It is still completely procedural, but now I need something for better rapids. I may find it by trying out the blue nodes in some educated guesses, but if any of you math wizards can produce something in no time, I'd be much obliged
I use a strata and outcrops shader now for rapids, but that is actually too sharp. What would be better is a smooth stepped! grayscale, from black to white (along X or Z axis), which I could combine with a distance shader or other soft ramp to get something like the attachment.
@TheBadger: I might give that a try. Never did exporting before.