NATURE-BASED FLOOD RISK REDUCTION VIA MULTIPLE LINES OF DEFENSE

Abstract

Sea level rise, land subsidence and population growth lead to steadily increasing flood risks in low-lying coastal areas. Hard flood defense structures such as dikes and dams should be regularly heightened and strengthened to sustain their protective function. Further, such hard structures can induce negative effects on the surrounding ecosystem. Therefore, nature-based approaches to flood risk reduction are increasingly promoted. Vegetated foreshores (such as salt marshes and mangrove forests) reduce wave loads on coastal dikes (Vuik et al., 2016). Furthermore, they are able to keep pace with sea level rise due to natural sediment accretion. However, foreshores cannot always exist in front of flood defenses, for example because of shipping lanes, protected habitats or harsh waves and currents. Even in such situations, coastal safety can be enhanced by creating salt marshes in between multiple lines of defense (double dikes). In this study, we investigate the effectiveness, costs and coastal protection benefits of nature-based flood risk reduction via multiple lines of defense.