March 18, 2013 03:46

What’s New in Green Erosion Control Solutions?

When it comes to environmentally friendly erosion control, there are two kinds of products. There are these that have a cordial, but distant, relationship with Mother Earth, and products that practically hold hands and go skipping down the street with her.

Erosion control in itself is a green practice, keeping dirt and contaminants out of waterways, controlling dust and conserving beachfronts and land. Green erosion control speaks softly, but carries a big, biodegradable stick.

It’s not meant to be seen. Ideally, it disappears, either partially or completely, over time, as nature fills in where it couldn’t before. Think of a plaster cast on a broken bone. Once the bone heals, the cast is unnecessary. Until the bone knits, however, that cast is indispensible. A green erosion control method is that plaster cast, protectively shielding and supporting a wounded ecosystem while it heals.

Of course, environmentally safe erosion control methods have been around for a long time.

Hydroseeding or hydromulching, blown straw, straw blankets and wattles, coir logs and blankets, turf reinforcement mats (TRMs), filter and compost socks and silt fences are nothing new. Even some hard armor and gabion can be considered green when they allow water to flow through and vegetation to eventually cover it. What’s new, or newish, are some of the ways these things are being made or reconsidered.

In general, the greener the erosion control solution, the less permanent it is. Sensitive areas require eco-sensitive solutions, often mandated by law. “Sometimes, people don’t have any options as to doing permanent erosion control,” said Shan Halamba, CEO of Riococo Worldwide in Irving, Texas. His company owns a factory in Sri Lanka, where they process coconut husks into coir erosion control products such as logs, sandbags, wattles and blankets that are all 100 percent biodegradable. Native trees or other plantings can be installed on top of the coir bags or wattles. In a couple of months, natural restoration starts, as the roots penetrate the coir and enter the soil.

Hydroseeding

Hydroseeding or hydromulching is a green solution mainly used for roadside erosion control. Because it’s sprayed on, it can be used on the most extreme slopes. A slurry of seed, mulching material, fertilizer and tackifiers is mixed together and applied with large hoses from a tank truck or trailer. The tackifiers keep the seed stuck to the soil, and the fertilizer encourages rapid growth. There are a large variety of hydromulch products available from many different companies.

When deciding to use hydromulch, you’ll have many different kinds to choose from. One of the variances is whether they use straw, wood, or cellulose as a base matrix.

The wood fiber used in hydromulch comes from wood waste from lumber mills or urban sources. It biodegrades more slowly than cellulose and holds more moisture. It also requires less water to be applied. However, the cost of wood fiber-based hydromulch is higher than that of cellulose-based products.

The cellulose fiber used in hydromulch comes from recycled paper.

These fibers are shorter than those made directly from wood, and when applied, may tend to clump. While cellulose-based hydromulch is less expensive than the wood fiber type, when applied at high rates it may create a kind of “papier-mache” layer. This can result in poor seed germination. A good way to combine the beneficial characteristics of both cellulose and wood fiber hydromulches is with a 50/50 blend of each. A newer approach is to use alternative fibers, such as corn, natural feed stock or reclaimed cotton fibers (waste products from the ginning process) in hydromulch. Jill Pack, product manager at North American Green, says, “We went this way because there are definite benefits to using these alternative fiber types.”

One of the benefits of cotton fiber, besides its biodegradability and absorbency, is that each fiber is covered with tiny barbs. These barbs help “lock” the straw fibers together, and trap or encapsulate the soil. There’s another advantage, too. “Every particle of carbon an organic product contains ‘steals’ a certain amount of nitrogen from the soil as it biodegrades,” Pack explains.

Blankets, mats, logs and blocks

Erosion control blankets (ECBs) typically have cores composed of coir, straw, coir mixed with straw or wood shavings, encapsulated by netting. Their purpose is to hold onto moisture, thus promoting seed germination, while protecting the nascent vegetation from being washed away. They can be made fully biodegradable, depending upon the netting material used. Some ECBs are made with photodegradable (material that depends on exposure to sunlight to degrade) plastic netting. They last about one year.

TRMs are similar to ECBs but are made of tougher stuff, intended for more severe applications. They’re mattresses, usually composed of a matrix of synthetic fibers held in by filaments, nets or wire mesh. Like ECBs, they hold moisture while protecting vegetation as its being established. They are considered a hard armor solution that is green, because though they’re generally not biodegradable, they can be vegetated. TRMs last longer than blankets, generally about three years.

Both TRMs and ECBs have the limitation that rocks and debris may lift them above the soil, allowing erosion to occur between the blanket and the soil surface. They’re unlikely to improve compacted, nutrient depleted, or poorly draining soils to promote healthy, long-term vegetation growth.

Coir logs and blankets are great green solutions, particularly as growing media. But there’s a bit of an environmental tradeoff. Because we don’t have the climate to grow coconuts in this country, coir must be imported.

“Conservationists came to us, and other manufacturers, to see if there was something we could make here in the U.S.,” said Kurt Kelsey, director of technical services for the American Excelsior Company in Arlington, Texas. “They were saying, we’re putting in all this vegetation along the streambanks and shorelines, and yet we’re using products that have to be shipped from halfway around the world, leaving a huge carbon footprint. We’re working at cross purposes, helping the environment with one hand, but hurting it with the other.”

To address this concern, the company developed its newest product, the Curlex Bloc, intended as a substitute for coir logs. It’s made flat on the bottom for tighter contact with the soil and to resist rolling from wave action. Like all the Curlex products, it’s made from shaved aspen wood fibers called “excelsior.” This material is biodegradable and has a “swell factor,” meaning that like all wood fiber, it expands when moistures hits it.

