Landscape Architect Articles

2008 April LSMP Irrigation: Big Turf Rotors08-04-08 | News

Big Turf Rotors

Underhill?EUR??,,????'???s M-115 retracting rotor features a 115-foot throwing radius and an 8 inch pop-up height. The sod cup is 4 inches deep and holds a 9-inch-wide section of natural grass. Like other retractable rotors, the unit provides protection against vandalism and damage from mowing equipment. The design also ensures a flat playing surface that supports field performance and helps to prevent injuries. Photo courtesy of Underhill

Irrigation design for athletic fields and golf courses tends to favor big rotors that cover large areas per rotor. The strategy is designed to limit the number of rotor heads to limit chance for injury and to cover large areas with a reduced number of sprinkler units. Using a lower number of rotor heads per area makes calibrating the system for efficiency even more important, however.

Many of today?EUR??,,????'???s rotor heads have a small surface diameter and a protective thick rubber cover that makes them a safe alternative to the older-style sprinklers. Additionally, many of the newer heads have a strong spring for positive retraction so the head will not endanger the public by staying in the up position after the watering is completed. Many of today?EUR??,,????'???s safer heads also have a heavy-duty body cap to stand up to the large equipment now being used in routine maintenance.

Designers also like to choose a rotary sprinkler with a large nozzle selection. The nozzle is chosen to fine-tune the flow of water out of the system. The experienced irrigation system designer will use correct nozzle sizes to obtain matched precipitation. (The precipitation rate for sprinkler systems is the rate, expressed in inches per hour, at which water is applied over the surface of the turf. Matched precipitation means the entire field is receiving about the same amount of water per unit of time.)

Inspect for Efficiency

In order to determine distribution uniformity, an inspection and test of the turfgrass area should be performed. This is a fairly easy procedure and often can uncover fixable problems, even when a system appears to be functioning correctly.

The first step in conducting a catchment test is to determine existing site conditions. Draw a sketch of the field, with measurements, showing head locations. Write down all significant information, including the type of heads used and their condition. Perform an actual head-by-head inspection to determine their condition, model number and the nozzle type. While walking the field, look for signs of poor irrigation coverage, such as brown or bare spots.

Using a soil probe, take a few soil samples from different areas around the field to determine soil type and root depth. This information will be helpful later in writing an irrigation schedule for the system.

Next, turn on one zone at a time and perform a visual inspection. Adjust the radius and the arc of water flow from each head, and align all heads to be perpendicular to the turf for maximum coverage. While adjusting the heads, watch for heavy leaking at the riser seal and for failure to rotate properly.

Clean any clogged nozzles and be sure the filters are free of debris. Check for correct pressure and for donuts of brown grass around the heads.

Complete Pressure Check

Using a pressure gauge, check the pressure and pressure variation at the rotor?EUR??,,????'???s nozzle. (Be sure to write down these pressure readings.) Variations of more than 20 percent from the highest-pressure reading to the lowest within one zone may indicate a problem with the system, and the need for further inspection by an irrigation expert with a background in irrigation hydraulics. Frequently, pressure can be increased or decreased simply by adjusting the flow control on the valve for the zone.

Check the station start times and run times in the controller to see if there is a station with a longer run time than the others. This could indicate a problem with that particular valve or the rotors in that zone; the additional run time may be keeping the grass green and hiding the problem.

Check the run times overall. Are dry spots causing longer run times? In most areas, turf will require about 1 1/2 to 2 inches of water per week in the hottest months. Calculate precipitation rates based on manufacturer?EUR??,,????'???s published performance information and determine if the run times are close to where they should be.

From Professional Turf Manager?EUR??,,????'???s Guide to Efficient Irrigation Practices and Equipment, www.hunterindustries.com, reprinted with permission.