>> This is a sidebar to Demi Fortuna’s main feature, “A Pump and Plumbing Pond Primer”
What if you wanted to know the flow of an existing waterfall, perhaps because you want to recreate the same effect? You can measure the thickness of the water flowing over a spillway or fall rock. Turn a ruler or tape sideways or perpendicular to the flow to get as accurate a reading as possible. (Remember, the water will be in motion.) For an irregular surface, measure every 4 — 6 inches and take the average depth of the water spilling over the top of the waterfall rock or spillway. Just like before, multiply by the width of the waterfall to get the total flow.
- ¼” — 3/16” depth of water over spillway ≈ 50 gph/inch
- ½” — 5/8” depth of water over spillway ≈ 100 gph/inch
- 1” — 1¼” depth of water over spillway ≈ 200 gph/inch
For a more accurate reading on smaller falls, it’s sometimes possible to measure the flow directly using a piece of scrap liner and some gravel. Turn off the pump and cover the falls with the liner, anchoring the upstream edge with gravel. Fold the rest of the liner into a 5-gallon pail and turn on the pump. Measure the number of seconds it takes to fill the pail. (You will get wet.) The flow in gph will be equal to the number of seconds in an hour, times 5 gallons, divided by the time it takes to fill the bucket in seconds:
GPH = 3,600 sec/hour x X gal / Y sec
Question about Waterfall pump requirements- I have at the top of a hill a 30×24 pond falli falling down one level to a 20×8 and then falling down to another 12×6 – and from there a lazy stream back down to the original water source of 3acees of pond water. What size pump do I need?
Hey Trace! Sounds like a fantastic feature! Unfortunately, there are three crucial pieces of information you need to know to choose the perfect pump. The first is the actual height of the pond at the top of the hill above the water the pump is in, the VERTICAL HEAD. This can be difficult to measure because it needs to be the true vertical distance between the surfaces of the two bodies of water. The second number you will need is the amount of water you will want to pump up to the top pond, and that is dependent on the WIDTH OF THE STREAM between the ponds and down to the lake. Decide on a flow or an effect, like a slow flow that provides a trickle of water, or a medium flow that would create a thin sheet of water falling off a waterfall. Or you might want a high flow to create white water and significant noise that could be heard from a distance. A trickle can be achieved with about 750 gph per foot of stream width, a sheet requires about 1500gph per foot of width, but to get that “rapids” look you’ll need at least 2250gph per foot of stream width. Finally, you’ll need the LENGTH OF PIPE and maybe the number of fittings required if it isn’t a straight run. Together these three metrics will allow you to select a pump that gives you the right flow at the correct head height for your feature. Check out the Tech pages of our Catalog for a worksheet that will provide the Friction Head, the Total Dynamic Head and the right pump for your project, or write me at demi.fortuna@gmail.com, I’d be happy to help.