Ecology And Environment

Depletion of the Ogallala Aquifer



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Ground water is one of the United State's most important natural recourses. Approximately 40 percent of the water used by the public come from ground water, and 30 to 40 percent of agricultural water in the United States is supplied by ground water. The Ogallala aquifer is a uniquely important source of ground water. Over half the irrigated land in this country is fed by the Ogallala aquifer. The problem is, the aquifer is being depleted faster than it can replenish itself.

The Ogallala aquifer covers about 225,000 square miles, underlying eight states, making it one of the largest aquifer systems in the world. Farms and cities in South Dakota, Nebraska, Wyoming, Colorado, Kansas, New Mexico and Texas depend on the Ogallala for survival.

The Ogallala was once an expansive alluvial stretching eastward from the Rocky Mountains. As the gigantic mountains eroded to the size we see today, porous deposits of rock and gravel were washed down. The climate was different then, and gradually, the plain filled with water, like a giant sponge. When the climate changed, the rains grew less, glaciers retreated, and the erosion of the mountains slowed down. Now the rivers in the area began to cut down into the ground faster than it could than it could be deposited and cut off the alluvium from the runoff water from the Rocky Mountains, it's main source of recharge. The drier climate also hardened the surface of the plain, making a waterproof cover for the alluvium. Now, from this ancient formation, the water drawn is about three million years old.

The aquifer was discovered in 1899, and over the last 100 years, has been used extensively, mainly for irrigation of crops. With a low recharge rate due to the fact that it is cut off to most of the recharge means, the aquifer is currently losing over 1 foot per year. The climate plays a large part in the low recharge rate. The average rainfall varies across the aquifers great expanse, but a good example can be seen in Lubbock, Texas. In Lubbock, the average rainfall is 18 inches per year. The low rainfall is bad enough, but add in the semi-arid climate and persistent winds, and the evaporation rate in Lubbock is approximately 80 inches per year. Studies have shown that the natural recharge rate is somewhere between .35 and 3.24 inches per acre, in a year.

Ignorance and inefficient irrigation systems played a large part in the early depletion of the Ogallala. It wasn't until the 1950's, that people began to even suspect that the water supply might be limited. By that time 350 billion gallons of water per year was being pumped out in Texas alone. Open ditches were the primary method of transporting water from the wells to the fields, resulting in ten to thirty percent water loss per 1,000 feet of ditch. The high-pressure, hand-moved sprinklers used to irrigate the fields wasted up to fifty percent of what was left.
Advances in technology have helped reduce the amount of water pumped out of the ground in order to irrigate crops. Underground pipelines now transport water to the points of irrigation, eliminating evaporation loss during transport. In Texas, more than 10,000 miles of underground pipelines are in place.

More efficient sprinklers have helped to achieve a high level of water conservation. Low-pressure sprinklers with the heads closer to the ground increase the irrigation efficiency. Extra high efficiency sprinklers that apply the water at low pressure, directly in to the furrow increase the efficiency up to 95 percent. Also, farmers have reported an increase in crop production by as much as twenty percent after installing one of these systems.

The most efficient method of irrigating a crop is by using a buried drip irrigation system. This system consists of installing a network of porous or perforated piping below the surface, applying the water to the soil directly surrounding the roots. Drip irrigation can save as much as thirty to forty percent of the water compared to some other types of irrigation. Drip irrigation has also shown to increase the yield of crops.

As these new irrigation technologies become more widespread, the future of the Ogallala Aquifer becomes more sustainable. The water reduction rate has decreased significantly since the new technologies have come online. More Federal and State regulation encouraging the installation of more efficient irrigation systems would go a long way to completely eliminating the problem.

Sources

Ashworth, William. Nor Any Drop to Drink. Summit Books. 1982

Glantz, Michael, ed., 1989: Forecasting by analogy: societal responses to regional climatic change. Summary Report, Environmental and Societal Impacts Group NCAR, 77 pp.

Hinrichsen, D., Robey, B., and Upadhyay, U.D. Solutions for a Water-Short World. Population Reports, Series M, No. 14. Baltimore, Johns Hopkins School of Public Health, Population Information Program, December 1997.

Jeanne X. Kasperson, Roger E. Kasperson, and B. L. Turner II. Regions at risk: Comparisons of Threatened Environments. United Nations University Press. 1995.

Kennamer, Lorrin. 1959. Irrigation patterns in Texas. Southwestern Social Science Quarterly 40: 205-212.

New, Leon. Opportunities to Maximize the Utilization of Water by Irrigators. Aug 95. http://www.prsurge.com/otmtuowb.htm (6 Dec. 2003).

The Ogallala Aquifer. http://www.hpwd.com/ogallala/ogallala.asp (6 Dec. 2003).

Wyatt, A. W. 1988. Estimated net depletion shown. Cross Section 34, no. 1 (January): 2.
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