A LOCAL-SCALE APPROACH TO PREDICTING FUTURE TIDAL FLOODING DUE TO SEA-LEVEL RISE: LITTLE CUMBERLAND ISLAND, GA

Coastal communities that regularly experience tidal and storm flooding rely on publicly available data and predictions to best manage their communities in the face of accelerating sea-level rise. While many regional- and global-scale resources exist, such as NOAA’s invaluable Sea Level Rise Viewer, these resources typically do not consider local-scale variations, such as the way shifting topography and bathymetry impact wave set up and tidal funneling. Small communities require more local-specific data to make the most effective management decisions. This study focuses on one such small coastal community: Little Cumberland Island, Georgia. This island is accessible only by boat, and a small sand road connects the only dock to the mainland. This road is low-elevation, and residents report that tidal flooding has more frequently made the road impassable in recent decades. To validate these claims and provide community-specific management recommendations, seven HOBO pressure sensors were deployed in marshes and tidal channels surrounding the most flood-prone roads. Additionally, these roads were surveyed so that water-level measurements in the surrounding marsh could be translated to tidal flooding on the roads. After obtaining nearly a year-long time series to document modern flooding, sea-level rise projections based on data from Fort Pulaski (NOAA and USACE) were added to predict future flood magnitude and frequency. The impact of wind setup was also estimated by differencing recorded tidal elevations from those predicted by NOAA and performing a multi linear regression to quantify the influence of offshore wind velocity (speed and direction) on enhanced tidal flooding. Results indicate that tidally induced road flooding will likely not substantially increase over the next five years. However, flooding will increase significantly by 2030. By 2040, flooding with approximately 1-ft of water on the road is predicted to triple in frequency. We recommend that if communities such as Little Cumberland Island plan to implement a more permanent solution to road flooding, such as constructing raised wooden bridges, it should be undertaken within the next 5-10 years.