What is the Ogallala Aquifer?

Like a great lake hidden underground, the Ogallala Aquifer is a shallow water table aquifer surrounded by sand, silt, clay, and gravel located beneath the Great Plains in the United States. One of the world's largest aquifers, it underlies an area of approximately 174,000 sq. miles in portions of eight states (South Dakota, Nebraska, Wyoming, Colorado, Kansas, Oklahoma, New Mexico, and Texas). It was named in 1898 by geologist N. H. Darton, after the town of Ogallala, Nebraska. The aquifer is part of the High Plains Aquifer System, and resides in the principal geologic unit underlying 80% of the High Plains.

Before the rapid growth of irrigation for agricultural purposes started after World War II, the aquifer contained roughly a quadrillion gallons of water, enough to fill Lake Erie more than eight times. In the 1950s new pumping methods and irrigation systems enabled removal of significant quantities of Ogallala water. Since then, farmers have managed to suck up over half a Lake Erie’s worth — some estimates are closer to a whole Lake Erie’s worth — of water from the aquifer.

The explosive growth in irrigated acres transformed the High Plains from a vast expanse of semiarid prairie into the “breadbasket of the world,” giving birth to the enormous green-circle mosaic that blankets this land today. Today about 27% of the irrigated land in the entire United States lies over the aquifer, which yields about 30% of the ground water used for irrigation in the United States.

Though the Ogallala is far from dry, the decline in water levels presents a significant threat. In many places, the aquifer has already dropped to a level where irrigation is no longer feasible. In most parts of the Ogallala, the water removed far exceeds that which is returned. Without some kind of change, the ability of farmers to use Ogallala water will cease, putting 10 percent of all U.S. crop value at risk.

Sustaining an aquifer requires recharge from above. The rate at which recharge water enters the aquifer is limited by several factors. Much of the plains region is semiarid, with steady winds that hasten evaporation of surface water and precipitation. In many locations, the aquifer is overlaid with a shallow layer of caliche that is practically impermeable. This limits the amount of water able to recharge the aquifer from the land surface.

However, the soil of some wetlands is different and not lined with caliche, making these the areas where the aquifer can recharge. Recharge in the aquifer ranges from 0.024 inches per year in parts of West Texas and New Mexico to 6 inches per year in south-central Kansas.

The destruction of wetlands by farmers and development decreases the available recharge area. The prevalence of the caliche is partly due to the ready evaporation of soil moisture and the semiarid climate. The aridity increases the amount of evaporation, which in turn increases the amount of caliche in the soil. Both mechanisms reduce the amount of recharge water that reaches the water table.

The aquifer system supplies drinking water to 82% of the 2.3 million people who live within the boundaries of the High Plains area. Once it has been depleted, the aquifer will take over 6,000 years to replenish naturally through rainfall. That’s why we need to make efforts to restore wetlands and increase the recharge in other ways.

One possibility of a brighter future for the Ogallala comes from an unlikely source: climate change. The most recent National Climate Assessment suggests that future rainfall will occur in briefer, more intense bursts. This would result in more rapid runoffs toward wetlands, increasing the recharge.

Jerry Lincecum is a retired Austin College professor who now teaches classes for older adults who want to write their life stories. He welcomes your reminiscences on any subject: jlincecum@me.com