James E. Hairston, Auburn UniversityDonn Rodekohr, Auburn UniversityEve Brantley, Auburn UniversityMike Kensler, Auburn University Water Resources Center
Freshwater is one of Alabama's greatest assets. The state's many rivers and streams and abundant rainfall provide a vast supply of freshwater for electricity generation, thermonuclear power plant cooling, navigation, recreation, consumption, and commercial and industrial needs. In addition to water use by humans, Alabama's waterways are an integral part of a productive freshwater ecosystem that supports some of the most biologically rich and diverse plant and animal communities in North America.
The U.S. Geological Survey estimates that approximately 10 percent of the freshwater resources in the entire continental United States originate in or flow through Alabama. The total surface area of Alabama is about 52,000 square miles, or 33.3 million acres. Total outflow of water from Alabama averages about 29 inches per acre per year, with 7 inches coming from groundwater discharge and 22 inches coming from stream outflow. Groundwater is recharged by rainfall and until recent decades, annual groundwater recharge was about equal to annual groundwater discharge. In the last 20 years, with additional withdrawal of groundwater for human use and recent severe drought, some areas have seen a gradual drop in ground water levels as water has been withdrawn at a rate greater than natural precipitation can replenish it.
Land-use changes can also affect groundwater recharge rates as well as groundwater quality. Natural landscapes are particularly effective at capturing and directing precipitation to groundwater storage areas, or aquifers. These areas in the landscape are called groundwater recharge zones. When land is developed and covered by buildings, streets, and other hardened surfaces, water rushes off in a surface flow and is less able to find its way underground. If the land above the aquifer is contaminated with some type of pollutant and water is able to find its way to an aquifer (or to a stream), that water carries with it the contaminants it picked up on the land, thereby polluting the groundwater or surface water into which it flows.
Surface Water Sources
Few states can match Alabama's surface freshwater resources. At least one-sixth of the surface area of Alabama is comprised of lakes, reservoirs, ponds, wetlands, estuaries, and flowing rivers and streams. The state has a surface water supply of 33.5 trillion gallons annually moving through 14 river basins and coastal drainage areas. About 19.5 trillion gallons of this surface water is generated from annual rainfall runoff across Alabama's landscape, and about 14 trillion gallons flow into the state from surrounding areas. There are more than 132,000 miles of rivers and stream channels in Alabama. Alabama shares 170 border river miles of the Chattahoochee River with Georgia, 60 border river miles of the Perdido River with Florida, and 10 border river miles of the Tennessee River with Mississippi. Alabama also has 50 miles of Gulf Coast shoreline and beaches. Other surface water areas of the state include 3.6 million acres of freshwater wetlands located throughout the state, and 27,600 acres of coastal wetlands around places like Mobile and Gulf Shores, and 390,000 acres of estuaries, including Mobile Bay and Wolf Bay near the Gulf of Mexico. These areas are important habitats for many of Alabama's diverse native plant and animal populations.
Hydrological Modification to Surface Waters
Alabama has no natural lakes, and thus all lakes, reservoirs, and ponds in Alabama have been created through dam construction. Lake Guntersville, in north Alabama on the Tennessee River is the largest body of water in the state, covering 110 square miles or about 70,400 acres. Most of the modifications to Alabama's surface water systems have been constructed to facilitate power generation, improve navigation, and increase supplies for agriculture, industry, and drinking water. Most large reservoirs are designed to control floods and provide a variety of recreational activities, whereas some smaller reservoirs and lakes are designed primarily to supply potable water to nearby communities. These human modifications have created 563,000 surface acres in Alabama and include major modifications to the Tombigbee River System, which includes the Tennesee-Tombigbee Waterway and consists of 32 miles of canals and special drainage ditches and 43 large lakes, reservoirs and ponds, excluding farm ponds.
Ground Water Sources
Alabama has an excellent supply of groundwater from a variety of aquifer systems. There are limestone aquifers in the Tennessee River Valley capable of supplying high rates of water. Unconfined aquifers, which are open to receiving waters from the surface and that fluctuate depending on recharge rate, cover a high percentage of the state. The upper level of unconfined aquifers define the water table and mark the top of the zone where the spaces between sand and rock particles are completely saturated with water. There are several layers of confined aquifers throughout the East Gulf Coastal Plain physiographic section, which makes up about two-thirds of the state. Confined aquifers are sandwiched between layers of material such as clay that make it difficult for water to move into or out of the aquifer.
The Geological Survey of Alabama has estimated Alabama's groundwater supply to be 553 trillion gallons of freshwater stored in 19 major aquifers or aquifer systems across the state. Most groundwater is considered to be of good quality, except for some highly mineralized waters underlying the Blackland Prairie area of west Alabama. The lowest area for groundwater storage in Alabama is in the southern Piedmont section, where many wells are capable of yielding no more than 50 gallons per minute, and some no more than 10 gallons per minute. Wells in most other areas of the state are capable of yielding in excess of 150 gallons per minute.
