In Nov. 20-26 IssueBy Greg WellsTimes Journal Managing Editor
Crews have been working at the site of Center Hill Dam since the first large contract for stabilization of the dam was awarded in February.
In a matter of weeks grouting will begin at the Tennessee dam.
U.S. Army Corps of Engineers officials, during a tour last week said grouting will start immediately to make the dam more stable. And like Wolf Creek Dam, it has been done before.
But in the opposite situation faced by the dam holding back Lake Cumberland, this time there are more visible signs of the seepage at that dam.
The previous problems at Wolf Creek have been characterized as much more serious than those this dam is suffering now. In the late 60s and early 70s there were sinkholes in the down-stream face of the dam and muddy water could be seen welling up in the river. This time neither situation is apparent here.
Meanwhile in Tennessee the Corps is trying to control several sinkholes that have collapsed around the dam downstream. Sinkhole 11 in the left rim of the dam, is about 25 feet deep.
It collapsed in 2003, an indication that material is being pulled down by water flowing underneath.
"When the lake is 30 feet higher than it is right now, you can hear water roaring in the bottom of this," said Linda Adcock, project manager as she stood by the sinkhole last week.
If another sinkhole happens to pop up on the earthen embankment of the dam, it could be catastrophic.
"It's an indicator of why we're doing what we're doing," said Engineer David Loyd.
Exploratory drilling, where samples of the rock condition are taken, could begin in the next week to 10 days, and will take about two weeks to complete.
"We will be doing exploratory drilling to find out what's going on," said Lt. Col. Bernard Lindstrom, district engineer. "We know water is making it around and through (the foundation), we just don't know where it is."
When actual grouting begins, about 1,000 holes three inches in diameter will be drilled into the foundation. It's possible more holes could be drilled.
This step has been completed, for the most part, at Wolf Creek Dam.
Also just like Lake Cumberland the Center Hill Lake has been lowered to take stress off the dam and reduce the damage that water flowing under and through the dam is causing. That lake was ordered drawn down, but the drought there is likely to push Center Hill to its lowest level since 1956 by the end of this year, according to Bob Sneed, chief of water management at Center Hill. "This is an extreme event," he said
A lake level lower than 618 feet would have dire affects on water supplies for both Smithville and Cookeville. According to Corps officials, Smithville city officials are currently working to lower water intakes below the 618 maker.
As for Cookeville, the city receives all its water supply from Center Hill Lake, and the city also sells to Baxter, Algood and Double Springs, among others.
"The lower the lake, the less water we're able to pull," said Ronnie Kelly, director of the Cookeville Water Department.
Several marinas on Center Hill have been affected by the lower lake levels, and docks at both Hurricane and Sligo have been moved, Corps officials said.
Lindstrom said the Corps expects to know more by January about when lake levels could possibly be raised.
That might happen next year, Sneed said, or it might not.
"During this process, if there is an anomaly, something we find deeper in the structure we didn't anticipate finding, we could lower the lake level just as readily as we increased it," he said. "So it is a process that we're going to put into place that has no guarantees."
Center Hill Dam has always experienced seepage since it was completed about 57 years ago, and seepage has increased in recent years.
The dam was identified along with Wolf Creek in upstream Kentucky by the Corps in late 2005 as at high risk for failure.
The project is estimated to cost $260 million and is projected to be completed by 2014.