Evaluation of Methods for Relating Continuous Streambed Resistivity Data and Hydraulic Conductivity in the Mississippi Delta

Author(s): Killian, C.; Rigby, J.; Barlow, J.; Kress, W.; Schmitz, D.

Data worth and uncertainty analyses of an existing regional groundwater-flow model that includes portions of the Mississippi Alluvial Plain (MAP) identified streambed hydraulic conductivity as a notable parameter that affected model uncertainty, influencing the model’s ability to evaluate groundwater and surface-water interactions. The streambed hydraulic conductivity of each stream reach is currently represented by one value in the existing model due to the paucity of existing data, resulting in high uncertainty in model outputs. Waterborne continuous resistivity profiling (CRP) data was collected by the U.S. Geological Survey in 2016 and 2017 along selected streams within the Mississippi Delta to: (1) characterize near-surface lithology of the Mississippi River Valley alluvial aquifer for improved understanding of groundwater and surface-water interactions; and, (2) allow for increased variability of streambed hydraulic conductivity within the existing model. Multiple methods to translate resistivity values to estimates of streambed hydraulic conductivity were evaluated. Two-dimensional profiles of estimated streambed hydraulic conductivity data were aggregated vertically to develop one-dimensional streambed hydraulic conductivity values and horizontally to the scale of the existing model. Estimated streambed hydraulic conductivity values from the methods were incorporated into the existing model and model estimates of predicted streamflow and groundwater levels were compared to measured values to evaluate model performance for each translation method. This exercise to improve streambed hydraulic conductivity values will allow for reduction in model uncertainty by allowing the model to better estimate groundwater/surface-water interaction and improve tools to make informed decisions when creating and implementing best water-use management practices.

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