Erosion control measures, from single-net blankets to turf reinforcement mats, are an expanding segment of the industry. Rolled erosion control products (RECPs) are easily installed, and their variety means a choice that will be right for your project. Bonded fiber matrix (BFM) products are hydraulically applied and then cure into a mat surface.
These products range from applications that are intended to last only a few months to permanent solutions. Some are designed to cover seed, and others can have seed planted on top of the mat. Erosion control blankets made from straw or coconut fiber—coir—usually have a life span of 12 to 24 months. Products made from polypropylene last longer—several years—if they have UV protection incorporated in the fiber.
Before choosing a product, the following criteria should be considered:
- Slope gradient
- Flow velocity and rate
- Soil type
- Longevity required
- Wildlife protection
- Aesthetics
- Cost
For each of these factors, an RECP can be found to meet the requirements. Many of the products have been approved by state departments of transportation to meet the local regulations.
Several companies also offer software products that enhance the planning and design of erosion control projects. By entering parameters as in the list above, a plan can be developed to exact specifications and a product can be chosen to meet those requirements. The use of the software often saves the customer money.
Here are several projects that have employed these products in a variety of settings and conditions. You can learn from other practitioners what worked in their projects and what challenges they overcame.
Covering Wisconsin
Scott Bordeaux of Ero-Tex located in Cedarburg, WI, depends on the software supplied by North American Green to design erosion control projects. Using the Erosion Control Materials Design Software (ECMDS), Bordeaux says, he can design just the right solution for the customer. He notes that in the past he would use his experience to make recommendations for a project and then overdesign it to ensure success. With the software, however, he feels that a “good comfort level” is attainable. He requests engineering data from the customer and plugs the parameters such as flow volume and rate, velocity, slope gradients, and channel cross sectional area into the software. The software allows him to recommend a product knowing that it is the best solution, which also saves his customer money. “I used to be very conservative with these projects, because my name and reputation are on the line if we have to go back,” Bordeaux says.
He recently designed a project for the street department of Marshfield, WI. In a residential area, drainage ditches run in front of houses. One ditch had two 5-inch culverts and a 48-inch storm sewer draining into it. With these culverts, the ditch was handling runoff from a large portion of the town.
During heavy rains, the water was overtopping driveways and sometimes washing out the driveway culverts. Kurt Bornbach, assistant street superintendent, says the city approached Bordeaux with the challenge. He was able to plug in numbers with the software and tell the city that it could use a product a step below in strength and cost than the one it was considering. The switch saved the city a considerable amount of money.
The ditch runs for 250 feet in front of several houses, so the area needed to be aesthetically pleasing and have vegetation on the sides that could be mowed. The bottom of the ditch, about 6 feet wide, was filled with 12-inch riprap. The sideslopes ranged from 3:1 to 2:1.
North American Green P550 is a turf reinforcement mat (TRM) made of UV-stabilized polypropylene fibers encased in a heavy-duty polypropylene netting. According to the manufacturer, North American Green of Evansville, IN, the P550 TRM with vegetation will handle flow velocities up to 25 feet per second.
Bornbach says the TRM was installed along the sides of the ditch, using two widths of the product. In the middle of installation, with only one side done, the area received about an inch of rain. The slope held, but the work was delayed for a day to allow the uncovered side to dry out. A seed mixture of Kentucky bluegrass, rye, and fescue was applied, and the P550 was placed on top. The vegetation has come in with a healthy stand, and the homeowners are pleased.
Bornbach also installed the P550 at a detention pond between two streets. Two concrete storm drains, a 12-inch and the other a 30-inch, flow into the pond. The water first hits a concrete pad at the bottom of the pond, often hitting with such force that the water goes airborne and erodes the dirt on the opposite side. Bordeaux also recommended the P550 for this project.
The area was seeded, and about eight rolls of the product were installed; it has held for several years. Stricter requirements for water quality made this project a high priority. Bornbach notes it was one of the first projects on which he and Bordeaux collaborated. The success of this project convinced him to continue the relationship with Ero-Tex and North American Green.
Mike Martin, director of public works for the small village of Hales Corners, WI, is new at the installation of erosion control blankets. For a recent project, Martin consulted with Bordeaux. The Hales Corners area is rural, without a lot of curbs and gutters. Most drainage is through open ditches. The project involved a ditch bank stabilization, about 1,800 feet total along both sides of South 118th Street. Sideslopes ranged from 0.5% to 3%. The ditch bottom had been lined with asphalt years earlier. Drainage and roads in the area were being improved, and Martin wanted a product that would mitigate erosion in the ditch and support the growth of vegetation.
