Whether you want to add a waterfall to an existing pond, or are incorporating a waterfall into a new garden pond, it is a lovely way to accentuate the water feature and bring the trickling sound of water to your garden. Building a small waterfall is not a difficult task and will repay your efforts many times over with the soothing and calming effect of the waterfall.
Drain your pond to around 10 inches below the waterline if the pond is full. Dig a shelf into the side of the pond that is big enough to sit the pump inside and deep enough so that the pump sits below water level. Dig this shelf in the position where you want the waterfall to be. Grade the back of the shelf backward and upward until it reaches ground height.
Line the shelf and the surrounding sides of the pond with pond liner, extending back about 2 feet.
Place the pump in the shelf, attach the hose and then thread a length of PVC pipe, a little wider than the diameter of the hose, onto the first foot or so of the hose's length. Dig a small trench that goes back away from the pond and lay the hose, inside the pipe, in the trench. Run the electrical lead of the pump up the back of the shelf and away from the pond as well.
Place a large, flat stone over the top of the pump shelf, obscuring it from view but allowing access to the pump underneath. The stone should not be longer than the length of PVC pipe, so that the pump hose can come out freely at the back of the stone. The stone should rest securely on the sides of the shelf, not on top of the pump unit itself.
Construct the spillway of the waterfall on top of the pump and flat stone, with the pump hose at the back. Place stones laterally to give a more natural look, and do not make the spillway larger than 2 feet long or high. Before setting the top rocks in place, position the waterfall weir, a raised shelf off of which the water will fall, on the top and attach the pump hose to the back. Disguise the weir with rocks.
Test the spillway by flowing water from the top of the waterfall with the garden hose. Adjust as necessary to get a flow you like. Once you are happy, fill all gaps in between the stones and inside the spillway with self-expanding waterfall foam. Consult the foam manufacturer's instructions on proper application and drying times for the particular brand you have bought. Use plants to help further integrate the waterfall into the landscape, and disguise any hose or electrical lines that may be visible.
Refill the pond so that the pump is submerged, then plug the pump in and turn the power on.
Multiply the depth of the pond plus the height of the waterfall by the width and length of the pond, then multiply those results by 7.5 to get the gallons-per-hour rate you will need for the pump. Buy a pump with a built-in filtration system if you have fish or other aquatic life in the pond.