The Tennessee River has risen more than seven feet in Chattanooga since Wednesday when rains began dumping what has grown to nearly 5 inches of precipitation in as many days.
But without the network of dams and reservoirs built by the Tennessee Valley Authority in the 1930s and 1940s, the river would have risen at least 14 feet higher and caused more than $130 million of flood damage in the Chattanooga area, TVA said today.
If TVA was not controlling the river flow, the Tennessee River would have risen to 38 feet at the Walnut Street Bridge downtown, or 14 feet above its current 24-foot stage level. The higher river level without the TVA dams would be seven feet above flood level.
"That's a flood aversion value of about $130 million and with more rain on the way that value could go up," said James Everett, manager of operations support for TVA's river forecast center in Knoxville. "We're storing as much water as we can in our storage tributary reservoirs and managing the flow of the river to limit the flooding that occurs when we get these types of unusually heavy rains."
The Tennessee River basin drains more than 20,000 square miles of watershed through the Tennessee River in Chattanooga, which must pass through the often turbulent river basin between Signal and Elder Mountains where Suck Creek also flows into the river. Although controlled, the flow of the Tennessee River has still shut down barge traffic in Chattanooga with more than 800,000 gallons of water a second flowing down the river.
Even after nearly five inches of rain since last Wednesday, TVA predicts another inch or inch and a half of rain today.
"We should have a little break tomorrow before we get another half inch to inch of rain on Wednesday," Everett said.
Rainfall in the Tennessee Valley this year is about 15 percent above normal. Typically, the 7-state region gets about 52 inches of rain a year, but through Sunday the Tennessee Valley had already gotten 57.7 inches of rain "and we're expecting even more rain through this week." In 2013, the Valley got 64 inches of rain in the region above Chattanooga on the Tennessee River.
The final three months of this year — normally one of the drier period in the region — has already received more than 15 inches of rain and could end up being one of the wettest fourth quarters of the year in the 127 years of rain records in Tennessee.
More than 10 inches of rain fell on Christmas in scattered parts of North Alabama, causing some localized flooding around the Tennessee River in the Guntersville Reservoir.