By helicoptering an electromagnetic device above southeast Nebraska, a research team is generating 3D maps of ancient underground valleys that could help inform water management by predicting how groundwater will flow.

Jesse Korus, Matt Joeckel and Dana Divine—researchers from the Nebraska Geological Survey—conducted their recent study in southeast Lancaster County, which contains deposits created when glaciers passed through the central lowlands of the United States and Canada more than 640,000 years ago. The team discovered a complex network of overlapping and cross-cutting sedimentary deposits that affect the region’s aquifers and streams.

Jesse Korus, a groundwater hydrogeologist with the University of Nebraska-Lincoln’s School of Natural Resources, and colleagues using electromagnetic surveys. Image credit: University of Nebraska.“Airborne electromagnetic surveys are on the forefront of groundwater research,” says Korus, a groundwater hydrogeologist with the University of Nebraska-Lincoln’s School of Natural Resources. The technology has been used in mining for decades, he says, but its application to aquifers is a new development, and no one has used it to study buried valleys in these deposits.

“Fundamentally, we are trying to understand why aquifers are so variable and why they seem to occur randomly below the surface,” Korus says. “With this research, we are beginning to understand that there is indeed an order to the complexity.”

Traditional borehole drilling doesn’t work well for mapping buried valleys because it is too time consuming and expensive. So the team, which included Nebraska’s Natural Resource Districts and the U.S. Geological Survey, used a helicopter to tow an electromagnetic tool that recorded the electrical properties of the subsurface. Clay, which is electrically conductive, registers as blue, whereas sand and gravel appear red.

This method allowed the researchers to collect extremely detailed information 200 feet beneath the surface and along lines more than 900 feet apart. Limitations in resolution, though, still left a gap in data, requiring the use of borehole and water well data collected along the same flight line.

“We see as many as six generations of valleys in this area, overlapping in complex ways,” Korus says. “This pattern has relevance in predicting how groundwater flows in the area."

According to Korus, groundwater availability depends on the nature of the sediment fill. Some buried valleys contain fine sediments that act as barriers to groundwater flow. Other valleys act as hydraulic windows, allowing water to flow from the land surface to deep aquifers below.

The team has submitted a proposal to expand this work to other areas of Nebraska, hoping to focus on the cost effectiveness of airborne electromagnetics and how underground maps can be used to plan for water development and management.