Yoro River

This river originates from Mt. Kiyosumi in the southern part of Chiba Prefecture, flows north and empties into Tokyo Bay. It is 75 km long and has a drainage area of ​​246 square km. It creates the Yoro Valley in Otaki Town, and flows through Ichihara City, collecting the Koshikiya River, Heizo River, Uchida River, and others. The middle and lower reaches of the river are open, and rice cultivation is thriving, making it one of Chiba Prefecture's leading grain-producing areas. In addition to being used as agricultural water to irrigate about 9,000 hectares in the downstream Ichihara City area, it is also supplied as industrial water to 16 companies located in the Keiyo Industrial Zone with the formation of the area, and Yamakura Dam was constructed to store the water. Following a flood in 1970, Takataki Dam, a multipurpose dam that regulates the water volume, was built at the confluence of the Yoro River and the Koshikiya River, and river improvement projects were also carried out. Yoro Valley is the center of the Yoro Valley Okukiyosumi Prefectural Natural Park, where the sandy tuff has been eroded to create a splendid beauty of the valley, and is blessed with tourist resources such as Umegase Valley and Yoro Onsen, and the Kominato Railway has led to tourism development. The hills and plateaus in the middle and lower reaches of the river are home to the largest concentration of golf courses in Japan.

[Yamamura Junji]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

千葉県南部の清澄山(きよすみやま)に源を発し、北流して東京湾に注ぐ川。延長75キロメートル、流域面積246平方キロメートル。大多喜(おおたき)町で養老渓谷をつくり、古敷谷(こしきや)川、平蔵(へいぞう)川、内田川などを集めながら市原(いちはら)市域を流れる。中・下流域は谷が開けて米作が盛んで、千葉県有数の穀倉地帯をなし、下流の市原市域で約9000ヘクタールを潤す農業用水に利用されるほか、京葉工業地帯の形成に伴って立地企業16社の工業用水として供給され、その貯水用に山倉(やまくら)ダムが造成された。1970年（昭和45）の洪水を契機に養老川と古敷谷川の合流点に水量調節を行う多目的ダムの高滝ダムが建設され、河川改修事業も進められた。養老渓谷は県立養老渓谷奥清澄県立自然公園の中心地で、砂質凝灰岩が侵食されてみごとな渓谷美をつくり、梅ヶ瀬渓谷、養老温泉などの観光資源に恵まれるとともに、小湊(こみなと)鉄道が連絡して観光開発が展開した。中・下流域の丘陵や台地上には日本一といわれるほどゴルフ場が集中している。

［山村順次］

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