TSUNAMI MITIGATION EFFECT BY LOCAL SCOURING BEHIND COASTAL EMBANKMENT AND COASTAL FOREST

Abstract

 The Great East Japan Tsunami destroyed the coastal embankments because of local scouring behind embankment induced by tsunami overflow. Generally, tsunami attacks coastal area two or more times, and secondary tsunami wave is sometimes larger than first wave. The mitigation to the secondary wave of tsunami is important. However, the effects of coastal forests and local scouring behind coastal embankment on secondary tsunami wave have not been clarified. The objective of this study is to investigate the effects of coastal forests and local scouring on tsunami wave. From experimental results, the maximum water level increased on local scouring for effect of damming-up by tsunami flow mitigation of local scouring. On the other hand, the force acting on tree increased for effect of increase of water level. The numerical method was validated as compared with the experimental results. The KK-scheme has good reproducibility compared with the general up-wind scheme. Then, the numerical simulation of real scale based on non-linear long wave equations was carried out using the KK-scheme. There is not so much difference of the maximum water level by the existence of local scouring. The arrival time of tsunami has difference by the existence of local scouring.