Design: First, decide on the types or multiple types of returns you are hoping to achieve then layout a scale drawing on graph paper. Remember, returns should be opposite your skimmer. Once you are happy, transfer this to your yard using marking spray paint. Start with piping first since this will be buried. As discussed in previous articles – pipes should be large for the volume, have the slightest and fewest bends as possible, and the flattest, shortest distance as feasible. Noting the distance from the pumps to the filters along with the head height, add up all the capacities of the all the returns and how much flow you wish to have in them. This will help you gauge pump sizing; or if you already have the pump(s), what size and capacity the return(s) needs to be to match your discharge volume and capacity.
Example – My Pond: I have two pumps – my external pump (which takes water from the gravel filter on the bottom of my pond) and a submersible pump (which takes water from the skimmer box at the surface of the pond). I have a 2450 gallon pond, a 110 gallon filter tank, and ~40 gallons in the skimmer, primer pot and plumbing equaling 2600 gallons total system capacity. I need to turn over all that water in one hour. To be safe, each of my pumps can do this alone. Both my pumps discharge at ~50GPM. Together they give me ~1-GPS, ~100-GPM, or ~6000-GPH; I am effectively doubling the ponds filtering requirement. This means if a pump fails or is offline for maintenance, the other can maintain the pond. It also means I have double the flow to work with for my return capacity!
These are my returns:
Plumbed “Winter Bypass” Returns: My first “designed” returns were two “winter bypasses” attached to each pump. I plumbed tees right after both pump’s discharge outlets. A shutoff was placed on the return lines. If open, water would then immediately return back to the middle of the pond ending at diffusers about 2’ under the surface (see picture). This allows me to “bypass” my bio-filter tank (for maintenance) or to bypass all my returns (like in winter when the air temps are far too cold). Capacity volume of these returns will be nearly at the pump’s maximum flow since no elevation is gained (pumps noted maximum flow rating – 0’ head).
Spitter (Fountain) Return: If one or both winter bypass shutoffs are closed, water is forced through a check valve and up to the bio-filter tank which fills the tank. At the top of the tank, through the side is a ½” bulkhead union. On the outside of the tank a ½” hose is attached (~5’ above the pond surface). Water falls into the hose and down to the far end of my pond to a frog “spitter” statue (no pump needed!). My pond is kidney shaped and the main return is at the NE end of the pond (with my skimmer opposite at the SW end of the pond). I placed the frog at the SE end for four reasons. The water was rather still in this corner so I wanted to move the water so that floating debris did not float in a dead zone and become waterlogged (then sink); second to deter bugs, third an added boost of more oxygen, and last to liven up the far end of my pond with something interesting to look at. Flow is ~2GPM from 5’ head (gravity ~3.3’/s).
Spillways and Stream: If one or both winter bypass shutoffs are closed, water is forced through a check valve and up to the bio-filter tank which fills the tank. My weir consists of three 2” bulkhead unions through the tank near the top with about 4” of pipe attached to each. As my tank is sunk down to grade level (about 5’ above the pond surface), I began my stream and waterfall bed trough at the side of the tank where the spillways are. NOTE: even though my pumps both discharge into the bottom of the tank through 2” bulkheads, I needed three 2” spillways. Why? The pumps are pushing water out into the tank under pressure while the water is flowing out the spillways through gravity. With just two spillways, the difference meant that the water in the tank would overwhelm and inundate both spillways causing loud cavitations. The water did not flow out at a steady rate, but pulsed – thus a third spillway was added so that air remains in each and none would be submerged. If both pumps are running through the filter, ~100GPM of water filter through the bio-tank with ~98GPM falling through the spillways (~2GPM is diverted to the spitter line). Note, some filter tanks are designed with a built in weir – which is like a trough where water spills over like a waterfall. In my case, I wanted the water emerging from the side low as this is my stream bed running a mere 3’ before it reaches the brink of my waterfall. The stream is a little over a foot wide but it is 2-3” deep. I wanted a large volume of water for the plunge and for the stream to disappear from view giving the illusion that it continues on (the tank and spillways are hidden).
Cascade Waterfall: The trough for the falls is 2’ wide, on a steep, curving path dropping 5’ vertically in a little less than 5’ horizontally on a steep slope of ~57° degrees making this a true falls. There are a multitude of large rocks with about ten distinct drops. With both pumps running which attain ~6000GPH, the 2’ wide return equates to a turbulent flow of water. With just one of the two pumps, it still manages an average flow! The falls end at a plunge pool into the pond.
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