Overwash processes: spatio-temporal scales and dynamics of the coastal system in southern Santa Catarina, Brazil

Abstract This study evaluated the influence of overwash processes on the dynamics of the coastal system in southern Santa Catarina, Brazil. The analysis was conducted at two temporal scales: monthly and interannual, to investigate the controlling factors in the formation of washover fans within the sand spit barrier (2017–2023) and interdecadal, to understand the morphological behavior of the shoreline and the coastal system (1938–2021). The methodology involved the integration of remote sensing data, aerial photographs, tide gauge records, ocean-climatological data, and analyses of morphometric indicators. The study area was divided into five sectors based on foredune segmentation and the areas with the highest recurrence of overwash fan events. A total of 93 overwash events were identified, with a higher concentration during the autumn and winter months. The formation of washover fans was associated with a combination of storm surges, storm waves, and the presence of foredunes on the sand spit barrier during the passage of low-pressure centers (cyclones). Sectors 3, 4, and 5 exhibited greater vulnerability to overwash events, while Sector 1 was more affected by anthropogenic activities. On the interdecadal scale, the shoreline presented three evolutionary phases: a regressive phase (1938–1978), followed by two transgressive phases (1978–2005 and 2005–2021), with an intensification of the coastal system retreat after 2005. This study contributes to the understanding of how the high frequency of overwash events has driven a transgressive behavior across most of the Araranguá coastal system over the past 16 years, contrasting with the regressive pattern observed in the Holocene system as a whole.