Posted on January 13, 2011
The National Weather Service ignored flood forecast modeling that indicated the Cumberland River would rise well above flood stage at Nashville last May, relying instead on incomplete information from the U.S. Army Corps of Engineers.
Officials with the two agencies talked as the crisis loomed but didn't resolve the crucial discrepancies in a timely manner, according to a report the weather service issued Wednesday.
The Cumberland River floodwaters, as a result, took many by surprise.
The report also said that many people didn't respond to flood warnings because they didn't understand the threat to their homes and businesses. It's one thing to be told flooding is on the way. It's another to see a map showing how high the water will rise on your street.
Developing such maps will be a priority for Nashville, National Weather Service Director Jack Hayes said in a telephone conference Wednesday with reporters.
A prototype should be ready by spring for emergency management staff and would include neighborhood overviews, he said. Within about five years, more detailed maps could be available to show flooding forecasts for specific streets.
"Our view is that a picture is worth a thousand words," Hayes said. "And this is going to create a picture where if you're living in some particular neighborhood, you'll be able to see that you've got a threat and you can then begin to think about what I'm going to do if this threat increases."
A flooding simulation model, done without complete Corps data, and an experimental flood model both predicted major flooding, with a crest on the Cumberland River at Nashville possibly reaching 54 feet.
But after a conference call with the Corps at 8:30 a.m. Sunday, May 2, the weather service issued a public prediction of flood levels reaching only 41.9 feet, just below the "moderate" flood level.
That prediction relied on an outdated Corps estimate of how much water it was releasing from dams. The agency was constantly adjusting the flow from the dams, but the weather service didn't know it. The confusion wasn't apparent until late into the night as waters continued to rise.
U.S. Rep. Jim Cooper, D-Nashville, called the report "remarkably detailed and thorough."
"The National Weather Service report confirms the breakdown in communication during the historic flooding last year," he said.
"We can't stop the rain, but we can and must do a better job at warning people of the potential for dangerous flooding. A few hours of warning could have saved lives and prevented millions of dollars in damage."
The flood, which came with unprecedented rains over two days, caused about $2 billion in property damage in Nashville, and out of 26 people who died in the region, 11 were in Nashville.
Looking for a better way
Residents and business owners didn't know how to interpret warnings that referred to flood stages on the Cumberland River, which were the levels that the river might reach, according to the weather service report.
"They need to know when the river reaches 48 feet — what does that look like on the streets and at their homes and businesses?" said Jane Hollingsworth, a Reno, Nev., weather forecast office meteorologist.
She led a 10-person assessment team that produced the report about what worked as it should have and what went wrong.
The 93-page document calls for a series of changes to improve not only what happens in Middle Tennessee in the future but also in river basin cities throughout the country, Hayes said.
U.S. Sen. Lamar Alexander, R-Tenn., called the effort an important step toward making the agency's flood alerts more like its tornado predictions.
"Tornadoes can be devastating, but flooding causes three times as much damage nationwide each year as all other disasters combined," he said in an e-mailed statement.
Last July, in a Senate subcommittee hearing that he called for on lessons learned in the May 1-4 flood, Alexander urged a better way to inform the public about expected flooding.
"It was a complex, unprecedented, rapidly evolving event," Hayes said.
The Corps at one point on May 2 had opened the floodgates at Old Hickory Dam as wide as it could as it worked to save the dam. Massive amounts of rain had caused lake waters to rise within a few feet of the top.
The weather service through much of that critical day didn't understand that the gates were wide open and that increased quantities of water were headed downriver.
The Corps and weather service are already working together more closely, Hayes said. Corps dam managers along the Cumberland River Basin are calling directly to the weather service to report the opening and closing of gates and the water flow as it changes.
In August, when downpours came and flooding seemed possible, the communication system proved to be working, he said. The agencies hope to develop a system so that the gate changes can be electronically reported instantaneously.
The National Weather Service report also said that despite increases in staff in weather service offices during the May disaster, it still wasn't enough. The team recommended more personnel during a flood.
Weather service forecasters will now be sent to Metro's emergency management command center and to the Tennessee Emergency Management Agency office to better coordinate with them.
A stronger message
Communicating with the public came up repeatedly in the weather service telephone conference Wednesday.
"We learned from the assessment that people needed a stronger message to understand the gravity of a situation," Hayes said. "Everyone in Nashville knew there was major flooding but didn't understand their personal risk."
Some people didn't know what to do. Warnings went out not to drive because of rising waters, but many should have left before their houses and areas flooded. It wasn't clear who needed to do what.
Residents from Bellevue to Pennington Bend watched waters rise around them, coming into and ruining their homes and possessions or stopping short and sealing them off from neighbors.
A team at the weather service national headquarters is working to devise a standard language for use nationwide for winter storm and flood warnings, just as it has for tornado warnings, Hayes said.