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Estimation of Tsunami Force Reduction and the Breaking Mode of Coastal Trees Applicable to Coastal Forest Management as a Bioshield

Author(s): Norio Tanaka, Hajime Sato, Yuta Akasaki, Hiroyuki Torita

Linked Author(s): Norio Tanaka

Keywords: Ecosystem-based disaster risk reduction, coastal forest, fluid force, management of coastal forest, stand structure of trees

Abstract: The effectiveness of coastal forests to mitigate tsunami has received increased attention since the 1998 Papua New Guinea tsunami, the 2004 Indian Ocean tsunami, and the 2011 Great East Japan tsunami. When a large tsunami attacks the coastal forest, many of the trees were broken or overturned. For estimating the effectiveness, it is important to reproduce the forest breakage situation numerically. The objective of this study is to improve two-dimensional nonlinear long-wave equation model including the tree-breaking mode in detail considering the stand structure of trees, to demonstrate the energy reduction effect even when forest is broken, and to utilize the information to manage the coastal forest properly. In this these regards, two locations of coastal forests in Shiranuka and Taiki Town, Hokkaido, Japan were selected. Numerical simulation demonstrates that a tree whose crown is high from ground tends to be broken at the tree trunk when root anchoring strength is high. Pine trees and broad-leaved tree (Quercusdentata) tend to be overturned and broken at the tree trunk, respectively, at the two study sites. In addition, even when the trees with dense crown are broken, they contribute to resist tsunami to some extent. The reduction of fluid force is changed changes not only with the forest thickness but also with the tree species and the destruction mode. To maintain the fluid- force reduction and to reduce secondary damage by driftwood, large diameter trees at the landward side of forest can be planted to trap the driftwood produced

DOI:

Year: 2017

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