SCOUR OF SANDBED AROUND THE HEAD OF TSUNAMI BREAKWATER AT THE MOUTH OF URADO BAY DUE TO TSUNAMI

Abstract

 A large-scale hydraulic experiment was conducted in a large basin to investigate the scour and stability of the breakwater head at the mouth of Urado Bay due to tsunami. In this study, a new surveying method was introduced to precisely measure the ground height under water using a laser displacement meter. As a result, the followings were clarified. 1) The frequent tsunami caused scour hole up to 8 m in depth at the Tanezaki breakwater, resulting in scattering of rubble mound, armor blocks and sliding of caisson. 2) The largest tsunami caused severe scour and caissons to roll and move more than 50 m. 3) The scour around the head of the breakwater is estimated to be caused by the fast flow from the surface layer outside the harbor to the bottom layer inside the harbor.