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Low Water in the American High Plains
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20153 |
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Section : |
NATURAL SCIENCE
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| Issue
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2 / 1992 |
2,771 Words |
| Author
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David E. Kromm
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Water defines many regions. It determines their character and sustains their well-being. Ironically, this is especially true of areas with an inherent water scarcity. What would Southern California and central Arizona be like without water imported from distant sources? The green fields and golf courses would give way to dry plains and hills, populated more by grazing animals than by people.
A huge dry area in the middle of the United States depends no less on water to transform a dusty outback into a productive garden, This is the High Plains overlying the Ogallala Aquifer.
There exists widespread concern that America's largest underground water reserve is drying up. The vast Ogallala Aquifer that underlies 1,374,000 square miles of the High Plains from west Texas northward into South Dakota has been partially depleted as more than 150,000 wells pump water for irrigation, municipal supply, and industry. In some areas the wells no longer yield enough water to make irrigation possible. In others there remains sufficient water, but it lies 300 or more feet below the surface. The cost of lifting water from such depths makes it uneconomical for many uses.
Touching base with some key words in the groundwater vocabulary helps tell the Ogallala story more precisely. One is aquifer. An aquifer is a zone of water-saturated sands and gravels beneath the earth's surface. It is not an underground lake or river. It is the porous rock structure that contains the water that we tap with wells. Some aquifers release water to wells readily, whereas other hold the water tightly. This affects the rate at which water can be withdrawn and is called the specific yield of a well. Depth to water describes the vertical distance from ground level to the aquifer. Together with the volume and quality of water, the depth and specific yield define the economic limit of water withdrawal. The fresh water in an aquifer is called groundwater, in contrast to surface waters such as rivers and lakes. Over half the nation's population depends on groundwater for its drinking water. Although there are several aquifers, the Ogallala ranks as the main formation in the High Plains aquifer system. Most people in the region refer to the entire system as the Ogallala.
The unconsolidated sand and gravel that form the Ogallala aquifer were laid down by fluvial deposit in from the Rocky Mountains about 10 million years ago. More recent, near-surface deposits of the late Tertiary and Quaternary ages compose the High Plains
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