Amid public scrutiny of the U.S. Army Corps of Engineers’ actions during record flooding, the agency released descriptions of the steps officials took to lessen flooding in the Cumberland River basin.
“It is not the Corps’ intent to publicly refute criticisms or questions raised, but to merely state the facts,” said Lt. Col. Anthony Mitchell, commander of the Nashville District.
“Rainfall from the weekend of May 1-2 set and shattered records throughout the region,” he said. “With the amount of rain that fell in uncontrolled parts of the Cumberland River Basin, flooding was inevitable.
“This was a natural disaster, but our dams did their job by holding back much of the rain water, and with controlled releases of water that actually lowered the crest of the river through Nashville.”
To determine whether the Corps could have improved, the agency is working with the National Weather Service and other public agencies to launch an after action review and lessons learned investigation.
Results of this review will be made public when complete.
“We will continue to clarify or correct information as needed, because we want the public to fully understand how we operate our projects,” Mitchell said.
As for the historic flooding of May 1-3, the Corps said it took proactive pre-storm action to lower reservoir levels across the system.
The initial weather forecast on April 28 predicted 3 to 5 inches during the weekend. As a result, Corps water management professionals lowered Cordell Hull, Old Hickory, and J. Percy Priest lakes. Cheatham Lake was lowered a foot. The actual rainfall in some areas exceeded 17 inches, far more than the predictions.
Since the dams on the Cumberland River have been in place, the worst prior flood occurred in 1975, which crested at 47 feet in downtown Nashville. Much more precipitation fell in uncontrolled areas during this event than in 1975. For instance, the Harpeth River and Mill Creek basins received some of the largest rainfall totals, and their runoff flowed directly into the Cumberland River below Corps dams. The Corps stored as much water as possible, but the total rainfall overwhelmed the system capacity, which was greater than a 1,000-year event.
Old Hickory, Cordell Hull, and J. Percy Priest lakes all were within a foot of overtopping the facility, which could have led to greater flooding. Due to the time and location of the rainfall, the storage capacity at Dale Hollow Lake and Lake Cumberland were not major factors in reducing flooding downstream. The Corps did slow or stop releases at these two dams during the event to lessen impacts downstream.
Cordell Hull Lake, Old Hickory Lake and Cheatham Lake are all reservoirs created by dams on the Cumberland River. These dams are designed to control the passage of water as it flows through the Cumberland River and are not designed to store large volumes of water. J. Percy Priest Lake, Center Hill Lake, Dale Hollow Lake, and Lake Cumberland (Wolf Creek Dam) are larger reservoirs designed to store water. Outflows from all these storage lakes were reduced and controlled during the flood to reduce the flood crest down river.
“I believe our water managers did a great job in a tough situation,” Mitchell said. “They were caught in an extremely dynamic flash flood fight and were making minute-by-minute decisions on the operation of eight dams. They were also exchanging data with the National Weather Service and emergency management agencies, doing media interviews and answering public inquiries.”