Prediction of the hydrograph of a debris flow

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This study aims to present the methods to predict the hydrographs of debris flows in an actual mountain stream.First, a system of equations with which to predict the hydrograph of a debris flow at an arbitrary position in a channel whose bed varies in slope, width and thickness and is composed of a graded mixture of particles is presented. This system not only can be used to estimate the hydrograph of a debris flow under an arbitrary water supply but to determine the change in concentration of particles in the flow by separating them into coarse and fine components. Application of this system of equations to laboratory experiments and to the huge mud flow generated by the eruption of the Nevado del Ruiz Volcano in Colombia proved that it is a useful prediction method.Second, the deformation of the debris flow hydrograph observed in the channel of the Shiramizudani, a branch of the Gamada River, Japan, was compared with the kinematic wave theory. The result of observation showed large attenuation of peak discharge down the channel and this was successufully explained by the theory.Third, concerning with the debris flow genarated by the collapse of a natural dam, a series of laboratory experiments were done. The equation presenting the criterion whether a natural dam is formed in a channel was given as a relation between the slope of the channel and a function of the sediment volume and the stream discharge per unit width. There were two different processes in the failure of the natural dam in experiments and the peak discharge produced by the collapse of the dam in each case was different. The theoretical analysis of these processes should be done later.