ASSESSMENT OF WOODY DEBRIS DISASTER RISK AT ALL BRIDGES ALONG THE KAGETSU RIVER ACCORDING TO ITS GENERATION POTENTIAL CONCEPT

Abstract

 Recently, many big floods and soil disasters have occurred in Japan due to heavy rainfall events. Also, we can see a hazard due to woody debris in the events. In the present paper, we propose a concept of “drift woods generation potential.” The potential is defined by empirical formula with data set of geography and woods. It can express the maximum possible generation of woody debris at a given point in a river. We attempt to adapt this assessment to all bridges along the Kagetsu River, Oita. From the results, it was confirmed that this concept was able to express the actual woody debris accumulation on a few bridges which were affected by them in the Northern Kyushu Rainfall Event 2012. In addition, a change of the risk due to reformation of a bridge can be evaluated by this method.