I found an artificial canal that was tagged as a stream, and was connecting the basins of Danube and Elbe. I changed it in this changeset. We will see if this disconnects these basins in the next update!
I found this point that connects the Elbe and Oder watersheds. It is tagged with
waterway=turning_point which is the wrong tag, but the mapper clearly meant to tag a bifurcation (or pseudobifurcation how this wikipedia article says). Maybe we should invent a new tag like
waterway=watershed_bifurcation, used on nodes, which would allow us to tag where to stop one watershed, and start a different one.
New bifurcation in Ukraine, connecting Wisla and Dniester, Black sea with Baltic sea. This one quite small, stream without name, node untagged, changeset without special message. Here is the node.
And a new bifurcation between Donau and Wisla on the border between Slovakia and Poland. A spring that goes into two directions, connects the first, and ninth longest rivers in Europe. Now we have bifurcations: Elbe - Oder, Donau - Wisla, Wisla - Dniester. The only missing piece is the connection between Elbe - Oder and Donau (There is no connection between Oder and Wisla).
It seems there’s always one natural stream connecting watersheds in Europe, it just can’t be fixed by disconnecting them.
Would it be possible that one waterway is not oriented in the right direction ? Detailed elevation maps might help to check this.
Janjko has already tagged the watershed information board (this one I presume):
It sort of bifurcates indeed, although I don’t quite understand the (Google translation of) de:Ablach (Donau):
Die Ablach entsteht an der hier niedrigen Europäischen Hauptwasserscheide als heute meist zuflussloser rechter Zweig unterhalb eines Teilungswehres im Bereich der Schwackenreuter Seenplatte, der gewöhnlich die Mindersdorfer Aach der Stockacher Aach zuführt und nur bei Hochwasser auch die Ablach speist. Mit diesem ihr genommenen Oberlauf wäre sie etwa 41 km lang. Sie entwässert nur noch einen Teil des Moorgebiets der sogenannten Waltere.
There is en English page.
Great, so there is 100m of stream that should be tagged as canal. Is it obvious which 100m? Maybe part of this stream?
Judging on the description, I think that it is this part of Aach. The part that you linked is the one that only takes excess water into Ablach. It’s an open question what the upstream (southern) stream should be named – today it is the headstream of Aach rather than Ablach.
I found a long research paper in German about the history. I can have a closer look later today or tomorrow.
Found a photo on Google maps, courtesy Emanuel Arnold.
Aach to the left the bridge, the (kind-of-)weir below it and the Ablach drain to the right. I’ll tag the latter as an intermittent drain (it may have natural origin but now serves only to drain excess water).
That artwork at centre of picture has a text halfway up something like Pho… | Donau.
It reads “Rhein ↔ Donau”, we have it mapped already.
Just read the paper. I agree with your edits though ditch might be more appropriate for this way than drain. Also, it’s unfortunately unclear how long the
intermittent part is (on the photo it looks like it might be fairly short). We could leave a note and hope that a local mapper can help?
The article doesn’t say anything about a 100m canal. Instead it says the part between Eckartsmühle and the sharp bend further north (that’s this point I believe is artificial which becomes clear when you look at the contour lines (this is much more than 100m).
We could change the tag on this part from stream to ditch and give the part south of the bifurcation old_name of Ablach? That’s all I can get from the article that’s relevant for the map, the rest is mostly of historical interest.
Here’s a somewhat better photo; you’re right, the water in that ditch seems permanent, only the flow across the weir (below the deck) is intermittent.
In the meantime, I created a relation for Mindersdorfer Aach but I’m unsure about its extent, particularly downstream. Those parts are named “Mindersdorfer (Aach)” but were also included in the Ablach relation; I changed their role from
unused, but on retrospect that was pretty lame; instead, it’s better to remove them from Ablach and include
old_name=Ablach as you propose.
…I’ve also sent a message to local mapper @mathesoft, pointing him to this discussion, Wikipedia entries and my edits. I wasn’t very specific though, just asked him for a general review.
Now what is left are two Elbe - Donau connections, and I believe those are the only ones that connect Donau with the Atlantic ocean. They are both in Czechia and are named, so there might be a chance to find they also have an artificial fork.
I separated this thread from the original with it pertaining specific river basins. The migration of this discussion to its own thread was done per the request of @Duja Best Regards.
Boldly resolved this one – this was generated by a rather old import. However, from all aerial photos available, the original source of Slavkovický potok has been rechannelized some time in the past, and flows only to the Elbe.