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Tennessee Reinforces Dams Against Extreme Weather

KNOXVILLE, Tennessee, November 24, 2009 (ENS) – The Tennessee Valley Authority, TVA, is raising the elevation of four of its dams to help reduce the risk of flooding in the event of precipitation more extreme than any ever recorded in eastern Tennessee.

TVA will place temporary, wall-like structures on top of earthen embankments of the Fort Loudon, Watts Bar, Tellico, and Cherokee dams in eastern Tennessee, raising the top elevation of each embankment about four feet. The extra height is expected to prevent water from overtopping and damaging the earthen embankments.

“TVA evaluates its dam safety program regularly,” said TVA River Scheduling General Manager Chuck Bach. “As technology and standards evolve and more or better data becomes available, we update our flood forecasting calculations to determine whether we need to change our flood control operation or modify our dams to better protect public safety.”

Bach says a recent update of TVA’s river modeling program determined that the maximum floodwater elevations could be higher than previously calculated if a highly unlikely, worst-case winter rainfall were to occur in the upper part of the Tennessee Valley watershed.

Bach stressed that this action is not related to September rainfall that caused flooding in unregulated tributary streams, which was only a fraction of the amount used to forecast a “worst case scenario.”

“The magnitude of rainfall used in the calculations has never actually occurred in the region, but it could produce floodwaters that would be higher than previously thought,” said Bach. “Although the probability of such an event is extremely rare, TVA must design and operate its dams to safely withstand such events.”

TVA’s Fort Loudon dam (Photo courtesy TVA)

He said structures to raise the embankments are scheduled for installation by January 1, 2010, because large regional floods are most likely to occur in winter and early spring.

The interim measures are expected to remain in place until long-term, permanent solutions can be identified, evaluated and implemented.

To calculate the maximum flood levels in its river modeling, TVA assumes an extremely large storm within the watershed area being evaluated, which is critically centered to produce maximum flood levels.

The higher predicted flood levels are the result of improved data gathered in part from experience gained during large storms, revised analysis of spillway water flow rates at dams, and higher initial reservoir levels in TVA’s new reservoir operating policy.

The Fort Loudon Dam is a hydroelectric dam on the Tennessee River in Loudon County. The TVA built the dam in the early 1940s as part of a plan to provide electricity and flood control in the Tennessee Valley and create a continuous 652-mile navigable river channel from Knoxville, Tennessee to Paducah, Kentucky.

The uppermost of nine TVA dams on the Tennessee River, this 122-foot-high dam impounds the 14,600-acre Fort Loudoun Lake and its tailwaters are part of Watts Bar Lake.

Watts Bar Dam is a 112-foot-high hydroelectric dam on the Tennessee River in Meigs and Rhea counties that is one of the nine TVA dams on the Tennessee River. The TVA’s Watts Bar nuclear power station is located just south of the dam. Watts Bar Lake extends behind the barrier for over 70 miles, and a number of arms of the lake also lead off from the dam. In addition to the Tennessee River, the dam impounds the waters of the Clinch and Emory rivers, which were impacted by a massive ash sludge spill from the TVA’s Kingston power plant last December.

Tellico Dam is on the Little Tennessee River just above the main stem of the Tennessee River. This dam does not produce any electricity but directs almost all the flow of the Little Tennessee into a canal that enters the Tennessee River on the upstream side of Fort Loudoun Dam, adding to the hydropower capacity at that dam.

The Cherokee Dam is a 175-foot-high hydroelectric dam on the Holston River in Grainger County and Jefferson County, Tennessee. All four dams were built in the early 1940s to help meet urgent demands for energy at the outbreak of World War II.

The nation’s largest public power provider, TVA powers large industries and 158 power distributors that serve approximately nine million consumers in seven southeastern states. TVA also manages the Tennessee River system for flood damage reduction, navigation, water quality and recreation.

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