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Indices for Evaluating the Breaking and Wash-Out Condition of Trees on Gravel Bar at Flood Events

Author(s): N. Tanaka; J. Yagisawa

Linked Author(s): Junji Yagisawa, Norio Tanaka

Keywords: No Keywords

Abstract: Rehabilitation of gravel river bed and the removal of trees have been discussed recently for increasing flow capacity and the biodiversity in a river habitat. For elucidating the possibility to maintain the river habitat as a gravel bar by natural flood, tree breaking and wash-out situation after two flood events were investigated with different location on a gravel bar in the Arakawa River, Japan. Two-dimensional unsteady depth-averaged flow model was applied to the river. Threshold drag moments and shear stresses at bed for washing out the representative trees were evaluated. Shear stress was more suitable than the drag moment for expressing the wash-out situation. The dimensionless shear stress of d84 (τ*84) can evaluate the wash-out situation more accurately than the dimensionless shear stress of d50 (τ*50). Using the information, optimal indices for evaluating the breaking and wash-out condition of trees on gravel bar at flood events are proposed.


Year: 2009

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