Experimental Study on the Effect in Reducing Tsunami by the Coastal Permeable Structures

In order to understand the tsunami reduction effect of the coastal permeable structures as the coastal forest and the artificial wave dissipating structure, the hydraulic experiment is carried out. The hydraulic experiment for the tsunami of two different amplitudes with five kinds of models; mangrove, coastal forest, wave dissipating block, rock breakwater, houses, with different structure and porosity was carried out in order to measure an effectiveness in reducing tsunami disaster. Wave height, the horizontal velocity, and wave pressure were measured for each model case. The measuring points are arranged by considering the impact of the tsunami due to the existence of permeable structure, and the change of tsunami at the front and rear side of a model, and the reduction effect by model conditions was compared. Comparing with the forest case and the artificial structure case, the quantity of reduction on the forest case is smaller than the artificial structure. Although there is the reduction effect by the forest existence and the coastal forest is effective in the damage mitigation by tsunami. Experimental results suggest that the tsunami reduction effect in the water level, the flow velocity and fluid force in the structure back by the permeable structures was fully expectable.