Simulating coastal storm hazards at the Algarve coast (Portugal)

Abstract

<p>Many important European cities are under the threat of coastal storm-related hazards. Recent examples in Portugal, England, France, etc. have demonstrated the vulnerability of their coasts, and this risk is expected to increase under a scenario of global warming. Numerical models are very valuable tools to predict and simulate these hazards, and ultimately, help coastal managers and authorities to reduce damages in goods and people's lives. In this research, the numerical model XBeach was applied to investigate the vulnerability of two risk hotspots located in the south Portuguese coast of the Algarve: Quarteira and Praia de Faro. XBeach is a widely used state of the art model and it is capable of simulating interactions between hydrodynamics and beach morphology. The beaches at these study sites can be classified as dominantly reflective turning to intermediate during high energetic events.  The study site of Quarteira consists of a set of three sandy beaches laterally limited by rock groins and backed by a long promenade with several touristic facilities. In contrast, Praia de Faro is a natural open sandy beach located in the narrow Ancão Peninsula, promoting a natural barrier between the ocean and an interior lagoon. The urbanized area is either directly exposed or naturally protected by the dune that helps to reduce damages in buildings and other services. Two different 2D-XBeach models have been developed and calibrated to simulate coastal hazards including overwash, overtopping, inundation and erosion impacting these sites. The models have been calibrated and validated using topographical measurements of cross-shore profiles, along with visual inspections of the inundated areas after the impact of severe storms. Specifically, data from the coastal storm Emma (2018), that hit the region with dramatic consequences were used in this study. The observed vertical erosion reached more than 3 m at Praia de Faro, while the runup promoted important overwash at both study areas. Additionally, storm Elsa (2019) hit the sites driving significant erosion. To obtain realistic results, the models display a high resolution that captures all natural and manmade features. The results provided by XBeach at both sites demonstrated that within the same study site, the calibration of only one profile was sufficient to properly reproduce the erosion along the site. However, the results of the calibration cannot be transferred from Praia de Faro to Quarteira and vice-versa, even if the study sites are separated by less than 10 km. Moreover, the model successfully simulated the flooding extension that was observed in the field after the storm Emma (2018). These validation efforts are the base for the development of an Early Warning System that will provide advice to coastal managers, civil protection and population in general about the risk associated with severe storms. Furthermore, the findings of this research can provide guidance for modellers working in similar environments.</p>