Getting your erosion control needs met the first time you roll out protection for your project is essential. In this economy, erosion control budgets don’t allow for a margin of error within total costs. Making your project dollars stretch further by choosing the product that can handle all that nature throws at it in an ecofriendly way can only help enhance your business reputation. During a recession, becoming the go-to contractor for sites built for long-term wear brings security and stability for more than the soil you labor to protect. Selecting an erosion control blanket or turf reinforcement mat (TRM) for your site can be challenging with so many choices-biodegradable versus photodegradable versus synthetic are just a few possible considerations. The sensitivity of your site, government regulations, product pricing, climate, water velocity, and soil conditions should help you make an informed decision.

Weighing modern materials with products that have worked for you in the past is inevitable, but before deciding your approach has to be an either/or decision, consider combining several techniques to protect your site for the future.

Erosion Control Blankets
Erosion control blankets, which typically consist of wood excelsior, straw, or other natural fibers nestled between layers of geosynthetic netting or fabric, are versatile solutions that can conform to the ground on which they’re placed. This type of cover seemed ideal for a 28-acre highway site located in Castle Rock, CO, that was completed under the unforgiving sun during the summer of 2010.

The Colorado Department of Transportation (CDOT) widened the I-25 highway in the area of Fifth Street to Douglas Lane, replaced bridges in the area, and completed some stream restoration, according to Mike Doyle, the Region One water-quality manager for CDOT. The work was part of a project with a budget totaling $30 million, and water-quality items, including erosion sediment control, made up about 5% of that cost. Nestled in the Rocky Mountains, the rocky soil in the area was poor-a sandy loam-and erosion was a concern at the construction site where work began in 2009. A straw-coconut soil retention blanket was used in combination with various soil stabilization techniques, including riprap and Profile Products’ Flexterra Flexible Growth Medium.

Although the soil issues at the site were natural to the area, another challenge, arguably aggravated by nature, was more clearly manmade.

“Back in the early ’60s, there was a big flood. The stream was littered with old debris, like cars, buried in sediment,” says Doyle, describing the area near Plum Creek at the site where crews were working on bridge construction and a bike path. “Somebody might think we created the mess. We pulled out the piping and the cars and the concrete, and we stabilized the slope with riprap and cleaned it up a little bit. We’ll drill-seed where we can.” In steep areas, workers hand-broadcast seed before returning with straw, mulch, and tackifier. In addition to using the straw-coconut soil retention blanket, TRMs were also used at this site. CDOT didn’t hydroseed the site, but paired Flexterra with the erosion control blanket to stabilize soil.

“We use it a lot where the soil retention blanket creates a lot of voids because of rock,” explains Doyle. “With a soil retention blanket, I think insulation is crucial, especially the trenching. If that isn’t done adequately, the water will get up under it.”

Thermally processed wood fibers, cross-linked hydrocolloid tackifiers and activators, and proprietary crimped, interlocking fibers are used in Flexterra’s composition, according to the product’s specifications.

Erosion control blanket was staked carefully at the site because, as Doyle explains, if a passerby doesn’t see it and walks across it, it can become damaged.

“When installed correctly,” he says, “the product performs well.”

According to the permit, Doyle says, 70% of the site must achieve revegetation. “We try to meet 100% of existing,” he says. “We have stormwater control permits on any project over an acre.”

Even the smallest detail was not overlooked on the large-scale site. Provisions were made at the site for the jumping mouse, an endangered species local to the region.

“We created a clear, object-free path,” says Doyle, “so the mouse could travel from one side of the creek to the other.”

Contractors must look not only to what has worked to control erosion in the past, but also to what will prevent erosion in the future. Products from East Coast Erosion Blankets were selected for an ongoing industrial site project in Linden, NJ.

“I have utilized this material on many other sites and recommended to the owner to assist with vegetation growth and erosion prevention,” says Barry Longenecker, project manager for the site and vice president of the construction division at Thomas F. Corbett Associates. “We started the surcharge pile probably three years ago.  We just recently reseeded and placed the erosion mat this past spring.”

The approximately 200-acre project faced challenges from both above and below.

“The imported soil is not the best. Apparently, there were some problems early on, which resulted in the failure of a hydroseeding application two summers ago,” says Don Knezick, president of Pinelands Nursery & Supply based in Columbus, NJ, noting the dry construction conditions. “This summer has been one of the driest on record, but germination under the erosion control blankets has been very good.”

The site of the future manufacturing center has 3:1 slopes and was suited for the East Coast Erosion Control Blankets’ product. “The goal was to get a permanent stand of turfgrass to satisfy New Jersey DEP regulations,” explains Knezick.

