A solitary wave almost halves its propagation speed passing over a submerged breakwater for coast defense. This is the basic assumption made by Filianoti & Piscopo (2008) for their calculation of horizontal wave loads on the breakwater. They calculated this slowing down, through a BEM model, on assuming that it has the same value both for a periodic and a solitary wave. Once estimated the speed slowing down, it is straightforward to obtain solitary wave loads thorugh the calculation of the Froude-Krilov force. Laboratory tests carried out on a small scale model of submerged breakwater interacting with solitary waves, permit us to experimentally reproduce the phenomenon, to check whether the speed slowing down exists, and to measure it.
Tsunamis are catastrophic natural events which act globally. Indeed, unlike other calamities (floodings, heartquakes, volcanic eruptions etc.), which act locally or regionally, tsunamis (and their effects) travel thousands of kilometers away from the generation area. The implementation of an early detection and real-time reporting of tsunamis in the open ocean, such as that realized by the American NOOA, is perhaps the only way to face a global issue on a global scale. However, in the more developed coastal areas, where to prevent economic losses is so important as to save life, it is necessary to adopt more articulated defensive strategies. The first defense line against tsunamis is formed by detached breakwaters. The use of artificial reefs in front of bays has proved to be one of the most effective systems to reduce tsunami damages in several Japanese ports (Hiraishi et al., 2000). The study of solitary wave loads on a submerged rectangular barrier was carried out by Dong & Huang (2001) [HD01, hereafter] and Filianoti & Piscopo (2008) [FP08, hereafter].