[Tagging] tagging extremely large flood control features.

[Warin]

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 <tagging at openstreetmap.org> 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 <pla16021 at gmail.com> wrote:
>>>
>>> 
>>>> On Thu, 24 Oct 2019 at 10:56, John Willis via Tagging
>>>> <tagging at openstreetmap.org> 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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