Transition of Condition on Hillsides Terraced against Avalanche

The authors have been carryiing out a survey about the transition of condition on hillsides where the terracing works for ground avalanche prevention were executed before. This paper presents the results of investigation conducted during the period of 1963-1965 on the snowy area with maximum snow depth of 2-3m in winter.The matters deduced from obtained data are as follows : 1) The terracing work shows gradually a decline of its function against avalanche in the course of breaking of executed terracing and soil accumulation on terraced steps. However, the function of terracing lasts effectually 20-25 years on every place except.the area susceptible to erosion such as sandstone zone.2) It is estimated that natural trees on the terraced hillsides generally begin to show the function against ground avalanche from the time of about 15 years after terracing execution.