Streams and waterfalls can be incorporated into a pond design very simply with Beutyliner pond liners.
Where the connection between the pond and the waterfall is above the level of the still water, you simply overlap the two liners with the upper section sitting on top of the lower section. The water will flow over the top of the liners and will not leak.
Where the connection between the two liners will be at or below the still water level the pond must be welded to the stream. This style of liner is known as a composite liner and requires accurate measurements to be supplied so it can be manufactured.
Any combination of ponds, streams and waterfalls is possible and is really only limited by your imagination and budget.