Eai River

A tributary of the Kitakami River that flows through northern Miyagi Prefecture. It is about 80 km long. It originates at the eastern foot of Mt. Arao-dake (992 m), flows counterclockwise around the foot of the mountain, joins the Oya River near Naruko Onsen, then turns southeast and flows slowly through the Osaki Plain before joining the Kitakami River at Maeyachi in Ishinomaki City. The upstream part from Iwadeyama in Osaki City is called the Arao River. In the Osaki Plain, it flows parallel to the Naruse River to the south, but there are wetlands such as Nabire Numa, making the flow path complicated. During floods, the water of the main Kitakami River also flows backwards, so a diversion embankment has been built to channel the water of the Eai River into the Naruse River. Until the early modern period, it ran parallel to the Kitakami River, flowing south along the current course of the Jogawa River before emptying into Ishinomaki Bay, and during the Sengoku period, it was also used for water transportation.

[Kotaro Aoyagi]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

宮城県北部を流れる北上川の一支流。延長約80キロメートル。源を荒雄岳(あらおだけ)（992メートル）東麓(とうろく)に発し、山麓を逆時計回りに巡って鳴子(なるこ)温泉付近で大谷川(おおやがわ)をあわせ、南東に向かい大崎平野を緩流して石巻(いしのまき)市前谷地(まえやち)で北上川に合流する。大崎(おおさき)市岩出山(いわでやま)より上流は荒雄川とよばれる。大崎平野では南の鳴瀬川(なるせがわ)と並行して流下するが、名鰭(なびれ)沼その他の湿地帯があり、流路は錯綜(さくそう)している。洪水時には本流北上川の水までが逆流するので、江合川の水を鳴瀬川へ流入させる導流堤がつくられている。近世初期までは北上川と並行して、現在の定川(じょうがわ)の流路に従って南流して石巻湾に注ぎ、戦国時代には水運も開けていた。

［青柳光太郎］

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