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Time-Varying Beach Memory Applied to Cross-Shore Shoreline Evolution Modelling

ABSTRACT Jara, M.S.; González, M.; Medina, R., and Jaramillo, C., 2018. Time-varying beach memory applied to cross-shore shoreline evolution modelling. A new cross-shore Shoreline Evolution Model Based on the Equilibrium Wave Energy—the SE-WE Model—is presented in this article. This simple model predicts the shoreline position S as the equilibrium shoreline response under a specific wave forcing, i.e. the proposed Equilibrium Wave Energy (Eeq) is computed as a weighted average of antecedent wave conditions, according to a new formulation. This new approach allows for the prediction of S at any time from a small fragment of the incident wave-energy time series as the only input of the model. In contrast, previous, similar models needed to evaluate the entire time series from an initial shoreline position to the target time. The proposed model addresses shoreline changes derived from wave-driven, cross-shore sediment transport. Consequently, the SE-WE Model has limited applicability in beaches in which the gradient in the longshore sediment transport or the longshore sediment transport itself are not negligible. The time frame considered for the computation of Eeq refers to the set of antecedent wave conditions having significant influence on the current shoreline position and, therefore, alludes to a certain beach memory (BM). In contrast to existing, similar models, the SE-WE Model BM varies over time. This time-varying BM is in agreement with observations in which high wave energy events erase all trace of past configurations of the beach (“short beach memory”), whereas at the same beach, the effects of past events usually remain after long periods of calm conditions (“long beach memory”). Results from the SE-WE Model applied at the beach of Nova Icaria, Spain, show a good agreement with observations. Additionally, the new model is compared with existing similar models, showing remarkably similar skills in spite of the differences in model approach and model input.