LAWRENCE — The average groundwater level for western Kansas fell slightly in 2015, but the rate of decline was the slowest in five years, according to preliminary data compiled by the Kansas Geological Survey. Much of Central Kansas also experienced small declines, although levels rose substantially around Wichita.
The KGS and the Division of Water Resources of the Kansas Department of Agriculture measured groundwater levels in approximately 1,400 water wells in early 2016 as part of an annual program to monitor the condition and outlook of the state’s invaluable groundwater.
In 2015, drought-busting precipitation helped slow the depletion rate of groundwater because less irrigation — the region’s primary use of water — was required, especially in southwestern Kansas where dry conditions have been most persistent.
“Last year was not only a very wet year, with much of southwestern and west-central Kansas receiving 150 to 200 percent of normal annual precipitation, but the timing was good,” said Brownie Wilson, KGS water-data manager. “Above normal precipitation levels in May and July during the growing season, and in some places again in August, really helped to ease pumping demands, which led to an overall reduction in water-level declines.”
Most of the state is no longer considered to be under drought conditions, Wilson said, although a few small areas are still classified as abnormally dry.
The vast majority of groundwater pumped in western and central Kansas is drawn from the High Plains aquifer, a massive underground network of water-bearing rocks that underlies parts of eight states. In Kansas, it comprises the far-ranging Ogallala aquifer as well as the smaller Equus Beds around Wichita and Hutchinson and the Great Bend Prairie aquifer that encompasses Great Bend, Kinsley, Greensburg and Pratt.
About 90 percent of the wells measured by the KGS and DWR are drilled into the High Plains aquifer. The rest obtain water from the Dakota aquifer and other deeper systems or shallow alluvial aquifers along creeks and rivers.
Substantially used for crop irrigation since the mid-20th century, groundwater from the High Plains aquifer is also the prime source of water for many municipalities and industries.
Water levels in the 1,400-well network as a whole in 2015 declined an average of 0.37 feet, which was the smallest decline since 2009. From 2010 to 2014, the average annual levels fell, cumulatively, 7.21 feet. The last positive water-level change was in 1997 when the network average rose about 3 inches.
Most of the wells in the network monitored by KGS and DWR are within the boundaries of the state’s five groundwater management districts (GMDs), which are organized and governed by area landowners and local water users to address water-resource issues.
Southwest Kansas GMD 3 wells continued to register the greatest average decline, although the 0.84-foot decrease in 2015 was a marked improvement over the previous five years. Collectively, 2010 to 2014 sustained a nearly 15-foot decline, including a 2.15-foot drop in 2014. Since 1996, the average water level in the GMD has dropped 38 feet.
Wells monitored in GMD 3 are drilled into the Ogallala aquifer except in a few areas where they draw from the Dakota aquifer. The district includes all or part of Grant, Haskell, Gray, Finney, Stanton, Ford, Morton, Stevens, Seward, Hamilton, Kearny and Meade counties.
Western Kansas GMD 1 nearly broke even in 2015 with an average groundwater-level decline of 0.04 feet, or about 5 inches. From 2010 to 2014, water levels declined 5 feet, including a 0.67-foot drop in 2014. The GMD includes portions of Wallace, Greeley, Wichita, Scott and Lane counties, where the majority of wells are drilled into the Ogallala aquifer.
Northwest Kansas GMD 4 was the only region to experience a greater average decline than the year before, although the difference was not highly significant. In 2015, the average level fell 0.58 feet — nearly equal to the average of all annual declines since 1996 — compared with 0.43 feet in 2014. GMD 4 covers Sherman, Thomas, Sheridan, and parts of Cheyenne, Rawlins, Decatur, Graham, Wallace, Logan and Gove counties. Groundwater there is pumped almost exclusively from the Ogallala aquifer and alluvial sources.
Big Bend GMD 5 is centered on the Great Bend Prairie aquifer underlying Stafford and Pratt counties and parts of Barton, Pawnee, Edwards, Kiowa, Reno and Rice counties. The average groundwater level there fell 0.38 feet after falling 0.60 feet in 2014 and rising 0.53 feet in 2013.
Groundwater levels in the Big Bend GMD are more responsive to large rain and snow events than in western Kansas because normal precipitation rates rise from west to east. The water table is also nearer the surface there, which increases the chance that water percolating through the ground will reach the aquifer. In the past 20 years, average annual levels increased seven times in GMD 5, including 3.14 feet in 2007 when torrential summer rains and flooding occurred.
Equus Bed GMD 2 is a major source of water for Wichita, Hutchinson and surrounding towns. The average water level there rose 1.45 feet in 2015 after dropping 1.23 feet in 2014 and rising 2.81 feet in 2013. In 10 of the past 20 years the average level rose, keeping the long-term water level of the Equus Beds relatively steady.
“Given that the Equus Beds is on the eastern edge of the High Plains aquifer system, it typically has much higher recharge rates because it receives higher precipitation amounts and the water table is very close to the land surface,” Wilson said. “It can be subject to stress from continued drought conditions like we saw in 2011 and 2012, but overall it is managed as a sustainable system.”
The influence precipitation rates have on water levels in the Equus Beds can be seen not only by comparing water level and rainfall amounts from year to year but also by comparing the different amounts of precipitation the eastern and western portions received during 2015.
“GMD 2 in 2015 is a good example of how the overall average of a region is often made up of extremes,” Wilson said. “Although the average water level increase across the GMD was 1.45 feet overall, it was made up of one-half to one foot declines found only in the western counties of the GMD while levels in the eastern counties rose up to 7 feet in some places.”
Those differences in water level measurements coincided with prevailing precipitation patterns, as Rice and Reno counties to the west experienced normal or slightly below normal precipitation while Harvey and Sedgwick had above normal precipitation.
The KGS measures approximately 550 wells in western Kansas each January, and DWR staff from field offices in Stockton, Garden City and Stafford measure about 850 in western and central Kansas. Most of the wells, spread over 48 counties, are used for irrigation and many have been measured for decades.
Measurements are taken primarily in January because water levels are least likely to fluctuate when irrigation wells aren’t in use. Infrequently, however, later-than-normal pumping due to dry conditions may unduly affect measurement results.
Measurement results are provisional and subject to revision based on additional analysis. The data is scheduled to be available in late February.