Environmental Engineering Reference
In-Depth Information
The Ogallala Aquifer
Twenty percent of America's water use comes from underground aqui-
fers, the largest of which by far is the series of sandstones and conglom-
erate called the Ogallala Formation (fi gure 1.3). 11 It extends over an area
of about 174,000 square miles in parts of eight states, from Wyoming
and South Dakota in the north to New Mexico and Texas in the south.
About 27 percent of the irrigated land in the United States overlies this
aquifer system, which yields about 30 percent of the nation's groundwa-
ter used for irrigation. Water from the Ogallala aquifer serves an area
that produces 25 percent of U.S. food grain exports and 40 percent of
wheat, fl our, and cotton exports. In addition, it provides drinking water
to 82 percent of the people who live within the aquifer boundary. 12
Ogallala water irrigates more than 14 million acres of farmland, areas
with only 16 to 20 inches of rainfall—not enough for the abundance of
corn, wheat, and soybeans American farmers have come to expect. The
aquifer averages 200 feet thick and holds more than 70 quadrillion
gallons of water (70,000,000,000,000,000 gallons) in its pores. The
water accumulated undisturbed from rainfall over millions of years, but
for the past eighty-fi ve years, the water has been withdrawn from thou-
sands of wells at a rate that is eight times the current replenishment rate
from the low annual rainfall. 13 Farmers are pumping more groundwater.
In 1950, 30 percent of irrigation water came from aquifers; in 2005, 62
percent did. 14 Water levels have declined 30 to 60 feet in large areas of
Texas, and many farmers in the High Plains are now turning away from
irrigated agriculture. Wells must be deepened, and the costs of the deep-
ening and increased pumping have caused some agricultural areas to be
abandoned. If overpumping of the Ogallala continues, the aquifer may
be effectively dry within a few decades, with disastrous effects on the
economy of a large area of the United States.
Prospects for the Future
Our ability to irrigate at low cost is coming to an end, not only in the
Midcontinent but in other areas as well. As noted earlier, the Great Lakes
will come under increasing pressure from states in the Midwest and
Southwest up to 1,500 miles away to share the enormous volume of
water currently under the control of the eight states bordering the lakes.
The cost of transporting water is determined largely by how far it has
to be carried and how high it has to be lifted. The elevations of the three
largest Great Lakes are between 577 feet and 609 feet, but the elevations
of the area served by the Ogallala range from about 2,000 feet to 3,600
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