We have found that in general waterfalls make noise, and we would rather they do not. So most of the time we take a fine net like a cheese cloth or tulle and use it to guide the water down the surfaces we want.
We did one last summer. I made the pond frame out of 2x4 and oversized then lined it with a tarp then one piece of thick plastic. I used a sump pump for the water. It moved much more water than the water fall pumps and at a better price.
Be sure your liner is NOT permeable, some pond liners are. I learned that the hard and wet way.
Depending upon size and effect, buy the pond liners and felt sub-liner and remind students not to screw liner at the bottom. Build your frame to handle the weight of the water. I made my own rocks out of foam that I sealed. Most pond pumps give info to get proper pump size for lift of water and flow. Really quite easy. Add lights to pond for great effect for night scenes.
The major problem we have had is that the water fall can become too LOUD for the director and that we have to have more intermissions for bathroom breaks. It will take some playing with flow and how much of a free drop into pond to achieve effect. Also, if actors are falling into the water, it will get cold. A floating water heater helps. Any splashed water tends to seep under pond and warp floor. Plus plan how you are going to remove the water at end of show. Also consider putting a bio tablet in water to keep down bacteria build-up.