Fix my Heads, Austin Tx — Sprinkler Repair

2011 Drought Sprinkler System Run Times by Justin Wilson

Summer 2011 Drought
Justin Wilson
American Irrigation Repair LLC

This year has been one of the driest summers in history. We have broken all kinds of records and the heat has been immense. Everything is drying out. How quickly the lawn dries out depends on the weather each specific day. During the week around the first of August between plant use and evaporation, the rate has been as high as .4” per day. That’s almost a half inch a day.

In order to keep a green lawn or living plants that water has to be replaced. This is where the issues can arise. Most folks don’t know how long it takes to apply .4” with their sprinklers. There are some complex formulas for calculating irrigation system distribution uniformity, and plant stress factors, but for the purpose of this write-up I am going to keep things simple.

Generally Rotor style sprinklers apply water at a rate of .4” per hour, and spray / mister type heads apply at a rate of 1.2” per hour. These are general terms and depend on the spacing and pressure and other variables. So in order to totally replace the water lost on a day such as 7/28/2011 you would need to run your system one hour on rotor style heads, and 20 minutes on sprays / mister style heads… EVERY DAY! WOW!

The average residential sprinkler zone uses approx. 14-18 gallons per minute that the zone runs. So let’s run some numbers…
If you have a 10 zone system, four of which are sprayers and six of which are rotor style heads here is how your water bill would break down to keep a totally replenished yard in this drought…

6 zones (rotor style) x 60 minutes each(.4” application) = 360 minutes of run time
4 zones(spray style) x 20 minutes each(.4” application) = 80 minutes of run time

Total run time of 440 minutes would use between 6160 and 7920 gallons of water… FOR ONE DAY. So watering like this every day would yield a monthly water use age of between 184,800 and 237,600 just for the sprinklers in the lawn. This translates to a water bill for the Irrigation of between $1288 and $1659 to have a zero stress lawn on an average residential system of ten zones. This assumes a top tier rate of $7.00 per 1,000 gallons. Yours may be slightly higher or lower.

Generally no one wants to spend that on their water bill, and we wouldn’t want to risk running out of water in a drought. We have to find a happy medium. Generally speaking watering to get to ½” is your best bet. I do not recommend short run times under at least ½” as the irrigation cycle will dry out before the plants / turf is able to use the water. This correlates to approx. 75 minutes on rotors style heads and 25-30 on spray type heads. Water this as often as your water district or budget allows. Additionally we have found that watering in the evening allows the plants and turf to sit cool and they respond well to this. It is important to remember watering in the evening is not recommended in the fall / winter.

Nearly daily in the drought we get the question of why if the sprinklers are working correctly are their green splotchy areas and then dry areas in the yard. Folks assume the system is not working efficiently when they see this. If we have checked your system and reported that your system is operating correctly other factors may be the cause.

Irrigation is not like rain. It does not apply water nice and even. There are inherent inefficiencies which is called distribution uniformity. Most sprinklers at their maximum run about 65% uniformity which is not very good. This means some areas get less, some get more and if your lawn is not getting enough water as a whole, the areas that are getting more often times will be green. Those are the over watered areas in that efficiency spectrum. Add those issues to things like poor soil conditions such as rock, gravel, base, compaction and there is a huge range of what the lawn will look like as it starts to dry out. Some areas dry quicker, some slower and good soil will hold the water longer than rocky. The only solution to this is to slightly overwater some areas to get water to the less efficient areas.

No lawn when irrigated to a certain level of stress will dry to a completely uniform level. Under-irrigating will always show itself as splotchy dry and green areas.

I hope this information will be of use to you and that you will continue to trust us with your business in the future.

Justin Wilson


1 Comment so far
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nice post

Comment by Vasilij

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