[Tagging] Waterway equivalent of noexit=yes?

Joseph Eisenberg joseph.eisenberg at gmail.com
Fri Aug 14 14:40:16 UTC 2020


The “rise” where the stream comes back to the surface would usually be
mapped as natural=spring

If there is also a cave entrance at the same spot where the watercourse
exits a cave, then the tag natural=cave_entrance can be used

- Joseph

On Fri, Aug 14, 2020 at 6:21 AM Kevin Kenny <kevin.b.kenny at gmail.com> wrote:

> On Fri, Aug 14, 2020 at 7:08 AM Paul Allen <pla16021 at gmail.com> wrote:
>
>> On Thu, 13 Aug 2020 at 06:42, Mark Wagner <mark+osm at carnildo.com> wrote:
>>
>>>
>>> For a larger and far more dramatic example of this sort of situation,
>>> look at the area to the west of Death Valley Playa.  It looks like
>>> someone stacked hundreds of river deltas on top of one another, but
>>> forgot to add the water.
>>>
>>
>> As I understand it (possibly not all that well) a sinkhole as the wiki
>> defines it
>> is a large hole in the ground which water enters and vanishes without
>> pooling.
>> What Ordnance Survey calls "sinks" appears to be more akin to a hole in a
>> golf
>> course that water enters and vanishes.  What Ordnance Survey calls
>> "spreads"
>> is a sand or soil or gravel surface that water vanishes into without
>> pooling and without there being any noticeable hole.
>>
>
> The WIki picture of a sinkhole happens to be large, but in karst terrain
> they come in all sizes. https://www.openstreetmap.org/node/5599524737 is
> a sinkhole of quite a small stream. I couldn't find a good way to tag the
> rise a short distance to the west.
> https://www.openstreetmap.org/way/226924460 is a much larger sinkhole. In
> a wet season there's significant outflow to the east, but in a dry season
> all of the outflow from the lake runs through the caves, exiting through
> cracks in the limestone below the cliffs to the east. Many of the small
> streams thus formed haven't been mapped because there are significant
> technical challenges to mapping them. GPS coverage at the cliff bases is so
> poor that one would probably have to resort to alidade and plane table, and
> the evergreen cover is dense enough that you can't see much that's useful
> on satellite imagery.
>
> I'm not sure if any of those fit what you have and maybe what you have is
>> more of a network of intermittent streams.
>>
>
> What Mark is showing is usually called an alluvial fan.
> https://en.wikipedia.org/wiki/Alluvial_fan
> Some fans have well-defined (perennial or intermittent) distributary
> streams flowing through them. Often, though, most of the stream channels
> are ephemeral in nature. Sometimes an individual channel was cut in a
> matter of hours by a debris flow coming from upriver.
>
> In arid climates, it's entirely possible for the entire flow of the
> stream, except during flash flooding events, to vanish by percolation and
> evaporation, so that there is no river downstream. There's no well-defined
> sinkhole, and no well-defined specific point at which it transitions from
> perennial to intermittent, intermittent to ephemeral, ephemeral to a dry
> wadi that has seen water only in geologic time, eventually disappearing
> entirely into a salt flat.
>
> It's relatively rare to find a fan that's still actively depositing
> sediment. One example is that Mòlèqiē Hé (莫勒切河) in Xinjiang forms an
> enormous and nearly unique one near 37.4°  north, 84.3° east.
> --
> 73 de ke9tv/2, Kevin
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