著者

土屋 信行

出版者

一般社団法人 日本治山治水協会

雑誌

水利科学 (ISSN:00394858)

巻号頁・発行日

vol.56, no.5, pp.11-34, 2012-12-01 (Released:2017-07-12)

参考文献数

23

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The formation of the part of Tokyo East Lowland(below sea level area)and the uncertainties of flood hazards there: Tokyo East Lowland is characterized by the gather of mouths of the Tone,the Arakawa and the Sumida rivers in a narrow area. Therefore, Edogawa city at their down streams always fears flood disasters, which is the low land less than zero mean sea level. The heavy inundation will happen in the drainage area even pumping up water, in the coastal area by high tide and at any local areas with guerrilla rainfall. Tokyo East Lowland including Edogawa city is on the deep as the maximum of 40m alluvium soil layers, which are composed from loose sands and soft clays. The ground water used to be significantly pumped up for the industry and to obtain methane gas. The significant ground settlement by the dewatering made the land to be below the sea level. If the river dykes were collapsed by the earthquake, the 70% of Edogawa city would be flooded. As Japan is also located just on the course of the typhoons,the huger ones than ever might possibly attack Tokyo. Therefore, in this study the worse cases of the Kathleen typhoon in 1947 were assumed and several typhoon patterns were simulated in Kanto area for the uncertainties of flood hazards. Finally, it was found that the design flood at Yattajima of the Tone river might be exceeded in the case of shifting the course of Kathleen in 1947 by only 50km to the northwest. Therefore, the author has concluded that flood prevention works must be conducted for the such worse situations. It is concluded that Tokyo and Edogawa city are always feared by huge flood disasters never experienced and their dykes will be the key of life line for Tokyo and Japan.

著者

土屋 信行

出版者

水利科学研究所

雑誌

水利科学 (ISSN:00394858)

巻号頁・発行日

no.330, pp.57-72, 2013-04

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治水対策は国が国民に対して備えなければならない必須の最重要施策である。これは国の責任において国民の命と資産を守る安全保障と捉えるべきである。気候変動に関する政府間パネル(IPCC)の第4次報告によれば,気候システムの温暖化には疑う余地がなく,大気や海洋の全球平均温度の上昇,雪氷の広範囲にわたる融解,世界平均海面水位の上昇が観測されていることから今や明白である。このことにより干ばつ,熱波,洪水など極端な気象現象のリスクの増加,水災害の危険性も増大している。台風の大型化,降雨強度の増大などによりこれまで100~200年確率を目指してきた河川でも実際には既に,治水安全度は著しく減じていると言える。さらに,地球温暖化というさらなるリスクの増大を捉えたとき,これまでの計画高水流量という指標に対し行ってきた水災害対策を,超過洪水をも視野に入れて検討する事が求められている。このような状況から超過洪水はもはや起こることが確実であり,これに備えることは予断を許さないところまで来ていると考える。首都圏のように中枢機能が集積している地域では,国家機能の麻療を回避するため,被害の最小化を目指すことが必要である。

著者

土屋 信行

出版者

一般社団法人 日本治山治水協会

雑誌

水利科学 (ISSN:00394858)

巻号頁・発行日

vol.55, no.6, pp.63-77, 2012-02-01 (Released:2017-07-24)

参考文献数

27

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The history of water disasters and hazards characteristics in the part of Tokyo East lowland(below sea level area): In the present paper, the author has studied the history and characteristics of water disasters in low ground of east part of Tokyo, where the ground surface is almost below-sea-level. Tokyo East lowland was basically formed by transforming Tone River to the east and Arakawa River to the west in the Tokugawa era. Through the flood disasters from the Meiji to Showa era,Arakawa Chanel and Edogawa Chanel were newly opened and a reclamation land at Kasai was constructed to avoid flood disasters in Tokyo East lowland. However, the numerical simulations at present study reveals that the existing of fundamental risks of flood disasters in Tokyo lowland and Edogawa ward is still in danger by the lower height of dykes on the left side of Arakawa River. From a case study of numerical simulation assuming high tide with a supplemental high water by climate change around Arakawa River mouth,Edogawa ward might be easily flooded within 2 days. As there is now a high density population in Tokyo East lowland, the countermeasures against the coming flood disasters must be planned and conducted properly and urgently.