Ground Avalanche Prevention Function of Broad-Leaved Young Stand

Abstract

The function of broad-leaved young stands to prevent the occurrence of ground avalanche was analyzed by aerial photograph and field survey on the forest land in the basin of the River Uono, Niigata prefecture, northern central Japan, where the normal snow depth in winter was about 3 m. Result of the study is as follows :
1) On the coppice land where no trees can overtop the snow cover, snow cracks occur on the slopes with the inclination angle of 25 degrees or so. Ground avalanches begin to occur on the slopes of about 27 degrees. On the slopes of 30 degrees or more ground avalanches occur almost usually.
2) On the broad-leaved young stands with the height of 2-5 m above the snow cover and the diameter of 2-5 cm at the snow surface, it is estimated that the stands with the density over 200 coppicelike stumps per ha or so on the slope of 30 degress, 500 stumps 35 degrees and 800-900 stumps 40 degrees respectively, show the function against ground avalanche.
3) It is concluded from the findings above mentioned that the distribution of dangerous site for ground avalanche could be defined on the whole by the aerial photograph pictured in the snowy season.