Simulation of landslide-induced debris flow - The atsumari debris flow disaster in Minamata city, Japan

Heavy rains sometimes cause landslide on mountain slopes. Some of the landslides change into debris flows and then move into mountain rivers. The debris flows erode river bed and banks, and increase their discharge. As a result the debris flows overflow the river banks and cause serious damage to houses along the river. Simulation of these debris flows lays the foundation for assessing the debris flow disaster. The present study proposes a simulation method of the development and termination of a landslide-induced debris flow. It is composed of three parts: First, the response function and runoff coefficient is introduced for a transformation from landslide to debris flow. Second, the debris flow discharge along the middle reach is estimated. Finally, the flooding process of a debris flow along the downstream reach is simulated.