Cross‐shore sediment transport on natural beaches and its relation to sandbar migration patterns: 2. Application of the field transport parameterization

[1] A cross-shore sediment transport parameterization (shape function) based on data from intensive field experiments carried out on five European beaches is incorporated into a simple time dependent model to explore its capability for reproducing sandbar generation and evolution in the medium term (O(months)). Model results are compared with bar-crest migration patterns observed at Duck, North Carolina. The model comprises a simple wave transformation routine that accounts for linear shoaling and assumes a saturation law for wave decay inside the surf zone. Second-order statistics derived from the cross-shore distribution of wave heights are used to scale the sediment transport parameterizations which estimate the cross-shore structure of the third and fourth velocity moments. Cross-shore gradients in sediment fluxes, calculated with an energetics approach, produce bed elevation changes. The updated morphology affects the wave propagation in the next time step forming a fully coupled model for predicting sandbar evolution. Bar generation close to shore and the details of the sandbar evolution are successfully reproduced (R2 = 0.86) over the 77-day period of the observations using default values for drag coefficients and efficiency factors. In accordance with the observations, the model shows rapid offshore sandbar migration in response to individual storms, and weak onshore bar movement for lower energy conditions. Owing to its simple nature, the model is not capable of reproducing the whole profile morphology especially in the trough (no trough generation), and it is only valid for replicating bar crest position. The results suggest that a convergence of sediment near the breakpoint (breakpoint hypothesis) combined with morphological feedback, can successfully explain the evolution of bar crest over periods of months from the details of forcing (incident waves and water levels).