Pump Size

Your pump at a minimum should pump half of the ponds volume of water every hour.
For example, if your pond holds 1000 gallons of water your minimum pump rating should be 500 GPH (gallons per hour) at the top of your falls.

Another way to determine pump size is the amount of water you want coming over your falls. For a ¼ inch depth of water over your falls you need 37.5 gallons per hour of water for every inch in width.
For example, if your falls are 8 inches wide and you want a ¼ inch of water flowing over them you would need to pump 300 GPH 8x37.5=300

Pump Head (lift)
Most pumps are rated in GPH at various heights above the water surface. The higher you place the discharge above the surface of the pond, the harder the pump needs to work. As a rule, every 10 feet of horizontal pipe equals 1 foot of vertical rise as dose every fitting.
For example, if you are running a horizontal pipe 30 feet, you would have 3 foot of rise, 4 fitting 4 feet of rise.

Let’s put it all together now.
The pond is 1000 gallons: The pump sets 1 foot above the water surface (we used 2 45* bends). We need to pump the water horizontally 60 feet and up 30 feet (2 90* bends one to go up and the other into the first water fall). So, we are going to have 41 feet of vertical rise. We want ½ inch of water coming over the falls that are 10 inches wide. (That’s 750 GPH. So, we need a pump that has a minimum head rating of 750 GPH at 41 feet of vertical lift.
We have met the requirements of pumping half the ponds volume every hour, as well as the desired flow of water over the falls.

(Had we used a pump that only pumps the (minimum) 500 GPH needed we would not have made it, because we didn’t account for the 41 foot vertical rise or the desired water flow over the falls.)
A 500 GPH pump on flat ground may only pump 100 GPH at 40 feet of vertical rise.

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