Large-Eddy Simulation of Wave Attenuation and Breaking on a Beach with Coastal Vegetation Modelled as Porous Medium

Erosion and flooding are the main threats for most coastal regions. Nature-based solutions, such as coastal vegetation (CV) fields, have received significant attention in recent years because they effectively dissipate wave energy while maintaining biodiversity. In this study, a porous medium model was implemented in an in-house software to simulate the three-dimensional, two-phase (water/air) flow induced by wave propagation past CV fields. First, the model was validated against experimental measurements of wave propagation past a CV field on a horizontal bed. Then, the model was used to assess the influence on wave behaviour of the equivalent porosity, n(eq), and the cross-shore length, L-CV, of a CV field with a constant plant height on a beach with a constant bed slope. Results were obtained for the non-vegetated case (n(eq) = 1) and five vegetated cases with different n(eq) and L-CV values. It was found that decreasing n(eq) moves wave breaking offshore at larger depths (40% increase for the case with n(eq) = 0.82), while it does not affect much the breaking height (4% was the largest difference). For very high n(eq) (0.98 in the present study) and/or small L-CV (83% of the wavelength just offshore of the CV field in the present study), wave breaking may occur at depths smaller than in the non-vegetated situation due to increased wave shoaling over the corresponding CV fields. The undertow distribution is strongly modified and an increased wave setup (highest for n(eq) = 0.82) is observed for all vegetated cases in comparison to the non-vegetated one.