Pro tip! DAS clay shrinks when it dries - quite a noticeable amount over a period of time, in fact. Basing it on fairly flexible plastic card and relying on the natural 'stick' of the clay is enough for the shrinkage to bow up the edges quite noticeably. It's easy enough to straighten out, but doing so, obviously enough, pulls the clay off the base and/or cracks it in several places. Which is not going to be conducive to keeping the scenic water where it's meant to be.
So tomorrow's job is to work around the existing grass/scenic work, reseat the DAS, and touch up the places where it's pulled away from the plastic card or cracked. Once that's dry, we'll see about the water.
You live and learn :D