The material on the verticals is displaced, turn that off to speed up your renders.
Also included is an image map and alpha that you can play with to create the foamy texture; on an alpha plane, for example. Try it different ways to see what works with your image and atmosphere.
Cool idea, the waterfall in that other picture of yours is well done, one can even try using it on terrains with a steep dropoff (unless that's what you did already )