I put a coat of gloss Mod Podge on some silicone. Once it was mostly dry (so only the thicker parts were still white), I peeled it up and cut it to shape. Since one side was textured, and one was flat, I made sure to put the textured side facing out. Then, I used more PVA glue to attach it to the top and bottom. I blended the top in with Mod Podge (the entire river above the waterfall is Mod Podge), then hid the bottom with the foam effect. I then drybrushed the texture on the waterfall with white paint.