[Tagging] "Feature Proposal - RFC - Qanat"

Joseph Eisenberg joseph.eisenberg at gmail.com
Fri Jun 19 21:43:45 UTC 2020


> a spring is groundwater as well.

A spring is "a place where water naturally flows out from the ground". In a
spring, the water table reaches the surface.

The source of a qanat is underground, at least several meters depth (and
often quite far underground), below the underground water table. Sometimes
a well was dug first and then a qanat was built.

Please see the illustrations and examples on the Proposal page and
wikipedia, e.g:
https://en.wikipedia.org/wiki/Qanat#/media/File:Qanat_cross_section.svg

> if there are parts that are in pipes, will the qanat be interrupted? If
vertical shafts are not present, it is not a qanat (e.g. short enough to
not require these shafts)?

Qanats were not built from pipes. They are free-flow canals, usually cut
directly into bedrock, though that's not a requirement.

Currently, if a canal goes into a pipeline, it is standard practice to map
the pipeline as `man_made=pipeline` + `substance=water` and
perhaps `waterway=pressurised` if relevant. See for example
https://user-images.githubusercontent.com/42757252/76671649-dcce3980-65da-11ea-8dfb-55f9a21c1f12.png
- at https://www.openstreetmap.org/#map=17/41.70543/9.05265

>If vertical shafts are not present, it is not a qanat (e.g. short enough
to not require these shafts)?

The vertical shafts are part of the proposed definition.

If you check out some examples, you will see that the shafts are usually
only 10 to 50m apart, so even quite short qanat usually have more than 1.
E.g.:
https://www.openstreetmap.org/edit?way=624008315#map=17/31.43160/-4.36968 -
several parallel qanat are visible here (though I don't know if all are
still operational) in Morocco.

Examples in Afghanistan: https://overpass-turbo.eu/s/Vhk

>> The short definition of the tag will be "A gently-sloping man-made
underground channel for transporting groundwater via gravity, with shafts
visible from the surface."
> my suggestion would be to add a "typically" before "with shafts visible
from the surface", because it would seem strange to need a different main
tag just because the shafts aren't visible for one reason or the other
(e.g. hidden on purpose)

Sometimes there are small walls or caps over the shafts to prevent sand or
dirt from falling in. I was considering that to be still "visible" in a
way, but sure, we could change that.

– Joseph Eisenberg
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