I painted a mask for the contours of the waterfall. For the bending (lateral and horizontal) of the card object, I used the gradient tool in Photoshop corrected with the curves tool to create a displacement map. The water structure is also a displacement map created using a combination of photos and painting, but I think that I can achieve better results with procedural textures.,
Rocks sticking through the waterfall are indeed problematic, so you have to find a place suitable for the placement of a waterfall, or prepare a part of the terrain. I intend to investigate whether the waterfall can be inflected naturally around the rock by using the rock displacement as a warper.
I hope that this gibberish makes sense.