Water Use in Alabama
Approximately 56 percent of Alabama's 4.5 million people obtain their drinking water from the major rivers or other surface sources. Alabamians use surface water sources available through cities, counties, the state, and federal or privately developed parks for a variety of recreational activities. Today, six of Alabama's 14 major rivers are used for navigation. There are 16 navigational dams, five of which also generate hydroelectric power. Commercial fishing has been successful in coastal waters, estuaries, and rivers for more than 100 years, and commercial catfish farming in developed ponds has increased substantially during the past 40 years.
Hydroelectric power is produced at 21 dam sites on these rivers, which contribute about 10 percent of Alabama's power needs, whereas thermonuclear plants contribute about 20 percent of the state's electricity. Most of the state's water, approximately 78 percent, is used to cool thermoelectric power generation at facilities. Self-supplied industrial and commercial uses account for 10 percent of the water consumed, whereas public water supply use is 8.6 percent, agricultural use is 3 percent, and private water systems, mostly wells, and mining operations consume 0.3 percent and 0.1 percent, respectively.
Comparison with Other States
Alabama is seventh in the country in perennial stream miles but first in navigable stream miles. Alabama ranks sixth and tenth, respectively, in water used for thermonuclear power generation and water withdrawn for industrial, commercial, or mining uses. Alabama ranks 14th in the nation in its number of acres of lakes, ponds, and reservoirs and 24th in the number of acres of wetlands. Alabama ranks 14th in total freshwater withdrawals but has access to more freshwater than most states. Alabama ranks low in making use of its water resources for supplemental irrigation in agriculture.
Alabama rivers are among the most biologically diverse in the world. The state is home to 303 freshwater species of fish, 20 of which are endemic to Alabama. In addition to possessing 38 percent of the fish species found in North America, the state also has 43 percent of the freshwater gill-breathing snails and 51 percent of the freshwater turtle species. Alabama rivers are home to 60 percent of the freshwater mussel species in the United States. There are more fish species in the Cahaba River alone than in the entire state of California.
Rainfall and Stream Flow
Alabama has a humid, subtropical climate and receives an average annual rainfall of 55 inches. This precipitation varies from a low of 48 inches in some east-central and west-central areas of the state to a high of 68 inches along the Gulf Coast. The relationship between rainfall and stream flow varies somewhat from year to year and even from one storm event to another. The primary reason for this variability is the difference in preceding weather conditions. If heavy rainfall comes after an extended dry period, more water goes to groundwater recharge and less goes directly to stream flow. If the period just prior to heavy rainfall has been wetter, then more rainfall goes immediately to stream flow.
Alabama Water Data
The Water Divisions of both the U.S. Geological Survey and the Geological Survey of Alabama, in collaboration with other state and federal agencies, obtain and publish yearly data pertaining to Alabama's water resources. The Office of Water Resources within the Alabama Department of Economic and Community Affairs (ADECA) also collects and publishes water resources-related information. A number of other federal and state agencies, as well as private corporations, organizations and education institutions, collect annual primary water-quality data across the state. The collection sites consist of 131 full-recording and 41 partial-recording stream flow gage stations and 47 stations that record stage and content for 14 lakes and reservoirs. In addition, there are 12 stream-flow gage stations, 17 ungaged stream sites, and two precipitation stations that provide water quality records, whereas 14 surface water stations collect water temperature data. Also, dissolved oxygen information is gathered at 12 surface water stations. In fact, there are numerous other sites throughout the state that measure turbidity, sediment, water levels, and other measures of water quality and water supply. More groundwater stations are being established and a network of National Weather Service stations and other stations collect and record precipitation data across Alabama.
Alabama's water resources are plentiful indeed, but they are also limited, and Alabama is changing. Rapid population growth, urban and suburban development, and a changing climate, mean Alabamans can no longer take seemingly unlimited supplies of fresh water for granted. Having clean water in sufficient supplies to keep our forests and streams alive and meet human needs depends on several things, including stewardship of the natural areas of land and water that keep supplies of fresh water flowing, conservative use of existing water supplies, and reduction and elimination the pollutants that make fresh water unusable. With reasonable planning, careful stewardship, and conscientious monitoring activities to protect and maintain the high quality of water resources residents currently enjoy, Alabama should have adequate supplies of clean fresh water into the foreseeable future.
Arello, Guy, Todd Keith, Beth Maynor Young, and Mac Dean. Alabama, the River State: A Collection of Historical Essays Exploring Alabama Rivers. Birmingham: Natura Press, 1998.
Barlow, Maude. Blue Covenant: The Global Water Crisis and the Coming Battle for the Right to Water. New York: W. W. Norton, 2008.
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