Optimal Placement of Isolation Valves in Water Distribution Systems Based on Valve Cost and Weighted Average Demand Shortfall

In this paper a method for optimal placement of isolation valves in water distribution systems is presented. These valves serve to isolate parts of the network (segments) containing one or more pipes on which maintenance work can be performed without disrupting service in the entire network or in large portions of it. The segments formed after the installation and closure of isolation valves are identified and characterised using an algorithm which is based on the use of topological matrixes associated with the structure of the original network and the one modified to take account of the presence of (closed) valves. A multi-objective genetic algorithm is used instead to search for the optimal position of the valves. In the application of the method different objective functions were used and compared to solve the problem as to the optimal placement of the valves. The results showed that the most appropriate ones are the total cost of the valves (to be minimised) and the weighted average “water demand shortfall” (likewise to be minimised); in particular, the weighted average shortfall is calculated considering the shortfalls associated with the various segments of the network (shortfall is the unsupplied demand after isolating a segment) and the likelihood of failures tied to mechanical factors occurring in the segments. The methodology was applied to a case study focusing on a simplified layout of the water distribution system of the city of Ferrara (Italy).