The relation between the percentage of the surface area receiving the target water depth and the depth of water applied at different CU (or DU) values can be calculated if the data distribution is known. For sprinkler irrigation, a normal distribution is assumed by Keller and Bliesner  and a uniform distribution is adopted by Mantovani etal. . Several distribution functions are analyzed by Seginer . The use of these relationships for irrigation design and management is discussed later under "Set Sprinkler Systems."
Statistical Uniformity Coefficient Us. Calculated as a percentage (%), this indicator is defined as where Vq is the coefficient of variation of emitter flow, Sq is the standard deviation of emitter flow (L h—1), and qa is the average emitter flow rate (L h—1).
This indicator often is used in microirrigation. Bralts etal.  adopted Us for design and defined Vq as the geometric mean of the coefficients of variation relative to emitter clogging, manufacturing variation, and pressure variation.
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