Making the best choice for the job
By Roberta Baxter
Sediment control wattles or rolls made from straw, coir, or other fibers have become so familiar that even the general public recognizes them along a highway or around a construction site. People may, of course, have misconceptions about them—thinking they are to stop water—but their familiarity testifies to their widespread use.
When designing a project, experts must decide what the best choice is. Should they specify a straw wattle, a manufactured device, or a combination? What environment is best for each choice?
Wattles can be used on hillsides. Installation consists of digging trenches perpendicular to the slope, placing the wattle in the trench, and staking it in place. The stakes should be driven in at an angle against the slope. For flat surfaces, stakes can be placed vertically. Wattles are flexible enough to be bent along the contours of the land. Some can even be coiled into a circle and used for sediment traps.
California Fires and Erosion
After the recent fires in California, Jason Locklin, president of Sierra Construction Services, was contacted for help with damaged land near reservoirs. The Rainbow Municipal Water District operates several reservoirs near Fallbrook, CA. The vegetation surrounding four of the reservoirs had been burned by the wildfires, endangering the town’s water supply. Locklin and his company prepared a plan to mitigate erosion and sedimentation at the sites.
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Photo: Earth Saver |
| Rice straw wattles easily become part of the landscape. |
The plan called for a combination of silt fence, fiber rolls, and hydroseeding. Locklin installed Earth Saver Rice Straw Wattles around the reservoirs and every 10 feet on the 2:1 slopes. The Earth Saver wattles are filled with weed-free California rice straw; the netting can be biodegradable, photodegradable, or made of burlap, and they come in a variety of sizes and lengths.
Locklin notes that the wattles serve a dual purpose; they protect from both erosion and sediment loss. The wattles reduce the velocity of runoff down the slopes near the reservoirs, turning it into sheet flow rather than direct flow. This decreases the amount of erosion. The wattles also trap suspended sediment. The soil at these sites did not have the crust that sometimes is present after a wildfire. Instead, the soil was silty and soft with a lot of ash.
For installation of the wattles, 4-inch trenches were dug, and the wattles were placed and then staked every 4 feet. More than 38,000 feet of wattles were used. The wattles reduce the runoff by absorbing much of the water and filtering the rest. The sediment that is captured provides a good seed bed for vegetation.
Once the wattles were down, Sierra Construction Services hydroseeded the areas with wood fiber, tackifier, and San Diego County–specified native seed mix. Locklin says that the area experienced heavy rains during the winter of 2007–2008, but all the wattles were holding and had worked effectively. The wattles were retaining sediment, so the water supply for Fallbrook was safe. In February, Locklin was hoping for a gentle half-inch of rainfall to help promote seed growth.
Locklin has also used the Earth Saver Rice Straw Wattles on several residential projects. He says nearby residents like their appearance because they quickly become part of the landscape, blend in with the vegetation, and eventually disappear. The product is “cheaper than gravel bags and a little more than silt fence” for initial cost, according to Locklin. The wattles are bulky, but not heavy, so they can be loaded onto a forklift and moved to installers on the hillsides.
Gabe Ramirez of Inland Erosion Control in Riverside County, CA, has also used the wattles in numerous projects, both residential and commercial. Some homebuilders in his areas are incorporating erosion control costs into the price of a house. Even though homebuilding has slowed, his company is still performing checks on erosion control measures installed on empty lots.
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Photo: Earth Saver |
| Wattles placed on fire-damaged land around a resrvoir |
Ramirez says his standard uses of the wattles include behind curbs, on the lengths of slopes, and as sediment control in burned areas. He notes that a three- or six-person crew easily installs the wattles. A crew of six can put down as much as 3,000 feet per day. Cost-wise the wattles are about $1.80 per foot installed, compared to double bags of gravel at $2.20 per foot. Silt fences cannot be used on steep slopes or uneven ground, so the wattles are the better choice for these situations. In addition, he points out, they can be left in place, alleviating the extra cost of removing a silt fence.
For installation of the wattles, crews dig a shallow trench—3 to 5 inches in sandy soil and 2 to 3 inches in heavy soils. The wattles are staked down on center every 4 or 5 feet and at the end of each wattle. Stakes used can be 1x1 wood stakes or live stakes. The ends of the wattles should meet closely, but not overlap, he says.
Virginia Development
A new housing development in Roanoke County, VA, was suffering significant sediment problems. The area of rolling hills was primed for erosion with 2:1 and 3:1 slopes. Silt fences and straw bales had been installed and the roadside swales had been seeded. However, during heavy rains, both the fences and the bales failed to keep the sediment on site. In some places, the fences and bales acted as barriers to the water rather than letting it filter through while capturing the sediment. In other areas, sediment flowed under the fences and bales. The sediment load was migrating to nearby waterways, and gullies were cutting through seeded areas, causing eyesores for potential homebuyers.
