The Water Is Falling! The Water Is Falling!

Irrigation, drought are cited

LINCOLN — Information from nearly 5,000 groundwater wells across Nebraska indicates groundwater in the state declined by one to five feet from 2002 to 2003 in many heavily irrigated areas.

Continuing drought and recent legislation to prevent conflicts between groundwater and surface water users have contributed to the recent declines, said Jim Goeke, a University of Nebraska hydrogeologist.

"At least some of the depletions shown on the latest groundwater-level change map produced by the university are a result of drought-related spikes in well drilling and well pumping statewide," Goeke said.

The map shows groundwater level changes in the High Plains aquifer that underlies much of Nebraska. Rises and declines in aquifer levels are common and also are affected by soil types, differences in geology and precipitation, said Mark Burbach, an assistant geoscientist with the University of Nebraska-Lincoln.

The latest map, which shows groundwater level changes between spring 2002 and spring 2003, indicates groundwater declines of from less than a foot to more than five feet over much of Nebraska, particularly in the heavily irrigated Platte, Republican, Loup, Blue and Elkhorn River basins. Only the Sandhills and parts of southeast Nebraska indicate little to no changes in groundwater levels over the past year.

Very few locations indicated a rise in groundwater levels over the past year. In the past 50 years, there has been significant recharge of the aquifer in parts of Dawson, Gosper, Phelps and Kearny counties, where rises of more than 50 feet have been recorded.

This groundwater mound is estimated to contain six to eight million acre feet of water, or about four to five times the 1.75 million acre-foot capacity of Lake McConaughy, Burbach said.

An acre foot of water equals nearly 326,000 gallons.

Other than the groundwater mound, significant, measurable rises in the aquifer are primarily confined to smaller groundwater mounds in Lincoln County and another in Valley, Greeley, Sherman and Howard counties. In both those areas, rises of from five to as much as 40 feet have been recorded.

Other than these notable exceptions, water levels in aquifers underlying Nebraska have remained largely constant over the last 50 years, Burbach said.

"Significant and persistent declines in some areas of the state have only become more obvious in the last few years, due mainly to current drought conditions and resulting increases in groundwater pumping," Burbach said.

Spring water level information from more than 4,800 irrigation, domestic, observation and monitoring wells in all of Nebraska's 23 Natural Resources Districts (NRD) is used to assemble the map.

Rises and declines in the aquifer from predevelopment to spring 2003 also are depicted on the map. Predevelopment is generally regarded as before 1952, when irrigation usage became more widespread, Burbach said.

"You can begin to track declines in aquifers after the 1960s and 1970s when drilling irrigation wells showed a dramatic upswing, due in part to the advent of center pivot irrigation," he said.

A similar spike in well drilling is occurring now due to the drought and the Legislature's passage this spring of LB962, which makes the state and NRDs more proactive in anticipating and preventing conflicts between groundwater and surface water users.

"Under this law, any river basin whose water is determined to be fully or over appropriated has to develop and implement an integrated surface water and groundwater management plan," Goeke said. Such plans have the potential to limit irrigation use of both surface water and groundwater.

The increase in groundwater irrigation and recent groundwater declines due to the drought and increased pumping of wells also has a direct bearing on why some stretches of Nebraska's rivers and streams are dry, said Goeke, who is with UNL's School of Natural Resources and is based at the West Central Research and Extension Center in North Platte.

"The increase in pumpage and diminished recharge to the aquifer due to the drought disrupts groundwater flow to streams, delaying or diminishing the flow of surface water to many basins," he said.

The High Plains aquifer underlies more than 104 million acres of land in South Dakota, Wyoming, Nebraska, Colorado, Kansas, New Mexico, Oklahoma and Texas.

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