Experiments in a model channel have been conducted with respect to the motion and stopping conditions of floating logs in torrents. The formulas were obtained for calculating to determine the boundary between the start and stop of motion for floating logs on torrent bed. The passage and stop of the floating logs at narrow passes are also reviewed experimentally. The floating log capture ratio T at narrow pass can be calculated by the following equations: T=1. 0 where Fr·≤0. 1 T=log(1/Fr·θ) where 0. 1<Fr·Θ<1. 0 T≅0 where 1≤Fr·Θ} where, Fr is the Froude number, Θ=hw2/dl2, h is the water depth immediately upstream of narrow pass (m), w is the width of narrow pass (m), d is the diameter of floating log (m) and l is the length of floating log (m) . The results of surveys for the actual situation of floating logs accompanied with and generated by debris flows have been compiled, and criteria for calculating the number, volume and size of floating logs generated and flowed are proposed. The maximum volume of floating logs generated per 1km2 of catchment area υga(m3/km2) can be estimated from the equation υga=200/A, where A is the catchment area (km2) of a torrent. The maximum volume of floating logs generated in a torrent υg (m3) can be estimated frome the equation υg=0. 02Vy, where Vy is the volume of yield sediment (m3) .
In the present investigation, the exist of the Manning's equation for the flow velocity in small rill has been examined in relation to the V-shape and U-shape of rough surface fixed-bed rill models. We have conducted the laboratory system models for the flow hydraulics study, especially, we have focused at the velocity factor. Our collective results provided the extend knowledges on the characteristic of the flow hydraulics in small rill that it is supercritical and transitional range. Interestingly, the exponent in Manning's equation is likely existed for the exponent in formula of rill U-shape but, however, there is limitation in rill V-shape. Furthermore, we have found that in contrast to the good correlation between friction factor (f) and Reynolds number (Re) value of rill V-shape, the rill U-shape showed the inverse correlation of this both value that f decreased while Re increased. The exist of the Manning's equation in the rill U-shape and the limitation in rill V-shape might be explained by the different correlation of the mean velocity (Vq) and surface velocity (Vs), f and Re values occur in both different rill-shapes.