I expected that you’d get problems with the AO bake, but you could use the existing AO with their UV Map and make a new (straightened ) UV Map for the river flow. Yes, you can use more than one UV Map in your shader.
Maybe I should have told you that right away, but I thought I’d let you struggle for a bit first and see if you came up with that yourself…(sorry)
Haven’t though about how I would deal with the reflections to be honest.
