Terror movie? Not quite… It's actually a safety system to prevent the flooding damages!
Tuesday, early morning.
Not heading to the office. On route to the World's Largest Drain System. Our destination is the next prefecture on the North of Tokyo: Saitama-ken「埼玉県」. Today, we will visit the Shutoken Gaikaku Housui Ro 首都圏外郭放水路 aka Metropolitan Area Outer Underground Discharge Channel [G-Cans Project].
Tokyo is filled with sky-high views, but today is all about underground wonders.
From the top of the storage tank, it is possible to see where the collected water is led back into the Edo River.
But let's take one step at a time.
Saitama is a region located North of Tokyo, with many rivers, particularly prone to flooding. In the past, the rice paddies served as natural drain system. Nowadays, they are replaced by cities. Concrete, asphalt, development but no drainage at all. When the rainy season (or typhoon) arrives, damage may be considerably high in this area.
Therefore, in 1992 the ambitious [G-Cans Project] was started. Concluded in 2009, with the completion of the Shutoken Gaikaku Housui Ro, or the Metropolitan Area Outer Underground Discharge Channel.
This massive drainage system consists of five huge silos, a 6.5km connecting tunnel, a storage tank and 78 pumps (4 of which are MAJOR airplane-motor powered turbines).
Water from the rain that falls through the huge tubes (silos), is then conducted through the connecting pipe. Because of communicating vessels effect, they will balance to the same level. When this is high enough, water will enter the storage tank (in the left of the drawing), until 6.17m height is reached in the 177m * 70m surface. At that moment, the pump will start to function and pour the water back to Edo river in a controlled way.
Since the structures are so huge, it is a really impressive visit. Highly recommended, provided you got some time in Japan, along with someone mastering the local language (they won't let you in without knowing Japanese because of safety reasons).
Let's go once again over it. Water is collected from the surface into the silos. The shape of the tube forces the water to slow down. Unfortunately, as smartly pointed out by my friend Kenneth, there is NO renewable electricity generation system in place :_(
Then, the connecting tubes guide the water over to the next silo.
The five concrete containment silos are 65m deep and 32m in diameter. They are located within certain limits from the rivers. The five silos act as flow regulators.
The silos are connected to a 10.6m diameter tunnel. The tunnel is constructed 50m underground, passing through the silos. The tunnel sends the water to the storage tank when the silos reach their capacity. The pillars of the storage tank appear as an underground cathedral. It's just very impressive to be there, but even more to understand how engineering may make life safer for so many people.
The water storage tank, popularly called the Underground Temple, is 25.4m high and 177m long. It is supported by 59 pillars which are 20m tall and weigh 500t.
Here can you see, how little we are.
When the water reaches the level marked by the sign (about 6.17m high) up to four airplaine motor powered turbines start pumping the water, from the storage tank into the Edo river. So the water is slowly disposed in a controlled way.
View of the pump.
Last but not least… The cleaning.
When the silos are half empty (or half full, as you prefer :P) smaller pumps bring the water outside, to avoid pollution in the "contained" water. This leaves a layer of mud that needs to be cleaned, specially at the huge water storage tank. So this huge vehicle is brought down to get it all shiny.
To visit the site [MAP]:
[0] Find great friends to get there with.
[1] Make a reservation over the internet [reservation form]
[2] Get a weekday off
[3] Ride Shonan-Shinjuku Line to Omiya and then change to Tobu Noda Line, get off in Minamisakurai
[4] Ride a cab to the facilities (bus is convenient for the way back) and enjoy the 1.5h tour
Special thanks to Hiro-kun "the 外人の友だち", without him this would have not been possible.
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