Understanding Mats and Blankets
Water and wind, they’re elemental. You can’t live without them. But together— next to fire—they can be a most destructive force in nature. In the right place, in the right amounts, they can make a landscape beautiful. But too much in the wrong place for too long will wreak havoc on the landscape, the environment and your wallet.
Sediment is the number-one pollutant of our waterways, and soil erosion, by wind and water, isn’t just a minor impediment to progress. It’s an ongoing, destructive natural process that requires ingenuity and determination to control.
Two of the most effective weapons in this ongoing battle with Mother Nature are erosion control blankets (ECBs) and turf reinforcement mats (TRMs). They are members of a family of innovations called rolled erosion control products (RECPs).
Erosion-control blankets are degradable products that are used to provide immediate protection for exposed soil in areas where vegetation will eventually serve as the primary means of controlling ero sion.
While they’re holding soil in place, they also help give vegetation a healthy start by keeping the soil moist, protecting seeds and supporting fragile young plants. Once they’ve done their job, they’re designed to break down and disappear.
How quickly they break down depends on what they’re made of and how they’re constructed. Blankets are composed of degradable synthetic fibers and/or organic materials, such as wood excelsior, straw, or coconut fiber (coir). Straw breaks down relatively quickly, while coconut fiber can last about three years.
Many blankets use a combination of materials to produce fabrics that meet specific criteria for controlling erosion and longevity.
When it comes to longevity, blankets are classified as ultra short term (three-month), short-term (12-month), extended term (24month) or long-term (36 month).
Compost erosion-control blankets (CECB), first introduced in the late 1980s, are very much in vogue today because of increased stormwater management regulations. CECBs can be applied to any soil surface: rocky, frozen, flat, or steep. Composts used in CECBs are usually made from a variety of waste products, including municipal yard trimmings, food residuals, separated municipal solid waste, bio-solids and manure.
Seed can be applied onto the blanket itself, but the more effective method is to have the seed and compost mixed together before it’s applied to the slope. Compost blankets facilitate plant growth by capturing and retaining moisture, providing a suitable micro-climate and nutrients for the seed to germinate. Compost blankets can be applied by themselves, or in with other types of organic mats, such as straw or coconut.
Turf Reinforcement Mats
Turf Reinforcement Mats ( T R M s ) are used for applications where vegetation is never expected to do the job of controlling erosion on its own. These include high-flow ditches and channels, stream banks, steep slopes, or other areas where vegetation will always be limited or where the expected erosive forces won’t allow plants to thrive without support.
TRMs are made of synthetic fibers, wire mesh, or other nondegradable elements (sometimes combined with degradable components). These are formed into a sturdy, three-dimensional matrix. This matrix provides the structure that supports plants for the long haul, essentially giving plant roots something to cling to in a turbulent environment. Plant roots mesh with the mat to create a strong, permanent reinforcement system.
One of the biggest advantages of TRMs is that they don’t replace vegetation as a means for controlling erosion. Instead, they work in tandem with vegetation, giving it the support it needs to do its job more effectively. This allows for green space in many applications that would otherwise require hard armor.
A number of innovations have grown up in the last few years, in large part as a response to environmental concerns and in an effort to “green up” the erosion control industry.
While TRMs can solve big problems, they also have created some smaller ones. Jonathan Koepke, general manager of sediment control and soil erosion division, ENCAP, Inc., points to the growing use of biodegradable netting products, especially on projects of high environmental sensitivity. Koepke says that concerns about wildlife safety and the desire to go green have driven local and county governments and forest preserves, as well as the EPA, to specify more ‘natural’ netting for their projects. The nets in TRMs have been found to harm some wildlife and trap animals.
Realizing the need to secure ECBs and protect small animals, Global Netting Solutions, Minneapolis, Minnesota, created a line of wildlife-friendly biodegradable netting with greater spacing, to lower the possibility that animals will become trapped. Wanting to improve on the way their netting degrades, the company launched their Ecocycle line of netting in 2007.
Roger Meyers, of American Excelsior Company, the creator of the erosion control blanket industry, tells us that they are now marketing a line of TRMs called Recy clex, made from post-consumer green and brown plastic bottles. The plastic bottles are reformed into fibers which make up the matrix of the Recylex TRM. The plastic fibers are designed to mimic the hooked and interlocking characteristics of the original excelsior, which is made from aspen fibers. The specially formed synthetic fibers help the TRMs conform to terrain details and, thus, train water flow to follow the Recyclex curled fiber matrix. In turn, water flow velocity is reduced.
The scour preventer is another new product designed to be used in conjunction with a TRM to help break up ice-induced friction on the shorelines of lakes and ponds. The plastic scour preventer—sometimes rigid, sometimes flexible—is staked or anchored for additional protection against very high flow. “It’s a greener protection than the riprap more commonly used for the same purpose,” says Koepke.
The right stuff
As technology improves, more and more options are available to the developer, engineer, and contractor to get the job done right. It can be a boon, but also a bane. It is to everyone’s benefit that jobs turn out well, so from the manufacturer to the contractor, people have stepped up to make the industry work, and to keep the industry working.
Manufacturers provide very specific criteria for the use of each of their products. No one product is good in every situation. “Many manufacturers provide good software apps that allow you to plug in criteria for your project and generate a recommendation for the most cost-effective product for the job,” Koepke says.
The right way
As effective and innovative as these products are, if they aren’t installed properly, they end up costing rather than saving time, money and resources. Designers need to do their homework in creating specs. Contractors need to follow those specs.
When specs are vague and contractors don’t do their own homework, the project is open to errors and misguided attempts to save money. Often the biggest mistake is simply going for the cheapest product on the market. Choosing a product without understanding the demands of a site can lead to an absence of vegetative establishment, and in some cases, serious erosion and sediment loss.
Using the right product is one way contractors can ensure themselves from having a redo; following manufacturer’s instructions to a ‘T’ is another. For instance, man ufacturers recommend specific stapling or anchoring patterns. These patterns are based on tests that show that they are the best way to ensure that the product maintains intimate contact with the soil.
Skimping on staples or anchors on a blanket can result in the product blowing away, or lifting away from the soil.
Much of the innovation in the erosion control industry has been driven by the need for developers and contractors to comply with ever more stringent requirements of the EPA. And while there is a temptation to cut costs by cutting quality, the price for failure to comply with government regulations only continues to rise. It behooves people at every level of the industry to disseminate accurate information about RECPs, and to keep up with new innovations.
Work harder and smarter
Change is inevitable; success is not. Unless you stay on top of advances in the industry, you can’t stay competitive. To stay competitive, contractors need to take advantage of training, and stay upto-date on new products.
Competition can be fierce in today’s economy, so work smarter and harder. Know the product you’re using, so you can install it with confidence.
RECPs are all around us—running along highway embankments, lining channels and streams, and climbing steep slopes. Most people don’t know that they’re there. But noticed or not, erosion control blankets and mats are quietly making a big difference in the aesthetic appearance and environmental quality of our country.