Near-optimal rehabilitation scheduling of water distribution systems based on a multi-objective genetic algorithm

An increase in breakage frequency and a decrease in system efficiency are observed when pipes become older. Rehabilitation strategies are necessary to face this problem in order to define when, where and how to operate for renewing the pipe system. These strategies are constrained by the amount of funds, which are usually available not in a single instalment but yearly and spread over a time period of several years. A procedure based on a multi-objective genetic algorithm to search for a near-optimal rehabilitation scheduling is proposed. With reference to a fixed time horizon, the goal is to minimize the overall costs of repairing and/or replacing pipes, and to maximize the hydraulic performances of the water network; the constraints are represented by the maximum costs that are allowed yearly, over a pre-selected time spell. A head-driven hydraulic simulator is linked to the optimizer to represent the different hydraulic and breakage scenarios, which become possible in consequence of the rehabilitation schedules generated by the genetic algorithm. Results regarding a simple case study and a real water distribution system show that the proposed procedure has the potential to be a useful tool for rehabilitation scheduling.