WEBVTT
Kind: captions
Language: en

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The city of Tokyo is built
around and over rivers.

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When you travel around here, it is striking
just how often you cross water.

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And from up above, you can see this
whole area is flat, low-lying coastal land.

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Some parts of Tokyo even sit below sea level.

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They've sunk because of decades of
pumping out groundwater.

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The two and a half million people
in those low-lying areas

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are protected by a network of
flood gates and aging levees,

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which'll be fine unless sea levels rise.

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But even inland,

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a huge part of this megacity is built
in river basins and flood plains.

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And as the climate breaks down,

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rain storms here are getting more intense
and more frequent.

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If you want to prevent river flooding,

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or drain neighbourhoods
that are starting to flood:

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where do you put the water?

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If you pump it out of that neighbourhood,

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you're likely just moving the flood next door.

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The best plan would, in theory,

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be to pump the floodwater
all the way to the ocean,

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or at least to a tidal river
that can deal with it.

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But for that, you would need tunnels and
buffer tanks on an almost unimaginable scale.

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Now, despite what some
breathless blog posts might claim,

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the whole metropolis doesn’t have that.

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But there is one place, about an hour
north of the centre of Tokyo, that does.

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This is the Metropolitan Area
Outer Underground Discharge Channel,

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or at least, one part of it: the holding tank.

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It is almost impossible to convey the scale
of this on camera.

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[IN JAPANESE:]

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If the Otoshifurutone and Naka rivers
start to flood,

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this is where the water will drain to.

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Actually, where the water
is sort-of still draining to.

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There was a massive rainstorm about two days ago,

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and there is still water in the system.

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I am not allowed down on the floor,
just in case.

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[IN JAPANESE:]

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This tank, and the kilometres of tunnels and
all the silos that bring water to it,

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cost nearly a quarter of a trillion yen,

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that's about two billion US dollars,
at the end of the 20th century.

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That was when the Japanese government was
spending money

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to finance enormous
infrastructure projects like this,

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to try and stimulate the economy.

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Which, for long-term security, is great:

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but it took a national recession
to make this happen.

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A plan like this only works if a government
wants to spend a colossal amount of money,

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and in the 21st century,

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there aren't many governments
willing to do that.

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Thank you to all the team here
for letting me down in the tank,

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and up on these catwalks.
You can find out more about them

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and their work
at the link in the description.

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Echo!

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[echoes continue and fade]

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That goes for a long time.