In our country, many peoples are killed and many houses and fields are destroyed by Debris flow every year. So they request to do the countermeasure for Debris flow, but dangerous torrents are too much (more than 62000 torrents), so that it can not execute the countermeasure with civilengineering works for each torrent soon. Then it is need for the social countermeasure such as establishment of refuge system and control of land use. Especially for such countermeasure, it is important to know the hazard area of Debris flow. Usually Debris flow hazard area is studied with empirical and theoritical way, but it is difficult to generalize the hazard area by only such studies. Then author studied on the Debris flow hazerd area experimentally. In this paper, author made clear the followings ; (1) Experimental method is favorable as regards evaluating the effect of geomorphological condition in Debris flow deposit zone. (2) Side step phenomena causes in some geomorphological condition and deposit length of Debris flow changes by that phenomena. (3) Sediment volume of Debris flow has an upper limit and that value is able to be estimated. (4) Debris flow has a harmful effect on the human life compared with Sediment flow.
By estimating the age of deposits with the instrument of the ages of trees which stand on the deposits are by measuring the yearly quantities of deposits, the auther studied the life of deposits and the characteristics of bed load movement, deposition and removement. The results are as follows ; (1) In conformity with destribution of ages of deposits the channel can be divided into two characteristics zones, deposition zone and transportation zone. (2) The survival time span of deposits, that is the time span which the deposits have remainedd unmoved in situ, is estimated by the age of the daposits. This survival time span corresponds to the difficulty of bed load removement. (3) The deposit survival time span in years T is related to the accumulaled quantity, per 1km, of deposits through T, QTa/l and is expressed as log(QTa/l)=α log T+β The coefficient α is thought as an index which stand for the stage of desolation. (4) The ratio of accumulated quantity of 100 years Q100a to that of 1 year Q1a represents the degree of basin desolation : the smaller Q100a/Q1a the greater is the degree of basin desolation. (5) Values α, β and Q100a/Q1a are considered to be effective indice for comparing different basins in their characteristics in bed load movement as well as for planning sabo-projects.
A simulation model is built applicable to sediment transport in a torrent. Water contained in deposit on a torrent bed is considered in the equation of continuity since the sediment concentration is often high. Water flow into the torrent channel is calculated from rain falling on the slope, using hydrological analysis. The Meyer Peter-Müller equation is chosen as the sediment transport equation since it is comparatively fit to the experimental results in the transition region between bed load tran-sport and debris flow. This model was examined on the basis of observed changes in deposits on torrent beds during a flood. The kinematic wave run-off model was used as hydrological analysis after it was tested by the results of the observation of stream flow. The model for sediment transport could be applied well to one torrent, but in the other torrent, the calculated value of sediment discharge was much less than the observed value. It appeared to be due to the occurrence of a very large debris flow. Calculation by Takahashi's equation for sediment concentration of debris flow was made for the latter. Although the value of sediment discharge was neary equal to the observed value, the fact that the deposits on the bed were eroded throughout its profile could not be explained by the calculation. This model can be applicable to the case that deposition occurs at the concave sections of the torrent bed profile and erosion occurs at the convex ones. The case of bed load transport and that of small debris flow seem to be simulated under this model.
At the first flood in 1981, the falling water from a sabo dam made an abnormal noise and a tremor. Since the people living downstream were suffered for them and complained about them, Etsumi Sabo Work Office at the basin took steps with them. In this paper the situation of noise and treatments are reported. The results of the frequency analysis of the noise are also shown.