EROSION AND ACCRETION ON CURVED BEACH

The performance of a large nourishment project on Bethany Beach, Delaware is evaluated using available beach profile, wave and tide data during September 2007 to September 2010. The volume of the placed sand with the median diameter of 0.31 mm was about 500 m3/m along the curved shoreline of 1.8 km length. The nourished beach was attacked by two severe storms in May 2008 and November 2009. The eroded sand volume above the mean sea level (MSL) was about 70 m3/m for each of the two storms and emergency repairs were necessary. The numerical cross-shore model with multiple cross-shore lines is used to compute the cross-shore and longshore sediment transport. The beach erosion above MSL is shown to be caused by the offshore sand transport and the alongshore gradient of the longshore sand transport rate. The performance of the nourished beach is predicted to be sensitive to the sand diameter in the range of 0.23 to 0.45 mm.