
Berlin Is Becoming a Sponge City [video] - flohrian
https://www.youtube.com/watch?v=uWjGGvY65jk
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jorleif
These kinds of techniques are often claimed to be effective against flash
floods, which makes sense since they slow down water transfer to rivers. Does
anyone know any studies about how effective it could be against seriously
heavy precipitation of the scale of Harvey or South Asia floods right now? In
other words, how well does the approach scale?

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ethagknight
Civil engineering has pretty well quantified the rate at which water is
absorbed by certain soils, accounting for groundcover, trees, pavement, local
detainment, etc. Berlin's sponge mission is baiscially distributed detainment,
working to offset hardscaping (driveways and roofing). In other words, it's a
well known and very predictable science, but we (we being US land development
industry) has not cared. HOWEVER rain at the scale of Harvey cannot
practically be planned for beyond "don't build on land that's lower than
average"

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Declanomous
Well, that's partly true. A lot of the flooding is due to the fact that the
entirety of Texas doesn't care about hydrology, and all that water is ending
up downstream, in Houston.

There'd still be flooding, and it would still be bad, but a certain degree of
flooding was avoidable.

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microcolonel
The other thought, I imagine, is that they felt the probability was low that
they would see a flood of this scale even within their lifetime; that ended up
being a poor bet. Even so, flood insurance is also cheaper when the perceived
likelihood of a flood is low.

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robotresearcher
Since cities usually survive much more than one human lifetime, this is not
good reasoning.

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microcolonel
People build houses, cities don't.

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robotresearcher
As you almost certainly know, the city controls permissions for every
building.

A city that gives planning permission for a development that is probably going
to be destroyed with loss of life in the next hundred years is not serving
people well.

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asciimo
My first thought is that it might be hard to prevent decay and leaks into the
structures supporting these spongy surfaces. 80cm of water logged soil above a
parking garage, for example.

~~~
wongarsu
Planting grass on top of parking garages isn't that unusual or new in Germany
(though usually done for aesthetic reasons), so I assume this is a solved
problem.

Sufficiently deep buildings and parking garages might also encounter ground
water, so adding soil on top might not even add new problems to the
engineering side.

Similarly, the rooftop plants are shown on rooftop designs that would already
have to deal with stagnating water

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mkesper
Municipalities can (and commonly do) grant a reduction of fees for reducing
sealed soil, so it's not only aesthetic reasons.
[https://de.wikipedia.org/wiki/Niederschlagswassergeb%C3%BChr](https://de.wikipedia.org/wiki/Niederschlagswassergeb%C3%BChr)

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erikb
funny just watched this yesterday night. Was really surprised by it. When you
live in Berlin it's not something you see that yet. But of course Berlin is a
more green city than something of the size of New York just by being smaller.

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ekianjo
The video only shows relatively small buildings - would that system work with
high rise towers?

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F_r_k
High towers have got the same land footprint, so yeah, it would work

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ekianjo
Land footprint, yes, but they do have higher volume to surface ratios and that
should play some role in heat absorption and dissipation I think.

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visarga
What happens to the plants during the summer if there is too little rain? Do
they also install watering systems? That would be expensive to maintain.

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hibbelig
This is Berlin! Too little rain? I don't think so.

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doener
[https://news.ycombinator.com/item?id=15128428](https://news.ycombinator.com/item?id=15128428)

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the-dude
Interesting, but no new ideas. These rain water management ideas are being
implemented for a couple of years now in The Netherlands when developing new
real estate.

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haakon
And The Netherlands probably got the idea from China:
[https://www.theguardian.com/sustainable-
business/2015/oct/01...](https://www.theguardian.com/sustainable-
business/2015/oct/01/china-sponge-cities-los-angeles-water-urban-design-
drought-floods-urbanisation-rooftop-gardens)

~~~
vanderZwan
Hopefully they steal good ideas from all over the place. The video mentions
swales, which is a mainstay of permaculture, which has been tried out in
various ways all over the world since the 70s.

