By Dave Ostdiek, Communications Associate
UNL Panhandle Research and Extension Center
As a growing population competes for available freshwater supplies, depletion of groundwater aquifers will be a growing challenge to water policy managers in the United States. Adopting policies to address this issue is a matter of understanding the causes and the local hydrology, then choosing a policy that fits water-management goals.
These are some of the lessons that emerge from a recent issue paper published by a national science policy group. The paper is based partly on experience and expertise from western Nebraska. It highlights a case study of what happened in the Panhandle when over-development caused aquifer depletion along a stream.
Steve Sibray, hydrogeologist with the UNL Conservation and Survey Division based at the Panhandle Research and Extension Center in Scottsbluff, is one of seven authors of the paper titled “Aquifer Depletion and Potential Impacts on Long-term Irrigated Agricultural Productivity.”
The article is Issue Paper 63 for CAST, the Council for Agricultural Science and Technology (http://www.cast-science.org/).
The paper is available on the CAST website, and also has been presented to a number of key audiences around the nation, including congressional staffers and Farm Bureau officials, according to Sibray. Additional presentations are planned.
The 20-page paper reviews the causes and consequences of groundwater depletion, focusing on impacts to agriculture as the largest sector of groundwater use.
“This understanding can aid in developing effective policies and practices for groundwater development, use, and management,” the paper states.
CAST is a nonprofit organization composed of scientific societies and individual, student, company, nonprofit, and associate society members. The organization’s primary work, according to its website, is publishing task-force reports, commentary papers, special publications, and issue papers written by scientists, “to assemble, interpret, and communicate credible, balanced, science-based information to policymakers, the media, the private sector, and the public.”
The aquifer depletion paper reviews the basic science of groundwater and discusses the consequences of depleting aquifers, including reduced flow to connected streams and rivers; loss of productivity of wells; subsidence of land and ground failure; and degradation of groundwater quality.
Approaches to mitigating these consequences are discussed, including ag management and policy and institutional approaches.
Sibray helped write a number of sections in the paper, but his primary role was writing a case study on Pumpkin Creek, a basin in western Nebraska (Banner and Morrill counties), just south of Scottsbluff, where he has been involved in research projects for more than 20 years.
Sibray was invited to help write the article by a former Nebraskan who is also familiar with the area. David Baltensperger, head of the Department of Soil and Crop Scientists at Texas A&M University, was formerly based at the Panhandle Research and Extension Center as an alternative crops breeding specialist. Baltensperger is CAST liaison on the article.
Sibray also cowrote sections that discuss depleting aquifers and the relationships between aquifers and streams. He said the article is a broad overview of the impact of overdevelopment on aquifer depletion and streamflow in the United States.
The most important lesson from Pumpkin Creek is that “… where groundwater and surface water are scarce and hydrologically connected, groundwater pumping will degrade and possibly eliminate surface water flows and severely impair the ability of senior water users to receive water …”
Another lesson is that, contrary to common belief, there is not a sustainable rate of groundwater pumping that is tied to aquifer recharge.
Signs that the aquifer was overdeveloped appeared first in streamflows in Pumpkin Creek, not in declining water tables: “There were no noticeable groundwater level declines until the surface water was completely depleted because the surface water in Pumpkin Creek replenished water extracted from the alluvial aquifer.” The impacts on streamflow happened quickly because the wells were close to the creek and the aquifer had a high hydraulic conductivity.
The policy implications are not simple, and not necessarily obvious, according to Sibray’s conclusions.
“In contrast to a simple concept of a single ‘sustainable’ pumping rate policy, there is a range of groundwater pumping policy options depending on the desired flow in Pumpkin Creek.”
Because the aquifer along Pumpkin Creek is shallow and variable, the current allocation puts the regulatory burden on the most productive wells. Policymakers who want to increase flows in the creek must choose between lowering water allocations or retiring marginal acres as the most effective and economic step.
Sibray said Pumpkin Creek is an illustration of a concept known as the tragedy of the commons. When there is a shared resource (the original example was an unfenced pasture), the resource is likely to be over-used if individual users act in their self-interest.
Sibray suggested that overdevelopment is part of the cause of aquifer depletions in Pumpkin Creek basin, and retiring marginal irrigated acres to reduce the overall development would have a positive impact.
Outside of Pumpkin Creek, the paper has lessons for broader attempts at groundwater policy in western Nebraska and elsewhere, Sibray said.
Aquifer depletion is an increasing problem. The western states, from the Great Plains to the West Coast, were the first to experience it, but today there are concerns elsewhere in the nation as well.
In Nebraska and other places, there are concerns about aquifer depletion harming future agricultural production, as well as stream flows. In some areas cities depend on aquifers for municipal and industrial uses, so depletion will affect urban uses. And urban water use will increasingly compete with agriculture for groundwater.
In Nebraska, well pumping has caused both aquifer depletion, in areas like Box Butte County, the southern Panhandle, and the Republican River basin, but also streamflow depletion, in areas such as Pumpkin Creek and the North Platte River basin.
One lesson in the article, according to Sibray, is that there are ways to increase water-use efficiency, but efficiency is not always the answer. Sometimes it would be more effective to address the over-development. In parts of the Platte Basin, one part of the solution might be increasing recharge via irrigation canals when excess water is available.
The article recommends that several factors be considered in efforts to mitigate or reverse impacts from groundwater depletion:
- Growing population will increase competition for food and water, and the heightened stress on water resources will increase reliance on groundwater.
- This will continue to put groundwater at risk of depletion, resulting in declines in water tables, decreased well yields, and shallower wells going dry.
- In arid areas, where aquifers rely on recharge from seepage from irrigation systems, groundwater depletions will be made worse by increased efficiency in water delivery and irrigation systems.
- Long-term consequences of groundwater depletion must be considered, including lower flows to streams, springs, wetlands and other surface water; shifting or subsidence of land; and lower water quality.
- The article concludes that groundwater depletion can be mitigated through a combination of water-management policies aimed at either increasing recharge or decreasing groundwater demand through more efficient irrigation or conversion of irrigation to other types of ag systems.