Regarding the Kite demo river material and POM:
There were two prototype versions of that material.
One used a material wetness type function to make the water in the rock material. The material wetness material function is set up like this:
In a basic form it looks like this:
The only caveat here is that incoming “Height” should be sampled from Parallax UVs. often that means resampling the heightmap texture again. If you pack your heightmap into the diffuse it can help reduce the cost.
The other just used worldposition with some height modulation to make the edge of the rocks look wet and to kill the specular under the water plane, and translucency did the water. This was one prototype image from early on:
Doing it with POM should really be no different other than that you’d have to use the parallax UVs as above in order to get accurate water intersection.