Modularity-Based Procedure for Partitioning Water Distribution Systems into Independent Districts

In the last years, the Water Distribution System (WDS) design paradigms changed, moving from traditional pipe redundancy criteria, which lead to heavy looped distribution systems, to the development of water system partitioning aimed at an easier management of the water distribution system. Water system partitioning consists in partitioning a water distribution system into subsystems called District Metered Areas (DMAs), with specifically defined and permanent boundaries, whose inlet and outlet flows can be metered and controlled (also regarding their pressure) through suitable valves and measuring instruments. Partitioning existing water distribution system is a very difficult problem, because the removal of many redundancies (that is a consequence of the partitioning process) can compromise the compliance of nodal pressures to the required constraints and reduce to unacceptable values the water distribution system reliability. The solution of this problem requires the use of graph-theory-based methodologies, coupled with water distribution system hydraulic analysis, able to work out the water distribution system characteristics (for example the topologic structure) in order to identify the best divisions into districts. Nevertheless, in this approach, it needs not lose sight of practical aims of partitioning and the consequent technical criteria. Among these, the independence among districts seems particularly important, especially in order to apply control pressure strategies.

In this paper, a new methodology for the automated identification of DMAs is proposed. It is based on the prior identification of the pipes with prevalent transport service (transmission mains) that are not included in the partitioning design and on the identification of independent sectors directly connected with the transmission mains. The procedure decomposes sectors exceeding the maximum DMA size constraint (fixed in terms of number of costumer connections) thanks to a modularity based optimization algorithm. Then, the districts obtained by the division process are isolated from each other by closure valves. Finally, the pipes that have to be closed by isolating valves and the pipes that have to be left open and equipped with flow meter are selected among the pipes connecting the DMAs to the transmission mains.

The successful applications of the new methodology to a real case study, i.e., Castelfranco Emilia (Modena, Italy) water distribution system, already tested by other Authors, has proven its effectiveness for the DMA design in existing water distribution systems. The proposed methodology represents an improvement in comparison with other methodologies proposed in the last years since it combines a suitable algorithm for the automated creation of DMA boundaries and convincing practical criteria for the DMAs design. A further plus of the proposed methodology is its ability to identify alternative feasible solutions among which the decision maker can choose the division that best meets not only technical performance requirements, but also economic requirements that are never directly included in the automated procedures (e.g., the available funds allocated to ensure the costs of flow meters and of isolation valves for the creation of DMAs).

Since the implemented procedure enables schematization of the water distribution system as a “weighed graph”, also important aspects (e.g., ground level of nodes, elevation of buildings, user types) for the homogeneity of DMAs can be included.