Ground-water depletion has been a concern in the Southwest and High Plains for many years, but increased demands on our ground-water resources have overstressed aquifers in many areas of the Nation, not just in arid regions. In addition, ground-water depletion occurs at scales ranging from a single well to aquifer systems underlying several states. The extents of the resulting effects depend on several factors including pumpage and natural discharge rates, physical properties of the aquifer, and natural and human-induced recharge rates. Some examples are given below.
Atlantic Coastal Plain - In Nassau and Suffolk Counties, Long Island, New York, pumping water for domestic supply has lowered the water table, reduced or eliminated the base flow of streams, and has caused saline
ground water to move inland.
Many other locations on the Atlantic coast are experiencing similar effects related to ground-water depletion. Surface-water flows have been reduced due to ground-water development in the Ipswich River basin, Massachusetts. Saltwater intrusion is occurring in coastal counties in New Jersey; Hilton Head Island, South Carolina; Brunswick and Savannah, Georgia; and Jacksonville and Miami, Florida (Barlow).
The chart below shows monthly-mean water levels from 1964 to 2003 for a well in Cook County, sourthwest Georgia. The well is used for irrigation and public-supply purposes and offers a good visual representation of long-term ground-water declines due to excessive pumping.
West-central Florida - Ground-water development in the Tampa-St. Petersburg area has led to saltwater intrusion and subsidence in the form of sinkhole development and concern about surface-water depletion from lakes in the area. In order to reduce its dependence on ground water, Tampa has constructed a desalination plant to treat seawater for municipal supply.
Gulf Coastal Plain - Several areas in the Gulf Coastal Plain are experiencing effects related to ground-water depletion:
- Ground-water pumping by Baton Rouge, Louisiana, increased more than tenfold between the 1930s and 1970, resulting in ground-water-level declines of approximately 200 feet.
- In the Houston, Texas, area, extensive ground-water pumping to support economic and population growth has caused water-level declines of approximately 400 feet, resulting in extensive land-surface subsidence of up to 10 feet.
- Continued pumping since the 1920s by many industrial and municipal users from the underlying Sparta aquifer have caused significant water-level declines in Arkansas, Louisiana, Mississippi, and Tennessee.
- The Memphis, Tennessee area is one of the largest metropolitan areas in the world that relies exclusively on ground water for municipal supply. Large withdrawals have caused regional water-level declines of up to 70 feet.
High Plains - The High Plains aquifer (which includes the Ogallala aquifer) underlies parts of eight States and has been intensively developed for irrigation. Since predevelopment, water levels have declined more than 100 feet in some areas and the saturated thickness has been reduced by more than half in others.
Pacific Northwest - Ground-water development of the Columbia River Basalt aquifer of Washington and Oregon for irrigation, public-supply, and industrial uses has caused water-level declines of more than 100 feet in several areas.
Desert Southwest - Increased ground-water pumping to support population growth in south-central Arizona (including the Tucson and Phoenix areas) has resulted in water-level declines of between 300 and 500 feet in much of the area. Land subsidence was first noticed in the 1940s and subsequently as much as 12.5 feet of subsidence has been measured. Additionally, lowering of the water table has resulted in the loss of streamside vegetation.
Chicago-Milwaukee area - Chicago has been using ground water since at least 1864 and ground water has been the sole source of drinking water for about 8.2 million people in the Great Lakes watershed. This long-term pumping has lowered ground-water levels by as much as 900 feet.
Source: USGS
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