Slope failure and land-slide as geologic hazard have been studied in numerous districts up to the present based on the examinations of both the topographical and geological environments. Concerning debris flows, on the other hand, only a few researches have been reported from the same viewpoint. This is because the debris flow has been occurred in the relatively spreading space-time regions concerning topography and geology.
In this paper, debris flows occurred in Rokko district on July, 1967 were examined in detail based on the concept of “drainage system”from topographical and geological viewpoints. The results clearly indicate that the debris flow occurs at the null order streames and develops downstream systematically to the higher order one.