Erosion control catalyst

August 2010 » Products » ENGINEERED SOLUTIONS
Evolving mandates drive new technologies and systems.
Pamela Accetta Smith

Evolving U.S. Environmental Protection Agency (EPA) regulations such as the National Pollutant Discharge Elimination System (NPDES) permit program and Effluent Limitation Guidelines (ELGs) are influencing the development and application of erosion control technologies. “The EPA continues to push excellence from erosion control manufacturers who must respond to the ever-increasing regulations being imposed on construction sites,” said Jill Pack, CPESC, manager of technical services, North American Green. “New technologies will need to address not only erosion and sediment control in the form of soil loss reduction but also in their ability to limit NTUs (Nephelometric Turbidity Units) or the measurement of water’s turbidity.”

Strict regulations must be in-place to achieve effective erosion and sediment control in construction sites, said Lanka Santha, P.E., CEO, RoLanka International, Inc. “These regulations are the key to development of efficient and cost-effective erosion and sediment control technologies.”

But according to Jim Tanner, senior vice president of sales and marketing, Conwed Global Netting Solutions, “In many cases these regulations have been loosely applied at the state and local level, leaving open the opportunity for use of inferior materials and technologies.” The market is saturated with false claims and there appears to be little in terms of real enforcement, said Tanner, adding that this is hurting the manufacturers who put significant effort into developing and manufacturing good quality products. “I have also heard from manufacturers that testing labs are backlogged and that there is concern about testing equipment consistency between labs,” he said. “The result can be slow time to market for new products and inconsistent results across multiple testing facilities. The regulations are important, but without enforcement and testing standardization, the industry will not reach its true potential.”

Establishment of NTU standards will require designers, and ultimately earthmoving contractors, to implement additional best management practices (BMPs) on disturbed soil sites, said John T. Ravert, director of technical services, East Coast Erosion Blankets LLC (ECEB). “Disturbed sites will have to be ‘buttoned-up’ with temporary BMPs at the close of each workday to minimize the potential discharge of sediment-laden stormwater,” he said. “The traditionally accepted past practice of establishing permanent vegetation at the conclusion of the project will no longer meet the intent of the regulations,” adding that temporary erosion control blankets (ECBs) and rapidly establishing vegetation will be required to minimize the exposure of bare soils to the impacts of rain and wind.

According to Marc S. Theisen, vice president of business development and engineered products, Profile Products LLC, ELGs will soon require primary responsible parties managing construction sites to monitor and submit samples and/or turbidity measurements for water exiting projects and entering designated receiving water bodies. “Construction site managers may use whatever BMPs they desire; however, the burden of responsibility will move to the all-important water monitoring aspect,” he said. “Thus, the bar is being raised to design and implement products and technologies that are more effective at reducing erosion, decreasing turbidity of runoff, and/or increasing capture and treatment of sediment/pollutants.”

Newer and more stringent pollutant discharge regulations are setting up a measurable responsibility platform for property owners, public or private, through total maximum daily loads (TMDLs), said William D. Murphy, P.E., engineer, Landmark Earth Solutions. “Owners are compensating civil engineers to design projects that meet legal requirements, during construction and after, and to at least consider regular and long-term maintenance costs of design features,” he said. “All of the stakeholders (including contractors) should have an incentive to utilize erosion control technologies meeting these goals because of the encompassing liability.” To this end, said Murphy, the erosion control industry is developing more effective technologies, such as hydraulic mulches for covering the soil better and longer, as well as protecting the seed a longer time for better germination results.

Directing technology
Since many erosion control technologies rely on establishment of vegetation to achieve their full performance capability, there are several ways civil engineers can ensure erosion control plans provide effective protection beginning with initial product installation through to maturity.

“The success of the project relies on the knowledge the engineer has regarding the site. The engineer must not rely on one approach or design for erosion control and must take into account factors such as slope length, time of year, rainfall, temperature, and many other conditions,” said Tanner. “For example, specifying straw to be blown on a hillside in the middle of the summer does not make a lot of sense due to the lack of rainfall and other factors. The first thunderstorm will most likely create havoc with the installation. A properly specified blanket would make a lot more sense in this type of application since it provides longer-term performance and, if properly installed, can better handle rain events until vegetation is established.”

According to Pack, engineers can develop site plans that offer the protection needed during each site phase without over-engineering by keeping in mind the phase of the installation and the typical expected storm event. Design programs, such as North American Green’s ECMDS, allow engineers to analyze and design for all three vegetative phases — unvegetated, immature vegetation, and mature vegetation, she said. “Engineers may also consider an erosion control system in areas where the erosive forces exceed the performance of traditional solo products,” Pack said. “Systems can include multiple products and/or anchors that together create high-performance solutions.”

