Oonogawa River

It originates near Mt. Sobo (Miyazaki side) which stands on the border between Oita, Kumamoto and Miyazaki prefectures, flows northeastward through the eastern part of Kumamoto prefecture and the southern part of Oita prefecture, and flows into Beppu Bay, joining the Tamarai River, Inaba River, Ogata River, Okudake River, Akane River, Notsu River, Shibakita River and others in the upper and middle reaches. It is the largest river in Oita prefecture and a first-class river. It has a length of 107 km and a drainage area of ​​1,460 square km. Its irrigation area is 9,800 hectares. Because it deeply erodes the rift valley covered by Aso welded tuff, it does not flood in the upper and middle reaches, but causes flooding in the lower reaches, while the thick sedimentary soil of the floodplain has provided the blessing of vegetable cultivation. There are many small power plants in the midstream, and in recent years the river has become increasingly valuable as industrial water.

[Shunichi Kaneko]

"Oono River - Nature, Culture and Education" (1977, Faculty of Education, Oita University)

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

大分・熊本・宮崎県境にそびえる祖母山(そぼさん)付近（宮崎県側）に源を発し、熊本県の東部、大分県の南部を北東方へ流れ、上・中流で玉来(たまらい)川、稲葉(いなば)川、緒方(おがた)川、奥岳(おくだけ)川、茜(あかね)川、野津(のつ)川、柴北(しばきた)川などをあわせ別府湾に注ぐ川。大分県下最大の河川で、一級河川。延長107キロメートル、流域面積1460平方キロメートル。灌漑(かんがい)面積9800ヘクタール。阿蘇(あそ)溶結凝灰岩に覆われた地溝帯を深く侵食するため、上・中流では氾濫(はんらん)することなく、下流部に水害をもたらすと同時に、氾濫原の厚い堆積(たいせき)土は野菜栽培の恵みを与えてきた。中流には小発電所が多く、近年は工業用水としての価値も大きくなっている。

［兼子俊一］

『『大野川――自然・文化・教育』（1977・大分大学教育学部）』

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