Hydraulic reliability as a tool for performances evaluation and design of pressure irrigation networks with demand service

The design of “on demand” pressurized irrigation distribution networks raises interesting challenges, both in terms of sizing individual network elements (typically, the internal diameters of the pipes and, in some cases, the power ratings assigned to the pumping systems located at the beginning of the network) and in terms of the subsequent verification of their hydraulic functionality. This paper therefore presents a methodology aimed at the interactive, probabilistic design of “on demand” pressurized irrigation networks. The methodology is based on the one hand, on an initial sizing of the diameters to be assigned to the various sections of the network, which uses a probabilistic approach widely used in technical literature, made easily usable through the proposal to use any hydraulic solver, even an old type, capable of conducting DDA (Demand Driven Analysis) type analyses; on the other hand, on a probabilistic approach that couples the ability to generate a particularly high number S of ʺrequest scenariosʺ from users, all equally possible, with the use of a hydraulic simulator, capable of carrying out PDA (Pressure Driven Analysis) type analyses and, therefore, capable of taking into account, if duly implemented, the actual relationships existing between the discharges supplied by the various sprinklers and the existing piezometric heads at the sprinkler itself. The definition of specific local and global ʺperformance indicatorsʺ constituting actual random variables to be analysed, ʺa posterioriʺ, on a statistical basis, together with: i) the identification of specific ʺthreshold valuesʺ of these ʺproxiesʺ; ii) the estimation of the probability of exceeding or not these threshold values (depending on the specific proxy considered); and iii) the knowledge of the nodes (and/or sections) in which the values of these indicators are inadequate allows not only an objective assessment of the reliability, from a hydraulic perspective, of the network being designed, but also the identification of the interventions that can be implemented to improve it.