A resilience index of a water lifeline system using an optimal restoration strategy

Water distribution networks (WDNs) must deliver water to its customers 24/7. Disruption of this important service after a strong seismic event impedes post-disaster activities and poses health and sanitation problems. Hence, WDNs must be able to quickly restore services after the occurrence of a major seismic event. This ability to return the water service can be a metric for resilience. In this paper, the resilience is quantified by developing a framework that translates various restoration strategies into an improved resilience measure for a multi-source water distribution network. This framework is then applied at Surigao Metropolitan Water District (SMWD), a local WDN in Surigao City. The seismic hazard at the site was mapped using a Probabilistic Seismic Hazard Analysis (PSHA). The results show that peak ground velocities (PGV) surrounding the WDN ranges from 35.62 cm/s to 50.14 cm/s at the site for a Level 1 (475-year return period) earthquake while the peak ground velocities (PGV) surrounding the WDN ranges from 48.77 cm/s to 67.92 cm/s at the site for a Level 2 (2475-year return period) earthquake. Using Prim’s algorithm, the WDN was decomposed into Minimum Spanning Tree (MST) and Minimum Spanning Forest (MSF) for single-source and five-source case of repair, respectively. Subsequently, Horn’s algorithm and Maximum Slope Method were used to optimize repair sequences for the WDN. Based on the repair sequence obtained, restoration curves were obtained. Finally, the resilience index (with zero as lowest and one as the highest) of the WDN was quantified by generating a resilience curve. Sixteen resilience indices were computed that represented 16 restoration strategies used. The optimal resilience index (RI) of SMWD against Level 1 and Level 2 seismic events were 0.932 and 0.556, respectively. However, if SMWD increases the monetary resources for transportation, monitoring, excavation, and manpower by 211%, 108%, 210%, and 184%, respectively, the best RI of SMWD against level 1 and level 2 seismic events improved to 0.974 and 0.830, respectively. The result shows that resources can reduce the restoration time of damage elements and thus increase the resilience of the WDN against seismic hazard. Finally, resilience indices were found out to be an effective indicator of determining the most efficient restoration strategies or repair scenarios for the damaged water distribution network due to level 1 and level 2 earthquake events