Dynamics of mud banks and sandy urban beaches in French Guiana, South America

Abstract Beach rotation is a widely described process characterized by periodic alternations in sediment transport involving erosion at one end of the beach and accretion other. The 1500-km-long coast Guianas, South America, unique system dominated large migrating mud banks, muddy, mangrove-rich shorelines, rare sandy beaches. Interactions between waves beaches on this are affected banks which separated ‘inter-bank’ areas. Kourou situated near site European Space Agency’s satellite-launching pad French Guiana. has maintained multi-decadal stability, but its interaction with led to phases severe erosion. To understand these changes, constitute risk for urban front Kourou, we combined mesoscale temporal (1950–2017) analysis shoreline fluctuations short-term approach based photogrammetric monitoring change conducted 2017–2018 bathymetric surveys nearshore zone. results show that evolves context ‘rotation’, recovery. Rotation during inter-bank ‘normal’ sand northwest generated prevailing NE waves, mud-bank drift reversal southeast refraction leading bank. Due aperiodic nature bank phases, involved may prevail over variable periods time (several years decades). from east west first protect southeastern sector beach, blocking northwestward longshore transport, generating, through differential refraction, southeastward counter-drift. These processes irregular timescale they entail have not been compatible recent urbanization sector, resulting sense threat beachfront property. Insight gained an understanding timescales should contribute better beach-front management.