Tachikawa Walk: Tamagawa Aqueduct and Sunagawa History Guide

Kodaira Monitoring Station, where the water splits into two lives

Walk east from Tamagawa-Josui Station and you reach the Tokyo Metropolitan Bureau of Waterworks’ Kodaira Monitoring Station (小平監視所). Its name says Kodaira, but the city’s walking-course notes call it “the Kodaira Monitoring Station in Saiwai-cho.” It calls itself Kodaira and lives in Tachikawa. Like someone whose family register and home address don’t match, it is oddly endearing.

This is where the aqueduct’s two lives divide. The story starts in Meiji.

According to the bureau, some time into Meiji the aqueduct faced a pile-up of problems: rubbish and muddy water flowing in, wooden pipes rotting, and cholera outbreaks in the city. A modern water system was needed, one that filtered water at a treatment plant and distributed it through iron pipes, and in December 1898 supply began from the Yodobashi water purification plant to the Kanda and Nihonbashi areas. In 1901 the Tamagawa Aqueduct stopped supplying the city directly and changed its role to a channel carrying raw water to the treatment plant.

To protect the channel, water guard stations were set up at eight places: Kumagawa, Sunagawa, Ogawa, Sakai, Kugayama, Wadabori, Yodobashi and Okido. They inherited the role of Edo’s watch-houses, and each station’s staff were responsible for the stretch from their own station upstream to the next one. In Tachikawa, the site of the Sunagawa station survives upstream of Konpira Bridge.

In 1963 the Ogawa station was abolished and the Kodaira station — today’s Kodaira Monitoring Station — was established. In 1980 the Sunagawa and other stations were abolished too. When the Yodobashi plant closed in 1965, the aqueduct’s raw water began to be sent from here to the Higashimurayama water purification plant. The roughly 12 kilometres from Hamura to this monitoring station are the stretch that has carried raw water for Tokyo’s supply ever since it was dug in the Edo period, and it still does. Its end point is in Saiwai-cho, Tachikawa. The whole of the aqueduct within Tachikawa lies upstream of it. The water flowing beside the green path is still on its way to someone’s tap.

Downstream of the monitoring station, things are different. When the Yodobashi plant closed, water stopped flowing below the station. The bureau writes that while parks and green paths were laid out over the culverts and along the channel, the banks suffered collapses and illegal dumping. Thanks partly to the efforts of people who loved the aqueduct, the Tokyo Metropolitan Government decided on a “clear stream revival” project in 1982, and in 1986 water flowed again from the station to around Sengen Bridge in Suginami Ward, about 18 kilometres downstream. From there, it joins the Kanda River through a pipe. The Nobidome Canal in 1984 and the Senkawa Aqueduct in 1988 had their flows restored under the same project. What runs downstream today is water sent through an underground pipe from the Tama River Upstream Water Reclamation Center in Akishima City. In 2003, marking 350 years since its completion, the aqueduct was designated a national historic site.

From 1965 to 1986, the aqueduct below the monitoring station was a dry channel for 21 years. People who grew up in the downstream towns in the later Showa years (the decades after the war) grew up calling a ditch with no water in it “the aqueduct.” For young people today, a Tamagawa Aqueduct without water is probably much harder to imagine.

Even upstream, in Tachikawa, the banks looked a little different in the Showa era. The Sunagawa water guard station, whose site remains upstream of Konpira Bridge, stood until 1980. Its staff covered the stretch from downstream up to the next station. There were people whose job was to keep watch over the water on these banks. Today the people who come and go along the same banks are dog walkers, runners, and now and then a curious type like me.

The Tachikawa stretch has never once stopped being a josui, a water supply, since the Edo period. That it remained a channel for drinking water is what would later decide which went over and which went under, the aqueduct or the river.

Azusami Tenjin-sha Shrine and Konpira-yama: prayers on a dry plateau, and the memory of boats

Go down from the aqueduct to the Itsukaichi Kaido and you come to the heart of old Sunagawa village.

Azusami Tenjin-sha Shrine is Sunagawa’s guardian shrine. It was founded in 1629 as a branch of the Azusami Tenjin-sha in Tonogaya, Murayama-go (today’s Mizuho Town). Its main sanctuary, which preserves a ridge tag dated 1708, is the oldest wooden building in the city, and its worship hall, completed in 1862 and built entirely of zelkova wood, is a magnificent structure rare even in Tokyo, the city writes. On New Year’s Day it holds the earliest Daruma fair in the Tama area — a market selling the round red Daruma good-luck dolls — and the great bonfire is lit from midnight. You could not be more impatient for a new year to begin.

