By JULIE TOLLEFSON
Kansas Geological Survey
LAWRENCE — The Kansas Geological Survey and its research partners recently completed an airborne survey in northwest Kansas that will allow scientists to create a 3-D image of the High Plains aquifer in that area at a level of detail that has not previously been possible.
With funding from the Governor’s Office and the Kansas Water Office, the KGS and Northwest Kansas Groundwater Management District No. 4 contracted with Aqua Geo Frameworks, LLC of Fort Laramie, WY, to conduct the first-ever airborne electromagnetic survey of this type in Kansas.
“We are hopeful that the results of the survey will help change the narrative of what the future holds for this portion of the High Plains aquifer in western Kansas,” said Jim Butler, KGS senior scientist and project lead.
To conduct the survey, a low-flying helicopter towed a large frame holding scientific equipment designed to measure the electrical resistivity of materials below the land surface. Beginning on May 28, AGF flew 2,443 miles over portions of Cheyenne, Sherman, Wallace, Rawlins, Thomas, Decatur, and Sheridan counties. Flights could not be flown over residential areas and other buildings, livestock feeding operations, or wind turbines.
In addition to reconnaissance flight lines that allowed researchers to gather general information about aquifer conditions, the research team identified some areas within GMD4 for more detailed examination using closely spaced flight lines.
One area of special interest was the Sheridan-6 Local Enhanced Management Area, a groundwater conservation area established in 2013 in Sheridan County in response to serious aquifer depletion.
“The irrigators in the LEMA have decreased groundwater pumping by over 30% relative to the pumping prior to the establishment of the conservation area,” Butler said. “We wanted to get further information about the ‘innards’ of the aquifer so we could better assess what the future holds for the LEMA.”
The research team completed its last flight on June 16. The surveys provided resistivity measurements to about 1,000 feet below land surface, but the project’s focus was on the interval above the Pierre Shale, which marks the bottom of the High Plains aquifer and lies 200 to 300 feet below the surface over most of GMD4.
Resistivity measurements help scientists distinguish types of rock and other materials underground. Sands and gravels — prime aquifer materials that readily yield water to wells — have high resistivity. Clays, silts, and shales that yield little, if any, water to wells have low resistivity.
“Resistivity measurements will provide information about how intervals of sands and gravels are distributed in the aquifer and the role that less-transmissive materials play in the aquifer’s response to pumping stresses,” Butler said.
“We are already obtaining important information about variations in aquifer composition and thickness across the district and getting hints about possible areas of higher recharge to the aquifer. Ultimately, survey results will provide valuable insights into the geologic factors that are controlling the distribution and yield of pumping wells and how those factors will impact the future of the aquifer in GMD4.”
Using preliminary data from the flights, researchers have created cross sections of the subsurface. To ensure the AEM equipment worked properly, they compared the new data to existing well records that describe the sediments encountered during drilling.
“While the existing records provide information about vertical variations in sediment type at individual well locations, they provide little information regarding the lateral extent and connectedness of sediment bodies. The AEM data give us a much clearer picture of what’s going on between wells,” said Geoff Bohling, a KGS associate scientist on the project. “Both records work together, however, to establish the connection between electrical resistivity and sediment type, so the existing records are critical to interpretation of the AEM data.”
The Ogallala aquifer is the major water resource for agricultural, industrial, and municipal use in GMD4. Intensive pumping of the aquifer over the last 60 years has resulted in large groundwater level declines in Sherman, Thomas, Sheridan, and Cheyenne counties.
The KGS and AGF plan to conduct a similar airborne survey of Western Kansas GMD1 in 2025. GMD1 covers portions of Greeley, Lane, Scott, Wallace, and Wichita counties. Contingent on funding, the research team will survey parts of Southwest Kansas GMD3 in 2026. GMD3 includes all or part of Finney, Ford, Grant, Gray, Hamilton, Haskell, Kearny, Meade, Morton, Seward, Stanton, and Stevens counties.
The Kansas Geological Survey is a non-regulatory research and service division of the University of Kansas. KGS scientists study and provide information about the state’s geologic resources and hazards, including groundwater, oil and natural gas, rocks and minerals, and earthquakes.
For more information, contact Jim Butler, [email protected], 785-864-2116, or Scott Ishman, [email protected], 785-864-1971