Regional-scale Airborne Geophysics Reveals Hidden Complexity of Mississippi River Alluvial Valley
Wednesday, 12 June 2019: 09:25
Davie West Building, DW103 (Florida Atlantic University)
Wade Hampton Kress, U.S. Geological Survey, Lower Mississippi-Gulf Water Science Center, Nashville, TN, United States, Burke J Minsley, USGS Geology, Geophysics, and Geochemistry Science Center, Denver, CO, United States and James Rigby, USDA Agricultural Research Service Oxford, Oxford, MS, United States
Abstract:
In 2018, the U.S. Geological Survey began a multi-year airborne geophysical mapping initiative, incorporating both regional and high-resolution airborne electromagnetic (AEM) surveys as part of the Mississippi Alluvial Plain water availability project. The initial high-resolution survey in March 2018 comprised approximately 2,500 line-km of airborne geophysical data over a 1000 sq. km survey block near Shellmound, MS, using the CGG Resolve
1 helicopter system. Later that year, the first phase of the regional AEM survey began (also with the Resolve AEM instrument) and acquired nearly 17,000 line-km of data mainly along west-east flight lines at 12 km intervals in the northern and southern portions of the study area, and 6 km intervals in the central portion of the study area. Additionally, approximately 2,000 line-km were acquired along several rivers to better characterize the connectivity between surface water and groundwater. Additional flight lines will be flown each year to increase the resolution of the regional hydrogeologic framework to the targeted 3 km-spaced flight lines.
Comparison of preliminary resistivity data to previously-published Mississippi River Valley alluvial (MRVA) aquifer base maps and borehole data indicate that the EM sensor was able to fully penetrate the Quaternary alluvium. Resistivity data below the MRVA aquifer base show the spatial extent of several subcropping aquifer (high resistivity) and confining (low resistivity) units from the Mississippi Embayment sequence. Resistivity data also show that the Quaternary-Tertiary contact may have more topographic relief than previously interpreted from borehole data.
We will illustrate the tradeoffs between the high-resolution survey (sub-1 km spacing) with the regional survey grid (3+ km spacing). Interpretations of the resistivity models will be used to refine interpreted surfaces of the base of the MRVA aquifer, subcropping units, and shallow confining layers that can be incorporated into groundwater models. By better quantifying and reducing uncertainty about the geologic framework, we hope to improve estimates of hydrologic uncertainty to better aid and inform management decisions.
1Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
