Water bans, water shortages, and water restrictions are becoming more and more commonplace. They can make things complicated for the green industry, and it’s easy to resent them. Different municipalities may have different laws, different restrictions—it can be very difficult for us to keep track of them all as we move from city to city. However, you can’t really blame the lawmakers for enacting these laws. Laws like these are a logical response to what people are increasingly seeing: wasted water.
Of course, people in the green industry aren’t the only ones responsible for wasting water, but some of our most common design techniques can result in water-use inefficiency. For example, the spray sprinklers used to water many smaller lawns and gardens are only 60 percent efficient. This means that they’re 40 percent inefficient—for every 100 gallons of applied water, the landscape never sees 40 gallons of it. This water is lost to the wind from misting, lost on hardscapes from overshooting the area, or pushed too deep into the soil, past the root zone.
No wonder we’re having a problem with water availability. But luckily, these issues are fairly easy to correct by designing irrigation systems with efficiency in mind. You just have to think outside the box.
The first step toward an efficient design is to study the site. Know the plants, the soil, slopes, exposures, wind speed and direction, water source, POC (the point of connection where the irrigation system joins the supplied water line) gpm and psi, etc.—know exactly what conditions you’re designing for. Water pressure, for example, is an important consideration.
Pressure—too much or too little
Misting from high pressure is one of the areas where major water losses occur. Manufacturers recommend an operating pressure for most sprinklers of 30psi. In reality, we sometimes end up operating sprinklers at two to three times that amount. This can waste 25 percent of the water being applied, meaning you have to apply 25 percent more water than if you operated the system at the optimum pressure rating.
What you may not know is that having water pressures too low can also cause problems. Low pressure systems emit large water droplets with poor distribution uniformity (DU). The lack of pressure just can’t give droplets the velocity they need to be thrown out evenly over the area of coverage. The temptation for irrigators here is to just turn up the station runtime and flood-irrigate—not a very efficient solution! Instead, investigate. See why the system has low pressure and take corrective action.
Nozzle up to meet the size of the area
Nozzles can make all the difference when selected and used for the correct application. You should always look at spacing and decide what nozzle will fit an area best, with the highest distribution uniformity. For example, many times a 15-foot spray nozzle is used to water a 12-foot section. Why? Commonly, that was all that was in the truck at installation or servicing time. This is a problem even if it is a matched precipitation rate (MPR) nozzle.
Manufacturers allow us to diffuse the stream of water leaving the nozzle by as much as 25 percent to achieve a shorter throw pattern. I say that doing this causes you to waste water by disturbing the efficiency built into the nozzle pattern, by blocking it with the nozzle retention/diffuser screw. Instead, try to choose a nozzle that fits the distance without diffusing the stream. I try not to shorten the stream of water more than five percent.
Spacing—85 percent of radius
Head-to-head designing means sprinklers are spaced at 100 percent of their radius. In other words, if you have a sprinkler with a 10-foot radius, the next sprinkler on the line is usually placed 10 feet away. However, this does not accomplish a high enough level of efficiency. In a sprinkler’s throw, the first two to three feet nearest the head and the last five feet furthest from the head are commonly where dry spots can be found. A system sometimes has to be run longer to fill in for these dry areas.
If, on the other hand, you space sprinklers at 85 percent of their radius, the next sprinkler on the line has a better chance to fill in for these dry spots without the system needing to run longer. For example, if a sprinkler has a 10-foot radius, I recommend that the next sprinkler on the line be placed 8.5 feet away instead of 10 feet away. The extra overlap helps ensure that the area to be watered receives a more even amount of water, with much fewer dry spots. This achieves a higher-than-average efficiency level and lower-than-average water consumption.
Circuiting sprinklers—the old way or MPR?
There are two schools of thought when looking at the most efficient method to group or circuit a project’s sprinklers. One is to circuit the sprinklers as we have always been taught to do by combining “like” sprinklers and keeping rotors with rotors, sprays with sprays, etc. We were also told that quarter patterns, half patterns, and full patterns should be kept on their own stations so that we could adjust the application rate through timing. Then MPR nozzles were introduced for rotors. We can now achieve matched precipitation rate watering throughout the desired area of coverage by selecting the appropriate nozzles to fit the distance and pattern we desire. This means that we can have our quarters, halves, and fulls on the same station.
Some designers still like to keep the full circle sprinklers on their own station, separate from the other nozzle patterns, so they can control the application rate more effectively. For this question, I don’t have an answer. Time will tell what the best approach is. All of these simple considerations can really make a difference when it comes to efficient watering practices. While some of these ideas differ from the conventional, accepted method of irrigation system designing, that’s what I mean when I suggest we think outside the box. If lawmakers see the green industry making a concerted effort to conserve water through new, more efficient watering practices, they may lessen the water restrictions giving us headaches.
Editor’s Note: Lorne Haveruk is a certified irrigation designer (CID), auditor (CLIA), irrigation consultant (CIC), and water conservation practitioner (WCP). He is principal of DH Water Management Services, Inc., a water management, training, and consulting firm. He may be reached at email@example.com or visit www.watermgm.com.