Yahagi River

A river that runs through the Nishi-Mikawa region of Aichi Prefecture from north to south. Its source is in the mountainous region of Nagano and Gifu prefectures, then passes through the granite-rich Mikawa Mountains and the Okazaki Plain before emptying into Mikawa Bay (Koromogaura Bay). Its length is 117 km, and its drainage area is 1,830 km2. The Yahagi Furukawa River was the former main stream, but the current main stream flowed into Kinugaura Bay in 1605 (Keicho 10). The upstream area is mountainous, the downstream area is the Okazaki Plain, and the bayside is made up of farming and fishing villages where seaweed farming is thriving. The eight cities of Toyoda, Okazaki, Kariya, Anjo, Nishio, Hekinan, Chiryu, and Takahama in the Okazaki Plain are industrially active areas, mainly in the automobile industry. In other words, the area is faced with severe water resource problems due to its layout: mountain villages upstream, fishing villages downstream, and industrial cities in between. During the Meiji period, the Yahagi River was a source of water for agricultural use, and the Meiji Irrigation Canal and the Shidare Irrigation Canal were excavated. The flow of water through these two canals turned the Hekikai Plateau into rice paddies covering an area of ​​about 10,000 hectares.

[Gohei Ito]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

愛知県西三河地方を北から南に貫流する川。源流は長野・岐阜両県の山地、途中は花崗(かこう)岩類の三河山地、岡崎平野を経て三河湾（衣ヶ浦(ころもがうら)湾）に注ぐ。延長117キロメートル、流域面積1830平方キロメートル。矢作古川(やはぎふるかわ)が旧本流であるが、1605年（慶長10）に人工開削によって現本流は衣ヶ浦湾に注ぐようになった。上流は山地、下流は岡崎平野、湾岸はノリ養殖の盛んな農漁村で、岡崎平野の豊田(とよた)、岡崎、刈谷(かりや)、安城(あんじょう)、西尾、碧南(へきなん)、知立(ちりゅう)、高浜の八都市は自動車産業を中心に工業の盛んな地域である。すなわち、上流は山村、下流は漁村、中間に工業都市という配置から厳しい水資源の問題を抱えている。明治期の矢作川は農業用水の給源で、「明治用水」「枝下用水(しだれようすい)」が開削され、碧海(へきかい)台地は二用水の通水によって約1万ヘクタールの水田と化した。

［伊藤郷平］

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