Okay, so instead of working (who does that?) I fiddled around with it some more.
I moved the grass down to a SUBLOOR sheet, and split the water into a WATER sheet and SUBWATER sheet (below the FLOOR sheet) then added a drop shadow to the FLOOR sheet, which really gives the appearance of depth. I added a two Glow (inner) effects to the water, one white with 0 strength, 2 blur, and a black one with 1 strength and 1 blur, so it looks cut out from the floor. I added a slight Bevel to the FLOOR sheet as well to make a lip.
I'm liking it more now--but I still can't figure out a good way to do a "white water" effect of the falls and landing. (It's only supposed to be a 10 foot drop or so.)