Thursday, May 15, 2008

Mining Groundwater

Mining groundwater or aquifer overdraft is a serious problems in the West. Some Cities (and farming areas)in the west are already experiencing problems associated with overdraft including the need to deepen wells, land subsidence, and poorer water quality being extracted. Examples of some cites with overdraft issues are Denver, Las Vegas, and Tucson. In Utah the farming area of Beryl has experienced similar problems leading to restrictions in withdrawals and a stricter water right policy (
Below are the definitions of overdraft and subsidence.

Groundwater is a highly useful and often abundant resource, however over-use or overdraft can cause major problems to human users and to the environment. The most evident problem (as far as human groundwater use is concerned) is a lowering of the water table beyond the reach of existing wells. Wells must consequently be deepened to reach the groundwater; in some places (e.g., California, Texas and India) the water table has dropped hundreds of feet due to excessive well pumping. A lowered water table may, in turn, cause other problems such as subsidence and saltwater intrusion.

Groundwater is also ecologically important. The importance of groundwater to ecosystems is often overlooked, even by freshwater biologists and ecologists. Groundwaters sustain rivers, wetlands and lakes, as well as subterranean ecosystems within karst or alluvial aquifers.

Not all ecosystems need groundwater, of course. Some terrestrial ecosystems, for example those of the open deserts and similar arid environments, exist on irregular rainfall and the moisture it delivers to the soil – supplemented by moisture in the air. While there are other terrestrial ecosystems in more hospitable environments where groundwater plays no central role, groundwater is in fact fundamental to many of the world’s major ecosystems. Water flows between groundwaters and surface waters. Most rivers, lakes and wetlands are fed by, and (at other places or times) feed groundwater – to varying degrees. Groundwater feeds soil moisture through percolation, and many terrestrial vegetation communities depend directly on either groundwater or the percolated soil moisture above the aquifer – for at least part of each year. Hypoheic zones (the mixing zone of streamwater and groundwater) and riparian zones are examples of ecotones largely or totally dependent on groundwater.

When we extract groundwater linked to a river system, we extract water from that river, even if the result is not evident for some time. And of course vice versa. Water management agencies around the world are still struggling to come to terms with this simple fact. See Kansas Geological Survey.

In its natural equilibrium state, the hydraulic pressure of groundwater in the pore spaces of the aquifer and the aquitard supports some of the weight of the overlying sediments. When groundwater is removed from aquifers, due to excessive pumping, pore pressures

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