Evaluating Water Demand Shortfalls in Segment Analysis

In this paper, two procedures for assessing water demand shortfalls following segment isolation are compared. The first (topological) procedure is based on a simple topological network analysis, and identifies the water demand shortfall as the water demand (under normal operational conditions) relative to the directly and/or indirectly isolated segment (s). The second (hydraulic) procedure is based on a pressure-driven hydraulic simulation of the network after segment isolation. Each of the two procedures was applied to two case studies, and the reliability (expressed in terms of maximum D-max and weighted average (D) over bar water demand shortfall) and economic burden (expressed in terms of number N-val or cost C-val of installed valves) of the resulting isolation valve system solution were compared. As a whole, the results show that network analysis and redesign are affected by the choice of the global variables (D-max or (D) over bar) used to characterize the demand shortfalls in network segments. Analysis of the case studies is followed by a discussion of the rationale behind the choice between the two procedures, which needs to balance accurate demand shortfall characterization with limited computation times, particularly in the multi-objective design stage.