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Hard- and soft-armor options
By Mary Ellen Hare
While Ol’ Man River continues to keep rolling along, and while his waters have largely been cleared of pollutants, traces of both yesterday’s industry and today’s litter are still being found in his banks. Streambanks have become the target of restoration all across the country. From Maine to California, nature is getting a facelift after years of neglect. And while cosmetic surgery is never cheap, the results are worth it—and not just for the streams themselves. Animals and fish are returning to areas they had long departed, while native plant species once again thrive in their natural habitats. It would seem that we can, indeed, fix what has been broken. It just takes time and money.
Industrial Residue and City Pride Drive Cleanup in Maine
The Northeast had bragging rights in the 1800s for the proliferation of factories that provided the mainstay of their economy. Much of that success was attributable to the immense power of the rivers in that region. When harnessed, those streams became a driving force of the Industrial Revolution. Now much of the work has gone overseas, and the factories are vacant or demolished. But traces of them still remain, hidden in the subsoil of riverbanks and streams.
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Photo: MACTEC Engineering |
| The entire
site from across the Androscoggin
River |
Travis Carpenter is a project geotechnical engineer for MACTEC Engineering and Consulting Inc., located in Portland, ME, and headquartered in Alpharetta, GA. MACTEC provides engineering, environmental, and construction consulting services to public and private clients worldwide.
A recent project for MACTEC involved a 600-foot stretch of riverbank along the Androscoggin River in Lewiston, ME. One of the largest of Maine’s rivers, the Androscoggin is 178 miles long, running from Umbagog Lake in New Hampshire until it joins the Kennebec River in Merrymeeting Bay and finally emptying into the Atlantic Ocean. The Androscoggin drops an average of 8 feet per mile, making it ideal for industry, and it was once polluted by textile mills, paper-making factories, and other industries located along its banks. Environmental work and the departure of much of Maine’s industry have benefited the river, but there is still work to be done along the riverbanks in some areas.
“The City of Lewiston has a vision of redeveloping the former mill portion of the city along the riverbank,” Carpenter says. “Lewiston’s Southern Gateway redevelopment project is an initiative to reclaim the area as an incentive for private development and to revitalize access to the downtown.”
The Lewiston Gas-Light Co. operated a manufactured gas facility along the river from 1854 to 1962. Most of the site has since been cleared, and today the property is the location of one of Northern Utilities’ natural gas distribution regulator stations, according to Carpenter.
“Historic fill materials along the riverbank were eroding due to river flow and periodic water-level fluctuations,” he says. “There were MGP [manufactured gas plant] residuals in the fill materials on the bank. And at times there were odors from those residuals.
“Northern Utilities had the bank stabilization work done voluntarily,” Carpenter notes. “It was driven by environmental issues, but there was no direct order. The work was completed under the Maine Department of Environmental Protection’s Voluntary Response Action Program. The cost to Northern Utilities was on the order of $2.5 million to $3 million.”
In addition to natural erosion, rivers in Maine have a problem unique to the frigid winter climate. “The river freezes each winter and melts in the spring. There is potential in the spring melts for ice jams to gouge and scour the bank,” Carpenter says. “In a spring melt with precipitation added, the river could rise as much as 15 feet. We were looking for a particularly robust system to stand up to the water and ice flows.”
The product of choice for this project was Tensar International Corp.’s marine mattress. “Tensar’s product provides significant resistance to scour and erosion with minimal thickness,” Carpenter explains. “The geogrid materials are formed into long, thin, compartmentalized mattresses and then filled with 3- to 6-inch pieces of crushed stone. Because the project took place in a flood zone, permit restrictions limited the amount of filling that could take place, effectively ruling out the use of cobble and boulder-sized riprap and making Tensar’s product even more attractive.”
The riverbank stabilization work, completed in stages, began in November 2005 and was finished in the spring of 2006. “The goal was to stabilize 2.5 acres of steep riverbank, to remove surficial fill and debris such as bricks and concrete intermixed with soil, and to mitigate erosion of any remaining MGP residuals from the previous manufacturing operation,” Carpenter says. “The project also called for restoring upland areas at the top of the bank as a recreational park with walking trails and a scenic overlook.”
