Even the tiniest garden is enhanced by the sound of water trickling over a cairn of rocks into a small reservoir. Commercial, preformed waterfall units are available, but you can create your own with scraps of the same flexible rubber or PVC liner used to make your pond. Here's how to build a low waterfall on a relatively flat lot.
As you dig the pond, pile the subsoil on a tarp beside the excavation site; you'll use all or part of this to form the waterfall's foundation. Once the pond is fully lined and filled with water, decide where the cascade will go and how high it will be. For a flat lot, keep it low—one 30 to 45 centimetres high is easiest to fit into the landscape. If there's a natural slope behind the pond, work with the grade; you may not even have to use the excavated soil to build up the waterfall. Then follow these steps:
1. Make sure the flexible tubing used to recirculate the water from the pond to the top of the waterfall is hidden by concealing it as you work (the pump will be attached later). Use black, anti-kink, reinforced tubing with a two- to six-centimetre diameter. Place one end at the bottom of the pond; the other should comfortably reach the top of the waterfall. Don't cut the tubing too short; leave enough to play with and thread it just under the soil as you design your cascade.
2. Begin mounding the subsoil removed from the excavation to form the waterfall's course, compacting it well. If it's light or sandy, you may need to make a concrete footing to prevent shifting, and reinforce the mound with cinder block.
3. Using a shovel, cut out a depression for the top—or header—pool and carve out a few steps down to the pond. The steps should funnel slightly away from the sides of the waterfall and slope gently backward, so some water will stay in each section if the water is turned off. Each level should have a vertical drop of between 15 and 30 centimetres.
4. Once the steps have been dug, install a synthetic, geothermal textile underlay (available at water garden centres and many nurseries) then cover each level with a pond liner. Start at the base and overlap each piece, as illustrated at left.
Place flattish stones, slightly tilted forward, at the edge of each step; chisel grooves if necessary to make sure water flows well. Fill in each level with more of the same kind of material, or use rock garden stones, cobbles or boulders to achieve a natural look. (Protect the liner from punctures by first placing pieces of underlay or special protective rubber pads under each stone.)