Method for determination of the hazardous area due to sefiment runoff

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This study aims to present the methods to predict the hazardous area due to sediment runoff, which will be used to determine the areas to be evacuated or prohibitted to live.In respect to the prediction of the quantity of sediment runoff, a seepage flow simulation method which is usable to predict the time and place of occurrence of landslides is preseeted. Scale and form of a natural dam produced by the inflow of slided sediment into the stream channel and the hydrohraph of a debris flow which is generated by collapse of the natural dam are discussed. These discussions together with so far presented debris flow hydrograph prediction method will be made good use in determining the quantity and quality of sediment runoff in the hazardous zone delineating processes.Numerical simulation methods to predict the flooding and deposition of debris flow and mud flow are given. The applicability of these methods are proves by analysing the actual Horadani debris flow and Mt. Nevade del Ruiz huge mud flow as well as the laboratory experiments. As the hazard due to the erosion of the debris cone thus produced and redeposition downstream is another important problem to be taken into account in the hazard risk assessment, a numerical simulation model is developed. A method which can predict the particle size distribution on the surface as well as inside of debris fan is also presented.