Watarase River Reservoir

Japanese: 渡良瀬川遊水池 - わたらせがわゆうすいち

This reservoir was constructed in 1918 in the downstream of the Watarase River as part of flood control in the Tone River system. It is located in Fujioka Town, Tochigi Prefecture. The original planned area was 33 km2. In addition to the Watarase River, the Omoi River, Uzuma River, and others converge here, and in the event of flooding, the water from the Tone River would block the flow of the Watarase River, causing great flooding. As a result, Yanaka Village, which was plagued by the problem of mineral poisoning from the Ashio Mine, was abandoned, and a large reservoir was created that included Akama Numa and Ishikawa Numa. It was later given the function of flood control, and it was planned that all increased water during flooding would flow over the overflow levee into the reservoir, reducing the flow rate of the Watarase River to zero.

Source: Heibonsha World Encyclopedia, 2nd Edition Information

Japanese:

利根川水系における洪水調節の一環として，渡良瀬川下流域に1918年に造成された遊水池。栃木県藤岡町にある。当初計画の面積33km2。渡良瀬川のほか，思川，巴波（うずま）川などが集まり，さらに洪水の際は利根川の水が渡良瀬川の流れをふさぐため，洪水が非常に多かった。そこで足尾鉱山の鉱毒問題に悩む谷中（やなか）村を廃村とし，赤麻（あかま）沼，石川沼を含む一大遊水池とした。その後，洪水を調節する機能をもたせ，洪水の際の増水分はすべて越流堤を越えて調節池に入り，渡良瀬川の流量を0とするように計画されている。

出典　株式会社平凡社世界大百科事典第２版について　情報

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