In order to investigate the processes of rainwater infiltration on fine soils, infiltration experiments were carried out under several conditions-changing dry density, initial water content, boundary condition, rainfall pattern. The transient change of degree of saturation in the experimental apparatus was detailedly measured by electric conductivity meters. Infiltration processes was verified by proposed equations on taking into consideration of influence of pore air. The results were summarized as follows : 1) The moist area being incompletely saturated and the fraction of soil pores occupied by water, being less than unity. 2) In case of the loosed compaction, velocity of the wetting front is increased in proportion to increase of the initial water content. On the other hand in case of the densed compaction, it is decreased. 3) Pore air influenced to infiltration process. But in case of rise process of the water table, influence of pore air can be neglected.
Methods to predict the peak discharge of debris flow have not been established. Peak discharge is one of the most important factors when designing debris flow control structures or estimating debris flow prone areas. A lot of data from a debris flow observatory in China are analyzed statistically and empirical equations are developed to predict debris flow peak discharge. The maximum ten-minute rainfall intensity, accumulative rainfall and density of debris flow are found major factors to control debris flow peak discharge. The empirical equations are applied to Japanese debris flows. The result shows some good agreement.