The slope of the riverbank was a particular challenge to design and construct, Carpenter says. “The riverbank is 25 feet tall with a 45-degree slope. The first stage of the work called for the installation of the passive liquid MGP residual collection trench at the toe of the riverbank slope. Temporary sheet piles were driven in vertically and interconnected with another 500 linear feet of sheets, driven in parallel. This allowed for the excavation, the pipe installation, and the backfilling to take place at the toe of the steep slope and beneath the river.”
The trench was designed to intercept liquid MGP residual, Carpenter explains. “When backfilled with crushed stone, it becomes a passive collection trench.” Once the existing bank was cleared and grubbed (stripped of any organic materials), it was re-graded, and a series of the Tensar stone-filled mattresses was placed along the toe of the bank, primarily from the toe of the slope up to the 10-year flood zone.
To address odors, Carpenter says, the upper part of the riverbank was covered with a multilayered cap system to minimize odor and stabilize the surface. “The cap system consisted of a gas collection layer [geotextile fabric] with piping, a geomembrane, a geocomposite drainage layer, and a topsoil-filled and vegetated geocell stabilization layer. The project did not extend across the river but terminated at the approximate low water elevation.
“This was once a visually degraded area,” Carpenter says. “Now, it has been transformed from a rundown former manufacturing area into a well-landscaped public park overlooking the river.”
Eroded Streambank Sets Stage for Revitalization in New Jersey
Millville, NJ, with a population of approximately 28,000, is located in the southeastern corner of the state, not far from Philadelphia. The city derives its name from the great number of glass factories that flourished there in the 1800s. As part of a stated commitment to revitalizing its downtown, the city authorized a $950,000 project in 2005 to rebuild the slopes of the Maurice River, construct a public boat dock, and create a small park across the street from the City Hall.
Rick Scaffidi is vice president of construction for Environmental Quality Resources LLC (EQR) in Arbutus, MD, located on the outskirts of Baltimore. EQR, in business since 1991, specializes in stream restoration, wetland mitigation, reforestation, shoreline reinforcement, and stormwater management.
“It was a highly eroded area,” says Scaffidi, about the site located at the edge of land formerly occupied by a glass factory. The Maurice River is a “tidal stream” with a 6-foot tide that works its power daily on the riverbank before emptying into the Delaware Bay of the Atlantic.
“First, we set up turbidity curtains—floating plastic drapes on a boom—to minimize sediment discharge from the work zone. Then we excavated the bank using heavy equipment. We took out soil, screened it, and removed debris from the glass factory. We removed any other anthropogenic, or manmade, debris and screened it. Then we rebuilt the banks using Tensar geogrids, a combination of mats and geogrid fabric.” Scaffidi says crews worked at low tide when placing the geogrids.
“The advantage of using a geosynthetic is that you can replant an entire bank. It creates a better environmental geosystem and is supposed to last 50 to 90 years. Actually, once you have good stability on the bank, it will last by itself.”
At the mean high water level of the bank, the crews planted natural grasses; at 1.5 feet above that area, they used native herbaceous and woody species. On the edges of the bank, landscape materials set the stage for a park.
Scaffidi says the fish population stands to gain from this type of stabilization as opposed to riprap or other hard-armor applications. “This way we can reintroduce a natural system”—good news for those who use the several fishing piers adjacent to the park.
For its efforts, EQR received the Ecological Excellence Award from the Firman E. Bear Chapter of the New Jersey Soil and Water Conservation Society.
Hurricane Damage Control a Never-Ending Job in Florida
A recent stabilization project, C-51 Canal at West Palm Beach, FL, involved repair of 7 miles of shoreline following 2004–2005 hurricane damage. “There was severe erosion on the bank of the canal where varying water levels had washed out the shoreline,” says Lowell Barden, vice president of National Erosion Control in Lakeland, FL. “A sub-contractor, Globe Tech Incorporated, did the site work. They rebuilt the slopes to specifications provided by the South Florida Water Management District.”
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Photo: Soil Retention Systems |
| The Forester Creek channel improvement project's energy dissipater |
National Erosion Control acts as erosion contractor for public agencies such as the EPA, the Federal Emergency Management Agency (FEMA), the Department of Environmental Protection, and the South Florida Water Management District. “We do everything except residential work,” Barden says.
