When it comes to the use of blankets and mats, every site presents its own challenges. It’s rarely a “one approach fits all” proposition.
Russ Paton knows that well. He is the owner of Western Seed and Erosion in Langley, BC, and his company has become a one-stop shop for erosion control. The company had its genesis in material supplies but has evolved into offering specifications, installing, consulting, and managing contracts, says Paton. As such, the company has worked on many projects and has developed an expertise for finding the right solutions to unusual challenges.
“We have a unique outlook, because we started as material suppliers and have worked with every blanket supplier that supplies the Northwest: American Excelsior, North American Green, Profile Products-you name a blanket, and we’ve probably had some dealings with it over the last 20 years,” he says.
Blankets played a pivotal role in a recent job at a large mineral exploration project in northern British Columbia, where his company used blankets and earthworks designs to mitigate erosion in a watershed that affects 25% of the Fraser River sockeye salmon run.
Paton says those working on the site are creating resource trails where they truck in drills and supporting equipment to conduct test drilling at various spots.
“This is typically across streams, up mountainsides, and through all sorts of different terrain, so once they finish doing that, there is a patchwork of bare earth,” Paton says. “From the air, it looks like somebody has taken a big stick and has drawn lines down the side of a mountain or across the valley.”
Naturally, those areas are going to pick up and accelerate water, forcing erosion and bringing sediment down into small tributaries, the lakes, and the larger tributaries and on into the main rivers.
Western Seed and Erosion was called in two years ago to assist in repairing damage to a few of the fish-bearing streams that had been affected by the activities on the project site.
“We assessed it and repaired it last season, and now the company is being more proactive and having us come in and do this work as soon as they’re drilling or the roadwork is done so that they don’t have any impact at all in those systems,” Paton says.
Along the roadsides, material is taken from inside the slope and placed on the outside of the slope to create a bench or a road area.
“We use blankets in those zones to protect from both raindrop and surface erosion and to help establish vegetation,” says Paton. “Anytime you’re going around the corner of a hill or down into a creek area to cross a creek, you’re going to have these cut-and-fill slopes where you have to place blankets to protect the surface.”
Another way blankets are being used is on the drill pads.
“It’s like a cul-de-sac. You take this little resource trail up and then they widen it up to move their equipment around and do their drilling work,” Paton explains. “We would cover those areas with a blanket if there’s an erosion or sediment issue.”
Not only does the blanket help prevent erosion, but “by having that hardened surface for that water to flow over, we’re actually using it in this situation as a filter as well.
“In a lot of these situations, you can’t get down the slope below them, but you have areas you want to protect, so by putting the erosion blanket across the whole site, when the water flows it looks like a large biofiltration area where the water can filter down into the fibers of the blanket and the sediment be retained on the surface.”
The company uses a host of BMPs, Paton says.
“In resource work, we try to use everything we can naturally first instead of bringing materials into remote locations,” he says. “We use a lot of log bundles from the road clearing to create weirs to allow water to flow through without getting plugged up. We’re creating ditching and swales with small excavators and also doing hydroseeding in places where [vegetation] can be established in time to be able to be of benefit.
“If it can’t, then we use a blanket to armor it. A blanket provides initial protection, whereas with hydroseeding-unless you use a very high bonded fiber matrix or flexible growth medium-you won’t get that initial control until the vegetation starts. But with a blanket, as soon as it’s down, you have control.”
The blanket choice is site dependent. Paton says he’s a big fan of biodegradable blankets.
“Photodegradable tends to be a poly, welded mesh that doesn’t move around at all,” he points out. “If you have things like snakes, or amphibians such as frogs, or even small animals that try to go through the mesh, they will get stuck, because it just works like a gill net. The biodegradable blankets that are truly biodegradable-not just photodegradable-and made of hemp or jute or coir can move because they are just woven. I could put my whole hand through if I really wanted to. They’re much more forgiving in that sense. It’s really protection of those small species that is the reason we use those blankets.”
Paton says he doesn’t believe one manufacturer’s blanket is superior to any other.
“It’s just like hydroseeding or any other process. You have to use the tools that are in your toolbox,” he says.
“Straw blankets are great because they break down quickly and they don’t have a high impact on the soil,” Paton says, adding that the lower carbon-nitrogen ratio of straw blankets in contrast to products such as wood excelsior mats means more nutrients will be available to the plant, because products with higher carbon-nitrogen ratios will require a lot of nutrients from the soil to break down. Straw blankets also hold more moisture and are more flexible, Paton adds.