Bordeaux took the parameters and recommended C125, a biodegradable coconut fiber encased in natural fiber netting. The top net is leno woven to increase strength and decrease the threat to wildlife. The life of the C125 is about 24 months, plenty of time to have vegetation well established.
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| Seed growth may occur in as few as 12 days. |
For the project in Hales Corners, a seed mix and starter fertilizer were applied and then covered with the C125. Martin says the installation was “pretty idiot proof,” requiring crews to put the staples on the dots printed on the mat. They obtained the installation instructions from the company Web site.
With a few thunderstorms and some supplemental watering, the project is “a remarkably good success,” according to Martin. He notes that seed growth occurred in about 12 days—not a perfectly green blanket, but a good start. About three weeks after installation, the area had a 10-year rain event, and the ditch received minimal damage. The RECP did its job, but a driveway culvert was washed out.
Martin says that with his small four-person department, this type of solution will make sense for many projects. The department doesn’t have the manpower to continually be watering sod or seed, so the moisture retention of the blanket or mat is great. “It’s well worth it,” he says. “Just adhere to the installation manual.”
Arizona Wash
The rapidly developing town of Maricopa, AZ, needed a product to stabilize the banks of Santa Rosa Wash. The wash abuts a residential development, with several homes having backyards ending at the wash. The wash is about 300 feet wide and drains a large portion of the town and the surrounding region.
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| Choose short-term RECPs or permanent solutions. |
Paul O’Malley of Propex Inc. in Chattanooga, TN, was involved in the design of this project. He says that in the past, he would have recommended riprap, gabions, or concrete for a project of this size. This time the product chosen was Propex Pyramat, a TRM constructed of polypropylene fibers. The yarns are woven together to form a pyramid structure, which adds to the strength of the mat. O’Malley explains that the company starts with the raw pellets of polypropylene, adds UV protection additives and color, and spools out the yarns. Once they are woven together, the expected lifespan of the mat is about 50 years. The tensile strength is 4,000 pounds per foot, allowing the TRM to function under high velocities and even wave action.
Pyramat was chosen for the Santa Rosa Wash project for three reasons. One was the cost advantage; at about $18 per square yard, it was about half the cost of hard armor. Another was the UV protection, necessary to withstand the Arizona sun. Finally, it will stabilize the bank of the wash even before vegetation becomes established.
The mat was installed down to scour depth, 10 to 12 inches below the existing bottom level. The bottom was left unlined. A native mix of Sonoran grasses and plants was seeded, and then a layer of topsoil was put down.
The wash received a flow event soon after installation. Tucson and Sierra Vista had a heavy rainfall, and the flow reached the Santa Rosa Wash about two days later. The unpredictable flow level and rate made this a challenging project.
California Canyon
Pyramat was also installed for a channel stabilization project in a high-end development in the Simi Valley of California. Brad Cooley of Propex explains that riprap and concrete in a channel were replaced with Pyramat in February 2006. The channel runs through a canyon area, and several different stretches between bridges were covered with the mat. The bottom width varies from 10 to 20 feet. After installation of the TRM, native seed was planted.
Aesthetic considerations as well as improved water quality were parameters for this project. A more natural-looking channel was desired. The mat was chosen for its high tensile strength and UV protection.
So far, it has performed even better than expected. In March and April after the installation and before vegetation could be established, heavy rain events occurred. One of the challenges of the project was that installation took place in the winter months, during the rainy season. The soil in the canyon was also a challenge—a mixture of fill and loose weathered rock, with some alluvial soils. The TRM application needs to have high strength to contain these soils.
Nebraska Creeks
The City of Lincoln, NE, was cleaning up a creek that is a tributary of Antelope Creek. The creek passes through a park setting and an older residential section. Slopes range up to 2:1.
According to Steve Pudenz of the geoproducts division of Lumbermen’s, the erosion control blanket chosen was manufactured by Erosion Control Blanket, with headquarters in St. Andrews, MB. The product was the C32 BD, a biodegradable coconut-fiber blanket. The 100% coconut fiber is stitched with cotton thread between leno-woven jute nettings top and bottom. The blanket’s longevity is 12 to 24 months, depending on site conditions. Pudenz says that one big advantage of this blanket is that the leno weave is both top and bottom, allowing independent movement of each layer and giving great protection for wildlife. In addition, the cotton thread and the leno weave construction provide good moisture retention.
