The Ogallala Aquifer

Underlying portions of South Dakota, Wyoming, Nebraska, Colorado, Kansas, Oklahoma, New Mexico, and Texas, the Ogallala Aquifer (High Plains) is the largest in the country and arguably the most important. It supplies freshwater for millions of acres of irrigated agriculture land and to millions of Americans for domestic use.

84% of Nebraska's land area falls within the Ogallala basin, equating to roughly 77,352 square miles (Dang et al., 2020). Research has shown that since the commencement of groundwater extraction for irrigation purposes in the 1950s, many areas have experienced a loss of more than 250 feet of groundwater levels (McGuire, 2014). The rate of groundwater withdrawal exceeding the rate of recharge has been an area of concern for many years now, with potential consequences resulting in crop yield declines, drought conditions, and even land subsidence.

The primary goal of this study is to utilize geographic information systems (GIS) technologies to map Ogallala groundwater level fluctuations across the state of Nebraska and in three chosen counties of study - Boone County, Cheyenne County, and Dundy County. These three counties were chosen due to the availability of groundwater level data, varying geographic locations, and evidence of unique trends depicted from other research. Various interpolation methods are employed to compare against one another and calculate differences in groundwater levels from 2000 to 2023. The interpolation methods used in this study include Empirical Bayesian Kriging, Inverse Distance Weighted, and Ordinary Kriging.

Ideally, the findings uncovered in this study can equip stakeholders of the Ogallala Aquifer region with an increased understanding of the trends and current state of the aquifer, and what measures and policies can be taken to improve the sustainable use of the resource. Additionally, this study can assist other research and public understanding through offering unique perspectives and sharing the findings on an engaging and interactive platform.

It should be stressed that the maps presented in this study are represented at certain scales and with limited resolutions. Therefore, they are valuable at providing an overview of groundwater levels and trends, but limited in providing precise locations, extents of gains and losses, and magnitudes.

First, statewide groundwater levels within the Ogallala were calculated and analyzed via Empirical Bayesian Kriging. For more information on EBK, go  here .

From 2000 to 2023, most areas have remained fairly stable with a general trend of slightly decreasing groundwater levels. There are several large areas for both significant increases and decreases in levels. Notably, much of the panhandle region of the state has experienced gaining levels, with some areas increasing over 300 feet. On the other hand, especially throughout the southern regions of the state, areas have declining levels of 150 feet in some cases.

Groundwater level changes from 2022 to 2023 are much more stable, with most of the state experiencing minimal changes. A few locations stand out that show significant declines, recording nearly 330 feet of groundwater level decreases. In locations where levels have risen, gains of approximately 200 feet have recharged the aquifer.

These results show us how dynamic groundwater levels are from year to year and throughout the decades. Many factors play into the status of groundwater levels in any given area, which highlights the need for continual monitoring and reporting of these conditions as well as more specific, smaller study areas to analyze finer details and variabilities.

Boone County groundwater levels were calculated and analyzed via Inverse Distance Weighted and Ordinary Kriging. For more information on IDW, go  here . For more information on Kriging, go  here .

The difference in 2000 values between IDW and Kriging are minimal, with a few feet difference in the calculated statistics.

The 2023 results are where things get a little interesting between IDW and Kriging. This is where the sharper boundaries of Kriging interpolations versus the smoothed boundaries of IDW can start to be seen. In the calculation of Kriging, the points of groundwater wells are pronounced and do not estimate surrounding areas as well as IDW.

For this reason, the IDW values are used in this study to caculate differences for all three counties. The difference in groundwater levels between 2000 and 2023 for Boone County reveal that there is one large area and one small area, both near the northeastern portion of the County, that have increased levels. The greatest amount of gain is approximately 83 feet. Conversely, there are also large areas of decreased levels, where declines have reached nearly 100 feet.

Cheyenne County groundwater levels were calculated and analyzed via Inverse Distance Weighted and Ordinary Kriging. For more information on IDW, go  here . For more information on Kriging, go  here .

The results of 2000 and 2023 values between IDW and Kriging are fairly consistent in Cheyenne County. Again, the sharper boundaries are evident in the Kriging map compared to the IDW map. Some differences between the two are at most 15-20 feet.

The difference in groundwater levels between 2000 and 2023 for Cheyenne County reveal that several significant portions of the County have increasing groundwater levels, with some less pronounced areas that have decreased. The greatest amount of gain is approximately 150 feet in the central and northeastern portions of the County. The greatest decreases are approximately 30 feet.

Dundy County groundwater levels were calculated and analyzed via Inverse Distance Weighted and Ordinary Kriging. For more information on IDW, go  here . For more information on Kriging, go  here .

Similar to the previous results, there are noticeable but minimal differences between the IDW and Kriging results in Dundy County. While on a large scale these minor differences may not seem like much, the discrepancy of even 15 feet can mean a lot for irrigated crops.

The difference in groundwater levels between 2000 and 2023 for Dundy County reveal that there is one very large and one small area that have experienced significant declines, with the rest of the County either with minimal changes or slight increases. The greatest amount of decrease is approximately 135 feet in the eastern portion of the County. The greatest amount of gain is approximately 65 feet, coincidentally not very far from the largest declines.

The findings of this study reveal significant temporal and spatial variations in groundwater levels across the study area. While some regions exhibit minimal changes, othes exhibit increases or declines in groundwater levels, highlighting the complex and dynamic nature of hydrological processes and withdrawal rates throughout the Ogallala. These findings underscore the importance of informed decision-making and proactive interventions aimed at conserving the integrity and longevity of this freshwater resource.

For stakeholders involved in water resource management and agricultural practices, it is recommended to prioritize the implementation of targeted conservation measures and sustainable groundwater extraction practices. This study only covered three counties, but the same methodology and process can be applied to every county that lies within the Ogallala, and other vital aquifers, to highlight specific areas that might require intensive conservation interventions. By leveraging the insights gathered from this study, decision-makers can develop evidence-based policies and strategies to mitigate groundwater depletion and ensure the long-term viability of the Ogallala Aquifer.

It is also encouraged to continue future research efforts to build on these and other findings and explore factors that influence groundwater dynamics, such as land use changes, climate variabilities, and aquifer recharge mechanisms. The adoption of a mutlidisciplinary approach and incorporating advanced artificial intelligence modeling techniques, researchers can enhance the understanding of hydrological processes and contribute to the development of innovative solutions for water resource management challenges.

If you would like to learn more about the state of the Ogallala Aquifer, here is a list of resources that will educate and, possibly, inspire you to get involved for improving the management of one of the nation's greatest assets.