Canyon Lake / River Test

[RichTwo]

Earlier I tried a canyon scene with a rushing river below.  Render took 20 hours and I was not overly impressed with it.  So as a test I attached a water shader to a dark surface layer as a child.  I fully expected it to not work, but it did.  Now it needed a nearly flat surface, which fortunately was already there.  And the surface layer had to have like a 5 degree max slope constraint with a very low fuzzy zone.  Render time was reasonable, less than 3 hours.  I doubt it'd work for scenes close to the water's edge.  I'll check that out later.

[bobbystahr]

That worked well. Better than my attempt but mine was going down a steep slope.

[Dune]

Why wouldn't that work? You don't need a lake, plane or sphere to make water. Only thing is that you can't get the breaking of lightwaves and such, no real transparency. But even transparency you can fake for distant views if you use a reflective shader over some darkened terrain colors.
You can also use a warped simple shape (as mask) in the valley to keep an area totally flat. Then you have some control over how it bends. And if you start out with a soft SSS, you could use a derivative of that to fake depth.