During the winter of 2009 through 2010, slope stabilization was a priority at Meadowbrook, a site with an open, natural-flowing river in the western slope of the Cascades in Oregon. The Oregon Department of Transportation (ODOT) used a combination of techniques during the emergency project undertaken to protect the west bridge abutment from further scour at the Molalla River in rural Clackamas County, Oregon, explains Magnus Bernhardt, the landscape architect for ODOT’s Region One. With a $98,000 budget, ODOT’s Region One Construction Office, Tech Center staff, and Landscape Maintenance Department collaborated on the project.

Rock embankment was one stabilization technique employed at the site.

“For an immediate fix, it’s still considered one of the most reliable approaches in areas of concern,” says Bernhardt. “We usually try to incorporate a “˜green’ with a “˜hard’ and not solve all our problems with rock embankment.”

Ridding the area of a vigorous, rampant weed-Japanese knotweed-was yet another priority at the site prior to the revegetation.

“There are challenges of quick coordination and materials onsite, and we’re making sure the project is built correctly,” says Bernhardt. “We had tree revetments as part of this project as well, to deflect the flow of the river back into the river channel, to help protect the new embankment.”

Live stakes of red alder and poplar were placed in the silty clay and rocky cobble layer of soil along the high-water line, he explains. Revegetating the area while improving the habitat of the riparian buffer was important: “It was more or less nonexistent,” Bernhardt says. ODOT wanted to improve the shear strength of the soil “through the very depth of the root masses, both from a herbaceous and woody plant perspectives,” he notes.

Naturally biodegradable materials were used for this project, a common practice for ODOT. The North American Green C125BN BioNet extended-term erosion control blanket stretched up the 1:1 to 1:1.5 slopes of the entire bank from the ordinary water line after regrading. “Because [the C125BN] had a greater shear stress and could handle higher velocities, we went with that,” says Bernhardt. The biodegradable coconut-fiber blanket is designed to assist revegetation onsite for between 18 to 24 months, according to the product specifications, after which root systems will take on the role of controlling erosion as the blankets degrade.

A compost blanket embedded with native seeds was also employed at the site. California brome, blue wild rye, red fescue, and large-leaf lupine were incorporated into the upland seed mix. Lightweight, relatively inexpensive, and easy to install, several erosion control blankets come preseeded. With a goal of establishing a quick cover, ODOT added a cover of winter wheat that Burkhardt describes as so successful it was “almost too aggressive.”

“We wanted to get seed started right away. Compost provided a great seedbed for our seed,” he says, noting that it acted as a temporary erosion control measure before the blanket was installed. “Compost is good at retaining heat, and we found we could seed later into the season. Compost was placed underneath the matting. It’s a recycled organic product. It has a sustainable component as well.”

Turf Reinforcement Mats
Steep slopes and waterways with concentrated flow can benefit from the use of TRMs. Their durable synthetic material or heavier, fibrous coir helps hold them in place where lighter, more flexible blankets might not survive. Although TRMs may cost more than erosion control blankets, they are often less expensive than other options such as riprap.

In 2009, Barr Engineering used TRMs at the Hastings Industrial Park Ravine in Hastings, MN, to stabilize the soil at the commercial site.

“The site was an eroding wooded ravine that normally is dry but took substantial runoff flows during and immediately after rainstorms and snowmelts,” explains Steve Klein, senior civil engineer with Barr Engineering in Minneapolis. “The tributary watershed was predominantly industrial with some single-family residential development as well.”

Workers faced a tight deadline with the onset of the harsh Midwest winter. Budget constraints posed another challenge, as did the considerable tree canopy that included primarily ash, oak, and maple trees with some additional variations of box elder, cottonwood, and poplars. Finding a low-maintenance way to permanently revegetate the area beneath the shady splendor of such trees was a unique challenge.

Profile Products’ GreenArmor System was used at the site, along with other techniques. The system employs the company’s Flexterra flexible growth medium, which was sprayed into UV-stabilized, nylon Enkamat. The GreenArmor System was used on parts of the channel and a dike overflow. Riprap was used at pipe outlets, with TRM keyed in below the riprap. Seed and a temporary erosion control blanket were used in areas that would receive non-concentrated flows, such as flow diversions, detention basins, and rainwater infiltration gardens, says Klein.

Experience played a role in the selection of the GreenArmor System. “We have had significant experience with TRMs in ravines-more than 30 years. The city wanted the area to be vegetated with minimal exposed rock,” says Klein. “And both the city and Barr were willing to give the GreenArmor application a try, as opposed to the double-seeding process we typically specify with TRMs.”

GreenArmor encourages root growth and reinforcement with 95% open space and can hold 15 times its own weight in water.

