One of Alabama’s great natural treasures is the variety and quantity of its water resources, with 586.5 trillion gallons of water, of which 553 trillion gallons of water is stored in underground aquifers (GSA, 1994).
Groundwater is a reliable source of water for many people in Alabama (roughly 44 percent of the population) (Moore and Szabo, 1994), with several large cities and many smaller towns utilizing groundwater for water needs, particularly in south Alabama. Approximately 7 inches of the state's 55 inches of annual rainfall enters the ground to become groundwater (GSA, 2001).
Fresh water in some areas of Alabama extends to 2,000 feet or more below land surface, however in a few areas, fresh water extends to only 150 feet below land surface (GSA, 2001).
The Aquifer Recharge Map (available for download at Maps/GIS) shows the aquifer recharge areas for the water-bearing aquifers in the state of Alabama. The Aquifer Recharge Map shows the 17 water-bearing units within Alabama and the corresponding recharge areas for these aquifers. These water-bearing aquifers have characteristics that are controlled by various geologic factors, such as permeability, type, and structure of the rocks comprising the aquifer
Geological Survey of Alabama., 1994, Poster of Alabama Water Facts: Geological Survey of Alabama.
Geological Survey of Alabama, 2001, Groundwater: The Underlying Issue.
Alabama Water Facts
Seventeen major streams flow through Alabama; 10 of these have their headwaters inside the state, and the other 7 originate in other states.
Approximately 15 percent of all surface water flowing through the lower 48 states flows through Alabama.
Approximately 40 percent of public water supplies in Alabama are from ground-water sources.
Twenty-seven of 36 south Alabama counties receive all of their public water supplies from ground-water sources.
Alabama has 20 major aquifers that supply water from the land surface to depths approaching 3,000 feet. The deepest public water supply well is constructed in the Tuscaloosa Group aquifer in Dale County (2,750 feet).
Alabama receives approximately 55 inches of rainfall each year, but, on average, only 6 inches move underground to become ground-water recharge.
Since 1930, Alabama has experienced severe drought, on average, every 12 years. Each drought event lasts from one to seven years.
A recent investigation by the Geological Survey of Alabama in Coastal Plain sediments revealed that water moves underground through the Tuscaloosa Group aquifer in southeast Alabama at 3 to 7 feet per year, and the age of the water 50 miles from the recharge area is approximately 60,000 years. If water demand is high and aquifers are relatively thin, water supply wells are not recharged rapidly enough to meet those demands. Therefore, water levels in some wells decline as much as 3 to 8 feet per year.
In contrast, two Geological Survey of Alabama investigations in Highland Rim karst terrain indicated that water moves underground through carbonate rocks at rates of 3,000 feet per day to 4,000 feet per hour. Large quantities of water may be found in these areas. However, short residence time may cause water-quality problems related to transport of surface contaminants.
Water exploration and development is becoming increasingly complex and in most cases requires scientific information that was once used only in oil and gas exploration or in academic research. Remote sensing, geophysical techniques, and comprehensive geochemical and stratigraphic assessments are commonly used to explore for water sources.
Maintaining adequate supplies of clean water is critical to the high quality of life enjoyed by the citizens of Alabama. Water is necessary for maintaining agricultural production, industrial processes, power generation, and public health. As Alabama grows, the demand for clean water continues to increase.
All the water in the world is constantly moving through the hydrologic cycle. The hydrologic cycle is continuous, it has no beginning and end. Precipitation (average of 55 inches/year in Alabama), which, when reaches the land surface, either soaks into the ground or runs along the surface as runoff to streams and lakes (22 inches/year), with some plants absorbing some of the water, which returns to the atmosphere as transpiration (33 inches/year).
Some of the precipitation moves through the soil as recharge, in Alabama 7 inches of the average 55 inches/year of precipitation is considered as recharge to the aquifers. Water in the aquifers is located in a zone of saturation, through which water can flow and is capable of yielding water to wells and springs, and through interconnected spaces in the aquifer, groundwater flows in the general direction of large bodies of surface water such as rivers, lakes, and oceans. In Alabama, the Coastal Plains aquifers of south and west Alabama produce the larges quantities of water, with these aquifers composed of sand and gravel.
The groundwater flows out of the aquifer as discharge when it seeps into rivers, lakes, or oceans from below the land surface, but can also flow directly from the ground as a spring, which occurs where the water table intersects the land surface (total stream outflow 22 inches/year). The hydrologic cycle is completed as the water returns to the atmosphere by evaporation from rivers, lakes, and oceans.
Geological Survey of Alabama, Alabama's Waters, Educational Series 11.