Highway 290 abuts an environmentally sensitive area known for its small ponds, gentle waterfalls, herds of deer and a piedmont stream, which would have to be bridged. Piedmont streams typically meander across flood plains, often forming oxbows. Oxbows can eventually be cut off by excessive sedimentation, creating oxbow lakes or ponds—an important reason to create as little sediment disturbance as possible.
Contractors knew they needed to create stability for the soft soil banks of the stream in addition to implementing erosion-control measures to ensure there was no soil runoff from the steep 2H:1V slopes to compromise the stream’s flow. They were also aware that solutions for both considerations called for products that would help keep the soil in place while quickly establishing vegetation.
“Any project that has fills that are 30 to 50 ft high pose a challenge in preventing erosion,” said Ray Vaughan, South Carolina DOT storm water manager.
For solutions to these challenges, the South Carolina DOT worked with erosion control experts, John Faulkner of Four Seasons Environmental and Steve Zwilling of Profile Products.
All agreed that Profile’s Flexterra® FGM , a flexible growth medium, and the industry’s new Terra-Tubes™ fiber filtration tubes (FFT) would provide the optimum solutions for stabilizing Highway 290’s slopes and adjoining riverbed.
Rated at 99% effective for controlling erosion on steep slopes, Flexterra® FGM is a hydraulically applied matrix that requires no cure time to develop intimate soil contact. Terra-Tubes are engineered composites of wood fibers, man-made fibers and performance-enhancing polymers encased in heavy-duty, knitted tubes. Terra-Tubes have been proven through independent testing to be the construction industry’s most effective storm water treatment device, and are designed to effectively trap, filter and treat sediment-laden runoff.
Four Seasons Environmental installed the FFT at parallel intervals of 25 to 50 ft to disperse water runoff. Once the FFT were in place, Four Seasons hydraulically applied the FGM at approximately 3,500 lbs./acre over the 200-ft long, 2H:1V slopes. Despite being applied under cold, wet and wintry conditions, the combined technologies quickly created a stabilized environment for growing vegetation.
“Both products have performed excellently,” Faulkner said. “With Flexterra, we got 100% ground contact using the hydraulic application—even over hard-to-reach spots such as the crests of hills.”
Faulkner said using FGMs on the slopes of Highway 290 proved to be so successful that the South Carolina DOT has written Flexterra into its standard construction specifications as an equal to double-sided blankets for applications on slopes up to 2H:1V. In addition, the use of FGM and FFT resulted in a savings of over $1,000 per acre versus the use of erosion control blankets.
“In the case of Highway 290, combining these products provided contractors with a unique and efficient erosion-control solution,” Zwilling said.