Flooding Along Oda River Due to the Western Japan Heavy Rain in 2018
Yasuo Nihei*1,, Asataro Shinohara*1, Kaho Ohta*1, Shiro Maeno*2, Ryosuke Akoh*2, Yoshihisa Akamatsu*3, Takashi Komuro*4, Tomoya Kataoka*1, Shiho Onomura*1, and Ryo Kaneko*1
*1Tokyo University of Science
2641 Yamazaki, Noda, Chiba 278-8510, Japan
*2Okayama University, Okayama, Japan
*3Yamaguchi University, Yamaguchi, Japan
*4Port and Airport Research Institute, Kanagawa, Japan
The heavy rain that hit Western Japan in July 2018 triggered the worst rain-related disaster in the Heisei era, with the total of dead and missing persons exceeding 230, mainly in the Hiroshima and Okayama Prefectures. At several locations along Oda River (of the Takahashi river system) and its tributaries, dikes were breached due to large-scale flood, leaving 51 persons dead. This paper aims to shed light on the scale of inundation along Oda River and its tributaries and identify the characteristics of and critical factors for human damage. Field surveys were conducted to measure flood marks in flooded areas and river channels, and gauge the extent of damage to people and property. The surveys found that a large area was inundated on the north side of Oda River, with an inundation depth exceeding 5 m for 1 km in the south-north direction and 3.5 km in the east-west direction, which made vertical evacuation of residents difficult. The findings that about 80% of the dead were found on the first floor of their houses, with those who had lived in a one-story house and those who had lived in a two-story house accounting for 50% each of the deceased, indicate how difficult even vertical evacuation was. The findings appear to be related to the considerable inundation depth and high rate of water level increase, along with the fact that the majority of the deceased were elderly people.
-  Japan Meteorological Agency, “Heavy rain in July 2018 (heavy rain from the front line and typhoon no. 7,” https://www.data. jma.go.jp/obd/stats/data/bosai/report/2018/20180713/jyun_sokuji 20180628-0708.pdf [accessed March 20, 2019]
-  Japan Meteorological Agency, “Feature and factor of “Heavy rain in July 2018” and record high temperature after the middle of July,” https://www.jma.go.jp/jma/press/1808/10c/h30goukouon 20180810.pdf [accessed March 20, 2019]
-  T. Sato, T. Fukuzono, and S. Ikeda, “The Niigata Flood in 2004 as a Flood Risk of “Low Probability but High Consequence”,” T. Fukuzono, T. Sato, and S. Ikeda (Eds.), “A Better Integrated Management of Disaster Risks: Toward Resilient Society to Emerging Disaster Risks in Mega-Cities,” TERRAPUB, pp. 177-192, 2006.
-  K. Asahiro, M. Tani, and H. Kanekiyo, “Support for Farmland Restoration Through Mutual Assistance After Flood Disasters in Hilly and Mountainous Areas – Cases of the Cities of Yame and Ukiha Affected by the Torrential Rainfall in Northern Kyushu in July 2012 –,” J. Disaster Res., Vol.10, No.5, pp. 794-806, 2015.
-  Y. Miyabuchi, F. Maeno, and S. Nakada, “The October 16, 2013 rainfall-induced landslides and associated lahars at Izu Oshima Volcano, Japan,” J. of Volcanology and Geothermal Research, Vol. 302, pp. 242-256, doi: 10.1016/j.volgeores.2015.07.012, 2015.
-  F. Wang, Y.-H. Wu, H. Yang, Y. Tanida, and A. Kamei, “Preliminary investigation of the 20 August 2014 debris flows triggered by a severe rainstorm in Hiroshima City, Japan,” Geoenvironmental Disasters, Vol.2, Article No.17, doi: 10.1186/s40677-015-0025-6, 2015.
-  S. P. C., T. Nakatani, and Misumi, “Hydrological Simulation of Small River Basins in Northern Kyushu, Japan, During the Extreme Rainfall Event of July 5–6, 2017,” J. Disaster Res., Vol.13, No.2, pp. 396-409, 2018.
-  Cabinet Office, “Damage situation by heavy rain in July 2018 (as of January 9, 2019),” http://www.bousai.go.jp/updates/h30typhoon7/pdf/310109_1700_h30typhoon7_01.pdf, [accessed March 20, 2019]
-  S. P. C., R. Misumi, T. Nakatani, K. Iwanami, M. Maki, T. Maesaka, and K. Hirano, “Accuracy of Quantitative Precipitation Estimation Using Operational Weather Radars: A Case Study of Heavy Rainfall on 9–10 September 2015 in the East Kanto Region, Japan,” J. Disaster Res., Vol.11, No.5, pp. 1003-1016, 2016.
-  Okayama Prefecture, Disaster verification committee due to heavy rain in July 2018, http://www.pref.okayama.jp/page/574750.html [accessed March 20, 2019]
-  Ministry of Land, Infrastructure, Transport and Tourism, Levee Investigation Committee in Oda River of Takahashi River water system, http://www.cgr.mlit.go.jp/emergency/odagawateibochosa.htm [accessed March 20, 2019]
-  T. Sayama and K. Takara, “Estimation of Inundation Depth Distribution for the Kinu River Flooding by 2015.09 Kanto-Tohoku Heavy Rainfall,” J. of Japan Society of Civil Engineers, Ser. B1 Hydraulic Engineering, Vol.72, No.4, pp. I_1171-I_1176, 2016.
-  Ministry of Land, Infrastructure, Transport and Tournism, Levee Investigation Committee in Kinu River, http://www.ktr.mlit.go.jp/ktr_content/content/000643703.pdf, [accessed March 20, 2019]
-  A. Shinohara and Y. Nihei, “Flood process in Oda River due to the 2018 western Japan heavy rain,” Advances in River Eng., Vol.25, pp. 327-332, 2019.
-  K. Ohtsuki and Y. Nihei, “Evaluation of Fast Flood Diffusion through a Drainage Channel: A Flood Disaster Case Study of Japan’s Kinugawa River, September 10, 2015,” J. of Water Resource and Protection, Vol.9, No.9 pp. 1063-1081, doi: 10.4326/jwarp.2017.99070, 2017.
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