Nakayama is in between Narita And Haneda International Airport

Tonegawa River / Tone River

Tonegawa River is one of the longest rivers (322km) in Japan passing through Kanto region from the north-west to the south-east part of it. The river starts from Mt.Ominakami and many small rivers join to it, finally, it flows out to the Pacific Ocean at Choshi city in Chiba Prefecture. Tone River has the largest catchment area in Japan (16,840 square kilo-meters). Over 12 million of people live in the areas flowing the river.

Originally, Tonegawa River flowed to Tokyo Bay. In early Edo Period in 1594, Ieyasu Tokugawa, the founder of Edo Bakufu, started the Tonegawa Tosen Project (the project to move Tone River to the east). Finally, the stream of it directly went to the Pacific Ocean at Choshi City in 1654.

Now there are some advances of the origin the name of Tonegawa River and sometimes it is called Bando Taro since Tone River is the largest river in Kanto then it is the first son (Taro) in Bando (Kanto). Some say that the name 'Tone' comes from 'Tonnai' in Ainu means 'a large valley' or 'a large river like a lake' in Ainu. And some says there are many sharp peaks near the springs 利き峰 in classic regional Japanese word and the words are abbreviated in 'Tone'. It comes from person’s name 'Tone no Atai' or 'Tonetsuhiko'. And it also comes from the name of some regional name 'Tone Dake' and 'Otone Dake'. But it has been not decided which one could be correct.
Moreover, Tonegawa River was called in 'Tone' in the Myriad Leaves.


参考
大辞林
国土交通省ホームページ

Tonegawa Tousen / The Project of Moving Tone River to East

Initially, the stream of Tonegawa River went to Tokyo Bay. And Arakawa River and Watarasegawa River also went to Tokyo Bay, too. Before Tonegawa Tosen (the project of Moving the streams of Tone River to east), the boarder areas between Shimousa and Musashi province had got several floods every year. And the courses of these rivers had not been fixed. Therefore, people could not cultivate the land well.
To protect the land from the floods to reclaim it under cultivation, the first Shogun of Edo Bakufu Ieyas Tokugawa planned the project called Tonegawa Tosen. He had other aims that the new course to east could be a new route of transporting goods from northeast Japan and a great boundary like a moat to protect Edo. The construction to change the course of the streams of Tonegawa River from south into Tokyo Bay to east into the Pacific Ocean at Choshi City started in 1594 and it finished in 1654, so it spent 60 years.


参考
国土交通省ホームページ