Sprinkler spacings: Do they matter?

Brian Vinchesi

A few months back, I explored whether more sprinklers actually use less, not more, water. I used the example of 65-foot spacing versus 80-foot spacing. A golf course architect acquaintance took issue in how I’d characterized the water savings and implied I made it sound like large spacings were bad and only small spacings were acceptable. His point was that small spacings with lots of sprinklers may be efficient, but efficiencies can be obtained with larger spacings for substantially less cost. As much as I do not want to inflate his ego, he had a point.

There’s nothing wrong with larger spacings on today’s courses. Modern sprinklers are better designed than sprinklers from as little as 10 years ago. Newer sprinklers apply water with much higher uniformities when properly spaced during installation. This higher uniformity results in the use of less water as the sprinklers don’t operate as long to cover up the weaker coverage areas. Just replacing old sprinklers with new sprinklers in the same location alone results in higher uniformities and less water use, no matter what the spacing is due to the uniformity improvements inherent in newer sprinklers.

Larger spacings of 75-85 feet are acceptable with higher uniformity sprinklers, but will still not apply water as efficiently as a smaller spacing because they are putting more water into the air to be subjected to evaporation and wind drift. The difference in efficiency, though, is much smaller than with sprinklers from the past. This argument, however, will not work with single-row fairway spacing as it is inefficient no matter what sprinkler is used or how it is spaced.

Many designers budget new irrigation systems on a per-sprinkler basis. The more sprinklers, the greater the cost. This number may vary slightly based on the quantity of sprinklers, but not much. However, it will vary based on a courses geographic location. Wage or union labor rates also influences the per-sprinkler number by as much as 30 percent. Using sprinkler numbers works well as more sprinklers equals more pipe, more wire, more swing joints and more control stations or decoders. It’s an effective way of providing preliminary budgets used by irrigation designers for decades. For example, a system may cost $1,300 per sprinkler. If there are 1,000 sprinklers, the cost would be $1.3 million; 800 sprinklers, $1.04 million; and 1,500 sprinklers, $1.95 million.

Sprinkler spacings for greens and tees is never part of the discussion as the spacing is dictated by their size and shape. Spacings get manipulated in fairways and rough. The fairway/rough spacing is based on how much coverage you want into the rough if you are not doing a wall-to-wall system. But even with wall-to-wall, an average spacing needs to be determined. Say you want to effectively irrigate a 60-yard width down your fairways. That will cover, depending on your fairway width, approximately 30-45 feet of rough on each side. To achieve the 180 feet of effective coverage, a double row would require a sprinkler spacing of 80 feet and a triple row a spacing of 60 feet. Remember, effective coverage is 60 percent of the sprinklers throw when there is no overlap. The double-row 80-foot sprinklers are going to use approximately 43.1 gpm and the triple-row 60-foot sprinklers 22.0 gpm. Precipitation rates are going to be 0.65 inches per hour and 0.59 inches per hour, respectively. So the time to irrigate will be close to the same. If an 18-hole course with double row has 282 fairway-rough sprinklers, the same course with triple row would have 422 sprinklers. At $1,500 per sprinkler, the cost difference would be about $210,000 using the outlined budgeting method. In the approximate 1,000 sprinkler system, the difference is between $1.3 and $1.5 million – or a 14 percent savings. It may not sound like much, but it could be the difference between project approval and being deemed unaffordable.

You can use larger spacings and achieve close to the same results in terms of water window, coverage, precipitation rate and water use with larger spacings that have high uniformities. An irrigation designer is best equipped to determine the best sprinkler spacing and count to fit into your available budget. Bottom line: Yes, sprinkler spacings matter.

Brian Vinchesi, the 2009 EPA WaterSense Irrigation Partner of the Year, is president of Irrigation Consulting Inc., a golf course irrigation design and consulting firm headquartered in Pepperell, Mass., that designs irrigation systems throughout the world. He can be reached at bvinchesi@irrigationconsulting.com or 978/433-8972.