California coastline courtesy of the object below..

Since the distance to object below effect is triggered from underneath the surface and not from the intersection of terrain and water, you sometimes don't have enough white stuff or it's in the wrong place. By using other terrain objects with the effect mat applied below the surface as effect activators, you can get as much shore foam as you need where you need it. Also, the bottom layer of the rock mats have the object below node as well and helps carry the water effect onto the rocks.