Numerical Model for On-Offshore Sediment Transport with Moving Boundaries

Abstract

The development of a finite difference model with moving boundaries for on-offshore sediment transport prediction in the surf zone is presented in this paper. The governing equations used are the conservation of sediment volume and empirical sediment transport rate equation suggested by Kobayashi, which is, for a special case, identical to that of Kriebel and Dean. The resulting inhomogeneous diffusion equation is solved for arbitrary initial profiles and time-varying storm surge conditions. More important, moving boundary conditions at the shoreline and breaking point are rigorously accounted for in our time-marching numerical scheme to adquately predict beach erosion and dune recession. The present numerical model is validated through cross-checking with independently developed numerical schemes and comparison with semianalytic solutions, experimental data of large-scale model test, and the field data of Hurricane Eloise. In addition, our model satisfies the conservation of eroded/deposited sediment volume. The present numerical model is particularly efficient and robust and free of numerical instability. Using the developed program, we have extensively investigated the sensitivity of beach evolution to several important sediment transport parameters, initial profiles, and storm surge hydrographs. It is shown that the model reasonably predicts the erosion of beaches with berms and dunes, and the offshore movement of breaking point. The present numerical model is also used to analyze the evolution of beaches consisting of different sediment characteristics. In our numerical model, the formation and movement of small-scale bars and longshore sediment transport are not considered.