I just attended a 2 day advanced waterfall build. 2 or 30 ton of large moss boulders, 20,000 gph. Water originates from a "wetlands" that will be planted, and splits into 2 separate falls. It rained hard half of the first day. It was amazing how large a project this was to be completed in 2 days. Helps to have a bunch of guys there that basically know what they are doing, and some really good lead designers. I learned a ton about placing large boulders to achieve a natural look.