Experimental Study on Scouring of Land behind Seawall due to Overflowing Tsunami

In March 11th 2011, Tohoku off Pacific Ocean Earthquake Tsunami damaged the coastal area seriously. Some of coastal protection facilities such as breakwater, seawall, etc. were destroyed by scouring due to overflowing tsunami or draft wave of tsunami. If a tsunami exceeding the design wave height hits the seawall, it is considered that the seawall loses the supporting ability of the land behind it, and it slides or falls. When seawall loses its function due to sliding or falling, it is considered that second wave and third wave of the tsunami reach aboveground, and cause serious damages. Therefore, it is necessary to investigate scouring of land behind seawall due to overflowing tsunami. This study investigated scouring due to overflowing tsunami by the experiment using the seawall model in a newly developed Tsunami and Storm Sure Reproducing Channel (45m * 4m* 2m). Experiments were performed by using solitary wave that push the wave plate forward at a stroke to generate a single large wave, and long waves that are generated sinusoidal waves by moving the wave plate back and forth. The seawall model (4m * 15cm * 5cm) is a scale of 1/50. There is sand ground behind the seawall model of 6cm in depth,60cm in length, 4m in width. The scouring phenomenon of land behind seawall was investigated by measuring the sand ground after generating tsunami.