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How to control a killer flood on the Sumida River

This is epic! It started with mild curiosity. Why doesn't Tokyo do more with its rivers? Instead of entombing them in concrete, why not more parks and boats and bridle paths?

Then it escalated. Where does the Sumida River start? Why is the Arakawa in Tokyo such a straight line? Surely that's not natural? Iwabuchi sluice. What's that? Great Kanto Flood 1910. Cripes, look!, Sensō-ji was under water. Why is there so little information in English? Wait, hang on, Wikipedia is wrong!

Thus idle speculation unleashed a growing fascination with Tokyo's flood control techniques: a complex system of rivers, canals, sluices, locks, controlled water levels, super levees, evacuation areas and a massive underground discharge channel in Saitama. Research proved interesting but frustrating, so I rejected academia in favor of empirical evidence: I walked along Tokyo's most important waterway, the Sumida, from its origin in Kita-ku to Tokyo Bay. I covered 25 km and passed over/under 26 bridges for cars and pedestrians.¹

The original red sluice gate, Akasuimon, at Iwabuchi

This is such a complex topic that it justifies its own blog – nay, book! – but I'll do my best to limit myself to three parts:
  • the upper section of the Sumida and the origin of its present-day flood control system;
  • the middle section in Taitō, where I live, undeniably the part with the most interesting history, sights and bridges;
  • the lower section where the river forks at Tsukudajima before flowing into Tokyo Bay.

Let's start at the top, shall we?

What we now call the Sumida River² (隅田川 Sumidagawa) starts in Kita-ku where the Arakawa (荒川) splits into two: a river that flows through the Iwabuchi sluice gate and follows a natural course (called the Sumida) and an entirely man-made canal that follows a straight course (called the Arakawa).

Yes. This was another surprise. The Arakawa in Tokyo itself is actually a massive artificial canal built with one single purpose: to prevent disasters in the shitamachi. We forget that Tokyo is a harbor city crisscrossed with rivers, and that the shitamachi deserves its name: a low-lying area that used to be a swampland and is still vulnerable to floods.

Japan's rivers are prone to flooding because they are relatively short and flow rapidly down steep slopes. The ratio of peak flow discharge³ to basin area is relatively large, ranging from 10 times to as much as 100 times that of major rivers in other countries. The water level rises and falls very quickly. The river regime coefficient – the ratio of the maximum discharge to minimum discharge – is between 200 and 400 times larger than that of continental rivers.

Yakumo Jinja (八雲神社in Iwabuchimachi  is one of the oldest shrines
in this area. Yes, of course I visited shrines, too!

Yakumo Jinja

Tokyo's main river is the Sumida. I couldn't determine the origin of the name, but early Heian literature refers to a ferry that transported travelers across the river at a settlement called Sumida Juku (near present-day Mukōjima). Old records indicate, for example, that Minamoto Yoritomo stationed many troops at Sumida Juku. 

The river – and life – trundled along until the arrival of Tokugawa Ieyasu, the man who created a new capital at a little fishing village called Edo in the early 1600s. Edo, which used to be a huddle of huts near the mouth of the Sumida, was transformed into a huge political city by aggressive public works including land reclamation, new canals and clean water supply systems.

The first bridge across the Sumida was Senju-Oohashi, originally built in 1594; the second was Ryōgokubashi, built in 1659. Ryōgoku means "two provinces", because it connected the old provinces Musashi and Shimōsa.

Life continued, the river flooded, people died. A turning point arrived in 1910, when a torrential downpour of 300–400 mm fell between 8 and 10 August. The Sumida swelled, broke through several embankments and turned the city from Iwabuchi to Kameido into a vast inland sea. The flood water took two weeks to subside, affecting 1,5 million people and leaving 270 000 homes flooded. Damage totaled more than ¥120 million yen, equivalent to 4,2% of the gross national income at the time.4

The government's response was to build an artificial channel to protect downtown Tokyo from further flood damage.5 The project involved construction of a sluice gate at Iwabuchi in Kita-ku and a massive diversion channel 500 meters wide and 22 km long.

This notice board indicates the old red sluice (赤水門), the new blue sluice
(青水門), the Sumidagawa (隅田川) and the Arakawa (荒川).

The old red sluice gate with a marker that indicates previous flood levels.


The first sluice gate, called Akasuimon, was completed in 1924, on the spot where the Shingashi River joins the Arakawa. It was designed by Aoyama Akira, an engineer who was an architectural consultant on the Panama Canal a decade earlier. When the river was in flood, the sluice gates would be closed, controlling flow volume in the river’s main course and dumping the flood waters through the wide channel directly into the sea. Construction, which took a total of twenty years, was completed in 1930. This channel is also called the Arakawa, but it's not a real river: the "real" Arakawa actually morphs into the Sumida.

This sculpture on Nakanoshima, a small island near the red sluice gate,
is called "piercing the moon".

Tokyo's only sake brewery, Koyama Shuzō, can be found in Iwabuchimachi.
It's said to be the only place in Tokyo with water pure enough for sake.

