As rolled erosion control products (RECPs) become increasingly sophisticated, they’re being used in applications ranging from light covers that allow snakes to pass through to heavy-duty replacements for riprap. Vegetation can grow through all of them, and some varieties come with seeds already embedded in them.
Erosion control blankets are used on relatively flat surfaces to stabilize disturbed soils, reduce erosion from rainfall impact, and enhance plant germination and establishment until vegetation becomes established, rarely for longer than one growing season.
They’re essentially mulch, usually sandwiched between lightweight layers of fabric or netting, and flexible enough to conform easily to the contours of the ground. They are typically composed of straw or a combination of straw and coconut matting; jute loosely woven into a mesh; or excelsior, a curled wood fiber fabricated into a mat.
The blankets are held together by either single or double netting, or mesh, which can be a lightweight plastic or natural material. Plastic netting has an open weave and is typically photodegradable and biaxially oriented, so it stretches in length and width. Mesh of spun coconut or corn fibers is thin and permeable and can last for several years. One hundred percent biodegradable blankets are held together by biodegradable netting, thread, or glue. A netless blanket is made of a network of thermally bonded wood and interlocking manmade fibers, so no net can get caught in a mower or entangle wildlife.
Turf reinforcement mats (TRMs) are designed to give immediate erosion protection on extremely steep slopes and in hydraulic applications such as high-flow ditches, streambanks, and drainage channels. They are generally heavier, less flexible, and more expensive than blankets, but they’re less expensive than concrete or riprap and in many situations just as effective. Once vegetation has grown through them, they become part of a permanent, invisible system of soil, roots, and geomatrix.
These mats are made from heavier fibers like coir (coconut fiber) and wood fiber as well as synthetics such as polypropylene, polyethylene, or nylon. Synthetics form a three-dimensional matting, typically with more than 90% open area to facilitate root growth. The netting is usually composed of a mesh of durable synthetic fibers that resist chemicals and ultraviolet light.
According to the California Stormwater BMP Handbook, proper site preparation is essential to ensure complete contact with the soil. Erosion control blankets and TRMs must be held down with stakes, staples, or geotextile stake pins. They should never be driven on or walked on in wet soil conditions. They should be inspected regularly especially during the rainy season, before rain is forecasted, during extended rain events, and after rain events. Damaged ones should be repaired or replaced as soon as possible.
Cottonwood Creek Drainage Project
Stormwater runoff in Cottonwood Creek, CO, had been eroding streambanks so severely that a Qwest Communications building, a multimillion dollar communications hub in Colorado Springs, was just yards from a 40-foot cliff.
“If we’d lost it, it would have wreaked havoc for the city,” says Brian Huth, P.E., the project manager for the city.
A number of entities helped fund the channel reconstruction, including the Federal Emergency Management Agency (FEMA), which awarded the city a $3 million Pre-Disaster Mitigation Grant. When the project was completed, there were 24 acres of land that needed permanent erosion control, including staging and stockpile areas, the channel bank, and the new channel bed.
Seedmasters Inc., which specializes in erosion control, landscaping, and wetland reclamation, installed Profile Products’ Green Armor System, a combination of Flexterra FGM (Flexible Growth Medium) and Enkamat 70/20 TRM, and a coconut mat from Erosion Control Blanket.
“We didn’t want an entirely riprapped channel,” Huth explains. “Our engineer, AMEC, selected this TRM to provide a more environmentally pleasing and sustainable protection in lieu of exposed riprap. The erosion protection from plant growth was a critical element of the project.”
Rice and Rice, a general contractor in Fountain, CO, began the channel bank stabilization in June 2009 and completed it in the fall of 2010. The reconstructed section is approximately 2,700 feet long, with a bottom width around 80 to 100 feet and side slopes of 3:1 or 4:1. Water can flow 10 to 15 feet deep, and a 100-year storm can generate about 13,000 cubic feet of water per second through this section.
Seedmasters first tested the soil, which is a loamy sand with fine clays and very low in organic matter, and then added nutrients and seed. The company used wetland seed for the bottom 2 feet, from the toe of the channel; riparian seed for the next 2 feet; and upland seed to the top. Partway through the process, a new consultant joined the project: the new, local landscape architect consultant, Thomas & Thomas, which advised Seedmasters to increase the amount of seed.
“I’m glad we did,” Huth says. “Seed is relatively cheap. I’d rather add more to get good ground cover.”
Crews installed two different types of rolled erosion control measures on the side slopes of the channel, which was approximately 10 acres.