“In Minnesota, green soil erosion control is split into three types: hydromulching, blankets and straw,” said Mark Jeffries, division manager for Terra Services, a division of Hardrives, Inc., a Lakeland, Minnesota, paving company. “Our Department of Transportation (DOT) is starting to specify more and more of the wood fiber products, relative to other blankets.

And natural net has also become a big part of what the state expects. I think MN-DOT perceives that the wood fiber products are more three-dimensional than their straw counterparts. They give you more moisture retention and a better blanketing effect than straw.”

However, they are more labor intensive to install than blown straw, according to Jeffries. “The wood fiber products typically come in 500-square-yard rolls. you unroll them with a tractor or skid loader, with a few guys following behind installing six-inch staples, one every square foot. With straw, you blow, you crimp, and you’re done.”

Yellowstone National Park in Wyoming is one of the most abundant wildlife areas in the United States. But severe wind and water erosion due to construction was causing excessive sediment deposits in its rivers and streams, endangering the freshwater fish population.

A comprehensive erosion control plan was mandated by the U.S. Forest Service. However, only 100 percent biodegradable erosion control products are allowed for use inside or near the park’s boundaries, and with good reason. Animals of all sizes have been known to become entangled in the plastic netting used in some erosion control blankets and gabion.

More companies are making environmentally-sensitive alternatives, held together with biodegradable thread. They are good choices for environmentally-sensitive jobsites. They also reduce the danger that animals may become entrapped in the netting.

Compost socks and bags

Compost socks (sometimes called filter socks) and bags consist of tubular netting, usually filled with compost, soil, or a blend of those, and sometimes other materials. They can be completely or partially biodegradable, depending on the sock material used—usually cotton or burlap—and can be left in place permanently. Compost socks are used to reduce stormwater runoff volume and to slow it down. They are a good green solution, because you can plant right on them, and the roots will go right through. Among their disadvantages is that they must uniformly contact ground surfaces to be really effective. They can also be difficult to install on rocky or steep slopes.

Compost or filter socks do double duty. They keep soil and water contained, but also collect sediment and pollutants from the water that seeps through their porous media (the ‘filter’ part of filter socks).

They are heavy enough, especially when wet, that trenching isn’t necessary to hold them in place.

“In green erosion control, the way things break down depends upon the energy of the water system involved,” says Rob Llewellyn, director of business development for Evansville, Wisconsin-based Envirolok, LLC.

Their system consists of bags made of “a four-ounce, nonw-oven vegiotextile material, the same type of stuff that is put behind riprap.” They’re sewn with a special stitch, then filled onsite with “engineered soil,” a blend of sand, high-grade compost and topsoil customized for the site and zip-tied closed.

“We consider Envirolok a kind of green hard armor,”said Rich Oscarson, president of Kenosha Grounds Care, Inc., a full-service landscape company in Pleasant Prairie, Wisconsin. “We’ve used it in lieu of hard armor for restoring streambanks and pond shorelines.”

However, Envirolok’s outer bags are not exactly biodegradable. According to Llewellyn, “this is a kind of gray area for the industry. At a typical low-energy flow site, they want a biodegradable solution that’s going to go away over time.”

He continues, “At a moderate-energy site, they want something that reinforces vegetation. We get into kind of a circular conversation with the permitting agencies. They ask, ‘So the bag doesn’t biodegrade?’ It’s a tough conversation to have, depending on who you’re working with and what they’re accustomed to doing. We explain that over time, you don’t see the product anymore. you still have a fully vegetated solution.”

There are many different kinds of compost and filter sock products available. Most of these are very eco-friendly.

Filtrexx International, LLC, in Grafton, Ohio, uses only ‘locally made, annually renewable, bio-based recycled compost and other organic materials’ inside their patented mesh containment systems. The mesh selection includes options of 100 percent biodegradable materials.

Another filter sock product is the Erosion Eel, from Friendly Environment in Shelbyville, Tennessee.

It uses shredded rubber from recycled car tires inside the tube.

Green grid systems

Some of the newer erosion control products on the market are grids made from environmentally friendly or biodegradable plastics. These products can be used to prevent surface erosion of roadbeds, for slope stabilization, streambank erosion control and stormwater management.

The plastic grid is laid over a subbase of soil, sand or gravel, and then the grid is filled with a mix of the same. Water seeps through the grid, down to the subbase, instead of running across it. They are a green substitute for concrete, asphalt or paving stones. Because you can plant seed right through them, they are often used for green roofs as well. But plastic grid products tend to be more expensive in general.

Certainly, some hard erosion control materials can be made semipermeable by drilling holes through them. However, the cost of transportation and excavation might be high enough to offset the higher price by using the more expensive plastic products instead. “The actual amount of nonpermeable surface area is extremely significant [when using those other methods],” says Terrafirm President John Manestar.

Eco-friendly erosion control is here to stay

“We’ve seen a definite push toward using sustainable erosion control products,” says Pack. “A lot of states are starting to spec in completely biodegradable products, or express a preference for greener design. Also, more contractors are trying to garner Leadership in Energy and Environmental Design (LEED) or Green Build points.”

Just as with all green technology, green erosion control technology will see continued innovation. The demand for it is expanding constantly, driven by the market as well as the regulatory climate. Many of the green erosion control solutions discussed in this story were undreamed of just a few short years ago. It’ll be exciting to see what the entrepreneurs and inventors in this field will come up with next.


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