Impact of Grid Orientation on Groundwater Contaminant Transport Modeling Using the U.S.G.S. MOC Modelby John J. Warwick, Univ of Texas at Dallas, Richardson, United States,
Roger Stoffregen, Univ of Texas at Dallas, Richardson, United States,
Abstract: The U.S.G.S. method of characteristics (MOC) model was enhanced to include the input of measured contaminant concentrations, the calculation of computed and measured contaminant plume centroids, and the calculation of a root mean square (RMS) error statistic for comparing measured and computed concentrations. The impact of grid orientation upon numerical modeling of a well-defined conservative plume was investigated. Use of a grid orientation, which was nonorthogonal to the flow, resulted in significant numerical dispersion problems such that the predicted extent of lateral plume spreading was greater than observed even with zero transverse dispersivity. The best fit RMS was 148 grams for this orientation. An alternate, orthogonal to flow, grid orientation resulted in superior predictions with an RMS value of 70 grams.
Subject Headings: Hydrologic models | Grid systems | Pollutants | Plumes | Two-dimensional models | Errors (statistics) | Water resources
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