Ryusen-ji Temple (流泉寺), on the road, is the family temple of all ten groups of Sunagawa village. According to the city, it was established in 1650 and formally founded in 1654 — the same year the aqueduct opened. Coincidence, or did they set the temple in order once the water supply was assured? The records show only that the years coincide. For about 30 years in the Meiji era, a school stood in its grounds.

Kokage Shrine (蚕影神社), in the grounds of Azusami Tenjin-sha, enshrines a god of silkworms whose spirit was brought in 1860 from Tsukuba District in Hitachi Province (today’s Tsukuba City, Ibaraki Prefecture). The city writes that sericulture was so prosperous in Sunagawa, and so important to the village economy, that people invited a guardian deity from distant Hitachi. A plateau with few paddies grew silk instead of rice. This shrine is also known as the “cat-returning shrine.” It began when a magazine reported that a famous person living nearby had prayed here and their missing cat came home. The city’s notes add that, because rats ate silkworm cocoons, the shrine used to issue paper charms with pictures of cats to keep rats away, and that this may also be part of the connection. The cat on an anti-rat charm became, over time, a god who brings lost cats home. Quite a promotion.

Near Konpira Bridge, in Sunagawa Sanban, stands an artificial mound about 10 metres high: Konpira-yama. The walking map the city produced introduces it as Tachikawa’s only mountain. You will not need hiking boots, but a mountain it is. One theory says it was piled up from earth dug out for the aqueduct; another says it is a Fujizuka, a miniature Mount Fuji of the kind that was popular in the Edo period. Nobody knows exactly when it was built. In the Ansei era (1854–1860), the Murano family, village heads of Sunagawa, are said to have sponsored the enshrinement of Fuji Sengen Shrine, Konpira Daigongen and Akiba Shrine here.

Konpira Daigongen was probably enshrined as a god of boats in the days when boats ran on the aqueduct, the city writes. According to the Bureau of Waterworks, proposals to run boats on the aqueduct were never realised in the Edo period because of concerns about water quality and local opposition. In Meiji, local village heads petitioned and finally obtained permission. Records say that from April 1870, boats came and went on the aqueduct from Hamura to Naito-Shinjuku, and it was a great success. Downstream of Mikage Bridge is the site of Tomoe-gashi, a boat landing, and according to the city’s walking map, several boats a day passed along, not only carrying goods but also including boats for sightseeing. But in May 1872, after just two years, the service was abolished. The reason is thought to have been declining water quality. The village heads petitioned again and again to restart it, but were refused.

The boats changed the shape of the branch channels too. According to the city’s notes, in 1870, partly because of the boat service, the branch intakes were consolidated, and the Sunagawa branch was connected with ten branch channels as far as Musashino and Mitaka. The Sunagawa channel’s intake was moved to its present place at Matsunaka Bridge, and the following year the Jindaiji branch was built, becoming a long channel that reached as far as the Nogawa River in Chofu. The small intakes lined up above Matsunaka Bridge today once sent water all the way to the Nogawa. A small mouth, entrusted with a job reaching to Chofu.

Sightseeing boats sailing on top of the drinking water. No wonder it lasted only two years. If anything, the fact that it lasted two years shows how easygoing the Meiji era was. And here, for the first time, the words “water quality” show their face in the history of the aqueduct. The Meiji aqueduct was starting to get dirty. And that dirt would eventually turn its relationship with the river upside down.

By Tenno Bridge, the river and the aqueduct swapped places

The scene of the mystery lies a little downstream of Tenno Bridge (天王橋). It is the spot the city’s notes called “the fusekoshi under the Zanbori River.” The bridge, which carries the Itsukaichi Kaido, is said to take its name from a Tenno shrine that stood to its south, and it was once also called “Itsukaichi Bridge.” Where a river, an aqueduct and a road meet, even the bridge cannot settle on one name.

In the annual report of the Tokyo Metropolitan Government’s Civil Engineering Support and Training Center, there is a paper tracing the history of the Zanbori River. Reading it, I found the relationship between the two waters was far more tangled than I had imagined.

