Fairway irrigation - know where the water is falling
A simple understanding of your system will let efficiency reign on your golf course.
On an 18-hole golf course, turfgrass fairways may account for more than 50 acres. It is important that high-quality fairway turf is grown densely to provide a smooth surface so the golf ball will "sit up." Cutting heights range from 0.25 to 0.5 inch, which promotes a shallow root system. The combinations of these elements make it imperative that golf course superintendents follow effective irrigation practices to produce and maintain healthy, dense turfgrass. Efficient irrigation also conserves money and water.
Valve-in-head units Golf course irrigation often utilizes valve-in-head sprinklers. Each sprinkler head contains its own valve and can be turned on and off separately. This differs from most residential irrigation systems where a valve installed on the pipe allows water to flow through laterals and operate several heads grouped into what is called a zone.
In some golf course irrigation systems, a satellite control box sends a 24-volt signal through a 12-gauge wire to the solenoid in the head. Electrical signals are sent to each head on a separate control wire, but the current returns to the controller to complete the circuit on a common wire that is shared by all valves.
The electrical current activates a plunger inside the solenoid. The plunger releases water pressure on the valve. The water pressure subsequently closes the valve when the electrical current is shut off. Only when the solenoid is receiving the signal will the plunger stay open. Water flows through the open valve, through the sprinkler head and out a nozzle. The water turns gears in the sprinkler that slowly rotate the head.
Other systems operate by hydraulic control with less wiring. These systems use pressurized water in 0.25-inch tubing instead of 12-gauge wire. A solenoid is located in the satellite controller, and the tubing is connected to the valve controlling the head. When the tubing is pressurized, the valve remains closed. Lightning strikes cause less damage to these systems, and when a control tube is cut, the valve will open. In the case of electrical solenoids, if a wire is cut or damaged, it may not be discovered until the surrounding turf becomes drought-stressed.
Soil and terrain variations are common in fairways. Low areas need less water than sloped areas, and soil texture can change from clay to sand. By controlling each head in the fairway, superintendents can accommodate site-specific needs. Greg Matthews, superintendent of the newly-built Golf Club at West Scott Plantation, Charleston, S.C., found that he has to change irrigation programs as the fairways become established. "I'm slowly discovering areas that have poor drainage due to excess surface runoff or high clay content. I'm always adjusting the irrigation schedule for each head. Every area needs to stay adequately moist - during grow-in, you'll find that out in a hurry."
Sprinkler specifications An irrigation head used on a fairway typically has a radius of 60 to 100 feet. Each head throws 20 to 30 gpm at water pressures from 90 to 120 psi. Most irrigation heads are full circle, but adjustable heads are available.
Rough is mowed higher and its water requirements are considerably different than the fairway. Irrigation heads may be located on the edge of the fairway and set to water the rough on a different schedule than the fairway.
Fairway irrigation layout q Single row. In single-row systems, heads are lined in the middle of the fairway and spaced so they overlap. As water is thrown from the head, wind and evaporation affect the amount that reaches the ground. The farther away from the head the water travels, the more difficult it becomes to maintain uniform distribution. Thus, sprinklers in single rows are spaced to throw "head-to-head." Single-row systems cost less to install, but less fairway is irrigated because of the limited distance a single head can spray.
q Double row. Double-row systems use two rows of sprinklers installed in the fairway. The sprinklers are spaced to throw "head-to-head." Double-row configuration is preferred over single-row systems because the increased overlap between sprinklers is less affected by wind, and therefore, more uniform distribution is achieved. Also, the fairways can be cut wider with this system.
Double-row systems can use smaller heads that spray shorter distances. This requires less volume and operating pressure. Double-row systems are more expensive, but the increased efficiency can offset the cost.
q Triple row. Triple-row systems operate on the same concept as that for the double-row system. Three rows of sprinklers are installed in the fairway. This system can be used to create wider, irrigated fairways.
Uniformity of distribution Uniformity of distribution describes how evenly water is dispersed over the turf. Ideally, water would be distributed evenly over the entire area, but that is impossible. Not even rainfall is 100-percent uniform. When irrigation is non-uniform, dry and wet areas develop. When dry spots develop, irrigation run time is increased, resulting in overwatered turf elsewhere. It is important to coordinate the following factors so that a system operates with maximum uniformity of distribution.
q Pressure. At what pressure should the heads operate? If pressure is too high, the result is small water particles that are blown away or evaporate before they reach the ground. Some heads have pressure-reducing solenoid valves that prevent excessive pressure. If pressure is too low (often when too many heads are running at one time), "donut" patterns are created where the nozzle is not operating properly. The water "streams" to the outside of the spray radius.
