STUDY ON MECHANISM OF FLOW AND DEPOSITION OF DEBRIS-MUD FLOW

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(1) Profiles of concentration and velocity of mass movement of bed load type.The mass movement of bed load type was treated as a two layr flow. To the under layr high concentration, equations of force balance were set in flow and its vertical direction. The averaged concentration and velocity distribution were derived from these equations. The depth of the under layr was estimated by using empirical equation. In the upper layr, equation of velocity distribution was derived from the force balance in flow direction. The velocity profile of whole flow was given by integrating velocity distribution of each layr. From these results, equations of velocity coefficient and concentration of flow were obtained. The validity of these equations were examined by comparing with flume data.(2) Sediment transport rate.By using equations mentioned above, equation for sediment transport rate was derived. This new equation coincides with that of debris flow on steep channel, and is similar with conventional bed load function on very mild slope channel. These facts suggest that the new equation is applicable in the wide range from bed load to debris flow.(3) Simulation of flooding and deposition.Simulation method by using equations of flow resistance and sediment transport rate was proposed. This new method was applied to the Mizunashi River in Unzen Volcano to estimate the hazard area due to debris flow. In the simulation, the upper boundary conditions were calculated from the hydrograph obtained by using runoff analysis of neural network. New equations of sediment transport rate was also used in the simulation. The simulated results show good agreement with the field data. By this method, estimation of hazard area for a given rainfall is possible.