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Drought and groundwater supplies
Posted May 15, 2013
By David Ostdiek, Communications Associate
UNL Panhandle Research and Extension Center
During times of drought people often ask University of Nebraska-Lincoln water scientist Steve Sibray the same question: Will the groundwater aquifer dry up?
The answer isn’t simple and also varies from one location to the next, said Sibray, a hydrogeologist with the UNL Conservation and Survey Division who is stationed at the Panhandle Research and Extension Center.
“It’s a lot more complicated than that,” Sibray said. Which wells might go dry “depends on the geology of the system.”
The effects of groundwater level declines vary according to which part of the water-bearing formation a well was drilled into. For users on the aquifer’s edge, with less saturated thickness, pumping will become too expensive at some point.
Cities and irrigators with wells in deeper areas aquifers (often closer to the middle of the formation) might need to deepen their wells, but usually will not run completely out of water, according to Sibray.
Nebraska groundwater users, both in towns and on farms and ranches, have been concerned about water supplies for many months. Despite several snowstorms this spring, precipitation is below normal in western Nebraska, and as of mid-May the entire Panhandle was designated as being in either “extreme” or “severe” drought, on the Nebraska Drought Monitor map posted at droughtmonitor.unl.edu by the National Drought Mitigation Center at UNL.
In Nebraska, groundwater is closely monitored because it provides the vast majority of water used both by irrigation and municipalities.
A well’s location in the aquifer is one of several factors that affect its security. Another factor is recharge, the process by which aquifers gain water from precipitation or other sources.
When it comes to recharge, Sibray most of the municipalities in the North Platte Valley are lucky. Their major source of recharge is not precipitation, but surface water from the North Platte River that seeps from the canals of the large irrigation project constructed more than 100 years ago.
Surface water recharge accounts for a significant volume of water and moves into and through the aquifer relatively quickly. By contrast, very little precipitation usually makes it to the saturated zone of an aquifer. Most of the rain or snow runs off, is used by plants, or evaporates before it can infiltrate the soil and trickle downward. The water that does trickle through might take years or decades to reach the saturated zone.
Because of annual recharge from irrigation canals, groundwater levels in the North Platte Valley are much higher than before the irrigation project was constructed, and usually don’t fluctuate much from one year to the next, Sibray said.
This effect has been documented by research, he said. Studies conducted years ago at University Lake north of Scottsbluff, conducted in conjunction with the North Platte Natural Resources District, demonstrated a distinct difference in water chemistry between river water and native groundwater. “We can see that most of the groundwater in the North Platte Valley is derived from irrigation.”
“There are cities like Scottsbluff and Gering that shouldn’t have water quantity problems as long as you have the North Platte River and the system of irrigation canals,” Sibray said.
Water tables have declined over the years in some areas, such as Box Butte County. But Sibray said Alliance is situated above the aquifer’s deep point, so even if declines continue, the city should not run out of water.
Over the long term, Sibray said he’s optimistic about the continued availability of water in towns in most areas. One reason is that municipal water use generally has a higher value than other uses. So as water supplies get scarcer, high-end uses such as towns and municipalities will still be drawing water down past the point where irrigators can afford to.