"Soft" shore protection by a beach drain system

In this study, the effects of seepage flow in the swash zone on beach profile evolution under the wave action are examined numerically. The seepage flow is induced artificially by a porous drain pipe buried beneath swash zone parallel to the coastline. The system includes minimal environmental impact compared with the hard protection methods. A higher order Boussinesq model for breaking and non-breaking waves is extended in the swash zone and is coupled with a porous flow model, in order to take into account the influence of infiltration-exfiltration processes in the sediment transport. This influence is introduced in a simple and well-proven sediment transport formula by using a new modified Shields parameter, which is derived after the modification of the shear stress and the immerged sediment weight. In order to incorporate the suspended sediment transport rate, the depth-integrated transport equation for suspended sediment is solved. Model results are compared with experimental data. The agreement between numerical simulations and experiment is quite satisfactory. It is concluded that the beach drainage method is efficient for shore protection from erosion.