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Updated April 2, 1998
The Lower Tennessee River Basin NAWQA study unit extends from Chattanooga, Tennessee, to near Paducah, Kentucky, at the confluence of the Tennessee and Ohio Rivers. The study unit area is about 19,500 square miles (mi²) of which about 57 percent is in Tennessee, 35 percent in Alabama, 5 percent in Kentucky, 2 percent in Mississippi, and 1 percent in Georgia. Population in the study unit is about 2.7 million (1995). The most populated cities in the study unit are Huntsville, Alabama (160,000), Chattanooga, Tennessee (152,000), and Decatur, Alabama (52,000). In 1995, about 220 million gallons a day were withdrawn from surface- and ground-water sources in the study unit to provide public drinking water to about 1.5 million people. Surface water is the principal source, accounting for about 70 percent of the water withdrawn for drinking water.
The main stem of the Tennessee River is highly regulated with few free-flowing stream reaches. Six major reservoirs constructed primarily by the Tennessee Valley Authority from the 1920's through the 1940's for purposes of power generation, navigation, and flood control are located along the lower Tennessee River. Three additional reservoirs are located on major tributaries. Reservoirs along the Tennessee River are also used extensively for drinking water and recreational activities such as fishing, swimming, and boating. Water-resource managers and the public are extremely interested in maintaining the high quality of these reservoirs.
Nine reservoirs in the study unit are used extensively for water
The mean annual discharge at the outlet of the Tennessee River near Paducah, Kentucky, is 65,600 cubic feet per second (ft³/s). The mean annual discharge of the Tennessee River at the upstream boundary of the study unit at Chattanooga, Tennessee, is 35,900 ft³/s, thus the lower Tennessee River Basin contributes about 29,700 ft³/s on an annual basis. The two largest basins in the study unit are the Duck River Basin, draining 2,700 mi², and the Elk River Basin, draining 2,250 mi². The combined mean annual discharge of the Duck and Elk Rivers is about 7,700 ft³/s, or 26 percent of the mean annual discharge from the Lower Tennessee River Basin study unit.
There are numerous industries along the main stem of the Tennessee River in northern
Alabama. These industries manufacture and produce a variety of products, such as missiles
and rockets, electronics, pulp and paper, synthetic fiber, terephthalic acid, alkalis, chlorine,
steering gears, polyester film, refrigerators, aluminum, and nickel-plated foam.
(Photograph courtesy of the Tennessee Valley Press, Decatur, Alabama)
The study unit lies within three physiographic provinces. The Coastal Plain Province is located along the western edge of the study unit and encompasses about 18 percent of the basin. To the east, the Interior Low Plateaus Province encompasses about 59 percent of the basin. The Cumberland Plateau Section of the Appalachian Plateaus Province is located along the eastern edge of the study unit and encompasses the remaining 23 percent of the basin. Land-surface elevations in the study unit range from about 300 feet above sea level in the Coastal Plain Province near Paducah, Kentucky, to more than 2,900 feet above sea level in the Cumberland Plateau, along the eastern edge of the Sequatchie River Basin. Annual precipitation varies from 47 inches in the Coastal Plain to 63 inches in the Cumberland Plateau. Average runoff ranges from 18 inches in the Coastal Plain to 30 inches in the Cumberland Plateau. The study unit has a temperate climate with an average annual temperature of about 58 degrees Fahrenheit.
Ground water is an important source of drinking water in rural areas and for numerous small public supply systems in the study unit. The Coastal Plain Province generally consists of a series of unconsolidated sands, gravels, silts, and clays. Shallow ground water in these sands and gravels is an important source of drinking water. In the Interior Low Plateaus Province, ground water moves through an overburden from 10 to more than 200 feet of regolith, a mixture of soil and weathered rock, and subsequently into an underlying carbonate aquifer. Carbonate aquifers are important sources of drinking water in many areas throughout the study unit. Thin regolith, caves, and sinkholes in this province increase the susceptibility of ground water to contamination from surface water. Most of the Cumberland Plateau is underlain by sandstones in which ground water occurs primarily in interconnected fractures.
The main land use in the study unit is forested land, which covers about 55 percent of the study unit (1992 land cover data from the Tennessee Valley Authority). Additional land uses include row crops and pasture land (41 percent), urban (1 percent), and other land uses (3 percent), such as wetlands, water, and barren land. Row crops occur predominantly along the main stem and small tributaries of the Tennessee River in northern Alabama and along the western edge of the study unit. Cotton, corn, and soybeans are the primary row crops. Confined animal operations are concentrated primarily in northern Alabama.
Cotton is a major crop grown in northern Alabama.
Assessing water quality in the lower Tennessee River Basin is important for the protection and efficient use of water and aquatic resources. The Lower Tennessee River Basin NAWQA study will increase scientific understanding of surface- and ground-water quality within the basin and the factors that influence water quality and aquatic resources, such as fish and mussels.
The Lower Tennessee River Basin study is known for the prolific
distribution of Cumberlandian mollusks. The Muscle Shoals area,
near Florence, Alabama, once contained the most diverse
assemblage of mussels in the world. Many of these species are
now endangered or threatened.
The NAWQA study also will provide information needed by water-resource man- agers to implement effective water-quality management actions and evaluate long-term changes in water quality. Some of the major water-quality issues that currently face water-resource managers in the Lower Tennessee River Basin include:
Sedimentation and increased concentrations of sediment in streams and reservoirs from erosion related to urbanization and agriculture.
Impacts upon native species, including endangered Cumberlandian mollusks, related to changes in water quality and degradation of instream and riparian habitats.
Bacterial contamination of surface and ground waters.
Pesticides and other toxic compounds in streams and aquifers from agricultural, industrial, and domestic activities.
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