Some of coastal structures were collapsed owing to the local scouring by overflows after Tohoku tsunami. In order to understand the characteristics of the scouring behind seawalls due to tsunami, experimental studies and numerical simulation were carried out. The sour profiles formed behind a seawall could be classified into two types. The turbulent kinematic energy has effects on the development of the scour hole. The kinematic energy will decrease with an artificial trench behind a seawall. The rate of energy decay depended on the scale of trench not the shape.

After a mega earthquake occurred off the Pacific coast of Tohoku region in Japan, some of coastal structures were collapsed owing to the local scouring by overflow from seawalls. In order to understand the characteristics of the scouring behind seawalls due to tsunami, experimental studies and numerical simulations were carried out. Also tsunami energy damping was estimated by artificial trenches. As soon as overflow starting, the local scouring profile reached 80% of the maximum profile in a short time. Turbulent energy and dissipation distribution had effects on development of scouring. A trench can reduce tsunami energy, but the differences of tsunami energy damping due to shapes of the trench is small.

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