Design of Zero Slope Microirrigation Laterals: Effect of the Friction Factor Variation

Microirrigation has become quite a common practice in agricultural production in various parts of the world. To achieve the optimum (hydraulic and economic) system performance, designers are often faced with the problem of designing a maximum lateral length which results in a desired coefficient of uniformity (CU) or an allowable pressure head variation (${\delta }_H$). Previous theoretical design approaches are usually based on a constant Darcy–Weisbach (DW) friction factor along the lateral and this assumption can lead to substantial errors. In the research reported in this paper, a new analytical design approach does not require the constant DW assumption for zero-slope laterals while it still takes into account the emitter exponent and the effect of minor friction losses caused by emitters. Assuming a constant friction factor along the lateral might result in errors up to 14% in the calculation of the maximum lateral length. Conversely, the maximum relative error caused by the application of the proposed method compared to the stepwise solution generally does not exceed 1.1%. The suggested technique for determination of maximum lateral length is simple to use and does not require iteration, as is usually the case for previous analytical methods. The method is applicable to various types of emitters for lateral lengths less than 300 m. It also provides an additional check on other analytical and numerical methods that are available elsewhere.