Coastal South Carolina Water Resources: Isolated Wetlands Risk Assessment using NASA Earth Observations to Support Further Wetland Protections in Coastal South Carolina

Following the 2023 Sackett v. EPA court case, the redefined definition of protected waters of the United States law excludes freshwater wetlands disconnected from navigable waterways. These now “isolated wetlands” are no longer federally protected and are vulnerable to future land cover changes. To understand threats to these newly vulnerable wetlands and potential community impacts, the Coastal Conservation League partnered with NASA DEVELOP to evaluate isolated wetlands in three South Carolina counties (Jasper, Berkley, and Horry). Using Landsat 8 and 9 data, spectral indices including the normalized difference vegetation index (NDVI), normalized difference moisture index (NDMI), and normalized difference water index (NDWI) were computed to assess vegetation health, moisture quantities, and water availability, respectively. The team then conducted wetland classification using these indices along with National Wetlands Inventory data. Following the new legal framework, the team categorized wetlands as either protected (connected) or unprotected (isolated) by analyzing their connectivity to navigable waterways from the United States Department of Transportation database and major rivers defined by the Hydrologic Unit Code 10. Lastly, the team derived a 10-year change detection map identifying wetland change from 2015 to 2025. Using Earth observations proved applicable in delineating isolated wetlands, but it can be improved using finer resolution imagery. Results showed that 48% of wetlands in the study area are isolated, with an overall 4-6% wetland decrease over the past decade. These results indicate a negative wetland loss trend that can inform state policy plans for protection.