Basic Waterfall/Stream Construction
This side view sketch of a waterfall is a basic design that most waterfalls are based upon. There is generally a header pool that overflows at the top of the falls so the pressure of the pump doesn't shoot the water out over the rocks. The small gravels and stacked rocks hide the liner and support the waterfall.

To make your waterfall unique, vary the stone type and size, plan the drop-offs at different heights, and add holding pools here and there to add sound. So the water flows overtop of the main waterfall stones, we use triple expanding foam like Great Stuff™, or black waterfall foam, underneath the rocks to seal the rocks to the liner.

Pumps for waterfall depend on the widest point of the waterfall and the lift / height of the falls. Typically when sizing a waterfall pump we allow 100 GPH (Gallons Per Hour) for each inch across the widest point of the waterfall. For example, a 12 inch waterfall would take 1200 GPH before the lift of the falls was considered.