Flood waters from the Nolichucky River rage near Jackson Love Highway and Interstate 26 in Erwin, Tennessee on 9/27/24.
Heavy rainfall and widespread flooding made Hurricane Helene more than a generational storm for Southern Appalachia. But what characteristics of the region intensified the billions in damage and dozens of deaths hundreds of miles inland?
When the hurricane hit Western North Carolina and East Tennessee as a tropical storm Sept. 26-27, it caused a deadly interaction between the Appalachian mountains, small tributary streams and major rivers.
Reservoirs made a life-or-death difference in some spots, bottling up floodwater behind dams, even as those dams spilled record flows downstream and provoked a flood warning.
By the morning of Sept. 28, the town of Busick, North Carolina, near Mount Mitchell, had received more than 30 inches of rain. Rainfall across North Carolina broke records as Helene traveled north after battering Florida's Big Bend region as a Category 4 hurricane.
Runoff from the mountains caused three rivers that flow from North Carolina into Tennessee – the French Broad, Nolichucky and Pigeon – to burst far beyond their banks as they tore through towns like Erwin, Greeneville and Newport.
The rivers ran uncontrolled and unmoored from their banks for miles, carrying away houses, roads and bridges before converging and flowing into Douglas Lake.“There are other areas that have flooding damage, numerous small creeks and tributaries, but that is the concentration of damage,” Tennessee Emergency Management Agency director Patrick Sheehan said, describing the rivers during a press conference on Sept. 30.
In East Tennessee, the rivers flow primarily through Cocke, Greene, Unicoi and Washington counties, though there also was extensive flooding in Carter, Hamblen, Hawkins and Johnson counties.
Tennessee Gov. Bill Lee declared a state of emergency in Tennessee on Sept. 27, and requested money and assistance from the Federal Emergency Management Agency, which the agency approved on Sept. 28.
The first round of federal assistance includes a 75% reimbursement for restoration work in Carter, Cocke, Greene, Hamblen, Johnson and Unicoi counties, and a 75% reimbursement for evacuation and shelter support in Hawkins and Washington counties. The remaining 25% will be a combination of local and state funds.
On Sept. 30, Lee wrote to the Biden administration again to request an expedited major disaster declaration, which has been approved in Georgia, Florida, North Carolina and South Carolina, but not Tennessee. The declaration would allow individuals in the eight counties to directly apply for federal aid, including grants for temporary housing or home repairs.
How Helene broke flooding records in East Tennessee
The day before Helene arrived in East Tennessee, the National Weather Serviceoffice in Morristown warned of the potential for two rounds of flooding. The first was Sept. 25-26, as the region received 2-4 inches of rain. The next was the tropical storm herself.
The first rain, a so-called "predecessor event," was caused by a band of moist air that came from the outer bands of the storm. It saturated the ground in parts of Tennessee and North Carolina, making runoff from Helene move faster and fuller.
As Helene moved across the Gulf of Mexico, it picked up more moisture. As it moved up the mountains, the uplift enhanced the amount of rainfall.
The heaviest rains in East Tennessee and Western North Carolina fell the night of Sept. 26 into the morning of Sept. 27. It was not long before the water came down the mountains and across the state line. Shortly after noon Sept. 27, as the Nolichucky swelled, 62 people, including 54 patients, were stranded on the roof of Unicoi County Hospital for hours.
They were eventually rescued by helicopters from across the region. Farther downstream at 11 p.m., the Nolichucky Dam near Greeneville withstood record flows nearly twice the amount that pours over Niagara Falls.
Some counties in East Tennessee absorbed more than 10 inches of rain on Sept. 26-27.
Tennessee already is one of the rainiest states. In a normal year, the Great Smoky Mountains National Park receives between 55 inches and 85 inches of rain, depending on elevation.
Helene pushed the region beyond its breaking point. It was not just a generational storm, but a millennial one. The Nolichucky River watershed got rainfall "equal to about a 1-in-5,000-years rain event," TVA spokesperson Scott Brooks said in an email Sept. 30.
The French Broad River in Newport swelled more than 13 feet higher than its flood stage in its largest flood in the area since 1867, according to the TVA update.
The Pigeon River in Newport was more than 20 feet higher than its flood stage, beating the previous record set in 1904. TVA's Watauga Dam broke its water level record by 3 feet, and the Watauga River was around 5 feet above its flood stage in the highest level in Elizabethton since 1940.
The storm led TVA to open spill gates on the Cherokee Dam for the first time in more than a decade. Typically, all water flowing through hydroelectric dams runs through turbines.
As it cleans up and restores the Nolichucky Dam, TVA is urging people to stay away. TVA Police will be on-site at the dam through the rest of the week. The utility expects commercial traffic along the Tennessee River to be interrupted for several days as it closes locks and sends massive amounts of water through the river.
Helene was more than a "500-year-event" for state infrastructure, said Will Reid, deputy commissioner and chief engineer of the Tennessee Department of Transportation. Fourteen state bridges are closed, and five are destroyed:
Greene County: State routes 107, 350 and 351
Unicoi County: Interstate 26 at mile marker 39.6
Washington County: State 81 (Alfred Taylor Bridge)
A section of Interstate 40 washed away near the Tennessee-North Carolina border.
TVA reservoirs store water from Helene
The Nolichucky and Pigeon rivers eventually flow into the French Broad River before Douglas Dam impounds the river to form Douglas Lake. As the crisis unfolded, reservoirs like Douglas Lake functioned as storage for floodwaters. The water level in the lake rose nearly 22 feet in three days.
But the water still needed to move through the river system. Through Oct. 1, the Tennessee Valley Authority spilled about 440,000 gallons of water per second through Douglas Dam. The National Weather Service office in Morristown issued a flood warning for parts of Knox and Sevier counties downstream of the dam until 7:30 p.m. on Oct. 1.
Douglas Lake, mostly in Jefferson County, and Watauga Lake, in Carter and Johnson counties, were the two reservoirs TVA relied on most to store water from Helene and move it downstream.
"Most of our tributaries have crested," Darrell Guinn, senior manager of TVA's River Forecast Center in Knoxville, said in a video update Sept. 30. "Some of those reservoirs still remain elevated, though. Watagua Reservoir (and) Douglas Reservoir continue to be elevated."
South Holston Lake and Watauga Lake stored much of the water not long after it poured into the northeastern corner of Tennessee through rivers and streams.
By contrast, the three rivers at the center of the flooding rushed with no storage through Cocke, Greene, Unicoi and Washington counties before reaching Douglas Lake.
Historic spilling from Douglas Dam led to some evacuations downstream, Tennessee Emergency Management Agency director Patrick Sheehan said in a news conference on Sept. 30.
The evacuations were small compared to those ordered in Newport when a dam on the Pigeon River was feared to have failed. Walters Dam, operated by Duke Energy, did not end up failing, though muddy and debris-filled water poured through itafter record flooding.
TVA's first mission during the Great Depression was to build a system of dams that would prevent flooding and produce electricity for the rural South. It prevents around $309 million of flood damage annually.
"We are aware that these record releases are causing localized flooding on the Tennessee River," Brooks said. "However, the controlled releases are resulting in much lower river levels than would be possible if the dams weren’t in place."
Written & Reported by; Daniel Dassow is a growth and development reporter focused on technology and energy. Phone 423-637-0878. Email daniel.dassow@knoxnews.com.
