Water/Sediment Two-Phase Flow Relating to Natural Disaster

Multi-Phase flow is often related to natural disasters. Especially large flows cause drastic geomorphic changes and can lead to catastrophy in downstream areas. Debris flow is a typical two-phase flow in such phenomena. In this paper, the authors explain the behaviour of debris flow obtained by observations and experiments. A consititutive equation for debris flow is developed by considering the mechanism of energy dissipation in the flow of the mixture of water and sand particles. The consititutive equation is applied to discuss the distributions of velocity and particle concentration in uniform debris flow. The authors describe the characteristics of two-phase flow in catastrophic events by taking such examples as the Mt. St. Helens eruption, Mt. Asama's eruption and the Mt. Ontake land slide.