The Zanbori River is a Class A river that rises at Sayama Pond in Mizuho Town and flows through Musashimurayama, Akishima and Tachikawa before joining the Tama River. According to the paper, when the Tamagawa Aqueduct was built in the Edo period, the course of the Zanbori was rerouted so that it would meet the aqueduct around Tenno Bridge on the Itsukaichi Kaido. Upstream, too, a channel was cut from Sayama Pond to link it to the Zanbori, as josui, “helper water,” to top up the aqueduct. In other words, the “river of sand” began as the aqueduct’s helper.

The wind changed in Meiji. The paper says that in the Meiji era, as industries such as silk raising and weaving flourished, the water quality of the Tamagawa Aqueduct was markedly worse than in the Edo period. Between 1903 and 1908, the Zanbori was rebuilt so that it passed under the aqueduct. This was carried out as part of the City of Tokyo’s waterworks improvement project, the result of giving up on using the Zanbori’s water as helper water for the aqueduct. Around 1907, the water of the Tonogaya branch, which had also become dirty, was rerouted to drop into the Zanbori instead of the aqueduct.

Here I cannot help thinking of Kokage Shrine. The silk raising that enriched Sunagawa was also one of the industries that clouded the Meiji aqueduct.

And then came Showa. As the river basin was developed, the Zanbori became prone to overflowing in every heavy rain. According to the paper, so that the swollen Zanbori would not mix with the aqueduct’s water — and because the aqueduct, with its steady flow, was hydraulically easier to control — in 1963 the structure was rebuilt into its present form, with the aqueduct passing under the Zanbori.

That solves the mystery. The aqueduct does not pass under the river out of deference to it. It hid underground to protect the drinking water from an unruly river. And 1963 was also the year the Kodaira Monitoring Station was set up. On Tachikawa’s northern edge, two measures were taken in the same year so that the aqueduct could go on being a water supply.

Summoned as helper water, forced underneath in Meiji, and then promoted to the upper level in Showa: that is the life of the Zanbori River. The dry “river of sand” had, at some point, become a river the aqueduct had to dodge.

The year 1963 was a turning point for Sunagawa, too. That year, Sunagawa Town merged with Tachikawa City to form today’s Tachikawa. The history newsletter says that Tachikawa is a city formed from two municipalities joined together: Shibasaki village in the south and Sunagawa village in the north. A little before that, Sunagawa had another history. According to the city’s walking map, in 1955, when Sunagawa Town was asked to allow the expansion of the US military’s Tachikawa Air Base, the whole town mounted a resistance movement known as the Sunagawa Struggle. (After the war, the former Japanese army airfield in Tachikawa had become a major American base, which shaped the city for decades.) After a long campaign, the runway extension was abandoned in 1968, and the following year the US military decided to move to Yokota Air Base. In 1975, a monument called the Cornerstone of Peace was erected to mark the movement’s 20th anniversary. Walk a little south from the aqueduct’s banks and you can touch the memory of postwar Sunagawa as well.

To anyone who thought there was nothing at the northern end of Tachikawa, I want to tell them about this crossing. Here is the end of the stretch where Edo’s aqueduct still carries raw water, and the place where it swapped levels with a river to protect that water. Here the earliest Daruma fair in Tama is held, and the city’s oldest wooden building sleeps inside its protective outer hall. If it looks unremarkable, that is only because its stories are hidden under the ground and inside the records.

Looking down at more than 300 years of exposed earth, I do the division once more. Ninety-two metres over 43 kilometres. To protect that slender gradient, this channel has kept coming to terms with rivers, people and the times for more than 370 years.

At the bottom of the channel, the water flows east again today. It makes almost no sound.

Quiz answer

The answer is (A), 2 years. Boats ran on the aqueduct only for the two years from 1870 to 1872. Not only goods but also sightseeing boats made several trips a day, but the service was abolished to protect water quality. It is from here that people began to talk about the aqueduct getting dirty.

