Counter Measures for Debris and Flood Flows Disasters by Using Natural Woods

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Natural woods along the rivers and at the base of mountains have been used as the counter measures for flood and debris flows disasters. Recently, the roles of woods is noticed form the point of natural environments. It is important in river management work to take into account the influence of trees in the flow.The results obtained in this study are as follows :(1) Transport rate of bed and suspended loads were investigated in an open channel with cylinders installed across the whole channel width. The cylinders were placed in stagger with their equal spacing on the bed. Measurements of their transport rate agree with that without cylinders by using effective frictional velocities.(2) Drag forces on a single cylinder of the model woods was measured in this open channel. It is found that drag coefficient of a single cylinder in the model woods becomes larger than that in a uniform flow without woods.(3) Critical conditions for break of trees were investigated by using the debris-flow disaster reports.