Impacts of Dredging on Shoreline Change

Abstract

Nearshore dredging for construction aggregate or beach nourishment can result in a perturbation of natural littoral processes, changes in wave transformation patterns, and a net loss of sand from the littoral system. A method is described for estimating both direct and indirect effects of dredging on shoreline change. The direct effect results from infilling of the dredged pit via cross-shore sediment transport and is addressed statistically, assuming that the beach profile is in some arbitrary equilibrium shape. The indirect effect arises from project-induced wave transformation, which alters longshore sediment transport patterns, and is described using both spectral and monochromatic, numerical wave transformation models to provide input to a one-line model for shoreline change. Infilling of the pit is neglected when estimating the indirect effect, providing a worst-case estimate of the indirect effect. The methodology is applied to a site on the Turkish Black Sea coast, using hindcast wave data. The influences of pit location and geometry are investigated systematically, and recommendations regarding optimum pit dimensions and locations are made.