I was recently cycling in Spain and my routing app (based on OSM and ‘Brouter’) tried to take me across a river. It’s marked on OSM as a ford (https://www.openstreetmap.org/edit?node=4539676292#map=18/36.72868/-4.67321) but in reality it would only be possible to cross here at the end of a very dry season. In November it was impossible to cross safely by bicycle; a 4-wheel drive vehicle might manage. During winter / early spring I doubt any vehicle could cross. I had to backtrack and wasted over an hour finding an alternative route.
Is there a way of marking such a ford as unusable - other then removing it and breaking the tracks either side?
I would say that removing it would be a bad idea. There’s a track. There’s a stream. They intersect. There’s no bridge or culvert, so it’s a ford. It’s just not always usable, but it’s there and the presence of the track shows that it does get used. Incidentally, if you remove the ford node then various bug-checkers will complain about a stream crossing a way.
The best I can find to cover this situation is seasonal=dry_season. The wiki page on season=* says that you can expand upon this, if you know the times of year when it’s likely to be dry enough, with something like access:conditional=no @ Nov-Apr (read the syntax for access:conditional very carefully before using it). Adding depth=* for typical depth would also help people decide whether or not it’s crossable by their modes of transport.
How well these things get rendered, and how well routers cope with them is something you’ll have to play with to find out. Maybe there’s a better way that I haven’t stumbled across.
I have also had the experience of having to backtrack in the Guadalhorce valley due to an alleged ford turning out to be completely impractical (although I was not using OpenStreetMap at the time). Given the drought conditions this year, if the ford is not usable now, I think it is reasonable to ask whether it is ever usable. Although the fact that there are dams further upstream may mean the flow is not directly related to the time of year.
Maybe try contacting the original mapper to ask if they know if the ford is in current use and if so by what kind of vehicle? They didn’t comment their changeset so we don’t know if they added the ford based on local knowledge, aerial imagery, or some other source.
Looking at the DigitalGlobe Premium imagery which seems to be about the clearest here, it looks like the track to the north of the river turns towards towards the west parallel to the river (not mapped in OSM). I wonder if there is really a genuine track in current use crossing the river, or just two tracks leading to the river.
seasonal=yes on the way is a good all-purpose, broad-brush tag.