q Nozzles. The nozzle opening greatly affects the amount and distribution of spray. Plastic nozzles wear over years of operation and can be damaged during repairs. A golf course located in arid Southern California discovered that nozzles were causing poor uniformity of grass growth. By retrofitting the entire golf course with brass nozzles containing plastic stream-straightening vanes, they increased the uniformity of distribution by 50 percent.
q Spacing. If heads are spaced too far apart, poor distribution will occur. Do not cut corners and stretch spacing to less than head-to-head. Occasionally, the edge of fairways dry out, especially in single-row layouts. This results from cutting the fairway too wide. Designers consider effective coverage to be 50 to 70 percent of spray radius. Fairway width should based on the effective coverage of irrigation heads.
q Trajectory. Following repairs, irrigation heads are sometimes accidentally reinstalled at an angle, resulting in a shorter spray trajectory on one side of the head and a longer one on the opposite side - poor uniformity. Be aware that maintenance operations can affect sprinkler performance.
Evaluating the irrigation system q Operating pressure. Use a Pitot tube to test the operating pressure of your sprinkler heads. Place the opening of the tube in the spray stream and measure the pressure. Know the specified pressure range for your sprinklers. Test a sample of fairway heads. Be sure to measure the operating pressure of the heads farthest from the pumping station. Because pressure is lost due to pipe friction and other heads operating at the same time, heads farthest from the station will have the lowest pressure.
q Catch-can test. This simple test can tell you the uniformity of distribution and precipitation rate (how fast water is being applied). A catch can is any can that has straight sides and a flat bottom. A coffee can is ideal. On a calm morning, place 16 to 20 catch cans in the fairway. Test an area where you have head-to-head coverage. Place one-third of the cans near the heads, one-third towards the edge of the radius of throw and one-third in the middle. Sketch a map of catch-can placement to record the data on.
Run the irrigation system for 30 minutes. Ideally, you want to catch an inch of water in the cans. Measure the depth of water with a ruler or tape. If you have not collected an inch of water, continue irrigating for a total of 60 minutes. When complete, measure the depth of each catch can in millimeters and record on the map. After you've taken all the measurements, you can determine the distribution uniformity.
q Distribution uniformity (DU). DU is a measurement of uniformity. Rank the catch-can measurements from highest to lowest. Take the average of the lowest 25 percent of readings. For example, if you had 20 measurements, the bottom 5 should be used. Divide the average of the lowest 25 percent by the average of all of the measurements (in this case, the average of all 20 measurements). Multiply this number by 100 to get the distribution uniformity percentage.
The higher the percentage, the more uniform the distribution of water applied. As a guideline, 70 percent or higher is satisfactory. If DU is below 70 percent, observe the map for areas of low application. Are nozzles worn excessively? Are the heads level? Is there adequate spacing and adequate pressure?
q Precipitation Rate (PR). Most superintendents have a good feel for how long to run each head. Using the PR, you can schedule heads to run according to the amount of water that needs to be replaced. You can obtain evapotranspiration (ET) rates (water loss) by installing a weather station on your site or subscribing to a service that calculates this information for your area. Donald Dunlap, superintendent at Crowfield Golf Course in Goose Creek, S.C., subscribes to a weather service that provides him with daily ET rates for his area. "At the end of any given day, I can look up how much water was lost to the atmosphere and set my irrigation accordingly," says Dunlap.
PR is measured in inches of water delivered per hour. Convert the catch-can measurements to inches by dividing the measurements by 25.4. Then take an average of all the measurements. Next, convert the amount of water caught in the catch can to a per-hour reading. For instance, if the catch-can test was run for 30 minutes, double the average. If the test was run for an hour, this is the PR per hour of your system. For example, if the overall average of a 30-minute test was 0.44 inches, then the PR (inches per hour) of your system would be 0.88 inches.
To use the PR, divide the ET rate (amount of water lost) by the PR to determine how long you need to operate your irrigation system to replace the amount of water lost.
If you water every other day, calculate how much water you have lost after 2 days. For this example, the water loss is 0.70 inch for 2 days.
The benefits of efficiency By fine-tuning your irrigation system, you will be an efficient irrigation manager. Golf courses that purchase water can save a great deal of money by reducing annual usage. Further, water-use restrictions often necessitate greater efficiency.
Use your irrigation data to argue for new irrigation components. Poor fairways may be the result of outdated irrigation systems, worn parts or poor design. Convince greens-committee members with actual data of poor uniformity and explain the cause and effect. Show how the current system fails to properly irrigate. The long-term effects of an inadequate system are costly.
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