A sign warns visitors to stay off of sand baskets that line the earthen dam portion of Watts Bar Dam near Spring City, Tenn. The baskets were designed as a prevention to flooding in a worse case disaster.PROBABLE MAXIMUM FLOODA “probable maximum flood” is the result of the most severe and reasonably possible combination of rainstorm, snow accumulation, melt rate and ground saturation in a particular drainage area. Dams, reservoirs and other heavy hydraulic structures must be designed to withstand such an event.DAM MODIFICATIONSTVA has raised the height of earthen embankments around four dams by 3 to 4 feet. The length of the embankments around the dams varies by site.• Cherokee: 7,000 feet, up 3 feet• Fort Loudoun: 4,000 feet, up 4 feet• Tellico: 6,000 feet, up 4 feet• Watts Bar: 1,400 feet, up 3 feetSource: TVA
Sand baskets installed to protect against extreme flooding and protect nuclear plants at Watts Bar and three other TVA dams have upstream neighbors unhappy about their new views.
But the safety vs. beauty question – prompted by a decades-old mistaken calculation by TVA – may mean even more dams must be raised with sandbags or permanent fixes, according to the Tennessee Valley Authority and the Nuclear Regulatory Commission.
“We had to fix the problem by raising the embankments as soon as we could or possibly have to shut down [Watts Bar and Sequoyah nuclear] plants. That could result in $3 million to $5 million a day in lost generation,” said Mike Eiffe, TVA program manager for hydrology and hydraulics.
Compared to those numbers, TVA’s cost to prepare for what utility officials have called a “highly unlikely probable maximum flood” would seem to be chump change.