Best laid plans, as they say…. When we built our farm pond, we recognized the drainage area wasn’t very large, though we figured it would be sufficient to keep the pond full. One dry summer later, though, I must admit that Mother Nature proved us wrong.
Does this matter in all cases? No, not necessarily. But I stocked this particular pond with fish last year. So I need to ensure there’s enough water to keep all these aquatic creatures healthy.
What to do? Well, one handy solution is to collect and divert rainwater from the buildings on our property—our outbuildings, as well as the roof of our house—to the pond.
I know how much drainage area my pond receives thanks to some quick calculations on Google Maps. In all, the pond gets water from about 1.5 acres, calculated by measuring the perimeter area of the pond.
But, of course, not all of the rainwater gets to the pond, as much of it soaks into the ground first. Not so with a building’s roof, though, which provides instant runoff when collected and diverted to the pond.
Where does this rainwater usually go? Typically, it makes its way into the yard and pastures. But when it rains, these areas receive water, so I consider roof runoff to be excess.
In the video you’ll see I’ve got pipe sitting on the ground to move this runoff water to the pond. In the long run, though, my plan is to bury these irrigation lines underground for a more permanent solution.
How Much Water Will This Collect?
How much rainwater can I actually collect for my pond by simply attaching piping to my downspouts? The answer might be more than you think. And there’s a formula for an accurate prediction.
First, you need to get the square footage of your roof, either using a land wheel and walking the building’s perimeter or using mapping software.
Once you have the total square footage of all the roofs you’re collecting from, just multiply this number by .625. The resulting number will give you the gallons of water you can expect to collect per inch of water that falls.
With the amount of square footage I have, and given that my area typically gets about 40 inches of rain a year, I can expect to collect 98,000 gallons of rain per year for my pond.
One note: Check your local county or municipality rules for any restrictions on catching rainfall. And check out the video above to see how my system looks and the pond I hope to fill with this cheap and easy catchment system!