Muscle is a good idea. And yes, it's all one terrain, all masked by simple shapes and fractals. Plus is that you don't get a sharp distinction between water and (wet) sand. In reality, there's some adhesion between sand grains and liquid, and on small scale renders, I always miss that.
I made one mistake, having the RT reflectivity creep into the sand grains too much, so these parts took forever to render. I changed that now, reducing lower half from a 1hour render to 10mins.