Yoshii River

One of the three major rivers in Okayama Prefecture. A first-class river. It originates at Mikuniyama (1,252 meters) in the Chugoku Mountains on the border with Tottori Prefecture, merges with the Kamo River in the Tsuyama Basin, cuts through the Kibi Plateau, flows south and merges with the Yoshino River, and when it leaves the Kibi Plateau, it merges with the Kongo River, flows through the eastern Okayama Plain, and empties into Kojima Bay. It is 133 kilometers long and has a drainage area of ​​2,110 square kilometers. In ancient times, it was called the Ogami River and the Wake River, and in modern times, the Higashiokawa River and the Yoshii River. We know that Takase boat transportation had been developed since ancient times, as evidenced by the fact that in 1607 (Keicho 12), Suminokura Ryoi saw the boom in boat transportation on the Wake River in Mimasaka and devoted himself to the development of river transportation. The river was a major artery connecting the Tsuyama Basin and the castle town of Okayama, and there were river ports along the river, such as Tsuyama, Nagaoka (Kurigo, Misaki Town, Kume County), Yuuka (Misaki Town), Kurashiki (Hayashino, Mimasaka City), Susai (Akaiwa City), and Tahara (Wake Town, Wake County), with guard posts set up at various points. Boat transportation continued until the construction of the Chugoku Railway (JR Tsuyama Line) in the early Showa period. Currently, it is mainly used for agricultural water, with the Taharaizeki and Itaneizeki weirs downstream, and large irrigation canals such as the Tahara Canal, Oku O-o Canal, and Kurayasu River have been built there. It has suffered several major floods in the past, and after World War II, the Ministry of Construction (now the Ministry of Land, Infrastructure, Transport and Tourism) carried out large-scale repair work. There was no dam on the main stream, but in 2005 (Heisei 17) the Tomata Dam was completed in Kagamino Town upstream, and Lake Okutsu was born.

[Shogo Yuihama]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

岡山県の三大河川の一つ。一級河川。鳥取県境の中国山地三国(みくに)山（1252メートル）に発し、津山盆地で加茂(かも)川と合流、吉備(きび)高原を下刻して南下し吉野川と合流し、吉備高原を出た所で金剛(こんごう)川をあわせ、岡山平野東部を流れて児島(こじま)湾に注ぐ。延長133キロメートル、流域面積2110平方キロメートル。古くは雄神川(おがみがわ)、和気川(わけがわ)、近世以後は東大川(ひがしおおかわ)、吉井川とよばれた。1607年（慶長12）に角倉了以(すみのくらりょうい)が美作(みまさか)和気川の舟運盛行をみて、河川交通の発達に尽くした史実から、古くより高瀬舟交通が発達していたことが知られる。津山盆地と岡山城下を結ぶ交通の大動脈で、川筋には津山、長岡（久米(くめ)郡美咲(みさき)町栗子(くりご)）、飯岡(ゆうか)（美咲町）、倉敷(くらしき)（美作市林野(はやしの)）、周匝(すさい)（赤磐(あかいわ)市）、田原（和気郡和気町）などの河港があり、番所も所々に設けられた。舟運は昭和初期の中国鉄道（JR津山線）の敷設まで続いた。現在、主として農業用水に利用され、下流に田原井堰(たはらいぜき)、板根井堰があって、田原用水、邑久(おく)の大(おお)用水、倉安川などの大灌漑(かんがい)用水路がつくられた。過去に何度か大水害を起こし、第二次世界大戦以後、建設省（現、国土交通省）によって大規模な改修工事がなされた。本流にはダムがなかったが、2005年（平成17）上流の鏡野町に苫田ダム(とまただむ)が完成し、奥津湖が誕生した。

［由比浜省吾］

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