Irrigation System Distribution Uniformity, Application Rate and Calibration Audit – Basic Audit
IRRIGATION SYSTEM DISTRIBUTION UNIFORMITY, APPLICATION RATE AND CALIBRATION – BASIC AUDIT* Figure 27 illustrates soil profiles at various levels of saturation following an irrigation event. In Figure 27a, the sprinkler heads evenly deliver water to all areas of the lawn, sufficiently saturating the root zone. This can be achieved by ensuring the heads are properly spaced or that each has an adequate throw radius. Figure 27b shows a lawn with uneven water distribution with patchy areas that do not receive enough water. Many lawns operate under the third or fourth scenario (Figure 27c and d). These occur often after the irrigation runtime has been increased to ensure the patchy areas receive enough water, while other areas consequently receive too much. All water percolating below the root zone is wasted. While the appearance of the lawn may meet expectations, excessive costs are incurred due to wasted water, increased frequency of fertilizer applications (since excessive water leads to increased leaching), and an increased need for weed and fungus control.
Background and Description This audit procedure consists of two sections. The first focuses on whether the irrigation system applies water evenly over the irrigated areas (distribution uniformity). The second will guide you through the steps to determine how much water is applied by the irrigation system in inches per hour so it can be calibrated to deliver a specific amount of water during each irrigation event. These two exercises are presented together because they can be done simultaneously. This audit procedure is best suited to open areas of high volume irrigation, such as lawns or athletic play areas. These areas account for most irrigation water use in many irrigated landscapes.
System Distribution Uniformity 172B9
Distribution uniformity (DU) is a measure of how evenly water is applied over an irrigated area and is one of the most significant parameters to determine a system’s efficiency (Rainbird Irrigation 2010). A system with good DU mimics rainfall by applying water evenly across the landscape and saturating the active root zone. Poor DU can result in brown or wilted patches of grass among an otherwise healthy looking lawn. To remedy this situation, irrigation contractors typically increase the irrigation runtime of a zone with wilted spots. This can improve conditions in the patchy areas, but at the expense of excessive watering of formerly healthy areas and can increase the occurrence of weeds and fungus.
When tested by certified professional irrigation designers and landscape architects, DU is expressed as a percentage of maximum efficiency. The value results from a series of calculations that account for plant watering needs, soil type, and detailed spacing measurements. A trained professional is able to determine which areas or zones require adjustments or modifications, as well as the specific adjustments or modifications needed to increase the DU to an acceptable level. Such calculations and determinations are complex, require expertise, and are therefore outside the scope of this guide. This section’s audit procedure is a simplified version of the test done as part of an irrigation system evaluation.
*Florida Green Lodging Applicants: This Irrigation System Distribution Uniformity, Application Rate and Calibration – Basic Audit is optional as part of your application. For more information on this program, see page iv.
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