Wave attenuation over porous seabeds: A numerical study

- A macroscopic approach to simulate the flow through porous media is employed in this work.
- A VARANS model is calibrated with laboratory data of wave attenuation on porous seabeds.
- New parametric formulations dependent on porosity and mean diameter are derived using the numerical results.
- The role of the spectral shape in the wave spectrum bulk dissipation is investigated.
- Model results suggest that nonlinear energy transfer plays an important role on wave attenuation over porous beds.

We investigate wave attenuation over porous seabeds by means of a phase- and depth- resolving numerical model that solves the Volume-Averaged Reynolds-Averaged Navier-Stokes (VARANS) equations. The numerical model is calibrated with laboratory data from Corvaro et al. (2010). The numerical model predicts the wave attenuation and the velocity field near the porous bed for different regular wave conditions. Subsequently, a parametric analysis on the physical characteristics of the porous media is made to investigate their relative role on wave attenuation. The results of the analysis indicate nonlinear dependencies of wave attenuation on both, total porosity and mean grain diameter. The widely used parabolic model in terms of the dispersiveness parameter predicts both types of dependencies, effectively. Hence, new parametric formulations are derived for the determination of the coefficients involved in the parabolic model for each type of dependence. On the other hand, the role of the spectral shape on the wave spectrum bulk dissipation is investigated. Numerical results for irregular waves show a clear dependence of the dissipation rate with the Ursell (Ur) parameter. The dissipation rate becomes sensitive to frequency spreading for Ur < 20. Moreover, forcing the model assuming an f − 5 tail in the incident wave spectrum underpredicts seabed attenuation with respect to an f − 4 formulation. Finally, bispectral analysis of irregular wave propagation allow us to investigate the mechanism of wave attenuation. The numerical results suggest that energy is directly dissipated at the peak frequency, whereas nonlinear energy transfer plays an important role in energy attenuation at higher harmonics.