How to build a waterfall
There are few things more pleasing than the sight and sound of running water in the garden. Many of us would like a waterfall or watercourse of our own but are unsure how to build or install one. The good news is that they are easy to create - and you don’t even need a pond!
To create the most basic of waterfalls you simply need water to drop from one level to another below it. To do this you’ll need a vessel to hold water, a pump, and a hose. The pump goes in the bottom, pumps water up and out of the hose, and is returned to the pump in the vessel below. Simples!
The vessel is typically a pond, either preformed or made from a pond liner and to return the water from the high place to the pond, we typically use a preformed watercourse or a waterfall we make ourselves from liner placed at an angle on a mound of earth.
For a natural-looking waterfall you need the pond to be at ground level. Dig the pond, making a large mound of earth about two feet high to one side of it. This will be where the waterfall goes. If using a preformed watercourse, first run some pond hose up the slope and then place the watercourse on top of it, with the lip of the watercourse hanging over and into the pond.
If using a liner, you could use an oversized liner to also line what will be the wet side of the mound. By using one piece of liner you will ensure that both pond and waterfall are watertight and one self-contained system. If using a separate strip of liner, make sure that it overlaps the other liner and terminates in the pond, or better still stick it to the main pond liner with either silicone or liner repair tape sandwiched between the overlap.
Create a U shape in the earth below the liner on the mound, forming a natural valley for the water to flow down, back towards the pond. Ensure that no water escapes from the sides of the lined waterfall by raising up the edges, again with earth or stones, beneath the liner. Run a hose up underneath the liner, connect to a pump in the pond and turn it on. This way you will have a bare liner waterfall, but you can check that it's watertight and the water is of the correct flow rate and running the way it should be - back to the pond - with no leaks.
Once the mechanics of the waterfall are done you can think about how you would like it to look. If you want simplicity and something you can create in an afternoon, just dress the waterfall with large stones. If you are experienced in mixing concrete and mortar you could build a stream on top of that liner from rocks and cement.
Any exposed concrete or mortar should be sealed afterwards with pond sealant, the pond emptied and refilled several times to remove any traces of cement (which contains lime,) and the pH of the water tested. Additives are also available especially for the cement to be used for building ponds, so this and a sealer will give a belt and braces approach to a fish safe concrete stream.
When pumps pump water up out of the pond we refer to it as head. The higher and further a pump is expected to pump water, the more it experiences head loss, from gravity, and the flow is reduced. A small waterfall, 90cm in length and raising up 30cm above the surface of the pond will require a flow rate of about 2000lph. Pump flow rates are stated by the pump manufacturer as maximums, so a 2000lph pump will pump 2000 litres per hour at zero head. To find out how much it will pump at 30cm of head, many manufacturers will publish pump curves, showing the reduction in flow and head loss.
In extreme cases, like if a waterfall is three metres long and a metre high, an average pump simply may not be able to pump any water to the top of the waterfall. In these cases refer to the pump curves to see how much water each pump would produce at a metre of head. An 8000lph pump may be reduced to 4000lph at one metre of head for example, whereas a 4000lph may be reduced to zero, depending on style, make and model, so research beforehand and you won't have to buy twice.
A more powerful pump can always be turned down, but a pump that is not powerful enough will be useless. DC pumps are also available that can be turned up or down electronically. These are great for powering waterfalls as you can finely adjust the output and when you turn them down, they use less energy. Always use the largest diameter hose that will attach to the pump in order to minimise frictional flow loss.
So all you need to power a waterfall is a pump, but if you want the water to stay crystal clear like a natural stream you’ll need a filter and UV. Filters trap waste and break it down and UVs stop green water. Many filters and UVs are combined, and the best filter system for a pond with waterfall is a pressurised filter and UVC combined, powered by a solids handling filter pump in the pond.
Unlike standard black box filters, which need to sit at the top of a waterfall, pressurised filters are sealed units which can be placed behind or below waterfalls, out of sight. Even buried in the ground up to their lids. So you get clear, healthy, filtered water fed to your waterfall, from a filter thats out of sight.
The pond-less waterfall
But as stated above you don’t even need a pond to have a waterfall, and that means that can be created to be childsafe too. Use a water feature tub buried in the ground with a strong, purpose-built grid over the top of it. Cover with large pebbles and your waterfall will simply fall onto and then through a bed of stones, safe to walk on, with no pond. The waterfall can be created in the same ways as suggested above.
If your pond is raised you can still have a waterfall returning to the pond, with the most popular method being by way of a stainless steel lip, also known as a blade. These can mount to the edge of a raised pond or a wall and return a very neat, sheet of water. Power them in the same way, by using a pump, pressurised filter and hose connected to a hosetail, at the back.
For the sorts of waterfalls and water features you see outside hotels and conference centres, you’ll need a big pump. To cover a 30cm waterfall with a lot of water, you need 4000lph, so if you intend on building a 90cm wide waterfall you’ll need at least 12,000lph, and that’s after any headloss. Big pumps are purpose made for the job.