Barr added a quick ground-cover solution: rye. The seed mix at the site also included a variety of shade-tolerant and sun-tolerant natural grasses, says Klein, who is pleased with the revegetation results at the site and its successfully stabilized future.

“It is more aesthetically pleasing and natural appearing, and our experience has shown the TRM application will likely involve less maintenance in the long term,” he says.

TRMs are often used for permanent cover to outlast the toughest Texas hydraulic events. The growing population of the Houston suburbs created the need for construction of a new school in Livingston, TX. Begun in August 2009, Livingston High School will soon meet the community’s need for more space. The approximately 73-acre site required permanent matting to combat the soil, weather, and engineering challenges found there.

“We have three detention ponds on that site,” says Larry Walker, president of Walker & Associates, which was contracted to work on the project. “The soil is real sandy. It’s very hard to control the silt and the sand on that site. Erosion is greater on a sandy site than it is on another type of soil.” Recyclex from American Excelsior was used for its long-term stability. “I don’t want to go back in three to five years and explain to the owner why he doesn’t have any erosion control in place,” says Walker.

Made with 100% post-consumer recycled brown or green bottles, Recyclex’s crimped, interlocking fibers are held together by two layers of UV-resistant polypropylene netting, forming a three-dimensional matrix.

“We’ve had real good luck with it,” he says. “It’s an expensive item, because you have a lot of area to cover. This is one of the things that often gets downgraded or value-engineered out. But most of the time, once we install this product, it corrects the [erosion] problem.”

About $300,000 was spent on about 100,000 square yards of Recyclex as part of the project, which is expected to total $60 million. The site is located beside a large hill, with 25- to 30-foot slopes surrounding the area. Weather posed a challenge for workers, who had to regrade specific areas after a heavy Texas rainstorm.

Usually, we will call for hydromulch. More times than not, we’ll put it down and put staked sod over the top of it,” says Walker. “Because of the heavy rains we’ve had, they’ve had to regrade some areas before they could properly install it.” Hydromulch was then placed as a permanent top layer of protection at the site.

“Because of the stormwater pollution prevention laws, you have to have permanent cover over any site,” says Walker. “It doesn’t work 100% properly until you have a good root system and a healthy stand of grass.” Native grasses were used at the site.

Walker’s company has worked on about 300 school sites during the past 15 years, and he always comes back to Recyclex for erosion control. “I’m definitely pleased with it,” he says. “I’ve specified this material hundreds of times.”

Biologs
Biologs, often made of biodegradable coir encapsulated in netting that is rolled, are another time-tested erosion control measure. They are used especially along rough shorelines, where they can be staked to protect beaches. Biologs are also successful in trapping runoff sediment at a wide variety of inland sites, however, and can be paired with erosion control blankets for an extra layer of protection. These products were recently combined for use at Llanerch Quarry. Workers have been filling in the Havertown, PA, site over the past 10 years.

“They had to build a swale to relieve the amount of water running off the site,” explains John Cervo, vice president of operations at Earth Care Inc., based in Honey Brook, PA.

“The site contractor, Allan A. Myers, was in charge of building the swale and hired us to stabilize the site as they were constructing the swale. The engineer had specified excelsior erosion control blanket for the steep side slopes.

“Along with the excelsior matting, they also had rows of Biologs [coir logs provided by ACF Environmental] staggered along the slopes. They were stacked three high with rope tying them, stretching from the bottom of the logs to the top, keeping them secured on the slope.”

Workers were trying to prevent erosion in the center of the swale and along its slopes from the onslaught of water passing though. To stabilize the center of the swale, the site excavator installed riprap in that area. The end wall, where water flows into the area from a pipe, is supported by a gabion wall. Plugs of native grasses will be installed within the Biologs before the site is completed. Taking no chances and hoping to establish the strongest root system possible, crews will also plant shrubs and trees along the slopes of the swale, says Cervo.

“All of them are to help bind the soil and over time prevent the soils from eroding when the erosion blanket biodegrades,” he says. This natural process should take place during the course of a few years. Still, when working on an ongoing project like the quarry site, every minute matters.

“This was about a $135,000 project for us, and we were only installing the blankets, Biologs, seed, and plantings,” says Cervo. “We haven’t had the opportunity to really see the product in action.  It’s been a dry summer. We finished installing them two weeks ago.”

Ultimately, thriving growth of vegetation on a site can help filter runoff and stabilize soil. Providing these plants with the best possible blankets and matting to enhance growth and root establishment can help turn a temporary fix into a permanent solution.

About the Author

Tara Beecham

Based in Morgantown, PA, Tara Beecham is a frequent contributor to Forester publications.