Geomorphological processes due to intermittent sediment movements such as land slides and slope failures

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A mathematical model is proposed to describe the channelization on slopes composed of weakly cohesive fine sediment. The analysis is extended to include the case of slopes with arbitrary shapes. The spacing of incipient channels is found to be on the order of 1000 times the Froude critical depth of surface sheet flow. A mathematical model of channel bifurcation is also proposed. The analysis reveals that channel heads become unstable and channel bifurcation takes place when the discharge decreases. The results are found to be consistent with observations. The formation of channels due to seepage erosion is studied experimentally. It is found that governing parameters are discharge, slope and seepage layer thickness and that the spacing increases with those parameters.A liquefaction analysis for capillary zone above ground water level is developed based on porous media theory with three phases. Simplified governing equations are derived with the assumption that the relative acceleration of pore fluid with respect to soil skeleton is small. The proposed method can reproduce the tri-axial test results well when the degree of saturation is larger than about 70%. The numerical results show that liquefaction occurred in the capillary zone when the initial saturation degree is about 60% and over.Hydraulic gradient was analyzed by infiltration analysis with consideration of snowmelt. The probability and the road damage in the Tohoku region are shown in maps with 1 km resolutions. These maps show spatial-temporal risk distributions of sediment hazard due to some snowmelt conditions. We also focus on the influence of dam reservoirs to cause excessive sediment disasters due to anomalous weather conditions by global warming. Results of this study conform that the sediment hazard probability model performs well to predict macro scale sediment storage in dam reservoirs.