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.