Since the early 1990’s lower quarter distribution uniformity (DULQ) has been used to evaluate the performance of sprinklers. Data obtained from irrigation audit cup tests is used to calculate DULQ. Although it has been used for improving irrigation scheduling since the mid 1980’s, DULQ is not without its detractors. Problems include not being consistent with operational conditions, only testing single sprinklers, using computer simulation to group sprinklers and having no allowance for sprinkler interference. DULQ focuses toward the “dry” and, as a result, when used as a basis for scheduling – such as in the IA/GCSAA golf auditor program – has a tendency to over water. It also does not measure whether the water is on target.
Today, every drop of water is important and how to measure whether the water is on target has become the new challenge. With new sprinkler technologies, there is the ability to be very precise with sprinkler spacing’s and grades. As a result, stream interference is also becoming a big issue. Technically called “jet interference”, measuring jet interference occurrence has become of interest to some researchers and water regulators. Throw in the normal losses due to deep percolation (seepage), atmospheric evaporation and overspray to the calculation and there is a new way to characterize sprinkler performance that is more accurate and hopefully useful than DULQ, called “sprinkler operational efficiency”.
Measuring and calculating sprinkler operational efficiency requires sprinklers operate simultaneously and cup tests be performed. So what is a good measurement of sprinkler operational efficiency? For starters, 75 percent of the targeted area receives the scheduled amount of irrigation. The percolation loss and overspray losses are also calculated. Jet interference is shown graphically much like the densogram you might be familiar with that was used with DULQ.
You probably have never looked at the sprinklers on your golf course from the standpoint of jet interference. You may want to take a look. The newer your system, probably the more noticeable it is as the sprinklers apply water more uniformly and they are most likely installed closer to grade and level. Operate your sprinklers in groups, beside and across from each other. See how often the streams interfere with each other. You might be surprised. Data shows eliminating jet interference improves sprinkler operational efficiency. What we have learned is you need to be more careful about operating sprinklers in close proximity to each other. Eliminate this by scheduling your sprinklers differently so sprinklers beside and across from each other do not operate at the same time.
Why is sprinkler systems efficiency a concern to water purveyors and regulators. To start, if you are on a potable water supply it may impact how much water you can use in the future. It may also end up in a standard dictating various irrigation techniques and allowable water use for golf courses or as part of a state’s water withdrawal permitting process and approval.
Measuring and quantifying how sprinklers more precisely apply water has been a result. Expect this trend to continue and for your irrigation practices to be impacted long term.