Water wisdom from the Irrigation Association
EDITOR’S NOTE: Superintendent magazine has teamed with the Irrigation Association for a bimonthly column, SuperTip, to focus on various water issues that affect golf course maintenance. Dedicated to ensuring water is available for future generations, the Irrigation Association promotes efficient irrigation technologies, products and services.
Over the last 10 years, golf irrigation systems have become more complicated in response to changes in course design and intensified maintenance practices, including water application. The irrigation systems are designed and installed to apply water to specific areas; however, wind impacts the effectiveness of a scheduled irrigation event. Golf rotors are inherently susceptible to wind and the potential of water drifting away from the target area. While this applies to both full- and part-circle heads, it is perhaps more critical with the latter because they are typically used to restrict or confine the water application to the intended irrigation area.
The use of part-circle heads has increased substantially to prevent or minimize overthrow into so-called “native” and transition areas. These heads are located along the borders of in-play areas. The borders separate adjacent turf areas that have different moisture requirements because of varying turf species, soil type, heights of cut and maintenance practices.
For example, part-circle heads on the perimeter of a green allow coverage of the adjacent rough and approach without getting undesired water on the putting surface. Other examples include the fairway/rough border, where some designs have part-circle heads throwing into the rough only; and the “five-row” layouts have back-to-back part-circle heads. Some irrigation design systems have back-to-back part-circles at the green/approach border, and others have them at the approach/fairway boundary.
Wind can easily disrupt the uniformity of these systems and push water away from its intended area of coverage. Here are some common ways to control wind drift:
- Install a parallel irrigation system using fresh water. With fertigation or reclaimed water systems, regulations often dictate drift control measures. Many local codes prohibit the location of heads in these systems within a specified distance of adjacent housing, schools, playgrounds or potable water well fields. If irrigation is necessary within the stated distance, the only solution is to install a parallel system using fresh water.
Other regulations specify a maximum wind speed beyond which reclaimed water systems cannot be operated, and they apply to all heads in a system not just those close to the sensitive areas listed above.
- Install low-trajectory or wind-tolerant nozzles. The major manufacturers of golf sprinkler heads have addressed the drift control issue by providing low-trajectory or wind-tolerant nozzles. While the trajectory of main nozzles is typically in the 22- to 25-degree range, alternative nozzles are also available in the 11- to 17-degree trajectory range. The latter have a lower stream apex and are therefore less impacted by the wind.
One manufacturer lists the apex for a specific low-angle nozzle and pressure combination at 7 feet above grade. For the same pressure with a high-trajectory nozzle of similar GPM, the apex is 13 feet, nearly double the height of the low-angle nozzle. In a longer radius head, the low angle apex is at 9 feet, and the high-trajectory apex is 19 feet.
Care must be used in the layout of heads using the low-trajectory nozzles. While the flow through a given nozzle/pressure set can be similar in high-and low-trajectory models, the radius can be different enough to change precipitation rates and to seriously affect distribution uniformity. The same applies if high- and low-trajectory nozzles are mixed in a specific pattern.
Some golf rotors have a diffuser screw that can be adjusted to extend into the nozzle stream. While this can shorten the radius, it can also have a detrimental effect on uniformity and can break up larger water droplets, leaving them more susceptible to pattern distortion in wind.
Typically, a system incorporating shorter radius heads operating at a lower pressure will be more wind tolerant than a system with longer radius heads operating at higher pressure. However, the former will have more heads, and thus will cost more.
- Regulate pressure using the pilot valve in electric valve-in-head sprinklers. Another equipment option to help in drift control is pressure regulation by the pilot valve in electric valve-in-head sprinklers. The major manufacturers provide either adjustable pilot valves or a series of fixed pressure ones set at 10 PSI increments from 50 or 60 PSI to 80 or 100 PSI. The theory is that a nozzle operating at lower pressures produces larger water droplets, which are not affected by the wind as much as the finer sprays produced by higher pressures in the same nozzle.
- Schedule irrigation when local wind speeds are low. One obvious way to reduce wind-caused drift is to schedule irrigation when the local wind speeds are at their lowest and incorporate one or several anemometers into the system. While there are many factors involved to determine when to irrigate, wind speed and time of day should be included in the decision-making process.
With today’s central controller capabilities, it’s not difficult to set a wind speed parameter so the controller will pause irrigation when wind speed goes beyond that point. When the wind speed falls back below the set point, irrigation resumes.
Finally, remember that water pushed by the wind out of the intended target area not only has a potentially detrimental effect on nontarget areas, but it’s also water that is completely wasted. The money spent on buying and/or pumping it is also wasted, and system uniformity will be seriously compromised.