Author(s): Juan L. Garzon; Oscar Ferreira; Theocharis Plomaritis

Linked Author(s): Juan L. Garzon

Keywords: Coastal erosion; Open coast; Manmade pocket beaches; Steep profile; XBeach

Abstract: Sandy beaches are among the most populated areas worldwide and they host many socio-economic activities. However, these environments are vulnerable to the impact of coastal storms causing severe erosion and shoreline retreat. In order to improve our understanding of simulating storm-induced coastal erosion, several one-dimensional and two-dimensional XBeach simulations were performed. In this study, two locations of the southern Portuguese coast were selected: Praia de Faro and Quarteira. The former is a natural open beach, while Quarteira, located ten km north, consists of a three-cell beach laterally limited by groins and a promenade at the backside. Both sites can be classified as intermediate or reflective beaches. Thus, in these environments, the modelling of sediment transport represents a challenge since the physical processes occurring are only fully solved by wave-resolving models. A sensitivity analysis of a 1D model, in terms of horizontal erosion, to three parameters, the wave asymmetry induced- sediment transport component (‘facua’), the initiation avalanching slope (‘wetslope'), and an enhanced onshore sediment transport component (‘bermslope’) was performed. The results revealed that the model was highly sensitive to ‘facua’, and 'wetslope' (especially in the foredune). However, if ‘bermslope’ was activated, the effect of ‘wetslope’ was partially reduced. The calibration in Praia de Faro showed that when ‘bermslope’ increased, ‘facua’ must be reduced to properly simulate the erosion since both affect the onshore-offshore sediment balance. The findings of the 1D validation were applied to a 2D model, and it was observed that 1D and 2D models, using the same settings, simulated similar erosion in the beach face, but the erosion in the dune highly increased in the 1D simulations. Moreover, the ability of a 2D model to simulate erosion during two storm events was classified as excellent. The evaluation of the recently implemented parameter ‘bermslope’, displayed for the first time that the model can simulate properly the erosion in a 2D scheme, without unrealistically enhancing the wave asymmetry sediment transport component. On the other hand, in the groin-protected site of Quarteira, a 2D model was successfully validated for the same storms, although different settings were required (lower ‘facua’ and ‘bermslope’ off). These engineering protections controlled the morphodynamics of the site during the storm events and might affect morphological modelling. This work demonstrates the application of XBeach at steep beaches, providing new insights on how to obtain the best calibration parameters, and contributing for the accurate modelling of coastal erosion and development of early warning systems at intermediate to reflective open and protected beaches.

DOI: https://doi.org/10.3850/IAHR-39WC25217119202283

Year: 2022