TVA’s odd dam out, Great Falls, began operations in January of 1917 as a premier project of the Tennessee Electric Power Company. It was purchased 22 years later by TVA, and remains the quirkiest hydro project in the portfolio.
JANUARY 12, 2017—Stand on Powerhouse Rd. atop the Caney Fork near the confluence of the Collins in Middle Tennessee, and you’ll have your choice of numerous breath-taking views: Look to the right, and you’ll be treated to a vision of the spectacular, naturally occurring Twin Falls. Look dead ahead, you’ll see an historic powerhouse that dates back to 1915. Look upstream and you might spy Great Falls Dam, a hydroelectric facility that celebrated its 100th year of operation in 2017.
The latter is, in so many ways, an oddity in TVA’s portfolio of generating assets. For starters: It doesn’t sit on the Tennessee River or one of its tributaries. It’s not even in the watershed. Rather, it is located on the Caney Fork River near the confluence of the Collins River in Middle Tennessee in—well, the middle of nowhere, really. It lies midway between small towns Sparta and McMinnville, 45 minutes from Cookeville and an hour and a half from Nashville.
It’s a little slice of rustic paradise that for kayakers, trout fishermen and especially hydro geeks, is well worth the drive.
“Great Falls was one of four of dams we purchased from the Tennessee Electric Power Corporation (TEPCO) in 1939—it came along with a package that also included Hales Bar Dam (decommissioned in 1968 and replaced with Nickajack Dam), Ocoee dams No. 1 and No. 2 and Blue Ridge Dam,” says Robby Floyd, plant manager for Watts Bar and Great Falls. “It’s one of the oldest dams in our system—construction started in 1915, was completed in 1916 and Unit 1 started generating power in 1917.”
When a second unit was added in the early 20s, the powerhouse was rebuilt to accommodate it; all told the dam has a net dependable generating capacity of 36 megawatts. That’s small potatoes in the world of TVA hydro. “But you have to remember that it was sizable for the time—they made huge strides between the time this dam was built and when TVA started building dams in the 30s and 40s,” Floyd says. “In fact, Great Falls features one of the oldest vertical generating units in the country.”
What’s really interesting is the way the Great Falls works. Though the dam and its powerhouse are built on the Caney Fork, the water that drives the turbines is drawn from the Collins River, which travels by means of dual 650-foot long steel penstocks drilled though the mountain between the two bodies of water. So strong is the pull when the generators are running that the water on the Collins can temporarily flow backwards. The dam itself is merely for flood control, and—as Floyd notes—spills a lot of water during rain events to keep balance in the two-river system.
“We have four locations at Great Falls,” explains Floyd. “There is the intake on the Collins and the control building the switchyard right across the street from that. Then there is the powerhouse about 150 feet down in the ravine on the Caney Fork River side and upstream from that is the dam. It all works together, but you almost have to see it to wrap your head around it.”
Great Falls was an engineering marvel when it was built it, which is reflected by the dam’s status on the National Register of Historic Places, notes Pat Ezzell, TVA historian. “That means TVA takes its significance into account whenever we do projects at Great Falls so as not to impact the historical integrity there,” she explains. “Our Cultural Resources department works hard to make certain that cultural integrity is maintained.”
Here’s a for-instance: The turbines at Great Falls are air-cooled—yet another thing that makes the facility unique in the TVA hydro world. (Most other dams are cooled by mechanical means.) “When generating here, we have to use ambient air to keep the units cool,” Floyd explains. “We have many windows we can open; we can crack open big bay doors. It’s an archaic system, but it works.”
This year, TVA will undertake an initiative to rehab the windows at Great Falls. “Anything we do at this site has to go through a historical review,” he says. “We will work closely with the State Historical Preservation Officer to make sure we are restoring these windows as closely as possible to their original condition.”
For Floyd, that’s all in a day’s work. “We’re working with a lot of original equipment here—100-year-old generators that run like tops,” he says. “It’s like operating a running museum—it’s a little piece of history still in motion.”