Shoreline change rates along Samborombón Bay, Río de la Plata estuary, Argentina

Abstract

Samborombón Bay is an extensive microtidal wetland located in the outer Río de la Plata estuary. Shoreline change rates (erosion or accretion) were quantified at six control areas situated along the bay's coastal area. Digital Shoreline Analysis System 4.3 (DSAS) was used to process aerial photographs and high-resolution satellite images, aiming to quantify shoreline change. A larger ‘Total Period’ (the last 50 years) and a ’Recent Period’ (the last decade approximately) were considered for analyzing shoreline evolution. Erosion and accretion rates increased in five of the six control areas during the last decade. The alongshore (PlN) and the incident (Pi) wave energy fluxes were computed from numerical wave simulations. Highest mean annual Pi values were observed at the southern and northern sectors of the bay, and lower values were obtained at the center. Mean annual PlN shows a convergent pattern in Samborombón Bay. Some differences between adjacent locations regarding annual mean PlN were detected. These differences could generate a slight divergence in PlN, leading to mild coastal erosion. Pi presents generally positive trends along the bay. On the contrary, PlN only presents a significant trend in the southern part of the bay. Then, while the erosional capability (Pi) is increasing, transport capacity (PlN) is quite stable along the coastal area of the bay. Finally, the hydro-sedimentary processes at the coastal area of Samborombón Bay were interpreted by means of a simple conceptual model, which includes internal and external sources of sediments.