The Georgia barrier islands naturally experience broad tidal amplitude, from 2.0 meters (6.5 feet) to 2.8 meters (9.2 feet), with an average of 2.3 meters (7.5 feet). Tides, waves, storms, and storm surges—as well as longshore currents and littoral drift of sediment—shape the beaches, alter the marshes, and erode the Pleistocene core of the island. The major erosional agent affecting Georgia beaches is northeasterly storms, which are more frequent in the winter months. Summer storms and hurricanes dramatically form the beaches, but are infrequent and less predictable.
Inundation from extreme high tides and storm surges destroys the nests of sea turtles and shorebirds. Sea turtles nest above the spring high tide line on the beach and sparsely vegetated low dunes, while shorebirds prefer sandy flats, overwash flats, and sparsely vegetated dunes. Historically these nesting habitats were rarely inundated. Inundation from high tides is more frequent now than in the past. The average high tide has increased from 8.4 feet (2.5 meters) to 9 feet (2.7 meters) between 1935 and 2012, and the average high tide has been above 9 feet in 16 months of the last three years.
Erosion significantly influences Georgia beaches. On St. Catherines Island, the rates of beach erosion range from 0.33 feet (0.1 meter) a year to more than 29 feet (9.0 meters) a year—with most of the beach eroding at rates between 4.3 to 11 feet (1.3 to 3.3 meters) per year. From 1996 to 2008, the erosion rates on Yellow Banks Bluff ranged between 1.6 feet (0.5 meters) to more than 8.2 feet (2.5 meters) a year. Using aerial photography, the erosion rates have been measured at 7.5 feet (2.3 meters) per year from 1972 to 2008 in the Flag Pond area and 17.7 feet (5.4 meters) per year from 1951 to 2008 further south on South Beach. Assessing the beaches from the perspective of sea turtle nesting, less than 15 percent of the beach area is considered adequate. Erosion is also eliminating shorebird nesting habitat and eroding the Pleistocene core in areas with mature maritime live oak forests and the maritime longleaf-slash pine forest.
Erosion also exists on the marsh side of the island. An assessment of the total marsh side shoreline of St. Catherines Island, found erosion at a rate of nearly 3.3 feet (1.0 meter) a year from 1933 to 2004. A more specific study that assessed erosion along the boundary between three meanders of Wamassee Creek and upland near the Mission Santa Catalina de Guale site, found annual rates between 0.6 to 5.5 feet (0.2 to 1.68 meters) per year, with the highest rates near the mission site.
Extreme storm events, primarily hurricanes, remain a constant threat to coastal regions throughout the southeastern U.S. The Georgia Bight — while less likely to lie in the path of a hurricane than other coastal regions — still experienced several major storm events over the last 200 years. Only four hurricanes made landfall on the Georgia coast during the 20th century: 1911, 1940, 1947, and 1979. Hurricane David in 1979 resulted in lost power on the island for over 30 hours and damaged roads and buildings. Fourteen hurricanes hit land in the 19th century—six considered major hurricanes of Category 3 or greater. Several of these included storm surges that swept over parts of the island.
Source: A Strategic Conservation Plan for St. Catherines Island, Georgia, Prepared for the St. Catherine’s Island Foundation – Robert D. Sutter, L. Gregory Low, Sara J. Gottlieb, June 2013