Optimal Rehabilitation of Water Distribution Systems Using a Cluster-Based Technique

Optimal rehabilitation of large water distribution systems (WDSs) with many decision variables is often time consuming and computationally expensive. This paper presents a new optimal rehabilitation methodology for WDSs based on the graph theory clustering concept. The methodology starts with partitioning the WDS based on its connectivity properties into a number of clusters (small subsystems). Pipes that might have direct impact on system performance are identified and considered for the rehabilitation problem. Three optimization-based strategies are then considered for pipe rehabilitation in the clustered network: (1)rehabilitation of some of the pipes inside the clusters, (2)rehabilitation of pipes in the path supplying water to the clusters, and (3)a combination of Strategies 1 and 2. In all optimization strategies, the decision variables for the rehabilitation problem are the diameters of duplicated pipes; the objective functions are to minimize the total cost of duplicated pipes and the number of nodes with pressure deficiency. The performance of proposed strategies was demonstrated in a large WDS with pressure deficiencies. The performance of these strategies was also compared to the full search space optimization strategy and engineering judgment-based optimization strategy in which all pipes and selection of pipes are considered as decision variables, respectively. The results show that Strategy 3 is able to generate solutions with similar performance that are cheaper by around 53% and 35% in comparison with the full search space and engineering judgment-based optimization strategies, respectively. The results also demonstrate that the cluster-based approach can reduce the computational efforts for achieving optimum solutions compared to the other optimization strategies. (C) 2017 American Society of Civil Engineers.