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Labor Day weekend marks the start of the unrestricted drawdown

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TVA River Neighbors
august 2006

 

Reservoir operations update

Labor Day weekend marks the start of the unrestricted drawdown

After Labor Day weekend, reservoir users can expect to see a more rapid decline in pool levels as restrictions on the drawdown (lowering) of TVA-managed reservoirs end, and the water stored in the tributary reservoir system is used to meet power demands and provide other benefits.

Prior to 2004, when TVA implemented a new reservoir operating policy, the unrestricted drawdown began a month earlier, on August 1.

TVA’s new policy restricts the amount of water released from tributary storage reservoirs from June through Labor Day, says Steve Adams, manager of River Scheduling at TVA. “That helps conserve water in upstream reservoirs for recreational use, especially when the weather is dry.”

This summer provides a good example, he says. “August 1 levels on most TVA-managed reservoirs were within a foot or two of where they were in 2005 even though we didn’t get nearly as much rain this year.”

The reason, he says, has to do with the flow requirements specified under TVA’s operating policy. “Our flow targets vary depending on how much water is stored in the tributary system. If we get a lot of rain and there’s plenty of water in storage, the systemwide flow targets are higher. But if the weather is dry and the water in storage falls below a specified level, then our flow targets are lower.”

That’s what happened this year, he says. “In mid-July, the total volume of water stored in the tributary reservoir system dropped below the minimum level. That automatically reduced our flow target at Chickamauga Dam and helped us conserve more water in upstream reservoirs.”

The fact that releases are restricted during the summer doesn’t mean there won’t be any drawdown prior to Labor Day, says Adams.

“Even during June, July, and August, we need to release enough water to meet several types of flow requirements. In addition to the systemwide flow requirement measured at Chickamauga, each dam has specific flow requirements set to keep water in the downstream riverbed, which is critical to aquatic life. Some dams also have flow requirements related to whitewater and other recreation-schedule commitments.”

Typically, reservoir users will see a gradual drop in pool levels over the course of the summer as water is released to meet these flow requirements.

The exception, says Adams, is in wet years.

“If rainfall is above normal, as it was in 2004 and 2005, reservoir users hardly notice that we’re releasing water to meet downstream flow requirements because the water is replaced as fast as it’s released.”

Adams says several factors helped TVA cope with this summer’s dry weather. “We began keeping reservoir levels higher in the winter months in 2004, which meant that we started the spring with more water in the system. Plus, in late February of this year, we began operating in a water-conservation mode.

“Because of those actions, we were able to reach targeted summer-operating levels on most tributary reservoirs despite the dry conditions.”

All but four tributary reservoirs were at summer level by Memorial Day weekend. The exceptions — Fontana, Chatuge, Nottely, and Hiwassee — were in western North Carolina, where conditions were even drier than across the rest of the Valley.

To track your reservoir’s elevation and to see how it compares with last year and an average year, go to TVA’s Reservoir Information page; then find the name of your reservoir in the pull-down menu and select “Operating Guide.”

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