Major maintenance work that could last up to five years is expected to begin next fall at Rough River Lake Dam.
The U.S. Army Corps of Engineers recently announced plans to fill cracks, fissures and other openings in the bedrock under the earthen dam, which was built in 1958.
The cracks and fissures are a natural outgrowth of the limestone rock in the area. Limestone erodes in water, meaning over time cracks can appear in and around the bedrock.
“Generally speaking, the problem involves seepage under the foundation,” said Carol Labashosky, a public affairs specialist with the Corps’ Louisville District. Surveys, she explained, have discovered paths in the limestone rock that could carry water under or around the dam, posing a potential safety risk.
She said the flooding during the spring and summer of 2011, when the dam held back record high water levels, didn’t cause the problems.
Jeff Esterle, the Loiusville District’s dam safety program manager, said the work amounts to preventative maintenance.
“There was no specific discovery or incident that is prompting this work. The karst nature of some of the geologic formations (the bedrock) that underlie the dam are well known. We know this from regional geologic knowledge and site specific documentation from construction and explorations - including drilling and core samples - and assessments that have taken place at Rough River Dam throughout its operation,” he said. “In 2005 we began evaluating the risks at Corps operated dams. The Corps developed risk reduction, risk assessment, and risk management procedures for implementing a nationwide evaluation process that prioritizes the funding and allocation of dam safety resources. (The Corps) began an approach to consistently take appropriate actions to address our dam safety issues. Rough River Dam began this process in 2005 with a screening assessment which gave it priority for further investigations and study. This national initiative prioritizes remedial repairs to address our aging infrastructure.
“There has been no distress observed at the dam related with these features; however, these formations have been identified to have the potential to weaken the dam embankment,” Esterle said. “It is imperative to address these potential concerns — solution features — before they worsen over time.”
Esterle said the Corps expects to wrap up any preliminary design work next year and start construction sometime in the spring of 2014. The first phase of the work will involve boring into the dam to place a type of grout into the foundation. Highway 79, which runs across the top of the dam, will be moved several feet over in order to create a work platform on the dam’s crest.
“We may also have to build out several feet on the downstream side of the dam, to have the room we’ll need,” he said.
Depending on the extent of the solution features, the Corps may have to advance to a second phase of the project: building a “cutoff wall” in front of the dam, Labashosky said.
That wall would go down about 200 feet and span the roughly half-mile length of the dam, Esterle said.
“I think we think we’ll go on to Phase 2,” he said. “You’re always happy if things come out to be less costly, but I don’t know if that will be the case here.”
He said the Corps doesn’t anticipate having to deviate much from the lake’s normal summer pool depth to do the work. “If critical problems do come up, we’ll try to work around the normal pool drawdown times,” he said.
In all the work could cost “tens of millions of dollars” and take from three to five years to complete, Esterle said.
The solution features are similar to ones the Corps has been trying for years to repair at Lake Cumberland — but not as serious.
In 2007 the Corps began drawing down Lake Cumberland, worried that a weakened Wolf Creek Dam could break and cause massive flooding. At that time the dam, which was built on fissure-riddled limestone, was assessed as one of the five riskiest in the country.