Optimal submergence of horizontal plates for maximum wave energy dissipation

Rubble-mound breakwaters are widely used for beach protection and generate shelter zones in the water, although their feasibility diminishes as water depth increases, due mainly to construction costs. In this paper an alternative structure, a fixed submerged horizontal plate, is tested in the hope that such a design may be a practical engineering option for the protection of small ports and marinas, and/or providing a sheltered zone for recreational purposes. The interaction of irregular unidirectional-waves with the plates was studied using CADMAS-SURF software and validated experimentally. Several non-dimensional parameters were tested in order to evaluate their contribution in dissipating the incoming waves. Results suggest that energy loss depends to a large degree on the combination of the relative depth, wave steepness, relative thickness, relative length and relative submergence, with the last being the most important, as it significantly affects the wave-plate interaction. The plate produces greatest dissipation when placed at a depth of 3% of the water column. It should therefore be deployed near the surface and in regions with low tidal range conditions. Plate lengths of 20% of the incoming wavelength and a relative thickness of 0.08 are recommended to produce greater energy dissipation with lower transmission and reflection.