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With today’s golf course irrigation systems, there is always talk about sprinkler uniformity. Some manufacturers try and tell you that your entire product decision should be based on uniformity. But is uniformity, or the lack thereof, really as big a deal as some will have us believe? First, let’s define uniformity and then discuss what affects it. Simply put, uniformity is how evenly a sprinkler or sprinklers apply water. In theory, the more uniform the sprinklers apply water the less water the irrigation system should use. This is one of the reasons why uniformity has gathered so much industry attention over the last few years. Uniformity is affected by a number of factors. Sprinkler spacing is the big one; ideally spacing the sprinklers at their optimum spacing provides the highest uniformity. But uniformity is built into the sprinkler and you have no control over that no matter what you do. Face it, some sprinklers – especially older ones – do a lousy job at putting down water. That is fixed by replacing the sprinkler or maybe retrofitting it with high-performance nozzles. In addition to the spacing, there is operating pressure. A sprinkler will operate over a wide pressure range, but what is its optimum operating pressure? The sprinkler is also available with a number of different nozzles. Which is the best nozzle for the preferred spacing at the preferred operating pressure? Once you have figured that out, you should have the best achievable uniformity. However, the sprinkler has to be installed. Is it installed at the proper grade and is it installed level? If not, all of your hard work at picking the most “theoretically” uniform sprinkler nozzle, spacing, operating pressure combination is all for naught. In golf, uniformities of 0.70 and above are considered achievable and over 0.80 considered excellent, but how many golf courses achieve these high numbers? If you expand your view of uniformity, it’s probably more than you think. When you measure uniformity out on the golf course you perform an audit using catch devices. The catch devices are set at some spacing depending on the feature being audited, its size, how many catch devices you have and other proper auditing practices – hopefully those outlined by the Irrigation Association. The sprinklers are operated for a set amount of time and water is collected in the catch devices. You gather the data from the devices, put it through a simple calculation and out pops a uniformity of somewhere between 0.1 and 0.99. You are then either happy or sad, but probably not surprised by the results. In most cases you have just documented what you already knew. But that is not the end of the story. When you audit a sprinkler system you are calculating the uniformity of the water landing on the ground – actually, slightly above the ground. What you have not taken into consideration is what happens once the water is in the ground. Does the distribution of water get better or worse? This is a difficult question to answer. There are even more factors that impact the movement of water through the soil than you just overcame trying to apply the water evenly. You have slope, soil type, soil repellency, compaction and thatch, just to name a few. So what is your gut feeling? Will it be better or worse than the audit showed? Is it measurable? I am a big proponent of portable soil moisture sensors. They are useful tools in determining how well your water is penetrating and moving around in your soil. So let’s say you do an audit and you had a 20-by-20-foot catch devise spacing with a resulting lower quarter distribution uniformity of 0.59. Before removing the catch devices, mark where they were located. Once a sufficient amount of evapotranspiration has dried out the soil a bit, operate the sprinklers again for the same amount of time you did for the audit. Then with your soil moisture probe go out and measure the soil moisture at all of the previous catch device locations. You can basically use the same math to come up with a number based on soil moisture instead of milliliters of water caught in the catch devices. Is the number an improvement? The odds are it is. Although audits are a good indication of how your sprinklers are applying water, they may not be providing you with the true picture of what is actually going on in the soil/root zone. A number of universities are beginning to look at this below grade uniformity to see if there are any correlations. The results will be interesting. That said, however, if you start out applying the water uniformly the more uniformity it will probably infiltrate. Try it and see what you get. |
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