G-Cans Flood Channel
Interesting facts
- It is considered the largest underground floodwater diversion facility in the world.
- Its four pumps are driven by gas turbines adapted from Pratt & Whitney JT8D jet engines, and each impeller is about 3.8 metres across.
- At full power the pumps could empty an Olympic swimming pool in roughly 12 seconds.
- The pressure-adjusting tank alone holds about 670,000 cubic metres, roughly the volume of Tokyo's Sunshine 60 skyscraper.
- The main tunnel runs about 50 metres down, directly beneath National Route 16.
- Building the system cost roughly 230 billion yen.
- By July 2021 the channel had been activated 131 times, on average seven or eight times a year.
- During Typhoon Hagibis in October 2019 it filled to about 90 percent of capacity, one of the largest volumes it has ever held.
- The tank's ceiling stands about 25 metres above its floor.
- The visitor centre's name Ryลซ-Q-kan joins the dragon of a local legend with a Q taken from aqua.
Why it is worth it
Fifty metres beneath the rice fields and suburbs of Kasukabe, north of Tokyo, lies a room that people compare to a temple. Its official name is the Metropolitan Area Outer Underground Discharge Channel; engineers and fans know it as G-Cans. It was built for one purpose: to take floodwater that the small rivers of the low-lying plain, the Nakagawa, the Kuramatsu and the ลotoshi-Furutone, cannot hold and send it underground to the far larger Edogawa River. Construction began in the early 1990s, the first section went into partial operation in 2002, and the full system was finished in 2006.
The scheme is a chain of five vertical shafts, most of them about 31 metres across and around 70 metres deep, linked by a tunnel of roughly 6.3 km with an internal diameter near 10 metres. Rivers and channels spill into the shafts during heavy rain; the water runs through the tunnel to a vast pressure-adjusting tank next to the pump station. There, four pumps driven by gas turbines derived from aircraft engines can push up to about 200 cubic metres a second into the Edogawa.
That pressure-adjusting tank is what made the place famous. It measures some 177 by 78 metres, and its ceiling is held up by 59 concrete pillars, each about 18 metres tall and weighing around 500 tonnes. In the half-light the pillars recede in ranks like the columns of a hypostyle hall, their bases stained by past floods, and a single visitor on the floor looks like a figure in a Piranesi etching. The Japanese nickname, "underground temple", fits exactly. Film and television crews have used it in well over a hundred productions, from tokusatsu series such as Kamen Rider 555 to music videos.
The facility belongs to the Edogawa river office of Japan's national land ministry, and the tank and shafts can be seen only on guided tours; courses range from the classic walk down into the tank to routes through the pump room and the bottom of a shaft. The visitor centre, Ryลซ-Q-kan, explains the flood history of the plain that made this cathedral of concrete necessary.
Getting there
The channel runs between Showa and Kasukabe in Saitama Prefecture; Kasukabe city centre is about 6 km away. Tokyo Haneda International Airport (HND) is about 50 km off. The nearest station is Minami-Sakurai on the Tobu Urban Park Line, a 30โ40 minute walk or a short community-bus or taxi ride from the Ryลซ-Q-kan visitor centre.
On these lists
From the encyclopaedia
The Metropolitan Area Outer Underground Discharge Channel , popularly known as G-Cans, is an underground water infrastructure project in Japan. It is the world's largest underground flood water diversion facility, built to mitigate overflowing of the city's major waterways and rivers during rain and typhoon seasons. It is located between Showa and Kasukabe in Saitama prefecture, on the outskirts of the city of Tokyo in the Greater Tokyo Area.
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