Extreme rainfall, intense storms, destructive earthquakes, and tsunamis have made Tokyo one of the riskiest metropolitan areas in the world.
People are concerned that floods and typhoons can create havoc in the city due to its vulnerable drainage system. The concern has become even more serious as the city prepares to host the 2020 Olympic Games.
The city government aimed to resolve this issue once and for all
To protect Tokyo from floods, the city constructed the world’s largest underground water tank — it serves as a massive discharge channel for floodwaters. The channel directs excess water away from the metro area into an underground tank, larger than a soccer field.
The ceiling of the water tank is supported by 59 pillars, which are 18 meters tall and weigh 500 tons each. From this tank, 78 industrial pumps discharge the floodwater into a larger river system to flush the water into Tokyo Bay.
Built 22 meters below ground level, the megaproject took more than 17 years to complete. At a cost of $2.6 billion, it is the biggest such canal in the world.