Rolled erosion control products (RECPs), consisting of temporary erosion control blankets (ECBs) and permanent turf reinforcement mats (TRMs), have been a popular choice for effective erosion control for a number of years. With many companies and government agencies taking more of a “green” approach-moving away from hard-armor techniques such as riprap and concrete-the popularity of the fiber-based products seems to be on the increase.
Most ECBs and TRMs are manufactured from organic or synthetic fibers such as straw, coir (coconut fiber), and excelsior, which are sandwiched between two or three layers of netting. In most cases, both types of product are applied over the top of a seeded or planted area and have a two-fold purpose. One is to help the newly seeded areas maintain moisture, promoting germination; the second is to provide erosion control until the vegetation can provide adequate erosion protection on its own. Additionally, TRMs also provide effective stem and root reinforcement for the mature vegetation.
The main factor when it comes to choosing between an ECB and a TRM is the type of erosion control that is required for a specific site. Temporary erosion control, which can be defined as anywhere from a few months to a few years, can be achieved through the use of less expensive ECBs that break down after a specified amount of time. For permanent erosion control, TRMs are often the ammunition of choice. To be classified as a TRM, the permanent portion of the matting must be at least 0.25 inch thick, which is adequate when providing reinforcement for the vegetation.
Although TRMs cost substantially more than most ECBs, both products offer significant cost relief over the hard-armor methods they often replace. In some cases, erosion control professionals have found the “soft-armor” products like ECBs and TRMs work well in conjunction with hard armor, particularly on jobs where varying degrees of erosion control are required for different areas of the project.
“In some cases, where the shear stresses exceed the capability of TRMs, a designer might have to use riprap or concrete on the bottom of a channel but will use a TRM on the streambanks to create a more natural or softer look,” explains Roy Nelsen, CPESC, manager of technical services for North American Green in Evansville, IN. In addition to working for North American Green, Nelsen is extremely active with a number of different standards organizations, including the Erosion Control Technology Council and the American Society for Testing and Materials (ASTM). For both organizations, he is involved with writing standards for RECPs in terms of performance testing and physical properties, such as mass per unit area, thickness, and tensile strength. He also serves on three committees for IECA.
“Although that softer look is appealing, definitely one of the reasons the organic materials are so popular is the lower cost structure,” concedes Nelsen. “The installed cost of ECBs may fall below $4 per square yard, while TRMs normally run between $5 and $15 per square yard installed. Riprap and rock can run anywhere up to $80 per square yard installed, depending on the size and type of material used.”
Hard numbers can also dictate what product has to be used for a specific application, he notes. “Coming from the design side, we will look at a project and decide if vegetation alone can provide permanent erosion control. If it can, we will specify the lower-cost ECBs. If it can’t, then we go to the TRMs. Normally, if the shear stress exerted in a channel will be less than 3.7 pounds per square foot, we can use unreinforced vegetation where a blanket will then provide the erosion control until the vegetation establishes, while anything over that number will require the more permanent solution of a mat. The upper limits of some TRMs are comparable to the protection you would get from 40-inch-diameter riprap. Basically, if you use soft armor instead of hard armor, you are going to the see the environmental benefits of vegetation, such as the ability to remove pollution, at a much lower cost than hard armor.”
Photo: Trout Headwaters Inc.
“No Silver Bullet”
Mike Sprague agrees with Nelsen when it comes to using soft-armor techniques where possible for environmental and cost benefits. Sprague is president of Livingston, MT-based Trout Headwaters Inc. (THI), a river restoration company that specializes in “soft technologies.” His company, which has been in business for 11 years and employs approximately 18 people, works all over the country for private landowners, local governments, non-governmental organizations, and the Army Corps of Engineers. THI employs a team of biologists, hydrologists, engineers, and installation specialists and has completed almost 400 projects through the use of a multidisciplinary approach that includes design, installation, management, and maintenance. One of the most interesting projects currently under discussion by THI is close to home in the very environmentally conscious and highly visible Yellowstone National Park.
“Right now we are discussing a restoration project with the park where they are going to pull the road away from the river,” says Sprague. “For this project, they will be reconstructing a section of the road and building a significant bridge. The goal of the project is to restore the function and hydrology of the river back to its natural state.”
