Outside Engineer's Report
The U.S. Army Corps of Engineers this week released the outside engineers' review of problems at Wolf Creek Dam, which was used in making the decision to lower Lake Cumberland's to a low of 680 feet above sea level through this summer season. The report was delivered to the Corps last fall, and was released this Tuesday.
It indicates that had the Corps done nothing to fix a growing seepage problem, the dam could have failed in five years. "At this stage of failure mode development, the Panel believes there is significant potential for failure of Wolf Creek Dam under the normal operating conditions. The time at which such a failure would occur is very difficult to predict," according to the summary.
These are the recommendations pulled directly from that summary—
• It is essential to 1) take immediate short-term actions to avoid failure and to reduce risks to the public, and 2) to expedite investigations, design and construction of long-term repairs.
• The reservoir water levels should immediately be lowered and maintained at a lower level until short-term corrective actions arrest further development of the failure mode and long-term corrective actions have been completed. The Panel believes that a target drawdown level of between 640 and 650 is needed to help avoid the development of a failure due to seepage through the embankment dam and its foundation. The Panel further recognizes that the selection of a target drawdown level must consider a number of factors, the most important of which is to prevent loss of life.
• Conduct Foundation Grouting Immediately: The planned foundation grouting program is a critical short-term risk reduction program that must be completed as soon as possible under Monolith 37, under the embankment in the area immediately adjacent to Monolith 37, and in the area to the right of the point where the existing diaphragm wall was terminated.
• Improve Existing Instrumentation: The entire investigation, piezometer and settlement instrumentation system and monitoring program for the dam, including the planned investigations and instrumentation to be installed as part of the grouting program should be independently reviewed as soon as possible. The system for measuring ongoing deformations of the dam crest and key areas along the downstream slope and the wrap-around section of the embankment is not considered adequate and needs to be substantially modified as soon as possible so that reliable deformation measurements can be obtained. Additional investigations and instrumentation are recommended in two "depression" areas identified by the Panel including 1) a portion of the downstream wrap around section near the contact with the concrete dam, and 2) along the downstream slope near the end of the diaphragm wall to investigate the root cause of the depressions that have developed.
• Review Reservoir Restriction: Once completed, the results of the supplemental investigation and grouting program, along with the supplemental instrumentation monitoring, should be independently reviewed to determine whether adjustments to the target reservoir drawdown level are appropriate. Corps officials said this week that they don't believe it's necessary to drop the lake from its current level of 680 feet, though the panel recommended dropping it to 650 feet. The corps lowered the lake to 680 feet earlier this year to take pressure off the dam and reduce the consequences of a breach. Officials said they intend to do what they had previously announced: re-evaluate the stability of the dam this fall after having attempted initial repairs with grout injections. After that assessment, they will decide whether the lake should be lowered, stay the same, or possibly be raised. Bill Jasper, president of State Dock, was quoted in the Louisville Courier-Journal newspaper that he believes officials are overreacting to the dam's situation. He said corps officials and their outside advisers "seem to be concerned about the consequences" of a dam failure, "not the reality of it happening."