Above, the sake brewery; below, markers that
indicate the distance to the ocean and water levels



It wasn't the last of the floods. Typhoon Isewan in 1959, the strongest ever to hit Japan, killed 5098 people in Japan. Nagoya was the worst affected, but the typhoon also caused massive damage in Tokyo. Read about Isewan here and here (PDF).

Isewan won't be the last typhoon, but next time, perhaps, Tokyo will be better prepared. A bigger sluice gate, this time blue, was constructed slightly lower down the Sumida in 1982. Super levees and evacuation centres have been built along the river (the biggest evacuation centre, between Senju-Oohashi and Senju-Shiori-Oohashi in Minami-Senju, can accommodate 120 000 people), sluice gates and pumping systems have been added to various rivers in the shitamachi, and water levels in especially Kōtō-ku's rivers have been lowered. Finally, a massive underground discharge system called G-cans has been constructed in Kasukabe, Saitama. I haven't visited it yet, but you can read more about it here and here.

The new blue sluice gate

Here you can see the old and the new sluice gates in one shot.

You're wondering about tsunami damage in Tokyo? Uh-oh. If there's a quake right underneath Tokyo, or if it's so near that a tsunami comes funneling through Tokyo Bay … let's just say I hope this apartment building survives and I hope the 11th floor is high enough.

If not, shōganai.

If you'd like to walk along the Sumida yourself, I suggest you skip the upper part except for Iwabuchi. If you walk across the old red sluice gate, you'll reach a small, quiet island called Nakanoshima, where you can relax under a tree, have a picnic, watch the mighty angry river (Arakawa means angry river) as it divides into two.

The rest of the upper Sumida is really not that attractive. The Hero graciously offered to be my chauffeur, so we covered the section from Iwabuchi to Senju-Oohashi on a motorbike. I returned to walk from Adachiodai Station along the river, but had to take a shortcut via Kita-Senju Station to Horikiri Station, because there's no paved walkway along the river in that area.

I'll highlight two areas.

Firstly, Adachiodai Station on the Nippori-Toneri Liner is situated on the narrowest strip between the Sumida and the Arakawa. It's wide enough for a station, a row of apartment buildings, a road … and that's that. I tried to find a high spot where I could get both rivers into one shot, but didn't succeed.

If both rivers flood at the same time, that's it, bye-bye station.

This is the Sumida seen from Adachiodai Station.

Here's the Arakawa on the other side of the station.

The Nippori-Toneri Liner bridge across the Arakawa

Arakawa

See that apartment building? On its right is the Sumida, on its left is the Arakawa.

Toshibashi

Kodaibashi

Otakebashi

Otakebashi

Secondly, Horikiri Station, which is near the only canal that connects the two rivers downstream. It's a fairly bleak industrial area, but I wanted to see the sluice, the canal and the super levee on the Sumida in that area.

Sluice gate on a canal between the Sumida and the Arakawa, near Horikiri Station


The Arakawa, with the canal leading to the Sumida

The canal leading towards the Sumida

The canal flowing into the Sumida

Levee on the Sumida

Horikiri Station

Coming up, Part 2, from Shirahigebashi to Ryōgokubashi.

Sources

A Companion to Japanese History, edited by William M. Tsutsui
Flood Prevention and Remediation, edited by F. C. B. Mascarenhas
Inland Flood Hazards: Human, Riparian, and Aquatic Communities, edited by Ellen E. Wohl
River Basin Management IV, edited by C.A. Brebbia

Notes

1) There are 26 bridges for cars and pedestrians across the Sumida; several more for railways and water supply pipes. Once I've done all three Sumida posts, I'll publish a list of all bridges with their names and photos.

2) River is kawa in Japanese, but it's pronounced gawa when it's combined with certain words. Sumidagawa would be translated as Sumida River; Arakawa as Ara River. It's usually translated as Arakawa River, but that means Ara River River, which is silly. My imperfect solution is to refer to them as the Sumida and the Arakawa.

3) Data provided by the Ministry of Land, Infrastructure, Transport and Tourism

4) Data provided by the Arakawa Downstream River Office (荒川下流河川事務所) in the Ministry of Land, Infrastructure, Transport and Tourism

5) One wishes this government were in charge right now, to provide an adequate response to the lingering after-effect of the Great Tōhoku Earthquake.

This is the Arakawa just before the red sluice gate.
That's Saitama on the other side.

Fishermen

Taking a nap on Nakanoshima

Boats 'n stuff

He's playing a saxophone. This photo was taken near Adachiodai Station.

Suntanning next to the Sumida near Adachiodai Station

Fishing!

More fishing! The fishing shots were taken near Otakebashi.

Working!

There's The Hero, patiently waiting while Ru faffs with cameras.
He deserves a medal for his assistance.
(This is a bridge across the Shingashi River near the red sluice gate.)

Sunset on the Sumida, and time to say goodbye.


View Sumida River from Iwabuchi to Horikiri Station in a larger map

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