The upper Tennessee River Basin study unit encompasses about 21,390 square miles and includes the entire drainage of the Tennessee River and its tributaries upstream of the USGS gaging station on the Tennessee River at Chattanooga, Tennessee. The study area includes parts of four states; Tennessee (11,500 square miles), North Carolina (5,480 square miles), Virginia (3,130 square miles), and Georgia (1,280 square miles). In 1990, the total population of the study area was about 2.4 million of which about 1.6 million resided in the four metropolitan statistical areas of Chattanooga and Knoxville, Tennessee, Asheville, North Carolina, and the Tri-Cities area of Kingsport and Johnson City, Tennessee, and Bristol, Tennessee and Virginia.
Three physiographic provinces-the Cumberland Plateau, the Valley and Ridge, and the Blue Ridge-are included in the upper Tennessee River Basin. Altitudes in the study area range from 621 feet above sea level at the USGS gaging station at Chattanooga to 6,684 feet at Mt. Mitchell, which is the highest point in the Eastern United States and is located just northeast of Asheville. The study area contains some of the most rugged terrain in the Eastern United States, including the Great Smoky Mountains range, which crests along the Tennessee-North Carolina border between the Little Tennessee and the Pigeon Rivers. The Smokies crest exceeds 5,000 feet for 34 miles along the State line, has 16 peaks that exceed 6,000 feet, and caps the highest and most massive mountain range east of the Mississippi River.
Forest covers more than 64 percent of the study area. Much of the forest land is contained within the National Forests- Jefferson, Pisgah, Cherokee, Nantahala, and Chattahoochee. Agricultural land, which is mostly pastureland, is the second most common land use and accounts for more than 27 percent of the study area. Most agricultural land is located in the stream valleys and the more gently rolling areas of the Valley and Ridge Province. Other land uses are urban, 6 percent; open water, 2 percent; and barren land, 1 percent, most of which is related to mining activities.
The region generally has a temperate climate; temperatures and annual precipitation totals largely are, for the most part, related to land-surface elevations. Average annual temperatures in the area generally decrease by about 3° Fahrenheit for every 1,000-foot increase in elevation. At Knoxville, which has an elevation of about 1,000 feet, the average annual temperature is about 59° Fahrenheit. Annual precipitation ranges from about 40 inches in some low-lying, sheltered areas to more than 90 inches at elevations of more than 6,000 feet.
Five major tributaries account for about 86 percent of the annual mean discharge of 35,450 cubic feet per second at the Tennessee River at Chattanooga and over 87 percent of the total area of the upper Tennessee River Basin. The Clinch (4,413 square miles), the Holston (3,776 square miles), the French Broad (5,124 square miles), the Little Tennessee (2,627 square miles), and the Hiwassee (2,700 square miles) River Basins each exhibit distinctive climatic and runoff characteristics. Average annual precipitation ranges from about 45 inches for the Holston River to almost 60 inches for the Little Tennessee River, which is the heaviest rainfall in the continental United States outside of the Pacific Northwest. Average annual runoff totals show similar variation and range from about 18 inches for the Holston River to more than 34 inches for the Little Tennessee River.
The most prominent surface-water features of the upper Tennessee River Basin are the tributary and main-stem reservoirs constructed and maintained by the Tennessee Valley Authority (TVA). The four main-stem reservoirs are primarily flow-through systems that provide power generation but little flood storage and that have a combined total capacity of about 3.1 million acre-feet. A total of 17 TVA reservoirs that provide flood storage and power generation are located on the tributaries and have a combined total storage of about 10.0 million acre-feet. An additional 17 private reservoirs also are located in the study area and have a combined storage capacity of about 0.6 million acre-feet.
Ground water in the study area occurs almost entirely under water-table conditions and with no regional flow system. Ground-water systems are usually less than 10 square miles in area and are controlled principally by the bedrock geology. Pennsylvanian sandstones and conglomerates form the principal aquifer of the Cumberland Plateau Province where yields generally range from 5 to 50 gallons per minute from fractures, faults, and bedding-plane openings. The Valley and Ridge Province is underlain by folded and extensively faulted limestone, dolomite, shale, and sandstone in long sub-parallel belts that trend southwest to northeast. The principal water-bearing units are the carbonates, which provide water for some cities and industries. Yields generally range from 5 to 200 gallons per minute, but wells that penetrate extensive solution features may yield as much as 2,000 gallons per minute. The Blue Ridge Province is characterized by fractured crystalline igneous and metamorphic rocks that have low porosity and little storage capacity. Yields depend upon interception of water-bearing fracture systems and usually range from 10 to 25 gallons per minute.
In 1990, withdrawals of surface and ground waters in the upper Tennessee River Basin totaled about 5.0 billion gallons per day. Surface-water withdrawals for once-through cooling at thermo-electric plants accounted for 72 percent (3.59 billion gallons per day) of this total; industrial use, 805 million gallons per day; municipal use, 317 million gallons per day, and mining and agricultural use, 243 million gallons per day. About 530 facilities discharged wastewater to streams in the Basin in 1990. Although ground water represents only 3.2 percent of the total water use in the Basin, about 42 percent of the population in the Basin relies upon ground-water sources for drinking water.