Barden says the job at Lakeland involved digging top and bottom anchor trenches 3 feet below the average water line of the canal, which was then lined with Landlok 300 manufactured by Propex, a geosynthetics manufacturer based in Chattanooga, TN. “We put in 55,000 square yards at a cost [on our end] of over $250,000.”
Landlok turf reinforcement mats use a thick, three-dimensional matrix of voids to trap seed, soil, and water in place for a quicker, thicker vegetation growth, doubling vegetation’s natural erosion capacity and creating a permanent turf reinforcement solution.
“Landlok was the best product for that project,” Barden says. “The X-3 technology allows better erosion protection than a biodegradable blanket. If the grass dies in a freeze, the mat will still be there. Straw goes away after a year or two, but this will be there a long, long time.”
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Photo: Soil Retention Systems |
| Enviroflex installation at Forester Creek |
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Photo: Soil Retention Systems |
| Installation work at Forester Creek |
Due to the higher velocity of water under bridges, the project also employed two other technologies: rubble riprap and cable concrete. “We used those—the hard armor—immediately outside [the blanket] to protect the soil holding up the bridges,” Barden notes.
It took two three-man crews working eight-hour days to complete the project in four months, according to Barden. “All involved—South Florida Water Management, Globe Tech, the Everglades Restoration Project—were extremely happy. It looks now like it was never damaged in the first place.”
Barden says his team completed work on five more canals in 2006 and 2007 and has started work on another. “We’ve performed installation and materials on every canal project in the South Florida Water Management District in the past two years, and we hope to do so for the next two. We’ve used Propex in all the projects.”
Creek Flooding Closes Busy City Street in California
Forester Creek flows northwest from the city of El Cajon, CA, to beyond Mission Gorge Road, where it then joins the San Diego River. Its channel is concrete lined through the city of El Cajon and unlined throughout its 1.2-mile reach in the southwestern part of the city of Santee, CA. Julie Procopio was the principal civil engineer on a recent project to widen the creek, revegetate its banks, build a new bridge, and lengthen another, all in a particularly busy part of the city.
“The creek was not wide enough to convey storm flows; it had less than a 10-year storm capacity,” Procopio explains. “It was flooding residences in a subdivision built before the 1950s when FEMA floodplain guidelines had not even been established. Streets and residences were inundated in a heavy rain. There had been a long-standing need for improvement.”
A major issue for the city, according to Procopio, was the section of the creek that ran under Mission Gorge Road, the city’s busiest street, which supports up to 50,000 vehicles daily. “The city would have to close the street for hours at a time in a heavy rain.”
While the city’s first concern was to eliminate flooding, the project evolved over time, Procopio says: “Resource agency permits really pushed us in the direction of complete revegetation.” Although the city originally intended to line one-third of the 1.2-mile section with concrete and revegetate two-thirds of its length, the Regional Water Quality Control Board said it would not certify such a plan. In the end, the entire length of the widened section is a natural creek bed. The difference in cost was $10 million, she acknowledges, but she adds, “It is now a community asset rather than a concrete drainage structure.”
The project, which even includes a bike trail on one side of the stream, began in early 2006 and was completed in late 2007.
First, the channel was widened using standard heavy equipment. The new portion was then graded. The natural channel bottom allows the water to infiltrate the soil and thereby decreases the flow. “We used articulated block to reinforce the channel bottom,” Procopio says, “mainly under bridges to protect shallow utilities. Vegetation can grow into these blocks. We also used riprap to dissipate energy at the upstream end and slow down the water.”
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Photo: Soil Retention Systems |
| The Olive Lane Bridge, which was nearly flooded two years prior |
Articulated blocks from Enviroflex, manufactured by Soil Retention Products of Carlsbad, CA, adapt to ground movements and grade changes while providing resistance to erosion. The openings in the block units enable vegetation to become established, thus providing a green, natural appearance. Cabling or other connection devices are not required. Enviroflex is used to replace riprap, gabion mattresses, concrete, or asphalt linings and other hard-armor systems.
Procopio says the project employed native plants to line the banks from the water level up to 6 feet. Above that level, southern willow scrub was planted because it requires less water. “We took into account the velocity of incoming water from upstream and used riprap to slow it down and prevent erosion. Downstream, the water velocity is slower and not erosive.”
