LAWRENCE—Average groundwater levels throughout western and central Kansas dropped more in the past year than they had annually since 1996, according to preliminary data compiled by the Kansas Geological Survey, based at the University of Kansas.
In January 2012, the KGS and the Kansas Department of Agriculture's Division of Water Resources measured levels in approximately 1,400 water wells in 47 western and central Kansas counties as part of an annual assessment program.
This is the fifth consecutive year that the greatest declines in the state were in the southwest corner, the area hardest hit by persistent drought conditions. Areas in central and south-central Kansas that had shown significant gains or only modest declines the last four years, due in part to flooding in 2007, also showed significant declines this year.
“Southwest Kansas has had significantly below-average precipitation rates during the growing season—mainly March to August—for several years, but this year rainfall was consistently down during that season throughout much of the state,” said Brownie Wilson, KGS water-data manager. “Levels in the Equus Beds aquifer, a main water supply in south-central Kansas, dropped over 3 feet, the most we’ve ever recorded.”
Northwest Kansas was the only region in the assessment-program area where average declines did not exceed 2 feet. Increased levels were even recorded in some localized areas where wells were drilled into thinly saturated portions of the Ogallala aquifer and alluvial valleys and near normal precipitation patterns likely prevailed.
Ninety percent of the nearly 1,400 measured wells draw water from the High Plains aquifer, which includes the extensive Ogallala aquifer, the Great Bend Prairie aquifer in west-central Kansas, and the Equus Beds aquifer north and west of Wichita. The rest are drilled into deeper aquifer systems, such as the Dakota, or shallower aquifers along creeks and rivers.
For the entire 1,400-well network, average levels fell 2.25 feet during 2011. The year before, the overall average was down 1.18 feet, and since 1996 it has dropped nearly 12 feet.
Precipitation rates determine how much recharge enters the High Plains aquifer, especially in the Great Bend Prairie and Equus Beds where aquifer levels will likely recover. However, given the extremely low recharge rates in the Ogallala aquifer, the removal of water for irrigation and other purposes there, not the rate of recharge, has the biggest impact on water levels.
“When precipitation is low over an extended period, especially in the Ogallala, a much greater quantity of water is pumped out of the ground than during wetter years,” Wilson said. “The amount of water taken out rather the amount going in has the greatest influence on water-level changes from one year to the next.”
Most of the measured wells are within the boundaries of the state’s five groundwater management districts, organized by area landowners and large-scale water users and governed by local boards to help define and address water-resource issues.
In GMD 3 in southwestern Kansas, where the levels dropped 3.78 feet during 2011, the wells are screened mainly in the Ogallala aquifer and—in selected areas—the Dakota aquifer. Average water levels in the district dropped about 3 feet in the previous year and have fallen 29 feet since 1996.
Much of the district’s greatest decline occurred in a triangular area from Garden City to Liberal to northeast of Dodge City. GMD 3 includes all or part of Grant, Haskell, Gray, Finney, Stanton, Ford, Morton, Stevens, Seward, Hamilton, Kearny and Meade counties.
Western Kansas GMD 1, which had an average decline this year of 2.05 feet, includes portions of Wallace, Greeley, Wichita, Scott and Lane counties. Declines averaged 0.43 and 0.72 the two previous years and about 9.2 feet since 1996. Most wells in the district are drilled into the Ogallala aquifer.
Northwest Kansas GMD 4, covering Sherman, Thomas, Sheridan and parts of Cheyenne, Rawlins, Decatur, Graham, Wallace, Logan and Gove counties, showed an overall decline of 0.61 feet. Average levels there were up 0.10 feet two years ago, down 0.50 feet a year ago, and down 8.73 feet since 1996. Most groundwater here is also from the Ogallala aquifer.
The majority of wells measured in the area north of GMD 4, mainly in Rawlins, Decatur and Norton counties, had water-level increases up to 2.5 feet with even higher levels in a couple of locations. In this area, the Ogallala aquifer is generally less productive, and most of the higher-capacity wells are only found in alluvial river valleys.
Big Bend GMD 5, centered on the Great Bend Prairie aquifer underlying Stafford and Pratt counties and parts of Barton, Pawnee, Edwards, Kiowa, Reno and Rice counties, had a decline of 2.95 feet. Levels there were up 0.63 feet two years ago, down 0.44 feet last year, and prior to the 2012 measurements, the district had a slight overall water-level increase of 0.82 feet between 1996 and 2011.
Water levels in the Equus Bed GMD 2, which includes parts of Sedgwick, McPherson, Harvey and Reno counties, fell 3.17 feet following modest declines—0.26 feet and 0.70 feet—the two prior years. Between 1996 and 2011, the district had experienced an overall increase of 0.4 feet.
Much of the water supply for Wichita, Hutchinson and the surrounding area comes from the Equus Bed aquifer.
The High Plains aquifer is the primary source of municipal, industrial and irrigation water for much of western and central Kansas. Approximately 80 percent of the 33,000 non-domestic water wells in Kansas are in the High Plains aquifer region of the state.
The same wells are measured each year to get an understanding of how the aquifer is behaving over the long term and how water levels are affected by climatic conditions and pumping. Measurements are taken primarily in January because water levels are least likely to fluctuate when irrigation wells aren’t in use.
Results of the measurements are provisional and subject to revision based on additional analysis. The data will be available in mid-February here.