Cost-benefit analysis of a detached breakwater for coastal protection: a case study in the Portuguese seaside

Defining the most suitable intervention to mitigate coastal hazards in a specific area, under an integrated coastal management strategy, is complex for several reasons including the lack of stakeholders’ consensus. In this respect, Cost-Benefit Analyses (CBAs) can help decision-makers to better understand the environmental, social and economic implications of a planned intervention. Nevertheless, CBAs are not yet largely applied in coastal management studies, as could be expected. Hence, this work aims to consolidate the use of a CBA to support coastal management decisions, considering its application to a real case study. The case study consists in evaluating the long-term impacts, benefits and costs of a detached breakwater for the protection of a coastal village located on the Portuguese northwest coast against flooding and erosion. This assessment was made based on the estimation of the costs of the structure and the benefits associated with the protection of the coastal community and natural areas, considering morphodynamics’ forecasts determined through numerical modelling. Out of several configurations defined based on length (L; in meters) and distance to the shoreline (D; in meters), four detached breakwater scenarios were selected. Results demonstrate that scenario L200D200 can be a feasible solution with overall low costs and low benefits; L300D400 can be an alternative solution with higher costs but higher benefits too. The consolidation of the CBA described is a step forward to improving the expedition of future analysis and proof of its potential in what concerns analysis at the local scale.