A Cost–Benefit Approach to Assess the Physical and Economic Feasibility of Sand Bypassing Systems

Abstract

The artificial sand bypassing systems are coastal interventions designed to transfer sediments from areas of accretion to areas where erosion is observed. The goal of these systems is to reduce the littoral drift gradients where sediment transport is interrupted (vicinity of river mouths or port structures) and maintain a balanced sediment distribution along the shoreline. However, these systems present high initial investment costs as well as ongoing expenses for operation and maintenance. To assess the feasibility of sand bypassing systems in mitigating coastal erosion from a long-term perspective (decades), a comprehensive understanding of their performance is necessary, considering both physical and economic aspects. Thus, a cost–benefit assessment numerical tool, COAST, is applied to evaluate and discuss the effectiveness of bypassing systems during their life cycle. First, a comprehensive analysis is conducted for a generic study area, and then, the feasibility of the systems is discussed for two real study areas of the Portuguese West coast (Barra-Vagueira and Figueira da Foz-Leirosa). The generic results demonstrate as the importance of systems location or transposed flow volumes. On the other hand, the analysis of the two real case studies revealed that, under similar conditions, the results of the cost–benefit analysis can be contradictory. For the Barra-Vagueira stretch, the work indicates that the bypass system is not economically viable, whereas for Figueira da Foz-Leirosa, it is cost-effective. The study shows the importance of the site-specific conditions to evaluate the best option for a medium to long-term planned coast, highlighting the relevance of the proposed approach to assess the physical and economic feasibility of sand bypassing systems.