Metropolitan Area Outer Underground Discharge Channel
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Lair of the BalrogThe Metropolitan Area Outer Underground Discharge Channel (首都圏外郭放水路), also known as the G-Cans Project, is an underground water infrastructure project in Kasukabe, Saitama. It is the world's largest underground floodwater diversion facility, built for preventing overflow of the city's major waterways and rivers during rain and typhoon seasons.
Work on the project started in 1992 and was completed by early 2009; it consists of five concrete containment silos with heights of 65m and diameters of 32m—connected by 6.4km of tunnels, 5m beneath the surface, as well as a large water tank with a height of 25m, with a length of 17m, with a width of 78m, and with 59 massive pillars connected to a number of 10 MW pumps that can pump up to 200 tons of water into the Edogawa River per second.