At the center of Japan lies its capital, one of the biggest megalopolis worldwide: Tokyo. Besides all the advances, Tokyo seems to have a critical reality: flooding. At some points of its geography, the city is lower than the sea level. In fact, these low-lying areas regroup approximately two and a half million people. 

With people losing their houses, relocating each year, and some of the infrastructures becoming obsolete, and this flooding catastrophe couldn’t keep on anymore. Japanese authorities have decided to create underground flood gates that would protect the city from being drowned in water. However, this system works just fine, except for the rise of sea level: it could become a problematic issue. 

Japan:The Underground water reservoirs - Sheet2
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Today, we are facing a major global warming disaster. With that being said, these flood gates would, in theory, prevent nothing in the near future. This era of rainstorms, flooding, and water levels reaching record levels year after year, with around 30,000 houses flooding in Tokyo pushed the Japanese government to think about a new alternative solution.  

The two-billion dollars underground chapel 

Japan:The Underground water reservoirs - Sheet1
japan flooding hundreds of thousands ordered to evacuate – cnn

Trying to cope with this persistently growing concern, the Japanese government invested around two billion US dollars in an underground discharge channel, North Tokyo. This huge underground infrastructure is located in Kasukabe, Saitama. It is the largest facility of its kind in the world. Construction works started in 1992 and ended in 2006. 

There, we can find five concrete containment silos that are 65 meters long, with a diameter of 32 meters. The five silos are linked by a 6.4 meters tunnel. Adding on to that, there is a large water tank making 25.4 meters height per 177 meters long. Its width is around 78 meters, about 50 meters below the ground.

The underground tunnel is in use around seven times a year, to divert the rainstorms’ water and keep Tokyo’s streets from flooding. The rest of the year, this area is open to visitors, upon reservation of course. The site is characterized as an underground chapel since it regroups all these huge structures, forming a sort of holy place. 

These kinds of facilities diminish the risk of house flooding from 30,000 to 40 per year. Which is an enormous ratio! How Japan managed to create these underground chapels made the city a safe place again. If you are a mega-structure geek, I would highly recommend you to go visit this underground discharge channel. It is not only an engineering marvel, but a whole experience full of imagination. 

In fact, multiple movie scenes were shot in this gigantic construction. Not too shocking right? Just like heroes of movies play their act there, the discharge channel became in itself a hero for Tokyo and its suburbs. 

The tour

The tour must be booked at least a week in advance, and you shall either speak Japanese or be accompanied by someone who does. You will be visiting the “chapel” area, where you will see the reservoirs. But beware! There is not a lot of security in the spaces. So try not to slip! 

Regardless of the slight danger, this once-in-a-lifetime experience will open your eyes and bring out to light Japanese innovation. Just like always, Japanese’s’ intelligence knows how to make the world not blink an eye while listening and discovering their creations. 

Dima Fadel
Author

Dima Fadel is a passionate and curious architect, constantly seeking new knowledge. She graduated with a Bachelor Degree in Architectural Studies from the Académie Libanaise des Beaux-Arts in Beirut last summer, and is currently pursuing her MSc in Integrated Architectural Design at La Salle, in the urban laboratory of Architecture: Barcelona.

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