THE REPRODUCTION SIMULATION OF THE INUNDATION AND THE RUNOFF IN THE NAKAGAWA SYSTEM BY TYPHOON HAGIBIS

Abstract

 Typhoon Hagibis caused the most flood damage on the Nakagawa River, which is one of the major first-class rivers in the Kanto region since the flood damage in 1986. In this study, we recorded the disaster situation and conducted field survey in the damage concentrated segment from the bank breakage and overflow. In addition, we conducted the runoff analysis for the Nakagawa River System and the flood analysis for some regions near the Nakagawa River. As a result, it is clarified that 1) the large-scale inundation (average inundation depth: 1.9m) occurred near the tributaries Fujii, Tano rivers and 2) the inundation continued for four days because the drainage capacity was not sufficient. In addition, based on the water level changes of the Nakagawa Fujii rivers and traces of the flood flow, it was inferred that the Fujii River was affected by backwater. Furthermore, the reproduction simulation, which combined the runoff analysis and the flood analysis, reproduced the inundation depth obtained by the field survey and confirmed the backwater in the Fuji River.