How to find the pond pump flow you need
by: Demi Fortuna
For ponds up to 5000 gallons, the rule of thumb is to size the pump to turn over all the water at least once an hour, so a 3000 gallon pond would require a 3000 GPH pump. However, this minimum often falls short of the desired visual effect. For example, let's consider the size of a pond of about 2250 gallons. There are 7-1/2 gallons in a cubic foot of water, so a 2250 gallon pond would be 2250 divided by 7-1/2 or 300 cubic feet. This would be the volume of a pond 2' deep by 10' x 15'. With the waterfall at the far end of the pond, around 20 feet away from the viewer, 2250 GPH might fail to impress. It turns out that most folks want visual effects – sheeting, torrents, white noise – that require more than the bare minimum circulation requirement. Luckily, there's an easy way to size the pump by the visual effect desired and the width of the waterfall.
50 GPH per inch of waterfall provides a gentle trickle, with water breaking into individual rivulets off a clean edge, but this amount of water tends to underwhelm. 2400 GPH over a 4 foot wide waterfall just dribbles. Would you be impressed? This trickle effect is best for small, quiet, Zen-type gardens.
100 GPH per inch creates a solid sheet of water off a clean edge, about the least most folks want to see, so 4800 GPH would be suitable for a 48' wide waterfall. However, as nice as it may look up close, a sheet of water doesn't grab a lot of attention at a distance, nor does it make very much noise.
200 GPH per inch of waterfall width gives real action. Push 4800 GPH off a 24' waterfall, and you'll see and hear white water, even 30 or 40 feet away.