On 25/10/19 00:20, Joseph Eisenberg wrote:
I think describing these as "flood prone" in some way is a good idea.
I think it would be better to use "flood_mitigation" as that implies deliberate
design rather than natural event.
I imagine you've already mapped the individual features: the levees
(man_made=dyke), the individual basins and so on. I wouldn't want to
map the whole area as water + intermittent=yes because the water is
only rarely present.
Perhaps we need a new tag to map a whole area as flood prone? I've
seen that on French and Australian topo maps there is a specific
rendering for areas that are "subject to inundation".
These areas are inundated by their nature, where are the features to be mapped
are designed to be flooded to mitigate any flooding elsewhere. I think
rendering should reflect that.
-Joseph
On 10/24/19, John Willis via Tagging <[email protected]> wrote:
I am aware of the underground basins that are dedicated to the task, but I
am wondering how to map above-ground basins that are used as regular land
360+ days of the year - something you don't have to deal with when mapping
the underground tanks
There appear to be 2 things to be mapped.
Existing features that have this "flood_mitigation" use - this should be a sub
tag on those features.
Areas, that may have several features, that are used for "flood_mitigation" and
so need a primary key/value to stand alone.
~~~~~
The rest is not important, but read on if you Want.
Yea, Thats in Tokyo on the Arakawa/Edo rivers, the the Tokyo metro area. The
start of the Edo river is a lock-controlled flow from the Tone - as the
larger Tone goes off to the Pacific 70 Km north of Tokyo (it doesn't
discharge into Tokyo Bay).
As I understand it, those tanks manage the water going into the system in
Tokyo itself, absorbing the flow from the smaller channels/rivers in Tokyo
(Tokyo is big and flat) and buffering it before it gets discharged into the
rivers, absorbing what would normally be trapped behind the River levees.
The Tokyo tank system couldn't handle the river flow directly (it's immense)
- The rivers channeling water down through the region just use extra-wide
and tall 8-10m levees to provide ~ 10-15x normal flow volume to the sea.
(The river goes from 1-2m deep to 8-9m deep, and doubles in width)
Small towns in my area (pictured) were flooded not by a levee breach, but by
water trapped outside the levee that couldn't get into the river through the
normal gates.
The Tokyo system prevents that from happening - though I wonder if it could
absorb even a quarter of what the Usuichi trapped. The Usuichi is gigantic.
Javbw
On Oct 24, 2019, at 9:08 PM, Paul Allen <[email protected]> wrote:
On Thu, 24 Oct 2019 at 10:56, John Willis via Tagging
<[email protected]> wrote:
Inside, there are three “retarding basins” (numbered 1, 2 & 3), with #1
having with a large traditional reservoir, parks, golf course, and sports
grounds inside.
There is more to the system than that. There are also underground holding
tanks and
tunnels: https://www.youtube.com/watch?v=cfJOW2PtrGk
--
Paul
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