Pressure-driven modeling for performance analysis of irrigation systems operating on demand

Abstract

Assessing the performance of irrigation systems is required both to improve management activities and to identify appropriate modernization and/or rehabilitation measures. In pressurized irrigation systems, pressure and discharge variations cause low service performances and negatively impact farm sprinkler or micro-irrigation systems. Several models exist to simulate pressurized irrigation systems and assess the respective performance when a steady state approach may be assumed. However, when the variation in flow regimes and discharges at hydrants is pressure-driven, i.e., when the networks are not equipped with adequate flow limiters and pressure regulators at the hydrants, or when the pressure is insufficient at the hydrants, the flow rate delivered is a function of the available pressure and that approach does not apply. To allow the performance analysis of these systems, the FLUCS model has been developed and tested. It simulates flow in the pipe systems using a simplified solution of the characteristic equations of flow. The respective governing equations are described, as well as the boundary and initial conditions. The performance analysis adopted bases upon the computation of the relative pressure deficits at every hydrant within a given number of configurations of hydrants operating simultaneously. These configurations are randomly generated in a much larger number than the number of hydrants. This approach allows identifying which hydrants do not satisfy the preset pressure and discharge conditions and the areas where pipe sizes may be undersized, thus contributing to pressure deficits. This approach may be used for the analysis of performance of pressurized systems under operation or under design, including to assess the impact of different types of flow regulators and flow limiters. The model was tested with data collected in the Capitanata irrigation system (Southern Italy). Results demonstrate the ability of the model to reproduce the conditions observed at selected hydrants.