Landscape Architect Articles

LCN February Inside Irrigation01-30-08 | News

Rotors Rule Residential Landscapes

By Erik Skindrud, LCN Editor

Rotors usually have a relatively low precipitation rate, so one station of rotors can cover a large area. Rotor spray heads ("impact heads") deliver an average of 0.5 inches of water per hour in a rotating jet of water. Photo by Erik Skindrud

Rotors spread water more evenly and keep lawns evenly green with less water. Landscape contractors and designers should consider specifying rotors instead of spray heads, even in relatively limited residential areas, to save water and money.

That?EUR??,,????'???s the conclusion of a recent University of Florida at Gainesville study published in the Journal of Irrigation and Drainage Engineering.

Rotors use an internal gear system to apply streams of water over arc-shaped areas. Unlike spray heads, rotors rotate over zones repeatedly. Because they are concentrated streams, rotors have larger spray radii (stream distances) than spray heads.

The fact that rotors function more efficiently in many settings is an important one for landscape professionals to understand. What?EUR??,,????'???s more, fewer rotors per given area are needed, which means rotor-based systems may be quicker and easier for contractors to install.

Because they send water out in clouds of spray (as seen here) spray nozzles are more vulnerable to wind than rotors. With their directed streams, rotors are more consistent under a variety of wind and system-pressure conditions. Photo: irrigation.ifas.ufl.edu

The Brand Comparison

Interestingly, the 2005 study compared spray heads and rotors from three manufacturers and found significant differences between the brands. For example, the study?EUR??,,????'???s ?EUR??,,????'??Brand A?EUR??,,????'?? rotors produced a distribution uniformity number of .66, while low-performing ?EUR??,,????'??Brand C?EUR??,,????'?? turned in a number of .46.

Similar differences were found when comparing spray heads?EUR??,,????'??+although ?EUR??,,????'??Brand C?EUR??,,????'?? performed best in this case with a distribution uniformity score of .68. ?EUR??,,????'??Brand A?EUR??,,????'?? came in last place in the spray-head department with a .53. Interestingly, system pressure had more of an effect on spray head performance than it did on rotor performance.

The brand comparison caught LCN?EUR??,,????'???s attention, naturally, and we asked study leader Michael D. Dukes if he would share the identity of brands A, B and C. Not surprisingly, he declined.

?EUR??,,????'??Since the main objective of this study was not to identify the various brands, we don?EUR??,,????'???t think it is appropriate to release that information after publication,?EUR??,,????'?? Dukes said. ?EUR??,,????'??The main point is that spray heads don?EUR??,,????'???t perform with as high uniformity as rotors and adjustable spray heads tend to be less uniform than fixed pattern spray nozzles.?EUR??,,????'??

Watering times vary depending on the month. For example, when using rotor heads, 29 minutes per zone is good in May, 43 minutes in June, and 50 minutes per zone in July. Fixed spray heads and manual sprinklers take less time.

Results Apply Nationally

Despite seasonal rainfall, water is particularly scarce in Florida because of its sandy soil and limited groundwater. The Florida study notes a number of other recent studies that emphasize the depth of the problem.

?EUR??,,????'??Turfgrass is normally the most commonly-used single type of plant in the residential landscape,?EUR??,,????'?? the article points out. ?EUR??,,????'??Residential water use comprises 61% of the public supply category. The mostly-groundwater-derived public supply is responsible for the largest portion, 43%, of groundwater withdrawn in Florida.

?EUR??,,????'??Between 1970 and 1995 there was a 135% increase in public supply water withdrawals! Florida consumes more fresh water than any other state east of the Mississippi River! From a recent study in Florida, it was determined that the average household used 71% of the total water consumption for irrigation.?EUR??,,????'??

Similar numbers prevail over much of the country, especially the Southwest and the drought-impacted Southeast.

The University of Florida study found significant differences in efficiency between real-life home systems and specially designed test sites. As seen here, breezes and on-site drainage are probably contributing to the dry spot near the center of this view. Compensating for the dry spot by upping overall irrigation time would not be an efficient solution. Photo by Erik Skindrud

Other Key Findings

The Florida study also found that carefully-designed and installed rotor systems performed better than actual systems tested at actual homes and landscape sites.

?EUR??,,????'??Spacing the (rotary) heads properly under controlled conditions resulted in higher uniformities compared to actual residential sites,?EUR??,,????'?? the report concludes. ?EUR??,,????'??Therefore, irrigation system design is important to achieving higher irrigation uniformity distribution.?EUR??,,????'??

The bottom line? The study emphasizes ?EUR??,,????'??the need for properly-designed residential irrigation systems.?EUR??,,????'??

Irrigation Insights

18: Feet in width. Rotors are best for larger turf areas generally more than 18' in width.

25 to 35: Feet. Small rotors sold for residential use work best at 25 to 35 foot spacings, although with careful design some models can be spaced up to 50 feet apart.

3 or 4 : Inches. When using ?EUR??,,????'??pop-up?EUR??,,????'?? rotors on areas with Bermuda grass, dethatched yearly, it is best to use a three- or four-inch pop-up. On the other end of the spectrum, a 12-inch pop-up should be used on areas with medium-height ground cover.

Source: Jess Stryker?EUR??,,????'???s Irrigation Tutorials