When Frank Milchuck of Eco Turf Erosion Control in Raleigh, NC, was challenged by Tillett Development to find an alternative to heavy riprap for a channel lining, he came up with a unique solution. The developer wanted something more appealing and environmentally correct to handle stormwater runoff in the highly visible channel that ran through a new subdivision in Holly Springs, NC. A riprap channel lining would be unattractive and could pose a danger to children. What’s more, a hard-armor channel would not filter nutrients, would allow unwanted vegetation to grow, and could harbor rodents and snakes.
Milchuck’s bioengineered “eco-channel” consisted of a cellular confinement system, a turf reinforcement mat, and fescue and wetland plants. The channel has an 8-ft.-wide bottom on a 1% grade with the sides sloped back at 3:1. The bottom of the channel has a TerraCell cellular confinement system (3-in. cells) marketed by Webtec Inc. of Charlotte, NC. This system is lightweight and flexible; it is constructed of high-density polyethylene strips ultrasonically bonded together to form a three-dimensional honeycomb. The cell walls confine the infill material and prevent it from being moved by the water. Once it was anchored, it was filled with topsoil and seeded with creeping red fescue. Then a Terra Guard turf reinforcement mat was installed over the system. These mats are made of polypropylene fibers positioned between two nets, which are bound together by parallel stitching with polyolefin thread. Once the mat was properly anchored, it was sprigged with wetland plants. The mats provided erosion protection and contributed to the acceleration of plant growth because its open-weave construction allowed for maximum root and stem entanglement, thereby increasing the ability of the vegetation to withstand higher flow velocities and shear stresses. Finally, the sides of the channel were seeded with native wildflowers to enhance the appearance of the channel.
Milchuck believes there are many advantages to his eco-channel. “In theory, we are planting this channel with plants that are easily maintained. In effect, they will crowd out and not allow unwanted plants to grow.” The vegetation also filters out nutrients and sediment and provides a habitat for desirable insects and birds. Milchuck also points out that the cellular confinement system retains moisture that allows the wetland plants to thrive even during the driest periods of the year.
The channel, installed in September 1998, has held up well through the winter. Some silt was dumped into the channel from an unprotected building site upstream, but the vegetation and the turf reinforcement mat were able to capture most of it. After about a month, the fescue and the wetland plants had grown back, and the sediment could not be seen.
The developer is pleased with the performance of the channels and “has won many friends in Holly Springs and among the Wake County soil and erosion inspectors,” Milchuck points out. The homeowners like the fact that the channel is virtually maintenance-free as well as aesthetically pleasing.
