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from the issue of October 12, 2006
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UNL researchers track Nebraska groundwater declines of more than 30 feet in last 6 years
Statewide decline
BY STEVE RESS, UNL WATER CENTER
Spurred by increasing irrigation use and a statewide drought now in its seventh year, parts of Nebraska are experiencing groundwater declines of more than 30 feet, according to annual monitoring by UNL scientists.
"We certainly aren't coming to the bottom of the well, so to speak, but the level of groundwater declines in many parts of Nebraska are indisputable and could even be viewed as alarming," said Mark Burbach, assistant geoscientist in the School of Natural Resources. "There are now large areas of southwest Nebraska and Box Butte County that have experienced groundwater declines of greater than 50 feet since large scale groundwater development began."
While groundwater development for irrigation didn't develop at the same pace across the state, the beginning of large-scale development is generally regarded as 1952.
In recording groundwater aquifer level changes over the last six years, from spring 2000 to spring 2006, large swaths of the state show groundwater declines ranging from five to 10 feet to greater than 25 feet. Hardest hit are areas relying heavily on irrigated agriculture, such as Perkins, Chase and Dundy counties in southwest Nebraska and all along the Platte River valley.
"Areas that experienced groundwater level declines before the recent drought are some of the most heavily affected areas during the drought," Burbach said. "Hamilton, York, Polk and Butler counties show some of the largest declines."
These areas have not only been some of the most drought-impacted, but are also among the most heavily irrigated in Nebraska.
"These persistent and growing declines in the aquifer over much of Nebraska are mainly due to the current drought and resulting increases in groundwater pumping for irrigation," he said.
"The largest groundwater level declines since the drought began are in portions of Clay, York, Butler and Dundy counties, where in some cases, the declines have exceeded 30 feet over the past six years," Burbach said.
Counties experiencing declines of more than 15 feet include Box Butte in the Panhandle; Chase, Lincoln and Perkins in the southwest; Buffalo, Dawson, Hall, Hamilton, Merrick, Polk, Seward and York in south central; and Platte and Colfax in the east.
Over the past year, large parts of southern and eastern Nebraska have experienced aquifer declines of from one to five feet, though a one- to two-foot rise in groundwater levels was observed in parts of Hall and Merrick counties, as well as in Rock, Holt and Antelope counties along the Elkhorn River.
"Both of these areas experienced above normal precipitation in March, shortly before monitoring well measurements were taken, so that may be something of an anomaly since due to sandy soil and shallow water tables, these areas tend to respond quickly to rain or other aquifer recharge events," Burbach said.
A couple of spots along the North Platte River that rely heavily on surface irrigation also experienced aquifer rises of from one to two feet over the past year.
In the last five years, only a few areas have shown minimal increases notably Valley, Rock and Holt counties. Normal or above normal precipitation in parts of the Elkhorn River valley, combined with an absence of groundwater irrigation may explain the rises in Rock and Holt counties, while the area in Valley County is associated with a surface irrigation system, Burbach explained.
"Taken on the whole, the only areas of the state where groundwater levels have risen since development of groundwater irrigation are near man-made canals, reservoirs and other water impoundment projects," he said.
The groundwater level monitoring program Burbach coordinates collects aquifer water level data from a continually growing number of wells that now numbers more than 5,600. Readings from the wells are generally taken between March 1 and May 1, after aquifers have had time to recover from the previous year's irrigation season and before that year's upcoming irrigation season.
The data from these wells is used to produce color maps showing rises and declines in groundwater levels. The maps typically show the changes in terms before the development of irrigation to the present and over the past year.
Copies of the groundwater level change maps, including historical copies dating to 1954, can be accessed at http://csd.unl.edu/surveyareas/gwmaparchives.asp. UNL's groundwater level monitoring program dates to 1930.
GO TO: ISSUE OF OCTOBER 12
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