As much as 3 inches of rain forecast late last week for the Cumberland River Basin did not materialize and the level of Lake Cumberland has begun to fall. Rain Thursday and early Friday was not expected to be heavy enough to trigger another rise in the lake.
The lake level reached 727.95 feet above sea level late last Sunday; began falling at 4 p.m. Monday; and had dropped slightly more than a foot by noon Thursday. The level Thursday at noon was 726.80.
Water is being released rapidly –– 28,600 cubic feet per second –– through the dam’s six hydroelectric generators, and floodgates open at the top of the structure.
Benjamin Rohrbach, chief of the Hydrology and Hydraulic Branch at the U.S. Army Corps of Engineers’ Nashville District, said with considerations for flooding downstream, efforts will continue to bring the lake level down to the SEPA (Southeastern Power Administration) curve. SEPA curve is a lake water elevation guide that rises from February 1 with spring rainfall and reaches elevation 723 on May 15, then slowly draws down through the summer and fall.
This curve is designed to ensure an adequate level of water for continued hydropower production throughout the year. Electrical energy produced by the project is sufficient to supply the needs of an average city with a population of 375,000.
At the level Thursday, the lake was nearly four feet above pool stage and about two feet, depending on the location, above the tree line. The SEPA curve point Wednesday was about 710 feet. Without excessive rainfall, 710 would be the appropriate SEPA curve level in mid-March as the lake slowly rises toward summer pool, Rohrbach explained.
Another reason to bring the lake down quickly is the dastardly little duskytail darter. Rohrback pointed out the Corps has an agreement with U.S. Fish and Wildlife Service to protect the habitat of the endangered minnow in the Big South Fork of the Cumberland River.
If you recall, the duskytail darter got a bad name when it was discovered the darter had created new habitat in the Big South Fork while the lake was kept low for seven summers to repair Wolf Creek Dam. Without congressional intervention, the darters’ new habitat in the Big South Fork would have kept Lake Cumberland lower than normal this past summer.
Congress authorizes the Corps to operate Lake Cumberland within a 50-foot storage area between 723 and 673. Rohrback said the Corps has a non-binding agreement with SEPA, marketing agent for hydroelectric power generated at the dam, to operate within most efficient level.
“We try to operate in a more narrow band to bring up to summer pool for summer and down for fall. Level 723 is top of SEPA curve; 673 is the bottom.