Below the 100-year storm level, they used the Green Armor System, by Profile Products in Buffalo Grove, IL. They placed some 12- to 18-inch rocks, covered them with 6 inches of topsoil, and covered the topsoil with Enkamat, an open matrix TRM of UV-stabilized, thermally fused nylon filaments. They sprayed Flexterra, which is made with crimped interlocking wood fibers and additives, into the Enkamat. The Green Armor System protects against high water velocity and shear forces and encourages turf establishment and long-term root reinforcement.
Crews then stapled the mat into the ground. “We went through some field changes,” Huth says. “We asked for bigger, stronger staples. We also found that after a short time the staples would rust. That was good, because they adhered to the soil. Seed was mixed into the Flexterra as well as into the soil.
On the 9 acres that were used for staging and stockpiles during construction, Seedmasters trucked in soil, scarified the ground, dug about 1 foot deep, and tilled in crimped straw and a blend of dry grassland seed native to Colorado. On the 5 acres of the new natural channel bed, crews put in about 16,000 willow stakes and about 35 cottonwood stakes.
“Rice and Rice and Seedmasters did a fantastic job,” Huth says. “I’m very impressed with their work.”
The entire project went well, he says, although it hasn’t been tested by a storm event yet.
“We really tried to design it as a sustainable site. Deer have already moved in. They like the habitat we’ve created.”
Coal Creek Fish Passage
Another creek that was causing a problem was in Soldotna, AK, where a perched culvert under Kalifornsky Beach Road was preventing young salmon and steelhead trout from reaching their upstream habitat. The Alaska Department of Transportation contracted with GMC Contracting of Anchorage to remove the entire structure, beginning with the road, and rebuild it with a larger pipe. The result is not only effective, but also beautiful.
“It was a pretty unique project for our department,” says Gary Walklin, ADOT project engineer, who managed the project.
Coal Creek lies 50 feet below the roadway. GMC Contracting used two RECPs from North American Green, one on the rebuilt embankment and one on the creek channel, as well as hydroseeding.
The existing 9-foot-diameter pipe was installed in the late 1960s when the two-lane road was upgraded, Walklin says. The velocities inside it were causing two problems: First, they were too high for the smaller fry to navigate upstream, and, second, they’d created a perched outlet of about 4 feet and a 15-foot-deep plunge pool at the outlet end.
One of the major challenges was that of removing the 50-foot embankment. GMC Contracting started work on April 28, 2010, and finished in July. The company had a strict time limitation: According to the contract, the road could be closed for only two weeks.
“It’s a major collector road for local traffic, fish processing companies, commercial fishing guides, and fishermen,” says Walklin. “It took a lot of staging by the contractor. He did a great job.”
There also was a lot of coordination with other departments, including Alaska Fish and Game, US Fish and Wildlife Service, Kenai River Center, Soldotna M&O, and Kenai Watershed.
This was the first ADOT culvert and stream reconstruction project that had continual monitoring for sediment discharge. Two Hydrolab probes-torpedo-shaped instruments that monitor nephelometric turbidity units (NTUs), dissolved oxygen, specific conductivity, pH, and temperature-were placed in the creek, one approximately 100 yards upstream of the work site and another the same distance downstream.
Setting up effective systems to handle the suspended solids was a challenge, Walklin says. Crews did a temporary seeding with rye in areas that were disturbed early on in the project. They benched the slopes and used silt berms, silt filter bags, and silt basins as well as silt fence chevrons to discharge runoff to buffer zones, and they filtered the runoff through filter rocks.
They also used Visqueen, a reinforced plastic sheeting. “We used a fair amount,” Walklin says. “At the end of a shift we covered everything that was exposed. If there was a rain event, it hit the Visqueen clean and ran into a discharge basin.”
GMC removed a 600-foot section of the road and the embankment, the culvert, and the pipe. Crews hauled approximately 40,000 cubic yards of gravelly, sandy silt to the staging area, the Kasilof Airport, about half a mile away. They also salvaged some vegetation, including alders, willows, and spruce trees, that they’d had to remove during the demolition.
They excavated a diversion channel and intercepted the existing creek, which is approximately 10 feet wide and 1 to 3 feet deep, and then excavated 10 feet below the creek bed to create a solid foundation and to allow the diameter of the new 18-foot-wide pipe to sit at the creek’s flow line.
“Once we got to that stage, we had groundwater impact,” Walklin says. “One of the main challenges was dewatering while installing the pipe and backfilling the plunge pool. It was really wet.”
Crews installed ShoreMax from North American Green, a soft revetment scour protection mat that protects against much higher shear stresses and velocities than TRMs alone.
They built a geotextile-wrapped foundation of coarse rock, installed the new 188-foot-long multiplate pipe, and began backfilling around the new culvert immediately. They used 1,000 cubic yards of rock inside the pipe to avoid sheet flows as well as in the channel at both the inlet and outlet.
