A multi-scale assessment of shoreline changes at an undeveloped beach in southern Brazil

Abstract

This research aims to investigate shoreline variability at an undeveloped beach in southern Brazil on interannual and millennial scales. The long-term coastal evolution was investigated by GPR, whereas the interannual scale shoreline changes were analyzed by the Digital Shoreline Analysis System (DSAS). Simultaneously, a supervised Maximum Likelihood image classification was applied to the dune systems to differentiate vegetation from sand. The results show that the coastline in the Praia das Cabras region is retreating at different scales. The stratigraphic record in GPR shows that the coast has a retrogradational stacking pattern behavior in geological time. At the same time, the results obtained from the digital shoreline analysis revealed that the coast has suffered short-term erosion in the analyzed period, and this is attributed to natural causes. Another point is the higher values of erosion in the extreme parts of the study area, which are related to the presence of washouts. There is also a differentiation in the stage of the dunes and vegetation between the northern and southern parts of the stretch. The northern area is more densely vegetated and has a continuous foredune ridge with incipient dunes forming a ramp, whereas in the southern part, the vegetation is more dispersed, with interrupted dunes forming nebkhas. Between 2019 and 2023 there was a recovery of the dune field, by filling in the blowouts and minimizing the indentations, forming a more homogeneous foredune line.