Asahikawa

One of the three major rivers in Okayama Prefecture. It originates in the Hiruzen Plateau, flows south through the center of the prefecture, joining many tributaries, passes through Okayama City, and empties into Kojima Bay. It is a first-class river. It is 142 km long and has a drainage area of ​​1,810 square kilometers. Between the Chugoku Mountains and the Kibi Plateau, it forms the Katsuyama, Kuse, and Ochiai basins, carves deep valleys in the Kibi Plateau, and forms the Okayama Plain downstream. Iron sand was collected for a long period of time in the upper reaches, causing a large amount of sediment to accumulate downstream, and in the early modern period, a vast reclaimed land was created. In the early modern period, Takase boats traveled from Ochiai, and later from Takada in Mimasaka (now Katsuyama) to Okayama, playing an important role in transporting goods. At the time, the river ports included Katsuyama, Tandō, Nishikawa, Fukuwatari and Kanakawa, and timber was also floated down the river on rafts. The river course changed several times in the Okayama Plain, and there are traces of early rice cultivation, such as the Tsushima ruins at the prefectural general ground in Okayama City's Kita-ku. When castle towns were formed in Okayama, the river courses were fixed and the special scenic spot of Koraku-en was constructed on the sandbar. There was a major flood in 1654 (Shoō ​​3), and following a suggestion from Kumazawa Banzan, Tsuda Nagatada constructed the Hyakken River between 1669 and 1670 (Kanbun 9 and 10). This was one of the earliest spillway channels in Japan, a 12.9 km long, 200 to 300 m wide waterway that branches off over the Arate Levee upstream from the city of Okayama, flows south from the eastern side of Misao Mountain, and empties into Kojima Bay.

Currently, the water of the Asahikawa River is used for irrigation, industrial and urban water supply, and electricity generation, with the prefectural Asahikawa Dam located in the midstream and the Chugoku Electric Power Yubara Dam located upstream.

[Shogo Yuihama]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

岡山県三大河川の一つ。蒜山(ひるぜん)高原に源を発し、多くの支流をあわせつつ県中央部を南下し、岡山市を通過して児島(こじま)湾に注ぐ。一級河川。延長142キロメートル。流域面積1810平方キロメートル。中国山地と吉備(きび)高原の間では勝山、久世(くせ)、落合の諸盆地を形成し、吉備高原では深い谷を刻み、下流では岡山平野を形成する。上流部で長期間砂鉄採取が行われたため、下流に大量の土砂が堆積(たいせき)し、近世以降、広大な干拓地が造成された。近世初期に落合から、のちには美作(みまさか)高田（現、勝山）から岡山まで高瀬舟が通じ、物資輸送に重要な役割を果たした。当時の川湊(みなと)には、勝山、旦土(たんど)、西川、福渡(ふくわたり)、金川があり、木材の筏(いかだ)流しも行われた。岡山平野では流路は幾度か変遷し、岡山市北区の県営総合グランド内の津島遺跡のように初期稲作の跡もある。岡山に城下町が形成されると、河道は固定され、中州(なかす)には特別名勝の後楽園が造営された。1654年（承応3）に大洪水があり、熊沢蕃山(くまざわばんざん)の案により津田永忠が1669～1670年（寛文9～10）に百間川(ひゃっけんがわ)を建設した。これは、わが国でも初期の放水路で、岡山の市街地の上流で荒手堤を越えて分流し、操(みさお)山東側から南流して児島湾に注ぐ長さ12.9キロメートル、幅200～300メートルの水路である。

　現在では旭川の水は灌漑(かんがい)、工業および都市の用水、電力資源として用いられており、中流には県営旭川ダム、上流には中国電力湯原ダムがある。

［由比浜省吾］

出典　小学館　日本大百科全書(ニッポニカ)日本大百科全書(ニッポニカ)について　情報 | 凡例