A plan was developed using a variety of products from North American Green of Evansville, IN. SedimentSTOP, a straw and coconut-fiber matrix encased in multiple layers of netting, was chosen for sediment control. The logs trap sediment while allowing free flow of water, and they also reduce the velocity of the water runoff. Turf reinforcement mats (TRMs) and erosion control blankets completed the concert of products for the project. By working in conjunction, the logs and mats trap sediment and provide a growth environment for vegetation, and the TRMs protect from high velocity runoff in channel bottoms.
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Photo: Lucinda Dustin |
| A combination test of check dams including a filtration medium of wood fibers, manmade fibers, and polymers that are all encased in a knitted tube |
Four days after the installation, the area received 2 inches of rain, giving the combination its first test. The products performed well, in spite of lack of vegetation. Two months later, a heavy rainfall event of 11 inches proved the success of the project. The SedimentSTOP slowed the water enough to prevent sediment in the runoff.
Mining Waste
Near Raton, NM, coal waste piles from long-used-up mines were causing toxic and sediment problems for a nearby creek. The severely eroded piles were also threatening to avalanche into Sugarite State Park. The Sugarite Coal Gob Reclamation Project had a goal of stopping these dangers.
About 15 acres was reclaimed with the addition of gully diversions, gabion structures to stabilize the slopes, bank toe stabilizations, hydroseeding, and the installation of erosion control blankets. Straw bale terraces were built with coir straw wattles, completing the set of erosion and sediment control devices.
Square Wattles
Mid Valley Hay Processors of Merced, CA, has an unusually shaped wattle on the market. Developed by Ernie Montano and his son, Sonny, the Montano Erosion Control Wattle has a square or rectangular shape, rather than a cylindrical tube shape. The company says that the square wattle is stronger and will outlast round wattles. Foot traffic often deforms a round wattle, but doesn’t harm the square one. Another advantage, they say, is that the square wattle has more ground contact than the comparable round wattle.
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Photo: Lucinda Dustin |
| A clay particle sediment trap placed inside a storm drain inlet |
Montano has recently sold the square wattles to a contractor building a hospital in Merced and a homebuilder in the area. He says they were interested in the product because of the strength it retains even if walked on. The wattles are made of rice straw encased in netting. A rectangular wattle for use in slope sediment control is also planned, in 6- by 16-inch and 8- by 20-inch sizes. The wattles are available in 25-foot lengths, but can also be made to whatever length is needed.
Installation consists of plowing a square trench wide enough for the wattles and then staking the wattles in the same method used for the round wattles.
Reusable Products
Lucinda Dustin owns a stormwater pollution prevention plan (SWPPP) consulting company, operating primarily in California’s Napa Valley. In recent years, her work has shifted from mostly residential to mostly commercial. She also does contract work for the Pacific Gas & Electric Company (PG&E).
One challenge Dustin often faces when she comes into a project is that the SWPPP is already prepared and people don’t want to try something new. She says she has to work hard to convince people that making changes sometimes is better for the project and the customer. In California, officials are getting more adamant about enforcement, adding staff on the enforcement side; Dustin says that starting with a great plan is a big step toward meeting the regulations and passing inspections.
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Photo: Lucinda Dustin |
| Sediment control on slope prior to final stabilization |
She acknowledges that there are limits to any device. “People should understand them and know how they work,” she adds. She believes people in the industry should be on the lookout for new products that work even better than the old standards. She likes to learn about and test new products in the field of erosion and sediment control.
Among the measures she uses is the Perimeter Guard from ERTEC Environmental Systems of Alameda, CA. Dustin has been using Perimeter Guard for about four years. Using it in place of silt fencing drastically decreases maintenance costs, she notes, because silt fence often has to be repaired or replaced during the life of a project. The Perimeter Guard sediment control roll has an outer covering of HDPE with an inner particle filter to capture sediment. The units are reusable, decreasing the cost over the lifetime of the product.
Another device she frequently uses is TerraTubes, manufactured by Profile Products of Buffalo Grove, IL. The filtration medium of wood fibers, manmade fibers, and polymers is encased in a knitted tube. The tubes are attached with U-shaped staples along the bottom of a slope or as check dams. The fibers in the roll filter sediment out of runoff and the polymers provide flocculation to capture tiny particles.
