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Getting to the bottom of the alluvial aquifer with technology

New technology gives scientists a birds-eye view.

Until two or three years ago, scientists could only imagine what the Mississippi River Valley alluvial aquifer might look like if they could peer down below the soil surface.

Now they can not only examine the aquifer at different depths, but they can also show others what they are seeing as James Rigby did at the Arkansas Soil and Water Education Conference at Arkansas State University.

“So this is a view from within the aquifer, if you will,” said Rigby, research hydrologist with the USDA Agricultural Research Service. “Of course, if you were in the aquifer, you’d just be looking at a bunch of sand. This is as if you took out all the sand and just looked at the top and the bottom.

“This would give you an idea of where is the aquifer thick, where is it thin, where are there holes in the base and that sort of thing,” said Rigby, who works at the National Sedimentation Laboratory in Oxford, Miss.

Earlier in his presentation, Rigby said the new technology that allows scientists from USDA ARS and the U.S. Geological Survey to examine the aquifer at depths down to 300 meters helped them discover an old paleo-channel in the Tallahatchie Basin area near Shell Mound, Miss.

“This has really been a way to change how we look at the aquifer,” he said. “Right here we have a birds-eye view looking down at the resistivity map, and what I’m going to do now is I’m going to animate flying down into the aquifer along that paleo-channel.

“You can see the paleo-channel running right through here, and as we’re rotating so we’re looking back from where we came, you can see the banks of this paleo-channel.”

In the past, scientists could try to interpolate what the aquifer might look like from a series of boreholes in the Mississippi Valley alluvial aquifer from the Missouri Bootheel and West Tennessee and down through the length of the Delta region.

A conservative estimate would put the cost of those thousands of boreholes at $300 million over a period of three or four decades, he said.

In contrast the new technology, which uses helicopters and fixed-wing aircraft to fly hundreds of kilometers over the Delta region has cost about $1.5 million, Rigby noted.

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