Photo courtesy of Tennessee Valley Authority
TVA crews carefully rebuilt Hibbs Island with gravel and concrete to stabilize the two sections of weir dam, which help maintain oxygen-rich flowing water for fish and other aquatic animals.
The problem may sound small, but it was huge for aquatic life and fishers on an East Tennessee river: A 10-acre island downstream of the Norris Dam was washing away.
Hibbs Island, a popular spot for anglers, sits in the Clinch River just a few miles downstream of the giant Norris Dam, the centerpiece of a much smaller dam that controls the flow of water from Norris to keep the riverbed downstream from drying up.
Record rainfall between 2018 and 2020 eroded the slim island and threatened its essential function, the Knoxville News Sentinel reported May 24.
The Tennessee Valley Authority (TVA) rehabilitated the island by building a 217-ft.-long berm across its center — a massive pile made of 1,200 cu. yds. of soil and 3,200 tons of rock from local quarries.
Starting in April 2023, TVA crews drove tons of rock and soil across the river on small rubber-tracked dump trucks designed to have a minimal impact on the riverbed. For eight months, the island and the weir dam were closed to anglers.
To kick off the 2024 summer season, the federal utility hosted elected officials, fishing advocacy groups, and reporters to see the completed rehabilitation project May 24 as a gentle mist hung over the Clinch River island.
"These improvements for anglers benefit our quality of life as a community, they generate revenue for our region, bring joy and togetherness," said Terry Frank, mayor of Anderson County, which, along with Campbell County, is home to the dam and its reservoir. "For many, it also brings healing."
Norris Weir Dam Protects the Local Ecosystem
When the Norris Dam was completed in 1936, it was not only the TVA's first hydroelectric dam, but its first major power plant construction, and its initial source of renewable energy.
Today, there are 29 TVA hydroelectric dams in the Deep South that provide up to 10 percent of the utility's power generation.
Their design disrupts the flow of the rivers they are built upon, even as they help prevent flooding and produce clean energy. The Norris Dam, for instance, holds back the largest tributary reservoir in the Tennessee River watershed and is a major holding body for rainfall.
Smaller weir dams are built to help control the flow of water downstream from the large structures. For 60 years before the Norris weir dam was built in 1995, the Clinch River flowed unevenly out from Norris Dam depending on when and how much water TVA ran through its two generators, according to the Knoxville news source.
At times, the riverbed downstream from the dam sank to dangerously low levels or dried up, harming the ecosystem of fish and aquatic insects who call it home.
The Norris weir dam holds back some of the water flowing through the barrier and provides the minimum flow needed to keep fish and fishers alike happy. Insects like the Sulphur mayfly, used in fly fishing, have made a comeback, said Bob Stephan, president of Clinch River Chapter of Trout Unlimited.
"We're seeing it in areas of the river that we haven't seen it in for a long, long time," he told the News Sentinel. "I'm probably one of TVA's biggest fans right now."
Hibbs Island, which bisects the weir dam, began to erode until the Clinch River started to flow around the sides of the dam. TVA drones allowed staff to see how erosion was threatening to undermine the weir dam's careful system of control.
The new berm across the island restores its function.
Every 11 to 12 hours, TVA pulses the generators at Norris Dam to send more water downstream. Sirens blare at the weir dam to warn people that water will soon cascade over it. Those who have walked to the island and don't heed the siren can get stuck waiting for the flow to subside.
Along the Tennessee River and its tributaries, TVA manages 40,000 miles of waterway and 11,000 miles of reservoir shoreline.
TVA Hydro Dams Play an Important Role
The federal utility agency's fleet of hydroelectric dams is the bedrock of its renewable energy, providing enough power for around 2 million homes at peak capacity. The dams also allow TVA to prevent flooding and control safe water levels for summer recreation at lakes across the state and region.
Hydro power will become even more important as TVA brings other kinds of renewable energy onto the grid, especially solar, said James Everett, general manager of river management.
"These reservoirs are like batteries," Everett told the Knoxville news source. "We can turn this generator off, stop producing power when solar comes up, and store the water in the lake. Then when the sun sets, and the solar starts to decline off the grid, this water we stored is energy."
California and other western U.S. states have used hydro power this way as they build more solar and wind energy. Though TVA produces less than 1 percent of its power from its own solar projects, it plans to add 10,000 megawatts of solar power by 2035. Due to its fleet of dams and nuclear plants, the utility produces 55 percent of its power carbon-free.
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