Boxes of sand are set to be placed on top of the earthen embankments at four Tennessee Valley Authority dams, including Fort Loudoun and Tellico.

The temporary four-foot walls are designed to keep water from topping the structures in the event of a storm bringing more water than has ever been recorded in the area, according to Chuck Bach, TVA's general manager of river scheduling. He said the work is necessary because new data shows the integrity of the dams could be compromised if the "probable maximum precipitation" is reached. He said it would take more rain than a 100-year or even 500-year flood.

The highest level of recorded rainfall in the area occurred in 1857 and Bach said it would take more than four times as much rain to reach the levels in question.  A recent update of TVA's river modeling program determined the maximum floodwater elevations could be higher than previously calculated.

For comparison he said some areas of the state received more than 2 inches of rainfall during the downpours last week and to reach the levels that would create a problem for the embankments, 27 inches of rainfall would have to come.

The others on the list include Cherokee Dam and Watts Bar Dam. The engineered boxes of sand are set to extend 4,000 feet at Fort Loudoun Dam, and 6,000 feet at Tellico Dam. The wall is set to be built near or on the greenway at Tellico Dam, though Bach said the public should still have access to the area and be able to walk along the path.

The outcomes of the project were listed to include preventing overtopping of the embankments, protecting the integrity of the dams, enhancing public safety and keeping TVA's nuclear plants within the original licensing basis.

The project is set to be completed by the end of 2009 at a cost of almost $8 million. Bach said they will then look for more permanent solutions starting with an environmental review.