When the pipe backfill and the creek restoration were complete, GMC diverted the creek to the new culvert and rebuilt the embankment. Crews lay down topsoil and track-walked up to roughen the soil surface. Alaska Trailblazing hydroseeded a permanent Alaska seed mix, fertilizer, and mulch, then GMC put down S-75BN, a 100% biodegradable straw blanket from North American Green’s BioNet series.
“I use the lightest woven straw blanket I can get,” Walklin says. “It holds moisture in, protects seed from the cold, and helps it germinate faster. The seed grows through the netting, and the matting mulches out and goes away.” Crews then planted alders, along with some of the trees they’d salvaged during the demolition.
Fish aren’t the only ones swimming through the pipe now. Beavers and otters are using it, too.
“It was a pretty demanding project, but it turned out really well,” Walklin says. The project had a good contractor with great agency support, and the local supplier, Polar Supply, was very helpful, he says. “That made it a lot easier. The job looks beautiful.”
Joliet Intermodal Terminal
For the past two years, earthmovers have been carving a vast intermodal facility into the cornfields and prairie land just southwest of Chicago, IL.
The Joliet Intermodal Terminal is the largest of its kind in the US, says Ken Smith, purchasing manager for Allied Landscaping in Joliet, which worked on the project. The terminal, near Interstates 55, 80, and 355, will accommodate increased truck and freight container traffic to and from the West Coast. It’s in operation 24 hours a day, seven days a week.
The facility was developed in two phases and opened in the summer of 2010. The first, which Allied Landscaping also worked on, is approximately 3,000 acres. It connects with the current project, which covers roughly 3,600 acres some two miles away.
“It’s huge,” Smith says. The current project alone includes some 15 detention ponds to hold stormwater runoff, the largest of which is approximately 20 acres.
Allied installed two kinds of blankets from East Coast Erosion Control: coconut fiber on the steep sides of the detention ponds and berms, and a straw/coconut mix on the flatter areas. Crews seeded all the blanketed areas with native seed to establish permanent vegetation.
“East Coast Landscaping and Construction Solutions Inc. was willing to work within our parameters,” Smith says. “I’d call and tell them, “˜I need a load tomorrow.’ And they’d get it to me somehow.”
The erosion control portion of the project began in the late fall of 2008 and will be finished in the spring of 2011. “It came at the right time,” Smith says. “We bid on the job and were fortunate to get it.”
Ryan Companies, which has offices in Chicago and the Quad Cities in the state, dug the detention ponds and built berms with the black soil that was excavated. Ryan also did the rough grading. Allied did the final grading and installed the seed and the blankets. “We tried to get in as soon as possible before it rained,” Smith says.
The companies followed the specifications for the seed and the blankets. The materials for the project were very environmentally friendly, he notes. Crews spread shoreline seed mix along the shores of the ponds. Higher up, they planted mesic mixes, plants that grow a little farther from the water but are still used to getting wet. On the berms, the seed was a prairie grass mix that cost more than $1,000 per acre.
“It’s very pretty,” he says.
Crews used roughly 500,000 yards of blanket from East Coast Erosion Control to hold the seed in place and to keep moisture in. They lay a straw/coconut mix on the berms and triple coconut blankets on the bottoms and the sides of the steep-sided ponds, where there would be a lot of runoff.
Some ditches in flatter areas are being kept for future expansion and aren’t blanketed. The ditches that go through areas with high-flow water are lined with coconut blankets.
Allied used jumbo rolls of blankets that measure 540 feet long and 7.5 feet wide. The company installed them with skid-steers that have an attachment that is essentially a boom onto which the tube of the blanket roll can be inserted. The attachment swings to the side, so as the skid-steer moves ahead, it’s easy to lay out the blanket.
Allied used round-top steel staples, which were easy to insert. The staples fit onto a stick with a magnet on the bottom. A worker walks along the blankets with the stick and drives the staples into the ground.
Because of the size of the site, the rapid changes that took place, and the number of companies on the job, including other landscape companies, there were some challenges on this project.
“There were thousands of earthmovers on the site,” Smith says. “It changed physically every day. One day, a 2-mile stretch of road was there, and the next day it was gone. Another day, there was nothing, and the next there were 15 acres we’d need done tomorrow. It was a constant battle.”
On the other hand, he points out, Allied has been in business since 1978. Each season the company has more than 100 employees and is more than able to handle the work. In addition, the project was right in Allied’s backyard, so Smith could be onsite at any given time.
“It was crazy, but it was a good crazy,” he says. “It’s our business.”
