Abstract
The effect of limitations in the structural detail available in a network model on contamination warning system (CWS) design was examined in case studies using the original and skeletonized network models for two water distribution systems (WDSs). The skeletonized models were used as proxies for incomplete network models. CWS designs were developed by optimizing sensor placements for worst-case and mean-case contamination events. Designs developed using the skeletonized network models were transplanted into the original network model for evaluation. CWS performance was defined as the number of people who ingest more than some quantity of a contaminant in tap water before the CWS detects the presence of contamination. Lack of structural detail in a network model can result in CWS designs that (1) provide considerably less protection against worst-case contamination events than that obtained when a more complete network model is available and (2) yield substantial underestimates of the consequences associated with a contamination event. Nevertheless, CWSs developed using skeletonized network models can provide useful reductions in consequences for contaminants whose effects are not localized near the injection location. Mean-case designs can yield worst-case performances similar to those for worst-case designs when there is uncertainty in the network model. Improvements in network models for WDSs have the potential to yield significant improvements in CWS designs as well as more realistic evaluations of those designs. Although such improvements would be expected to yield improved CWS performance, the expected improvements in CWS performance have not been quantified previously. The results presented here should be useful to those responsible for the design or implementation of CWSs, particularly managers and engineers in water utilities, and encourage the development of improved network models.
Highlights
Water distribution systems (WDSs) can be contaminated intentionally by the injection of a contaminant into the system or accidentally, for example, by releases of contaminants into reservoirs or by contaminated water entering the distribution system when adequate pressure is not maintained
Results are given for four different contamination warning system (CWS) designs as a function of the dose level used for the design
If CWSs are designed using a skeletonized network model and implemented, they will be used in actual system, which is better approximated by the original network model
Summary
Water distribution systems (WDSs) can be contaminated intentionally by the injection of a contaminant into the system or accidentally, for example, by releases of contaminants into reservoirs or by contaminated water entering the distribution system when adequate pressure is not maintained. Janke: Influence of skeletonization on CWS design sors designed to detect potential contaminants can provide a warning that a system has been contaminated and reduce potential consequences associated with a contamination event. The design of contamination warning systems (CWSs) employing multiple sensors has been an active research area; Hart and Murray (2010) have reviewed strategies for placement of sensors in CWSs. Given that a CWS may be able to help reduce consequences associated with contamination events, understanding the factors that can affect the quality of a CWS design is important for those responsible for managing distribution systems. This paper focuses on one important factor, the accuracy with which the network model of a distribution system represents the actual structural details of the network, namely its pipes and junctions
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