Valuing Salt Marshes as Nature-based Infrastructure for Coastal Flood Mitigation: A Case Study of Chatham County, GA

Abstract. Flooding poses significant economic challenges to coastal counties, affecting nearly 40 % of the U.S. population. Nature-based solutions, also known as green infrastructure, are increasingly recognized as effective alternatives or complements to traditional gray infrastructure for flood risk mitigation. This study examines the flood damage reduction benefits of salt marshes, a key type of green infrastructure. We use physics-based spatially explicit hydrodynamic models to simulate storm scenarios and the resulting inundation depths with and without salt marshes. We then translate hydrological data into economic benefits by applying two distinct approaches, one based on the traditional US Army Corps of Engineers depth-damage function and another with an estimated depth-damage function derived from the National Flood Insurance Program (NFIP) claims data. Applying our integrated approach to the case study area, Chatham County in Georgia, we find that salt marshes contribute to significant damage reductions, ranging from $ 30 million to $ 40 million for a storm representative of the 1 % annual exceedance probability event. This study offers policymakers valuable insights into implementing flood mitigation strategies through marshland conservation. Our integrated modeling framework is readily adaptable to coastal regions worldwide where salt marshes or similar coastal ecosystems provide flood-mitigation services.