• Agriculture from South Dakota to Texas is has been supported by irrigation from the High Plains aquifer for nearly a century
• The aquifer is an open system mainly developed in shallow sands and gravels
• Much of the water originally entered the aquifer during a wetter climate during the last ice age
• Groundwater overdraft occurs when water is extracted from the aquifer more rapidly than it can be recharged

recipitation drops to less than 50 cm per year (20 inches) over much of the western U.S. The paradox is that this semi-arid region is the source of much of our produce and grain crops. Kansas, the wheat state, is too dry to produce wheat unless water is added by irrigation. Irrigation waters for many of the Great Plains states (North Dakota south to Texas) are taken from a single massive aquifer, the High Plains aquifer.

The High Plains aquifer underlies much of the Great Plains including parts of South Dakota, Nebraska, Wyoming, Colorado, Kansas, Oklahoma, New Mexico, and Texas.

The High Plains aquifer stretches from South Dakota to west Texas and has been a source for irrigation water since the early 1900’s. Approximately 170,000 wells draw water from the aquifer that has brought prosperity to an area described by Major Stephen Long in 1819 as "almost wholly unfit for cultivation and . . . uninhabited by people depending upon agriculture for their subsistence." The aquifer covers an area of 480,000 square kilometers, making it the largest area of irrigation-sustained cropland in the world.

Click on the image on the left to view a map of the aquifer showing variations in precipitation within the aquifer. (http://www-ne.cr.usgs.gov/highplains/ normprec.html)

The sand and gravel aquifer is unconfined (open) and is recharged by water infiltrating from above. Limited recharge occurs from precipitation and stream outflow. The aquifer's saturated zone is up to 425 m thick but aquifer dimensions vary along its length. It is always relatively shallow; the water table is typically less than 100 meters deep. The aquifer contains more than 3.3 billion acre-feet of water (1 acre-foot = ~326,000 gallons), more than the volume of water in Lake Huron.

Unfortunately for agricultural interests in the Great Plains the aquifer contains "fossil" water, the product of a wetter ancient climate associated with the end of the last ice age. There is no sufficient contemporary source for water to recharge the whole aquifer although substantial recharge does occur in some areas from streams (e.g. Platte River, Nebraska) and from irrigation projects supplied with surface waters.

Water table in High Plains aquifer has risen along stretches of the Platte River in central Nebraska in contrast to a regional decrease in water table elevation. Click on the red square to view satellite images of Platte River and irrigated agriculture.

The history of water use in the aquifer can be illustrated by reference to a single well in southwest Kansas. The hydrograph (graph of water use) from the well illustrates three periods of groundwater withdrawal.

Hydrograph of a water well from southwest Kansas illustrating the history of withdrawals from this section of the High Plains aquifer.

1. 1930-1950: water table depth remained relatively constant as withdrawal was limited to a few wells and kept pace with recharge;
2. 1950-1985: water table depth declined by 40 meters as increasing numbers of wells extracted water from the aquifer. Irrigated acreage in Kansas climbed from less than half a million acres in 1959 to nearly 2 million acres in 1978.
3. 1985 - present: decline in water table depth slowed considerably due to decreasing discharge attributed to heavier than normal rains, increased energy costs for pumping, and improved irrigation technology that consumed less water.

Groundwater from the aquifer was first widely used in the 1930's in Texas. Subsequently approximately 11% of the total groundwater supply has been extracted. The most significant declines in the aquifer have occurred in southwest Kansas and the Texas Panhandle and have been matched by population migrations from rural counties.

Maps of ground water level changes in the High Plains Aquifer up to 1980 (left) and from 1980-1994 (right). Click on the maps to view full size images. Maps courtesy of USGS High Plains aquifer website.

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Over the life of the aquifer the water table dropped 70 meters in parts of the Texas Panhandle. Western Kansas has consumed 38% of the groundwater in the underlying aquifer. Both are examples of groundwater overdraft - where groundwater extraction occurs more rapidly than recharge. In contrast, Nebraska is blessed with more than 60% of the aquifer underlying the state, relatively good recharge from the Platte River, and less intensive groundwater consumption. Groundwater supplies in Nebraska are sufficient to last for centuries at current consumption rates.