Corps of Engineers says releasing water from Tenn. dam prevented more damage to NashvilleBy Kristin M. Hall, AP
Wednesday, May 12, 2010
Corps defends actions during Tenn. flooding
NASHVILLE, Tenn. — The release of water from a dam upstream of Nashville during historic flooding has prompted a U.S. Senate inquiry into whether the public was adequately warned about rising waters downstream.
The U.S. Army Corps of Engineers said Tuesday the controlled release of water from Old Hickory Dam the weekend of May 1-2 prevented the lake from spilling over the dam and flooding Nashville with an additional four feet of water.
Sen. Lamar Alexander, R-Tenn., has asked for a hearing on how well the corps and other state and federal agencies delivered information to businesses and individuals in the midst of the flooding that killed nine in Nashville alone.
Alexander said during a session on Monday he wants to ensure that officials are taking the right steps to control floods and to keep people informed, “particularly that we have clear and correct information about the rising water and that we communicate it as broadly as we should.”
Gov. Phil Bredesen said Tuesday that communication about the flooding could have been better, but he had no reason to believe there were errors in the releasing of the water.
“I’ve certainly heard a lot of complaints, starting with Opryland, about projections that weren’t as accurate as they might have been in terms of that,” Bredesen said. “But I don’t have any technical judgment about whether what they did was right. I’d hope they go over it and look at all the decisions that were made.”
Dams all around Middle Tennessee took on large amounts of water during the record rainfall that weekend. Nashville received a total of 13.5 inches over two days, causing lakes and rivers to swell with runoff.
The dams around Nashville are mostly used for river navigation and have limited space to store floodwaters, said Bob Sneed, chief of water management for the Nashville District.
The Cheatham Dam on the Cumberland River downstream of Nashville was overflowing due to flooding on the Harpeth River and Mill Creek, so on Sunday, the Corps pulled out the spillway gates and allowed the water to flow freely through the dam. The Cheatham Dam was designed to operate like this during flooding, Sneed said.
But just 25 miles upstream of Nashville, engineers and water managers were desperately trying to stop the same thing from happening at Old Hickory Lock and Dam which is supposed to be able to hold back flood waters. That lake was rapidly rising and threatening to spill over the dam, Sneed said.
So the corps began releasing water starting at noon on Saturday.
During normal operations, some water is released almost all the time for the dam’s hydroelectric power units and to control the amount of water on the lake. A couple of days before the storm, the amount of water discharged from the dam was about 24,000 cubic feet per second. Over the course of the weekend, the water released from the dam peaked at over 212,260 cubic feet per second on Sunday afternoon, the highest rate of water discharge the dam has ever recorded, Sneed said.
The situation was rapidly getting worse on Sunday and workers at the dam were opening up the gates wider and wider as often as every 15 minutes, Sneed said. In a little over 24 hours, the dam went from releasing no water from its spillway gates to opening them up completely, he said.
“That’s the largest flow that Old Hickory has ever had,” he said. “And at that point, we are full. We are out of options.”
Sneed said they were discussing the option of completely pulling the gates out of the dam and evacuating, as was done at the Cheatham Dam.
“What that would have done is poured a lot more water onto Nashville, because there would have been no water control at that point,” he said. “It would have become a free-flowing river.”
By Sunday evening, the lake level stopped within a foot of overtopping the dam. Once the water stopped rising on the lake, the corps started decreasing the amount of water released from the dam. That happened around 9 p.m. on Sunday, in anticipation that the Cumberland River would crest on Monday morning.
But the crest didn’t occur until Monday evening. By that time so much water had backed up behind J. Percy Priest Lake on the Stones River that the corps had to open up the spillway gates there, too, after the Cumberland River crested at 51.86 feet.
Sneed said that the corps did exactly what they were supposed to do by notifying the weather service.
“Personally I think the best way is for the weather service to take that information and put together the most informed forecast and put that information out,” he said.
Alexander said he had not heard complaining during his tours of flooded areas last week and said recently federally funded repairs on dams along the river prevented tons more water from pouring into the river.
Associated Press Writer Erik Schelzig contributed to this report.
Tags: Dams, Floods, Lakes, Nashville, North America, Tennessee, United States, Water Environment