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.ke...@gmail.com> wrote: > On Fri, Aug 14, 2020 at 7:08 AM Paul Allen <pla16...@gmail.com> wrote: > >> On Thu, 13 Aug 2020 at 06:42, Mark Wagner <mark+...@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 > _______________________________________________ > Tagging mailing list > Tagging@openstreetmap.org > https://lists.openstreetmap.org/listinfo/tagging >
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