2016 Volume 22 Pages 339-344
The right side region of the Omoigawa River in Oyama City was seriously damaged by a flood caused by the heavy rain in Kanto and Tohoku region in September 2015. The topological characteristics and the hearing investigations to the residents revealed three factors of this flood; (1) artificial closing of the sluice gate of Oyama-Tochigi drainage channel converging to the Omoigawa River, which caused overflow into the inside area of the levee, (2) automatic closing of the flap gates to the Toyoho River (branch of the the Omoigawa River) due to rise of the water level of the Toyoho River, which caused difficult situations to drain the unprecedented heavy rain, resulting in concentration of rainwater to the lower landside area, (3) back water from the Omoigawa River, which caused overflow from the Toyoho River into this region. Flood inundation simulations were carried out, which supports these three factors, and showed that only the rain fall on to this region would have caused considerable inundation.
