Chilhowee Reservoir drawdown to inspect seepage at 44-MW Chilhowee hydroelectric project

Chilhowee Dam/Brian Stansberry

Project owner Brookfield Smoky Mountain Hydropower LLC (BSMH) is drawing down Chilhowee Reservoir, part of the 44-MW Chilhowee hydroelectric facility, to investigate seepage at the Chilhowee Dam on the Little Tennessee River in Blount and Monroe counties, Tenn.

Chilhowee hydroelectric facility was originally built and operated by Tapoco, a division of ALCOA, to generate hydroelectric power for the aluminum plant in Blount County. Brookfield Renewable Energy Partners purchased Tapoco's four dams in 2012 and renamed the operation Smoky Mountain Hydropower.

According to dam safety officials, they can see seepage getting out of the dam but are not sure where it is entering the dam wall. The drawdown will allow dam safety personnel to inspect and test the structure.

To date, BSMH has drained 20 ft of water from the reservoir, half of their planned 40-foot drawdown scheduled for completion by the end of October.

Construction on Chilhowee Dam began in 1955 and it opened in 1957. It is an 85-foot-high by 1,500-foot-long clay core dam that has two-rockfill embankments. The entire facility also includes a powerhouse and intake, a concrete gated spillway and two concrete non-overflow sections.

Past issue

During 2008, four years prior to being purchased by Brookfield, dam safety personnel repaired a sinkhole in the clay core on the upstream slope of Chilhowee Dam’s left embankment section.

According to the Federal Energy Regulatory Commission (FERC), “The underlying causes associated with the development of the sinkhole at Chilhowee Dam [in 2008] stemmed from issues related to the original construction, which became evident during the careful excavation of the embankment.

“Inadequate foundation preparation and missing downstream fine filter material allowed the slow process of migration of the clay core material in the downstream direction, opening a seepage path through the core. The steep and overhanging rock face at the abutment caused additional problems for the clay core, as settling clay caused a crack in the clay core following the rock face.

“A small section of fine filter was not placed at the rock contact during original construction, allowing downstream medium filter to be against the downstream clay contact.”

Current actions
On Sept. 8, BSMH began drawing down Chilhowee Reservoir at a rate of 1 foot per day to repair a different portion of the facility.

According to Andy Davis, community relations manager for Brookfield North America, "We are currently drawing down the reservoir to investigate seepage, a normal occurrence, on a different portion of the dam, which may or may not be related to construction, previous repairs or operations.

"As responsible, long-term, owners and operators of numerous hydro facilities, we feel a responsibility to investigate all activities such as this. We have worked, and continue to work closely with our partners at the FERC and our independent Board of Consultants on this issue."

David Schreck, dam safety engineer for Brookfield Renewable Energy Partners in published reports said, “Seepage is common and occurs in most dams to some degree, but finding the source can require a lot of work."

According to Schreck, the source of the seepage may be something minor that the facility will continue to monitor or it may be something that requires a significant amount of work to remediate.

BSMH and FERC continue to work with resource agency representatives including the U.S. Fish and Wildlife Service, Tennessee Wildlife Resource Agency and the Tennessee State Historical Preservation Office to ensure all environmental, historical and public safety concerns are mitigated.

Along with Chilhowee hydroelectric project, Brookfield also operates the 140-MW Calderwood and 140-MW Cheoah hydropower facilities upstream from Chilhowee Dam. The 45-MW Santeetlah hydroelectric facility located on the Cheoah River in Graham and Swain counties, N.C. was also obtained as part of the Tapoco purchase.

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