
Tokyo combats flood threats with second mammoth reservoir - thret
http://www.japantimes.co.jp/life/2014/08/17/environment/tokyo-combats-flood-threats-second-mammoth-reservoir/#.U_Pzq_mSyqm
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joezydeco
_Chicago, for example, stores water and sewage in a nearby quarry during
periods of heavy rain._

Um, it's more than a quarry. Chicago is 3/4 through a _sixty year project_ to
install more than 100 miles of underground tunnels and reservoirs which will
hold 66 million cubic meters of water when finished in 2029 (or thereabouts).
The quarry is a temporary reservoir.

[http://en.wikipedia.org/wiki/Tunnel_and_Reservoir_Plan](http://en.wikipedia.org/wiki/Tunnel_and_Reservoir_Plan)

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adventured
I wonder if anyone has data on Japan's typhoon history. How many have hit the
country per year the past century (I've been unable to locate such data). In
regards to this:

"Tokyo is becoming increasingly reliant on this unique-to-Japan solution as
more typhoons hit the country each year"

as the US has seen no increase in hurricanes, and the last decade in
particular has been remarkably lacking in hurricanes.

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userbinator
_the 3.3-km-long tunnel-shaped reservoir, which is 7.5 km in diameter_

That seems absurdly large. Then again, I suppose they want to avoid the
question "what happens when it overflows?"

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jws
I believe it is 7.5 meters in diameter.

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lotsofmangos
The picture in the article would seem to be a 7.5m tunnel, if the person in
the picture is about 1.8m high.

But this is Japan, so I'm going for 7.5km and the person is actually a 1.8km
high Super Dimensional Fortress.

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blueskin_
>But this is Japan, so I'm going for 7.5km and the person is actually a 1.8km
high Super Dimensional Fortress.

I like this one better. Why doesn't their flood defence plan involve giant
mecha to vaporise the water with lasers?

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Xylakant
Because that's totally absurd. Everybody knows that the water will condense,
form clouds and just bring you heavy rain again, stupid!

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qwerta
> will be able to hold 135,000 cu. meters of water, enough to fill 54 Olympic-
> size swimming pools.

It must be hard to build it in middle of metropolis, but this is hardly
'mammoth'.

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wisty
Once you're talking volume, things start scaling cubicly. It's not intuitive
to most people that a cubic meter of water weights a ton. It's certainly not
intuitive how to compare say, the Hoover Dam to a 7.5km long (but skinny)
reservoir.

This massive reservoir could be about 50 by 50 by 50 meters. Or 10 meters
deep, and 120 meters square. Which is in a lot of water, in a sense.

But compared to the Hoover Dam, which is 2,600,000 cu of _concrete_ (and about
about 300 million times the capacity of the Japanese reservoir, if you're
including Lake Mead) it's not very big.

Note - I might have made a huge mistake somewhere here. It's hard to tell when
you start cubing things, because intuition starts breaking down.

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qwerta
I was comparing it to other water reservoirs (Hoover Dam for example). 135,000
cu. meters is a droplet, small villages have larger reservoirs.

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blueskin_
There are a few similar tunnels to this in the UK, including one around where
I live. It's an interesting method, and probably one a lot of the US could
benefit from too.

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shubb
This £4.2bn scheme for instance:
[http://en.wikipedia.org/wiki/Thames_Tideway_Scheme](http://en.wikipedia.org/wiki/Thames_Tideway_Scheme)

However, following the 2008 crisis, the government followed a strategy of
immediate spending reduction (as opposed to US stimulus spend).

While mega projects such as this were still funded, the budget for
environmental management was reduced by ~30% accounting for inflation. This
impacted river and drainage channel maintenance, greatly increasing damage
inevitable from bad weather.

The cost of the 2012 floods post cuts was £1bn, compared to a cost of 0.5bn
from worse weather before the cuts in 2009 (similar rainfall accompanied by
strong winds as well).This is about 30% more than the total saving from budget
cuts.

The interesting thing is, I have not yet seen anyone in the press draw a
connection. The locals know, that the floods rose from ditches and rivers that
were not dredged. I've not seen the broader picture mentioned in the UK press
once.

Maybe no one cares, because drainage is boring, and doesn't do anything when
it isn't desperately needed. There are a lot of things like that.

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wodenokoto
11 CM of rain an hour? 7.5 km in diameter? Those looks like typos to me.

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kijin
7.5km diameter is definitely a typo, it's supposed to be 7.5m.

11cm of rain per hour is not a typo. The Pacific Ocean contains more water
than the rest of the oceans combined, and it can dump it wherever the hell it
wants. East and Southeast Asia are particularly vulnerable because the trade
winds blow hot moisture toward Asia (and away from the Americas). During the
monsoon or when a big typhoon hits, some locations can get more than 10cm of
rain per hour, although it's usually localized to a small area and only lasts
a few hours.

Just a couple of weeks ago, a typhoon hit Jeju island in South Korea and
dumped 1 meter of rain in 24 hours. That would be more than an entire year's
worth of rain in most parts of Europe and North America, and would have been
catastrophic if not for the highly porous volcanic geology of Jeju. The
current record for South Korea is around 15cm per hour. Since Japan gets more
typhoons than we do, I wouldn't be surprised if their record was even higher.

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cdr
Localized precipitation can be unbelievable when a front stalls over an area,
no major event like a typhoon / hurricane even required. The September 2013
floods in the front range of Colorado caused by a stalled front topped out at
9.6mm/hour on the worst day, with 430 mm total in 6 days - just under the
average _annual_ precipitation.

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kijin
9.6mm/hr is an order of magnitude lower than what this Japanese reservoir is
expected to handle. It would be considered heavy rain, but not at all unusual,
for monsoon season in East Asia. It happens a few times every summer, so most
cities in Japan and Korea are equipped to handle it just fine. If such events
were more common in Colorado, they would have been better prepared, too.

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TheLoneWolfling
"Sorry, but your browser needs Javascript to use this site. "

No thank you.

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userbinator
Agree with the sentiment but I can read the article with JS off.

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okasaki
Are you sure? I just get that message and no article.

