Some sites just need a little more protection. Steep slopes and some sites with flowing water often cannot be stabilized with applications of seed and mulch alone. Rolled erosion control products (RECPs) bring a little “weight” to the solution, along with a variety of choices.
Erosion control blankets are designed to degrade relatively quickly, sometimes after one growing season. If the vegetation planted can hold its own after that period, there’s little reason to use a product with more heft. For sites with moving water, heavier turf reinforcement mats (TRMs) can withstand greater shear forces. TRMs also typically last longer, sometimes several years. Both products are built with a layer of fiber (such as straw, coir, or wood excelsior) sandwiched between plastic netting; most TRMs, and many blankets, contain synthetic products, usually in the netting.
Demand has grown recently for natural, easily biodegradable, or even “net free” products. Factors behind this movement include concerns about maintenance-nets can sometimes get caught in mowers-and concerns for wildlife. As small rodents and snakes can get caught in the nets, and animals such as deer can get their hooves snagged on nets, most projects in federal parks require biodegradable products. In response, many manufacturers have made a variety of such products available.
What the Engineer Specifies
Choices for blankets and mats are very site specific. “A lot of times, we use wheat straw, because of the cost,” explains environmental specialist Todd Threadgill, who works for Erosion Pros LLC in Auburn, AL. “Of course, we always use the engineers’ recommendations. If we’re working on a gentle slope, we can use a wheat straw blanket. If the site’s watery, we use jute or coconut [coir] blankets. For a lot of our jobs we recommend coconut or jute, even though they’re more expensive, because they’re better for the environment-but it depends on the application. We use coconut and jute blankets in detention basins with skimmer systems, using blankets for a filter.”
He recalls a project from the summer of 2009. “We were working on a gas line. A creek runs across the gas line, so it had gullied out a bit,” Threadgill explains. “We put coconut blankets on it, fastened with wood stakes. The site was permanently stabilized. The blankets are holding what soil was there, and keeping what sediment flowed by. We applied the blankets by hand, as this was not really a large area. We rolled out the blankets, and since they were in water, they became weighted. Once we put in stakes, it all held. The creek drained into a 50- by 10-foot downgraded retention basin. Frogs, snakes, and deer live in the area, and our solution caused no problems for them.
“What wasn’t underwater, we hydroseeded, then covered with a blanket,” he continues. “Had it been a really steep slope, we would’ve hydroseeded, adding wheat straw, then topped with blankets. We usually get 80% germination, even after putting on blanket. Blankets help retain moisture, which we really needed a few years ago, when we were in a drought; now we seem to get rain at least once a week.”
For winter seedings, Threadgill recommends annual rye grass; in spring and the planting season, he installs perennial grasses. “For that streambank, we planted tall fescue, Bermuda grass, and Brown top millet. We needed to get a quick stand of vegetation. The rest of the gas line was well vegetated, but we needed to get this section in place.”
In the three years he’s been with the firm, Threadgill has also used products from American Excelsior in Arlington, TX. “We have used excelsior wattles and the Recyclex TRMs,” he notes.
Recyclex contains fibers made from 100% recycled post-consumer goods. Just as with the company’s Curlex excelsior, Recyclex’s fibers are crimped, which helps the TRM conform to terrain details; crimping also directs water flow to “follow” the TRM. Stitching the Recyclex fibers to two layers of UV-resistant polypropylene netting (buyers can choose brown or green) creates a three dimensional matrix.
“We also do NPDES [National Pollutant Discharge Elimination System] consulting, some hydroseeding, silt fence installation, and EC blanket installation,” Threadgill says. “When I first started here, most of our consulting was new home subdivisions, then we switched more to commercial buildings. These days, we’re again doing a bit more subdivisions.”
Recycled and green products are popular with the local university. “They like to use green products. We’ve helped the university with a study on soil on slopes and which type of vegetation is more effective against soil loss.”
Dependable and Easy-to-Use Wins the Day
Ease of use and dependability determine the choices made by Meadville Land Service Inc. (MLS) in Meadville, PA. “We find East Coast’s blankets easy to work with, easy to install, and we don’t have call-backs for blanket failure, which is a big plus,” explains Robin Ernst, who co-owns the company with Paul Phillis. She refers to Bernville, PA’s East Coast Erosion Blankets, which produces straw, coir, excelsior, and straw/coir mix RECPs, as well as polypropylene TRMs. MLS purchases the products through ACF Environmental.
