Design of water distribution networks for on-demand irrigation

Three fundamental aspects are studied in the design and operating process of a water distribution network for on-demand irrigation. The first determines plot discharge as a function of the average application rate of system, A_rs, in sprinkler irrigation or of the equivalent discharge per unit of area in drip/micro irrigation, and according to plot size. The second determines the maximum and minimum demand curves, aspects which have not yet been published. These constitute the possible operating points of the surrounding irrigation network. The third is the dimensioning and regulation of the pumping plant that minimises the investment and operating costs according to usage conditions in the irrigated area, with operation in different hourly periods with different energy costs. The results show that the use of hydraulic valves with limiting flow controllers makes the design of the network easier. Moreover, the installation cost decreases when adjusting the hydrant discharge to the exact size of each plot, thus eliminating excess discharge. The determination of the maximum demand curve allows dimensioning of the pumping plant, as well as its regulation and control in real time after including it into the PID (proportional, integral and derivative) logic of a programmable controller. Moreover, a simplified method for evaluating the energy consumption during the irrigation season is presented, valid for electricity tariffs with different hourly costs.