The High Plains Aquifer

By Dr. Stephen R. Overmann

Southeast Missouri State University

Introduction

There is a great inland sea hidden beneath the fertile soils of the Midwest. These waters are so vast, stretching nearly from Canada to Mexico, that they have been called the sixth “Great Lake” of North America. This huge underground water resource is the High Plains or Ogallala Aquifer.

Superlatives abound in descriptions of this water resource. It is one of the largest aquifers in the world and one of the largest bodies of freshwater in the world. It is estimated to hold over one quadrillion gallons or three billion acre-feet of water. This volume of water would cover all of the 50 states in more than one and one-half feet of water. The High Plains Aquifer ranks among the United States’ greatest, though least known, natural resources.

The High Plains Aquifer underlies parts of eight states, stretching from South Dakota to Texas. The largest portions of the aquifer are found within Nebraska, Texas, and Kansas, with smaller portions found in Colorado, New Mexico, Oklahoma, South Dakota, and Wyoming.

The geologic deposits containing the aquifer were deposited about 10 million years ago. These deposits consist of gravel, sand, clay, and silt. The water-saturated portions of these deposits that form the aquifer range from 20 to more than 1,000 feet in thickness. This geological water can be considered “fossil water” because of its ancient age. Much of the water in this aquifer is the remains of melt water from glaciers of the last ice age. It is estimated that at least 6,000 years were required to fill the High Plains Aquifer.

The vast fossil water deposit of the High Plains Aquifer has been a critical natural resource in shaping the landscape and society of the modern American Midwest and is a key to the bountiful agricultural production of this region. However, the waters of the High Plains Aquifer are being exploited beyond the recharge rate of the aquifer.

History

Pioneers of the westward expansion crossed seemingly endless arid prairie grassland as they moved from Missouri toward the Rocky Mountains. The flat land or rolling hills were home to buffalo herds with few forests and rivers. Settlers of the region, accustomed to the more moist farming conditions of the eastern United States, struggled to eke out a living on the harsh, dry land. Agricultural production and the well-being of the inhabitants were at the mercy of the weather to provide life giving rains to the region. Throughout the 19th and early 20th centuries the High Plains remained a sparsely populated, impoverished region of small farms. Poor land management and unfavorable climatic conditions lead to the devastating Dust Bowl of the 1930s.

All of this changed in the 1940s, when mechanized pumping was introduced and people began to tap the great water reservoir of the aquifer. The formerly dry land flourished under abundant irrigation water from below ground. More and more wells were drilled and pumping capacity dramatically increased. Center-pivot irrigation was introduced, which resulted in huge, lush green circles of agricultural crops on the dry brownish landscape.

Large-scale, mechanized pumping of groundwater transformed the environment, the agricultural productivity, the society and culture, and the economy throughout the area of the High Plains Aquifer.

The marginal agricultural lands of the formerly dry prairies blossomed into some of the most productive agricultural areas in the world. Amber waves of grain on the High Plains form the nation’s primary grain belt region and are the breadbasket to America and much of the grain-hungry world. Along with the huge increase in agricultural production came economic prosperity, business and industry development, urban growth, and increased ethnic and cultural diversity.

Current Status

The water of the Ogallala Aquifer has become the underpinning of the agriculture-based economy of the High Plains. This economic success has come at the expense of declining water levels in the aquifer. Nearly 200,000 wells are withdrawing water from the this aquifer. Estimates are that withdrawal rates are 10 to 50 times greater than recharge rates. In some areas, the water table has dropped 100 to 200 feet as a result of overdrafting of the aquifer. Earlier in the century it was assumed that the groundwater-riches of the aquifer were endless, but by the 1980s it became clear that the High Plains Aquifer was being rapidly depleted.

Several approaches are being used to slow depletion of the aquifer. Water conservation programs have become commonplace. Agriculture, the primary user of water, has grown more efficient at water usage. Improvements in agricultural methods and technology include increased use of reduced tillage to retain soil moisture, precision application irrigation equipment, and adjusting irrigation practices to meet crop water needs and local weather conditions. A bitterly contentious approach has been regulatory actions by states to meter water withdrawal and place limits upon groundwater pumping. Some farmers of the region are opting to return to dry-land, non-irrigated agriculture. Yet another approach has been an increase in agricultural acreage enrolled in the Conservation Reserve Program.

In addition to major concerns about water quantity, there is growing concern over water quality. Infiltration of agricultural chemicals and excess nitrogen from fertilizers has resulted in groundwater pollution of parts of the High Plains Aquifer. In addition, toxic chemicals from industry and military sites are contaminating the aquifer.

The Future

The future of the High Plains Aquifer is uncertain. What is certain is that water withdrawal in excess of water recharge is not sustainable. It is also certain that declining usefulness of the aquifer as a water resource will have significant impacts on the environment, the people and culture, the economy, and the agricultural productivity of the High Plains.

