As rain continues in the Tennessee Valley for the 10th straight day, local emergency officials aren't the only ones watching South Chickamauga Creek with worried eyes.
In a small office on the 10th floor of a Knoxville office building, TVA weather and river flow experts are running continuous rainfall models and sending messages to open and close dam spillways -- all to keep Mother Nature's excess from causing a flood mess.
"We began looking at this [heavy rain possibility] a week and a half ago," said Tom Barnett, manager of the Tennessee Valley Authority's River Forecast Center.
The planning has paid off.
What was forecast less than a week ago as a 2-inch rain event for the Tennessee Valley had, by Wednesday, become 5 to 7 drenching inches for the region.
As moisture from the Gulf of Mexico "trained" up through Alabama to the Appalachians on Tuesday and Wednesday, low-lying areas flooded in Brainerd, East Ridge and hundreds of other Tennessee and Alabama communities.
River forecast center managers brought in extra help and doubled up on modeling work.
Like choreographers, river managers make reservoir adjustments -- timing dam spills to follow creek crests and vice versa.
Even far upstream of the Tennessee River's headwaters at dams like Fontana, the aim is to handle rising water in neighborhoods from Fort Loudon to Chattanooga to Huntsville, Ala., and Paducah, Ky.
But sooner or later with enough rain, the Tennessee River still rises.
And the higher the river, the more slowly swollen creeks like South Chickamauga can drain.
The valley is a 40,000-square-mile area filled with thousands of creeks like South Chickamauga that drain to the Tennessee River.
To cope, Barnett and his crew have ordered spillways opened at the Fort Loudon, Watts Bar and Chickamauga dams.
They halted boat traffic in the Tennessee River Gorge, and the Chickamauga and Fort Loudon locks have been closed.
But by the end of today, forecasters expect another 1.5 to 2 inches of rain, and then snow.
"We're going to continue moving what water we can through Chickamauga to right before we would be 'getting damages' level in Chattanooga," Barnett said.
That would be a river level of 26 feet at the Walnut Street Bridge, covering manholes and roads and yards but not getting into houses, Barnett said.
In Chattanooga -- about midway on the Tennessee River's 652-mile run from Knoxville to Paducah, Ky. -- normal pool level is about 14 feet.
The National Weather Service says 30 feet is the flood stage here.
"About 25 feet is our goal," Barnett said. "We'll see where the next rain takes us."
The upside of the rain is cheap and renewable energy: 29 of TVA's 49 dams produce power, and in weather like this they are at full throttle.
"On the Tennessee River, that water [for generation] can get used nine times," once for each of the river's nine dams, said Chuck Bach, river scheduling general manager for TVA.
"I like to tell people I'm refueling right now," Bach said of the rains. "But when it gets like this, our first priority is flood control."
What about tomorrow?
This week's rain news would be much worse had this happened 75 years ago, before Chickamauga and other flood control and power generation dams were completed in the 1940s in East Tennessee.
On March 11, 1867, the river rose to nearly 60 feet. People were rescued from second-story windows as far into town as the Read House.
And between 1875 and 1938, the Tennessee River would exceed Chattanooga's 30-foot flood stage more than 70 times.
Since the reservoir system was completed, the highest Chattanooga flood stage was nearly 37 feet in 1973. Without regulation, the flood would have crested at 52.4 feet, according to TVA. A 2003 flood reached 36 feet here.
Now, new models show the Tennessee Valley by mid-century receiving as much as much as 17 inches more rain each year than the present norm of 51 inches -- much of it in intense drenchings.
Barnett and James Everett, manager for river forecasting operations support, said improvements in modeling and satellite digital gauge monitoring are improving all the time, as is research.
Everett said TVA already is offering free cellphone and tablet applications -- downloadable from sources such as iTunes -- that show river and creek levels around the clock.
Other TVA divisions are working to shore up dams and embankments, as well as the power plants that sit beside the river.
As for this week, Barnett was encouraged by the word "snow" in weather forecasts.
Especially the possibility of 1-3 inches on local mountains and about 9 inches at Cherokee N.C.
"I would welcome the snow if it hits on the mountains," he said. "Snow will help slow down that runoff."