I like what you are trying to do, but water just doesn't act that way. Several layers of clear resin might solve that, but it can be hard to use correctly. Basically you need to smooth out the folds a lot. You should also use water effect on the rocks as the spray from the waterfall would be making them slick, don't try to use the water effect on the waterfall itself, I don't think its intended for such large areas (this is not speaking from experience).