Coastline dynamics in the extreme south of Brazil and their socio-environmental impacts

Abstract

A coastal inflection of ∼45 km in the extreme south of Brazil demonstrates differences in coastline behavior with areas of deposition towards north and areas of severe erosion towards south, threatening coastal occupation. These areas are believed to be controlled by the sand wave behavior of the coastline with adjacent erosion and progradation areas that have relevant alongshore sediment transport imposed by S quadrant waves. In this study, we quantified the rates of change of coastline and described the erosion and deposition controls behind it, using ultra-high-resolution orbital images and UAV (unmanned aerial vehicle) orthomosaics obtained between 2005 and 2020 for three urbanized beach sectors within the area, i.e., the São Simão, Mostardense, and Lighthouse Beaches. The rates of change of coastline were calculated using the change polygon method. The results indicated total recession values > 40 m at the Mostardense and Lighthouse beaches corresponding to a rate of ∼3 m/y. Such values characterized the coastal erosive hotspots that have not been previously identified in the area. Future coastlines were projected from the estimated annual variation rates. Buildings previously destroyed or threatened by marine/wind processes were also mapped. A continuous high-resolution and high-frequency coastal monitoring approach for the area is essential for planning the future development of these beaches to minimize and possibly avoid environmental degradation.