Assessing the impacts of and resilience to Tropical Cyclone Bejisa, Reunion Island (Indian Ocean)

This paper highlights the high variability of the nature and severity of the impacts of Tropical Cyclone Bejisa (January 2014, category 3) along the 20-km-long beach-dune systems of the western coast of Reunion Island. Erosional impacts were reported on 17 out of 26 topographic transects, while nine transects exhibited accretion. Sediment loss and gain reached maximum average values of 1.23 and 0.36 m(3)/m of transect, respectively. Sediment deposition occurred on upper beaches and foredunes, which gained up to 1 m in thickness. After 1 year, beach resilience proved to be medium (from 0.4 to 0.8 m(3)/m) to high (> 0.8 m(3)/m) on 40 % of transects, but some transects exhibited permanent dune loss. Marine inundation reached a maximum distance of 70.8 m from the vegetation line and a maximum elevation of 6.9 m above sea level. The indigenous vegetation showed high resistance to the impacts of the cyclone and rapid regeneration, whereas introduced species were lastingly damaged. The cyclonic waves damaged 18 seawalls protecting either public infrastructures or private properties, half of which had been reconstructed 3 months later. Severe damage was also caused to a marina built in the downstream section of a river. Importantly, this study emphasises the vicious-cycle effects caused by "coastal compression" that exacerbates the devastating impacts of cyclonic waves on beaches, vegetation and protection structures, encouraging coastal residents to strengthen engineered structures. In accretional areas, the reworking of sediment deposits by residents reduced the long-term benefits of sediment deposition. Such human-induced processes increase asset exposure and vulnerability.