the pre-cyclone vegetation line) indicating landward sediment transfer. Natural back-reef beaches exhibited the formation of new beach ridges, marked (up to 2 m) upward growth and alongshore beach extension. The high spatial variability of inferred impacts is attributed to the cyclone's track, coast exposure, beach configuration and, importantly, human-driven environmental change. Whereas vegetation removal exacerbated marine inundation and inhibited the vertical accretion of beaches, shoreline hardening aggravated wave-induced sediment loss while also inhibiting sediment deposition. Four beach response modes are distinguished. Based on findings, we identified three major areas of action for risk reduction and adaptation to climate change. Depending on beach response and site specificities, relocation and the determination of set-back lines, coastal buffer restoration, or engineered structures' upgrading should be prioritized.