EVALUATION OF SLAMM MODELING OF MULTIPLE SCALES IN BEAUFORT COUNTY, SC

Salt marshes are dynamic ecosystems that provide ecological, water quality, recreational and economic benefits. South Carolina has the greatest amount of salt marshes on the east coast with 344,500 acres making up 2/3 of the state’s coastal wetlands and 30% of all salt marshes on the east coast. Understanding how marshes may respond to Sea Level Rise (SLR) will inform the potential need for proactive marsh conservation and/or land use management strategies. Marshes are expected to sustain substantial losses as the rates of SLR increase (Fretwell, Raynor, Wagner, 2021). SLR often results in smaller fragmented wetlands that often become isolated from shorelines.

The wetland changes within Hilton Head Island were assessed through the application of the Sea Level Affecting Marshes Model (SLAMM). The SLAMM conceptual model assumes that wetlands inhabit a range of vertical elevations that are a function of the tide range. (e.g. Low marsh is flooded daily by the high tide. This causes only plant life with a high tolerance for salinity to survive here.) The SLAMM model is a flexible decision tree model that incorporates geometric and quantitative relationships in understanding the changes in coastal land classes under changing SLR scenarios. The SLAMM model has been used since the mid-1980s (Smith, J. B.,1989 Park, R.A. 1991) and is the basis for most inundation mapping approaches commonly used today.

This study utilized high-resolution data sets that have been developed at the College of Charleston's Lowcountry Hazards Center. 30-meter, 10-meter, and 1-meter resolution GIS datasets were created, and a Python tool was created to move GIS layers to SLAMM-compatible layers. The output from SLAMM in GIS format provides insights into the location, magnitude, and type of marsh response that can be expected from increased sea levels. (Dewberry 2018). The SLAMM output shows the anticipated changes in wetland coverage from the baseline year of 2021 to 2100. The results show a substantial loss in marshes as the rates of SLR increase where wetlands are unable to keep pace with SLR and/or migrate landward. The 1-meter resolution datasets were concluded to be the most accurate for decision-making purposes. SLAMM analyses will provide coastal counties with a more powerful tool to plan and make decisions about their Marsh ecosystems.