Vessel wake contributions to erosion at exposed and sheltered shorelines near a tidal shipping channel

Abstract

This study investigates the role of low-frequency cargo vessel wake to erosion at Bird/Long Island in the Savannah River, Georgia. The island splits the river into the Main Channel that accommodates cargo vessels traveling to the Port of Savannah, and the shallower, sheltered South Channel. Pressure and velocity data from both channels are used to characterize wind waves, tidal currents, and vessel wake. The relevance of each process to erosion is estimated by using hydrodynamic power as a proxy for erosive potential. Instantaneous water level is compared to the elevation of an eroding scarp to identify “scarp-relevant” power contributions, power occurring when the eroding scarp is at least partly submerged and susceptible to erosion. The analysis shows that scarp-relevant power in the Main Channel is dominated by cargo vessel wake (88%), with smaller contributions from tidal currents (5%) and wind waves (7%). Power in the South Channel is also dominated by cargo vessel wake (65%), followed by tidal currents (34%) and wind waves (1%). A follow-up study confirms that low-frequency cargo vessel wake, which produces waves heights up to 2.01 m in the Main Channel, propagates readily around both ends of the island and into the South Channel, where it produces wave heights up to 0.32 m.