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It’s all downhill: Wet weather spawns Tennessee rockslides

It’s all downhill: Wet weather spawns Tennessee rockslides

Posted: Friday, February 5, 2010 8:53 pm
By: AP

 By RANDALL DICKERSON Associated Press Writer NASHVILLE (AP) — The prolonged wet weather that eased Tennessee out of drought has spawned a bumper crop of rockslides. The slides began in the fall and the largest so far is a section of Little Frog Mountain that slid onto U.S. 64 in the Ocoee River Gorge in Polk County. As transportation officials were assessing a Nov. 10 rockslide there, a second slide occurred. A contractor is working to clear the debris and scale away more loose rock that could otherwise fall. “It’s been a difficult winter,” said geologist and engineer Vanessa Bateman, who oversees geotechnical operations in three Tennessee Department of Transportation regions. Bateman said rain and rockslides are related in more than one way — big temperature swings pry rock apart by freezing and thawing. “A lot of water reduces friction at slide planes. The water can lubricate and soften and reduces the strength of joints,” she said. “If water starts building up a little bit, that increase in pressure provides a driving force. It says, ‘Hey, go downhill.”’ Plenty of soil and rock has done that from last summer into this winter. The department is about to award an emergency contract to clear a rockslide that occurred late last month on U.S. 441 between Gatlinburg and Pigeon Forge on a section called the Spur. Southbound lanes are blocked and a section of the northbound side has been made two-way. Hamilton County has seen several slides, including a soil slide on the W Road on Signal Mountain. On Wednesday, rocks slid onto state Route 73 near Townsend in the Smoky Mountains foothills. The same rain and rock dynamic played out with thunderous results just across the North Carolina line, where a massive rockslide has had Interstate 40 closed since Oct. 25. The only known injury occurred at the Spur slide as more rock fell when workers were beginning to clear debris. Additionally, a section of Little River Road was closed for a time by a landslide in August, said Nancy Gray, spokeswoman for the Great Smoky Mountains National Park. At the end of 2009, the Smokies had recorded 23 percent more rainfall than usual — 13.65 inches more than normal in the lower elevations. Rainfall across the state was above normal in 2009. Forecaster Mike Propst of the National Weather Service office in Morristown said Chattanooga ended the year 8.07 inches above normal at 62.59 inches. In Knoxville, 2009 rainfall was 12.44 inches above the 30-year average with a total of 60.66 inches. TDOT’s Bateman said the department has identified problem sites and tries to head off trouble. “If you had an infinite supply of money, that would be easy,” she said. A project in Putnam County involves containing rocks that fall along I-40 up Monterey Mountain. There are also ongoing projects in Anderson and Davidson counties to build fences, clear out ditches and scale the rock face. The problems are cyclical, and Bateman said an eventual return to more normal rainfall will help. In the meantime, the costs to clear and mitigate rockslides usually call for reallocating money within the department’s yearly budget. “We’re trying very hard to get ahead,” Bateman said. Published in The Messenger 2.4.10

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