Designing irrigation for greens and surrounds

Some golfers and superintendents argue that the golf green is the most important aspect of the game and should receive more care than tees, fairways or other parts of the golf course.

Many factors affect the look and performance of a green: initial construction, drainage, soil, air movement, height of cut, thatch and irrigation. However, this article focuses on just one: the design of proper irrigation for greens and their surrounds.

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Green irrigation Designing irrigation for a green can be easy or difficult. The degree of difficulty is determined by the shape of the green and how it is framed by the golf hole. Are there mounds, slopes or water around the green? Where are the bunkers, if any? Many greens are easily irrigated with four sprinklers on a square 65-, 70- or 80-foot spacing, providing more than adequate coverage. However, many greens do not fit into a set spacing so simply. As with all turf-irrigation systems, you ideally should install sprinklers "head-to-head." This means the water being thrown from one sprinkler should just reach the sprinkler adjacent to it. For example, a sprinkler throwing water a radius of 65 feet should be no more than 65 feet from another sprinkler. With gear-drive sprinklers, it is not uncommon to see a 65-foot spacing with a sprinkler that throws 70 feet to make sure that the turf around the sprinkler is adequately watered. To compensate on a windy green, you should space sprinklers (with the same throw) even closer.

The first rule in irrigating a green: no sprinklers on the green. Many golf course superintendents also want to keep sprinklers off the green collar. To do this, place the sprinklers around the green at a set spacing.

For example, you may plan to space five sprinklers, each having a radius throw of 68 feet, 65 feet apart (see Figure 3, page Golf 16). Although this may work in many cases, you can see from the figure that the middle of the green is dry. This is because the green is more than 68 feet wide and the sprinklers are not spaced head-to-head in both directions. This is a common mistake in green design where large greens may require a bigger sprinkler to maintain head-to-head spacing. To irrigate properly, the sprinklers need to be spaced 70 feet apart and throw a minimum of about 74 feet (see Figure 4, page Golf 16).

With today's irrigation technology, the best way to select the proper spacing and sprinklers for a green is to model the sprinklers' distribution uniformity on a computer. Do this by using a sprinkler-distribution profile, which shows how the sprinkler distributes water over its radius of throw (see Figure 2, above). When you look at the distribution profile for a given sprinkler at a designated spacing, you can produce a computer-generated densogram showing the theoretical sprinkler-watering pattern. The densogram indicates wet areas as dark and dry areas as light.

You can use a densogram-which is unique for each specific sprinkler/nozzle/spacing/pressure combination-to determine uniformity measurements, including scheduling coefficient and distribution uniformity. Manufacturers and designers are most interested in the scheduling coefficient, which is an indicator of how much water is being wasted when irrigating, to insure that all of an irrigated area is receiving its minimum amount. For example, a scheduling coefficient of 1.4 means that in order for the whole irrigated area to receive 1 inch of water, 1.4 inches of water would need to be applied. Scheduling coefficients of 1.5 or below are desirable, with 1.2 to 1.3 considered ideal. High scheduling coefficients indicate poor uniformity, increased watering requirements and longer run times.

Be aware that if you change the sprinkler, nozzle, operating pressure or spacing, the densogram will also change. Sprinkler distribution profiles and densograms are available from sprinkler manufacturers and the Center for Irrigation Technology (CIT), an independent testing laboratory, in Fresno, Calif.

The sprinkler you select should also depend on the amount of water it uses and the operating pressure it requires. Most modern irrigation systems operate sprinklers at a pressure of 65 psi to 80 psi. The amount of water sprinklers use at these pressures is indicated in the manufacturer's product literature along with the radius of throw. Higher pressures provide a greater radius, but also increase water use.

Once you determine which sprinklers to use for the green (based on the size of the green and sprinkler uniformity), you need to decide how to control them. A basic green-watering system may have three to five full- or part-circle sprinklers to water the green (see Figure 1, page Golf 8). These sprinklers should operate until the green receives an adequate amount of water and then shut off. Or you may set them to operate until the areas surrounding the green, which may have a higher water requirement, are adequately watered.

To water only to the green requirement and to avoid supplemental hand-watering of the surrounds, you can install a supplemental irrigation system with a second set of part-circle sprinklers to apply additional water to the surrounding areas to meet their higher water requirement as well as to deal with what is commonly a different soil type than the green. There are several ways to separate the green and surrounds watering. The approach you use may depend on the superintendent's management style or the geographic location of the golf course. The two most common approaches are: 1. full-circle sprinklers for green and surround watering and part-circle out sprinklers for surrounds only; and 2. part-circle sprinklers throwing in for the green and part-circles throwing out for the surrounds.

Valve-in-head As you design an irrigation system around the green, you also need to consider other factors besides the sprinkler types and locations. In a valve-in-head system, the piping loop around the green (which usually uses 2-inch pipe) will be pressurized at all times. The looped system allows all the green sprinklers to receive close to the same pressure, which results in better water distribution over the green (although elevation changes will alter pressure slightly).

Some superintendents are uncomfortable with pressurized pipe under their greens, so you may need to use a block design for the sprinklers, using an electric valve situated away from the green or a green master valve. You can also design the system so that the green and surrounds sprinklers can share piping, or so that the piping for each set of sprinklers is independent. Independent piping will provide for greater isolation, as the green sprinklers and surround sprinklers will then have their own isolation.

Another important aspect of green-irrigation design is the number and location of quick-coupling valves. Quick couplers allow you to attach a hose to the irrigation pipeline for hand-watering and syringing. Conventional design calls for you to install one quick coupler on the pressurized side of the green-isolation valve. This allows you to hand water if you need to shut down the green piping system for repairs. In the past few years it has become popular to install an additional quick coupler on the other side or the approach of the green. You may install this quick coupler after the green-isolation valve on the green piping, or install a separate pipe for it so that it is still pressurized even if the green-piping system is not. Most superintendents want quick couplers spaced at the green so that a hose for hand-watering needs to be no more than 100 feet long.

The control of the sprinklers is an important part of the green- and surround-irrigation-system design. It is important that you take into consideration all aspects of the green including turfgrass type, slope, soil and green construction. Individual control of each green sprinkler gives the superintendent maximum versatility. By having individual control, the superintendent can fine-tune the amount of water supplied in each area of the green, taking into account the slope of the green and also sun and shade effects.

However, this does not eliminate the need to hand-water, as the green could have hot spots or drainage problems due to its construction. Many superintendents prefer to hand-syringe greens to water more precisely instead of using the irrigation system. Surrounds sprinklers can be valve-in-head, dual control or blocked all at once. Your decision on which to use will depend on cost and how much control you need. Small- and medium-size sprinklers may require block valves, as valve-in-head is not available in these sizes, but you can group the sprinklers into as many areas as desired (see Figure 1).

The automatic irrigation-system design of a green and its surrounds depends on many factors including the sprinkler type, pressure, pipe size and spacing. With modern irrigation systems, you can and should treat the greens and surrounds separately. However, the method you use will depend on the available budget, type of green, geographic location of the golf course and the management style of the superintendent. Many different types of sprinklers and other irrigation equipment are available to do the job properly.

Brian E. Vinchesi is a design engineer with Irrigation Consulting, Inc., with offices in Pepperell, Mass., and Charlotte, N.C. He is president-elect of the American Society of Irrigation Consultants and a member of the Irrigation Association board of directors.

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