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Drinking Water Engineering and Science An interactive open-access journal

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Drink. Water Eng. Sci., 11, 25-47, 2018
https://doi.org/10.5194/dwes-11-25-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
06 Apr 2018
Mass imbalances in EPANET water-quality simulations
Michael J. Davis1, Robert Janke2, and Thomas N. Taxon3 1Argonne Associate of Seville, Environmental Science Division, Argonne National Laboratory, Argonne, Illinois, USA
2National Homeland Security Research Center, US Environmental Protection Agency, Cincinnati, Ohio, USA
3Global Security Sciences Division, Argonne National Laboratory, Argonne, Illinois, USA
Abstract. EPANET is widely employed to simulate water quality in water distribution systems. However, in general, the time-driven simulation approach used to determine concentrations of water-quality constituents provides accurate results only for short water-quality time steps. Overly long time steps can yield errors in concentration estimates and can result in situations in which constituent mass is not conserved. The use of a time step that is sufficiently short to avoid these problems may not always be feasible. The absence of EPANET errors or warnings does not ensure conservation of mass. This paper provides examples illustrating mass imbalances and explains how such imbalances can occur because of fundamental limitations in the water-quality routing algorithm used in EPANET. In general, these limitations cannot be overcome by the use of improved water-quality modeling practices. This paper also presents a preliminary event-driven approach that conserves mass with a water-quality time step that is as long as the hydraulic time step. Results obtained using the current approach converge, or tend to converge, toward those obtained using the preliminary event-driven approach as the water-quality time step decreases. Improving the water-quality routing algorithm used in EPANET could eliminate mass imbalances and related errors in estimated concentrations. The results presented in this paper should be of value to those who perform water-quality simulations using EPANET or use the results of such simulations, including utility managers and engineers.
Citation: Davis, M. J., Janke, R., and Taxon, T. N.: Mass imbalances in EPANET water-quality simulations, Drink. Water Eng. Sci., 11, 25-47, https://doi.org/10.5194/dwes-11-25-2018, 2018.
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Short summary
EPANET does not always conserve constituent mass during water-quality simulations. The failure to conserve mass can result in significant errors in constituent concentrations. We document the occurrence of mass imbalances, explain why they occur, provide recommendations for minimizing mass imbalances, and present a preliminary water-quality algorithm for use in EPANET that always conserves mass. Our paper should be of interest to anyone who performs water-quality simulations using EPANET.
EPANET does not always conserve constituent mass during water-quality simulations. The failure...
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