CRITICALITY ANALYSIS IN WATER DISTRIBUTION NETWORKS BASED ON A MINIMUM PRESSURE CRITICALITY INDICATOR

Water distribution networks (WDNs) represent an urban infrastructure essential for a safe and reliable water supply, whose management is complex and fundamental for public health. Growing urbanization and the increase in global water demand (estimated to rise by 20-30% by 2050) exacerbate the challenges posed by often outdated infrastructure, causing supply interruptions, excessive losses, and water quality problems.Traditional numerical models for WDNs, that are crucial for predicting network behavior, are influenced by considerable limitations in some specific scenarios: the demand driven (DD) approach produces unrealistic results under conditions of water deficiency or failures of network components, as it assumes that demand is always met. The head driven (HD) approach, while considering a relation between flow rate and pressure, overlooks the intrusion of air into the pipes. Air entrainment, which can occur at zero relative pressure, converts parts of the pressurized flow into free surface flow, altering hydraulic dynamics and potentially increasing velocities and degrading water quality (e.g. turbidity). All traditional models ignore the possibility of air intrusion, and this consequently impacts the computed results in terms of flow regime and pressures.The drawbacks of these models directly impact the validity of performance and criticality indicators, especially in pressure reduction scenarios. Many current indicators rely solely on network’s topological characteristics or hydraulic performance, without holistic integration and ignoring realistic scenarios such as air intrusion. A more accurate and comprehensive assessment of the weaknesses of each network element is therefore needed.To address these challenges, this thesis focuses on two main objectives: first, development of a new numerical model (Minimum Pressure - MP) for WDNs. This model aims to overcome the limitations of the DD and HD approaches by assuming pipe permeability to air and a zero minimum relative pressure in all nodes of the network. The MP model will be able to identify pipes where free surface flow, due to air intrusion, may occur, providing more accurate and realistic results, especially under water scarcity conditions.The thesis also focuses on the definition of a new criticality indicator (Minimum Pressure Criticality Indicator - MPCI). The MPCI will innovatively integrate the network's topological characteristics, derived from the "structural hole" theory, with the hydraulic solution provided by the numerical model used (MP or traditional). This indicator will offer a strategic perspective for prioritizing pipe maintenance, supporting water managers in their decision-making and asset management of WDNs.Results computed on the real WDNs selected as test cases showed that, while the output values calculated by MP model in normal functioning conditions of the network are similar to the ones provided by DD and HD approaches, in pressure deficiency conditions instead the results vary significantly and MP is able to correctly predict the hydraulic dynamics of the network, differently from conventional approaches. MPCI was calculated in the chosen networks to establish a prioritized maintenance for pipes, and it proved to be able to give priority both to pipes subject to hydraulic stress and to pipes crucial for network functioning, whereas other criticality indicators available in the literature could fail to identify critical pipes, especially in water reduction conditions.In conclusion, by providing a more physically grounded numerical model and a more accurate criticality indicator, this thesis aims to fill the current gaps in simulation models and assessment tools, crucial for the resilient management of WDNs in the era of increasing challenges related to water scarcity and water quality control, accentuated by climate change.