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Water in the Southwest
Part Two: Groundwater

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Desert wetlands, fed by a shallow aquifer near the Rio Grande.

Prodigious volumes of water are necessary to sustain a modern population. (It requires, for instance, nearly 3,000 gallons of water to produce the food for a typical family dinner, according to a "Facts Brochure," issued by the Utah Water Supply Internet site.) The water supply must serve not only individuals, but also agricultural and livestock enterprises, municipalities, businesses and industries. Indeed, 80 or 90 percent of the total consumption in agricultural areas may be attributable to irrigation alone. As a result of the relentless growth in demand, said the USGS, "Ground-water resources in the Southwest [have become] among the most overused in the United States.

Complicating an already difficult situation, much of the underground water lies beyond practicable reach. For example, in New Mexico, said Alletta Belin, Consuelo Bokum and Frank Titus, Decision-Maker's Field Guide 2003, the deposits may be "spread widely in small volumes in limited aquifers, remote locales, fluctuating (therefore unreliable) volumes, at great (therefore uneconomic) depths, of marginal quality, or [the water] is present in other situations that make it unavailable for other than local or small-scale use."

Desert grasslands windmill, which a rancher uses to draw livestock water from a shallow aquifer.

Within a typical aquifer, only part of the total supply may be accessible at all. Much of it, especially that in the deeper and more dense strata, may lie beyond reasonable reach, even with "high-capacity large-diameter drilled wells with turbine pumps." Moreover, water, especially from the deeper strata, may be saturated with minerals that render it unfit for use unless it passes through expensive treatment processes.

As water tables fall, rainfall, snowmelt and, in some instances, irrigation and treated waste waters help recharge aquifers, but through processes and at rates that have not been fully investigated by scientists. "The quantity of ground-water recharge to alluvial basins in the Southwest is one of the least known factors in the water budget," said the USGS in "Desert Basins of the Southwest."

As a consequence, the interaction of ground water and surface water has become the central focus of an important USGS program for evaluating aquifers in the Southwest. "Major study components," said the USGS, "include (1) regional synthesis; (2) effects of climate variability on recharge to and discharge from ground-water systems; (3) effects of development of ground-water resources on sustainability of riparian [i.e., streamside or lakeside] systems; (4) development of improved methods of estimating recharge to desert basins; and (5) development of improved methods of simulating interaction of ground water and surface water in arid and semi-arid regions."

Hopefully, data from the study will help agencies develop effective underpinnings for managing the use of ground waters. "We cannot continue [in New Mexico] to mine our ground water at current rates," said Belin, Bokum and Titus. That observation likely applies to most of the Southwest, where ground water withdrawals increased by more than 50 percent during the last half of the 20th century, according to the USGS report Water-Use Trends in the Desert Southwest—1950-200, by A. D. Konieczki and J. A. Heilman.

Click here to read about the Southwest's surface water.

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