Another critical, but commonly overlooked factor, is the soil, said Tanner. “The engineer must have the soil tested upfront to determine what nutrients must be added, if pH needs adjusting, et cetera. Without good soil the project is doomed,” he said.

In the field, establishment of mature vegetation with full erosion control capability takes time. “In many situations, development of a strong root structure in vegetation takes much longer time than development of green cover on the surface of [the] soil mass,” Santha said. If a product’s functional life ends before development of a strong root structure, erosion may take place with damage to the vegetation. Furthermore, said Santha, a product with good performance and functional life may create an environmental hazard (threat to wildlife or interfere with regular maintenance activities). “Therefore, biodegradable and natural products with good performance and longer functional life are excellent for erosion and sediment control,” said Santha.

Another factor that needs to be considered to ensure that erosion control plans provide effective protection is to write product specifications correctly. “Failure to give proper product specifications may lead to use of inferior products in the field where the product may fail to deliver intended performance,” said Santha. “Also, it is important to make sure that product specified by the civil engineer would not be substituted with lower quality product in the field.”

Multiple factors must be considered during the design of the erosion control plan that will lead to the establishment of nature’s greatest BMP — vegetation, said Ravert. “These include knowledge of the soils on the project site, the need for supplemental nutrients, and a schedule of the appropriate growing seasons for the specified plants,” he said. “Once the seeds are in the soil, they will need to be protected from the impact of raindrop splash erosion with either a properly installed ECB or properly sprayed hydraulically applied mulch.”

To ensure effective protection through maturity, the erosion control plan designer must have test data on product performance in both unvegetated and vegetated channel conditions, preferably in accordance with ASTM D6460, said Ravert. “The ECDesigner, an ECEB online calculator, will assist and provide the designer with appropriate products in both bare and vegetated conditions for both slope and channel conditions,” he said.

Vegetative establishment is indeed the single most effective method to control erosion, said Theisen. “Yet many designers fail to take a holistic and comprehensive approach to accomplish this fundamental idea,” he said.

First, said Theisen, one must assess his/her foundation for growth — by evaluating the agronomic potential of the soil. “Many projects employing the very best erosion control products are doomed from the start if the soils will not sustain long-term growth,” he said. “An assessment of pH, texture, organic matter, macro-micro nutrients, cation exchange capacity, and more soil properties should be conducted on every project.”

Simultaneously, added Theisen, one must select seeds and plant materials of species that are adapted to the site and climatic conditions that also accomplish the erosion control and other project needs. “Then designers should consider erosion control products that not only control erosion, but facilitate growth establishment,” he said. “Fortunately, holistic ‘soil solutions’ software is now available to assist designers with these important considerations.”

With less than 20 years of enforced regulation, erosion control is a relatively young industry; the hard science on installed performance of many erosion and sediment control technologies is limited, said Murphy. “To understand what is at stake, and make proper technical evaluations of solutions, civil engineers need to be well-versed in the dynamics of erosion, methods of sediment control, and stormwater hydraulics,” he said. “Engineering firms should consider employing an in-house expert and/or spend time with vendors and consultants to learn how different products and solutions work, how/if they were tested, and what the long-term costs are, to validate the investment being contemplated.”

Responding to current trends
Companies are responding to erosion control trends with new products and research and development. For example, Conwed launched several new products that better meet the needs of engineers to create more environmentally friendly applications, said Tanner. “We introduced netting with Ecocycle Technology for use in blanket applications. Ecocycle is programmed to degrade anywhere from two months to five years depending on the application requirements,” he said. “Most blankets have a net on the top and bottom. UV degradation is common for top nets but until Ecocycle the bottom nets would not degrade for 100-plus years. Ecocycle gives the engineer an environmentally friendly option without sacrificing the strength or performance of the netting.”

The company also introduced different netting patterns (NatureZone, for example) to minimize and eliminate animal entrapment. “We continue to work with several of our customers on creating new products,” said Tanner. “Just this year we launched a new fiber used in TRM applications called Prostran 100, which is made from 100 percent recycled materials.”

North American Green recently launched several new products that are designed for extreme situations. Its HydraCX2 Extreme Slope Matrix and HydraCM Steep Slope Matrix are hydraulically applied products that can nearly stop all soil loss in some slope protection applications, the company said. In recent testing by the American Association of State Highway and Transportation Official’s NTPEP program using the modified ASTM D6459 large-scale slope test, HydraCX2 matrix proved 100 percent control of soil loss and HydraCM matrix demonstrated 99.7 percent control of soil loss. Both products can be used in place of single- and double-net erosion control blankets in many steep to extreme slope protection applications, as well as to meet the new, more stringent NPDES requirements for turbidity reduction in runoff water from construction sites, Pack said.

