by Dan Eskelson
The first advice I give is to visit natural waterfalls or at least look at photos. Don't try to memorize just how they look...just get a general idea how the water flows around and over the rocks.
The design of your falls will depend on topography, pump and pipe size, length of water flow from pump to falls, pond size and possibly other site-specific factors. If your pond is just 4' x 6', you certainly don't want a large, three foot wide falls - keep the elements of your water feature in scale.
One of the most common mistakes results from the desire for a tall waterfall at a level building site...large amounts of soil are imported to build the falls up to a three or four foot height. Yes, you will achieve a dramatic waterfall, but the total effect will look more like an out of place volcano. A falls of just two feet will produce a very satisfactory effect both visually and audibly.
On a level site, with an "average" size pond of 11' x 16', the amount of soil needed to surround the biological filter and create the berm is just about equal to the amount of soil excavated from the pond...it works out quite well. To further enhance or enlarge the berm, you may want to import a little more soil, large boulders or other features.
If you are working on a slope, you have the option of placing the biological filter (waterfall source) uphill from the pond and creating a series of cascading waterfalls. This is how I built my falls, described in the photo essay here: http://clearwaterlandscapes.com/pondphotos.htm
It was definitely an exercise in visualization to determine exactly how the water would flow down the falls. I made a slight underestimation of the total flow and could have widened the falls somewhat, but the effect is very acceptable.
Even on a level site, it's a good design strategy to place the falls six to eight feet from the pond. This will create a short stream to the pond.
Be sure to use a wide EPDM rubber liner under the falls and/or stream...this will allow for twists and turns in the course of the water and also contain splashing. A ten foot wide stream liner is recommended. Underlayment under the falls and stream liners is usually not required.
When your excavation is complete for the falls, and liner is in place, add your stone. Don't be in a hurry - try several (or many) combinations and visualize how the water will flow.
When satisfied with your arrangement, use black waterfall foam to direct the water over the stone instead of under it. That is, stone that is directly in contact with the liner should sit on a bed of foam so the water goes around or over the stone instead of underneath it. Caution - the foam expands greatly...don't use too much!
Though it requires some creativity and patience, building a waterfall is extremely satisfying. Though you should give some time to preliminary research, you'll learn most by actually building your water feature - just do it! You'll find that your water garden is the most relaxing and enjoyable part of your yard.