The political narrative of a 1,000-year disaster in the United States typically goes something like this: First, there’s the event itself, which is followed by a few days of somber reflection, then an exuberant burst of civic pride, and finally an extended period of bickering and blame designation.
The last one there may appear to have the markings of the penultimate, but it’s not clear whether anyone is quite sure what happens next. Policy reforms, mass firings, criminal prosecutions? Sometimes, but by the time the wrangling process has played itself out, often nobody’s paying attention anymore. Ask New Orleans. Or, in a year or two, Nashville.
Last week, Rep. Jim Cooper joined with Sen. Lamar Alexander in demanding an investigation into the Army Corps of Engineers and the National Weather Service.
On Monday, Cooper gave a presentation at the Rotary Club of Nashville, suggesting that the post-rain flooding that destroyed neighborhoods in Nashville could have been caused by unnecessary dam releases upstream of the city — specifically dams like Cordell Hull in Carthage, Center Hill Dam in Smithville, Dale Hollow Dam in Celina, and Wolf Creek Dam in Jamestown, Ky.
Cooper also asked why there was so little warning before the flood.
“Here we have minute-by-minute warnings for tornados,” Cooper told The City Paper. “We have nothing for floods.”
On Thursday, Larry Vannozzi, the meteorologist in charge of the National Weather Service’s Nashville office, detailed the timeline. By Wednesday, April 28, he said, the NWS first predicted severe rain for the Middle Tennessee area. It wasn’t until Saturday, May 1, after the rain had already begun, that they began to realize just how severe. According to Vannozzi, the NWS didn’t even release a countywide flood warning throughout Davidson County. He said the unlikeliness of the weather made it nearly impossible to predict just how bad it would get.
“This is greater than a one-in-1,000-year event. There’s a one-in-one-thousand chance of this happening in a given year,” he said, noting that the previous record for a single rain event in Nashville was 6.7 inches. This storm produced more than 13. “We didn’t just barely edge out a record. We destroyed a record. We doubled it. … That certainly makes this more difficult to predict.”
The timing is important, too, because Cooper has also suggested that Corps dams didn’t do enough drainage in the days leading up to the storm, leaving them little room for flood storage.
“What we were able to do on Thursday and Friday was pull a half a foot out of Cordell Hull and Old Hickory,” said Bob Sneed, head of water management for the Army Corps of Engineers in Nashville, countering the claim that nothing was done to draw the pools down.
According to Corps water management records obtained by The City Paper, Wolf Creek Dam was releasing a daily average of between 10,000 and 16,000 cubic feet per second through its turbines in the days before the storm. Cordell Hull steadily increased its flow from around 10,000 CFS on Monday to 18,000 on Friday, also through its turbines. Neither opened its floodgates. In fact, Cordell Hull didn’t open its gates until Saturday, when it averaged 28,000 CFS for the day. By midnight Saturday, it was releasing more than 50,000 CFS.
Cordell, about 12 hours’ waterflow away from Nashville, is able to hold as much as 508 feet of water behind its gates. That is about 5 feet above its normal level, given over for surcharge storage, which basically means very short-term flood storage. But it began those major releases, sending that water straight into Old Hickory Dam and J. Percy Priest Dam, and ultimately, Nashville, at seemingly the worst time possible.
“We wanted to save that surcharge storage,” explained Sneed. That’s because, he said, the storm was headed east, toward Carthage. If surcharge storage had reached its limit when the storm reached it, Cordell may have had to release even more water then.
“It would have been on Monday. On Monday the storm began to move towards the east. We thought it was going to move out very quickly, but then it got into the Carthage area, and it seemed to stall out again. They began to get hammered really hard,” said Hershel Whitworth, a hydraulic engineer with the Corps in Nashville.
According to Sneed, Cordell got up to 508.33 by then, a record for the dam. By Monday morning, it was pumping more than 100,000 CFS from its gates. Old Hickory was averaging 175,000 CFS that day, and was half a foot above its maximum surcharge capacity.
Cooper acknowledged the overrun at Old Hickory, but he still asserts that many other dams that did releases had unused storage. Cooper insists that Cordell Hull’s true capacity is 513, not 508, pointing to a Corps of Engineers graph showing that height as the very top of the dam, not the storage limit. “I don’t know why that pink line is there, then,” he said. Plus, he said, he believes that Wolf Creek, the largest dam in the system, was underusing its storage capacity by as much as 58 feet, Center Hill by as much as 40 feet.
“I don’t know where he’s getting this from,” said Whitworth. He specifically criticized Cooper’s claim that Wolf Creek and Center Hill were underused. Both of those dams, he said, were rated at a high risk of breach; Wolf Creek in particular is rated extremely high risk. Corps estimates have maintained that a breach there could result in $3 billion in damages and as many as 100 people killed. Center Hill and Wolf Creek have been under construction to fix those issues, but in the meantime, the Corps has lowered their maximum lake elevations to 680 feet (from 720 feet) for Wolf Creek and 630 (from as much as 685) for Center Hill. Records show that both of those limits were surpassed during the storms, Wolf Creek by more than 20 feet. Still, Wolf Creek didn’t reach nearly those levels until Monday, after its turbines had been shut off entirely. It was still doing 13,000-plus CFS releases throughout the weekend.
Water levels must be kept at or below 695 feet (where the entrance ramp is) at Wolf Creek to permit construction. Asked whether those releases were done in order to expedite the process of getting back to construction, Whitworth said, “Yes and no. In order to expedite construction, we try to keep it below 695. We don’t try to keep it below 695 at the expense of downstream flooding. ”
Cooper still wonders why many of these dams are kept so near capacity so often.
“We’ve been battling the Corps for a long time about keeping lake levels down,” said Cooper.
‘Establish a balance’
The answer depends on the dam.
Many, like Wolf Creek, must be kept at or near 680 to keep power generation going. Before construction began on the dam, the Army Corps of Engineers considered going as low as 650 to protect the dam and increase flooding capacity. But an environmental impact study done before construction notes that at 650, “hydropower production would stop completely at Wolf Creek Dam. At elevation 650 [feet], the water level does not reach the intakes for the hydropower turbines. It is likely that water quality and water flow throughout the Cumberland River would be so adversely affected that hydropower would also stop or be severely impacted at the other projects as well.”
For many dams, explained Whitworth, there are other concerns, like federally mandated water levels for recreation.
“We do have a recreation mission. We do have recreation pools. One example is Percy Priest. We are, by law, supposed to maintain Percy Priest at the 489.5 to 490.5 range during the summer,” he said. “In doing that, we do use up some of the flood control capability that the project has.”
Cooper takes issue with that.
“If you ask the Corps, they’ll tell you they’re supposed to keep 9-feet minimum navigation on the river. And that’s great, but who was on the river during this rain?” he said. “Aren’t there emergency rules? Say someone’s drowning, isn’t there an exception? What if they were at 8 feet? Would that have been so terrible? The idea here is to establish a balance. That would be the purpose of a hearing, to find a balance for Nashville.”