North American Green’s ShoreMax Soft Revetment Scour Protection Mat is a flexible permanent rubber matting that allows for vegetation establishment while offering scour and erosion protection in turbulent flow and wave attack applications. It is used in conjunction with turf reinforcement mats (TRMs), geotextiles, or sod and, according to Pack, can greatly increase the unvegetated permissible shear stress of the underlayment products. North American Green’s new P550TX TRM is a permanent matting incorporating a triaxial geogrid that offers 360-degree radial strength. The Vmax3 Earth Reinforcement System (VERS) provides increased tensile strength, damage resistance, and load bearing capacities when used with percussion earth anchors. “Both products are ideal for enabling vegetative solutions to be used in place of hard armor rock or concrete in stream bank, shoreline, and pipe outfall stabilization projects,” Pack said.

RoLanka develops soil erosion and sediment control products with emphasis given to better performance, higher functional life, and friendly to the environment, said Santha. “RoLanka’s BioD-SiltCheck is developed to avoid many failures experienced by conventional check dams in construction sites. [It] has a body and upstream and downstream filter aprons. When installed properly, the upstream filter apron avoids undercutting in the check dam and the downstream filter apron protects soil erosion due to over topping flow.”

In addition, BioD-SiltCheck is all-natural, and can be left at the site for vegetation to grow over it. On the other hand, said Santha, if the check dam used at the construction site is made of non-degradable material, it has to be removed from the site and disposed in a landfill. “All check dams in the field accumulate sediment with time, and if they are subjected to removal, there will be a freshly disturbed area which could initiate erosion,” said Santha. “RoLanka’s BioD-SuperWattle product was also developed as a better alternative to traditional perimeter erosion and sediment control devises.”

ECEB recently introduced three products that Ravert said will meet the industry’s growing needs. The first product includes a series of ground control hydromulches comprised of straw and reclaimed cotton plant materials. “This new product has a lower carbon-to-nitrogen ratio than the popular wood fiber-based hydromulches,” he said. “With the introduction of this product, ECEB now offers products for a complete erosion control solution.”

For the past two years, ECEB has been developing a new product designed to provide a green alternative to hard armoring. Turf-Reinforcement Erosion Control Solution (T-RECS) has undergone extensive large-scale performance testing at a GAI laboratory and will provide another “tool” in the erosion plan designer’s toolkit, said Ravert. “In addition, ECEB developed an ECOSELECT line of products that are 100 percent biodegradable,” he said. “These include biodegradable ECBs and Sediment Retention Fiber Rolls (SRFRs) made from natural products that can be used in environmentally sensitive areas.”

Theisen said the foundation of Profile Products is predicated on offering comprehensive soil solutions via its Green Design Engineering protocol that creates cost-effective and environmentally superior solutions through the design, manufacture, and application of sustainable erosion control and vegetation establishment technologies. “We feel that our newest launch — Flexterra HP-FGM — epitomizes green design engineering by offering unprecedented erosion control and growth establishment performance while enhancing our natural environment,” he said. “This patented product is 100 percent biodegradable, hydraulically applied matrix — comprised of 100 percent recycled wood fibers and naturally derived manmade fibers/biopolymers to create a formulation that is 100-percent non-toxic.”

Flexterra HPFGM also contains absorbents and micro-pore particles to maximize water retention without compromising wet bond strength, said Theisen. “Performance and environmental claims have been validated using ASTM, EPA, ISO, and other testing standards conducted by the most prestigious laboratories,” he said. “Designers can take comfort knowing this formulation can effectively limit turbidity of construction slope runoff for up to 18 months.”

Landmark Earth Solutions’ ScourStop transition mats offer a permanent, no-maintenance, vegetated, NPDES-compliant alternative to rock rip rap, said Murphy. “We have invested significantly in independent, reproducible research — at Colorado State University’s premier hydraulics laboratory — to validate its performance,” he said. “The research demonstrates that, in areas of highest velocity and shear force, ScourStop dissipates hydraulic forces to levels that can be handled by other soil covers downstream.”

Fully vegetated, ScourStop can withstand hydraulic velocities of 31 feet/second and 16 pounds of shear; on day one, those values are 19 feet/second and 7 pounds of shear, on a 2:1 slope, said Murphy.

Murphy said the company is also preparing to market Safe Slope, a natural fiber hydromulch made from a blend of biodegradable cotton plant byproducts, crop residue, and polymers. “This technology utilizes both chemical and mechanical techniques to create a flexible, porous seal, absorbing and holding enough moisture to facilitate seed growth and reduce soil loss,” he said. “The product was developed through a Cooperative Research and Development Agreement (CRADA) with the U.S. Department of Agriculture — Agricultural Research Service.”

Pamela Accetta Smith is a freelance writer based in Albuquerque, N.M.


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