Calculating Water Amount In a Pond for Irrigation Use

If you read our previous article titled ‘Calculating 1” of water’, you’ll know that it can difficult to calculate how much water you need to deliver in order to effectively irrigate.  But the general rule of thumb is 1”, and there are constant values that you can use as a benchmark figure out how much water you need to apply per week.  If you are irrigating 1,000ft² of turf, you need 620 gallons/week.  If you are irrigating 1 acre of vegetables, you need 27,200 gallons/week.

Now the conversation becomes, where are we going to get this water? Typical water sources include a municipally supplied source, a well, lake, river or a pond.

Municipally Supplied Source, you can use the chart below to get a good idea of the rate of water you have access to from that service line:

If you are using water out of a well, your local well digger will be able to tell you how much water is available.  Our staff, or that same well digger, would be able to tell you the rate of water you could pull from that well with some information about your pump.

If taking water from a lake or river, you will need to get a permit.  In this instance, the government will tell you how much of that water you can take.

Now, if you have a pond on your property and you are wondering, “Is there enough water in that pond to supply my irrigation system?”, there are a few calculations you could do in order to know for sure.

Square/Rectangular Pond Gallons = Length x Width x Average Water Depth x 7.5

Example:                                       

= 100’ x 100’ x 8’ x 7.5

= 600,000 gallons in a pond that is 100’ x 100’ with an average depth of 8’

Round Ponds = Diameter x Diameter x Average Water Depth x 5.9

Example:

= 50’ x 50’ x 8 x 5.9

= 118,000 gallons in a pond with a diameter of 50’ and average depth of 8’

After calculating this, be sure that the pond could supply enough water to make it through a few weeks of drought to ensure you are fully covered from drought risk.  If the pond is able to recharge by a stream flowing in or a high water table underground, you are in an ideal situation.  But know that in a drought, the stream may dry up, the water table might diminish.  All you can do is know the factors you are working with and try your best to mitigate risk.