Sprague has always been a firm believer in using natural materials and the softest approach possible to get the job done. “From our standpoint, we have never really been enamored with the hard-armor technologies, and I don’t think you have to be a hydrologist to understand why. We believe there are construction issues with the hard armor, and by using soft technologies, we can obtain significantly lower costs with better environmental outcomes. There are a lot of reasons why these softer strategies make sense, and one of the biggest is definitely the cost savings. If we can provide a good environmental solution at 40% of the cost of some of the hard-armor strategies, then why not? Many of the sites we work in are very environmentally sensitive, and if you can stabilize a piece of the bank and reinstate the riparian functions, at the end of the day, you have done a good thing. And, it is also very difficult to grow plants through 40 inches of rock.”
But for Sprague, in the early years of the company, selling clients on the benefits of the soft-armor techniques was not easy. “The problem historically is that a lot of the newer technologies were unknown, but the manufacturers of blankets and mats have done a lot of work to educate the industry on how these products will perform. When we are designing a solution, we are designing for the moment of installation, as that is the weakest point in the whole process. It is also the point where people have seen the most failures, but often it is not the material that fails, but the method of how that material is attached to the world.”
For many of its applications, THI uses what it calls “live stakes,” usually cuttings from native willow, in conjunction with other methods. “When it comes to plant material and revegetation, we use what we call a “˜mixed construction methodology.’ An example of this is using plant materials to anchor the mats or blankets, because quite often, the failure of these products is due to the use of staples, which just lose contact with the soil and become unfastened,” adds Sprague.
When choosing between ECBs and TRMs, Sprague says THI evaluates things like velocities and shear stresses, but he adds that designers also spend a lot of time reflecting on the complexity of the channel. “You have to look at all of the variables right down to the fact that you need sunlight to make vegetation grow.”
When asked if, in his opinion, there are ideal applications for ECBs over TRMs and vice versa, Sprague immediately responds that “there is not, and that is part of the challenge.” It’s obviously a question he has been asked many times before, and he goes on to explain in more detail: “What people need to understand is that every site is made up of a number of micro sites, and you have to design your solution accordingly. For example, where you have much greater velocity, you are going to require materials with much higher performance qualities. In working with Yellowstone, using synthetic materials may not be conducive to the client. You have to look at each project, and match the goals and the budget against a set of performance and design criteria. If you try to use a “˜one size fits all’ solution, you will probably fail and that will not serve your client or the environment. There is no silver bullet in this business.”
The Urban Environment
Jim Lanier, who owns Aquascape Environmental, also likes to work around water. Aquascape is based in the metropolitan area of Atlanta, GA, but covers a geographic region that stretches up to a 300-mile radius of the southeast hub, taking his crews into South and North Carolina and Alabama.
“We primarily deal with issues regarding water, whether that is lake management issues, wetlands work, streambank restoration, or consulting for fisheries,” notes Lanier, who has been in the business for 14 years. “Most of our clients are private and commercial developers and golf courses, and probably 80% of our work is in an urban environment, including work on the Chattahoochee River, which is the main waterway through Atlanta. We spend a lot of time fixing existing problems that are caused by urbanization, such as watershed developments that are adversely effecting streams or riparian zones.”
Photo: East Coast Erosion Blankets LLC
With most of Aquascape’s work in urban settings, Lanier finds that he has to occasionally use some kind of hard-armor techniques in conjunction with blankets and mats because of space and access limits, but he prefers to take a softer approach whenever possible. “We prefer to use a natural type of process, but there are some limitations, so we will use riprap when we have to. Our goal is to restore a natural channel design, which involves getting a stream restored to its natural pattern, profile, and dimensions.”
When using soft-armor products, which the company often purchases from RoLanka International in nearby Stockbridge, GA, Lanier says the company will go with ECBs most of the time. However, he adds, they will occasionally work with TRMs when dealing with steeper grades and higher velocities or will use other products such as geoweb-type fabrics or coir logs.
“We like to work with native vegetation when possible, and we have found that the lighter materials, such as the blankets, work very well for us with nursery stocks,” notes Lanier. “These lighter stocks are also biodegradable, which we also feel is a positive factor, but for each job, we have to look at the conditions and then determine what the best solution is.”
