Land, nature, and weather often challenge site engineers, consultants, agencies, contractors, and other construction professionals. The magnitude of the problem of uncontrolled soil movement by water and wind is often overlooked by those unfamiliar with the impact of erosion. As a single example, sediment—the byproduct of erosion—accounts for more than two-thirds of all pollutants entering U.S. waterways and costs the public billions of tax dollars each year in mitigation efforts. Special care must be taken to prevent soil erosion and sedimentation.
Rolled erosion control products (RECPs) provide this special care. RECPs represent the fastest growing segment within the erosion control industry and have quickly evolved to include temporary degradable open-weave textiles and erosion control blankets as well as permanent turf reinforcement mats.
As the demand for RECPs has grown, several product types have been developed using varying compositions and structures. These products are designed to work in conjunction with vegetation to form a “bio-composite” solution to erosion control problems. The RECP industry draws on the combined professional disciplines of hydraulic engineering and agronomy. Hydraulic engineering addresses the capacity of stormwater drainage systems and agronomy addresses soil properties and vegetation establishment.
PICKING THE RIGHT PRODUCT
RECPs limit soil erosion; retain soil moisture, which in turn promotes seed germination; and protect seed and seedlings during heavy rainfall or winds, enabling better vegetation establishment. As there are many types of products available for erosion control, selection is based on factors such as functional longevity required (short-term, long-term, or permanent usage); relative cost of materials, installation, and maintenance; and visual impact.
For applications where natural vegetation alone eventually will provide sufficient permanent erosion protection, a temporary RECPmay be used. Temporary products provide longevity and performance properties needed to control erosion and help establish vegetation under the anticipated immediate site conditions.
One form of temporary RECP is an open-weave textile, a degradable product composed of processed natural or polymer yarns woven into a matrix. Another temporary RECPis an erosion control blanket—a degradable product composed of processed natural or polymer fibers mechanically, structurally, or chemically bound together to form a continuous matrix.
For applications where natural vegetation alone will not provide sufficient protection from soil erosion under concentrated flow conditions or provide sufficient long-term erosion protection, a permanent RECP may be used. Permanent products provide performance properties needed to control erosion and reinforce vegetation under the expected long-term site conditions.
A turf reinforcement mat (TRM) is a permanent RECP composed of non-degradable synthetic fibers, filaments, nets, wire mesh, or other elements, processed into a permanent, 3-D matrix of sufficient thickness. TRMs, which may be supplemented with degradable components, are designed to impart immediate erosion protection, enhance vegetation establishment, and function long-term by permanently reinforcing vegetation during and after maturation. TRMs typically are used in hydraulic applications such as high-flow ditches and channels, steep slopes, stream banks, and shorelines. They provide stability where erosive forces may exceed the limits of natural, unreinforced vegetation or in areas where limited vegetation establishment is anticipated.
State, county, and local municipalities increasingly are requiring plans for dealing with erosion prior to allowing soil on-site to be moved. Phase II of the National Pollutant Discharge Elimination System (NPDES), issued in July 2003, expanded stormwater regulations to cover construction sites greater than 1 acre whenever soil is disturbed. These regulations require a plan be approved and followed during construction.
The Erosion Control Technology Council (ECTC), a non-profit organization for the development of standards, testing, education, and installation techniques for RECPtechnologies, has a Web-based tool, available at www.ectc.org, designed to assist industry professionals with RECP selection based on their specific site requirements. Using this tool, designers and contractors can select the relevant application, either slope or channel, and enter parameters leading to a list of products that may be suitable for the project design, including links to manufacturer Web sites.