Understanding the Hydrogeology Beneath the Surface
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Understanding the hidden underground systems that sustain our region's water resources
Beneath the southern Nebraska Panhandle lies one of North America's most vital groundwater treasures — the High Plains Aquifer. The North Platte and South Platte Natural Resources Districts sit directly atop this legendary system. Ancient geologic formations, river valleys, and human ingenuity combine to create a complex yet fascinating hydrogeologic story.
An expansive and voluminous aquifer located in both districts is the Tertiary-aged Ogallala Group Aquifer — universally known as the Ogallala Aquifer. It dominates the South (Cheyenne) and North (Alliance) Tablelands and serves as the core of the High Plains Aquifer system.
Interspersed and often connected to the Ogallala are younger Arikaree Group sandstones (the Arikaree Aquifer), particularly noticeable in northern Kimball County, plus older sand and gravel layers within the Brule Formation. In the northeastern North Tablelands, the beautiful wind-deposited Quaternary sands of the Nebraska Sandhills overlie these formations.
Where these layers are in direct contact, they typically function as one interconnected system, allowing water to move between them. This interconnectedness provides reliable ground water for dryland farming and ranching across the high plains.
The Ogallala Aquifer is often called the “breadbasket aquifer” because it underlies one of the most productive agricultural regions in the world. Much of the irrigation water that grows corn, wheat, and cattle across the Great Plains comes from this single formation. Without it, the economy and food production of the Nebraska Panhandle would look dramatically different.
Interpreted base of the High Plains Aquifer (including the Ogallala Aquifer) across the Tablelands of the southern Nebraska Panhandle. Source: 2020 Hydrogeology of Western Nebraska study.
The standout in the NPNRD is the Quaternary Alluvial Aquifer along the North Platte River — the district’s largest and most productive water source. Closely partnered with it is the Brule Formation Fracture Aquifer, a Tertiary-aged system that often behaves like an extension of the alluvial aquifer.
Alluvial aquifers form from river-deposited sand and gravel — excellent water storers because of their high permeability.
What makes the North Platte Valley extraordinary is the scale of human-enhanced recharge. The 23 surface water districts and canal companies deliver an average of 600,000 acre-feet of water per year through canal leakage and irrigation inefficiencies.
This massive annual recharge has essentially created and sustains the thick, highly productive aquifer system throughout the North Platte Valley.
Canal leakage and irrigation “losses” are actually a blessing for ground water! What might seem inefficient on the surface becomes vital recharge underground. This engineered recharge helps maintain water levels and supports wells even during dry years.
Interpreted shaded relief of the saturated thickness of the combined Quaternary Alluvial (along the North Platte River), Brule Formation Fracture (in the North Platte River and Pumkin Creek Valleys), and Ogallala Aquifers. Blue colors show thick, water-rich areas while yellow, orange, and red colors show areas with less saturated material.
In the SPNRD, the South Platte River features a prominent Quaternary Alluvial Aquifer formed by river sediments, with secondary contributions from the Brule Fracture Aquifer. This corridor forms another key part of the High Plains Aquifer.
Along Lodgepole Creek, the hydrogeology is especially dynamic. The aquifer consists mainly of the Brule Formation Fracture Aquifer mixed with Quaternary alluvial deposits. The creek has eroded through much of the overlying Arikaree and Ogallala material. Water entering or flowing along Lodgepole Creek from west of Bushnell recharges the High Plains Aquifer near Potter and Dix. Between Kimball and Brownson, the underlying aquifer is primarily Ogallala Group material or reworked Ogallala deposits.
Interpreted saturated thickness map for the South Platte NRD including the South Platte River and Lodgepole Creek areas in the SPNRD.
The Brule Formation Fracture Aquifer stretches across both districts and ranks among the most unique features in the southern Nebraska Panhandle. Although smaller than the Ogallala, it serves as a primary water source for many wells along Pumpkin and Lodgepole Creeks and parts of the North and South Platte River Valleys.
What makes fracture aquifers special? Unlike porous sand and gravel aquifers, fracture aquifers store and transmit water through cracks in otherwise low-permeability rock (in this case, the Brule Formation). Water moves quickly through these fractures, making the system highly responsive to rain.
The full extent of the fracture network is still being mapped. Recent studies have advanced our understanding by analyzing driller logs and geologic records from production and monitoring wells.
Geologists still don’t fully understand how these fractures formed, but their shallow depth and rapid response to rain suggest they are part of an extensive, interconnected network connected to the surface. More work is needed to map and understand how the fracture aquifer functions which helps districts with their water management policies and how wells impact this important aquifer.
NPNRD Brule Fracture Aquifer Well Locations
A Game-Changing Update for Better Water Management
From 2017 through 2020, a powerhouse team from Adaptive Resources, Inc. and the University of Nebraska–Lincoln Conservation and Survey Division teamed up for an exciting mission: to dramatically improve our understanding of the High Plains Aquifer across the southern Nebraska Panhandle. This collaborative project, called the Hydrogeology of Western Nebraska, was funded by the Nebraska Environmental Trust and the South Platte, North Platte, and Twin Platte Natural Resources Districts. It was built specifically to give the Western Water Use Management Modeling (WWUMM) effort the most accurate foundation possible.
