Almost all superintendents believe reducing irrigation water use (or runtime) is a good objective. The reasons vary.Â
For some it’s to conserve water, either because they have a limited or expensive supply or they are being environmentally conscience. For others they recognize that reducing runtime reduces maintenance and operation costs.
The most important factor to really reduce irrigation system runtime, thus water consumption, is Distribution Uniformity (DU). If your system has a high DU, then you have a tool that can be very well managed. Poor DU negates good management practices.
What is DU?
DU is a ratio measuring how uniformly an irrigation system applies water. We want a perfect DU measurement of 1.00. But, since we are dealing with a man-made system operating in a harsh outdoor environment, we cannot have perfection.
Uniformity means we get the same amount of water applied over the whole irrigated area. Good DU means we have minimal areas that receive much less or more than the average collection. Users recognize those areas as “dry” or “wet” spots.
A golf course system can reach a DU range of 0.75 to 0.85, which we consider excellent. Get above 0.70 then we have a system that can be well managed for very efficient water use. 0.60 to 0.70 is OK but, operational efficiency results will not be as significant. A system with DU ratios below 0.60 does not provide water saving opportunity.
DU is measured by placing collection cups in a test area and running the system. It’s a process commonly called “auditing”. Once the collections are recorded some simple math tells us the DU ratio. To achieve a valid result, a golf course will require many areas to be tested, which can be a time consuming process.
Why Higher DU Systems Reduce Water Consumption.
Remember, DU is a way of measuring uniformity. Poor uniformity means there are areas receiving too much or too little water. Dry and wet spots are an indication of an issue.
The goal of the user is not to have dry spots, so irrigation runtimes and the resulting water consumption increase to cover the dry areas. Now, to get the dry areas with enough water, the rest of the area (the majority) is being over irrigated. There’s the wasted water. Improve DU and reduce the amount of irrigation water required.
How is DU improved?
Sprinkler manufacturers spend a great deal of time designing nozzles and sprinklers that can be installed to provide high DU. Some better than others. So, the hardware is available. The next step is how the product is laid out and installed.
The sprinklers must be spaced so the nozzle selected is at optimum for high DU. A good starting point is the old “Head To Head” adage. However many sprinkler/nozzle combinations provide higher DU when spaced closer. Consult manufacture data or others with such knowledge to learn best spacing for particular sprinklers.
Of prime importance after proper spacing is the hydraulics of the piping network. Each sprinkler must receive the flow required (gpm) at the pressure (psi) needed for optimum nozzle performance. Pressure required will fall within a narrow range. Typically 80 psi is a common pressure requirement. If so then we need to have at least 75 psi.
Because most progressive golf course sprinklers include pressure regulation, higher pressures can be regulated down at the sprinkler for optimum DU performance. Even though we want 80 psi, the pipe network may be operating well above that.
Computer simulations using 3rd party test data are very handy when deciding the optimum spacing for a sprinkler/nozzle/pressure combination. The Center for Irrigation Technology at Call Poly has a program called Space. You can buy it online at their web site.
Installation
Once a sprinkler layout and supporting pipe network are designed, installation must follow the plan! Good contractors will do a good job installing the system as specified. That will result in a high performance system. There is one other aspect that needs attention to keep the system DU from diminishing over time, maintenance.
Why Maintenance is Important
The irrigation system is exposed to all forms of weather, movement of the surrounding soils, abuse from man and animals, and wear.
Sprinkler nozzles will need replaced and damages repaired  to keep the system’s DU high. A good maintenance routine will not only support continuing high DU, but is less costly over the system lifespan.
Design a system for high DU, install it well, and maintain it. Now you have a tool for efficient management that results in water savings, lower maintenance costs, lower energy costs, and less headaches. And the golf course will look and play better!
Focus on high DU produces all positive results.  It gives you a finely tuned and useful tool. To make productive use of it is now a matter of management practices.
