NUMERICAL SIMULATION ABOUT IMPULSIVE FORCE ON A HOUSE BY TSUNAMI-DRIVEN WOODY DEBRIS FROM COASTAL FOREST Ichitsura Suzuki

One of the advantages of coastal forest against tsunami inundation is to reduce fluid force behind forest. However, the coastal forest also has a disadvantage to increase the damage to people and buildings because it produces floating debris when the trees are broken and washed out. The advantage and disadvantage are usually pointed out but have never been compared quantitatively. The tsunami caused by the Great East Japan Earthquake on 11 March 2011 passed through coastal forest with breaking trees and washing out trees. The coastal forest in Sendai Plains in Miyagi Prefecture could be assumed to reduce the tsunami force behind forest but it also produced much driftwood and could increase the impact force on houses. Therefore, in this research, the numerical simulation model including the judgment of tree breaking and washing out condition, motion of trees after the washout, and collision of houses has been developed and the influence of the driftwoods on houses was analyzed. For the tsunami-driftwood interaction model, two-dimensional non-linear long wave equations and the equation of motion for driftwoods have been combined