They're still sharp edges, and the top of the fall at least should be smooth and rounded. I've used a stretched perlin perpendicular to the river now, which is going slowly uphill. But then you get some dips.
Best would be if I could blend these perlin heights into the gradient only when they rise above it, then go horizontal until the next soft rise. I tried the conditional shader, but I haven't managed it yet. The interesting part of this would be that the perlin provides some irregularity. I need blue men