The basics for a permanent observatory of shoreline evolution in tropical environments; lessons from back-reef beaches in La Reunion Island

Under natural and anthropogenic pressure, the coastal regions are evolving rapidly (population growth, erosion, modification of services, etc.), and some of these changes increase their vulnerability. Monitoring the evolution of the coastal regions has thus become essential to understand how they respond to the various pressures and to define how their resilience could be increased. Among other outcomes, such monitoring should provide continuous, high-resolution data on the spatial and temporal evolution of the coastal areas, especially the shoreline zone. One appropriate way to acquire long, continuous, time series of data is to set up a permanent observatory in the zone to be monitored. This paper aims to provide recommendations and a methodological framework to set up a “shoreline observatory” dedicated to monitor some of the specific features and behaviours of tropical littorals, more particularly back-reef beaches and their geomorphic changes. After a brief review of carbonate sandy beach morphodynamics, we present survey solutions (TLS, UAV photogrammetry) to monitor at high resolution and repeatedly the geomorphic changes of the coastal area, both on land and in shallow water. The example case is that of the back-reef beaches in La Reunion Island.