Canals and drains do not seem to be included

[Beakerboy]

I’ve seen a few significant size streams that have sections tagged as “Canal” and “Drain” when the natural waters routed through man-made structures. It seems the map ignores these and sets them as isolated water networks.

[waldyrious]

Yeah, I second this. It would be nice if the modes that ignore man-made structures (e.g. planet-waterway-nonartificial) would still consider these if they are linking two ends of natural waterways.

For example, here:

Screenshot

...or here:

Screenshot

That said, I would still expect canals that don't connect endpoints of natural waterways to still be treated as separate — for example, here:

Screenshot

Would this be possible? Perhaps as an option in the settings?

[quincylvania]

This seems like an opportunity to improve tagging rather than simply trying to guess which canals are part of natural waterways. I think the core issue is that we want to filter out waterways that in the US we'd call "diversions": those that divert water out of a watercourse, sometimes into a different watershed. I wonder if just adding a tag like diversion=yes to these types of features would satisfactorily solve the issue?

[amandasaurus]

On Mo, 23 Jun 2025 0:03 +02:00, Waldir Pimenta ***@***.***> wrote: ...or here <https://waterwaymap.org/#len=1..inf&map=15.44/41.45048/-7.012674&tiles=planet-waterway-nonartificial>: Screenshot image.png (view on web) <https://github.com/user-attachments/assets/7bd449e1-7713-44af-b30f-0f890bb38426>

I find this example strange. The issue seems to be [way 844857929](https://www.openstreetmap.org/way/844857929), which is `waterway=canal`, (`tunnel=culvert,layer=-1`) but it connects to [way 844857930](https://www.openstreetmap.org/way/844857930) and [way 844857931](https://www.openstreetmap.org/way/844857931), both `waterway=stream`. However I can't understand how the middle way is a _canal_? If I was mapping this, I would have the middle way `waterway=stream`. This looks like a totally bog standard “stream that goes under a road in a culvert”. 😅😅😅 My initial impression is, this is incorrect mapping in OSM, and WWM is showing that.

…

-- Amanda

[waldyrious]

@quincylvania if I understand you correctly, from the examples I gave above, only the third one would qualify as a diversion, right? The second one (agreeing with @amandasaurus), does seem like it should be retagged as waterway=stream instead of waterway=canal. (I just did that.)

But what then would be the solution for the first case? The artificial segment connecting the two natural waterways is currently tagged as a waterway=drain. Is that incorrect? Should it be some other type of waterway? Would waterway=canal+usage=tailrace be considered by WaterWayMap as an exception for the purposes of connecting the network of non-artificial waterways? Or is there another solution I'm unaware of?

[amandasaurus]

I've often seen issues with WWM about water flowing out of reservoirs. I've seen many different tag combos to say “this is more than just a canal”.

You can see some of the accepted tagging schemes in the current WWM tagging rules. I'm open to supporting more tagging combinations.

Would waterway=canal+usage=tailrace be considered by waterway as an exception for the purposes of connecting the network of non-artificial waterways

Yes, if you do that, WWM will treat it like a river. (The exact rule is waterway=canal∧usage∈headrace,tailrace→T;, i.e. “If it's waterway=canal and the usage is either headrace or tailrace, then this OSM object passes the filter (and will be included) (→T;).

[amandasaurus]

NB, I'm quietly rolling out support for waterway relations on WWM. If a way with waterway=canal is in a relation with waterway=river, then the =river from the relation will be used. This can make “canals” be treated as rivers.

This wouldn't help small cases, like the culvert above. But it should help with much large rivers going through larger dams.

[waldyrious]

Would waterway=canal+usage=tailrace be considered by waterway as an exception for the purposes of connecting the network of non-artificial waterways

Yes, if you do that, WWM will treat it like a river.

Thank you! I'll make sure to tag that section and others like it with this in mind :)

Also, thanks for explaining the syntax of the relevant rule so didactically. You should consider writing some sort of "how it works" overview with these useful bits of information to help potential contributors! ❤️

[waldyrious]

Um, not to be too annoying, but what about this situation?

Screenshot

None of the current rules seems to describe a tagging scheme that would apply here. Should that also be waterway=stream, even though it's artificially shaped (though not linear, for what that's worth) and lined with concrete? Or is there another option that's escaping me?

[jarek]

But what then would be the solution for the first case? The artificial segment connecting the two natural waterways is currently tagged as a waterway=drain. Is that incorrect?

I asked about this on the Community Forum and the suggestion there was to apply waterway=river/stream and, if you wish, channelised=yes: https://community.openstreetmap.org/t/is-a-channelized-river-still-a-river/127905

Please take a look at the aerial photos posted in the thread and on the wiki page https://wiki.openstreetmap.org/wiki/Tag:channelised%3Dyes to see if that's what you mean?

[waldyrious]

Thanks for taking the lead in the discussion and documenting that usage, @jarek! That sounds exactly like what applies in the case I mentioned above. I'll start using channelised=yes from now on in such cases.