EXPERIMENTS ON SCOURING BEHIND COASTAL DIKES INDUCED BY TSUNAMI OVERFLOW

Abstract

2011 Great East Japan Earthquake Tsunami destroyed many coastal dikes located along the Pacific coast in Tohoku Region. From many field observations, it is found that most of the damages of coastal dikes were caused by scouring at a landward toe induced by the tsunami overflow. Characteristics of scouring around the landward toe of coastal dikes were discussed through hydraulic experiments. Bed shapes and water levels were detected from video images, and two types of flow patterns were observed; hydraulic jump and submerged flow. The flow types strongly affected the scouring processes resulting in significant differences of scouring depths. Relation between overflow heights and scouring processes was also discussed in this paper.