Silt fence and wattles keep sediment at bay on challenging sites.
Traditional erosion control measures such as silt fence and wattles may seem almost quaint as methods that let water flow but keep sediment in place. Yet, as with a fine wine that has stood the test of time, people like these products for a reason.
Silt fence allows water to filter through as it traps sediment on a site. It’s arguably the most commonly used erosion control method on construction sites across the country. A clear visual deterrent to pedestrians because of its noticeable size and sometimes bright colors, it can prevent traffic as easily as the measure itself stops sediment, and its ease of instillation and removal have earned silt fence some hard-won supporters.
Affordable and versatile like silt fence, wattles provide the filtration that slows water velocity while collecting sediment from runoff.
Wattles, which come in a wider variety of materials than ever before, can be created with biodegradable material as well as geotextiles and can contain everything from sand and gravel to compost. As the movement toward green erosion control methods advances, so, too, does the popularity of wattle use on project sites.
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Photo: Gateway Engineering
A commercial building site in Shelby Township, MI |
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Photo: Southface Energy Institute
Looking down into a vegetated swale at the Southface Energy Institute |
“I tend to use straw bales when I need the water channeled to a different location, and I use wattles when I need it filtered through,” says C. Todd Cheek, project manager at Mid-TN Erosion and Sediment Control based in Arrington, TN. “It really just depends on the terrain and how much rock is involved.”
When it comes to sediment control, many people have definite preferences. Frank Burdette, project manager with commercial green building services at the Southface Energy Institute in Atlanta, says, “I can’t think of an application where silt fence would be preferred over wattles.”
However, Joseph Vaglica, president of Gateway Engineering based in Shelby, MI, and professor of construction management at Wayne State University based in Detroit, says, “In my experience as professional engineer, we seldom use wattles. They flatten out over time, they don’t detour vehicles or pedestrian traffic, undermining is an issue along with overtopping, and they usually stack two to three high to get the height needed.”
He notes that some sites do lend themselves to wattles, however, in particular because of their easy installation and reduced need for monitoring. “We recommend wattles when working in heavy wooded areas where it’s difficult to trench for silt fence,” Vaglica says.
Around the country, contractors shared various examples of sites large and small that have benefited from silt fence, wattles, and, sometimes, a combination of the two methods.
LEEDing in Atlanta
In 2005, workers broke ground on the Southface Eco Office in Atlanta, GA, a 1-acre LEED [Leadership in Energy and Environmental Design] platinum site. The project was completed in 2009. The nonprofit organization promotes green building practices and energy and water efficiency, according to Burdette. For example, the organization offers solar instillation training through its Green Jobs Training Center. It uses donated products and services from various companies to help achieve and model environmental goals on the site, which received the US Commerce Association’s 2009 Best of Atlanta award in the environmental conservation category.
The building is open to the public and tours are available, with times posted on the company’s Web site, www.southface.org. But even a model of green living can face challenges from Mother Nature.
“We are also adjacent to city-owned property. We lease our parcel from the city of Atlanta. One side of the property is a parking lot where city environmental officers park on a regular basis,” says Burdette, highlighting why there is little room for any erosion control error. “We were constructing a concrete wall as part of a detention pond that was immediately adjacent to that parking lot. There was not an opportunity to trench in a silt fence there.”
Instead, the group selected Filtrexx International LLC’s Filtersoxx, compost-filled tubes, as the sediment control barrier in that location. Although the product had been donated to the organization, “we were the first in the city of Atlanta to be able to showcase that strategy for erosion control,” says Burdette, adding that on the rest of the site, the organization used silt fence in conjunction with Filtersoxx.
“It gave the city compliance officers a chance to see that traditional silt fence is redundant and obsolete,” says Burdette.
These sediment control methods are not the only ones visible at the site. “We try to incorporate a number of products for demonstration purposes,” Burdette explains. “In a vegetated swale, we also put down a coconut-fiber mat with recycled concrete riprap. That serves to disperse the energy from any concentrated flows that we have. It’s vegetated on both sides of the streambed.
“We also used gabions as part of our permanent streambank stabilization. We have one side of our stream—the bank opposite the Filtersoxx—lined with gabions filled with recycled concrete riprap. We installed the Filtersoxx to stabilize the streambank and to stabilize a steep slope on two sides of our detention pond.”
The site’s slope in this area is approximately 2:1.
“It helped us to contain a runoff issue that resulted from installing an impervious concrete walkway that ties into that parking lot. It was not the original design. It had not really undergone approval from the civil engineer. The owner was serving as general contractor,” explains Burdette. “What we learned is that we don’t want to install a pervious sidewalk that slopes down to meet an impervious hardscape. The pervious walkway was on a gravel bed to allow rainwater to filter through the sidewalk. But what we were finding was that after significant rains, the sediment would wash into the parking lot.”
The organization used Filtersoxx to contain the runoff while a raised concrete berm could be installed along the parking lot’s edge, with a gravel drainage field set behind it.