Changing Tactics
In some situations, that “ideal solution” to an erosion control project can change partway through a job, and contractors have to be able to quickly adapt to the new specifications. That has been the case for Valley Seeding Company Inc. in Sugarloaf, PA. Right now, the company is working on a three-year job for the Pennsylvania Department of Transportation (DOT).
Photo: American Excelsior
“We commenced work on a stretch of State Highway 222 in Berks County, near Reading, Pennsylvania, in the winter of 2003,” explains Valley Seeding’s President, Mary Lou Burke. “The original specifications called for hydroseeding and straw mulch, but with the amount of rain we have received this year, it just wasn’t holding, especially on the steeper slopes. We have since gone back and blanketed a large portion of the project.”
To date on the Highway 222 project, Valley Seeding, which employs between 35 and 40 people, has installed almost 8 acres of blankets along 18 miles of highway. The blankets, which are expected to have a 24-month lifespan, are a straw (70%) and coconut fiber (30%) blend with two layers of net. They were supplied by Sinking Spring, PA-based East Coast Erosion Blankets.
Burke, whose father, Joe Larock, started the company in the early 1950s when he got involved with work on the Pennsylvania Turnpike, says the specifications are generally supplied by the DOT or end customer. However, she is seeing an increase in demand for biodegradable and photodegradable products. The top mesh on the blankets being used on Highway 222 is a UV-stabilized polypropylene product with a mesh size of 0.75 inch by 0.75 inch, while the bottom net is a smaller 0.50-inch by 0.50-inch mesh made from a lightweight, photodegradable polypropylene.
Working Without a Net
Even though photodegradable and biodegradable products will break down over time, there are some situations where project managers don’t want to wait for this process to occur, especially where the area that has been blanketed will require early and frequent mowing. This was the case at the Stonebrook Golf Course in Pace, FL; Hiram J. Cook Jr., PGA golf professional and the owner/manager of the course, decided to go with a new product from Arlington, TX-based American Excelsior called Curlex NetFree, which the company promotes as being the “first ECB that does not contain any netting.”
According to American Excelsior, the product consists of a specific cut of 100% weed-seed-free Great Lakes Aspen curled wood excelsior, which is stitched together to form a consistent thickness and provide even fiber distribution. The curled and barbed properties of the fibers within the blanket eliminate the need for netting, which in most blankets maintains product integrity. The company completed performance testing on the product in the summer of 2003 at the Erosion Lab in Rice Lake, WI, following ASTM protocols for the testing of ECBs. But the first on-the-job test of the product was in the fall of 2003 at the Stonebrook Golf Course, where approximately 200 rolls were used on hill slopes up to 3H:1V, holding ponds, and stormwater retention areas, including what turned out to be the largest single application of the job-a stormwater retention ditch that was constructed to a trapezoidal shape with a 100-foot-wide bottom, 40-foot-long sideslopes at 4H:1V, and a total length of 700 feet. Following construction of the ditch, the soil was compacted, seeded with winter rye, and blanketed. Common Bermuda was then used to over-seed the area in the spring of 2004, as winter rye is only an annual grass.
The real test of the net-free product came shortly after installation when rainfall-induced runoff caused rills to form in the soil that was unprotected, while soil under the Curlex blankets was held in place. “We were extremely pleased with the results,” notes Cook. “The product lays down very well, and-providing the grass grows-we can be mowing within two weeks.”
Cold-Weather Adaptations
Keith Porter of Mid-Canada Hydroseeding uses a lot of blankets in his business, which is based in Winnipeg, MB, and serves the Canadian province of Manitoba and some areas of the neighboring provinces of Ontario to the east and Saskatchewan to the west. But for Porter, the biggest challenge can be the winter months, where Winnipeg and other areas he works in can be under snow and ice for up to seven months of the year.
“During our peak times, we can have up to 20 people working for us, but during the winter months, especially January and February, we have a very limited crew,” says Porter. “We used to shut down at Christmas and then start up again in March, but recently we have been working on riverbank projects during that time.”
Photo: ACF West
Porter primarily uses mats from Winnipeg-based Erosion Control Blankets.com, a company started in 1999 by Mark Myrowich, who was an installer in the business before opening his own mat plant. “We have used TRMs in the past, but most of the work we do can be satisfied with straw and coconut blankets,” explains Porter. “We also use other products, such as straw mulch, silt fence, wattles, and turbidity curtains, but for our winter riverbank work, we have found that the blankets work the best as we can attach them to the ground using drywall screws.” The soil in the southern Manitoba area is clay-based, and Porter adds that once that clay is frozen, the drywall (also known as sheetrock in some areas of the country) screws work very well.
