Toyokawa Irrigation Canal

This is a multi-purpose canal that irrigates the area including the eastern Mikawa region of Aichi Prefecture and Kosai City in Shizuoka Prefecture. Construction began in 1949 (Showa 24) as a national project run by the Ministry of Agriculture and Forestry, was taken over by the Aichi Water Public Corporation in 1961, and was completed in 1968. The total construction cost 48.8 billion yen, and it took 19 years from start to completion. A major feature of this canal is the large-scale change of watershed, where water from the Ochisegawa River, a Tenryu River system, was diverted to the Ure Dam (Lake Houraiko), which was built on the Uregawa River, a tributary of the Toyokawa River, and from Sakuma Dam it is diverted through a tunnel (about 14 kilometers) through the mountains to the Miwagawa River (Uregawa River). The discharge water from Ure Dam and the diverted water from Sakuma Dam are conducted via the Ono Headworks to the Hiyoshi Diversion Works, where they are split into two main waterways, east and west. The eastern main on the left bank of the Toyokawa River passes through Toyohashi City and reaches the tip of the Atsumi Peninsula, while the western main on the right bank passes through Toyokawa City and is distributed to Gamagori City. This has made it possible to develop the coastal industrial zone along Mikawa Bay, irrigate fields in the Atsumi Peninsula and elsewhere, and develop horticulture facilities. Water use is divided into 123 million tons for agriculture, 77 million tons for industry, and 68 million tons for urban use. The farmland that benefits is approximately 20,000 hectares, including Kosai City in Shizuoka Prefecture.

[Gohei Ito]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

愛知県東三河地方と静岡県湖西(こさい)市を含む地域を潤す多目的用水。1949年（昭和24）農林省による国営事業として着工され、1961年愛知用水公団に引き継がれ、1968年完成した。総工費488億円、着工から完成まで19か年を要した。大きな特徴は大規模な流域変更が行われたことで、天竜川水系大千瀬川(おおちせがわ)の水を豊川の支流宇連川(うれがわ)に建設された宇連ダム（鳳来湖(ほうらいこ)）へ導き、佐久間ダムから山中をトンネル（約14キロメートル）によって三輪川(みわがわ)（宇連川）に導水している。宇連ダムの放流水と佐久間ダムの分水は大野(おおの)頭首工を経て日吉分水工(ひよしぶんすいこう)に導き、日吉で東西二大幹線水路に分ける。豊川左岸の東部幹線は豊橋市を経て渥美半島の先端まで、右岸の西部幹線は豊川(とよかわ)市を経て蒲郡(がまごおり)市に配水される。これによって三河湾岸の臨海工業地帯の造成、渥美(あつみ)半島などの畑地灌漑(かんがい)、施設園芸の発展を可能にした。利水区分は農業用水1億2300万トン、工業用水7700万トン、都市用水は6800万トンの割合になっている。受益農地は静岡県湖西市を含めて約2万ヘクタール。

［伊藤郷平］

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