The Mountaintop Marvel

Raccoon Mountain Pumped Storage Plant an Engineering Wonder

Steep Raccoon Mountain, located along the eastern edge of the rocky Cumberland Plateau, has always been a remote place – sparsely settled and hard to reach, even though it’s only six miles west of Chattanooga, Tennessee, as the crow flies. Downstream from the city, even the mighty Tennessee River takes a sharp hairpin turn northward to avoid this massive bulk of limestone and pine.

As unchanging as the mountain may appear, it’s not the same as it was 40 years ago. Atop it now sits a man-made lake holding about 60 million cubic yards of water.

And deep below that lake, hundreds of feet down in the dark heart of Raccoon Mountain, are elevators, lighted tunnels and massive machinery. It’s not the underworld home of the spirit people of Cherokee legend, nor the lair of a James Bond villain. It’s TVA’s Raccoon Mountain Pumped Storage Plant – an unassuming name for one of the engineering marvels of the 1970s. There’s nothing else like it in the Valley.

Daring to Dream Big

TVA began exploring the idea as early as 1961, seeking a way to meet the Valley’s growing demand for electricity. By then, nearly every home had power, and many people were buying air conditioners, dishwashers and televisions for the first time. Demand was not only increasing – it was fluctuating wildly.

Electricity use was typically higher during the day than at night, but most generators produced power at a constant rate. TVA engineers needed a way to store energy and release it when demand peaked. One solution was to pump water into a reservoir and hold its potential energy until needed.

In the 1950s, TVA had tested the concept on a smaller scale at Hiwassee Dam in North Carolina, using a turbine that reversed during low-demand hours to pump water back into the upper reservoir. The experiment worked – and inspired TVA engineers to think bigger.

What if water could be pumped not just to the top of a dam, but to a reservoir on top of a mountain? And what if a long drainpipe could funnel that water down 1,000 feet to a powerhouse far below?

Making the Impossible Real

Most agencies would have dismissed the idea as impractical. When the Kennedy administration proposed a feasibility study of pumped storage systems in 1961, the response was lukewarm. Rep. James Haley, a member of the president’s own party, called it “a waste of the taxpayer’s money.” Walter Rogers, chair of the House Irrigation and Reclamation Subcommittee, dubbed it “a Rube Goldberg invention.”

But TVA secured funding and got to work. Studies of the Raccoon Mountain site showed the project would be difficult – but not impossible. Engineers proposed hollowing out a small lake on the mountaintop, sealed by an 8,500-foot-long dam. In a subterranean powerhouse, four massive turbines would generate electricity from the falling water. During low-demand hours, the turbines would reverse, pumping water back up at a rate of 7 million gallons per minute.

Throughout the 1960s, TVA engineers refined the idea using models built at the agency’s lab in Norris, Tennessee. In February 1970, the TVA board gave the green light. Construction began that summer.

More than 1,000 workers labored at Raccoon Mountain over the next several years. They excavated 10 million cubic yards of earth to build the lake, dug 12,000 feet of tunnels, carved a space the size of a football field out of solid limestone and installed four massive Allis-Chalmers pump turbines. More than 10 million cubic yards of fill was used to construct the mountaintop dam – the largest rock-fill dam TVA has ever built.

Engineering Beyond Expectations

In 1974, the National Society of Professional Engineers named Raccoon Mountain one of America’s most outstanding engineering projects. When completed, it was the largest water storage facility of its kind in the world.

The project took longer than expected. Originally scheduled for completion in 1973, it wasn’t finished until 1979, at a cost of just over $300 million. But it exceeded expectations.

The storage reservoir gives the plant tremendous flexibility to balance load and supply across the TVA system. It uses power during low-demand hours to pump water uphill, then releases that water to generate electricity during peak demand. The plant can also change output rapidly, making it ideal for load balancing and backup power.

With 1,700 megawatts of capacity, Raccoon Mountain generates 14 times more power than nearby Chickamauga Dam. It remains a cornerstone of TVA’s efficient, reliable power system.

For nearly 25 years, it has done just that – and with ongoing modernization and upgrades, it will continue to serve the region for decades to come.