The area recently experienced a 500-year storm event. The detention pond had been designed to withstand a 100-year storm event, so workers were unsure what would become of the precautionary measures.
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Photo: Gateway Engineering
Workers installed SiltShield to contain sediment and discourage pedestrians. |
“We were all looking out the window,” says Burdette. “At the height of the storm, it reached maybe only 20% capacity at the most. I think they [the Filtersoxx] actually served to allow water to percolate back into the vegetated swale. I think it reduced the quantity and the rate of the stormwater runoff.”
Filtersoxx were useful with another feature below the detention pond as well.
“We also have a cistern buried underground, and it’s actually underneath our detention pond,” says Burdette, adding that the 1,500-gallon tank collects stormwater that the organization uses for site irrigation. “The use of the Filtersoxx really facilitated the instillation of that structure, because it gave us a lot of flexibility to work around the Filtersoxx to relocate them as needed because we were backfilling.
“We capped that cistern with heavy-gauge filter fabric and gravel, but topped it off with 16-inch bioretention soil matrix. It was important that that particular product not be contaminated by any runoff. That was another application where Filtersoxx proved to be useful. The system preformed far beyond our expectations. We suffered no damage on site at all.”
Stopping Traffic
When working in an urban setting, you might as well be working under a microscope. It is as if you are on stage with all your progress and all your vulnerabilities open for the world to see, and high-traffic areas can certainly be vulnerable to damage. In one such downtown area, at a three-story commercial building project on the southwest corner of 24 Mile and Van Dyke roads in Shelby Township, MI, workers had to battle not only water-caused erosion, but the human-caused type as well, as the site was located in a popular area for pedestrians.
The site had two natural boundaries that would erode easily, and parking lots bordered its two other sides; hundreds of people tread across the site during the day. The geotextile fabric that was initially used was no match for that kind of foot traffic.
“We couldn’t afford to have people parking there while we were working,” says Vaglica. “You’ve got to be more careful about erosion control, because everybody is looking at you. We were getting stop-work orders because the silt fence was bent. People keep on stepping on it and the maintenance went up every day.”
With the option of reinstalling, repairing, or replacing the existing silt fence, three-quarters of the way through the project, the company switched sediment control products.
“We put up SiltShield, and that was the end of it,” says Vagrica, adding that the company provides a guarantee if the product doesn’t perform the way it’s supposed to, providing an end to many headaches. “It’s like a first defense with erosion, and simple to install. It’s a more durable product. It has a lot less maintenance involved in all the applications where I’ve used it.
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| Photo: Mid-TN Erosion and Sediment Control |
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Photo: Mid-TN Erosion and Sediment Control
Top and bottom: a belted silt-retention fence installed on a site in Tennessee |
“If you run this over, basically the thing just pops back up,” he continues. “[With the previous fence], I almost needed one person in charge of fixing it up every day.”
The fencing cost $2 per foot. When a pedestrian stepped on the original fabric, it would rip the fabric’s staples from the wood stakes where it was attached. “We had to buy the standard silt fence at least a dozen times. It was an acre-and-a-half site,” says Vaglica. “We had to put a fabric over the existing catch basin. From the erosion standpoint, it was a pretty standard simple design. From the maintenance standpoint, it was a hard site to work with.
“SiltShield has metal stakes, and the fabric is like a foam; it’s more like a wall,” he says. “I noticed that once I put that in, not only did it keep people out, but if people would step on it, it wouldn’t break.
Workers placed sod on the 24 Mile and Van Dyke section of the project. “There’s pavement everywhere,” says Vaglica. He opted to avoid using wattles on the site.
Rain in Tennessee
Two bridge projects at state route 567 and state Route 286 in McMinnville, TN, required sediment control measures. Begun in September 2009, two existing bridges are being demolished and replaced where they each extend over the Barren Fork River.
“We’re working on really tight and steep terrain,” says Cheek, referring to the 2:1 slopes. “It’s typical Tennessee soil. We’re 12 inches over for the year, rainwise”
Workers installed 1,861 feet of Silt-Saver Belted Silt Retention Fence (BSRF) at the State Route 56 site and 1,124 feet at the State Route 286 site, which Cheek says has held up well. The erosion control budget for the ongoing project is expected to total approximately $30,000, not including the grassing, according to Cheek.
The company installed straw bales in the same areas where the BSRF is located.
“Where there is rock so that we can’t get the fence in, we lay down the straw bales and hope to God they stay there,” says Cheek. Turbidity barriers were installed by a separate contractor.
The state department of transportation will continue to monitor the site. Cheek says it is the BSRF that has made a difference with the labor involved at the sites.
“It’s just so much easier to install,” he notes, adding that he has been pleased with the way the product has handled the sites’ challenges.
