HISTORIC RELATIVE SEA-LEVEL RISE IN SOUTH CAROLINA: HOW TO GET A GRIP ON LOCAL SUBSIDENCE AND THE IMPLICATIONS FOR FUTURE FLOOD RISK

Along the east coast of the United States, rates of relative sea-level rise vary greatly due to differences in ocean dynamics and local to regional subsidence (Van de Plassche et al., 2014). Within the southeastern region, there is a gap in accurate and modern data points related to relative sea-level rise between southern North Carolina and Charleston, South Carolina. In this region, lies Myrtle Beach, South Carolina, one of the fastest growing areas in the country and a hot-spot of tourism. The modern rate of relative sea-level rise in this area is significantly faster over the last century (4.6 ± 0.6 mm/yr) compared to Charleston (3.3 mm/yr; 100 km to the south) and Wilmington (2.5 mm/yr; 185 km to the north) due to a current undifferentiated subsidence effect of 2.9 mm/yr in the Winyah Bay region (Fink et al., in prep). Nuisance and compound flooding have become a common occurrence in the area over the past years. Myrtle Beach experienced 72 hours of nuisance flooding per year in 2001-2015 with a projection of 1,368 hours per year by 2045 (Dahl et al., 2017); Data collected from Georgetown, a low-lying historic city on Winyah Bay, indicated 436 hours of flooding in 2021 with a projection of a majority of the year having daily flooding events by 2040.

The demand is urgent for qualitatively and quantitatively understanding the natural and anthropogenic mechanisms that lead to rising coastal water levels. The three goals of this study are to a) Resolve historic sea-level changes (recent centuries) at inter-decadal resolution; b) Quantify local short-term (decades) and long-term (millennia) subsidence rates (land sinking) by distinguishing the various participating natural and anthropogenic processes; c) Informing and assisting local communities in assessing their current and future flood risk. The study will be conducted using a combination of geodetic, historic, geological, and on-site monitoring approaches. These data will be integrated into a regional framework to examine temporal and spatial variations.