EVALUATION OF WOODY DEBRIS HAZARD RISK REDUCTION EFFECT BY DAM AND SEDIMENT CONTROL DAM AND RISK VARIATION DUE TO BRIDGE REMOVAL IN THE YAMAKUNI RIVER, JAPAN

Abstract

 Assessment of woody debris hazard risk for all bridges in the Yamakuni River basin was conducted. Through the assessment proposed by Yano et al. (2016), the risk of historical stone bridges, variation of the risk due to a bridge removal, and the risk reduction effect of a dam and sediment control dams were evaluated. As a result, spatial change of woody debris hazard risk at bridges can be shown. In addition, it is clarified that reduction rate of woody debris by dam is about 14%, and the capture capacity 20-30% of sediment control dams can contribute to the risk reduction.