2021 Volume 9 Issue 1 Pages 175-183
The heavy rain in July 2018 caused huge damage in the west Japan area, including Hiroshima, Okayama, Ehime, and Yamaguchi. Noro-gawa River basin in Hiroshima Prefecture was also damaged by the heavy rain. This disaster was typical of complex heavy rain coupled with sedimentation and river flooding, which is peculiar to Hiroshima Prefecture. This paper reports the influence of sedimentations and driftwoods on Noro-gawa dam and on river flooding in the downstream region of Noro-gawa River.
The main results of this paper are summarized as follows: 1) The damage in Noro-gawa dam, Noro-gawa River, and Nakahata-gawa River was enhanced by the accumulation of sedimentations and driftwoods. On the other hand, the river blockage by driftwoods at the bridge in Nakahata-gawa River induced the flooding. 2) The estimated maximum inflow discharge to Noro-gawa dam and outflow discharge from Noro-gawa dam were 179 m3/s and 173 m3/s, respectively. 3) The inflow discharge to Noro-gawa dam was estimated, excluding the influence of sediment discharge and driftwoods. 4) The estimated river discharges during the flooding were 180 m3/s at the downstream side of Noro-gawa dam, 230 m3/s at Fujinami water level observation station, and 430 m3/s behind the connection points of two branch rivers.
