Waterfall width is a useful first measurement, but it is not the whole pump-sizing decision. A pump’s advertised flow is usually measured under specific conditions. The flow delivered at the top of your waterfall will change with lift, plumbing, fittings, and resistance from the feature.
Start with spillway width
Measure the actual spillway opening where water should pass over the edge. Do not include the surrounding frame rocks in that measurement.
As a starting estimate, the Toolkit source uses approximately 1,500 gallons per hour per foot of spillway width for a residential waterfall. A two-foot spillway would therefore start at about 3,000 gallons per hour before head height and plumbing losses are considered. Treat this as a planning estimate, not a guaranteed finished flow.
Check the pump curve
Before choosing a pump, compare the desired flow with the manufacturer’s performance curve at the required lift. Also check pipe size, total run, elbows, valves, filters, and the height from the water level to the spillway. A pump that looks large enough at zero lift may deliver much less at the waterfall.
Test the finished feature
Build in a way that lets you observe the flow before final landscaping. Check that water stays inside the liner, the basin does not overflow, the pump remains covered, and the waterfall looks balanced from side to side. Make adjustments only when the pump and plumbing instructions permit them.
FAQ
Does a wider waterfall always need a larger pump?
A wider spillway generally requires more flow to create the same visual depth, but width alone does not determine pump size. Lift and plumbing can change the delivered result significantly.
Can I use the pump’s maximum gallons-per-hour number?
Not by itself. Use the flow shown at the actual lift and plumbing conditions on the current pump curve.
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