Tone

Geography

The source of the Tone River is at Mount Ōminakami (大水上山) (1,831 meters; 6,007 ft) in the Echigo Mountains, which straddle the border between Gunma and Niigata Prefectures in Jōshin'etsu Kōgen National Park. The Tone gathers tributaries and pours into the Pacific Ocean at Cape Inubō, Choshi in Chiba Prefecture.

Major tributaries of the Tone River include the Agatsuma, Watarase, Kinu, Omoi, and the Kokai River. The Edo River branches away from the river and flows into Tokyo Bay.

History

The Tone River was once known for its uncontrollable nature, and its route changed whenever floods occurred. It is hard to trace its ancient route, but it originally flowed into Tokyo Bay along the route of the present-day Edo River, and tributaries like the Watarase and Kinu had independent river systems. For the sake of water transportation and flood control, extensive construction began in the 17th century during the Tokugawa shogunate, when the Kantō region became the political center of Japan. The course of the river was significantly changed, and the present route of the river was determined during the Meiji period, with the assistance of Dutch civil engineer Anthonie Rouwenhorst Mulder. Its vast watershed is thus largely artificial.