Wave Overtopping and Flooding Costs in the Pre-Design of Longitudinal Revetments

Wave overtopping, mainly caused by growing coastal erosion processes, directly affects populations, causing coastal flooding and potential damages. This work aims to develop the relationship between overtopping phenomena and their impact costs through an approach that considers wave runup, corresponding overtopping events, their flow volume and related flooding costs. Herewith, it is possible to evaluate the relationship between the structure construction and maintenance costs and the consequent costs due to overtopping and flooding damages, leading to the design of optimised coastal structures solutions. To apply the proposed approach, a real case study on the Portuguese northwest coast (Ovar municipality) was analysed, evaluating overtopping and flooding data recorded by the Portuguese Environment Agency (APA), allowing costs per unit flooded volume to be estimated. Then, future scenarios were predicted to assess the influence of climate change, discuss intervention scenarios and evaluate the uncertainty of economic parameters’ evolution. The proposed methodological approach represents a step forward in the estimative of coastal overtopping and flooding impacts, leading to increasing the knowledge about flooding and overtopping costs and optimised mitigation measures in artificialised coastal areas, where coastal defence works (longitudinal revetments) are present. This approach fills a gap in knowledge regarding this type of forecast in a medium- to long-term perspective.