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Photo: Lucinda Dustin |
| These rolls allow flow while controlling sediment |
At one high-end residential project on which Dustin worked, the discharge from the large site led to a major creek. The building sites were located along a canyon, with most of the runoff from the watershed passing through the building site. Loose soil at the site complicated the problem. Catch basin inserts were installed, but sediment was still reaching the creek. She had TerraTubes coiled up inside the inserts, and the water that flowed through was cleaner than the regulations required.
Dustin has used the Perimeter Guard and TerraTubes in tandem for many of her projects. One site had a naturally vegetated swale leading to a creek that in turn flowed into a lake. Every 5 feet, she installed a double layer of TerraTubes backed up by a Perimeter Guard. She notes that the Perimeter Guard captured and held the heavier particles, while the tubes grabbed the smaller particles.
For another project, the streets were already paved but were carrying a large amount of sediment. “I had to get creative,” Dustin recalls. Every 15 to 20 feet down the steep-sloping street she installed Perimeter Guard with TerraTube on the downside.
One important point Dustin makes is that the devices “only work as well as they are maintained.” They need to be checked in the dry season as well as in the wet. Even during dry times, the devices can be filled up by debris and by sediment from irrigation and landscaping.
One advantage to Perimeter Guard is that the pieces are reusable. For example, in Dustin’s work with PG&E, the work is usually done in phases. She can buy enough Perimeter Guard to cover one-third of the project, use it in the first phase, move it for the second phase, and so on. Straw wattles generally cannot be reused because they usually fall apart if moved.
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Photo: Lucinda Dustin |
| Used in place of silt fencing as check dams |
Compost Socks
In contrast to many sediment control rolls, the FilterSoxx from Filtrexx of Grafton, OH, is to be left in place. The mesh socks are stuffed with a compost mix that provides filtering and sediment control. The mixture is guaranteed to be weed free. In independent testing, the Filtrexx media was shown to remove total solids (TS) on a 3:1 slope at a rate of 95 to 99%. The devices were also effective at removing pollutants such as petroleum hydrocarbons, pesticides, and aromatic hydrocarbons. In the tests, flow rates were as high as 20 gallons per linear foot per minute.
Nick Strazar, general manager of Certified Erosion Control in Grafton, OH, says his company primarily uses Filtrexx products. He prefers the FilterSoxx in place of silt fence for several reasons. The FilterSoxx do not have to be trenched in for installation, as does silt fence; they are more durable than silt fence; and they have lower maintenance costs and therefore save money over the lifetime of the project. He also likes the fact that they are a locally made and recyclable product; they don’t have to be removed once a project is complete, but become part of the site as vegetation is established.
For a recent project at the Columbus Igel Company, Strazar says that four drilling sites needed sediment control. Chain link fences around the sites made for tight space, and it was impossible to bring in a trencher. A 4-inch blower hose was used to fill 8-inch FilterSoxx bags, and these were placed around the drilling sites. Two men were able to install about 4,000 linear feet in less than a day.
Strazar states that in many cases, the FilterSoxx are comparable in price to wattles or only slightly more expensive. Also, they are heavy—about 45 pounds per linear foot for the 12-inch sock. Therefore, he has used straw wattles, which are lighter, on extreme slopes in remote areas where equipment can’t be used. For many projects, he installs erosion control blankets with hydroseeding and places FilterSoxx at the bottom of the swales and as check dams perpendicular to the slope.
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Photo: Lucinda Dustin |
| Well-maintained sediment control devices may be reusable |
Doug Caldwell, president of River Valley Organics of Wrightsville, PA, also uses Filtrexx products. In his view, they have an advantage over silt fence because they can’t fall down or tip over, and they are more forgiving—even if run over by vehicles or other equipment, they still function. He has used them on a variety of projects, both pre- and post-construction and on commercial as well as residential sites. He adds that the FilterSoxx are easy to secure and the removal is significantly less expensive than for silt fence. Many times the products are left in place and eventually break down. For some projects, he stacks FilterSoxx in a pyramid shape for sediment traps. They are more economical than rock bags and are easy to install.
At Schriever Air Force Base in Colorado, erosion control ponds were being constructed. FilterSoxx bags were placed along the top of the dams, making a natural berm. Steep slopes were stabilized with more FilterSoxx attached every few feet. The entire area was seeded and the vegetation has become well established.
Wattles and sediment control rolls continue to be BMPs for controlling sediment in many situations. Whether the goal is keeping sediment on a construction site or providing long-term filtration, the right product can be found. Their effectiveness, cost efficiency, and flexibility mean they will be part of the landscape for many years to come.
Frequent contributor Roberta Baxter specializes in science and technology topics.
EC - July/August 2008 |
