Ground-Water Depletion Across the Nation
Ground-water use has many societal benefits. It is the source of drinking water for about half the nation and nearly all of the rural population, and it provides over 50 billion gallons per day in sup- port of the Nation’s agricultural economy. Ground-water depletion, a term often defined as long-term water-level declines caused by sustained ground-water pumping, is a key issue associated with ground-water use. Many areas of the United States are experienc- ing ground-water depletion.
needed for informed decisions, these effects must be observed over time to determine their impact.
What are some effects of ground- water depletion?
If intensive pumping from an aquifer continues, then adverse effects may occur.
Water-well problems Declining ground- water levels have three main effects on water wells. First, as the depth to water increases, the water must be lifted higher to reach the land surface. As the lift distance increases, so does the energy required to drive the pump. Thus, power costs increase as ground-water levels decline. Depending on the use of the water and the energy costs, it may no longer be economically feasible to use water for a given purpose. Second, ground-water levels may decline below the bottom of existing pumps, necessitat- ing the expense of lowering the pump, deepening the well, or drilling a deeper replacement well. Third, the yield of the well may decline below usable rates. Ground-water depletion is primar- ily caused by sustained ground-water pumping. Some of the negative effects A n aquifer can be compared to a bank account, and ground water occurring in an aquifer is analo- gous to the money in of ground-water the account. Hydrol- ogists refer to this type of accounting as a water budget. Ground water can be depletion include increased pumping costs, deterioration of water quality, reduction of water An aquifer can be compared to a bank account, and ground water occurring in an aquifer is analogous to the money in the account. recharged (depos- ited) by infiltration in streams and lakes, or land subsidence. from precipitation, surface water, or applied irrigation water; it can be kept in storage (saved); and it can be dis- charged naturally to streams, springs, or seeps, or transpired by plants (with- drawn). In a ground-water system prior to development, the system is in long- term equilibrium—discharge is equal to recharge, and the volume of water in storage remains relatively constant. Ground-water levels fluctuate in time over a relatively small, natural range. Once pumping begins, however, this equilibrium is changed and ground- water levels decline. Just as a bank account must be balanced, withdrawals from an aquifer by pumping must be balanced by some combination of in- creased recharge, decreased discharge, and removal from storage (or deple- tion). An inventory of ground-water levels in wells reflects the volume of water stored (or occurring) in the aquifer, and is analogous to a financial statement. Such effects, while variable, happen to some degree with any ground-water use. As with other natural resources, society must weigh the benefits against the consequences of such use. In order to provide the scientific information Ground-water budgets before and after development of the Gulf Coastal Plain aquifer system (all flows in cubic feet per second). The large withdrawals from the aquifers have been balanced by increases in recharge to the aquifer system and decreases in storage and discharge from the aquifer system (modified from Williamson and Grubb, 2001).
The volume of ground water in stor- age is decreasing in many areas of the United States in response to pumping.
S. Department of the Interior
S. Geological Survey
USGS Fact Sheet-103-03 November 2003