During the summer months, Porter says crews often use blankets in conjunction with riprap as they are always looking for a “green” solution to erosion problems. “In many cases, we run the blanket right up to the riprap, and then we incorporate native plants such as willows, as we feel that for areas with high velocities, this is a much better solution than rock alone.”
Dave Sherbrooke of Sherbrooke Turf Inc. is located a few hundred miles south of Winnipeg’s Mid-Canada Hydroseeding, in Detroit Lakes, MN. Like Mid-Canada’s Porter, Sherbrooke uses a variety of solutions for erosion control, including blankets and mats, but for steep or rough ground where the fabric products can’t make good contact with the ground, he uses Soil Guard, which is a bonded fiber matrix, manufactured by Mat Inc. in Floodwood, MN. Soil Guard, which was originally developed by the forest products giant, Weyerhaeuser, is essentially a spray-on blanket. It delivers the performance of a blanket but with the labor savings of a hydraulically applied product. Soil Guard dries to form a hard surface that can be repeatedly rewet, and will hold soil and seed in place. As the vegetation takes hold, the Soil Guard product slowly decomposes. Because it is wood fiber-based, this decomposition also enriches the soil.
“We find the Soil Guard to be a great product on really steep slopes where we can’t use roll-out blankets,” explains Sherbrooke, whose company worked on 105 projects in 2003. “In these types of conditions we can use the hydroseeder to shoot Soil Guard up to 250 feet and by applying the product hydraulically, we get excellent ground contact.”
Sherbrooke also likes to use ECBs, including products from Winnipeg’s ErosionControlBlanket.com, which he says is an excellent product that is very uniform and is packaged in a way that makes unrolling and installation fast and easy.
“We like to use blankets for smaller jobs,” notes Sherbrooke. “If we are only doing a few hundred square yards, it just makes more sense to throw a couple of rolls of the blanket in the back of a pickup, rather than having to bring out the hydroseeding truck.”
In some very demanding situations, Sherbrooke says he has combined Soil Guard with blankets. “On some really tough jobs, we have put down a straw blanket, and then applied Soil Guard over the top.”
Securing Soil on Sideslopes
In the rapidly growing Seattle, WA, suburb of Issaquah, Portland, OR-based ACF West Construction recently completed a huge job using a 4-inch cellular confinement system from EnviroGrid in Houston, TX, a product that can be used with blankets or on its own.
“The Highlands Project in Issaquah is a mix of high-end and affordable houses, along with town homes,” explains Jeff Boys of ACF West. “In total, the project will add approximately 3,000 new homes to the area, which has created a big requirement for stormwater detention ponds that will control the stormwater runoff. The designer wanted vegetated sideslopes; however, the ponds were lined with plastic liner, which meant the soil would just slip down to the bottom. The problem was solved with the EnviroGrid product, which is delivered as panels that are attached together onsite, to form a honeycomb-type confinement system for the soil.”
In total, the area required four detention ponds, which were constructed by the two excavating companies that did all of the dirt work. ACF West was responsible for lining three of the four ponds. The smallest was 92,000 square feet, while the largest was 240,000 square feet-almost double the size of a typical Costco wholesale store or Home Depot.
After the pipes and utility work were completed, ACF West went to work, installing a drainage composite and then a 60-mil textured high-density polyethylene liner on top of that. The sideslopes were covered with an 8-ounce nonwoven geotextile from Propex Fabrics (formerly BP Amoco Fabrics and Fibers), and then the 4-inch EnviroGrid product was installed and filled with topsoil. The area was then hydroseeded. In some cases, designers will specify that the filled and planted grid be covered with a blanket; however, in this case they felt this option was not required.
“The EnviroGrid is a permanent solution,” adds Boys. “But when the project is completely finished, you won’t see any of the product. The detention systems will just look like large ponds with grass on the side.”
When it comes to blankets and mats and other related products like Soil Guard and EnviroGrid, the bottom line is that there is no correct solution. It’s a matter of evaluating each project and then making an informed decision as to what product, or combination of products, will provide the best protection for the environment, while meeting the goals and budget of the end client.
