QUANTIFYING BOAT WAKE-DRIVEN EROSION AND LAND LOSS ALONG THE ATLANTIC INTRACOASTAL WATERWAY IN SOUTH CAROLINA, USA

The Atlantic Intracoastal Waterway is an inland transportation pathway along the Atlantic and Gulf of Mexico coasts, USA. In North and South Carolina, the construction of the Intracoastal Waterway was green-lighted in 1927 and completed in the late 1930s. Along many sections of the Intracoastal Waterway, boat wake causes erosion of the waterway shoreline, which includes marsh edges, sandy beaches, and bluffs. Here, we will quantify shoreline erosion along the Intracoastal Waterway and focus on a short section near Little River, SC, USA comprising about 11 km. This portion of the waterway was chosen because of the amount of infrastructure, recreational land, and marsh habitat that is at risk of being impacted by erosion. We tracked erosion on both sides of the waterway by digitizing shorelines and calculating change rates using aerial photos from the years 1977, 2006, 2010, 2015, and 2016. Initial results between 1977 and 2016 show spatially averaged shoreline erosion of 24 m corresponding to an average erosion rate of 0.6 m/yr. However, shoreline erosion is spatially variable ranging from negligible to hotspots with maximum shoreline erosion of 76 m, or 2 m/yr. In some areas, shoreline erosion appears to be accelerating, possibly due to increased boat traffic and increased wave energy reaching the shoreline. Implications of shoreline erosion along the Intracoastal Waterway include net marsh area loss, changes to marsh edge morphology and sinuosity, the construction of shoreline armoring to protect waterway infrastructure, rapid widening of the waterway, and possible additions to the waterway sediment budget. This study is the pilot phase of a long-term project into quantifying the relationship between erosion and shoreline type along the Intracoastal Waterway in South Carolina.