Dam Safety Modifications at Cherokee, Fort Loudoun, Tellico and Watts Bar Dams

UPDATE – On July 7, 2014, TVA issued an amended record of decision (ROD) for the dam safety modifications project. The amended ROD documents TVA’s decision to change parts of the actions comprising the Alternative B selected in the May 24, 2013 ROD. The changes include the use of roller-compacted concrete (RCC) or a combination of RCC and earthen fill for modifications at Cherokee Dam, increases in the height of flood barriers at Fort Loudoun, Tellico, and Watts Bar Dams, and use of RCC for some barriers at Fort Loudoun. These changes, comprising Revised Alternative B – Permanent Modifications of Dam Structures: Combination of Concrete Floodwalls, Earthen Embankments, and Roller-Compacted Concrete, are the subject of a supplemental environmental analysis. The amended ROD and Supplemental Analysis can be viewed at the links below.

On May 24, 2013, TVA issued the final environmental impact statement (FEIS) for the proposed permanent dam safety modifications at its Cherokee, Fort Loudoun, Tellico, and Watts Bar Dams in Tennessee. The Record of Decision (ROD) to implement the preferred Alternative B: Permanent Modifications of Dam Structures: Combination of Concrete Floodwalls and Earthen Embankments/Berms was signed on July 2, 2013. The FEIS and ROD can be viewed by clicking on the links below.

The proposed permanent dam safety modifications are designed to minimize the potential effect of a Probable Maximum Flood (PMF) event. The PMF is defined as the flood that may be expected from the most severe combination of critical meteorological and hydrologic conditions that are reasonably possible in a particular drainage area. Recently updated modeling of flood conditions during a PMF event showed the maximum floodwater elevations at the four subject dams are higher than previously calculated. 

The purpose and need of the proposed dam modifications is to (1) minimize the potential for the failure from overtopping of the four subject dams during the PMF; and (2) prevent an increase in flooding during the PMF at downstream locations including Watts Bar, Sequoyah, and Browns Ferry Nuclear Plants.

In 2009, TVA implemented temporary and permanent measures at the four dams to remain consistent with Federal dam safety guidelines, to comply with nuclear plant operating regulations, and to minimize the potential effects of the PMF. These modifications consisted of installing stone-filled HESCO barriers at the four dams and strengthening the downstream embankment of Watts Bar Dam. 

The FEIS addresses three alternatives. Under Alternative A, No Action, the approximately 19,100 feet of HESCO barrier floodwalls (7,000 feet at Cherokee, 4,500 feet at Fort Loudoun, 6,000 feet at Tellico, and 1,600 feet at Watts Bar) would remain in place and TVA would maintain them as necessary. Under Alternative B, Permanent Modifications of Dam Structures: Combination of Concrete Floodwalls and Earthen Embankments/Berms, TVA would replace the HESCO barriers with a combination of concrete floodwalls and raised earthen embankments or earthen berms. Heights of the replacement floodwalls and embankments/berms would range from 3.5 feet at Watts Bar Dam to 6.6 feet at Cherokee Dam. The length of embankment/berm and floodwall at each dam are as follows: Cherokee Dam - 3,150 feet of embankment and 4,800 feet of floodwall; Fort Loudoun Dam - 3,400 feet of floodwall; Tellico Dam - 2,450 feet of embankment and 3,400 feet of floodwall; and Watts Bar Dam - 1,650 feet of embankment. Under Alternative C, Permanent Modifications of Dam Structures: All Concrete Floodwalls, TVA would replace the HESCO barriers with concrete floodwalls at all locations. Under both Alternatives B and C, TVA would also install post-tensioned anchors and enlarge an existing training wall at Cherokee Dam and strengthen an existing floodwall at Watts Bar Dam.

Public Involvement

TVA published a notice of intent (NOI) to prepare an EIS or an environmental assessment of the proposal in the Federal Register in June 2011; a copy of the NOI is available below. Public comments were invited on the scope of the project, including alternatives to meet the project need, and environmental issues that should be addressed, from June 14 to September 30, 2011.  Public meetings were held by TVA in July and September 2011. TVA has considered the numerous comments received during public scoping in designing the alternatives and developing the DEIS.

The DEIS was issued for public review and comment on September 28, 2012. TVA held a public meeting to accept comments on the DEIS on October 25, 2012 in Lenoir City, Tennessee. The public comment period closed November 19, 2012. TVA received comments on the DEIS from three governmental agencies, one Indian tribe, one local homeowners association, and 14 individuals. TVA carefully reviewed the comments and responses to them are included in the FEIS. The most frequently mentioned topics in the comments were recreation and visitor use at the dams, visual impacts of floodwalls, potential flooding related to the revised PMF elevations, transportation safety, and NEPA compliance.

Following the completion of additional engineering and design studies, and after considering the comments on the DEIS, Alternative B was modified by increasing the use of embankments and decreasing the used of concrete floodwalls. These changes reduce the anticipated impacts to some of the resources mentioned in the comments on the DEIS.