Rocky Terrain in New Mexico
Sensitivity to a site’s environment is key to a good erosion and sediment control plan. In August 2009, a construction site at the new Amy Biehl at Rancho Viejo Community School in Santa Fe, NM, required straw wattles and silt fencing alike to contain soil and slow water velocity.
Tim Slatunas, owner of Superior StormWater Services based in Los Lunas, NM, says workers used Pleasantville, IA–based McCormick Equipment’s silt fence plow to install Silt-Saver’s BSRF. He says the McCormick equipment performs well on rocky terrain, including that found on this 14.5-acre site.
“If you’ve got rock in the soil, it can get into the clay,” says Slatunas. “Turn the vibrator on—it helps you go through the ground easy.” More than 3,400 feet of BRSF will be installed at the site.
The BRSF fabric is a polyester material with a fiberglass scrim or net sandwiched in between the layers. By creating this support system, the manufacturer strives to eliminate the problem that can occur when fabric in a traditionally supported fence becomes separated from supporting wire.
“It worked well,” says Slatunas, referring to the school site. “Holding up against the wind, it’s superior.”
Straw wattles were added as temporary sediment control used to slow the flow of water.
“The site is very hilly. It will go from 5 feet to 25 feet, a 3:1 slope on natural vegetation,” says Slatunas, who explains that the although the climate is typically dry, when it rains, a large quantity of rain can fall at one time. “Since we started the project, we’ve had about three rain events; one produced 2 inches of rain in a five-hour period.”
The project, which is slated for completion in June or July 2010, will not add more vegetation other than reseeding a retention pond onsite. The construction crews, therefore, are “very particular about roping off trees,” including pinon pine and cedar trees at the site, he explains. Work is performed around existing yucca plants and natural grasses.
Kentucky Hills
A children’s camp is a place to sleep at night and play soccer and baseball during the day. When improvements were made to one such camp located in Allen County, Bear Creek Run, KY, in August 2009, a local company used a 2006 model tommy Silt Fence Machine as it worked to improve the site’s erosion and sediment control measures.
“We were putting in 60 to 70 feet of fence to stop runoff into another part of their camp and prevent runoff into a small creek,” says Charlie Davis, owner of CLS, based in Bowling Green KY. He stresses the steepness of the approximately 2:1 to 3:1 slopes on the site. “The [tommy] will just cut right through it. The overall performance is excellent.”
CLS installed some silt fence in the red clay soil at the site about a year prior to this instillation. “That one had 10 feet of dirt over the top of it,” explains Davis.
A burnt-orange silt fence is used at the site for visibility. It can be difficult for construction workers to see the black fencing from dozers, notes Davis.
The tommy Silt Fence Machine reduces time and labor on the project, says Davis. “It’s all the way you put it in. It’ll do everything they say it will do,” says Davis. “It’s like the credit card: don’t leave home without it.”
California Freeways
In Livermore, CA, an ongoing freeway extension project begun in early 2009 needed erosion and sediment control measures as well. The city of Livermore has contracted workers to extend Isabella Avenue across Interstate 580, tying the avenue to Portolla Avenue.
“Caltrans [the California Department of Transportation] specifies where it wants wattles: cut slopes and fill slopes,” says Eric van der Welle, project manager for Selby’s Soil Erosion Control based in Loomis, CA, which was contracted to work at the site. “Usually they are part of the whole overall design of the project. They’ll specify the exact size of the wattle—the size and the type they are looking for.”
The agency considers the site and any endangered species located in that area when determining what type of wattle will be used at the site.
“They are speccing out wattles that are jute-encapsulated as opposed to photodegradable” to protect animals from getting tangled in the netting, says van der Welle.
Yolo, CA–based Earth Saver Erosion Control Products’ rice-straw wattles were selected as part of the erosion and sediment control plan. Approximately $120,000 was allotted for two portions of the contract just for erosion and sediment control. Among a trio of contracted portions of this project, the final segment was the Caltrans portion. “It’s 5 acres on one side that will need treating,” says van der Welle. “The site is bigger that.”
There is continued monitoring of the site, which also uses silt fence, check dams, erosion control blankets, and hydroseeding as erosion and sediment control methods. Native grasses including creeping wild rye, hybrid sterile wheat grass, California barley, and California poppy were used as part of the site revegetation plan.
“Weather’s a factor any time it rains, of course,” says van der Welle, who is in charge of the erosion and sediment control of the project. “If there is significant rain, then basically we can’t get on the job site. Tracking of mud is a big issue.”
Whether you’re trying to contain soil on a temporary site or working to stabilize an unsteady, permanent location, traditional measures like silt fencing and wattles remain an important part of a site’s erosion and sediment control plan, working independently or paired as a team. The materials they are made of may have evolved during the past few decades, but holding back sediment will always be their primary use.
“The construction industry has been going through changes, and usually new application trends follow construction industry trends,” says Vaglica. “The new word in construction is ‘sustainability,’ so I would say that any type of erosion control that is made of biodegradable, recycled, or local material would be in line with new trends.”