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玉川上水の分水の沿革と概要
History and Overview of Water Diversion of Tama River Aqueduct

一般研究
General
Research
No.210
代表研究者
Principal
Investigator
小坂 克信
Katsunobu Kosaka
所属(採択当時)
Affiliation
日野市立七生緑小学校 非常勤講師
Part-time Teacher, Hino City Nanao Midori Elementary School
研究内容要約
Research
Summary
1655(承応4)年以後、玉川上水の分水によって、水の乏しい武蔵野台地南部に継続的に居住することが可能になる。特に、享保の改革時には多数の分水が開削され、現在の東京都の市部のもとになる多くの新田がつくられた。1791(寛政3)年頃には33分水あり、飲料水や生活用水、田用水、水車の動力源として使われた。しかし、ペリー来航に関する軍事力の強化や通船といった新しい利用により、水の確保に苦労した村もあった。

1870 (明治3)年6月分水の改正により34分水は17に統合され、その後、紡績、製紙、火薬製造など工業用水としても使われた。1910(明治43)年には22分水あったが、和田堀下流6分水は近代水道事業の影響を受けて水量が減少した。上流16分水は62カ町村に給水し、田2,246町歩の灌漑、18,775人の飲用、205台の水車が利用した。1922(大正11)年には23分水あり、水車はほぼ同数が利用し、飲用は24,768人と増えるが、灌漑面積は半減する。この他に雑用、防火用、灌漑用、酒造、庭園など用途が多目的化し、組合外の使用も広がる。1931(昭和6)年、雑用水の利用は増えるが、下流での宅地化や水道・電気の普及により、田用、飲用、水車の利用は減っていく。1965(昭和40)年淀橋浄水場の移転後には、16分水が10分水に減少したが、小平市のように防災や環境など地域用水としての活用を考えている自治体もある。

一方、江戸時代から名主や村役人を中心に水利用組合をつくり、共同で分水の維持管理をしてきた。明治以降は1891年水利組合条例、1909年耕地整理法、1949年土地改良法などにより、普通水利組合や土地改良区になり、行政の監督下に置かれた。しかし、公法人としての規定ができても、町村組合や任意団体として存続した分水もあった。それは、分水が農業以外の多目的に使用され、伝統的な用水慣行などにもとづいた水管理システムが有効であったことによる。

2003年玉川上水が国の史跡に指定された。その理由の1つに「武蔵野の灌漑用水としての役割を果たした価値ある土木遺産である。」とある。これは、玉川上水の分水が果たした役割であるが、玉川上水と分水は切り離せないのでよいと思う。しかし、分水は①飲料水・生活用水として、武蔵野に新田を開発し継続的に住居した人々を支え、現在の市部の元をつくったこと、②穀類の精白や製粉などを行った水車の動力源となり、③近代には製紙や麦酒製造、紡績などの工業用水や内国勧業博覧会の飲料水、庭園用水、消火用水としても利用された。この役割をきちんと記す必要がある。今後、機会を捉えてこのことを広く伝え、社会的にきちんと評価されるようにしたい。また、水道以前の分水の歴史、それに伴う人々の苦労や工夫によって、現在の社会や生活が支えられていることにも気づかせたい。
After 1655, the water diversion of the Tama River Aqueduct made ongoing habitation of the southern part of the water-poor Musashino Plateau possible. In particular, numerous water channels were excavated at the time of the Kyoho Reforms (1716-1745), leading to the creation of many new rice paddies that formed the basis of present-day Tokyo’s urban areas. By around 1791, there were 33 water channels, which supplied water for drinking, household tasks, and rice paddies, as well as being a source of power for water mills. However, some villages eventually struggled to secure water, due to the development of new uses, including for barges and the strengthening of military capacity after the arrival of Commodore Perry’s ships.

As a result of the modification of the water channels in June 1870, the 34 channels were consolidated into 17 and the water was subsequently used for industrial purposes as well, including spinning, papermaking, and the manufacture of gunpowder. There were 22 water channels as of 1910, but the volume of water in the 6 channels downstream of Wadabori Pond dwindled as a result of early modern water supply projects. The 16 upstream water channels supplied water to 62 towns and villages, irrigated almost 2,246 hectares of rice paddies, provided drinking water for 18,775 people, and were used by 205 water mills. By 1922, there were 23 water channels and these were used by almost the same number of water mills, but the number of people drinking the water had increased to 24,768, while the area of rice paddies irrigated had halved. The water was also used for many other purposes, including for fire prevention, irrigation, sake brewing, gardening, and miscellaneous other uses, and its usage outside the water use union system also spread. By 1931, the use of reclaimed water had increased, but the development of residential land downstream and the increasingly widespread use of tap water and electricity led to a decline in the use of the water for rice paddies, drinking, and water mills. After the relocation of the Yodobashi Purification Plant in 1965, the number of water channels fell from 16 to 10, but there were some local authorities such as Kodaira City that began considering using the water as a regional resource, for fire prevention and environmental purposes.

In Japan, water use unions led by village headmen and other village officials began to be formed in the Edo period. These cooperatives jointly maintained and managed the water channels. As a result of legislation from the Meiji period onward, including the 1891 Ordinance on Water Use Unions, the 1909 Readjustment of Arable Land Act, and the 1949 Land Improvement Act, these became common water unions and land improvement districts and were placed under the supervision of government bodies. However, even after they began to be regulated as public corporations, some unions survived as municipal unions and private organizations. This was because these water channels were used for multiple purposes other than agriculture, so a water management system based on traditional water usage customs was effective.

In 2003, Tama River Aqueduct was designated a national historic site. One reason for this was that it was deemed to be “a valuable public works heritage site that provided irrigation water for the Musashino area.” This role was actually played by the water channels created from the Tama River Aqueduct, but it would seem to be a fair description, given that one could not have the water channels without Tama River Aqueduct. However, the water channels (1) provided water for drinking and daily life, sustaining the people who developed new rice paddies in the Musashino area and have inhabited it continually since then, creating the basis for the urban areas of today; (2) provided a source of power for the water mills used to refine grains and mill flour; and (3) were used in early modern times to provide water for industrial purposes, including papermaking, beer and sake brewing, and spinning, as well as drinking water for the National Industrial Exhibition, water for gardening, and water for fire prevention purposes. One must make proper mention of these roles. In future, I would like to seize all opportunities to spread the word about these roles and ensure that they are properly appreciated by the public. In addition, I would like to ensure that the public become aware of the history of the water channels that preceded tap water and realizes that our modern society and lifestyle are supported by the efforts and creative ingenuity of the people who developed those water channels.
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