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Measuring uniformity When an audit of a sprinkler irrigation system is carried out using catch cans and other measuring devices the uniformity or evenness of the application of irrigation water is usually calculated. There are three commonly used statistics that describe reflect the evenness of application. Coefficient of Uniformity (CU) is a statistical measure of the evenness of application based on the variations of the application rate, measured over the whole wetted area, compared with the average application rate. It is more commonly used in agricultural situations and, as a rule of thumb, irrigation system are designed with a CU of at least 85% Distribution Uniformity (DU) is more commonly used in landscape irrigation and compares the average of the lowest quarter of application measurements with the average of the whole wetted area. As a general rule a landscape irrigation system should have a DU of at least 75%. Scheduling coefficient is a measure of uniformity in an area which compares the lowest precipitation rate for a defined contiguous area (catch device test) to the average precipitation rate. Computer programs such as SPACE PRO enable designers to evaluate alternative sprinkler spacings to check on the theoretical uniformity of application. Figure 1 details a SPACE densogram showing the pattern of water distribution. In this example with sprinklers are spaced in a triangular arrangement of 15.5m between laterals and 15.5m between sprinklers within a lateral. The values are CU 89%, DU 81% and SC of 1.3. Figure 1 SPACE PRO Densogram
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