Urban Resilience: Restoration Analysis of Urban Water Infrastructures in A Potential Earthquake (Case study: Region 2 of Tehran Municipality)

The increasing dependence on urban infrastructure systems especially, water infrastructure, have led to an increased emphasis on disaster-resilience infrastructures. Recent damages caused by earthquakes around the globe have attracted researchers’ attention to the infrastructure resilience concept. Water infrastructure resilience is the ability of a system to both withstand uncertain conditions caused by natural disasters and to recover quickly from the disastrous events. Urban infrastructure resilience evaluates by a model which analysis restoration time, serviceability index and resistance features.The purpose of this research is to promote a new practical approach to analyze urban resilience. In this research water infrastructures’ restoration time, serviceability and supply interrupted population in a metropolitan area are analyzed based on new proposed urban resilience methods. The methodological approach of this paper is practical and focuses on the water system in district two of Tehran city, Iran, in the context of the earthquake. Results of this research demonstrate the vital importance of urban resilience features, restoration time and functional recovery team to increase urban water system resilience. For the case study area, results indicate that in a potential earthquake, water infrastructures would suffer more than 28% of disruption of service in the immediate aftermath, which more than 172982 people will experience almost severe disruption of water availability. To better understand the system resilience, three restoration scenarios were analyzed. In the first scenario, one emergency post consist of 3 teams were allocated. Results indicate that complete restoration of the system takes more than 89.5 days.Furthermore, analyses of the second scenario indicate that the increase of the resilience factor will reduce restoration time to less than 45 days. In the last scenario, changing sources base on the organizational analysis, decreased the restoration time to less than 29.8 days. Based on the standard target for emergency water supply which should be less than one month, the third scenario seems to improve the resilience of the system dramatically. MethodologyThis article’s methodological approach is practical and concentrates on the restoration period of water infrastructure services in a probable earthquake. In this research, analytical techniques and resilience models were used to analyze the restoration time of water infrastructure based on three scenarios of damages caused by a scenario earthquake. We focused on district two of Tehran municipality where active faults and main urban infrastructures cross the area. The Probabilistic Seismic Hazard Analysis (PSHA) was used to estimate the seismic features such as PGA and PGV of a most probable earthquake in the case study area. At the next step pipeline damages including breaks and leaks were analyzed based on damage models. At the next step, serviceability was evaluated based on average break rate (equation 3). Besides, the system and was classified and prioritized in 6 levels based on HAZUS methods (Table 3). In this research, ArcGIS software was used to analyze and evaluate restoration time model and produce damage maps. In this article, the restoration function for the water system is analyzed based on the minimum resilience model and damages caused by the earthquake. At the final stage, based on restoration functions and serviceability index, water supply interrupted population and required time for restoration process in three scenarios were analyzed. Results and DiscussionUnderstanding restoration time, as one of the main elements of water infrastructure resilience model, is critical for decision-makers and urban planners. It can improve the disaster resilience of cities in high-risk areas around the globe.Damage analysis indicates that in 43 points break and 175 points leak will happen in a case of the earthquake scenario. Results of this article indicate the vital importance of restoration time and repair functional team to increase urban water system resilience. Results show that water serviceability index was 72% which means that in a potential earthquake, more than a quarter of study area’s population or 172982 people will experience severe disruption of water availability. Based on three restoration scenarios, restoration time will be between 90 to 29.8 days. In the first scenario based on the real data of the emergency department, one urban emergency post consist of 3 teams were analyzed as the model input. Results indicate that complete restoration of the system takes more than 89.5 days.Furthermore, analyses of the second scenario with two posts consist of 6 teams reduced the restoration time to less than 45 days. In the last scenario, by increasing team numbers, the restoration time decreased to less than 29.8 days. Emergency restoration efforts are predicted to reduce the service disruptions to moderate levels within two weeks, but complete restoration would need more than four weeks.Conclusion This article proposed a practical method to increase water infrastructure seismic resilience and specified quantitative measures of restoration time and serviceability index as key parts of urban resilience. The keys to this framework are the three complementary measures of resilience: Reduced time to recovery, increased serviceability index to reduce the consequences of the earthquake and increased the stability of the system. The finding suggests that increasing infrastructure resilience and repair team would reduce the restoration time and damage. However, team numbers should be limited because two teams cannot work at one time on the same area. Since serviceability index has a direct relation with water supply interrupted population, then we found that by increasing serviceability, system resilience will be increased. Furthermore, retrofitting and improving the system would reduce the damage and restoration time which will increase system resilience by 20%.Based on this article's results, we recommend the following actions to increase urban water infrastructure resilience:• It seems that three posts consist of 9 teams are essential to achieving the standard resilience target • A long-term comprehensive earthquake restoration plan should be prepared based on the priority of potable water pipelines (Map 3) • Developing mid-term and long-term restoration and rehabilitation plans to change vital urban lines with more flexible pipes based on the results of the model to reduce the damage by 70% and increase the urban resilience• Finally, we encourage more academic studies with a practical approach to propose new urban resilience models