Flood Storage

TVA's series of dams and reservoirs is well designed to hold back floodwaters as well as to provide power to the citizens of the Valley.

The space allocated for flood storage in the TVA reservoir system varies with the time of year and potential flood threat. From January 1 through March 15, the system has the capacity to store about 11 million acre-feet of water—or a volume equal to one foot of water covering 11 million acres of land. A capacity of about 5 million acre-feet is maintained during summer to reduce flooding caused by summer storms.

Flood Storage Above Chattanooga

Chattanooga is the most flood-prone city in the Tennessee Valley because the city sits just above the point where the Tennessee River passes through the Cumberland Mountains.

Before TVA started flood control operations, major storms occurring in the 21,400-square-mile drainage area above Chattanooga would cause the river to rise rapidly. When it reached Chattanooga, the swollen river would attempt to carry more water through the narrow mountain gorge below the city than the river channel would allow. The excess water that could not flow immediately through would back up into the city, flooding it at least once a year.

At least one reservoir was built on each of the five major tributary rivers above Chattanooga with enough space to store floodwaters from large storms in the drainage areas above them.

These seven reservoirs do the main work in controlling floods:

  • Norris Reservoir on the Clinch River
  • Fontana Reservoir on the Little Tennessee River
  • Douglas Reservoir on the French Broad River
  • Cherokee Reservoir on the Holston River
  • Chatuge, Nottely and Hiwassee reservoirs in the Hiwassee River basin.

Three main-river reservoirs above Chattanooga—Fort Loudoun/Tellico, Watts Bar and Chickamauga—provide additional, limited storage capacity. Together, all TVA reservoirs above Chattanooga can store about 5 million acre-feet of water during the winter flood season.

Flood Storage Below Chattanooga

Kentucky Reservoir, near the mouth of the Tennessee River, has 4 million acre-feet of flood storage space during the winter and early spring. This represents more than 40 percent of the flood storage in the entire TVA reservoir system. This capacity can be used to reduce flood crests on the Mississippi River at Cairo, Ill., by as much as two to three feet.

Three other main-river reservoirs upstream from Kentucky but below Chattanooga—Pickwick, Wheeler and Guntersville—provide about 1 million acre-feet of storage space. This is used to supplement storage in Kentucky Reservoir and to reduce flooding immediately below these dams.

Storage space in main-river reservoirs is limited by topography and the requirement in the TVA Act for a 9-foot waterway for commercial navigation from the beginning of the Tennessee River at Knoxville, Tenn., to its mouth at Paducah, Ky.

The Unified Development of the Tennessee River plan stressed TVA was to provide flood control, navigation and electricity for the region. TVAs dams are tangible evidence of its primary mission: improving life in the Tennessee Valley. We’re celebrating the 80th anniversary of the plan with an in-depth look at 32 dams it comprises.

 

Chattanooga’s Biggest Flood

The largest flood in Chattanooga's history occurred in March 1867, before the TVA system was created. The flood crested at 58 feet and completely inundated the city. Since the completion of the reservoir system, the highest Chattanooga flood stage was nearly 37 feet, which occurred in 1973. Without regulation, the flood would have reached 52.4 feet.