FloodsTVA considering raising height of dams to prevent future floods

The dams located on the upper Tennessee River never had flood waters top them, and government officials want to keep it that way, saying that due to recent disasters such as the 2010 Nashville flood and the 2011Fukushima tsunami, they need to prepare the worst possible situation.

Times Free Pressreports that Mike Eiffe, Tennessee Valley Authority’s(TVA) program manager for hydrology and hydraulics, said preparing for a “probable maximum flood” means raising the levels of the dams and the earthen berms that flank them.

“The drainage area for Chattanooga is a little over 20,000 square miles, and for the type of flood events that we’re talking about, we would be looking at an average of 15 to 16 inches of rainfall over that entire 20,000-square-mile drainage area,” Eiffee told the Times Free Press.

Three years ago the TVA began making improvements, including sand baskets to heighten the berms near the Cherokee, Fort Loudoun, Tellico, and Watts Bar dams, but Eiffe said that the temporary improvements are not intended to last very long, so more work is needed. More long-term fixes include building concrete floodwalls and embankments ranging from 2.3 feet to 6.6 feet in height, depending on the area.

The TVA and the Nuclear Regulatory Commission(NRC) met earlier this week in Atlanta to discuss additional safety methods.

The talk of improvement began when the TVA determined that an old faulty calculation, improved technology, and changes in water management increased the probable maximum flood levels for the Watts Bar and Sequoyah dams.

The effort cost between $8 and $10 million and was finished on a tight deadline set by the NRC to alleviate the potential of water reaching over the dams. TVA spent another $2 million studying to see if the other dams needed improvements.

TVA spokesmen Bill Sitton and Travis Brickley told the Free Press that permanent fixes could cost between $20 and $30 million.

According to a draft safety modification document from September, flood-proofing the Watts Bar, Sequoyah, and Browns Ferry nuclear plants could cost up to $1 billion.

The reason that work has not started yet is that  the first priority is to keep the dams, plants, and even the town of Chattanooga standing.

A 15-to-16 inch rainfall would raise the probable maximum flood level from 734.9 feet above mean sea level to 739.2 feet.

“I’m not so worried about the nuclear plants. But I think a flood like that would be a substantial threat to Chattanooga,” Hamilton County Emergency Management chief Bill Tittle told the Free Press.

“The weather systems are changing. We see and hear about it every day. If the Nashville rains had been a little east, that would have been us,” Tittle added.

Officials recently said that if the same amount of rain that hit Nashville were to hit Chattanooga, the monetary effect would have been greater than in the Nashville flood.

According to Tittle, local emergency officials are working with TVA and weather forecasters in order to produce methods to warn residents in advance of a major storm. This system worked in the past as residents were warned three days before tornados hit the region last year.

“The frustrating thing is we don’t have a way to stop it [the weather],” Tittle said.

David Lochbaum, the director of the nuclear safety project for the Union of Concerned Scientists, said TVA plants now have a higher safety threshold because of the new flood calculations.

According to Lochbaum, the Oconee Nuclear Plant in South Carolina has a double-digit gap between former and revised levels. Lochbaum also gave credit to the NRC for preventing a nuclear disaster in Nebraska, when a 2010 inspection found that the Fort Calhoun Plant had no flood protection and procedures. Due to the improvements made after the inspection, a flood in 2011 caused no damage to the plant.

TVA spokesman Ray Golden said that additional safety features are being installed at the plants themselves, including elevating pumps and improving seals around the doors, pump lines and conduits. Equipment modifications are also taking place.

“What we want to tell them is that we take this matter very seriously,” Golden told the Free Press.