CHARACTERIZATION OF HYDRODYNAMIC PROCESSES DRIVING TIDAL RIVER ISLAND SHORELINE CHANGE

Abstract

Bird/Long Island is a dredge-spoil island located between the north and south channels near the inlet of the Savannah River at the border of Georgia and South Carolina. The island is in a tidally dominant environment and contains cultural and natural resources, including remnants of a Civil War era artillery battery. As a wetland mitigation bank, it is particularly important to the state of Georgia. However, these resources are under threat from documented and ongoing sea level rise, shoreline change (i.e., erosion and accretion) from natural and anthropogenic causes, and land subsidence. In addition to substantial tidal and freshwater flows, the island is subject to locally-generated wind waves primarily from northeast winds, as well as wake from the large container ships transiting to and from the Port of Savannah. A previous study examined the effects of wind and vessel-generated waves on shoreline retreat for the Fort Pulaski National Monument on nearby Cockspur Island (Houser, 2010). The study concluded that while the vessel-generated waves account for nearly 25% of the energy, the wind waves during storm events with increased water levels accounted for the majority of the marsh retreat. Although the proximity of this previous study site to Bird/Long Island is relevant, the different orientations of the islands and the narrowing of the channel create a different hydrodynamic environment. The present work uses field data to characterize the hydrodynamic processes affecting Bird/Long Island, which will improve modeling of its shoreline change.