News Release, Kansas Geological Survey, Feb. 9, 2004
LAWRENCE--While much of western Kansas depends on the Ogallala aquifer for its water supply, a new report confirms that water naturally moves back into the aquifer at the rate less than an inch per year.
The report is from the Kansas Geological Survey, based at the University of Kansas.
In fact, the average rate of recharge--or natural movement of water back into an aquifer--is a half-inch or less across 28 counties in western Kansas.
The new report is by Survey water scientist Marios Sophocleous, who has studied recharge across the High Plains of western Kansas for the past two decades.
Groundwater declines across western Kansas averaged about one foot per year since 1980. Because recharge rates are so low across western Kansas, recharge does very little to stem those declines.
"To manage groundwater, we need to know how much water is removed from the aquifer and how much naturally moves back into the aquifer," said Sophocleous. "Without that, we really can't manage groundwater in a knowledgeable fashion."
In his study, Sophocleous examined both the theoretical models of recharge across the state and field studies that actually measured water as it moved underground. Previous theoretical models of recharge have shown that it ranges from a high of 8 inches per year in the southeastern corner of the state--where average annual precipitation is high--to less than 0.5 inches per year in western Kansas, where conditions are much more arid.
A field study done in cooperation with the U.S. Geological Survey in southwestern Kansas, however, showed that recharge to the Ogallala aquifer at two sites in irrigated fields in Finney County was less than a quarter of an inch per year, while recharge at a grassland in Morton County was less than a hundredth of an inch per year.
In addition to precipitation, other factors influence the movement of water back underground, including the type of soil at the surface, the depth to the aquifer (the deeper the aquifer, the less the recharge), land use, and topography. The type of crops grown at the surface also affect recharge. Grassland allows less water to return to the aquifer than cultivated ground.
And irrigated ground has somewhat higher rates of recharge than dryland.
"But with irrigation, most of that recharge is coming from water that was removed from the aquifer to begin with," said Sophocleous. "More irrigation to increase recharge is not the answer to declining water levels."
In general, said Sophocleous, recharge in western Kansas is about one percent of average annual precipitation.
In addition to describing methods of estimating and measuring recharge, the new report discusses the process of recharge and analyzes the major recharge studies conducted in the Kansas High Plains.
"Understanding the rate of recharge is one of the most difficult factors in understanding groundwater resources," said Sophocleous. "But it is critical to the long-term management of our water."
Copies of Sophocleous's report, Groundwater Recharge and Water Budgets of the Kansas High Plains and Related Aquifers, are available from the Kansas Geological Survey (785-864-3965 or by e-mail at email@example.com). The cost is $20 plus $4 for shipping and handling. Kansas residents should add 7.3% sales tax to the entire order.
A short extract
from this publication is available.
Story by Rex Buchanan, (785) 864-2106
For more information, contact Marios Sophocleous, (785) 864-2113
Kansas Geological Survey, Public Outreach