Tama River

A river that flows through the southern part of the Kanto Plain. It is a first-class river. It originates at Mt. Kasatori (on the border between Yamanashi and Saitama prefectures) in the Kanto Mountains in northeastern Yamanashi Prefecture, flows east (also called the Taba River), enters Tokyo, and collects tributaries such as the Nippara River, Aki River, Asakawa River, and Ookuri River before emptying into Tokyo Bay. It is 138 kilometers long and has a drainage area of ​​1,240 square kilometers. Up until the midstream near Mizonokuchi, it forms a braided alluvial fan river, but below that it is a single stream with a large meander, typical of a delta river. In the early Edo period, the shogunate's magistrate, Koizumi Jidayu, was ordered to dig the Nikaryo Irrigation Canal on the right bank and the Rokugo Irrigation Canal on the left bank, which allowed the development of rice fields in the delta at the river's mouth. The river frequently flooded during autumn floods, and the Rokugo Bridge on the Tokaido Road was not built after it was washed away in 1688 (Genroku 1). The Tama River was also frequently used for the transportation of people and goods. Ferries were established on the Tokaido Road and other side roads at Noborito, Futago, Yanoguchi, Maruko, Rokugo, Haneda, and other locations. Boat transport was available in the middle and lower reaches of the river, and high-quality cedar and cypress wood from Okutama was sent down the river on rafts to Edo, with Noborito being a stopover point for the rafting, and a raft lodge was established there. The sweetfish in the Tama River have long been known for their delicious flavor, and were listed as one of the "official sweetfish" in the Edo period, and fishing was also known for recreational purposes at that time. In the early Edo period (1654), the Tama River Canal was diverted from Hamura in the middle reaches to the city of Edo, and the water of the Tama River became available for drinking by the Edo townspeople. It was also diverted to the villages along the canal, which led to the establishment of Musashino Shinden. The former meandering section of the lower reaches was renovated at the end of the Taisho period, and the river became almost straight, and many sports fields and golf courses were built on the lowlands within the banks.

Even today, Okutama is rich in natural beauty with its mountain streams, mountains, and forests, and is part of Chichibu-Tama-Kai National Park. The forests are protected as Tokyo Metropolitan Government land as the Tama River's water source forest. In 1957, Ogouchi Dam was completed and became a water source for Tokyo residents, and the reservoir, Lake Okutama, has been equipped with tourist facilities and has become a recreational area.

The midstream and downstream coasts of the river in both Tokyo and Kanagawa Prefecture have been turned into residential and industrial areas, and are almost entirely urbanized. The river downstream from Rokugo Bridge on National Route 15 is also called the Rokugo River, and the southern bank was used as a river port from the end of the Meiji period to the Taisho period, which led to the establishment of food and electrical equipment factories. Currently, Tokyo International Airport is located at Haneda, on the northern bank of the river's mouth, and large-scale petrochemical, steel, and other coastal factories are located on the vast reclaimed land on the southern bank, making it the core area of ​​the Keihin Industrial Zone.

[Yukio Asaka]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

関東平野の南部を流れる川。一級河川。山梨県北東部の関東山地の笠取山(かさとりやま)（山梨・埼玉県境）に源を発して東流し（丹波川(たばがわ)ともよばれる）、東京都に入り日原(にっぱら)川、秋(あき)川、浅川、大栗(おおくり)川などの支流を集めて東京湾へ注ぐ。延長138キロメートル、流域面積1240平方キロメートル。中流の溝口(みぞのくち)付近までは網状流をなして扇状地河川、以下は単流で大きく蛇行し三角州河川の典型をなしている。江戸初期に幕府の代官小泉次太夫(じだゆう)が右岸に二ヶ領用水(にかりょうようすい)、左岸に六郷用水(ろくごうようすい)の開削を命ぜられ、その水利によって河口の三角州に水田が開かれた。秋の増水時にはしばしば氾濫(はんらん)し、東海道の六郷橋は1688年（元禄1）の流失後は架橋されなかった。多摩川はまた人や物資の交通・輸送によく使われていた。東海道をはじめいくつもの脇(わき)往還には登戸(のぼりと)、二子(ふたご)、矢野口、丸子、六郷、羽田(はねだ)などの渡しが設けられていた。中・下流では舟運が通じ、奥多摩産のスギ・ヒノキの良材が筏(いかだ)で川下げされて江戸へ送られ、登戸は筏下げの中継地で筏宿が設けられていた。また、多摩川のアユは古くから風味のよさで知られ、江戸時代の「御用鮎(あゆ)」の一つにあげられ、当時から遊漁でも知られていた。江戸初期（1654）に中流の羽村(はむら)から玉川上水が江戸の市街地へ引かれ、多摩川の水は江戸町民の飲料に供されることとなり、また上水沿いの村々にも引かれて武蔵野新田(むさしのしんでん)起立のきっかけをもなした。下流部のかつての蛇行部は、大正末期に改修工事が完成して直線に近い流路となり、堤内低地には多くの運動場、またゴルフ場も設けられている。

　奥多摩はいまも渓流と山地、森林の自然美に富み、秩父多摩甲斐(ちちぶたまかい)国立公園の一部をなし、森林は多摩川の水源涵養林(すいげんかんようりん)として東京都有地とされ保護されている。1957年（昭和32）には小河内ダム(おごうちだむ)が完成して東京都民の用水源とされ、貯水池の奥多摩湖には観光施設が整えられ、レクリエーション地域となっている。

　中流部、下流部の沿岸は、東京都、神奈川県ともに住宅地、また工業用地となり、ほとんど都市化されている。国道15号の六郷橋から下流は六郷川ともよばれ、南岸は明治末期から大正時代にかけては河港に使われ、それを利用して食料品や電気機器の工場も立地した。現在河口北岸の羽田には東京国際空港が設けられ、南岸の広大な埋立地には大規模な石油化学、鉄鋼などの臨海性工場が立地し、京浜工業地帯の核心地域となっている。

［浅香幸雄］

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