A cost-reliability optimization framework for aging water distribution networks with partial demand surges considering time-dependent deterioration effect

The synergistic impacts of structural deterioration in aging urban water distribution networks (WDNs) and nonlinear demand surges in partial regions pose dual threats to water supply security. Current research inadequately addresses the dynamic time-dependent effects of aging pipelines on network operational reliability. This study proposes a cost-reliability optimization framework for aging WDNs under partial demand surge scenarios, integrating time-dependent reliability theory and evolutionary algorithms. The framework employs a Gaussian stochastic process-based corrosion power-law model to quantify time-dependent pipe failure probabilities, subsequently transformed into deterioration coefficients. These coefficients are systematically integrated with topological connectivity, junction hydraulic importance, and pipeline uniformity coefficients to formulate a novel Time-dependent Reliability Index (TRI). Comprehensively evaluate pipeline stress strength to establish deterioration pressure boundaries, ensuring safe operating conditions for aged WDNs. Within a Non-dominated Sorting Genetic Algorithm II (NSGA-II) architecture, Pareto frontiers are established for operational decisions on variable-speed pump groups, simultaneously minimizing energy cost and maximizing reliability. Implementing Anytown and a Chinese city's large-scale WDN reveals critical insights: TRI provides a more robust assessment than traditional reliability metrics in quantifying the long-term time-dependent system reliability of WDN, and preventive maintenance based on pressure thresholds effectively mitigates the progressive reliability degradation associated with pipeline deterioration. A more critical finding is that differences in WDN topology and scale cause partial demand surges to slightly enhance the reliability of large-scale aged WDNs, while small-scale WDNs exhibit weakened reliability. This framework offers a scientific WDN reliability enhancement pattern that delivers cost-effective and highly reliable operation solutions in aging WDNs.