The tsunami of the 2011 Great East Japan Earthquake was higher than tsunamis that had been estimated for tsunami disaster management in each area damaged by the tsunami, resulting in catastrophic disasters. The tsunami flowed over coastal defense facilities such as a levee and dike, and flooded coastal areas widely. Further, it caused not only destruction of buildings and infrastructures, but also much debris such as ships, boats, cars, logs and others. We should predict and understand what may happen if tsunamis hit an area of interest, in order to prepare well for disaster management. Based on lessons learned from the 2011 Great East Japan Earthquake, tsunami hazard estimation has been conducted and prepared for largest-possible tsunamis. Since largest-possible tsunamis may flow over coastal defense facilities in a similar way to the 2011 Tohoku tsunami, we need to investigate and develop solutions to reduce effects of such a high tsunami.
At present, tsunami hazard estimation is commonly conducted with horizontally two-dimensional numerical simulation models in which the hydrostatic pressure is assumed. However, the hydrostatic pressure assumption cannot be applied for tsunamis interacting with structures and transforming into undular bores. It is well known that the undular bore causes higher water surface elevation and wave pressure than a tsunami that is not the undular bore.
The Port and Airport Research Institute has been developing a numerical simulation system for estimating inundation and debris motion induced by storm surge and tsunamis, named as the Storm Surge and Tsunami Simulator in Oceans and Coastal Areas (STOC). The STOC system includes a three-dimensional model in which the hydrostatic pressure assumption is not applied. This report will introduce improvement for increasing accuracy after the previous report in Reports of PARI in 2005, and development for calculating wave breaking and tsunami-induced debris. Model verification and validation are also conducted through comparison with results of hydraulic model experiments and application to actual damage by the 2011 Tohoku tsunami.