Abstract
A lot of slope failures were generated by Typhoon No.17 in 1976 and Typhoon No.10 in 2004 in the upstream of the Nakagawa River located in southern Tokushima Prefecture. Shallow slope failures were generated in Typhoon 200410 while deep slope failures were generated in Typhoon 197617. In this study, the maximum value and time series of subsurface water storage on forest slopes were estimated using a distributed runoff model, and the reason why the form of slope failure is different was discussed. We found that: (1) the collapsing forest slopes have large capacity of subsurface water storage. (2) the ratio of groundwater storage to soil water storage became large on the slope where a deep collapse was generated. (3) the ratio of soil water storage to groundwater became large on the slope where a shallow collapse is generated. (4) rain-fall intensity and its waveform are related to the generation form of slope failure, too.
