Attempts have been made to evaluate some rainfall characteristics related to outbreaking time of disasterscaused by debris movement. The procedure and the results are as follows: 1. Several discharge records were obtaind in a small catchment (17.6 ha) in Rokko hilly mountains consisted of weatherd granite. 2. The set of parameters of Tank Model method, the simulation model of this catchment, was determined. 3. Some hydrographs of the experienced disasters in Rokko hilly mountains were calculated from their hyetographs by this model. 4. In this calculations, water stored depth in the first and second tanks and the discharge rate were related to the critical condition of disaster outbreaking. 5. The method was applied successfully on the analyses of disasters in Shodoshima Island (occured in 1974 and 1976) and in the watershed of Niyodo River, Kouchi Pref. (occured in 1975).
Some effects, which the existence of suction has upon shear strength and the transmission of pore pressure in clay beds, are considered in this paper. Shear strength becomes strong on account of existence of suction, but a drop of shear strength becomes remarkable when clay loses suction owing to contained water. The transmission of pore pressure is approximated by the equation of thermal conduction into which suction is introduced as negative pore pressure. Suction delays an appearance of positive pore pressure and makes pore pressure smaller, but it increases the quantity and the rate of increase of pore pressure. Further, if Darcy's law and other some assumptions are set up, swelling strain can be explained, too.