THE CAHARACTERISTICS OF LEVEE-BREACH PHENOMENA AND SCOURED REGION OF THE KINUGAWA RIVER AND SOME BRANCHES OF TONEGAWA RIVERS AT KANTO & TOHOKU HEAVY RAIN IN SEPTEMBER 2015

Abstract

For clarifying the scoured characteristics around levee breaching point at the 2015 Kanto & Tohoku heavy rain, post flood survey was conducted not only for the Kinugawa River but other rivers in Ibaraki Prefecture where levee breaching was occurred, and the breaching length and the depth of the scoured region were investigated with the hydraulic parameters. Flume experiment was also conducted in a flume with 1/60 scale. The levee shape were selected as the full shape and the half-scoured levee shape. Clear water scour condition was set at the downstream of the levee. The number of scoured region for the full shape levee condition were around 5-8, and is similar to the actual situation at the breaching point of the Kinugawa River. The scoured depth for half scoured levee shape was 1.5-1.8 times larger for full-size embankment case. The breaching widths for Miyato, Nishinire, and Hachikenbori River, were relatively small, but was similar to the initial breaching width of the Kinugawa River.