Unsteady Flow Indicators for Pressurised Irrigation Networks

Pressurised irrigation systems have been developed during the last decades with considerable advantages with respect to open canals. For evaluating obstacles, constraints and opportunities, and setting up a consistent modernization strategy and improving the irrigation service to users in case of pressurised irrigation systems, FAO is actually developing a methodology called “MASSPRES”, Mapping System and Services for Pressurised Irrigation Systems, using an approach that looks very similar to that was used for MASSCOTE (Mapping System and Services for Canal Operation Techniques, Renault et al., 2007). One of the main steps of MASSPRESS is to map the perturbation.

In pressurized networks for irrigation systems, the perturbation is mainly created by the sudden changes in flow rates occur into the pipes; in hydraulic systems operating on demand is essentially due to hydrant’s operations and depends mainly on the gates’ closure time. Such perturbation may lead to a large pressure change which may cause pipes breaking.

In a recent study (Lamaddalena et al., 2018), a computer code simulating unsteady flow in pressurised irrigation systems generated by the farmers’ behaviour was developed and the obtained results summarized introducing an indicator called Relative Pressure Variation (RPV) in order to evaluate the pressure variation occurring into the system in respect to the steady-state pressure.

In this study, two new indicators have been set up. The first one, named Hydrant Risk Indicator (HRI) for providing the hydrant degree of danger on the system, whereas the second, the Relative Pressure Exceedance (RPE), is for providing the variation of the unsteady state pressure in respect to the nominal pressure; both the indicators could help the water managers in better understanding the network behaviour as regards to the perturbation by locating the most dangerous hydrants and the potential affected pipes.

A large number of configurations has been run in order to reflect the farmers’ behaviour, where a configuration is known as the change between groups of hydrants operating at the same time. The study was applied to an on-demand pressurised irrigation system in Southern Italy.