A social cost-benefit analysis of shellfish beds on the Dutch coast as a nature-based measure against climate change

Every five years, the Dutch government employs sand replenishment to combat coastal erosion and to accommodate sea level rise. However, the transportation of sand from the North Sea to the coastline has negative societal consequences such as air pollution and habitat loss. Through a social cost-benefit analysis, this study raises the question of whether the current replenishment policy is optimal for preserving the coastline. The alternative approach studied in this analysis is the installation of the nature-based solution of shellfish reefs that hold sand and adapt to rising sea levels. Implementing shellfish beds would reduce the need for sand deposition, thereby decreasing emissions and aligning with climate goals such as the Green Deal Shipping. Moreover, shellfish provide extra benefits such as denitrification and biodiversity conservation. By weighing the costs and benefits against each other, deploying shellfish reefs for coastal defense along the Dutch coastline is found to be welfare enhancing. Despite the positive result, the sensitivity analysis reveals two nuances. First, the placement of shellfish beds is only beneficial for society when they also give provisioning services like food supply. Second, there is uncertainty regarding the sand retention capacity of shellfish beds and the ecosystem development of shellfish. Conducting pilot studies can provide more insight to reduce these uncertainties. This study raises the question of the adequacy and long-term viability of the current sand nourishment policy in the Netherlands in the context of climate change and the increased frequency of extreme weather events.