Canals, Tunnels and Penstocks

Ocoee No. 2: The little dam that could

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Ocoee No. 2: The little dam that could
(photo courtesy TVA)

By Tennessee Valley Authority staff

The Tennessee Valley Authority concedes that its 23 MW Ocoee No. 2 dam and powerhouse are not the linchpin of the TVA river system in the U.S. However, it’s still a valuable piece of the company’s overall portfolio and has some claims to fame. For example, Ocoee Dam No. 2 and its flume were front and center at the 1996 Olympics, and that flume is now ensconced on the National Register of Historic Places.

Ocoee No. 2 was a 2022 inductee into the Hydro Hall of Fame. Read on to learn the important history of this hydroelectric project and how TVA is maintaining it into the future.

Hydro Hall of Fame

Overcoming challenges

TVA didn’t invent hydropower in the Tennessee Valley, of course. Waterwheels had been used to power sawmills and grain mills all over the region since the 18th century.

And over a hundred years ago, companies began using hydropower to generate electricity in the valley — sometimes going to great lengths to do so. In the 1930s, as TVA was setting up its valley-wide complex of dams, it discovered one such remarkable system already in place in a remote corner of southeastern Tennessee.

Hydropower is based on gravity: the farther water falls, the more power it can generate. Water in a gently sloping stream dissipates its energy as it descends and doesn’t produce nearly as much power as water falling from a great height. But nature doesn’t always put waterfalls just where you need them.

In 1912, the East Tennessee Power Company built a couple of modest-sized dams and hydropower plants on the Ocoee River, a fast-flowing stream that originates in Georgia. (The first of those facilities, Ocoee No. 1, was inducted into the Hydro Hall of Fame in 2012.) Below the site of one of the dams in Polk County, Ocoee No. 2, the river ran as whitewater down its twisting bed, losing most of its potential energy as it splashed over the rocks.

The dam, which consisted of a timber crib filled with stone, would be only 30 feet high when completed, so by itself it didn’t offer much electricity-generating potential. But if engineers could somehow keep the water high up on the mountainside until it reached a place where it could plummet from a height of, say, 250 feet, its power would be formidable.

The big solution

There was a sense of urgency about the project. A new aluminum company called Alcoa was setting up shop in Blount County not far away, and the plant would need massive amounts of electricity for its manufacturing process. (In time, Alcoa became one of TVA’s biggest customers.)

The problem was that the ideal spot to build Ocoee No. 2’s powerhouse was nearly 5 miles downstream from the dam. By that point, the river’s bed had dropped to a level 250 feet below the height of the water behind the dam. The dam was 450 feet long, stretching across the Ocoee River.

The power company’s engineers went to work. On a sort of shelf carved into the side of the mountain, they built a flume, or wooden trough, to carry the water from the dam down to the power plant. The flume was of a size unprecedented in the region — about 14 feet wide and 11 feet deep. Descending just 19 feet on its 5-mile course, barely enough to keep the water flowing, it arrived at a bluff, where the water roared through two large steel pipes to the generating plant far below. That plant contained two turbine-generator units.

Ocoee No. 2 was completed in October 1913 and had been in operation for 25 years by the time TVA acquired it in 1939. TVA engineers admired the eccentric throwback to another time. They studied the system and found ways to improve its generating capacity by about 15%.

Impressed with the hydropower potential of the Ocoee River, TVA also built another small dam and power plant upstream, Ocoee No. 3, using the same hydrodynamic principles exploited at the earlier dam. Ocoee No. 3’s powerhouse is 2.5 miles downstream from the dam. In this case, water is diverted through a tunnel rather than a flume, but as at the older dam, it generates significantly more power than it would have otherwise.

Preserving the past

The flume at Ocoee No. 2 chugged away until 1976, when TVA shut it down for safety reasons — in part because it could no longer support the rails and handcar that topped the structure and were used to maintain it. There was talk of disabling the flume or removing it altogether.

But an outcry from preservationists, including some sentimental old engineers, saved this monument to early hydraulic engineering. With TVA’s help, it was placed on the National Register of Historic Places.

In the early 1980s, TVA rebuilt the old flume with treated wood. This necessitated the release of all Ocoee River flow through the original river channel, rather than being diverted through the flume. As a result, a burgeoning whitewater rafting enterprise developed along that stretch of the river.

By 1983 the flume was back in business, as it is today. Parts of it are visible from U.S. Highway 64. Even the train track on the top was rebuilt. Rather than a handcar, though, a propane-powered tram now patrols the flume.

Through an agreement reached in 1984, today TVA provides recreational whitewater releases into the Ocoee River channel below the Ocoee No. 2 dam and is reimbursed by the State of Tennessee for the power production foregone by not diverting the river flow through the hydropower units.

The workers who run the three TVA dams and powerhouse on the Ocoee River even enjoyed a few weeks of worldwide attention in the summer of 1996, during the Atlanta Olympic Games. The whitewater kayaking events were held on the Ocoee River, between dams No. 2 and 3.

Today, the two turbine-generator units at Ocoee No. 2 still use the flume system to provide a capacity of 23 MW of electricity. TVA has modified the generating plant by adding new components and safety systems, but parts of the plant – such as head covers, generator frames and rotors — still date to the early 20th century.

Very few historic sites actually produce electricity. Thanks to TVA, Ocoee No. 2 is one of them.