Optimal Design for Pressurized Irrigation Subunits with a Minimum Cost and Maximum Area for Uniformly Sloping Fields

Abstract

The optimal design for pressurized irrigation subunits is a complicated problem that not only requires a confirmation of the layout but also requires a pipe diameter combination. Using a subunit with single lateral and a subunit with paired laterals as research objects, four mathematical optimization models were established to identify the optimal microirrigation subunit design. The optimization criteria were minimizing the annual total cost (C_T) and maximizing the subunit size (A); it was assumed that all the emitters have equal discharge, and only rectangular subunits were considered in this study. No allowable pressure differences allocation between the lateral and the manifold were made in this study, considering that there are many factors that affect the distribution ratio and the overall optimization of the subunit. A genetic algorithm was used to obtain the optimal design when simultaneously considering the layout and pipe diameters of the subunit. The results indicated that the investment cost (C_a) is the most important factor, and it makes up 43–66% of the C_T, followed by the water cost (C_w), which accounts for 28–49% of the C_T. A subunit with paired laterals is superior to a subunit with single lateral in terms of both the total cost and the control area. On the whole, with the increase in the lateral diameter, both the total cost and the control area will increase. With an increase in the emitter discharge, the total cost increases, while the control area decreases. The change of slope in the lateral direction has little effect on the total cost and control area. The method proposed in this study is applicable to the simultaneous optimization of the subunit in which the layout and area are undetermined, and it may provide a new path towards subunit optimization.