It looks like "ford=yes" is the right tag for those crossings, with an estimated "depth" tag, if possible. It's just one of those cases where the intended purpose of the tag may well be broader (or sometimes narrower) than what the word itself suggests to you. Happens with me all the time.

Another tag that might be useful in some areas of the park:

https://wiki.openstreetmap.org/wiki/Key:flood_prone