Plunging into Nebraska’s Groundwater Depth: A Massive Reservoir
Measuring Water Quantity and Quality in the Nebraska Sandhills
Nebraska’s groundwater is a fundamental building block of life and a valuable resource for livestock and agriculture, according to Troy Gilmore, assistant professor and groundwater hydrologist in the University of Nebraska–Lincoln School of Natural Resources – Conservation and Survey Division and in the Department of Biological Systems Engineering. Gilmore studies Nebraska’s groundwater and surface water as valuable natural resources.
Groundwater is located underground, typically in large aquifers. It must be pumped out of the ground to use for human and animal consumption and for crop irrigation, Gilmore said. Much of Nebraska overlies one of the largest reserves of groundwater in the United States — the High Plains Aquifer, commonly referred to as the Ogallala Aquifer. The High Plains Aquifer underlies approximately 174,000 square miles in portions of eight states, from North Dakota to Texas.
“Nebraska is atop some of the deepest and largest reserves of groundwater,” Gilmore said.
Groundwater and surface water are interconnected, he said. The quality of one affects the quality of the other.
“One of the major advantages Nebraska has is this vast storage of groundwater below our land surface,” he said. “The uniqueness of such a vast water resource below Nebraska soil allows the opportunity for groundwater research, which in return can lead to a resilience in resources.”
What is an Aquifer?
Gilmore said an aquifer is simply pore spaces in sediment where groundwater can be stored and accessed.
“Sometimes, aquifers are pictured as an underground lake, which is not an accurate description,” he said.
In fact, there are small spaces between soil particles where water infiltrates, forced downward into the spaces by gravity. Beneath the soil, there are often deposits of permeable materials such as sand and gravel, which act as a giant sponge to soak up rainwater to recharge — or refill — the aquifer.
In many parts of Nebraska, there are “unconfined aquifers,” meaning that the water that infiltrates moves freely downward to the water table, which rises or falls during wet or dry periods.
Approximately 69% of the entire High Plains Aquifer volume underlies Nebraska, and a substantial portion of that lies under the Sandhills in central and western Nebraska, Gilmore said. The region plays a key role in replenishing the aquifer and keeping water levels stable.
Sandhills Spring Water
The Nebraska Sandhills covers a quarter of the state and is the largest contiguous area of grass-covered sand dunes in North America. According to Gilmore, the Nebraska Sandhills region has a profound impact on the state’s overall water culture and the resiliency of water resources.
Due to the nature of its sandy soil, there typically is little runoff, he said. Instead, the water infiltrates, or seeps into, the sandy soil. After precipitation in the Nebraska Sandhills, the land soaks up a portion of the water, but the rest infiltrates past the roots of the grasses and into the aquifer.
“The Nebraska Sandhills is a landscape that really kind of captures water without it quickly running off to streams and leaving the area,” Gilmore said. “That is a unique aspect in the Sandhills.”
Nebraska has over 79,000 miles of rivers, and in many areas streams are fed by groundwater, Gilmore said. For instance, groundwater-fed streams flow out of the Nebraska Sandhills into the Platte River, flowing eventually into the Missouri River. Groundwater originating from the Nebraska Sandhills travels a long distance and has a great impact, Gilmore explained. The value of Nebraska Sandhills groundwater is high because it is a steady resource that continually moves into streams and rivers.
“Looking back at the history of streamflow out of the Sandhills, you can see that it’s a very steady resource. If you look at streamflow data for more recent decades, there is even a slight increase in the flow out of the Sandhills,” Gilmore said.
In Nebraska, Natural Resources Districts (NRDs), the Conservation and Survey Division, the Nebraska Department of Natural Resources, and the U.S. Geological Survey all work together to use technology to measure groundwater and surface water levels, Gilmore said.
These agencies also use real-time wells, which is on-demand data transmission connected to a satellite for more detailed groundwater-level monitoring. Gilmore said data from real-time wells and transducers can update databases instantly to generate maps online. This information indicates how much groundwater is currently stored in the aquifer, and when compared to surface water levels, can indicate when groundwater is more likely to seep out of the aquifer and into streams.
Gudmundsen Sandhills Laboratory
Gilmore and his team use a university laboratory located in the heart of the Nebraska Sandhills, in Grant, Hooker and Cherry counties. The Gudmundsen Sandhills Laboratory location, which is used for beef research and other environmental studies, has groundwater-fed ditches, hay meadows and streams.
Gilmore said the laboratory is an excellent research location because it is located directly over the top of the thickest part of the Ogallala Aquifer. He is working to estimate the recharge rate of water in the Nebraska Sandhills in a more consistent way.
“In the Sandhills environment, the stream flow is derived largely from groundwater. It’s just a really accessible interface where you can get in the stream and sample groundwater as it actually seeps out into the stream,” he said.
Gilmore and his team of scientists take groundwater samples from the Gudmundsen Sandhills Laboratory and send them to the Water Sciences Laboratory on the university’s East Campus. Gilmore said the Water Sciences Laboratory is on the cusp of being able to estimate the age of groundwater by analyzing isotopes. Gilmore added that this is one of the few laboratories in the United States that is working on these kinds of innovations. Knowing the age of groundwater is key in determining contaminants it might contain, which determines the overall quality of the water.