By BILL MARDIS, Editor Emeritus
Somerset — Slight material movement in a critical area at Wolf Creek Dam has caused a suspension of work in a 600-foot section of the earthen structure and may have wiped away any chance of an anticipated higher lake level during the summer of 2011.
Dave Hendrix, manager of the $584 million rehabilitation project at the dam, said instrumentation indicated a “ ... less than an inch” movement in soft material in one of the limestone cavities beneath the embankment near where the earthen and concrete sections of the dam join.
The material movement did not trigger an emergency declaration but emergency management personnel in communities below the dam were notified “ .... so they will know what is going on,” Hendrix said. Asked if the situation significantly increases danger of a breach in the dam, Hendrix said “no.”
“As a precautionary measure, we have suspended construction in Critical Area 1 while we evaluate the most recent monitoring and instrumentation data,” stated Barney Davis, chief of the Engineering and Construction Division for the Nashville District. The suspension affects only 600 feet of the 4,400-foot long, 275-foot deep concrete barrier wall, which is the major structural component of the rehabilitation project. Work is continuing in non-critical areas of the dam, and Davis indicated that the Corps does not foresee any changes to the lake operation plan at this time. This apparently means the Corps does not believe it is necessary to lower Lake Cumberland below its current level.
Hendrix said the suspension of work in this critical section “ ... makes an evaluation of the lake level for the 2011 vacation season “unlikely.” Previously, the Corps said that when the permanent barrier wall was installed in Critical Areas 1 and 2 –– projected earlier between next December and March 2011 –– an evaluation of the lake level could be done. Lake Cumberland has been maintained nearly 40 feet below pool stage since January 2007 to facilitate repairs at the dam.
Wolf Creek Dam was built on limestone rock and naturally occurring caves in the rock were filled with clay. Because of this porous foundation, the dam has been plagued with seepage, sometimes uncontrolled, since it was completed in late December 1950.
Two critical areas, dubbed Critical Area 1 and Critical Area 2, are places in the earthen structure where most of the uncontrolled seepage occurs. Critical Area 1 is near the wraparound of the concrete area of the dam where it joins the earthen section. Critical Area 2 is in the earthen section about halfway between the concrete and Halcomb’s Landing.
Serious leaks in the dam, including two sinkholes and muddy water in the tailrace, were repaired during the 1970s with extensive grouting and a barrier wall. The initial wall was not long enough or deep enough to be a permanent fix and the seepage continued and worsened.
The Corps announced in August 2005 that an outside panel of experts had declared the dam in high risk of failure and a major rehabilitation of the structure was necessary. A second barrier wall, longer and deeper than the first, is currently being installed. Hendrix said analysis of the current situation will take four to six weeks and at this point it is not known if the December 2012 project completion date will be extended.
Instrumentation used to monitor the dam's foundation is one of the Interim Risk Reduction Measures (IRRM) in place at Wolf Creek. IRRM are designed to minimize risk to public safety in the short term while pursuing long-term permanent fixes, such as the ongoing rehabilitation project.
“Wolf Creek Dam is one of the most heavily monitored dams in the country,” stressed Davis. “Our instrumentation is doing its job and giving us the information we need to protect public safety and effectively rehabilitate the dam.”
