The granular rock material within a debris flow experiences jerk (change in acceleration) as it runs over a rough basal bed or collides with sidewalls. This creates a pressure – the so-called dispersive pressure – which acts to change the configuration of the granular mass and therefore the frictional relationship of the debris flow with the basal boundary. Normal pressures are no longer hydrostatic and pressure fluctuations are created in the fluid phase. In this paper we formulate relationships between internal shear work, free mechanical energy, dispersive pressure and configurational changes within a debris flow. We associate the potential energy of the debris flow configuration with dilatant kinematic motions and show why it is necessary to integrate the shear work over time to calculate boundary jerks which cannot be represented by closed-form, analytical pressure functions. The effect of the dispersive pressure is mediated by the presence of the viscous muddy fluid which consists of two types: a) the free fluid and b) the bonded fluid attached to the solid granular phase.
Debris flows and floods caused by outburst of glacial lakes have frequently occurred in the Himalaya of South Asia. The frequency of these disasters has been increasing tremendously due to global climate change. It is thus necessary to investigate debris-flow and flood characteristics due to outburst of glacial lakes in order to manage the hazards and risk in the areas. In this study, the characteristics of debris flows and floods caused by potential outburst flood from the Imja glacial lake in Nepal due to moraine dam failure by water overtopping were analyzed using developed numerical model. The numerical model was validated with the flume experimental cases. The relationship between peak outburst discharges with the volumes of lake water for experimental conditions was also analyzed. The erosion and deposition processes along the river valley were also considered in the analyses of potential outburst floods from the Imja glacial lake. Sensitivity analyses of the parameters of river bed sediment were also conducted. The predicted results of debris-flow and flood characteristics such as outburst discharge, flood arrival time, sediment concentrations, peak flow velocity and maximum flow depth can be useful for effective preventive measures, river basin management and infrastructure planning in the river basin.
A physically based slope stability model was applied to predict topographic and climatic control on shallow landslide initiation processes in mountainous terrain. We applied two simple hydrological models, coupled with the infinite slope stability analysis, to the July 2006 landslide event in Deokjeok-ri, South Korea. The rainfall predicted to cause instability in each topographic element is characterized by duration and frequency of occurrence. The incorporation of a rainfall frequency–duration relationship into assessment of landslide susceptibility provides a practical way to include climate information into estimation of the relative potential for shallow landsliding. A GIS-based landslide inventory map of 748 landslide locations was prepared using data from previous reports, aerial photographic interpretation, and extensive field work. This landslide inventory was used to document sites of instability and to provide a test of model performance by comparing observed landslide locations with model predictions. The area under curve of QD-SLaM was 0.79, which means that the overall accuracy of the landslide susceptibility is 79% and the prediction result is good.