One approach to the problems of the aquifer that is sorely needed is to achieve political and legal consensus on groundwater policy and management among all states that share the water resources of the aquifer. While a coherent regional approach is clearly needed, there is currently a patchwork quilt of laws, regulations, and policies that varies from state to state.

Impaction is a problem associated with excess water withdrawal from aquifers. As water is withdrawn, space is left in the porous strata, which subsides to reduce the potential future volume of the aquifer. Impaction has occurred in the High Plains region. Even if withdrawal rates can be reduced below recharge rates, the High Plains Aquifer will not be capable of holding as much water as in the past. Several possible scenarios for the future of the High Plains region have been proposed. One suggestion has been for the U.S. government to buy out many of the landowners in the region and allow the land to revert to its prior state of open prairie. This idea has been called “the buffalo commons” approach.

Another proposal suggests that efforts be made to preserve communities in areas where future water supplies are most secure and to abandon communities in areas where future water supplies are most in jeopardy. Agriculture is the largest user of the High Plains Aquifer, and it has been suggested that large-scale, irrigation-intensive agriculture shift toward smaller farms using little to no irrigation, with an emphasis on more sustainable approaches to food production.

There are highly ambitious visions to construct pipelines and/or canals to the High Plains from the Mississippi/Missouri Rivers, the Great Lakes, or water-rich areas of western Canada. Obviously, realization of such dreams would necessitate monumental engineering efforts, expenditure of tremendous economic assets, and widespread sociopolitical support and cooperation. There are pessimistic forecasts that foresee a return to the more arid conditions of the recent Dust Bowl era or more dramatically, a return to the prehistoric conditions that resulted in formation of the Nebraska Sand Hills.

Perhaps the largest uncertainty is the potential impact of global climate change. Current models suggest adverse impacts on agriculture of the Plains region. In addition, reduced precipitation in the Plains region, as predicted by some climate-change models, could reduce aquifer recharge and therefore exacerbate reduced groundwater storage in the High Plains Aquifer.

Connection to Environmental Science

· Chapter 7 (Water: Hydrologic Cycle and Human Use), Section 7.2 (“Hydrologic Cycle: Natural Cycle, Human Impacts, pages 181–189) discusses the hydrologic cycle, groundwater, and how human activities affect the cycle.Section 7.3 (“Water: A Resource to Manage, a Threat to Control", subsection, “Groundwater,” pages 194–195) describes the general problem of overdrawing water and the specific issue of the High Plains or Ogallala Aquifer. This chapter also includes a map (Figure 7-16 on page 195) illustrating the geographic extent of the aquifer and photographs of the center-pivot irrigation system.

· Chapter 9 (The Production and Distribution of Food) describes the impact of food production on the environment. The problems associated with the High Plains Aquifer are intimately tied to agricultural production of food, water pollution (Chapter 17), and economic and policy issues (Chapter 22).

· Chapter 20 (The Atmosphere: Climate, Climate Change, and Ozone Depletion) discusses climate and precipitation patterns across North America. The long-term outlook for the aquifer and the High Plains will be related to future climate and precipitation patterns in the Midwest.

Hyperlinks

Ground Water Primer: Hydrogeology

This site provides simple, straightforward text and illustrations to provide an basic introduction to groundwater.

Ogallala Aquifer

This brief page from the North Plains Groundwater District of Texas describes the general geology, stratigraphy, and hydrology of the Ogallala Formation in Texas.

Impact of Senate Bill 1 on the Depletion of the Ogallala Aquifer

This article provides background information and describes legislation passed by the Texas Senate in 1997 to better manage water withdrawal from the aquifer.

High Plains Aquifer

This is an informative and well-illustrated section of the Ground Water Atlas of the United States from the U.S. Geological Survey.

High Plains Regional Ground Water (HPGW) Study

This part of the National Water Quality Assessment (NAWQA) Program focuses on the High Plains Aquifer. The page has many links to related Websites.

Water Resources of the United States

This is arguably the most comprehensive Website on the topic. A drop-down menu allows access to Websites for water resources of each state, including those of the High Plains. The site has a search engine that returns hundreds of hits for the Ogallala or High Plains Aquifer.

High Plains Aquifer Information Network

This Website presents reports and extensive data from the Kansas Geological Survey.

Water-Level Changes in the High Plains Aquifer, Predevelopment to 2001, 1999 to 2000, and 2000 to 2001

This informative and well-illustrated fact sheet from the U.S. Geological Survey is available as a Web page or as a PDF file.

Surviving the Dustbowl

The Public Broadcasting Service produced this video documentary and Web page as part of the PBS series American Experience.

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