[Tagging] Feature Proposal - RFC - Check dam

[Joseph Eisenberg]

Looking at the examples, I think the solid check dams where water is
designed to flow over the top can be mapped with the current waterway=weir
tag.

The slot and slit dams might be categorized as a sub-type of waterway=dam
since they are mostly solid but allow a small amount of water to pass
through the dam. Many standard dams have gates, spillways or other channels
for a small amount of water to pass through the structure.

However, I agree that the "fin", "rake", "beam" and "frame" structures are
not at all like a waterway=dam or =weir, since they are not solid
structures and do not normally impede passage of water, rather they are
designed to catch debris, rocks and logs which might otherwise be swept
downstream during flooding.


On Mon, Jun 7, 2021 at 2:30 PM Enno Hermann <enno.hermann at gmail.com> wrote:

> <https://goo.gl/maps/PrtuW627ndkc3NbX7>
>
> On Mon, Jun 7, 2021 at 6:03 PM Mateusz Konieczny via Tagging <
> tagging at openstreetmap.org> wrote:
>
>>
>> https://wiki.openstreetmap.org/wiki/File:Check_dam_on_Miya_River_(Jinzu_River).jpg
>> for me it looks like waterway=weir
>>
>> "Solid check dams usually have water flowing over only a small part of
>> their width and
>> are designed to handle sudden increases in water flow."
>>
>> Are you sure that thing depicted on image is not also a weir?
>>
>
> I agree that it's not the best example and from this picture alone it
> could be hard to tell, although the construction is typical for check dams.
> I managed to find the location and on Google Streetview (
> https://goo.gl/maps/PrtuW627ndkc3NbX7) or the Japan GSI seamlessphoto
> imagery (https://osm.org/go/7QeF1CmI6) the water level is clearly
> different and water seems to be flowing only through the bottom of the
> structure. Given that, the mountainous terrain and similar structures
> nearby I would say it is clearly a check dam.
>
>
>> And "designed to handle sudden increases in water flow." is applicable to
>> any sanely constructed waterway engineering.
>>
>
> "sudden and significant" might fit better. Often those streams are
> normally only a trickle or even completely dry but then can see sudden
> debris flows like this: https://www.youtube.com/watch?v=2Rfuoylv34k This
> is different from floods on already larger rivers.
>
>
>> See
>> https://en.wikipedia.org/wiki/File:Culverts_under_yass_river_walkway_weir.JPG
>> on Wikipedia weir page.
>>
>> Or https://en.wikipedia.org/wiki/File:Grial%C3%ABces_cuecenes.jpg with
>> description
>> "During periods of high river flow, this nineteenth century weir of
>> porphyry stone on
>> a creek in the Alps would have significantly more water flowing over it."
>>
>
> An early example of a check dam? ;) I'd say very small structures or
> simple constructions that can't be clearly identified as a check dam may
> just be tagged as weirs.
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