Estimation of Tsunami Wave Force on Collapsed Coastal Dyke in the Ryori Bay

Abstract

This study aims at the estimation of tsunami wave force due to the 2011 Tohoku earthquake tsunami. Field survey in Ryori, Iwate Prefecture, suggested multiple mechanisms for the collapse of 8.6 m high coastal dikes. Numerical tsunami simulation based on the nonlinear dispersive wave theory revealed the concentration of tsunami-induced flow to the northern area which is considered to develop severe scour of the foundation. The model also simulated the large wave force was exerted to the dike due to the tsunami overflow as well as the impulsive breaker force due to 10m high short period wave generated at the wave front. The estimated wave force was consistent with the collapse of the parapet observed in the field study.