Properly mapping dry washes

Kai_Johnson · February 7, 2024, 3:45am

I think “wash” feels more natural, but that may be just my biased opinion.

If I can put up with place=neighboroughood, I can deal with natural=wadi.

n76 · February 7, 2024, 6:16am

The wikipedia article on wadi seems to imply the valley rather than an ephemeral water course that is often but not always in a well defined valley.

dieterdreist · February 7, 2024, 8:26am

Last time we deprecated the term “wadi” was because it was perceived as local term and not suitable to use globally.

SomeoneElse · February 7, 2024, 8:33am

A link to that discussion would be helpful - my recollection was that a number of people thought** that it added no extra value over intermittent

** I didn’t agree, but it didn’t affect what I mapped as deserts are rare in England

dieterdreist · February 7, 2024, 8:53am

I don’t have the exact link to this discussion, but here are some links to past discussions about this topic:

https://lists.openstreetmap.org/pipermail/tagging/2014-August/019027.html

https://lists.openstreetmap.org/pipermail/tagging/2015-January/020946.html

https://lists.openstreetmap.org/pipermail/tagging/2015-September/026692.html

github.com/gravitystorm/openstreetmap-carto

Rendering Wadi and Intermittent River/Stream

opened 11:16PM - 24 Jan 15 UTC

closed 08:07AM - 25 Jan 15 UTC

RAytoun

@mkoniecz , @math1985 Hi, my name is Ralph (RAytoun) and I have been a cartogra…pher all my working life. I was Senior Cartographer in Philip's School and World Reference Atlas section...responsible for the research and compilation of all new mapping, additions and amendments for the full range of Philip's World Atlas products. I am at present a member of HOT and a principal tutor for the Missing Maps Project, London. I have raised a few points in this regard and have been pointed in your direction by Blake Girardot. I see this issue was under discussion in September last year. Math1985 mentions intermittent should be different to wadi which is quite correct....mkoniecz said wadi is a term for a whole valley as well as dry stream which is also correct but may I add that in the parched and arid areas where wadis abound the sides of these "valleys" are sheer cliff walls and the floor of the valley is a dry flat flood plain. The sides of the flood plain would be added the same as for river banks but the outline would be a pecked line with no fill or is sometimes depicted with a light brown stipple fill. My points are... I would like to raise the issue of tags for waterway=river, waterway=stream and waterway=wadi. The problem that exists with the existing tags is that there is no visual difference on the map for a stream (perennial) and a stream (intermittent) and the only other option is wadi which gives a blue pecked line. Accepted mapping standards for this would be to show:- all perennial rivers and streams as a continuous solid blue line (indicating that there is flowing water all year round) or solid blue outline (river banks) with a light blue fill. all non-perennial rivers and streams as a continuous blue pecked line (indicating that there is flowing water during the wet season but not the whole year). River banks would be pecked blue line with light blue fill. A wadi would be depicted with a continuous pecked brown line (indicating that it is dry watercourse and could be dry for years at a time...only flowing if there is a flash flood or unusually heavy rain). For wider wadis (valleys) a pecked brown outline with no fill or brown stipple fill. This would then convey the correct meanings with symbols on the map and make reading the map a lot easier. The categories would still be searchable and distinguish between the three categories of water flow. The proposed tags would then be waterway=river ...... waterway= stream ...... continuous solid blue line waterway=river_intermittent ...... waterway=stream_intermittent ..... continuous pecked blue line waterway=wadi ..... continuous pecked brown line (a wadi can be so wide that another tag would be needed similar to the tag for river banks) waterway=wadi_bank which would still be a brown pecked line either with no fill or a brown stipple fill. This would then ease the path for introducing the tags for perennial lakes with a solid blue outline and lighter blue fill, intermittent lakes with a blue pecked outline and a light blue fill and dry pans with a brown pecked outline with a brown stipple fill. If it is deemed appropriate is there someone who could do this or help me? Reference...... http://pubs.usgs.gov/gip/TopographicMapSymbols/topomapsymbols.pdf

https://lists.openstreetmap.org/pipermail/tagging/2016-September/030016.html

cactolith · February 7, 2024, 9:18am

Some resources for differentiating a wadi vs wash

World Atlas - wadi
World Atlas - Major wadis of Egypt
AZ Central - wash, arroyo, gulch
Wiktionary - wash
I did a search on wadi within OSM communities and came across this discussion years ago in the Israel forum: Rivers, Wadi, width ?

Since then waterway=wadi got deprecated as noted earlier in the case of linear features to waterway=stream|river; intermittent=yes.

Areas are still an issue which leads me to…

Wadi can indicate the portion in a confined valley and also continue to semi-confined sections or even out in a broad plain where subtle topography affects the course of the waterway(s) when flowing.

I like wadi for several reasons since it works well as a scalable area. I have mapped intermittent streams (waterway) connecting to intermittent rivers (waterway) which then broaden into a broad confined area (area=wadi & main channel waterway=river; intermittent=yes) which broadens further into a semi-confined area (still a wadi + waterways) to either a shoreline of a large water body (Persian/Arabian Gulf) or a terminus where the water budget of inflow<<(evaporation + absorption) results in a small (unnamed) or large (named) wadi.

