Protecting cities from floods - Metropolitan Area Outer Underground Discharge Channel

From the outside, the Metropolitan Area Outer Underground Discharge Channel, which is located in Kasukabe, Saitama, looks like any other building along the Edogawa River. However, there is a discharge channel that extends for 6.3km at about 50m under the ground. The channel has a capacity of 670,000㎡, taking in water from 5 sources (Nakagawa, Kuramatsugawa, Ohotoshifurutone River, #18 Water Channel and Komatsugawa) to be diverted to Edogawa, and is one of the largest underground channels in the world.

The large silos in the facility evoke images of a shrine, and “It was used as a meeting place for local citizens who wanted to save Saitama in the movie `Fly Me to the Saitama`. We began holding tours of the facility in August 2018, and they’ve become quite popular.” (Mitsuru Arai, Assistant Manager, Edogawa River Office)

There is a large space with countless oval pillars when you reach the bottom of the long staircase. Even with the humidity, no scent of sewage could be detected. And even though it was quite hot and humid outside, this underground space was cool and pleasant. This is the huge surge tank (177m long, 78m wide, 18m high) or the “underground shrine”. It’s often used to film fight scenes in movies using special effects when there’s no water (no filming access at this moment). The space and view is unlike any other.

The 5 vertical silos are 70m deep and have an inner circumference of 30m. This is where the flood waters are taken in and released into the surge tank.

The area around Kasukabe where the Metropolitan Area Outer Underground Discharge Channel is located, has been a highly populated area due to its convenience to Tokyo. But the area was prone to floods due to its lower altitude. Plans for the Metropolitan Area Outer Underground Discharge Channel　began in the 1960’s as part of a water management plan, with research and planning beginning in 1993, and partial operations in 2002 before becoming fully operational in 2006.

In October 2019 when Typhoon Hagibis wreaked havoc in many nearby areas, the Metropolitan Area Outer Underground Discharge Channel was key in minimizing the damage in the area, taking in flood waters from nearby channels and strategically releasing it into Edogawa River. Its success was covered widely in the media.

This kind of facility is still very unusual globally, so there are many requests for visits from overseas. Tours of the facilities are held to encourage an understanding of how the Metropolitan Area Outer Underground Discharge Channel works, and visitors have a chance to observe the underground shrine “surge tank”, walk along the formerly off limits access catwalks, and even walk down part of the staircase in the silos. (Tour details differ by course, and the pump course is closed temporarily as of December 2020.) While the tours are only available in Japanese, there are apps to virtually experience the tank filling with water, as well as guide apps in different languages. Nakata even took an acquaintance from abroad on a surprise visit. It’s apparent the underground channel is key in protecting residents in nearby areas. And it’s a beautiful and mystical facility as well, an example of beauty in action.