A Long-Term Coastal Evolution Model with Longshore and Cross-Shore Transport

Palalane, J. and Larson, M., 2020. A long-term coastal evolution model with longshore and cross-shore transport. Journal of Coastal Research, 36(2), 411–423. Coconut Creek (Florida), ISSN 0749-0208.This study encompasses the development of a long-term coastal evolution model with enhanced capabilities to simulate simultaneously the cross-shore and longshore evolution of the coast. The paper starts by reviewing the theory related to cross-shore and longshore sediment transport, which are the major components integrated in the model. Major advances were made by introducing modules to better account for dune erosion and overwash, dune buildup by wind, and exchange of sediment between the berm and the bar into an existing coastal evolution model. Then, the model performance was tested by simulating the evolution for a stretch of coastline corresponding to the conditions at Westhampton Beach (United States), first for a case with open boundaries representing a situation of dynamic equilibrium and then for the placement of a terminal groin causing advance of the shoreline, berm crest, and dune foot. Subsequently, the model was employed to simulate the combined cross-shore and longshore evolution along Macaneta Spit (Mozambique), and the results were compared with available data. Overall, the model succeeded in reproducing the expected combined cross-shore and longshore evolution at the selected case study sites. For the Westhampton Beach case, the model was able to qualitatively simulate the observed advance of the cross-shore dune system, following the placement of the terminal groin. For Macaneta Spit, the model reproduced the alongshore variation in cross-shore profile shape in response to the incident waves and water levels, as well as the net longshore sand transport pattern as identified in previous studies. In summary, the model produced reliable and robust predictions, showing the capability of running simulations for a period of decades in a few minutes on a personal computer.