Since Tokyo is surrounded by large rivers like the Arakawa, Edogawa and Tone, when there is high rainfall, it is easy for water to accumulate and overflow. Even though the banks of the rivers are quite wide, there is still a possibility of water levels to rise to dangerous levels. Most areas of East Tokyo are under sea level and many areas are reclaimed land increasing the risk of submersion.
The Metropolitan Outer Area Underground Discharge Channel, a facility built in 2006, located in Kasukabe, Saitama, is the world’s largest underground discharge channel at 50 m below ground. It was used for the fifth time since being built on October 12, 2019, to prevent flooding.
The Metropolitan Outer Area Underground Discharge Channel is basically an underground river that connects small rivers like the Nakagawa, Kuramatsu etc, that flow into the Edogawa. Water from these rivers is pumped into five banks that are connected to the Discharge Channel. The Pressure-Adjusting Water Tank reduces the speed of water diverted to the Edogawa through stable pump operation. There are 59 huge pillars weighing 500 tons each in the pressure tank, giving it the impression of a temple. Approximately 670,000m3 amount of water, about half the size of Tokyo Dome, can be stored in the entire Tokyo Metropolitan Outer Discharge Channel including the pressure control tank.
When not in use, you can join tours to see the facility and learn about how it prevents flooding in Tokyo.
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