Erosion at Red Bank, Tenn.'s Walden Ridge had created environmental problems and liability issues for city officials. Located below a 1,200-foot ridge and along the side lawn of an elementary school, one of the city's main channels was battered so badly during rainstorms that sewer and water lines were exposed.
The 600-foot long, 6-foot-deep channel allowed water to flow through the school's property and empty into Mountain Creek. It posed a risk to children because of its depth and rocky bottom, and it allowed heavy amounts of sediment to discharge into the creek. To prevent erosion, filter sediment and provide for groundwater recharge, the city decided to line the channel with turf reinforcement matting. Provided by Synthetic Industries, Chattanooga, Tenn., the matting is a three-dimensional, woven geotextile matrix composed of UV-stabilized polypropylene monofilament yarns. It intertwines with the roots of vegetation, aiding plants' natural ability to slow the velocity of flow and filter sediment and other pollutants.
The velocity of water in the channel before the project began was 13 feet per second -- twice what most common species of vegetation can withstand. As a result, only rocks and exposed pipe remained in the Walden Ridge channel. By installing matting, the city was able to provide reinforcement for new plantings so that root systems could tolerate the heavy flow.
The channel is divided twice by entrance drives to the school, which created three 190-foot segments for installation. The segments were graded to a 2.5:1 slope and then sprayed with a combination of weeping love and fescue grass seed, water, fertilizer and liquid lime. An anchor trench was placed every 30 feet, and a row of staples was inserted every 5 feet to hold the mat in place.
J&J Construction, Chattanooga, served as general contractor on the project, which was completed over a two-week period last summer. Installation of the matting required three days of work. Vegetation has since grown throughout the channel, providing erosion control and filtering, as well as an aesthetically pleasing area near the school.
