Japan-China Joint Research on the Prevention from Debris Flow Hazards

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Mechanisms of occurrence and flow in the channel of the viscous debris flows have been studied. In the Jiangjia gully which is the field of the Donchuan Observational Station in Yunnan, China, the debris flows were observed several times in these three years and the conditions to generate viscous debris flows were compared to those of the Japanese stony debris flows. The conspicuous characteristics of the viscous debris flow is its intermittency and the reason for appearance of such behavior, apparent period, velocity, etc. were discussed by the observational data.The apparent viscosity and the coarse particle sustaining mechanism in the viscous debris flow were theoretically discussed and the vibrating interstitial viscous fluid flow produced by shearing the debris flow material was discovered to play the major role. The constitutive equations thus introduced were proved by the laboratory flume experiments. A possible mechanism for the intermittency of the viscous debris flow was suggested.The data of 818 Japanese debris flows and 269 Chinese debris flows were collected and stored in the newly constructed data base. Using those data the occurring conditions of the debris flows in Japan and in China were compared and the volumes of the run off sediment due to respective debris flows were correlated to the basin areas, landslide volumes, the maximum flood discharges, etc.. Some empirical formulae estimating the volume of a possible debris flow in Japan and China were proposed.The general idea for mitigation of the debris flow hazards both in Japan and in China was discussed in the opportunity of the several field visits. Some differences were made clear. A structure which separates water from the debris flow and thus stops the debris flow was introduced. The feasibility tests of this kind of structure were done in the actual basins in Japan and proved to work well for the case of the stony debris flow.