雲仙・水無川における土石流の流出特性と流出解析
1999 年 52 巻 1 号 p. 3-9
詳細
1999 年 52 巻 1 号 p. 3-9
After 198 years of dormancy, Mt. Unzen began to erupt in November 1990, and continued the volcanic activity until the spring of 1995. Due to the volcanic activity, a large amount of volcanic ash and stone were deposited around the mountain which caused frequent debris flows along the rivers in the volcano. Especially, in the Mizunashi river, the debris flow occurred more than one hundred times from 1991 to 1997. In 1993, the debris flow inundated the down reach of the Mizunashi river and deposited 400 million cubic meters of volcanic sand and rock. But with a peak in 1993, frequency and deposits of the debris flows decreased with declination followed by termination of volcanic activity.
In this paper, annual change in critical rainfall for occurrence of debris flow is investigated by using the threat score. A simplified runoff analysis method for debris flow is proposed and checked by the data at the Mizunashi river.
