Potential Impacts of Sea-Level Rise and Land-Use Change on Special Flood Hazard Areas and Associated Risks

Abstract

Current U.S. National Flood Insurance Program design standards and floodplain management policies are based on the special flood hazard area (SFHA), which is an area that has a 1% or more chance of being inundated in any given year. Current hydrologic and hydraulic (H&H) practices assume a stationary environment to estimate the SFHA, although future instances of land-use change and sea-level rise (SLR) are anticipated to transform the environment in many regions around the United States. The assumption of a stationary environment may lead to an underestimation of the SFHA and associated risks, such as number of inundated buildings and cost of flood damage. This study examined the potential impacts of projected land-use change, SLR, and combined impacts of land-use change and SLR on the SFHA and associated risks. A method is presented to integrate the projected land-use change and SLR when delineating SFHA based on geographic information system (GIS), hydrologic engineering center-Geographic river analysis system (HEC-GeoRAS), and H&H modeling. The method was applied to the rapidly urbanizing Dogue Creek watershed, located in the coastal physiographic region of Fairfax County, Virginia, where land-use change and highest SLR are projected to increase by 44.1 and 71.0%, respectively, from 2010 to 2100. The results indicated that the combined impact of the projected SLR and land-use changes would increase the extent of SFHA (10.5%), number of inundated buildings (59.3%), and cost of flood damage (77.0%). Therefore, it is important for community officials and engineers to consider the impacts of projected land-use change and SLR in determining the SFHA to accurately predict the level of future flood risks to infrastructure and communities.