What pump do I need for a waterfall?

Selecting the right size of pump for your waterfall, cascade or decorative stream can seem tricky.  There are a few things you need to decide upon and cater for, before deciding on buying the right pump.

1. How wide is the water ‘channel’?
2. How high is the pump lifting the water to the top?
3. How long is the pond hose from pump to the top?
4. What is the inside diameter of the pond hose?
5. Do you want a trickle or torrent?

What do these questions mean?  Let me explain…

1. The water ‘channel’ is the maximum width of the path the water will be flowing down.  For this example, let’s assume the water channel is 50cm wide.
2. The pump will lose water flow as it pushes water uphill, so we need to compensate for the ‘vertical lift’ or rise from the pond water surface to the highest point of the cascade.  It doesn’t matter if the pump is submersed 1.5m deep or 30cm; the pump only needs to push from the water surface, so we take the measurement from the surface, not the pond bottom.  Let’s say the waterfall is 1m high for this example.
3. The length of the hose is important, as we will also lose flow from the pump as it passes through a hose.  Short lengths are less of a concern but if you have a 20m or more run, this will certainly have an impact.  Let’s assume 5 metres.
4. The inside diameter of the hose is also important.  If the hose diameter is too small, this will drastically reduce the flow coming out of the hose.  Always try to use the largest hose diameter that the pump is designed to accept (most good quality pumps will have a stepped hosetail adaptor to push the hose onto and will state the hoses it can accept).  Let’s assume a 1.5” internal diameter flexible hose is used.
5. Finally, deciding on whether you want a gentle trickle or a more dramatic display is also important.  As a general guide, we would look for a flow rate of 1000L/Hour for every 10cm of channel width for a gentle trickle, or 2000+L/Hour for a more dramatic flow.  We’ll assume 1500L/Hour for every 10cm of channel width.

Let’s put this all together using the things we know...

• Cascade channel width:  50cm
• Vertical Lift:  1 metre
• Hose Length:  5 metres
• Hose I.D:  1.5”
• Flow per 10cm Channel Width:  1500L/Hour

So;

5 X 1500L/H (five lots of 10cm)  = 7500L/Hour needed at the top of the waterfall.

A great choice of pumps for this size of waterfall is the OASE AquaMax Eco Classic range.  We can use the ‘performance chart’ to estimate the pump by accounting for the 1 metre of lift and the hose diameter (here at Water Garden Ltd, we use a special ‘friction loss calculation chart’ but if you allow a little extra, you should be fine).  From the range, the Classic 11500 will give us around 7500/Hour once we have catered for the lift to the top and the hose length and diameter so this pump is our best choice.

What if I have too much flow I hear you say?  Too much flow is an easy issue to rectify as you can use an In-line Flow Regulator to crack back some of the water flow and this can easily be inserted anywhere along the length of the flexible hose.  Too little flow is a far more problematic issue, so always aim for the next model up if you are in any doubt.

Still need help?  Call our experts on 02392 373735 or email us for friendly advice!