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

沿着、山脚天然林已被用作洪水和泥石流灾害的防治措施。近年来，人们从自然环境的角度来关注森林的作用。本文主要研究结果如下：（1）在全宽设置圆柱体的明渠中，研究了床沙和悬移质的输沙率。圆筒在床上等间距地交错放置。用有效摩擦速度测量了它们的输运速率，结果与无圆柱时的结果一致。(2)在明渠中测量了模型木材的单个圆柱体上的拖曳力。结果表明，在模型树林中单个圆柱的阻力系数比无树林均匀流中的阻力系数大。(3)利用泥石流灾害报告资料，研究了树木折断的临界条件。

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.