I am a geologist so I am trying to avoid overly technical jargon but need guidance on how to handle the mapping of geologic features, in particular the braidplain in a desert setting (Oman, Salalah region).
In the mountainous regions the intermittent rivers and streams are generally confined and can be easily represented by a line:river or intermittent stream. Once the channel spills out to a broad flat area the channels become highly interwoven and you are faced with either mapping the ever-changing individual channels OR creating an area. area:sand doesn’t really convey the feature and there doesn’t appear to be a tag for braidplain. Is anyone else experienced with how to resolve this?
There was a discussion about this sort of thing on the tagging mailing list a while ago:
It veers off topic to talk about manholes a bit before circling back. I’m not sure what the mapper decided to go with in the end, but taginfo/overpass might tell you if any of the suggestions made it into the database.
Most of the discussion seemed to be about
waterway=spreads on an end node or area, possibly with the incoming waterway tagged as intermittent.
Thanks for the reply. The discussion did touch on the topic of terminal fans of varying types and how to treat something that “just ends…” It’s not entirely dissimilar to a road that ends in a parking lot. You don’t put a line to each parking space and the lot isn’t always full but the area (in my case braid plain or flood plain) would be an area of intermittent flow. I have used intermittent lake for some streams that fill a small basin and then water disappears between evaporation and absorption leaving behind the basin area.
Some of these features are confined, hit a large flat area and fan out and in high flow events continue and become confined again if they fill the braid plain area. I guess philosophically are you mapping the water and dominant flow or the container and when is it too wide to be a line and becomes an area?
I did not map any kind of such river myself but I have seen a couple here and there. In some cases the mapper has chosen to map “the ever-changing individual channels” which I believe is super accurate for a very short period but becomes inaccurate bevor actual aerial images are at hand as the individual braided streams may change their way with every haevy rainfall.
I think the solution chosen for Gascoyne River in West Australia could be the better choice. Besides the way representing the river an aera tagged as natural=water + water=river + intermittant=yes has been created, representing the braid channel of Gascoyne River. Would that probably suit your case?
I have a feeling I’ve used natural=riverbed in places in the Himalaya, but perhaps not for the large braided outwash areas, such as these.
I would 100% agree the feature referenced is what I am struggling with. I would also say that as mapped the area could be even wider to cover the entire area affected as evidenced by the vegetation and you can see some evidence of an established “bank full” area in times of excessive or flood stage flow. That said, I’ll use a similar approach and try to be disciplined between a more confined channel and when to use an area if it becomes less confined.