Tuna Can Lesson #5 - Professional Water Audits

This is the last tuna can article. I hope these have helped you visualize that your sprinkler system applies water in measurable amounts of water. And the more water you apply, the deeper it will soak into the ground. Using tuna cans is a good way to measure sprinkler system performance but there are advanced techniques to get this job done.

The Irrigation Association has a 2-day training course to teach water management professionals how to conduct a "Water Audit." Certified Water Auditors use catch cans to test a system, which are more accurate than old smelly tuna cans. Auditors also have software that uses test results to generate accurate irrigation system performance reports. The report provides zone by zone precipitation rates and distribution uniformity calculations. This information helps refine irrigation schedules because control settings are based on actual sprinkler system capabilities. As part of the process, auditors will also be able to offer suggestions to improve system performance. In some cases, simple improvements can significantly improve system efficiency.

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Tuna Can Lesson #4 - Optimum Irrigation

What have we learned so far?  In the last blog I wrote about improving watering uniformity.  Don’t expect a smart control system to fix a bad sprinkler system. Tuna Can Lesson 2 reminded us that sprinklers apply water at different rates.  Valve run-time is based on how much water needs to be applied and how fast the sprinklers apply water.  I remember the very first time I setup a computer controlled irrigation system.  After a week the customer called and said, “Take it back”.  I said, “What’s wrong?”  He said, “The grass is dying and the shrubs are drowning.”  We checked it out.  The wiring was wrong.  The shrub bubblers were watering for over an hour and the big lawn sprinklers were watering for only 10 minutes.  Once we fixed it, the system ran great.

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Tuna Can Lesson #3 - Even Watering

Years ago, as a landscape contractor, I met with the irrigation Foreman at a job site.  There was a spot in the yard with dying grass.  I told him it looked like the sprinklers were not getting the area wet.  He told me to stand in the dry spot, he would turn the sprinklers on to see if I got wet.  Not the best science and a poor excuse for a problem with the sprinklers.  As you can imagine, water was shooting over the dry spot and not landing in the area with dead grass.  I should have brought my tuna cans to show him the problem.
 When you do your tuna can test you will be surprised to see the difference in the amount of water in the tuna cans when the test is over.  No, sprinklers are not perfect; they do distribute water with perfect evenness or uniformity. Good sprinklers, with the right nozzle, properly positioned will get close, but never perfect.

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Tuna Can Lesson #2 - How Long?

I had the call again today, “How much should I water?”  My response was ½” is a good target.  Then she said, “I water 40 minutes, is that enough?”  So we started talking about tuna cans.  The lights came on.  When the sprinklers run for a given amount of time, they apply water to the landscape.  The application of water can be measured in inches and valve-run time is measured in minutes.
Irrigation professionals know that sprinklers apply water at different rates.  The application rate, also called the precipitation rate is expressed as inches of water applied in an hour.  For example, fixed spray sprinklers apply water any where from 1.50” to 2.00” of water per hour.  Rotating sprinklers apply water much slower; anywhere from 0.35” to 1.00” per hour.
Let’s go back to the tuna can test.  If, in 20 minutes your sprinklers put an average of ½” of water in the tuna can, what is the precipitation rate?  Yes, this is a test question.
60 x ½” inch / 20 minute test time = 1.50” per hour       (60 x .5 / 20 = 1.5)

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Tuna Can Lesson #1 - Fill it up

There are many things you can learn by putting tuna cans out on the lawn, and then running your sprinklers.  Let’s start with Lesson #1, is pretty obvious; here you can see how much water your sprinklers put down.  But where does it go?  How far will it soak into the soil?  That depends on the soil.  This simplified soil chart gives you an idea of how far a ½" of water will soak into the ground:

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Automated Water Management


Pipeline: Publication of the Florida Irrigation Society

Water agencies across the country are encouraging more efficient use of water in the landscape. A responsible homeowner responded to the message to conserve water founded by local water agencies. He felt he should do his part to reduce water waste, but he was passionate about his grounds and feared cutting back water use would sacrifice his beautiful landscape. Despite his fears, the homeowner began using the local water agency's, "Guide to Landscape Watering." Every week, he faithfully adjusted the sprinkler timer. Compared to neighboring properties, he used 20% less water. His landscape remained healthy and beautiful. 

Read more: Automated Water Management