Well.....IOHO, and only a lowly dep-u-tee I see no problems with that northern forest and the rivers flowing (both north and south) as they do, given that Opa has already stated that the area is explained as potentially magical in nature (be it "naturally" so or influenced by acane or divine magics is up to the characters to discover at some point I am sure ). In a more realistic, non magic world, I do mot think that there would be nearly as much water coming from that area.

One thing though, if you wanted to use thaose more southern mountains as a watershed for the river, shouldn't they be on the eastern side of the river?