Ernst, who with her husband started the company a dozen years ago, specializes in “mobile restoratio-streams and wetlands.” She described a typical job: “For eroding banks, we begin with excavation, to lay the slopes back. The blankets are used after excavation. When we have exposed streambanks or high-flow areas, we seed the installed blankets, and also incorporate blankets and matting with bioengineering. The project engineer will specify what to use, and we use a blanket from East Coast that’s comparable by specifications. We put the seed down, then the blankets on top. You can dampen the blanket if you need to; otherwise, when you do have rain, the blankets hold moisture in the soil as well as holding soil in place.
“In our 12 years of business, we’ve done about 20 miles of streambanks,” Ernst goes on. “When it’s dry, it’s easier, but it doesn’t matter the weather. We have to pump streams out anyway, because we have to divert the stream when working on it to keep sediment out of it. For our work, weather and times of the year can be a large factor, but always, when working in streams, we’re bypassing or pumping around, to work directly in the flowing stream. When we do pump around, we always pump our water though a filter bag, also supplied by ACF, to lower sediment movement.
“We do a lot of urban and rural work-most all of it federally funded, whether it’s city or county conservation work,” she says. “Very little of our work is done on private property. Our work is for aquatic enhancements, to make a better quality stream. It’s also to stop sediment load. From streams around here, sediment would travel down to Chesapeake Bay. And of course, the work is done to stop erosion; you don’t want damage to homes, businesses, farmland, roadways, and bridges. With the amount of snow this past winter, I imagine we’ll see a lot of washout from snow melt in Pittsburgh.”
Ernst’s firm usually installs blankets or matting that is stitched with biodegradable netting, which breaks down quickly and is more habitat friendly. “The length of lifespan depends on which one is used. Since we also want to watch out for wildlife, we use biodegradable or coir. In some instances, in streams we’ll use hard armorment-stones-that help to retrain or slow down the stream. We can use natural structures, such as logs or rootwads, but only at the right place in the stream. Natural structures are usually obtained from the clearing and grading that was done on site. In addition to retraining the stream-how it flows, backs up, creates pooling-and making a place for it to slow down, this “˜blockage’ can create an area for fish to hide or cool. It has a lot to do with placement.”
When seeding, Ernst favors native vegetation and riparian mixes. “I’ve been in this business all my life; I’m still part owner, along with my father, mother, and two brothers, of Ernst Conservation Seeds, the largest East Coast producer of native material.” Over the years, the seed business has changed: “When I was young, dad was one of the largest growers of Crown Vetch, which few people put in anymore. Instead, it’s native plants. At first, the industry began choosing plants “˜native to the US.’ Now there are specifications that call for “˜native to the East Coast,’ or to a particular state-sometimes even to the county. That’s when you get into ecotypes, which is really important for area wildlife.”
Others Believe Coconut Creams the Rest
Coconut is one of those love-it-or-hate-it foods. However, coconut husk fiber-coir-seems to get wider acceptance.
“I generally use coir blankets for streambank restoration,” says Paxton Billingsley, project manager for Doraville, GA’s Site Engineering Inc. “Project engineers tell us to use this product, but I like using it-it works.”
For a recent job restoring the Ronald Reagan county park in Lawrenceville, GA, Billingsley used Rolanka International Inc.’s BioD-Mat 90 bristle coir woven semi-permanent mats. “Streambanks are our typical job. We seed underneath it; because the fabric is so dense, it’s sometimes hard for seed to get through the fabric. Rolanka makes lighter fabrics, but engineers usually pick the strongest one, so it will last longer. We roll it out by hand. To get it really tight, we pull it with an excavator before staking it down. It’s like pulling bed sheets tight, so as not to have a lot of wrinkles in it. Then we stake it down, hammering the stakes by hand. For the park job, we installed 6,000 square yards of the BioD-Mat 90.”
Billingsley has used Rolanka products for about four years. “It has always done an excellent job. It’s a good product; I’m happy with it.”
Sometimes, What You Need Is Right Below Your Feet
For most erosion control projects, saving the soil you have, or replacing it, are the main tasks. In Washington state, one project entailed literally unearthing the best soil for the site.
“It was 2007, the project was in the South Midland Wetland Reserve, advanced mitigation wetland site, located in unincorporated Pierce County south of Tacoma in a residential area,” explains Ann Boeholt, project manager. “We worked on this site to receive credits for other areas where we have unavoidable wetland impacts.” Boeholt, who is a wetland biologist and certified as a Professional Wetland Scientist through the Society of Wetland Scientists Professional Certification Program, works for Pierce County Public Works and Utilities (Surface Water Management) in Tacoma.
“We were excavating within partial wetland-some of the area was wetland and some was non-wetland-that had been disturbed over the years. Below, there was a buried marsh surface,” Boeholt says. “We excavated 6 feet and found some nutrient-rich Dupont muck, an organic soil that’s considered “˜gold’ because it has the correct pH and nutrient balance we seek for wetland restoration. Plus, we suspected the muck might harbor a viable bank of seeds of wetland emergent plants. We were intent on preserving it-hence the need for soil moisture retention.”
