The 2015 Flood Impact due to the Overflow and Dike Breach of Kinu River in Joso City, Japan

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Heavy rainfall in September 2015 inundated the Kinu River basin and caused an overflow and dike breach of the river in the eastern part of Joso City, Ibaraki Prefecture, Japan. The area, which is bounded by the Kinu and Kokai Rivers, experienced deep inundation of more than 2.5 m, which continued for more than 3 days at the maximum level. Although the estimated maximum inundation depth and duration were basically related to the elevation and distribution of topographic surfaces, strong flood flow washed buildings away near the overflow and dike breach sites and caused deep inundation even though these sites were located on a relatively higher natural levee. In addition, serious damages such as interruption of emergency transportation routes and deep inundation over floor level occurred, isolating evacuation centers and important facilities including a municipal hall and hospitals. Few residents utilized the pre-prepared flood hazard map or understood the local geography, and evacuation orders were not fully transmitted to the local residents, which might have increased the flood’s impact.