[Tagging] New description of waterway=pressurised

[Kevin Kenny]

On Mon, Jun 3, 2019 at 4:28 PM Nita Rae Sanders <cosmicrae at gmail.com> wrote:
> Here is one possible example of what you seem to be describing … way 84255726
>
> Within Florida's Oleno State Part, the Santa Fe River vanishes into a
> sinkhole. It then reappears at River Rise Preserve State Park. the
> route, as depicted in the way (a mile +/-), is the presumed
> subterranean path. The way is tagged as tunnel=yes, which seems odd,
> yet descriptive (but as a tunnel, it would be natural and not
> man-made).

I live in glaciokarst terrain, so these things are interesting to me.

I've not attempted to map underground connections, since so many are
unverifiable - or would need specialized equipment and introduction of
tracers in the water.

Hence, I've mapped a few places like
https://www.openstreetmap.org/node/5599524737, in which I don't assume
an underground connection even though it *appears* pretty obvious. (I
also didn't tag the rise, since I couldn't observe it directly or
necessarily spot it on the available aerials. It's pretty well
screened by brush, and I'd be trespassing to stray that far from the
established trail there. I mapped the stream where I was confident of
its course.)

I would have Absolutely No Idea what flow regime most of the
underground connections have. Many of these little streams emerge from
'fools' crawls' in which the water is clearly not under significant
pressure at the outlet, but were there's too little headroom to allow
a caver to explore. It's likely a mixture of free flow, pipe flow and
percolation, in any case.

Similarly, it's pretty well established that
https://www.openstreetmap.org/way/226924460 is a dissolution sinkhole
and the water that flows underground through it has been traced into
multiple small streams emerging from cave entrances (too small to
explore) below the escarpment to its east. Alas, a lot of these
streams are as yet unmapped. Mapping would be difficult since they
cascade over unstable talus and off-trail travel there is prohibited.
I've not attempted to map anything about the subterranean hydrography;
it's not understood at all well.