The baymouth breakwater is to protect the port area from tsunamis as well as storm waves. A submerged dike is built at the central opening section of the tsunami breakwater to close the bay mouth as much as possible. Because of narrowness, strong current is expected at the occasion of design tsunami attack. The submerged dike consisting of a rubble mound foundation and a crown caisson must be stable against the strong current. The present paper points out stability of the crown submerged caisson on the basis of the result of experiment and numerical wave tank (CADMAS-SURF/3D), and according to these results, verifies the validity of pressure coefficients calculated from hydrodynamic forces.
