The saturated thickness also varies greatly. Although the average saturated thickness is about 60 meters feet , it exceeds meters 1, feet in west-central Nebraska and is only one-tenth that in much of western Texas.
Because both the saturated thickness and the areal extent of the Ogallala Aquifer is greater in Nebraska, the state accounts for two-thirds of the volume of Ogallala groundwater, followed by Texas and Kansas, each with about 10 percent.
The Ogallala Aquifer, whose total water storage is about equal to that of Lake Huron in the Midwest, is the single most important source of water in the High Plains region, providing nearly all the water for residential, industrial, and agricultural use. Because of widespread irrigation, farming accounts for 94 percent of the groundwater use. Irrigated agriculture forms the base of the regional economy. It supports nearly one-fifth of the wheat, corn, cotton, and cattle produced in the United States.
Crops provide grains and hay for confined feeding of cattle and hogs and for dairies. The cattle feedlots support a large meatpacking industry. Without irrigation from the Ogallala Aquifer, there would be a much smaller regional population and far less economic activity. Overall, 5. The Ogallala Aquifer is being both depleted and polluted. Irrigation withdraws much groundwater, yet little of it is replaced by recharge.
Since large-scale irrigation began in the s, water levels have declined more than 30 meters feet in parts of Kansas, New Mexico, Oklahoma, and Texas.
In the s and s, the rate of groundwater mining , or overdraft, lessened, but still averaged approximately 82 centimeters 2. Increased efficiency in irrigation continues to slow the rate of waterlevel decline. State governments and local water districts throughout the region have developed policies to promote groundwater conservation and slow or eliminate the expansion of irrigation. Generally, management has emphasized planned and orderly depletion, not sustainable yield.
Depletion results Center-pivot sprinklers are among the irrigation methods used in the High Plains. Large quantities of groundwater pumped from the Ogallala Aquifer allows these semiarid western lands to yield abundant harvests. The average specific yield for the High Plains Aquifer is about 0. This means that only 15 percent of all the water available in the aquifer can be recovered using irrigation pumps, while the rest remains unused and locked up in the unsaturated zone.
Groundwater depletion problems could be forestalled if this presently nonrecoverable water could be forced to the saturated zone. One experimental means of accomplishing this is by injecting air into the unsaturated zone, which breaks down capillary action and permits the movement of water down to the saturated zone.
Air injection experiments have shown positive results for very localized areas. However, the widespread applicability of this technology has not yet proven effective.
KS followed in Irrigation has decreased slightly in some areas as water levels have declined. Haacker et al. DOI: In Garden City, however, the severity of their circumstances is already forcing farmers to take action. They are grappling with how to maintain successful agricultural operations while relying on less and less water, an issue that water users throughout the region, and the world, must eventually face, Rude says.
Tapping the Aquifer On a hydrographic map, the Ogallala is a Rorschach inkblot that some describe as the shape of a mushroom, others the South American continent. Millions of years ago, when the southern Rocky Mountains were still spewing lava, rivers and streams cut channels that carried stony pieces of the mountains eastward. Sediment eventually covered the area and filled in the ancient channels, creating vast plains. The water that permeates the buried gravel is mostly from the vanished rivers.
It has been down there for at least three million years, percolating slowly in a saturated gravel bed that varies from more than 1, feet thick in the North to a few feet in the Southwest. Until recently, most of the region had no permanent settlements. Native American tribes who used the open plains for seasonal hunting retreated to river valleys to pitch their tents.
When Spanish conquistador Francisco Vazquez de Coronado came through in looking for the gold cities of Cibola, he marched his iron-clad men to the brink of exhaustion, never knowing that water to quench their near-maddening thirst lay mere yards beneath their boots.
Similarly, cattle drives in the s and s collapsed in a perfect storm of drought, overgrazing and falling meat prices. And early attempts at farming were plagued by soil erosion and cycles of drought that culminated in the s Dust Bowl. Industrial-scale extraction of the aquifer did not begin until after World War II. Diesel-powered pumps replaced windmills, increasing output from a few gallons a minute to hundreds. Over the next 20 years the High Plains turned from brown to green.
The number of irrigation wells in West Texas alone exploded from 1, in to more than 66, in But the miracle of new pumping technology was taking its toll below the prairie. By water levels had dropped by an average of nearly 10 feet throughout the region. In the central and southern parts of the High Plains some declines exceeded feet.
Concerned public officials turned to the U. Geological Survey, which has studied the aquifer since the early s.
What they found was alarming: yearly groundwater withdrawals quintupled between and In some places farmers were withdrawing four to six feet a year, while nature was putting back half an inch. In the overdraft equaled the flow of the Colorado River.
Today the Ogallala Aquifer is being depleted at an annual volume equivalent to 18 Colorado Rivers. Although precipitation and river systems are recharging a few parts of the northern aquifer, in most places nature cannot keep up with human demands. To avoid this fate farmers are using new irrigation techniques that preserve water use. Scientists are working to release more water from below the formation. While none of these techniques have been fully successful as of yet, the effort continues to save this valuable water source.
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