Mixed picture painted from state groundwater monitors
Statewide groundwater monitoring data from the University of Nebraska-Lincoln paints a mixed picture.
Based on data from just the last one to three years, the news is generally good as groundwater levels under most of Nebraska continued to gain, or at least slow their declines.
Overall, groundwater levels under most of Nebraska changed less than a foot from spring 2009 to spring 2010.
But longer-term data, from the past decade or more, is not quite as encouraging.
“We’ve had a few years of average to above-average precipitation, which have helped groundwater levels over much of the state, but if you look at the longer term, our groundwater levels are continuing to decline,” said Jesse Korus, UNL School of Natural Resources groundwater geologist.
The “Nebraska Statewide Groundwater-Level Monitoring Report 2010,” which Korus co-authored with other UNL groundwater experts, says “Long-term groundwater level changes in Nebraska primarily reflect aquifer depletion in areas of dense irrigation development and increases in (groundwater) storage due to seepage from canals and reservoirs.”
This and much more information is contained in the 19-page illustrated report that details and maps changes in Nebraska groundwater levels from spring 2009 to spring 2010, over the past 10 years, from predevelopment of irrigation to spring 2010, as well as average daily streamflows in 2009 and other related information.
“Increases in precipitation over most of the state since 2007, which also helped reduce demands for irrigation, have meant generally good news for Nebraska groundwater levels, but the long term trend is still that groundwater levels continue to decline from the period of predevelopment of irrigation to the present,” said Mark Burbach, report co-author and assistant geoscientist.
Looking just at the past year, the news is better.
From 2009 to 2010, groundwater levels under most of Nebraska generally changed less than a foot. There were rises in scattered locations, but there were also a few places showing declines.
“Some, but not all, of these trends are reflective of statewide precipitation patterns in 2009, compared to the long-term norms,” Korus said.
Groundwater level rises of more than two feet occurred around Lake McConaughy, Keith and Perkins counties and under most of the southern Panhandle. Much of the western and northern Sandhills experienced rises of one to two feet and areas south of the Platte River in west-central Nebraska and north of the Platte River in central Nebraska experienced rises of more than a foot, but generally less than five feet.
Some of the biggest recorded one-year gains were near the Missouri River and its major tributaries in northeastern and southeastern Nebraska, where groundwater levels rose by more than five feet, Burbach said.
Declines of more than a foot were relatively few and widely scattered across the state. The largest of these areas was in Clay and Fillmore counties, where declines were from two to five feet.
Despite the gains, or at least slowing of declines, in groundwater levels over much of the state in the last three years, levels remain below spring 2000 levels over most of Nebraska due to widespread drought from 2000 to 2007.
Gains or slowing declines since 2007 also don’t change the fact that large areas of groundwater level decline since predevelopment of irrigation remain in the south central, southwest and Panhandle, Korus said.
Predevelopment water levels are estimated, but generally occurred before the early to mid-1950s depending on when intensive groundwater irrigation began.
In areas of the state showing the longest long-term groundwater decline, “many are in areas of intense groundwater irrigation, but in a few areas wells are not particularly dense.
“Other factors such as aquifer characteristics, rates of recharge and irrigation scheduling could be contributing to the declines,” Burbach said.
Average daily streamflows across Nebraska were highly variable over 2009.
In central and parts of northeast Nebraska, flows were above average due to above-average precipitation, but in parts of western, southern and southeastern Nebraska flows were below the long-term average due to near or below average precipitation.
“The low flows in some streams in the Panhandle and southwest are part of a regional trend in the High Plains aquifer of long term reductions in baseflow to streams due to lowering of the regional water table,” Burbach said.
Groundwater level change maps included in the report can be downloaded free at the School of Natural Resources website. Maps from previous years are also archived there, dating to 1954.
Data for the maps, graphs and reports is based on recorded measurements from more than 6,000 observation wells taken by 27 organizations, including each of Nebraska’s 23 Natural Resources Districts, U.S. Geological Survey, Central Nebraska Public Power and Irrigation District, U.S. Bureau of Reclamation, and UNL’s Conservation and Survey Division.
Groundwater level change maps rely on well readings recorded as close to April 1 as possible, before the start of the irrigation season.