Evaluation of Beach Nourishment Evolution Models Using Data from Two South Carolina, USA Beaches: Folly Beach and Hunting Island

Weathers, H.D. and Voulgaris, G., 2013. Evaluation of beach nourishment evolution models using data from two South Carolina, USA beaches: Folly Beach and Hunting Island. Beach nourishment is a common method used for mitigating coastal erosion. However, it is also a costly undertaking and requires an appropriate cost-to-benefit analysis. Although the costs can be estimated relatively easily, the benefits are directly related to the life expectancy of the proposed project. With this in mind, three existing beach replenishment time-evolution models (the Linear Erosion, the Verhagen, and the One-Line models) were compared for their ability to represent data from two beach nourishment projects that have taken place in South Carolina, USA, at Folly Beach and Hunting Island. Another newly introduced model that combines the One-Line model with elements of the Verhagen model was also tested against the data from the beach nourishment projects. In addition to hindcast evaluation, the four models were employed to predict beach fill evolution at both locations, and those results were compared using the existing fill evolution data. Although all models provided a satisfactory statistical fit, the fitted parameter values from the Linear Erosion, the Verhagen, and the combined models failed to adequately describe physical processes associated with the development of each model. On the other hand, the One-Line model was able to describe beach fill volume evolution at both locations. The discrepancy between the models was exemplified in their application without the benefit of the statistical fitting. Overall, it was found that the One-Line model represented a more versatile approach to predicting volume losses because it is based on physical concepts of wave-induced sediment transport, and as such, it was better suited for use at any location as long as accurate information about the wave climate is available. Furthermore, detailed investigation at each site indicated that both the role of barrier island processes and the role of inlet dynamics in the evolution of beaches and beach fill were not fully recognized by the models and should be considered in the cost–benefit analysis of beach nourishment projects at barrier islands adjacent to ebb tidal deltas.