Improving Irrigation Efficiency

Irrigation Test:

Time to complete test: 15 minutes per zone. Following this simple procedure will be time well spent – your water bill will be less and your plants will be happier.

Supplies: Six straight-sided, flat-bottomed containers (coffee mugs work well), cardboard strips, a simple calculator and a ruler

Procedure: Concentrate on turf areas first, as that is where the most water waste occurs. Turn on your first sprinkler zone. Note where the sprinkler heads are located, and look for the problems described in Table #1. Place the containers in various locations in each sprinkler zone – some in the middle and at the edges.  Run your zone for exactly ten minutes.  Use a piece of cardboard if necessary to dip into the water and then use a ruler to measure the discoloration on the cardboard.  Mark these depths on a map showing the location of each container. If one or more of the containers has significantly less water than the others, then you have a dry spot. Refer to Table #1 and fix all the problems to get better distribution. Next, pour five of the containers into one and measure the depth again.  This is the application rate of water in inches per hour for that zone. Complete this procedure for each irrigation zone.

For each irrigation zone, answer these questions:

How much water does the plant need?

This depends on the type of plant and local weather patterns. In this example, we will focus on turf in Vail in July, the thirstiest plant in the hottest month of the year. In Vail, we should irrigate turf about 1.5 inches per week in July. Let’s apply half that amount (0.75”) on each of two separate days each week. (Be sure to irrigate less in other months, and turn off the system if more than a quarter-inch of rain falls at one time.)

How much water is my irrigation system applying?

Let’s assume that in this example you poured all the containers together and measured exactly one inch.

How many minutes should each zone run?

In order to calculate run time for that zone, use the following simple formula to see how long it will take to water one inch:

  Water to apply (inches)
Run time (minutes) =  Divided by X 60
Precipitation rate (inches/hour)

Water to apply (0.75 inch)
Run time (minutes) = Divided by X 60
Precipitation rate (1.00"/hour)    

Run time (minutes) =  45 minutes

Complete these calculations for each sprinkler zone and set your controller for the appropriate number of minutes. If your controller has the feature (and all newer ones will), set the ‘Water Budget’ feature to the following settings on the first of each month.

Keep in mind that if you have clay soil and/or a sloping turf area that this runtime will need to be split into sections to allow water to penetrate and avoid runoff.  In the above example, you would split the 45-minute runtime into three (3) sections of 16 minutes, allowing an hour between these irrigation periods for the water to soak in.

Table #1. Irrigation Efficiency Troubleshooting

What to look for... Caused by... Problem results in... How to fix it...
Tilted sprinkler heads Usually mowers hitting heads or traffic Poor water distribution and dry spots Remove a little soil from around the head and make perpendicular to grade
Misting/High pressure High pressure Waste of up to 50% of water used in irrigation Install pressure regulators on valves or replace sprinkler heads with new ones that regulate pressure*
Stready stream of water with large droplet size Low pressure Poor water distribution and dry spots Change nozzles, reduce number of heads on a zone*
Low sprinkler heads Installation errors or heavy mowers pushing them down Poor distribution and dry spots due to deflection Raise the heads by removing soil from around the sprinkler and gently pulling up.  There is usually a swing joint that allows you to do this without breaking the line
Deflection Tall plants in the way Poor distribution and dry spots Move the head or move the plant.  Consider retrofitting with a drip system in shrub and perennials beds*
Mismatched sprinkler heads in the same zone Poor design Widely fluctuating precipitation rates cause wet and dry spots Replace mismatched heads with appropriate types*
Irrigation during and after a significant rain event Lack of rain sensor or intensive management Water waste Install rain sensor which shuts off your system during and after rainfall ($30).*  Turn off the system during and after rainfall
Water is getting on adjacent hardscapes and running off Sprinkler adjustment Water waste Adjust sprinklers so that they stop before irrigating the hardscape; consider a landscape retrofit that pulls turf back from hardscape edges
Runoff Sloped areas, clay soils Water waste onto adjacent areas Split sprinkler times to irrigate a fraction of the total time in two or three start times on the same day

*An irrigation professional is recommended.

For more information call Sarah Fleury, Water Conservation Officer, Eagle River Water & Sanitation District, 970-477-5426.