Shimanto River

A river that flows through the western part of Kochi Prefecture. It is a first-class river. At 196 kilometers long, it is the longest river in Shikoku. Its drainage area of ​​2,186 square kilometers is second only to the Yoshino River. Under the River Law, it was called Watarigawa, but historically Watarigawa was the name of the downstream area, and the general name Shimantogawa has been commonly used since the early modern period. In 1994 (Heisei 6), the name was changed to Shimantogawa. The river originates on the slopes of Irazuyama in Funato, Tsuno Town, Takaoka County, near the border with Ehime Prefecture, flows roughly south before turning west in the southeastern part of Shimanto Town, where it merges with the Yusuhara River, which has been flowing south, at Tanono, Shimanto Town, and then, showing a typical incarcerated meander, merges with the Hiromi River (Yoshino River), which has been flowing east from Ehime Prefecture, at Ekawasaki in Nishitosa, Shimanto City, before turning south-southeast, joining the Ushiro River near Tsunosaki in Shimanto City and the Nakasuji River near Sanzaki, before emptying into Tosa Bay near Shimoda, Shimanto City. Most of the river basin is mountainous, with many meandering gorges. Apart from the small areas of lowland in the river valley, such as the Kubokawa Plateau upstream and the Nakamura Plain downstream, which are used for rice paddies, the river is used for forestry, cultivation of shiitake mushrooms and tea, and mulberry fields that utilize the floodplains. There has been little development of power sources, and the river is known as one of the few clear rivers in the country. Until the early Showa period, it was used as a transportation route by takase boats, and the transportation of firewood and charcoal was particularly popular between Ekawasaki and Shimoda Port at the river mouth. Many fish species live here, and unique fishing methods are also observed. There are also many submerged bridges that sink below the water surface during floods. In 2001, the prefecture enacted the Shimanto River Ordinance to maintain the purity of the Shimanto River. In 2009, five areas in the Shimanto River basin, including mountain villages in the headwaters and mountain villages and rice terraces in the upper reaches, were selected as Important Cultural Landscapes by the national government.

[Yasuhiko Owaki]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

高知県の西部を流れる川。一級河川。延長196キロメートルは四国一の長流。流域面積2186平方キロメートルは吉野川に次ぐ。河川法では渡川(わたりがわ)と称したが、歴史的には渡川は下流部の名称で、総称は近世以来、四万十川が一般に用いられた。1994年（平成6）名称を四万十川に変更。源流を愛媛県境に近い高岡郡津野町船戸(ふなと)の不入山(いらずやま)斜面に発し、ほぼ南流して四万十町の南東部で方向を西に転じ、四万十町田野々で南流してきた檮原(ゆすはら)川をあわせ、典型的な嵌入(かんにゅう)蛇行をみせながら、四万十市西土佐の江川崎(えかわさき)で愛媛県から東流してきた広見川（吉野川）をあわせて南南東に方向を転じ、四万十市角崎(つのさき)付近で後(うしろ)川を、実崎(さんざき)付近で中筋(なかすじ)川をあわせ、四万十市下田(しもだ)付近で土佐湾に注ぐ。流域の大部分は山間部で、曲流峡谷の部分も多く、上流の窪川台地や下流の中村平野などわずかな河谷低地が水田に利用される以外は、林業、シイタケ、茶の栽培、氾濫原(はんらんげん)利用の桑園などがみられる。電源開発もほとんど進まず、全国的にも数少ない清流として知られる。昭和初頭までは、高瀬舟による交通路として利用され、とくに江川崎と河口の下田港との間は薪炭(しんたん)輸送などが盛んであった。生息する魚類も多く、独特の漁法もみられる。なお、大水のときに水面下に沈んでしまう「沈下橋」が多く残されている。また、2001年（平成13）には四万十川の清流を保つため、「四万十川条例」が県によって定められた。2009年、源流域の山村、上流域の山村と棚田など5件にわたり、四万十川流域の文化的景観として国の重要文化的景観の選定を受けている。

［大脇保彦］

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