INFLUENCE OF FLOODING FROM A TRIBUTARY ON INUNDATION CONDITIONS IN A CASE OF LARGE-SCLAE FLOOD IN KAKEHASHI RIVER

Abstract

 In Japan, the flood management plans for the main sections of first-class rivers are formulated for rainfalls with return period from 100 to 200 years. On the other hand, for other than the main sections, the flood management plans are designed for smaller scale rainfalls. In the case of large-scale heavy rainfall in a wide area, the risk of flooding is higher in tributaries. In the flood inundation area maps produced by the Ministry of Land, Infrastructure, Transport and Tourism (MLIT) and local governments, inundation of tributaries is not considered, and the risk of large-scale floods may not be properly expressed. In this study, an inundation simulation model was improved to express flooding from both a main river and a tributary. The model was applied for the Kakehashi River Basin in Ishikawa Prefecture, Japan, and its tributary Hatcho River. The influence of the levee breach in Hatcho River was small for the maximum inundation depths. On the other hand, the inundation duration time was prolonged more than 9 hours in wide area when levee breaches occur both in Kakehashi River and Hatcho River.