There’s an old saying that one picture is worth a thousand words. For scientists with USDA’s Agricultural Research Service and the U.S. Geological Survey, multiple pictures may be able to tell the whole story of a regional aquifer.
Researchers with those two organizations have been working for years to try to get a better idea of what the structure of the alluvial aquifer in the Mississippi River Valley looks like underneath the soil surface.
“USGS conducted a regional survey with total planned line-kilometers of about 50,000,” said James R. Rigby, research hydrologist with the USDA-Agricultural Research Service’s National Sedimentation Laboratory in Oxford, Miss. The survey is producing impressive results.
“Last year from November 2018 to February 2019 we flew 17,000 line-kilometers with the helicopter towing this torpedo-like set of instruments,” he said, speaking at the Arkansas Soil and Water Conference at Arkansas State University. “Those are represented in this grid on the right.”
Last November, researchers began using a new system with fixed wing aircraft that generated data for 24,000 line-kilometers. They have plans to fly another 4,000 line-kilometers this spring.
Where scientists had to try to interpolate results from bore holes that might be miles apart in the Delta, the new systems are providing detailed analyses of the soil structures at greater and greater depths below the surface.
“In this slide, what we’re looking at are three different data sets we’re getting from the same set of flights,” he said, displaying a slide with three images of the Mississippi River alluvial aquifer. “On the left this is the radiometric data which is giving us concentrations of radio isotopes in the top foot of soil. This is basically like a soil survey based on the minerology.
“In the middle, this is the resistivity map. This is the bulk of the data we get back. This is one depth near the base of the aquifer, but we can look at this from any depth we want and see the conductivity of the aquifer where there are high-producing regions and where there are low-producing regions.”
The picture on the right provides magnetic data, “and the magnetic data is showing the deep structure of the bedrock that is thousands of feet below the soil surface,” he noted.