The U.S. Geological Survey (USGS) developed a groundwater-flow model of the Mississippi Embayment Regional Aquifer System (MERAS) that incorporated multiple aquifers including the Mississippi River Valley alluvial (MRVA) aquifer. In addition to groundwater withdrawal, two major fluxes in the model are recharge from precipitation and surface water-groundwater exchange. In order to determine appropriate values for recharge to the MERAS model, the USGS has utilized two published datasets- the geomorphology of Quaternary deposits and local soil surveys. At a regional scale, recharge in the MERAS model correlate well with large-scale geomorphological features. However, there is little spatial variability, so local-scale variations in recharge are not adequately represented. Higher resolution data such as soil coverages provide a more spatially-variable estimates of recharge, but, soil-survey data often characterize the shallow soil horizon and do not reflect the generalized geomorphological features in which the horizon lies. In addition, streambed sediments may differ greatly from the mapped geomorphologic areas and shallow soils due to alteration from stream mechanics. Thus, geomorphologic maps and soil information are both types of surficial information that may not accurately reflect the underlying hydrogeology that controls infiltration of recharge water or the composition of streambed sediments.
In 2016-17, the USGS conducted several waterborne geophysical surveys to characterize the near-surface (<12 m) lithology that controls recharge to the MRVA aquifer and surface water-groundwater exchange at selected locations within the Mississippi Alluvial Plain (MAP). Two-dimensional vertical profiles of resistivity identified differences in geoelectrical properties of the streambed. High resistivity values are associated with coarse grained sediments and low values are indicative of fine grained materials. These resistivity-derived lithologies were then transformed using several techniques to inform the estimated hydraulic conductivity of the simulated streambed and refine the characterization of streamflow interactions in the MERAS groundwater-flow model.
Ryan Adams, Lower-Mississippi Gulf Water Science Center, U.S. Geological Survey, Nashville, TN
Ryan Adams is a Hydrologist specializing in the application of geophysics to hydrologic and ecological problems. In the past these topics have included: The design of an underwater pressure field to prevent the migration of Asian carp, monitoring of construction vibrations impacting endangered bats in Mammoth Cave National Park, water quality and aquifer tests at a USACE confined disposal facility, and the reinterpretation of archived geophysical records with new processing techniques.
Wade Kress, Lower Mississippi-Gulf Water Science Center, U.S. Geological Survey, Nashville, TN
Wade Kress has been a hydrologist for the U.S. Geological Survey since 1996. He has a BS in geology from Louisiana Tech University and is currently working on an MSc in petroleum geosciences at the Petroleum Institute in Abu Dhabi. Wade has worked throughout the United States as well as the United Arab Emirates on environmental and hydrogeologic framework projects specializing in the application of hydrogeophysics
Steven Peterson, Peterson, Nebraska Water Science Center, U.S. Geological Survey, Lincoln, NE
Steve has worked in groundwater hydrology and flow modeling for over 20 years, mainly on the High Plains of Nebraska. At the USGS Nebraska Water Science Center, Steve incorporates the latest groundwater and integrated modeling approaches to provide comprehensive information for science-based water resources management at local, state, and federal levels. Steve has recently completed the High Plains Groundwater Availability Study, assessing the processes and current and future status of the water resources of the High Plains aquifer, a region sustaining approximately one-quarter of the Nation’s agricultural production through groundwater irrigation. Steve’s other local or regional modeling studies include depletion mapping, optimization modeling, soil-water balance modeling, landscape hydrology modeling, parallel computing for parameter estimation and collaboration on integration of geophysical and geologic data in groundwater models.
Brian Clark, Lower Mississippi-Gulf Water Science Center, U.S. Geological Survey, Fayetteville, AR
Brian Clark is a hydrologist with the USGS. He received a BS from Arkansas Tech (1998) and MS from Baylor University (2000). His research interests include groundwater-flow modeling and geographic information systems.
