To estimate debris flow peak discharge and hydrograph are important for effective disaster prevention. Ikeda et al. (2007) has presented occurrence criteria of debris flow must be evaluated not only rainfall condition but also supply process of materials. At the Kitamata Valley of Name River, three debris flows occurred in 1999 as the result of landslide dam that blocked the riverbed near an elevation 1800 m in 1998. The largest debris flow of these was occurred on June 27, forming a conspicuous peak with relatively high velocity. Analyzing the occurrence situation and flow property of this debris flow by field research, aerial photograph interpretation, and CCTV camera figures, we estimate the outbreak process and hydrograph of this debris flow. Using the two layer sediment transport model Takahama et al. (2000) have developed, shape of hydrograph and peak discharge was well explained with the exception of total volume and a duration of debris flow. Also the hydrograph shows that the supply process of materials will be an outburst of a landslide dam. Moreover, comparison the peak discharge and hydrograph between the case with landslide dam and without it, the peak discharge is larger than without landslide dam, also the total volume of debris flow.

Key wordsFdebris flow, outbreak process, supply of material, landslide dam, Kitamata Valley