Before you go

• Getting there: From JR Tachikawa Station, walk to Tachikawa-Kita Station on the Tama Toshi Monorail. Take a train toward Kamikitadai to Tamagawa-Josui Station, about 9 minutes (according to the monorail’s fare and journey-time table). The Tamagawa Aqueduct flows east to west on the south side of the station, with a green path along it. Tamagawa-Josui Station on the Seibu Haijima Line is in the same place.
• From central Tokyo: Tachikawa Station is on the JR Chuo Line, reached directly from Shinjuku without changing trains. Check the current timetable before you go.
• Suggested walks: The City of Tachikawa’s walking map shows a course of about 3.8 km (about 57 minutes) from Musashi-Sunagawa Station past the Tomoe-gashi site and Konpira-yama to Tachikawa City Hall, and a course of about 5.7 km (about 86 minutes) from Tamagawa-Josui Station via Azusami Tenjin-sha Shrine to the old folk house garden (Japanese PDF): https://tokyo-walkingmap.metro.tokyo.lg.jp/resources/course/502/pdf/tachikawa_2.pdf
• City of Tachikawa walking course, “Walking the Birthplace of Sunagawa Shinden” (Azusami Tenjin-sha, Kokage Shrine, Konpira-yama, branch intakes; Japanese): https://www.city.tachikawa.lg.jp/kanko/bunka/1004244/1004848/1004892.html
• History of the whole aqueduct and walking information: Tokyo Metropolitan Bureau of Waterworks, “Tamagawa Josui Historic Site” (Japanese): https://www.waterworks.metro.tokyo.lg.jp/kouhou/pr/tamagawa
• Note: The City of Tachikawa has announced that the Kawagoe-michi Ryokuchi Old Folk House Garden (4-65 Saiwai-cho, Tachikawa) is scheduled to close for renovation of its management facilities from 1 June 2026 to 31 March 2027. Check the official site for its status: https://www.city.tachikawa.lg.jp/shisetsu/1008065/1008100.html
• The main sanctuary of Azusami Tenjin-sha Shrine stands inside a protective outer hall and is not open to the public. Check that year’s announcements for the dates of the New Year’s Day Daruma fair and the September festival. At shrines and temples, keep your voice down and follow any notices; the old village plots along the Hawk Road are private homes and fields, so stay on the path.
• Practical tips: Carry an IC transport card such as Suica or PASMO; it works on JR, the monorail and Seibu trains. The aqueduct banks are steep — keep to the path and do not climb down.
• Combine it with: The view from the monorail window on the way there and back, and Tokyo udo, which grows underground in the same Sunagawa area (the farm shop is on the north side of Showa Kinen Park), let you walk the northern half of Tachikawa in a day.

After your walk, at the North Exit of Tachikawa Station

In autumn and winter, after walking the aqueduct’s green path and the Itsukaichi Kaido, you may find your body is colder than you thought.

Back at Tachikawa Station, one minute’s walk from the North Exit, is On the Shore Tachikawa (オンザショア立川店), on the third floor of the Etoile Building, 2-14-10 Akebonocho, Tachikawa. It is a hot yoga studio heated by lava-stone plates. As well as lava-stone hot yoga, it offers room-temperature yoga, Pilates, women-only kickboxercise, boxercise, HIIT and personal training, with more than 25 kinds of yoga lesson.

It is open every day from 8:00 to 23:30. Walk the aqueduct in the morning or get back to the station at night, and there is still time.

A trial yoga lesson costs ¥1,980 including tax, with two bath towels, one face towel and a yoga mat included in the rental, so you can drop in on the way back from a walk with next to nothing in your hands.

Pregnant guests cannot take part in lava-stone hot yoga, but room-temperature maternity yoga is available. Many of our yoga instructors speak English, and the studio’s owner, Naomi Fujita, who holds Japan’s top English qualification (Eiken Grade 1) and a perfect TOEIC score and once worked as a translator and overseas interpreter at Nomura Securities, and who lived in Alaska for three years, often helps guests from the US bases in English herself (visitors from abroad have even left Google reviews about the care they received in English); if you would like an English-friendly lesson, just say so when you book.

Studio information: https://ontheshore.jp/ — trial lesson booking: https://site.locaop.jp/C0aVK?_src=hp

From the rim of a 300-year-old channel, up to the third floor of a building by the station. For the aqueduct, that is a height it takes several kilometres to come down.

Cover photo: The Tamagawa Aqueduct seen from Mikage Bridge, Tachikawa: water flowing along stone banks under green trees. (Photo: sewmew / Public domain / Wikimedia Commons)

Information as of October 2026.

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