Design of concave and convex paired sloped drip laterals

Properly designed microirrigation plants allow water use efficiency to be optimized and quite high values of emission uniformity to be obtained in the field. Disposing paired laterals so that two distribution pipes extend in opposite directions from a common manifold contributes to provide more uniform pressure to all laterals in thesystem. Towards this end, an analytical procedure to optimize the uniform pressure when designing paired drip laterals on uniform slopes has recently been proposed, based on the assumption that the variations of the emitters' flow rate along the lateral and the local losses due to the emitters' insertions could be neglected. More recently, an easy method to fix the best position of the manifold (BMP) equal to 24% of the optimal lateral length was introduced. The mentioned procedures are valid under the assumption that the paired laterals are laid on straight slopes; however, real microirrigation units rarely follow an even gradient, whose topography is characterized by equally spaced contour lines. The objective of this study was to extend the analytical procedure to optimally design paired sloped drip laterals to the case in which the shape of the field is concave or convex. Results showed that the position where the minimum occurs in the downhill laterals and the optimal pressure head distribution lines vary with the shape of the drip lateral and that the easy method to fix the BMP = 24% cannot be applied for paired sloped laterals laid on complex topography. Accordingly, a BMP relationship as a function of the curvature parameter of the lateral profile is proposed. Moreover, it is demonstrated that the optimal length of the paired lateral has achieved its minimum value, for a particular concave shape, at what corresponds to a paired lateral length 6.6% lower than that for straight paired laterals. By varying the curvature parameter, and for an inside diameter value equal to 17.6 mm, some practical solutions are presented. The proposed procedure was successfully compared with that derived by the step-by-step exact procedure.