ROBBINS — For more than 100 years, the historic Burnt Mill Bridge over the Clear Fork River withstood floods and the tests of time — including the historic flood of 1929 and other major floods, including one in 1973.
That changed Sunday morning, when half of the 110-year-old bridge was swept away by flood waters after numerous thunderstorms combined to dump as much as eight inches of rain over the region.
Adding insult to injury, Honey Creek Road remained closed indefinitely on Sunday evening, as the new Burnt Mill Bridge awaited a visit from state bridge inspectors to determine the extent of damage done when the steel and wood from the old bridge was sent smashing into it by the rushing flood waters.
Kelvin King, Scott County’s road superintendent, told the Independent Herald Sunday evening that after a preliminary inspection, he would need to call in engineers from the TN Dept. of Transportation to more thoroughly inspect the damage.
In the meantime, the road — which was closed by the National Park Service at about lunch time on Sunday — remains closed.
“They’re usually pretty quick about responding,” King said of TDOT’s bridge inspectors. “The main thing is they’ll have to wait for the water to go back down before they can check it out.”
Built in 1911, Burnt Mill Bridge was used for more than 90 years as a single-lane, steel-structure bridge with wood plank flooring before the state deemed it unsafe for vehicular traffic in the early 2000s. Potter Southeast completed construction on a modern, concrete bridge just downstream in 2006, and earthen berms were placed on either side of the old bridge to prevent vehicles from crossing it.
The bridge was built using a Pratt through-truss span on the east side and a half-hip Pratt pony truss on the west side, connected by a concrete abutment in the middle of the river. The section of the bridge that washed away was the Pratt through-truss span on the east side.
Pratt truss bridges became commonplace in the United States in the late 19th century. They were designed by the American engineer Thomas Willis Pratt and his father, Caleb Pratt, and were preferred for their ability to span long distances with simple steel construction. The Pratts revolutionized bridge building when they figured out a design using triangular trusses that allowed the diagonal pieces to feel tension and the vertical pieces to feel suspension. The use of Pratt trusses became less common after World War II.
After the old bridge was condemned for vehicular use by the state in 2003, Scott County reached a deal with the National Park Service allowing the old bridge to remain for pedestrian use, given its historic value and significant interest from the public in saving it.
However, the bridge slowly became an eyesore, and its rotting timbers caused it to become a danger for pedestrians. In 2019, Scott County teamed up with the Big South Fork National River & Recreation Area to re-plank the bridge, making it suitable for pedestrian traffic once more.
The bridge renewal project followed years of contemplation about the bridge’s future. Scott County even reached out to a non-profit organization that repurposes old bridges for its rails-to-trails program, but the outfit determined it would be too costly to remove and reuse the bridge because the only way to get the steel beams out of the river gorge intact would be to use helicopters.
In 2017, Big South Fork National River & Recreation Area administrators expressed concern that a flood might cause the old bridge — the concrete base of which was determined to be crumbling — to be swept away. If that happened, they warned, significant damage might be caused to the newer bridge downstream.
The streamflow on Clear Fork at the USGS water gauge just downstream from the bridge peaked at 36,000 cubic feet per second at 1:30 p.m. Sunday afternoon. The norm for this time of year is less than 1,000 cfs.
The river crested at 20.61 feet at 11 a.m. It is the second-highest crest on record at Burnt Mill, trailing only the March 23, 1929 flood, when the river crested at 22.1 feet. In 1973, the river crested at 18.92 feet. Other Top 5 crests include 18.5 feet on Feb. 3, 1939 and 17.96 feet on Dec. 30, 1969.