This project was the first on which Pudenz had used the 16-foot-wide rolls of C32 BD. The extra width speeds the installation time and eliminates most of the seams. The area was seeded with native grasses and wildflowers, and the blanket was installed.
For two channel improvements projects in Omaha, the C32 BD was also the product of choice. The channels were regarded, and drainage structures were added to handle runoff from two neighborhoods. The work was completed during the fall of 2006, but Pudenz says the blankets will hold through the winter season and he expects full vegetation next year.
Pudenz notes that although the biodegradable blankets are a little more expensive than other products, the nets do not endanger wildlife or hinder mowing. Since these channels do not receive a heavy flow volume or velocity, the blankets were the logical choice.
Virginia Highways
ECS-1 blankets were installed for several miles along an interstate highway in northern Virginia. I-66 through Prince William County was being widened. The straw, single-net blankets were laid along the shoulders to provide erosion control until vegetation could grow. The ECS-1 has straw fibers stitched to a single photodegradable polypropylene net. Longevity is about 12 months. The manufacturer is East Coast Erosion Blankets, headquartered in Bernville, PA.
Thomas Diloreto, vice president of ACF Environmental in Richmond, VA, handled the project. He says many of the slopes were fairly steep. Seed was planted, and then the blankets were placed one roll wide along the shoulders. Crews used 600 rolls to complete the project. The installation occurred in late summer, but Diloreto says the blankets will hold the soil until the vegetation can be established next year.
Diloreto notes that products from East Coast Erosion Blankets are on the approved list for the Virginia Department of Transportation, which was critical for this project. Installation of the blankets went smoothly in spite of the large number required. Despite the late time of the year, vegetation has grown, and in many places the blanket is no longer visible through the grass that has grown.
Texas Mine
An east Texas mine was undergoing surface reclamation to comply with requirements. The area covered about 12,000 acres. Hills and ditches created during the grading processes needed permanent protection from erosion. Recyclex TRM manufactured by American Excelsior in Arlington, TX, was chosen. The product is made of 100% post-consumer waste—soda bottles—and the fibers are crimped into a strong matrix.
At the mine, a mix of common Bermuda grass and brown top millet was seeded. More than 2,000 rolls of Recyclex were then stapled down over the seed in drainage areas. Straw bales had been used but were susceptible to washout in the sandy soil. So far, the Recyclex has held well and the vegetation has grown.
Colorado Restaurant Goes Green
The builders of a Red Robin restaurant in Castle Rock, CO, wanted an environmentally friendly approach to the outside. They chose a biodegradable wood excelsior erosion control blanket. The product, Curlex NetFree, is manufactured by American Excelsior. It is made up of Great Lakes Aspen excelsior fibers stitched with biodegradable rayon thread. This construction eliminates the need for netting for top or bottom and alleviates the problem of wildlife entrapment.
Minnesota Combo
The site of a new high school in Savage, MN, proved to be an erosion control challenge that was met by combining products. Using EnkaGreen design software from Colbond, Anderson-Johnson Associates designed a plan that called for a combination of erosion control measures. The products chosen were Enkamat R2 M and Soil Guard, a bonded fiber matrix from Mat Inc. of Floodwood, MN. The installation was done in October, so the system had to hold through the winter months until vegetation could grow in the spring.
In a detention pond area, Enkamat R2 M was installed running perpendicular to the slope. In the opinion of the installer, this is more effective at keeping runoff on top of the Enkamat. Extra staples were added as needed. The mats were installed 2 feet below the estimated water level of the pond.
Once the Enkamat R2 M was in place, the contractor hydraulically applied seed, fertilizer, and Soil Guard over the mats. Once the BFM cured, the combination provided a long-term mat that increased the contact with the soil, allowing better germination and growth. The TRM acts as a permanent stabilizer for the slope. During the winter, the TRM held soil and seed in place, and in spring the vegetation responded with a thick stand of grass. No overseeding was necessary; the combo had done its job.
BFMs at Work in Idaho
BFMs are a different sort of erosion control product; they are hydraulically applied but, when dried, act like a blanket. Soil Guard was chosen for a highway project in Idaho. The Idaho Department of Transportation was conducting a widening of I-90 near Coeur d’Alene. After the overpasses were widened, seed was applied with Soil Guard. Again, the time frame for work on this project was heading into winter months, but the Soil Guard performed so well during the winter that the product was chosen for the remainder of the project once spring arrived.
Regardless of the location, conditions, and type of project, you can find a blanket or mat product that is right for the job. Follow the manufacturer’s guidelines for design and installation and you will have a project that you can stake your reputation on.