Hot/Cold Operations at Tims Ford Dam
Tims Ford Dam was completed in 1970, to provide hydroelectric power, recreation and flood control on the Elk River in south central Tennessee.
Dam operations also create a put-and-take trout fishery in the tailwaters, while maintaining a warmwater habitat for endangered species downstream.
Located between Winchester and Fayetteville, the 175-foot high dam and lake were named after an 1880s ford operated by a Franklin County settler.
Before the dam’s operation, the Elk River was warmer. The Tennessee Valley Authority (TVA) dams pull cold water from the lake’s depths, allowing trout species, which prefer colder water, to thrive in a 30-mile stretch downstream. Most of the trout angling, however, occurs in an 11-mile stretch below the dam.
Once biologists determined the colder water negatively impacted native species like the endangered Boulder Darter -- so rare it’s found only in the Elk River and one tributary – adjustments were made to provide warmer water for these. The Tennessee and Cumberland River systems have the highest number of rare fish species in the country, and the Upper Elk alone has nine federally listed endangered aquatic species, including eight mussel species.
TVA balances these water temperature needs in the 40-mile stretch between the dam and Fayetteville using several methods.
The dam’s low-level outflow is created with a hydroturbine that pulls roughly 4,000 cubic feet per second (cfs).
“The Tims Ford unit doesn’t have any flexibility in how much water it can release, so it’s either all or nothing,” said TVA Engineer Jessica Brazille.
It also uses a sluice, which can pass up to 240 cfs of cold water drawn from the deepest portion of the reservoir.
The high-level outflow is an emergency spillway that’s about 100 feet higher than the turbine and sluice, and pulls warmer water from the surface.
“The lowest spillway gate setting is 120 cfs, although I’ve seen it pass over 5,000 during significant flood events,” said Brazille. “In the summer, the spillway can be as much as 25 degrees warmer than the low-level releases because of thermal stratification in the reservoir.
“If we used only warm releases it could harm the trout. If we used only cold sluice/turbine releases, it could stress the darters,” she said.
“In the winter, this isn’t as much of a concern because surface temperatures in the reservoir cool off, and the temperatures throughout the water column become more unified.”
Brazille said during warmer months TVA runs sluice-only flows, varying from 80 cfs to 240 cfs, depending on the year. During wet summers, they run the higher of that range at 240 cfs. The trout like this cool water, and it is a low enough flow that summer temperatures warm the water by the time it reaches Fayetteville and the darters.
“During significant rainfall we may have to activate the spillway in order to pass the excess water and maintain flood storage,” she said. “When this happens, we release cold water through the sluice and mix it with the warm water from the spillway, to decrease the water temperature of the releases. Depending on how warm the spillway release temperatures are, we release a smaller amount over a longer period of time, allowing more mixing with the cooler sluice water. We also try to limit this spill flow to weekdays whenever possible, to provide more recreational opportunities over the weekends.”
TVA also installed blowers and oxygen injection systems in the hydropower units to maintain dissolved oxygen, critical for trout survival.
The Tennessee Wildlife Resources Agency regularly stocks trout immediately downstream of the dam, making it a popular fly-fishing spot.
For additional information about fishing go to https://www.tn.gov/content/tn/twra/fishing/trout-information-stockings.html#reports; and https://www.tva.com/energy/our-power-system/hydroelectric/tims-ford for TVA operations there.