Abstract
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) .
