Assessing the morphological evolution of a breakwater-protected sandy beach by means of UAV surveys at Mar del Plata, Argentina

Abstract

This paper aims to study the morphological evolution of a breakwater-protected sandy beach and its response to coastal storms at Mar del Plata, Argentina. The Unmanned Aerial Vehicles (UAV) and Structure from Motion (SfM) monitoring technique, was used to reconstruct the high-resolution beach morphology. Coastal storms characterization was done through the analysis of the significant wave height and sea level series. Two different indexes were applied to quantify storm severity and relate it to the magnitude of beach response, one based on the significant wave height (SPI) and the other on the surge level (SEPI). Accurate morphological changes were mapped and volume was computed by comparing four consecutive UAV monthly surveys between July and November (2019) and one last survey in September 2020. The beach suffered erosion between July and September 2019, and then, partially recovered because occurred only one storm with appreciable waves without the occurrence of storm surges, between September and October. The period elapsing between October and November was characterized by a prolongate calm because there were no significant storms. In addition, significant wave heights decreased from July to November, and the wave propagating direction turned from SSE to E. A significant erosive process was found in the whole period, July 2019 and September 2020. Finally, an apparent linear relationship between the morphological changes and the oceanographic variables was inferred. These results indicate that the SEPI and SPI indexes could be considered reliable indicators of sediment-mobilizing storms on this beach.