Distribution uniformity

Distribution uniformity or DU in irrigation is a measure of how uniformly water is applied to the area being watered, expressed as a ratio to avoid confusing it with efficiency. The distribution uniformity is often calculated when performing an irrigation audit. The DU should not be confused with the coefficient of uniformity (CU) which is often preferred for describing the performance of overhead pressurized systems. Distribution uniformity or DU in irrigation is a measure of how uniformly water is applied to the area being watered, expressed as a ratio to avoid confusing it with efficiency. The distribution uniformity is often calculated when performing an irrigation audit. The DU should not be confused with the coefficient of uniformity (CU) which is often preferred for describing the performance of overhead pressurized systems. The most common measure of DU is the low quarter DU expressed as DUlq, which is a measure of the average of the lowest quarter of samples, divided by the average of all samples. The higher the DUlq, the better the coverage of the area measured. If all samples are equal, the DUlq is 1.0. There is no universal value of DUlq for satisfactory system performance. A value of >.80 is considered above average. Distribution uniformity may be helpful as a starting point for irrigation scheduling. For example, an irrigator might want to apply not less than one inch of water to the area being watered. If the DU were 0.75, then the total amount to be applied would be the desired amount of water, divided by the DU. In this case, the required irrigation would be 1.33 inches of water, so that only a very small area received less than one inch. The lower the DU, the less uniform the distribution at the plane of data collection and the more water that may be needed to meet the minimum requirement.