Eight different sources funded the project, Procopio says. “It was a mix of state, federal, and local money.” Of the total cost of $36 million, construction cost $25 million. “We built one new bridge and lengthened another,” she says.
Even before actual construction had begun, the city won two awards in 2002 for the concept and design of the Forester Creek project. The awards were handed out by the Association of Environmental Professionals for Outstanding Environmental Solution and Outstanding Environmental Analysis Document for 2003.
Saltwater Threatens Marsh in Louisiana’s Rockefeller Wildlife Refuge
The Rockefeller State Wildlife Refuge and Game Preserve, located along the Gulf of Mexico, is managed by the Louisiana Department of Wildlife and Fisheries and originally encompassed 86,000 acres of wilderness. Erosion, however, has taken a significant toll, and the most recent surveys indicate that less than 76,000 acres remain.
The Chenier sub-basin lies between Louisiana Highway 82 and the Gulf of Mexico. The lake’s sub-basin is north of Highway 82 and includes Grand and White lakes and surrounding marshes. The Chenier sub-basin had been experiencing saltwater intrusion due to lack of freshwater and sediment input form the lake’s sub-basin. “As the salt was increasing, the marsh was dying, turning into bays and lakes,” says Wesley Pitre, operations manager for Wilco Industrial Services LLC in New Roads, LA. “We dredged 7 miles of small channels from White Lake to allow a greater volume of fresh water to flow south toward the gulf.”
While much of Wilco’s work involves “dredging for access” for oil companies, this recently completed project for the Department of Natural Resources involved freshwater introduction into a marsh that was rapidly losing its life to the sea. The project, officially called Freshwater Introduction South of Highway 82 (ME-16), was located in the north-central and eastern portions of Rockefeller State Wildlife Refuge and Game Preserve in Cameron and Vermilion parishes. The work, authorized to address saltwater and lack of freshwater and sediment input in the area, began in September 2005 and was completed in November 2006.
The work included the installation of four freshwater introduction water control structures. “Their function is to close when the water elevation on the saltwater side is higher than the freshwater elevation and open when the freshwater elevation is higher than the saltwater elevation,” Pitre explains.
In addition to controlling water levels, a major goal of the project was marsh restoration, involving the construction of 26,000 feet of earthen terraces, each 500 feet long. Plugs of native vegetation were planted along the perimeter of the terrace. “These decrease the flow of current and allow silt to build up between the terraces, thereby turning an open-water bay back into marsh,” Pitre says.
The effect on wildlife was considerable, according to Pitre. “Shoreline birds like plovers, ibises, and blue and white herons are able to nest. They are birds that like isolation, and there wasn’t room for them before.”
Coyotes and deer frequent the area, but they were less severely affected than the alligators, Pitre says. “Alligators don’t like salt, and they won’t nest if salinity levels are too high.”
For the dredging, the crews used an amphibious dredge they nicknamed “The Salamander.” Pitre says it’s the only one of its kind in the world. “It’s the only one built, and this is one of the only projects where it was used. On top of one of Wilco’s self-propelled amphibious undercarriages, we mounted an 8-inch dredge that was built and assembled by Dredging Supply Company [located in Reserve, LA]. It is set on tracks so there is no overcutting. And it creates a canal that is as close to natural as you can get, because it allows a small cut without having to dig for floatation.”
Wilco Manufacturing LLC in Lafayette, LA, manufactures amphibious hydraulic undercarriages for a wide range of equipment, primarily hydraulic excavators. Payload on these undercarriages ranges from a few tons up to 30 tons. In most instances, the hydraulic system of the excavator is used to propel the undercarriage. In these instances, Wilco supplies a mounting ring compatible with the excavator upper along with a hydraulic swivel, travel motors and brakes, and final drive gear boxes.
The project, funded by the US Fish and Wildlife Service, cost more than $6.1 million. The estimated net benefit over a 20-year period is an additional 296 acres in the Rockefeller preserve.
Pitre is optimistic about the marsh’s future. “As the terraces grow larger, there will be more vegetation, and the drop in salinity levels will allow the former vegetation to return.”
