Vulnerability assessment of water distribution networks under seismic actions

A methodology to analyze the vulnerability of water distribution networks (WDNs) to earthquakes by means of risk assessment is presented. The consequences of multiple pipe failures due to earthquakes are investigated in terms of unsupplied demand to customers. To this aim the steady-state WDN analysis is performed considering system topology changes due to closing isolation valves in order to separate the network segments where failures occur. The pipe failure probability is calculated using fragility curves from the American Lifelines Association (ALA). The identification of the worst pipe failure scenarios as trade-offs between unsupplied demand and probability of occurring is formulated as a multiobjective combinatorial problem and solved using a multiobjective genetic algorithm as optimization strategy. The methodology is applied to the Exnet network. Results show that WDN seismic vulnerability depends also on network segmentation due to the existing isolation valve system. The methodology allows analyzing and ranking the worst scenarios, being a valuable decision support for improving WDN preparedness to earthquakes and allowing planning appropriate asset enhancements and mitigation measures to improve system resilience.