Water Calculations For Furrer Farms

Our irrigation well produces 40-50 gallons per minute. It has too much arsenic to drink, but has been able to irrigate about 10 acres of pasture for cattle grazing throughout the summer. Here is a quick calculation of how much water this well actually produces:

So, how much water could be in a pond that would hold rainwater runoff, take in some seasonal creek runoff, and maybe be augmented by the well? Below is the calculation of how much water is in a certain size pond:

Length (ft.) x Width (ft.) x Average Depth (ft.) x 7.5 = volume of water. For example, a if your pond is 4 ft. Long x 8 ft. Wide x 2 ft. avg. depth x 7.5 = 480 gallons. I’ll put this in an Instacalc embed soon, but for now, I’ll see what a 200′ by 200′ pond that is 5′ average depth has for volume.

200 X 200 X 5 X 7.5 = 1,500,000 gallons. So, it would take about a month to fill with all of the output from the well.

Rainwater catchment from the barn would be about:

80 X 144 = 11,520 ft sq roof area.
.9 efficiency coefficient for metal roofing
3.7″ average monthly rainfall in Eugene, OR, USA area.
.6 conversion factor to get gallons
11,520 * .9 * 3.7 * .6 = 23,016 gallons per month.
23,016 * 12 = 276,192 gallons per year.

Wow, not much of a dent in filling the pond.

But, much, much more could be gotten from the seasonal creek. I will have to do some flow analysis to determine just how much water id flowing by the pond site from October to May of each year. I know it is a LOT.


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