The team scanned, digitized, and carefully interpreted an astonishing 15,421 oil and gas geophysical well logs from 13 counties. They combined these with data from water well driller logs, monitor well logs from the Conservation and Survey Division, and the U.S. Geological Survey airborne electromagnetic (AEM) surveys. Using specialized software, geologists examined key signals like resistivity (how well rock conducts electricity) and the spontaneous potential curve (which reveals permeability) to pinpoint exactly where the aquifer ends and the underlying layers begin.
To give you a sense of the enormous scale of this effort, here are three key maps from the study that show exactly what data went into the final interpretation:
This map shows the full scope of the project — the locations of all 15,421 oil and gas geophysical logs, CSD test holes, and Natural Resources District monitor wells that the team reviewed and evaluated.
NOGCC Oil and Gas Well, CSD Test Hole, and Natural Resources District Monitor Well Locations
Not every well provided usable data. Map 2 highlights the specific wells and logs where useful geophysical data existed and were ultimately used to create the final base-of-aquifer interpretation.
Locations of the NOGCC Oil and Gas Wells, CSD Test Holes, and Natural Resources District Monitor Well Geophysical Logs used in this study
This map pulls everything together — it shows all the information sources that were synthesized to create the refined base of the High Plains Aquifer surface.
Information Used to Create the Base of the High Plains Aquifer Surface Interpretation
Every single interpretation went through multiple rounds of in-depth expert review by teams of geologists. Picks were labeled “confident” or “questionable,” and structural cross sections helped double-check everything. The result? A much clearer, more detailed picture of the aquifer’s base — especially in the complex southern part of the WWUMM area (Kimball, Cheyenne, Deuel, and southern portions of Banner, Morrill, and Garden counties).
Geophysical logs are like underground X-rays. Oil and gas wells are logged with instruments that measure the electrical properties of the rock. Aquifer materials (sand, gravel, sandstone) show high resistivity and clear deflections on the logs, making them easy to spot compared to tight clays and shales. This high-tech detective work let the team map the aquifer’s base with far greater confidence than ever before.
This was an actual geophysical log using in the interpretation with the resistivity curve (which indicates material type) and the spontaneous potential (SP) curve (which indicates permeability). The aquifers and formations are highlighed in different colors.
One of the most fascinating (and tricky) parts of the study involved interpretation complexities. Oil and gas companies set steel surface casing early in drilling to protect fresh ground water before going deeper. Because the upper portion of the hole is cased off, it is rarely logged — leaving a “blind spot” right where shallow secondary aquifers or paleochannel deposits might sit.
This challenge is especially pronounced in Kimball and Cheyenne counties, where significant sand and gravel lenses were deposited in ancient paleochannels within the Brule Formation. Below the casing, geologists sometimes see aquifer material that could be interpreted in more than one way. The study team used multiple expert reviews, structural cross sections, and supporting data (including chemical analyses from earlier work) to sort through these possibilities.
The same geophysical log can support different geologic interpretations depending on how the geologist connects the aquifer materials. These four figures show the range of possibilities the team considered.
Ogallala Channel Sand Interpretation (Figure 2 from the study)
The study produced a refined contour map of the base of the High Plains Aquifer surface that captures deep paleochannels and the sometimes-tricky connections between the main Ogallala aquifer and certain Brule Formation sands and gravels. It also generated detailed geologic cross sections that reveal the three-dimensional architecture of the aquifer system.
These advances make our regional ground water models more reliable and give water managers the high-quality data they need for ground water planning and management across the southern Nebraska Panhandle.
The study created numerous detailed cross sections that slice through the subsurface like a giant layer cake. They beautifully illustrate the varying thickness of the aquifer, ancient river channels, and the relationships between different geologic layers.
Click any cross section below to open a large, navigable viewer. Use the arrows to cycle through all five detailed views.
SECTION 1
SECTION 2A
SECTION 2B
SECTION 3
SECTION 4
Cross Sections from the 2020 Hydrogeology of Western Nebraska Project Completion Report
To bring everything together, the study produced one of its most important deliverables: the Interpreted Surface of the Base of the High Plains Aquifer, Southern Panhandle of Nebraska. This stunning contour map shows the elevation of the aquifer’s base across the entire study area with 50-foot contour intervals and a striking color scale — from deep reds and oranges (higher elevations) to vibrant greens (lower elevations). It clearly highlights the dramatic paleochannels and the refined understanding of where the aquifer is thickest and most productive.
The Landmark Interpreted Surface of the Base of the High Plains Aquifer (Map 5 from the 2020 Hydrogeology of Western Nebraska Project Completion Report, Appendix A). This is the capstone deliverable that powers the WWUMM models.
This landmark 2020 study represents a major leap forward in our hydrogeologic knowledge and provides a much stronger and more detailed scientific foundation that powers today’s Western Water Use Management Modeling efforts. It’s a perfect example of how cutting-edge science, collaboration, and curiosity continue to help us protect and manage this precious underground treasure for generations to come.
The hydrogeology of the Nebraska Panhandle is a story of ancient geology meeting modern science — and the foundation for data-driven water management in the years ahead.