MONITORING OF A DISCRETE SHOAL BYPASSING EVENT AND RESULTANT EFFECTS UPON BEACH MORPHOLOGY, DEWEES ISLAND, SC

Shoal bypassing is the process by which packets of sand are released from an inlet’s ebb-tidal delta and migrate onshore, naturally renourishing the adjacent shoreline. Although these events are responsible for significant beachfront accretion, they can also be extremely erosional in the interim between shoal detachment from the swash platform and its welding on the beach due to irregular wave refraction patterns. Few studies exist that quantitatively describe the magnitude of this impact, particularly at fine temporal resolutions. Between November 2008 and September 2009, bi-monthly surveying of 20-25 shore normal transects was performed at Dewees Island, SC, a barrier island northeast of Charleston, SC, as a shoal was in the process of migrating onshore. Shoal attachment occurred in late February 2009. Initial data analysis suggests the shoreline in the area of shoal attachment prograded a maximum of approximately 60 meters. The adjacent downdrift shoreline experienced as much as 40-50 meters of erosion depending on the proximity to the attachment site. The beach now appears to be in a phase of recovery and will continue to be monitored. Results from this study will help island land managers formulate best shoreline management practices.