Lying fifty meters beneath the northern suburbs of Tokyo rests the Metropolitan Area Outer Underground Discharge Channel, affectionately known as G-Cans. Constructed between 1992 and 2006 for over two billion dollars, this colossal infrastructure marvel was built to protect the Greater Tokyo Area from severe typhoon flooding. The system works by collecting overflowing water from small and medium rivers across five concrete silos, each large enough to fit a Space Shuttle.
Water travels through a subterranean tunnel system spanning 6. 3 kilometers before entering a massive surge tank known as the Underground Temple. This cavernous space features 59 pillars, each weighing 500 tons, designed to break the energy of incoming torrents.
What truly makes G-Cans an engineering masterpiece is its propulsion system. To pump this water out into the Edo River, the facility relies on four massive water pumps powered by modified heavy-duty gas turbines adapted from aviation jet engines. Combined, these turbines generate 14,000 horsepower each, driving impellers that can discharge 200 metric tons of water per second.
That equates to draining an entire Olympic swimming pool every 12. 5 seconds. By utilizing aviation-grade propulsion engineering, Tokyo effectively created a subterranean drainage network capable of mitigating billions of dollars in flood damage during Japan's monsoon seasons.