Abstract
21 drainage areas were carefully selected according to 5 major geological units throughout Japan. An examination was done based on data about volumes of slope failure produced during several years period by means of repetitive airphoto interpretation. The main results obtained in this study are as follows:
(1) Volumes of slope failure production vary distinctly according to geological units. For example, granite areas product 1, 260 m3/km2/y, whereas Quaternary volcanic areas product 70 m3/km2/y. However, such volumes also vary according to duration in a same area. This fact implies that other factors including geology influence production of slope failure.
(2) Factors of topography and rainfall were then analysed to examine the relationship with volumes of slope failure production. A particular attention is paid to the following, in which the volumes have a direct relation with the ratio of relief to length of a drainage area and an inverse one with the ratio of area of less than 20° in slope gradient to the whole area, both in an exponential function.
(3) When the geologically identified data of the volumes of slope failure production and reservoir sedimentation are dealt with in a relatively long term such as a decade, both show a good positive correlation. This means that the latter could be predicted through the former in Japan as far as geology of an area is known.
