Author(s): Jun Okuda; Yasuyuki Shimizu; Tomoko Kyuka; Toshiki Iwasaki; Yoshiaki Ishida
Linked Author(s): Yasuyuki Shimizu, Tomoko Kyuka
Keywords: Flood disaster; Levee breach; River channel migration; Inundation disaster
Abstract: There was a record breaking rainfall by Typhoon Lionrock over eastern Hokkaido in August 2016. Two levee breaches were caused by this rainfall leading to inundation disaster at Ikutora region in Minami Furano town. According to a field survey, the inundation disaster started from an upstream point at first, then the flood flow went through a flood plain and reached a downstream levee, finally overtopping to a river channel caused the second breach at downstream point. Since the flood started during midnight, a detailed explanation of the flood’s behavior and a procedure of breaches remain unclear. In this study, we have investigated the river channel deformation and the levee erosion using a 2-dimensional numerical analysis. The computed results showed good agreement with field survey data regarding the inundation area, breach points, and the river channel deformation. Especially, the starting time of the inundation in the numerical analysis agreed with expected time estimated by field survey reports. The computational results indicate that with the increase of discharge, the development of a point bar pushed the channel near the upstream of the breach point toward outer bend of the channel meander. This channel migration may cause severe levee erosion. In the same time, the water level went up and overtopping flow happened. It suggests that both the bank erosion caused by the channel migration and overtopping flow caused the large-scale levee breach. Regarding the downstream breach, the results showed that the breach was caused by an overtopping flow from the floodplain to the river channel, which was expected by the field survey.
Year: 2018