Tennessee Valley Authority
Drought Update
Weekly Update
For the week ending Nov. 14, there was an average of 0.85 inch of rainfall recorded above Chattanooga. Runoff was 0.06 of an inch. (Note: All rainfall and runoff data included here is as of midnight Nov. 13).
While dry conditions have eased in the western Tennessee Valley, the drought persists in the central Valley, and the northeastern Valley remains in extreme drought.
For the calendar year-to-date (Jan. 1-Nov. 14), the Valley has received a total of 33.23 inches of rainfall and 11.39 inches of runoff. Rainfall for the calendar year-to-date is 76 percent of normal. Hydro production for the calendar year-to-date is 57 percent of normal (96 percent of budget).
Blue Ridge, Cherokee, Douglas, Fontana, Norris, Chatuge, Nottely and Hiwassee are below and expected to remain below their flood-guide levels. Under current conditions, a rainfall event of 3.2 inches would be required to fill these tributary reservoirs to pool elevations normal for this time of year.
South Holston and Watauga reservoirs continue to experience pool elevations well below flood-guide levels and are forecast to remain low. Under current conditions, an event of more than 8.5 inches of rain would be necessary in the upper northeastern Valley to fill these reservoirs to their normal pool elevations.
TVA will continue to schedule flows through the system to fill tributary projects while meeting downstream flow requirements, maintaining water quality, protecting aquatic habitat and providing for commercial navigation.
Reservoir Operations during Drought Conditions
During drought conditions, TVA operates the river system in a water conservation mode, releasing only the minimum amount of water from tributary dams required to meet downstream needs.
Water is released to meet reservoir-specific minimum flow requirements, which keep the riverbeds below tributary dams from drying out, and to meet system-wide minimum flow requirements, which are needed to maintain the channel depths for navigation on the main Tennessee River mandated by the TVA Act and to protect water quality and water supply along the length of the river system.
TVA generates as much power as possible with the water released to meet minimum flow requirements, but no additional water is released for the specific purpose of hydropower generation—even though it means relying on more expensive coal-fired and nuclear generation or buying power from outside sources
Beginning June 1, TVA is required to provide increased flow through the river system. The amount of flow depends on the total volume of water stored in the tributary reservoir system and varies depending on the time period.
If the volume of water stored in tributary reservoirs remains below the minimum system operating guide level, TVA is required to provide a weekly average flow of 13,000 cubic feet per second (cfs) at Chickamauga Dam from June 1 to July 31, if the dry conditions persist through that period, and a weekly average flow of 25,000 cfs from August 1 to Labor Day. (System-wide flows are measured at Chickamauga Dam, located near Chattanooga, Tennessee, because this location provides the best indication of the flow for the upper half of the Tennessee River system.)
If tributary reservoirs are above their minimum operating guide, flows at Chickamauga will increase weekly through the summer until the unrestricted drawdown begins after Labor Day. See what the different flows are here.
If there isn’t enough rain to meet the minimum flow requirement, TVA has to pull the needed water from the tributary reservoir system, which can cause water levels on tributary reservoirs to drop through the summer.
TVA uses balancing guides for each reservoir to ensure that water is withdrawn in an equitable manner. More water is drawn from reservoirs that are higher relative to their balancing guide levels—which means they have more water—and less from reservoirs that are nearer or below their balancing guide levels.
If it rains enough to fill the tributary system above the minimum operating guide level, the flow requirement at Chickamauga increases on a weekly basis.
Track your reservoir’s elevation. Choose your reservoir from the pull-down menu and then select Operating Guide.
Track Valley rainfall here.