Abstract
Quantitative effects of the coastal forest destruction by tsunami on the decrement of tsunami force behind the forest were evaluated for the different coastal vegetation width of Pandanus odoratissimus, and with or without including the destruction mode into the model. The analysis satisfies the previous field investigation knowledge that the critical breaking tsunami water depth is around 80% of the tree height when tree height is larger than 2m. It also shows that the critical tsunami water depth for breaking the frontal tree of forest increases with increasing forest width because of the reflection by trees. When the tree height is 2 and 4m, if the tsunami force exceeds the critical value most of the trees in forest has a possibility to be broken. However, the destruction is stopped inside forest for the case of 6 and 8-m trees, and high tsunami mitigation effects are maintained. Even when the trees are destructed at just above the aerial roots, tsunami force reduction rate are decreased by 20%, 10% for 2-4m trees, 6-8 m trees, respectively, because of the existence of dense aerial roots in case of a P. odoratissimus.
