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Mass Imbalances in EPANET Water-quality Simulations
Citation:
Davis, M. J., R. Janke, AND T. N. Taxon. Mass Imbalances in EPANET Water-quality Simulations. Drinking Water Engineering and Science Discussions. Copernicus Gesellschaft mbH, Gottingen, Germany, 11(1):25-47, (2018). https://doi.org/10.5194/dwes-11-25-2018
Impact/Purpose:
EPANET is widely employed to simulate water quality in water distribution systems. However, the time-driven simulation approach used to determine concentrations of water-quality constituents provides accurate results, in general, only for small water-quality time steps; use of an adequately short time step may not be feasible. Overly long time steps can yield errors in concentrations and result in situations in which constituent mass is not conserved. This paper explains how such imbalances can occur and provides examples of such cases; it 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, to those obtained using the new 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. 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. This research should be of interest to anyone who performs water-quality simulations using EPANET.
Description:
This journal article examines EPANET, which is widely employed to simulate water quality in water distribution systems. However, the time-driven simulation approach used to determine concentrations of water-quality constituents provides accurate results, in general, only for small water-quality time steps; use of an adequately short time step may not be feasible. Overly long time steps can yield errors in concentrations and result in situations in which constituent mass is not conserved. Mass may not be conserved even when EPANET gives no errors or warnings. This paper explains how such imbalances can occur and provides examples of such cases; it 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, to those obtained using the new 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.
URLs/Downloads:
DOI: Mass Imbalances in EPANET Water-quality Simulations
https://www.drink-water-eng-sci.net/11/25/2018/
Free access through PubMed Central