Advances in designing drip irrigation laterals

It is known that using paired laterals, in which two distribution pipes extend in opposite directions from a common manifold, contribute to increasing water use efficiency (WUE). Recently, an analytical procedure to optimally design paired drip laterals on uniform slopes was proposed. More recently, this design procedure was simplified by deriving simple explicit relationships, as a function of 16 calibration constants, with relative errors that were less than 2%. In this paper, further simple design relationships are derived that require only 3 calibration constants, thus more readily obtainable results are produced and the influence of the flow rate and diameter exponents of resistance equation are made more evident. Simple monomial relationships were also extended for the cases in which the lateral is laid on flat fields, on upward fields, and also considering layouts in which the manifold is located at the boundary, instead of inside, of the irrigation unit. For the five considered layouts, evaluations of the effects of design choices in terms of energy saving and comparisons between optimal lateral lengths, are carried out. Finally, simple linear relationships linking lateral pressure head tolerance (δ), coefficient of variation of pressure heads (CV) and emission uniformity coefficient of Keller and Karmeli (EU) are presented. Results showed that for any design solutions associated with the considered layouts and for δ < 0.1, the proposed procedure allows optimal design of the lateral, optimizing WUE, assuring low values of pressure head variability (CV < 6.1%) and high values of emission uniformity coefficient (EU > 95%).