Renovation and Upgrading of the Urban Water Distribution Systems by Multi-Objective Optimization Approach (Case Study: Part of Zahedan Distribution Network)

Pipe wear in urban water supply networks is one of the most important challenges faced by water authorities. Older pipes must be replaced by new ones once they reach the end of their service life or are no longer useful due to a rise in demand and changes in surface roughness. Budget limits are one of the most common reasons for the failure of renovation and upgrade plans in water supply networks. In the traditional approach, the whole renovation is done in one phase and does not take into account the growth and development of the system. Therefore, uncertainties due to unforeseen changes are not considered. The present study addresses the renovation and upgrade of a part of the water supply network in Zahedan city via a novel approach. This approach involves dividing the plan into phases and redesigning some of the pipes during 5-year phases based on budget partitioning. To improve the hydraulic performance of the network, a multi-objective simulation-optimization model was developed with the pipe replacement cost and the water supply network reliability as the objective functions that must be minimized and maximized, respectively. For this purpose, the EPANET simulator model was combined with the Gray Wolf Optimization (GWO) algorithm in MATLAB software. The model execution results in each Phase were presented in the form of a Pareto front between the objective functions. This allows the company to renovate the water supply network based on the budget in each phase. After optimization in phase 1, the results were presented as a Pareto front between the network reliability coefficient and the reconstruction cost. One of the optimal answers on the chart was selected as the final design. In this optimal design, 22 pipes at a cost of 276 million Tomans and a reliability coefficient of 48.2% were replaced. After applying changes in the diameter of the pipes according to the design, the first phase was optimized as the basic model of the second phase. In phase 2, 32 pipes were selected and renovated. Similarly, after the end of Phase 4, it was found that the network reliability has increased significantly (150%) and the pressure of all network nodes was within the allowable range. The results indicate that the used approach can considerably increase the reliability of the network in addition to appropriately managing the renovation budget.