Author(s): Nozomi Yusa; Nanako Utsugisawa; Koyo Ota; Takehiko Ito; Yuki Ogata; Shiho Onomura; Yasuo Nihei

Linked Author(s): Takehiko Ito, Shiho Onomura, Yasuo Nihei

Keywords: Flooding; Vehicle stability; Human damage; Fluid force; Typhoon Hagibis

Abstract: In recent years, vehicle deaths, which are one of the main causes of human deaths in flood disasters in Japan become more serious. Early horizontal evacuation and monitoring of flooding around the home are important measures to prevent vehicle deaths. Although there have been many experimental studies on vehicle outflow conditions assuming that vehicles are washed away by flooding, few studies have been conducted using actual disaster conditions. In this study, we conducted river-flow and flooding simulations in the Hata River, Tone River basin in Japan, in order to clarify the flood and vehicle outflow conditions at the time of vehicle deaths caused by Typhoon Hagibis in 2019. In the river-flow analysis, a one-dimensional unsteady flow model was used to calculate the water level, flow rate, and overflow from the Hata River. In the flooding analysis, a horizontally two-dimensional flood model was used to examine the inundation situation in the urban area using a overflow condition obtained by the river-flow analysis. Flooding analysis revealed that the inundation flow proceeded in the southwest direction from the overflow point at the Hata River, and the inundation depth was 0.5 m or less at many points. However, at the point of vehicle death, a rapid increase in flow velocity and water depth was confirmed immediately after the flood flow arrived. The fluid force and frictional force applied to the vehicle body were calculated from the simulated results of water depth and flow velocity, and the vehicle outflow evaluation index was created from the difference of two forces. As a result, the time when the index became 0 at the disaster point almost was comparable to the actual disaster data. Based on this result, when a vehicle outflow risk map was created in the surrounding area including the damaged point, the vehicle outflow point was limited, and no outflow point was found especially in the east-west direction of the damaged point. From the driving recorder records, it was inferred that the route of the damaged vehicle was from a road with no risk of loss to a road with risk of loss including the damaged point, which was one of the most dangerous routes for vehicle movement during river flooding in this area. This is almost the same as the inundation depth distribution affected by the topography of the alluvial fan and the railway embankment.

DOI: https://doi.org/10.3850/IAHR-39WC2521711920221467

Year: 2022