Inverse Estimation of Sand Transport Rates on Nourished Delaware Beaches

Abstract

The Delaware Atlantic coast of 40 km length is suffering from beach erosion. The State of Delaware placed approximately 1,100,0001 m3 sand on its four beaches in 1998. Beach profiles were surveyed along fixed 65 cross-shore lines almost semiannually for 9–11 times until 2005. The measured profiles are analyzed to obtain the shoreline displacement and the area changes in the landward and shoreward zones between the two successive profile surveys. The relations among these profile change parameters indicate that a standard one-line model may not be applicable to these nourished beaches because of the dominant summer and winter profile changes. An inverse method based on a two-line model is developed to estimate the cross-shore sediment transport rate and the gradient of the longshore sediment transport rate. The estimated rates indicate the importance of both cross-shore and longshore sediment transport to predict the evolution of these nourished beaches with large variabilities in time and space.