Mississippi Alluvial Plain (MAP): Electrical Resistivity & Facies Classification Grids

Electrical resistivity results from two regional airborne electromagnetic (AEM) surveys (Minsley et al. 2021 and Burton et al. 2021) over the Mississippi Alluvial Plain (MAP) were combined by the U.S. Geological Survey to produce three-dimensional (3D) gridded models and derivative hydrogeologic products. Grids were discretized in the horizontal dimension to align with the 1 kilometer (km) x 1 km National Hydrogeologic Grid (NHG; Clark et al. 2018), and vertically discretized into both 5 meter (m) depth slices and 5 m elevation slices. Ten “facies classes” were defined to categorize materials expected to have similar hydrologic and geologic properties based on their electrical resistivity (i.e. low classes correspond to clays and silts with low permeability, and higher classes reflect larger grain sizes (sands, gravels) with expected higher permeability). Facies classes were further separated based on position relative to the base of the Mississippi River Valley Alluvial aquifer (MRVA) to capture geologic distinctions in addition to hydrogeologic. Final 3D grids were exported into NetCDF format. All metadata from the NetCDF files are provided within the accompanying XML NetCDF Markdown Language file (*.ncml). Burton, B.L., Minsley, B.J., Bloss, B.R., and Kress, W.H., 2021, Airborne electromagnetic, magnetic, and radiometric survey of the Mississippi Alluvial Plain, November 2018 - February 2019: U.S. Geological Survey data release, https://doi.org/10.5066/P9XBBBUU. Clark, B.R., Barlow, P.M., Peterson, S.M., Hughes, J.D., Reeves, H.W., and Viger, R.J., 2018, National-scale grid to support regional groundwater availability studies and a national hydrogeologic database: U.S. Geological Survey data release, https://doi.org/10.5066/F7P84B24. Minsley, B.J., James, S.R., Bedrosian, P.A., Pace, M.D., Hoogenboom, B.E., and Burton, B.L., 2021, Airborne electromagnetic, magnetic, and radiometric survey of the Mississippi Alluvial Plain, November 2019 - March 2020: U.S. Geological Survey data release, https://doi.org/10.5066/P9E44CTQ.