Assessing a Local Losses Evaluation Procedure for Low-Pressure Lay-Flat Drip Laterals

Abstract

In the past, several research experiments have focused on the hydraulic characterization of traditional drip irrigation systems, and different design methodologies have been proposed with the aim of achieving very high emitter discharge uniformity (EU). The increasing use of low-pressure lay-flat drip laterals, characterized by a thin-walled polyethylene pipe, makes necessary a specific determination of their hydraulic properties, aimed to a correct design of such systems. Here, the validity of an empirical local losses estimation model was assessed for five different commercial lay-flat drip tapes. Moreover, the errors in the maximum lateral lengths obtained for a fixed emitter uniformity, when the local losses are neglected or empirically estimated, were evaluated. The step by step (SBS) procedure was then implemented to model the hydraulic behavior of each tested lateral with values of the upstream pressure head different than those investigated. The experiments demonstrated that under the examined flow conditions, local losses represent a percentage variable between 2.0 and 11.4% of the friction losses measured in the laterals. Due to the limited contraction of flow streamlines produced by the emitters, the resulting values of the kinetic head coefficient, α, were generally small and variable in the range between 0.020 and 0.060. The SBS procedure indicated that in lay-flat drip laterals, only when emitter spacing results are lower than 50 cm should it be necessary to take into account local losses, as the errors of ignoring such losses are negligible in the other cases. The results finally evidenced that the empirical local losses estimation model, valid for thick-walled laterals, generally overestimates α, allowing a more conservative evaluation of the lateral lengths when a fixed EU is desired.