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Understanding Trapping of Debris by Coastal Bioshield: A First Step into Modelling Debris Movement and Trapping

Author(s): Rowan De Costa; Norio Tanaka; Yoshiya Igarashi; Naoki Yamazaki

Linked Author(s): Norio Tanaka

Keywords: No Keywords

Abstract: Tsunami creates many debris. Previous research has shown that even though coastal forest produces driftwood, the benefit of a coastal forest and its capability to reduce the tsunami forces outweigh the negative aspect of the force of driftwood colliding with the houses. Therefore, this research was conducted, as a first step, to understand how driftwood gets trapped by a downstream forest. This study showed that there are four ways that a debris gets trapped in a coastal forest and each trapping type exhibits a different force on the tree trapping the debris. A trapping type where the debris collides with the trunk and rotates about that trunk exhibits high force on the trunk, because of the high cross-sectional area against the flow, compared with the other trapping types. However, this study also showed that if the debris’trunk height is small, then the occurrence of this trapping type, that produces the highest force, decreases. That said, if the coastal forest, designed for trapping, is designed such that the tree can handle a high moment force before breaking, then this type of trapping can provide a benefit in that it can increase the energy reduction of the tsunami flow by having a higher drag force.


Year: 2018

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