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Revista de Gestão Costeira Integrada

versão On-line ISSN 1646-8872

Resumo

OLIVEIRA, Filipa S. B. F.. Dune Erosion with the XBeach and Litprof Models. RGCI [online]. 2012, vol.12, n.2, pp.195-222. ISSN 1646-8872.

The present study aims to improve the evaluation and prediction of the vulnerability/resilience of dune systems to the wave action under maritime storm conditions. The objective was to evaluate the performance of the XBeach and Litprof deterministic numerical models for dune erosion. The models were tested for a case of dune erosion performed in a large scale channel laboratory test. The evaluation of the models performance was based on the analysis of the morphological evolution, on impact indicators (erosion volume, dune retreat and retreat of the top of the dune) and on an error indicator (Brier Skill Score). The default parameters (standard set of parameter settings) are presented and tested for both models. The conclusion on the models performance with the default parameters was that the XBeach model is good and the Litprof model is poor. It is recommended that for an engineering application of dune erosion prediction, where accuracy and safety are both important, the XBeach model with the default parameters should be applied with precaution since the erosion volume was underestimated. The calibration parameters are presented, discussed and tested. It was concluded that the most influent parameters on the morphological evolution were: beta, break, facua, gammax, hswitch, lws and wetslp for the XBeach model, and Maximum Angle of Bed Slope for the Litprof model. The parameters lws and wetslp of the XBeach model were those which provided to the final profile the most similar geometry to the one observed in the laboratory experiment. The results obtained for the error indicator BSS revealed that the best performance was obtained by changing the calibration parameter lws and that the second best performance was obtained by changing the calibration parameter wetslp, having both been classified as excellent. Since the morphological change reached by changing the lws parameter improved the prediction of the two characteristics, which are crucial under an engineering point of view, retreat of the top of the dune and sea side limit of the extension of the active zone (where was observed the formation of the submerged bar during the experiment), it was concluded that this parameter is of great relevance in the simulation of dune erosion for the XBeach model. The Litprof model after calibration simulated correctly the retreat of the top of the dune, simulated the development of the submerged bar in the location observed in the experiment, simulated incorrectly the erosion volume (approximately half of the observed volume) and the dune face slope, and consequently caused an advance of the dune at the water level instead of a retreat. For this reason, it is recommended precaution in the application of the Litprof model for dune erosion. From the comparison of the XBeach and Litprof models in both stages, i.e., in the stage of testing the default parameters and in the stage of calibration, it was concluded that it was the XBeach model that had the best performance in this case study. This study allowed testing and acknowledging the high capacity of the XBeach model and the reasonable capacity of the Litprof model in the prediction of dune erosion.

Palavras-chave : Coastal Erosion; Dune; Morphodynamic Modelling; XBeach; Litprof.

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