Helicopter survey maps the groundwater of the Illinois River Basin
You might notice an unusual-looking hoop hanging from a helicopter in the sky above central Illinois over the next month. It's all part of a decade-long United States Geological Survey project, called the Next Generation Water Observing System, to gain a better understanding about the water beneath our feet.
“They select a basin roughly every year,” said Geological Survey hydrologist Jim Duncker. “The Illinois River Basin is the third basin to start after the Delaware River Basin and the Upper Colorado.”
The Illinois River Basin is a sprawling area, including most of central and northeastern Illinois, and parts of northwestern Indiana. Low-flying helicopters outfitted with an electromagnetic sensor are covering the basin on flight paths separated by about 12 miles each.
“It sends a small electromagnetic signal into the earth. And depending on the geologic materials in the sub-surface, we're able to measure how well different materials conduct or don't conduct electricity,” explained geophysicist Burke Minsley. “So coarse-grained sediments like sands and gravels and bedrock don't conduct electricity very well. They look electrically resistive. Shales and clays and saltwater look electrically conductive, they're good conductors. So, we're able to map those properties out in the subsurface to depths of about 1,000 feet below ground.”
When the mapping is done by helicopters moving at 50 mph, Minsley said they can collect a lot of data very quickly. The information is then translated to tell researchers more about topics like geologic structures, aquifer materials and groundwater salinity.
Minsley said all of this information provides a clearer picture of the effects of groundwater and how it affects rivers and streams.
“We have information about groundwater, from boreholes, those tend to be very sparsely located, and coarse information,” he said. “So by applying airborne geophysics, we're able to systematically collect data over large areas to inform that geologic structure and map out groundwater systems with much greater fidelity than we're able to do in the past.”
For example, harmful algal blooms, or a buildup of algae that can pose a threat to the health of humans and animals drinking from contaminated water, are happening more frequently in the Illinois River Basin. Researchers hope data collected by the survey can help them figure out why.
“The groundwater definitely has a large role to play and its interactions with surface water,” said hydrologist Katie Hulsey. “So maybe we can provide the foundation of what's going on just below the surface and marry that with the surface studies and see what we can tease out.”
Hulsey said there are other valuable insights to be gained from the Illinois River Basin, in part because of its unique geographic placement.
“One thing unique about the Illinois River Basin is not only its large geographic and population footprints, so the things that we learn about this river basin will impact a great amount of people,” said Hulsey. “But it's also kind of representative of the watersheds in the area.”
With areas that are urban and densely populated, as well as sparse rural areas with a large amount of agricultural activity factoring into groundwater conditions, the Illinois River Basin provides a model that could be applied to other similar water basins in the Midwest.
Minsley said it’s common for people to ask if there are any health risks related to the survey and the use of the electromagnetic sensor. He said the answer is no.
“(The helicopter is) low, you know, so it can startle people when they don't see it coming. But that's about it,” he said. “The electromagnetics signal that you would feel if you were standing directly beneath it is about equivalent to what you would get if you were standing a foot away from a toaster oven.”
Also, because of FAA rules, the helicopters never fly directly over homes or densely populated areas. You can learn more about the entire operation on the USGS web site here. The surveys were set to start on Tuesday, Jan. 24 and are expected to take two to four weeks, depending on the weather.