Because hydrologic systems connect groundwater and surface water, groundwater pumping can also affect available water in rivers, streams, and springs.
Responsible aquifer management requires an understanding of the interrelationships among inputs and outputs of water in the aquifer. The goal of this project is to develop a scaling analysis to estimate water table conditions for potential basin-wide water development. The results of the project will determine the conditions under which drastic drops in the water table can occur.
The main misconception about groundwater pumping is that as long as the amount of water pumped from a basin doesn’t exceed recharge from precipitation, the basin can be sustainably managed. “It would seem to make sense because the amount of water in the aquifer will increase over time if annual pumping is less than what is added through recharge,” says Dr. Clay Cooper, who is the principal investigator for the project. “However, increasing the amount of water that is withdrawn can actually increase the amount of water available if recharge is induced from other sources of water on the land surface.” Induced recharge pulls water from surrounding surface water resources. This means that even though it refills the aquifer, the surface water sources from which the water is withdrawn suffer. “Some aquifers can be pumped so much that water is eventually withdrawn from distant rivers, streams, and springs,” Cooper adds, “which can significantly affect valuable surface water resources, particularly in arid and semiarid regions.”
This project will evaluate what happens during groundwater withdrawal and how it affects the stability of groundwater basins. “Groundwater pumping lowers the water table in unconfined aquifers and drops the pressure in confined aquifers until a new steady state is reached, which stabilizes the water level or pressure in the aquifer,” Cooper explains. “This is how aquifers are supposed to function. However, my hypothesis is that under certain scenarios, excessive pumping can result in a drastic water table decline in unconfined aquifers, and this bifurcation in water level could result in groundwater mining.” Cooper developed the idea for this project based on papers by USGS hydrologists Charles Theis, John Bredehoeft, Leonard Konikow, and William Alley, as well as Allan Freeze from the University of British Columbia. The research conducted for this project will help determine the conditions that might lead to significant bifurcating behavior or unstable groundwater levels.
This research is important for managing groundwater resources in Nevada because it will help water managers understand the available water in aquifers and how it interacts with surface water resources. “Overall, groundwater in Nevada is managed far better than many other states and has been for over one hundred years,” Cooper explains. “However, the competing water needs for mining and irrigation, as well as municipal, industrial, and recreational uses make managing water resources a complex issue. I hope that this work results in an easy-to-use tool that can help with basin management.”