Depletion of the Ogallala Aquifer
The vast grasslands of the High Plains in the central United
States were settled by farmers and ranchers in the 1880’s.
This region has a semiarid climate, and for 50 years after its
settlement, it supported a low-intensity agricultural economy of cattle ranching and
wheat farming. In the early twentieth century, however, it was discovered that much of the
High Plains was underlain by a huge aquifer (a rock layer containing large quantities of
groundwater). This aquifer was named the Ogallala aquifer after the Ogallala Sioux Indians,
who once inhabited the region.
The Ogallala aquifer is a sandstone formation that underlies some 583,000 square kilometers o
f land extending from northwestern Texas to southern South Dakota. Water from rains and
melting snows has been accumulating in the Ogallala for the past 30,000 years. Estimates
indicate that the aquifer contains enough water to fill Lake Huron, but unfortunately,
under the semiarid climatic conditions that presently exist in the region, rates of addition
to the aquifer are minimal, amounting to about half a centimeter a year.
The first wells were drilled into the Ogallala during the drought years of the early
1930’s. The ensuing rapid expansion of irrigation agriculture, especially from
the 1950’s onward, transformed the economy of the region. More than 100,000 wells
now tap the Ogallala. Modern irrigation devices, each capable of spraying 4.5 million
liters of water a day, have produced a landscape dominated by geometric patterns of circular
green islands of crops. Ogallala water has enabled the High Plains region to supply significant
amounts of the cotton, sorghum, wheat, and corn grown in the United States. In addition, 40 percent
of American grain-fed beef cattle are fattened here.
This unprecedented development of a finite groundwater resource with an almost negligible natural
recharge rate—that is, virtually no natural water source to replenish the water supply—has caused
water tables in the region to fall drastically. In the 1930’s, wells encountered plentiful water at
a depth of about 15 meters; currently, they must be dug to
depths of 45 to 60 meters or more. In places,
the water table is declining at a rate of a meter a year, necessitating the periodic
deepening of wells
and the use of ever-more-powerful pumps. It is estimated that at current withdrawal
rates, much of the
aquifer will run dry within 40 years. The situation is
most critical in Texas, where the climate is driest,
the greatest amount of water is being pumped, and the aquifer contains
the least water. It is projected that
the remaining Ogallala water will, by the year 2030, support
only 35 to 40 percent of the irrigated acreage
in Texas that is supported in 1980.
The reaction of farmers to the inevitable depletion of the
Ogallala varies. Many have been attempting to
conserve water by irrigating less frequently or by switching
to crops that require less water. Other,
however, have adopted the philosophy that it is best to use the
water while it is still economically profitable to do so and to
concentrate on high-value crops such as cotton. The incentive of
the farmers who wish to conserve water is reduced by their knowledge
that many of their neighbors are profiting by using great amounts of
water, and in the process are drawing down the entire region’s water supplies.
In the face of the upcoming water supply crisis, a number of grandiose
schemes have been developed to
transport vast quantities of water by canal or pipeline from
the Mississippi, the Missouri, or the Arkansas
rivers. Unfortunately, the cost of water obtained through any of these
schemes would increase pumping costs at least tenfold, making the cost of irrigated
agricultural products from the region uncompetitive on the national and international
markets. Somewhat more promising have been recent experiments for releasing capillary water
(water in the soil) above the water table by injecting compressed are into the ground. Even
if this process proves successful, however, it would almost triple water costs. Genetic engineering
also may provide a partial solution, as new strains of
drought-resistant crops continue to be developed.
Whatever the final answer to the water crisis may be, it is evident that within the High Plains,
irrigation water will never again be the abundant,
inexpensive resource it was during the agricultural
boom years of the mid-twentieth century.