Distribution (application) uniformity

Distribution uniformity (DU): This describes the evenness of an irrigation application across a landscaped area that is typically made up of turf grass. Poor (low) DU in turf zones is common, resulting in significantly reduced overall system efficiency and causing large quantities of wasted water. DU can be expressed as a percentage or decimal value.

Good DU: This figure shows an irrigated area containing turf grass with good DU. The depth of irrigation is relatively even, and no plant is receiving significantly more or less than another. There is always some variation in an irrigation zone, and therefore it is impossible to have perfect uniformity.

Poor DU: This figure shows an irrigated area containing turf grass with poor DU. During the irrigation cycle, the area on the right receives sufficient amounts of water, while the area on the left does not.

Consequences of poor DU: The figure showing poor DU depicts the increased potential for stress to the turf area on the left. When this results in apparent plant stress, irrigation system operators are likely to increase watering times, which results in overwatering of the turf on the right. The overwatering figure depicts what occurs when system run times are increased to compensate for poor DU. In this example, nearly twice the irrigation is necessary to meet the second plant’s watering requirements. If these plants require ¾ inch of irrigation water, then approximately 1.5 inches would be required.

Balancing pressure, flow and spacing: Change in any one of these variables will affect the others and shift overall DU. Consequently, the prerequisites described in this section typically address pressure, flow or spacing, and focus on those efficiency practices that lead to a better DU.

General uniformity practices should be implemented on any irrigation system designed for water efficiency, and these practices may include the following: