Multi-objective Optimization for Renewal Planning of Sewer Systems Under Changing Climate

The maintenance and management of sewer networks have become a growing challenge for municipalities. Sewer inspection and rehabilitation efforts are costly and often are constrained by limited budgets. Moreover, rapid urbanization, climate change impacts, and aging can increase the likelihood of more frequent and uncertain sewer pipe failure. In a reactive management approach, the assessment and maintenance of sewers are usually neglected until a failure occurs. This reactive approach can lead to significant consequences with substantial socio-economic and environmental costs. Therefore, a proactive management approach becomes essential to preventing these costly consequences while minimizing the cost of interventions. Municipalities face increasing pressure to adopt proactive management approaches to maintain acceptable conditions, performance, and service levels for their sewer networks. Proactive management requires the development of optimal renewal planning strategies that are typically characterized by conflicting objectives. This necessitates the utilization of an efficient and robust multi-objective optimization model. The optimization model will provide near-optimum renewal plans over a planning horizon that determines the timing and renewal strategy for each pipe, including repair, replacement, or resizing. Due to the complex nature of sewer system rehabilitation planning and the large number of pipes, the solution space expands significantly, making searching for the optimal solutions challenging. Moreover, the number of objective functions can influence the problem's complexity. Although using fewer objective functions can facilitate the optimization process, it requires aggregating various objective functions with different dimensions, potentially overlooking certain problem perspectives. This study will examine a proposed NSGA-II method to solve the problem. The outcome of this research has the potential to provide decision-makers with more accurate and effective near-optimum renewal planning strategies. These strategies are essential for the proactive management of sewer systems that can lead to effective stormwater management, enhanced flood resilience, and successful adaptation to the impacts of climate change.