Methodology of raising lake levels depends on several factors
By BILL MARDIS, Editor Emeritus Commonwealth Journal
If the U.S. Army Corps of Engineers gets a “green light” on April 1 to raise Lake Cumberland by 20 feet, historically there is a 70 percent chance spring rains will be sufficient to allow the lake to reach that level (700 to 705 feet above sea level) by June 1, the traditional start of the summer vacation season.
“It all depends on Mother Nature,” said Don Getty, manager of the Wolf Creek Dam Remediation Project. The lake will be higher than now, but it might not be 20 feet higher, Getty added.
The Corps announced late last week the contractor making repairs to Wolf Creek Dam is running ahead of schedule and there is “high probability” the lake will be raised 20 feet this coming summer. This is almost a year ahead of the previously projected December 2013 completion date and a rise in the lake for Summer 2014. Now, the Corps says its goal is to have the lake at pool stage (723 feet above sea level) summer after next.
But the higher lake level this summer “is not guaranteed,” Getty cautioned. The expected “green light” to raise the level of the lake depends on several factors:
• Completion of the permanent barrier wall in the cavernous Critical Area 1, a 600-foot-long part of the dam near the wraparound of the earthen and concrete sections.
• Recommendation of a panel of safety experts.
• OK from the commander of the Great Lakes and Ohio River Division of the U.S. Army Corps of Engineers.
As of last Saturday (January 19) there were less than 30 holes remaining to be drilled to finish the wall in the critical area, Getty said. Three drills are working in the area and averaging seven or eight holes a week.
The permanent wall is being created by drilling 50-inch diameter holes 275 feet deep from the work platform on the upstream side of the dam to about 100 feet into the limestone bedrock. Each hole, filled with 140 cubic yards of concrete, is called a pile. About 1,200 piles have formed the wall outside Critical Area 1. The wall inside the critical area is formed with 232 piles, 30 of which remain to be drilled.
The 50-inch holes overlap, like Olympic rings, forming a permanent wall that must be at least two feet thick. The new wall extends into a deeper and more stable limestone stratum than immediately below the dam.
Mid-March is the projected time for finishing the permanent wall in Critical Area 1, the key to raising the level of the lake. Getty said a two-day conference among safety expects after the wall is complete will end with a recommendation to Brigadier General Margaret W. Burcham, commander of the Great Lakes and Ohio River Division. It is she who will give the “green light” to raise the lake level, Getty said.
There will be little or no noticeable difference in the flow of Cumberland River below the dam while the lake is being raised, according to Getty. “We must maintain a minimum flow of 1,000 cfc (cubic feet per second) ... a significant amount of water,” Getty said.
There are six turbines and six sluice gates at the bottom of the dam through which flow can be reduced to raise the lake level. Spillway or flood gates at the 723 level obviously are not involved, Getty said. “Mostly, we will depend on spring rains,” he repeated.
Actually, the lake is now at the 693-foot level because of recent heavy rains in the Cumberland River Basin. This is about 13 feet above the target 680-foot level, and nearly 25,000 cfs are being released through the dam.
For the past six summers Lake Cumberland has been kept as nearly as possible to 680 feet above sea level, about 40 feet below normal, to facilitate repairs at Wolf Creek Dam. The mile-long structure was declared in high risk of failure in 2005.
A $594 million rehabilitation of the dam was begun early in 2007 and is now nearing completion.