NEW SIMPLIFIED APPROACH FOR HYDRAULIC DESIGN OF MICRO-IRRIGATION PAIRED LATERALS

A simple, direct, and easily adaptable analytical approach was developed for the hydraulic design of micro-irrigation paired laterals laid on uniformly sloping ground based on the locations where the same average emitter pressure head exists in the uphill and downhill laterals. Analytical expressions of the best manifold position, inlet working pressure head, maximum pressure difference, and water application uniformity of the paired laterals were separately developed using the energy gradient line method. All equations of the design parameters were regression analyzed by the numerical fitting technique with the specific velocity exponent and the pressure loss ratio of a single downhill lateral with the same length as the paired laterals. When the length, diameter, and designed emitter flow were given, the best manifold position and other parameters of the paired laterals could be directly designed without using iterative methods. When the designed emitter flow, water application uniformity criterion, and one parameter (either diameter or length) were provided, the other parameter, best manifold position, and the remaining parameters of the paired laterals could be easily determined by Equation Solver in Microsoft Excel. A comparison test with three numerical design examples covering various conditions indicated that the proposed approach could produce accurate results for practical purposes. By using the developed analytical expressions and regression relationships, the proposed approach provided a simpler and more adaptable design procedure than the traditional analytical methods. The proposed procedure is preferred to the numerical techniques, which need large amounts of execution time and complex computer operations. The proposed procedure also provided the chance to evaluate the influence of local energy losses on the hydraulic designs of paired laterals for a given uniformity level.