Coastal flood susceptibility assessment along the Northern coast of Portugal

Abstract

Assessing the susceptibility of sandy beaches to flooding during major storms is an important topic, given the implications that these events can have for beach-dependent coastal systems. A flood susceptibility index based on wave run-up, storm surge and beach morphology is applied to three sectors of the northwest coast of Portugal. An extended ERA5 wave dataset is used (1950-2022) to characterize the most frequent storm events, and topographic data from aerial UAV surveys are examined to obtain specific morphological parameters of the sandy beaches – mean face slope and height of the beach. The flood susceptibility index results show that 54% of the analyzed coast is classified with extreme or very high susceptibility. The most critical sector is the coastal stretch between Cortegaça and Torrão do Lameiro beaches, where mostly natural systems are present, while the urban front of Furadouro is frequently flooded during storm events. Between Miramar beach (south) and Paramos beach, with a susceptibility index classified between medium and extreme, the presence of some urban fronts points to high-risk exposure situations. The sector between São Jacinto and Poço da Cruz beaches presented lower susceptibility levels for the three urban areas. The problem does not end with the threat to urban fronts, which already have several defense structures, but it is also extends to dune systems and sand dykes.