|karst = yes|
|Anything, but typically a spring, related with a karst system|
|Used on these elements|
|Tools for this tag|
This tag has been approved for springs, to model the fact that their waters come from a karst system; it has been proposed to highlight the possible following characteristics, inherent in karst springs:
- chaotic, dangerous surroundings, because of the karst effects on the soils;
- quick and strong throughput variations, often related with surrounding rainfalls (if applicable, use intermittent=yes);
- average water quality, as such springs are often contaminated with surface pollutants.
Nonetheless, this tag is not limited to springs, and can be used on any non-sinkhole=* feature which is in relation with a karst system, such as shafts opening on a karst system.
The Chahalot stream, in France, is known to be a karstic spring, with its water coming through the karst system of theriver.
This spring would be tagged this way:
When a karst spring is known to be linked to some ponors along another stream (c.f. the water of the spring of the Loue, in France, is known to come from another river, the Doubs), but the exact location of the ponor is unknown (for instance, they are too numerous and merely render the bed permeable across kilometers), then the spring, and only the spring (the resulting river being frequently accepted as a different river than the losing one), should be tagged karst=yes and included in the losing stream's relation:waterway with the resurgence role.
Note that you should not try to map the underground streams between ponors and resurgences, as
- if the goal is to describe the connections between them, this aspect is to be taken into account by relation:site, so the modelling of these streams would merely be a duplicate;
- they practically can't be accurately mapped, being underground, without physical access for speleologists on many kilometers, and often flowing through a permeable stratum, which doesn't make it a single channel flow to be mapped;
- their paths, belonging to a karst system, are complex, ever changing, and probably not permanent enough to justify an inclusion in OSM.
For more information on the modeling of karst features, or on how to model a karst system, see sinkhole=*.