1999 Volume 51 Issue 5 Pages 19-27
Hydraulic properties of forest soils, the hydraulic conductivity, K, -pressure head, ψ, relationship and the volumetric water content, θ, -ψ relationship of forest soils, influence the transient process of storm water in the sudace soil layer on the mountain slope and occurrence of hillside landslides. In this study, to estimate influence of forest soils on mountain slope stability, numerical simulation was executed with the vertical infiltration experiment results, hydraulic properties of forest soils, to the Tsuchisawa basin where many hillside landslides occured in 1969. The typical results were as follows:(1)The surface soil layer on the mountain slope have a function of the shock absorber against storm water infiltration to the bed rock. (2) Forest soils have the control function against occurrence of hillside landslides and the water recharge function. Furthermore, regarding satisfactory forest as erosion control facilities, influence of slope shapes on the control function against occurrence of hillside landslides and the water recharge function of forest soils was estimated using the model for predicting hillside landslides, to find criterion for the proper arrangement of forest. It was clarified that it was more effective to arrange satisfactory forest in convex and parallel shapes than concave shapes in order to demand maximum effects of forest. In the future, it is necessary to examine appropriateness of these results obtained by this study and research into a limit of these functions of forest soils.
