Yasugawa River

A river that flows through the southeastern part of Shiga Prefecture. It is a first-class river. It originates at Mt. Gozaisho in the Suzuka Mountains, flows almost northwest, and empties into Lake Biwa in Moriyama City. It is the largest river in the prefecture, stretching 65 kilometers and draining an area of ​​387 square kilometers, irrigating about 10% of the Lake Biwa basin of the Yodo River system. Terraces have developed in the middle reaches, and a vast alluvial fan delta has formed in the lower reaches. In the past, it was also written as Yasukawa. The lower reaches are a prominent covered river, and the river has been plagued by floods many times throughout history. In 1951, the Yasugawa Dam was completed in Tsuchiyama Town (now Tsuchiyama Town, Koka City) upstream, but flooding continued to occur frequently afterwards, and in 1986, a project was completed to eliminate the north-flowing and south-flowing elevated rivers about 5 kilometers along the lake shore and create an artificial flatland river in between. It is said to be one of the three major river projects, along with the Chikugo River and the Asahi River. The Hattori Ruins, discovered in Moriyama City during the new river excavation work, are the remains of a large settlement dating from the Yayoi to Heian periods.

[Seiichi Takahashi]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

滋賀県南東部を流れる川。一級河川。鈴鹿(すずか)山脈の御在所山(ございしょやま)に源を発してほぼ北西流し、守山市で琵琶湖(びわこ)に注ぐ。延長65キロメートル、流域面積387平方キロメートル、淀(よど)川水系琵琶湖流域の約10％の地域を潤す県下最大の河川。中流域には段丘が発達し、下流域には広大な扇状地性三角州が形成される。古くは安河とも書いた。下流部は顕著な天井川をなし、古来たびたび水害に悩まされてきた。1951年（昭和26）に上流の土山(つちやま)町（現、甲賀(こうか)市土山町）に野洲川ダムが完成したがその後も水害は多発し、1986年、湖岸約5キロメートルの北流と南流の天井川を廃して、その中間に人工的平地河川をつくる事業が完成した。筑後(ちくご)川、旭(あさひ)川と並ぶ三大河川事業の一つといわれる。新川掘削工事の際に守山市で発見された服部(はっとり)遺跡は、弥生(やよい)から平安期に及ぶ大集落遺跡。

［高橋誠一］

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