Wadi Rum
Oman where Salalah escarpment directs flow from the highlands to The Empty Quarter

AwoowoArne · February 7, 2024, 10:38am

After Wadi was deprecated I’m using waterway=river/stream with intermittent=yes and I’m very content with it. As a remote mapper in the area of the Horn of Africa (see e.g. here) I don’t have the knowledge to distinguish different grades of intermittency.
Also, I like that waterway=river/stream + intermittent is a neutral term for dry rivers locally called wash/arroyo/wadi and probably many other local terms.

If one would change something for dry rivers I would plead for waterway=dry_river/dry_stream or natural=dry_river/dry_stream (analogous to dry_lake) with the optional tag intermittent to define the frequency of water flow.

Kai_Johnson · February 7, 2024, 3:50pm

I think all the references make it clear that “wadi” and “wash” really mean the same thing (although “arroyo” has other issues). Especially the link to Oman where Salalah escarpment directs flow from the highlands to The Empty Quarter, which is indistinguishable from an aerial picture from the US Southwest. Here’s what that looks like:

The most recently active channels are a lighter color and the older/abandoned channels are slightly darker. I don’t know if the processes are the same, but I would guess that the coloring in Oman is the result of accumulated desert varnish, the same as in the US. The banks on either side are clear and distinct.

There’s not much vegetation out there at all, but if you zoom in you can see that there is some scrub in the wadi, primarily at the margins of the active channels. And there’s little to no visible vegetation in the higher ground outside the wadi.

I would map that with a linear way tagged with waterway=river + intermittent=yes through whatever looks like the most recently active channel, but with the expectation that this way is an approximation that could be wrong each time the wadi floods.

Then, I would map the area between the banks as natural=wadi and hope that someday the renderers would do a good job of drawing that. Eventually, we would need a rendering that would be distinct from natural=sand, natural=bare_rock, or natural=ground.

Adam_Franco · February 7, 2024, 5:25pm

For the area features we’re talking about I am preferring the tag natural=wadi over natural=wash for a few reasons:

wash is more likely to be mistranslated from English into something to do with cleaning in other languages (e.g. “lavar” in Spanish). I’ve not tried the auto-translate in these forums, but Google translate messes this up.
wadi is easier to search for. Googling for “wadi” brings up results related to the landform. Googling “wash” on the other hand brings up hundreds of results for a variety of things that aren’t the land-form – everything from laundry to hair to sanitation.
wadi is used in a wider swath of the world across at least north Africa and the middle east, whereas wash is only used in American English in the south west US region.

As someone from the very wet US north east I wouldn’t know what a “wash” was without having traveled to the south west. Without significant context most American English speakers would not identify the term.

bradrh · February 7, 2024, 11:41pm

I voted for wash, but If we had more choices and ranked choice voting, I would rank it third behind dry_watercourse, and dry_wash.
It’s interesting to keep in mind that what brought this up was a bunch of NHD washes in the Rockies, which are more of a gulch than a wash or a wadi.
That’s why I like dry_watercourse since it’s more generic and not a localized term.

watmildon · February 8, 2024, 12:34am

Creating an OSM specific term is kinda nice because it avoids various regionalisms and we can make it what we want… it’s less nice because it’s less intuitive and discoverable. I would support one for sure but alas nothing is free.

Kai_Johnson · February 8, 2024, 12:34am

Actually, your post in the river topology thread was just a catalyst to get me to write up something that has been bugging me for a long time. I run into all sorts of odd tagging for these features in the desert southwest – as you can see from the examples in the first post.

Kai_Johnson · February 9, 2024, 2:26pm

With the additional discussion, it looks like natural=wadi is coming out on top, leading by 8 to 5 at the moment.

n76 · February 9, 2024, 6:55pm

As I understand it, we are pretty much at:

The waterway center line tagged as waterway=stream | river with intermittent=yes
The area between the banks as natural=wadi

What is the current procedure to formalize this? I assume it is still to have a proposal page on the wiki that is then voted on.

Kai_Johnson · February 10, 2024, 4:41pm

I guess we either need a proposal or enough organic usage of the tag for it to qualify to be documented as “de facto” on the wiki.

SomeoneElse · February 10, 2024, 4:55pm

… and possibly a “proof of concept” map in some format that shows them?

n76 · February 10, 2024, 5:25pm

I have put a polygon around “Big Wash" near Oro Valley, Arizona with natural=wadi on the tag. Once the extracts for this area get published, I will down load them and update my map rendering to show natural=wadi the same as I show an area of sand. Probably not ideal but a fairly easy change to my style information.

For what it is worth, Big Wash drains into the Cañada del Oro wash which has been previously tagged with natural=river, intermittent=yes and water=river so you can see the difference in how I render that. My rendering is quite different than the usual OSM but it might be useful.

Allroads · February 10, 2024, 6:46pm

How the wadi changes over the years ESRI wayback

On the left, draw mouse over dates.

A side note.
In cross country rally “wadi” is also used in roadbook tulips. FIM lexicon page 107 FIA page 101
Settting out a stage, survey is the important part.
afbeelding

n76 · February 10, 2024, 6:59pm

Hmmm. That map key distinguishes between a wadi and an sandy wadi. I guess we can do that with a surface=* tag. I don’t see how that would conflict with a top level natural=wadi tag.

Allroads · February 10, 2024, 7:09pm

In the paste the used paper roadbooks in black and white.
Now they start using color and tablets.
It is then only the color yellow that changes for small and large wadi when it is sandy.