“But excelsior and coir products have a longer lifespan. If you start with a really basic loose straw blanket, you get good establishment of whatever seed species you’re planting,” he says. “But you don’t have a lot of good shear strength or long-term protection.”
Going up to a coir or coconut-fiber blanket provides twice as much material and weight and takes longer to break down, Paton adds.
“It doesn’t hold quite as much moisture, and it’s going to have more of an impact on soil nutrients, so there’s much longer protection and less mulching or seed benefit on the top end. And on the bottom end, there’s better seed establishment, but not quite as good or long-term protection,” he says.
Paton says a job site may call for four different types of blankets.
“Sometimes we might even use synthetic blankets-turf reinforcement grid-for long-term installation,” he says. “I’ve used a lot of that on highways, where we lay it down and then put triple-mesh rock grid above it and bolt it to the surface to hold fractured rock in place but still grow grass where there are soil deposits.”
Canada Olympic Park
At the Canada Olympic Park, highly erosive 2:1 slopes of sandy soil existed along the south perimeter of the parking lot across from the Sports Hall of Fame building. The slopes were becoming rilled during a rain event, with a significant sediment washing onto a parking lot due north. The problem was compounded by a higher asphalt parking pad also draining onto the same slopes.
The polluted runoff going into the city storm sewers resulted in financial penalties. Because of the degree of the slope, erosion control blankets were not an option, as there would be major disruption to any hydromulch revegetation layer underneath during the installation phase.
Local landscaping firm Michele’s Landscaping in Calgary, in conjunction with Brock White Construction Materials, worked together to apply Verdyol Biotic Earth Black from Erosion Control Blanket at a hydroseeding rate of 3,900 kg/ha without any tackifying agents during late 2011.
A secondary application of Soil Guard BFM (bonded fiber matrix) provided a fibrous crust matrix to reduce rain impact and shear and wind erosion of the Biotic Earth underneath.
A year later, in September 2012, grass establishment on the 2:1 slopes was thick and robust, and some turf varieties were thriving as evidenced by spiking seed-bearing heads.
Legume establishment was about 15%. Throughout the spring and summer of 2012, slope erosion and sedimentation the Canadian Olympic Park was no longer an issue.
Biotic Earth and EarthBound products are composed of rich organics, natural fibers, macro- and micronutrients, mycorrhizae, and a proprietary blend of organic humates and soil stimulants. The products are designed to address the post-construction challenge of soil that is left onsite for revegetation, often being subjected to severe degradation and lacking in essential organic materials, nutrients, microbial populations, and pore space to establish, grow, and sustain effective vegetation that can withstand the forces of erosion. Such soils have between 3% and 4% organic content, where more organics are required.
The products kick-start the process by adding the first layer of organic material, soil builders, and growth stimulants designed to mimic nature and help poor soils come alive and allow vegetation to thrive.
In addition to improving the soil, the products are designed to control erosion, negating the need for hauling in topsoil or seeding on poor soil and waiting for vegetation to grow.
Verdyol Biotic Earth products are designed to create conditions in which the subsoils will begin to exhibit better aeration, reduced compaction, improved nutrient storage and transfer, and other essential traits for vegetation establishment and growth.
They also reduce soil crusting for improved water infiltration and reduced runoff. The rates of seed germination and plant establishment are also improved, which in turn revitalize the soil’s physical and chemical characteristics. The addition of numerous trace minerals, sugars, starches, proteins, and amino acids are designed to further improve the soil’s tilth.
Reserve at Spring Pointe
When the Metropolitan Management Group selected a 19-acre tract of land to develop the Reserve at Spring Pointe, a 160-unit luxury apartment complex in Muhlenberg Township, PA, a particular challenge presented itself. The tract was at the base of steep mountainous terrain and immediately upstream of a watercourse.
That watercourse has a Pennsylvania Department of Environmental Protection Protected Use for Migratory Fishes (MF) and for Warm Water Fish (WWF) designation. Extra care was necessary to minimize accelerated erosion and the resulting sedimentation during the phased construction of the various three-story apartment structures.
Working in concert, McCarthy Engineering Associates designed the erosion and sediment control plan and Forino provided the construction management, excavation, carpentry, and site work services.
The final plans called for 2:1 slopes at the base of the mountain. East Coast Erosion Control ECSC-2 Double Net Straw/Coconut erosion control blankets were installed on the slopes to promote vegetation establishment, which occurred within weeks of germination.
