Assessment of emission uniformity for micro-irrigation design

Emission uniformity E-U has been one of the most frequently used criteria for micro-irrigation design and evaluation. The original emission uniformity formula, which was derived by a worst combination of hydraulic variation and manufacturer's variation, can provide a very conservative design with a smaller value for E-U than that measured in the field. A revised formula for emission uniformity derived by a statistical approach can provide a more realistic emission uniformity for micro-irrigation in the field. The revised formula has the same parameters as the original emission uniformity E-U but a different form, which increases the calculated values by 5-8% more than the original values for E-U using the same design information in the field. The values for E-U can be applied to the hydraulic design using the same procedure as that proposed by the original E-U. Uniformity expressions of a micro-irrigation system can be shown in many forms from the simple range of maximum to minimum emitter flow, or minimum to mean emitter flow E-UK or emitter flow variation q(var) to the statistical terms, such as uniformity coefficient of Christiansen U-C and coefficient of variation C-V. For a micro-irrigation system designed for high uniformity all the uniformity expressions are highly correlated to each other. This high correlation among all uniformity expressions means any single uniformity expression, E-UK, q(var), C-V and U-C can be used as a design criterion. (c) 2005 Silsoe Research Institute. All rights reserved Published by Elsevier Ltd.