Coastline Protection by a Submerged Breakwater

Coastal communities are in danger of the impact caused by storm surge and waves. Storm surge brings the water level to a higher elevation and farther inland. This rise in water level increases the chance of a higher number and larger set of waves approaching shorelines, and it can potentially devastate the coastal infrastructure. In this study, we evaluate the performance of a submerged, horizontal breakwater located near shore. Unlike other types of breakwaters, such as the ones that extend to the surface, either fixed or floating, a submerged horizontal breakwater does not create any visual distraction or limit most of the recreational and commercial activities in the nearshore areas. The Level I Green-Naghdi (GN) nonlinear water wave equations are utilized here to study the wave transformation over a submerged breakwater that is located in shallow water. The GN theory is based on the theory of directed fluid sheets and assumes an incompressible and inviscid fluid; no assumption on the rotationality of the flow is required. In this approach, the nonlinear boundary conditions and the averaged conservation laws are satisfied exactly. The reflection and transmission coefficients due to nonlinear shallow water waves are determined implementing two approaches which use Goda’s (1976) and Grue’s (1992) methods. The results are compared with the existing laboratory experiments, and close agreement is observed overall. Preliminary results of the performance of the breakwater on dissipating storm waves during Hurricane Ike (2008), approaching the shore of Galveston, Texas, are presented.