TVA's series of dams and reservoirs are designed to hold back floodwater to protect 15 communities that are prone to flooding:
Flood storage and the potential for flooding vary throughout the year. From early winter to late spring, the reservoir system has the capacity to store 11 million acre-feet of water—a volume equal to 1 foot of water covering 11 million acres. During the summer, a capacity of 5 million acre-feet is maintained to reduce flooding caused by summer storms.
Chattanooga, Tenn., is the most flood-prone city in the Tennessee Valley because the city is just upstream of the narrow gorge where the Tennessee River cuts through the Cumberland Mountains. Before there was a TVA, high river flow would reach the bottleneck of the mountain gorge, and the flow would slow and start to backup—flooding Chattanooga at least once a year.
Throughout the eastern Tennessee Valley and upstream of Chattanooga, 32 dams (24 TVA, four Duke Energy and four Brookfield Smoky Mountain Hydropower) work collectively to protect Chattanooga. The seven tributary workhorses of the reservoir system providing the most flood storage are as follows:
Kentucky Reservoir, spanning 207 river miles upstream to Pickwick Dam, has 4 million acre-feet of flood storage during winter and early spring. This represents more than 40 percent of the flood storage of the entire reservoir system. This capacity is used to reduce flood crest on the Mississippi River at Cairo, Ill., by as much as 2 to 3 feet.
Other main-river reservoirs upstream of Kentucky, but downstream of Chattanooga—Pickwick, Wheeler, Guntersville—provide about 1 million acre-feet of storage. This is used to supplement storage in Kentucky Reservoir and to reduce flooding downstream of these dams.
All the storage in main-river reservoirs is limited by topography and the requirement outlined in the TVA Act of 1933 for providing a channel depth of 11 feet for commercial navigation from Paducah, Ky., to Knoxville, Tenn.