Talk:Tag:waterway=pressurised

Waterways in caves?

I'm skeptical about the suggestion to use waterway=pressurised in a cave, especially if this is meant for natural waterways. I would tag all underground portions of natural watercourses as waterway=river or waterway=stream and tunnel=*

I don't see how a mapper could safely verify if such a waterway was completely flooded or might contain air. Natural caves often have multiple openings where air could enter.

Are there any real-world examples of an artificial waterway which uses a cave as a conduit? All of the examples that I can think of use purpose-built tunnels or pipelines. --Jeisenbe (talk) 03:52, 31 May 2019 (UTC)

As some mapper may be speleologists, like other mappers can be climbers or any activity requiring special skills, we may take advantage of their experience and welcome their contribution to document what they saw underground

If you have to dive to progress in a cave, it's surely because of siphons I guess. Fanfouer (talk) 20:25, 4 June 2019 (UTC)

Facts are waterway=pressurised is the only value refering to pipe flow. I would rather agree with a different value for natural pressurised waterways but you'll have to make a formal proposal for it Fanfouer (talk) 20:25, 4 June 2019 (UTC)

The problem is, the page has always said that: "This regime [pipe flow] is obtained by design when the intake of the conduit is built below the lowest water level the source can reach. This is the only use case of waterway=pressurised."

Natural siphons and caves are not "obtained by design" and they do not have a "intake ... built below the lowest water level" because they are not designed or built by humans, therefore the usage of waterway=pressurised with a natural waterway would be excluded by this paragraph.

Should I've added that *artificial* pressurised waterways are obtained by design and you'll agree that natural ones actually have intakes below the lowest water level (which is base physics of the phenomenon).

The introducing proposal was mainly focused on artifical waterways and since there is no known tag for natural ones, waterway=pressurised is suitable for such situation if encountered accordingly (that's all I said). Fanfouer (talk) 19:22, 7 June 2019 (UTC)

I don't see a need for a new type of waterway for natural siphons, because these features are exceedingly rare and probably not verifiable by mappers. It's not possible for a mapper to verify if an underground river is in a pipe flow or open flow regimen at a certain location. --Jeisenbe (talk) 01:34, 5 June 2019 (UTC)

Tagging is not mapping. You can't evaluate the semantic consistence if you only focus on the subject you intend to map without considering the link between other concepts. As OSM tagging model is provided under creative commons and can also be exported out of the project to feed another databases, stating a tag isn't appropriate just because mappers won't be able to map a corresponding feature isn't fair. As I consider waterway=* only regards the water flow, I had to look at all situations at which it flows with pipe regime. waterway=pressurised + natural=cave is suitable for natural siphons also although it was out of the scope of the proposal. Fanfouer (talk) 19:22, 7 June 2019 (UTC)

Openstreetmap is a database specifically designed for use by individual, non-professional mappers to add real, current information about their local area. While anyone can add other tags and features, the features that are supported in the wiki should fit the description at verifiability - they need to be things that individual, local mappers can practically confirm to exist or not exist in a particular location. We can use GPS devices and aerial imagery to confirm the correct location of most features on the surface of the planet.

Artificial pressurised water pipelines and waterways at hydropower facilities are verifiable because they are often above-ground or have a clear, straight route, and it's possible to know if the intake is designed to be always below the water level. Natural siphons in caves are neither clearly visible nor certain to be a siphon instead of having airspace at some point, so they are not mappable in a verifiable way. --Jeisenbe (talk) 06:37, 8 June 2019 (UTC)

You assume that *all* siphons aren't verifiable and mappers can't be aware of their existence. You can see its intake in a lake and its outcome when a spring rises from nowhere a few km away. Any mapper could technically (not legally I presume, don't do this at home) put natural dye in the water and see the color of the spring changing accordingly as often done by speleologists.

At this point you'll need a term in OSM to qualify the single one feature found verifiable on the ground.

Many hydropower facilities I map are mixed between overground and underground. Data is taken from public display on the ground or public databases (Carthage database with waterways has been freed by French authorities). I can't go in the pipe to see water flowing, but I've got a photo of a chart displayed beside explaining me where the water is going. Fanfouer (talk) 15:09, 8 June 2019 (UTC)

Re: "You can see its intake in a lake and its outcome when a spring rises from nowhere a few km away. could ... put natural dye in the water and see the color of the spring changing accordingly." While this proves that the upstream river can be added as part of the same waterway relation, it does not show the route the water takes while underground - is there one cave, or hundreds, or does the water pass through a bed of pebbles and small stones? It also does not prove if the waterway is in a siphon or if it is open-air within the cave. Many caves have multiple entrances and many different passages.

Certainly it is fine to import data about hydropower facilities if you have a good source. This tag is perfectly good for mapping such things. I just don't think it works for natural waterways. --Jeisenbe (talk) 12:36, 10 June 2019 (UTC)