Tokyo's Flood Tunnel

Tokyo, a city built on the coast, intertwined with water has put in place a flood system you’ll have to see to believe. On this episode we bring you Tokyo’s flood tunnels.

Global oceanic city Tokyo has so much water access including cancels and waterways within the city that a grand plan was put in place to protect the city from flooding. There are 8 rivers that run through Tokyo all capable of flooding during a typhoon.

In the 1950s - 1960s typhoons flooded and destroyed the low lying old downtown of Tokyo.
Based on Tokyo’s geographical location disaster in many forms can strike at any moment. Over 38 sq miles or 100 sq km of the city is below sea level which was made worse by rapid construction in the 1960s and 70s. Water was extracted causing the are around Koto-ku to sink further down 2.2 feet or 70 cm.

Tokyo’s annual rainfall of 60 inches or 1530 mm hasn’t changed that much over the years but the pattern in which the rain falls has. In recent decades that rain pours heavy and hard putting people’s homes at risk of flooding.

Over 80 years ago an artificial waterway was dug, walled with concrete and armed with gates to control the rate of flow away from east Tokyo. Overtime more gates were added but eventually Tokyo devised an idea to build an enormous structure underground to soak up typhoon flood water at outrageous volumes. This came after the 1991 catastrophic flood that submerged 30,000 homes and left dozens dead. 3 billion dollars and 13 years later the Metropolitan Outer Area Underground Discharge Channel was completed. 5 stories tall this massive chamber is so long it’s length is greater than the height of this building, Fountain Place in Dallas. Outfit with dozens of pillars, each one weighs in over 500 tons. As the rivers start to fill up water is diverted into this surge tank which will then be redirected to the man made river that exits the city. Being the largest of its kind in the world, this surge tank sees water fill up inside 7 to 12 times a year. How this is possible is a 3.7 mile or 6 km network of huge pipes all positioned to take in water when the flow is too high that carries it through the pipes back to the surge tank.

4 Oversized turbines converted from aircraft engines can pump 13,000 cubic gallons or 50 cubic meters of water per second each. All this flood water is pumped into 1 of 5 mega cylinders that spans 20 stories deep into the ground. These tubes are so big the space shuttle could fit inside. Designed to absorb the anticipated water volume of a once in 200 year flood, these cylinders angle the water so that is spins around the outside of the tubes to avoid a crashing impact at the bottom. As water fills up it will be pushed over to the surge tank than out to the main exiting river. All the soil pulled from where the chamber and tanks are place was used to build up and strengthen the riverside dycks.

Since its implementation the flood tunnels and chamber have reduced flood damage in Tokyo by 90% which has led to other countries to come up with their own plans to build similar tunnels in their major cities.

Are you impressed with modern feats of engineering like Tokyo’s flood tunnels, let us know in the comments down below.

Source:
https://www.youtube.com/watch?v=Rp2l6nFIsZA
https://www.wired.com/2017/04/christoffer-rudquist-tokyo-drainage-system/

Footage:
https://www.youtube.com/watch?v=CsPxjRobjpk
https://japangasm.wordpress.com/2012/01/12/the-underground-wonder-of-tokyo/
https://www.citymetric.com/skylines/tokyo-sitting-worlds-biggest-flood-run-tunnel-917
https://www.insidejapantours.com/experience-japan/i-gcan-15/g-can-flood-surge-tunnels/

Check out some of our other videos:

Top 10 Fruits You’ve Never Heard Of Part 2
https://www.youtube.com/watch?v=hRdgPyZF45g&feature=youtu.be
Top 10 Fruits You’ve Never Heard Of
https://www.youtube.com/watch?v=OKTej1u-7-0&feature=youtu.be

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Intro music thanks to Machinmasound:
Rallying the Defense:
https://www.youtube.com/watch?v=ruPk4RD19Nw

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