Distribution uniformity is one of the methods which is preferred in determining uniformity in irrigated area. In this method, amount of precipitation is measured by means of caps placed in irrigated area. Then uniformity value is determined by estimating average catch amount belong to quarter which has least water with average catch amount of irrigated area (ASCE.1978). For example, 5 caps Where has the lowest catch amount represent average catch in the low quartile in a test where there are 20 measurement caps (Walker and Skogerboe 1987). Distribution uniformity (DU) should be greater than 75% and if greater than 85% is excellent and acceptable for any sprinkler irrigation. The value of Distribution Uniformity coefficient is calculated using the following expression.
DU: Distribution uniformity, %
Mq1: Average collected volume of lower quarter of catch cans, l M: Average collected volume of all catch cans, l
Distribution uniformity should be at least 70% in rotor heads and 50% in spray heads. As being different from DU, CU and SC parameters can be determined.
4.1.7 Christiansen coefficient of uniformity
Christiansen Coefficient of Uniformity is used commonly in irrigation sector. Christiansen (1941) developed a formula which depends on average value of irrigation water amount and standard deviation value which are measured through caps placed in irrigated area. CU is calculated by means of formula below.
CU: Christiansen coefficient of Uniformity, in %
Д qT th average absolute deviation from the mean, m3/h qT mean application rate, m3/h
While evaluating CU parameters values which are over or under average are considered as similar. This coefficient is developed for agricultural areas and is not highly useful for turf area. Total variation is applied to define applications which are not uniform. However visual quality should be spread over all area in turf area (IA. 2003). CU values being higher than 84% are suggested as acceptable (Anonymous. 2009).