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Irrigation—Principles & Practices

Part 1 – 248 | Unit 1.5
Appendix 3: Calculating Distribution Uniformity (DU)

Appendix 3: Calculating Distribution Uniformity

(DU)

Distribution uniformity (DU) is defined as how uniformly water is distributed

over an area being irrigated, and is expressed as a percentage: the higher the

percentage value, the more evenly water is distributed.

You can calculate distribution uniformity by collecting water in sample “catch

buckets” or rain gauges laid out in an even grid between irrigation pipes or

along the length of a drip line (see diagram). DU can then be determined using

the “low quarter DU” method, in which the average of the lowest quarter of the

samples collected is divided by the average of all samples to get a percent of

distribution: 80% or above is considered an acceptable distribution uniformity.

Low quarter DU calculation: Average volume of lowest 25% of catch buckets divided by Average

volume of all samples collected = Distribution Uniformity (DU)

Illustration by José Miguel Mayo

SPRINKLER UNIFORMITY OF DISTRIBUTION TEST