Nasa's shocking reports-Underground Aquifers Are Running Out of Waterby | 15-07-2015 02:02 |
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 Nasa's shocking reports-Underground Aquifers Are Running Out of Water Groundwater accumulates slowly in the underlying bedrock over millennia. And like oil, no one knows how much there is—but experts do know that when it's gone, it's gone. After entering an aquifer, water moves slowly toward lower lying places and eventually is discharged from the aquifer from springs, seeps into streams, or is withdrawn from the ground by wells. Groundwater in aquifers between layers of poorly permeable rock, such as clay or shale, may be confined under pressure. If such a confined aquifer is tapped by a well, water will rise above the top of the aquifer and may even flow from the well onto the land surface. Water confined in this way is said to be under artesian pressure, and the aquifer is called an artesian aquifer. There is no problem if it is withdrawn slowly, but human population has exploded threefold and water use has risen even faster. Of the 37 underground aquifers measured, one third was seriously stressed, with little or almost no natural replenishment. The Arabian aquifer system—the principal water source for 60 million people—is the worst stressed, followed by the Indus Basin of north-west India and Pakistan and then the Murzuk-Djado basin in northern Africa. When aquifers are depleted, they can be subject to an influx of surrounding contaminants such as saltwater—a particular problem near coastal areas. Also, like oil fields, depleting fossil water aquifers too quickly can reduce underground pressures and render large quantities of water essentially irretrievable. Underground aquifers supply 35 per cent of the water used by humans worldwide. Demand is even greater in times of drought. |
