ASSESSMENT OF THE EFFECTS OF PRECIPITATION AND EARTHQUAKE ON POTENTIAL DRIFTWOODS GENERATION IN THE SHIRA-KAWA RIVER

Abstract

 In this paper, we attempted to improve the evaluation method of the potential driftwoods generation by Yano et al. (2018) in the Shira-kawa River, in which a lot of volcanic soils are included. From the results by the modified evaluation method, it is clarified that i) the potential driftwoods generation can increase with a rise of 1, 3, and 6 hour precipitation; ii) the Kumamoto Earthquake in 2016 affected driftwoods generation, and more than 70% of the total driftwoods was generated from slopes which can collapse by only earthquake; and iii) the Tateno Dam, which is a stream type flood control dam, can trap more than 85% of total driftwoods generated in the overall Shira-kawa River basin.