Big Lake, Alberta
Sometimes a problem really is an opportunity. The Big Lake project in central Alberta, Canada, was slated for May 2010 completion, but because of delays it didn’t start until mid-November. By then, the ground was frozen solid, daylight lasted for only six or seven hours per day, and the wind chill factor had dropped the temperature to -20F.
“Some of the inventive things we did opened the door for winter applications,” says Ken Podlubny, a project manager for Clearflow Enviro Systems Group Inc. in Sherwood Park, AB, which installed the erosion control BMPs. “If used elsewhere, they would allow for diminished erosion in the spring, after the snow had melted.”
The project took place in the Big Lake Natural Area, 1,119 hectares of hills, lakes, and wetlands at the northwest corner of the city of Edmonton. More than 235 species of birds have been recorded there, including many species that are at risk. Work done on the project will keep soil erosion from disturbed areas on nearby farms and construction activities from going into the lake.
The project took place in a farmer’s field, which is on a swale that leads to a wetland. From there, runoff flows into a channel to the lake. It took five workdays to complete, between November 17 and December 8, and was done in three sections.
Clearflow began with the channel leading to the lake and then moved on to the swale, an area of approximately 983 feet by 35 feet. The swale installation included raking together dormant grass seed that was specified for the job, fertilizer, the two mulches, and the tackifier, Soil Lynx. Crews anchored the mixture with 9-inch nails and strips of plastic mesh.
“The ground was frozen,” Podlubny says. ” So we drove 9-inch nails into the ground to hold everything in place over the rest of the winter.”
The mulches are both from Verdyol in Manitoba. Biotic Black Earth contains 60% peat moss as well as straw and flax, and HydroGold contains approximately 60% straw. Both bond especially well with Clearflow’s patented Soil Lynx. When Soil Lynx gets wet, it bonds with natural fibers such as those in mulches and soil.
“Under a microscope it looks like a matrix or a spider web,” Podlubny explains.
Crews covered the swale with SC32, a straw/coconut mat from Erosion Control Blanket in Riverton, MB. Although dormant seed often has a 50% to 60% mortality rate, because of the cover Podlubny is expecting a very good germination rate, possibly as high as 80% to 90%.
“Then the question was, “˜How do we get everything to stay in place?'” he says. “Staples were too fine to penetrate the frozen ground.”
Crews cut some of the plastic netting, Enviroberm from Cascade Geotechnical Inc. in Edmonton, into strips 6 inches wide by 1 foot long. In places where the blanket had to remain in contact with the soil, they placed a strip of netting on top of the blanket and used 5-pound sledgehammers to fasten it down with the nails.
When the ground thaws and dries out, crews will go back and staple the mats down. The grass will grow through the mulch, the SC32, and the plastic mesh, so there will be no need to take the Enviroberm material out. It will continue to act as an anchor against high-water events.
Crews also seeded about 30 feet and 60 feet, respectively, on the downward slope of two hill faces to aid in erosion control-but only after the contractor had bladed off all the snow.
One advantage of doing the project in the winter is that crews won’t be working on the site in the spring, when it will be muddy and difficult to access. An added advantage, Podlubny says, is that Soil Lynx will remain preserved under the snow until the spring, when the melting snow will activate it.
The second part of the project was a 165-foot length of hilltop that required a wattle to prevent fallowed soil from washing into the channel. Again, crews used grass seed, fertilizer, the two mulches, and Soil Lynx and anchored the mixture using the stake-and-tie method. No blankets were used in this area.
The third section was a ditch that led to the lake, which crews excavated and recontoured to create a channel about 9 feet wide and 165 feet long. The channel was made large enough to withstand expected water flow and to hold the designed BMPs in place. On a section adjacent to the channel, crews raked grass seed, HydroGold mulch, and fertilizer on the soil and coated the section with Soil Lynx to guard against erosion.
On the slopes and base of the channel, they used grass seed, fertilizer, HydroGold, and Soil Lynx. They built up some areas with Geojute, a soft armor matting by Belton Industries in South Carolina. They placed the TRM P42, a double-net mat made of 100% polypropylene fiber by Erosion Control Blanket, on top of the mulch and the Geojute. And on top of it all, they placed Tenax Inc.’s ScourShield, a three-dimensional double-ribbed mat that can replace riprap and articulated concrete blocks in many applications. They used power screwdrivers to drill 8-inch aluminum screws, about three-quarters of an inch in diameter, into the frozen ground to hold all the layers down.
“The next day it snowed. It was the best thing that could have happened,” Podlubny says, because the snow cover will protect the blankets and seed all winter.
“I’m very proud of the way the project turned out,” he says. “I want to give credit to our supplier, Cascade Geotechnical Inc., and to our people for the job they did. We brought in Tim Horton’s coffee, but there was no shelter. By and large, it was a typical job for hardy Canadian guys.”