Runon from the steep slope above the project was captured by two large swales and safely conveyed around the project to a detention facility for passive treatment.
The 12-foot-wide swale that received the mountain runon was lined with East Coast Erosion Control high-performance turf reinforcement mat. Vegetation was observed within two weeks as it grew up and through the single-monofilament mat.
The second steeply sloped swale was lined with East Coast Erosion Blankets ECC-2 Double Net Coconut erosion control blanket. ECC-2 has a permissible shear stress of 3.3 psf and a permissible velocity of 10.0 fps in an unvegetated condition.
Both swales were quickly covered with vegetation that aided in the management of stormwater flows through the project. As a result, neither the swale nor the steep slopes protected with the East Coast Erosion Blankets’ products experienced any erosion problems.
Ricky Lynn owns LGS Pipeline Services, specializing in pipeline restoration work in Louisiana. He needs to guarantee final environmental protection for the pipelines, and the products he uses must be biodegradable to meet state and federal regulations.
“We do final grade work on the pipelines. When we come through, we have to do all of the creek banks and land slopes and we have to have a product that will haul that soil and not end up eroding and washing out,” he says.
To do so, he uses Curlex II, a biodegradable blanket manufactured by American Excelsior. The erosion control blanket product is a natural, stitched excelsior blanket made of Great Lakes Aspen, which is seed-free and polypropylene netting and also is available as QuickGrass. It has a design soil loss ratio of 0.022 and is suitable for slopes up to 1:1. It is rated for channel flows up to 9.5 feet per second and 2.5 lb/ft shear stress.
“It holds the soils better,” Lynn says. “We’ve been fortunate in getting a good stand of grass in using it. It eliminates a lot of erosion problems better than the other products we’ve used.”
Lynn uses other BMPs as needed for erosion problems, including American Excelsior’s sediment logs.
Stabilizing the Lagoons
In Savannah, GA, development on The Landings began in the mid-1970s, with plans for 4,000 housing units and four golf courses.
“They incorporated their lagoon systems not only for drainage, but for making an interesting golf course with water features,” says Bill Huffman, P.E., of
H & K Engineering Group in Savannah. “A lot of these lagoons were dug out, and they used the backfill material for building the greens and building roads, so they had a lot of purposes there.”
Because of many of the lagoons are tidally influenced, the water level is constantly going up on a daily basis along the banks, Huffman adds.
“Over the years, there has been undermining of the edges of the banks because they were cut fairly steeply, and that undermining caused some of the banks to collapse,” he says. “As the grass became established, it grew over the edge, but it was almost a dangerous situation where there would be an undercut place and there would be nothing there but grass. If you stepped too closely, you’d drop into the water.”
During the summer of 2013, H&K Engineering was called upon to stabilize a bank on the golf course where an old timber bulkhead along a very tall green extended up by 30 feet, says Huffman.
“The cost of the new wall was going to be extreme, so we looked at cutting back the slope of that tall green and doing the same stabilization there to eliminate putting in an expensive timber wall,” he says.
The solution: an Enkamat R45 HP-TRM from Bonar, fastened using percussive driven earth anchors, below water elevation and wetland grass plugs, also below water elevation.
The HP-TRM continued above water elevation, and conventional pins and sod were used to create a fortified vegetated bank to protect against future headcutting and the effects of constant wave chop.
There had been somewhat of a challenge with the slope that had a ledge on it that was under the water.
“In order to get the fabric down and get it pinned in place, it took a little more care for the contractor,” says Huffman. “Instead of sloping straight up from the bottom, he had to build a little bit of a ledge there, so that was a bit more of a challenge for him, but once they got the hang of it, it worked out really well.”
The Enkamat was placed under the vegetation to stabilize it for the future.
“If it ever gets uncovered, it’s got UV stabilizers in it so it won’t deteriorate,” says Huffman. “Our goal is different than using something that’s degradable. We wanted something that was going to last and last but not really been seen.
“We incorporated some of the wetland vegetation along the edges to create a buffer, and I think it came out beautifully,” says Huffman. “Everybody was real happy with it.”
Another benefit: By taking out the old timber wall, the company was able to get rid of some of the treated materials in the water as well, including chromated copper arsenate used to preserve the wood.
“All of those approaches worked together to give them a real nice slope and improve it, and it was more cost-effective, too,” Huffman says.