NASHVILLE, Tenn.—In late January, the U.S. Army Corps of Engineers’ (USACE), Nashville District began lowering the level of Lake Cumberland to an elevation of 680 feet in response to USACE and independent studies that classified the 258-foot-high Wolf Creek Dam, in Russell County, Ky., as being at "high risk" for structural failure. Normal pool levels for the maximum 6 million-acre-foot reservoir are 723 feet in the summer and 690 feet in the winter; flood storage pool elevation is 760 feet. Further water-level reductions to decrease water pressure on the dam and reduce the risk of dam failure may be necessary, depending on the effect that lower lake levels have on the dam, the USACE said. The Nashville District expects to maintain the 680-foot elevation for the remainder of 2007 and reevaluate lake levels in September or October for next year’s operation.
Because of the seriousness of foundation seepage problems at Wolf Creek Dam—which forms the largest reservoir east of the Mississippi River and is considered one of the USACE’s highest-risk dams—an accelerated grouting program is underway and the USACE is requesting full funding to accelerate construction of a remedial project.
Wolf Creek Dam, designed and constructed from 1938 to 1952, is founded on karstic limestone. The dam consists of a 1,796-foot-long concrete section and a 3,940-foot-long compacted clay embankment. The dam developed serious seepage problems in 1968, including wet areas downstream near the right abutment, muddy flows in the tailrace, and two large sinkholes in the embankment. Grouting stopped the leaks, but the USACE sought a long-term fix by constructing a concrete diaphragm wall. A partial wall was constructed between 1975 and 1979, extending along two-thirds of the length of the earth embankment and into the underlying rock foundation.
In recent years, the USACE said they have noted "persistent and increasing wet areas downstream." Instruments have shown a slow increase in water pressure in several areas of the foundation and exploratory drilling encountered soft, wet material in the embankment near the foundation, leading the USACE to conclude that water seepage has developed new paths under and around the concrete wall.
The USACE recommends building a new concrete wall starting near the concrete and earthen dam interface and running the entire length of the earthen dam—1,650 feet further than the existing wall and extending 75 feet deeper. Construction cost is estimated to be $300 million, with the project completed by 2014.
More information about Wolf Creek Dam, as well as progress reports on the rehabilitation project, are available online at www.lrn.usace.army.mil/pao/issues/WOLcommo.