Boeholt’s crews unearthed nutrient-rich Dupont muck at a 6-foot depth. After crews found the valuable muck, plans for the site changed slightly. “After reaching subgrade, the plan called for putting in topsoil,” Boeholt explains. “However, in the specs, it stated that if the contractor found a sizable source of muck, he could stockpile it and use that instead. That certainly made the contractor happy-he didn’t have to haul the muck away, then pay for and install topsoil, yet we paid him as if he had done that, so he made extra money on that project.”
“We knew the muck was down there, but not how much. If we’d done more potholing we could’ve found it, but that’s costly. What muck we unearthed, we needed to keep moist, or else it would shrink 50% from drying or decomposing. Because it’s usually in an anaerobic place, once it has oxygen, it breaks down. However, the muck drying up would be bad, too, because the undecomposed soil could become hydrophobic and resist water-not good for a wetland.”
Therein lay the problem: The muck was being used as topsoil. “We spread it over 6 acres of plots, and it was July; it would dry out. Furthermore, our stormwater permit required us to cover the soil once we were done working it, in order to prevent erosion-we had to cover it.” Boeholt considered her options: “Agricultural straw? No, it contained seed we didn’t want, and it could also blow away, or wash more easily downstream once the site, which contained a creek, was put online. Temporary seed? We wanted to hand-seed this area with locally collected wetland seed, so we didn’t want and cover crops to interfere with that. Mulch was costly, and it could cause problems: seeds might try to grow in the compost, rather than in the underlying topsoil. We even considered plastic-but 6 acres of it? Then all that plastic would end up in a landfill, not to mention the challenges of actually getting the plastic to stay put.”
Boeholt found her solution from a company just down the road: Forest Concepts LLC of Federal Way, WA. “We ultimately used WoodStraw,” she says. “Forest Concepts recommends 50% coverage for erosion control, but I also needed it for soil moisture retention, so we applied a 70 to 75% cover. It did the trick. I haven’t yet checked to see how deep the muck is now, because that’s hard to measure, and I haven’t felt it necessary, because the wetland plant community is restoring. However, 18 native wetland emergent plants have “˜volunteered,’ in addition to the three species we planted by seed, which have established very well within the salvaged marsh surface.”
In addition to its meeting the task at hand, Boeholt discovered a surprising benefit from WoodStraw.
“The site includes the tributary of a creek, which often expands. The creek’s velocity is low in spring, but the WoodStraw didn’t wash away; it stuck to the ground and was still there in the summer, providing mulch into the next summer. We laid in 2007, and it’s still there, slowly breaking down.”
“WoodStraw, cross-sectionally, provides a 1-inch wooden canopy to intercept raindrops, to capture and hold the moisture, and to protect seeds and seedlings,” explains Michael Perry, Forest Concepts’ chief executive officer. “WoodStraw lies on top of the soil, and doesn’t enter the soil matrix, until it oxidizes into a duff, in approximately four to five years following treatment.”
The WoodStraw used in the project was a special mix. “WoodStraw is usually composed of Douglas fir, but since it was being applied to a wetland, we were hoping to get cottonwood, which has better C:N ratio, is much more “˜pulpy,’ and naturally grows in wetlands,” says Boeholt. (Due to a shortage of material, Forest Concepts no longer sells a cottonwood product.)
However, the firm didn’t have enough cottonwood for the project’s needs, and it was more costly than Douglas fir. “”˜What would be better for me?’ I asked Forest Concepts. “˜Have you ever used them side-by-side to compare for erosion control? For microbiology?” says Boeholt. “They hadn’t tested. However, they said if I laid it out in grid pattern to do some testing, they would give the cottonwood to me for the cheaper Douglas fir price. The ratio of each type we used was about 2:1-twice as much Douglas fir as cottonwood. The grids were large, 300 by 100 feet. We applied the WoodStraw at a rate of 276 bales per acre, a total of 1,640 bales. I have started formally monitoring them, but no results yet.”
WoodStraw showed another advantage when it was blown onto the site: “Agricultural straw creates a plume of dust when it’s applied. With WoodStraw, there was very little dust,” she says. The seed, however, was not blown on. “I hand-seeded it with a whirligig seeder, much like you’d use to seed your lawn. It took me a couple of hours.”
This first experience with WoodStraw made Boeholt a believer. “In May, 2008, I gave a presentation about this project at a wetlands conference in Washington, DC,” she says. “We have used WoodStraw on more projects since, mostly for erosion control, in combination with hydroseeding.”