Despite Its Name, Soft Armor Stands Strong
In restoring and stabilizing any site, many experts stress using “soft,” less rigid best management practices whenever possible. Although the purpose for stabilizing the banks and the designated uses of the stream help determine the type of structures needed, most areas benefit greatly from armor that encourages return of a natural habitat. Concrete not only is increasingly expensive but also prevents any organic material from reaching the area. Hard structures placed on one eroding bank can displace the stream’s energy downstream to a previously stable bank and allow that bank to erode. For slope protection, erosion control mats, geosynthetic materials, and terraces can prevent the loss of topsoil, reduce surface erosion, and promote rapid establishment of permanent vegetative cover. This, in turn, encourages animal and fish species to return. The result is not only environmentally sound but also aesthetically pleasing. It comes as no surprise that many municipalities are creating parks on the site of former wasteland.
Hard Armor Has Merits, Too
Some situations, though, call for an immediate and practical solution, and soft-armor solutions aren’t always appropriate for the job. In the first of the cases detailed below, safety and cost effectiveness were real priorities. In the second, an unsightly ditch simply needed repair.
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Photo: Intl Erosion Control Sys |
| An articulated concrete block mattress prevents creek erosion. |
Cross-Creek Training Calls for Stable Surface in Georgia
Sometimes an eroding streambank is just part of natural evolution; that is, until the military starts using it for tactical training.
Ben Ansley is superintendent and owner of Sowega Construction Inc. of Americus, GA. In a recent project on Fort Benning Army base near Columbus, GA, he and his crew lined Randall Creek with Cable Concrete supplied by International Erosion Control Systems of West Lorne, ON, Canada.
Cable Concrete is an articulated concrete block mattress system that integrates strong, flexible stainless steel cable into high-strength concrete, resulting in both durability and flexibility. Cable Concrete is formed to cover an area of about 4 feet by 16 feet or 8 feet by 16 feet and is available in four weights: 20, 35, 45, and 70 pounds per square foot, allowing flexibility for a particular project.
At Randall Creek, the crew used the 8- by 16-foot mats to create a hard surface for heavy military vehicles used in training. “It’s a continual problem during the wet season—winter—to maintain these crossings,” Ansley says. “Instead of using bridges, these 80- to 100-ton vehicles such as Hummers cross creeks through water. The vehicles get stuck in the mud. You take an 18-year-old driver who gets stuck in the mud—heck, I’d play, too.”
Unfortunately, when the vehicles get stuck and the tires spin, the resulting sediment ends up downstream, and native habitat is endangered. Laying down Cable Concrete matting eliminates the problem, according to Ansley.
“The concrete is poured upside-down into a form with cable strung across through the blocks. Then you flip it over and release the cable, lift the form off the concrete mat, pick up the mat with a spreader bar, and place it down. It’s flexible and conforms to the contours of the subgrade. Then we backfill the voids with topsoil to create a hard surface so that vehicles won’t get bogged up in the creek.”
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Photo:Penda Corporation |
| SmartDitch following a night of rain |
Any disturbed areas on the site are planted with native grasses, Ansley says. An aggregate base lines the canal itself with riprap on the outside.
The federally funded project cost approximately $100,000 and was accomplished in 30 days, according to Ansley. And it was finished none too soon, he notes, as troops have been doubling at both Forts Benning and Stewart, resulting in ever-increasing traffic across the waterways.
Quick Solution for a Small Problem in North Carolina
Neil Bartlett is public works director for the City of Goldsboro, NC. Recently, the city completed a project involving lining a small swale or ditch running behind and between houses in a subdivision, Maplewood, in Goldsboro. Workers used approximately 300 linear feet of 12-inch trapezoidal SmartDitch to improve drainage and prevent future erosion.
“It was just an unsightly swale between residences,” Bartlett says. “It was difficult to mow, and trash had accumulated, from paper to tree debris, such as limbs.”
Bartlett says SmartDitch, provided free in this case by Penda Corp. of Portage, WI, was the only feasible alternative for the project. “We looked at concrete, but it is tremendously expensive, and the ditch wasn’t deep enough to use reinforced concrete pipe.”
SmartDitch is a high-density polyethylene channel ditch-lining system that is lightweight and easy to install. “We contoured the shape of the ditch to the shape of the product,” Bartlett explains. “We used shovels, but a backhoe with a bucket would be the proper equipment and would go a lot faster.” Crews then lined the swale with SmartDitch, anchored it, and landscaped. The entire project took only two days.
Seemingly unlimited options and a growing product market make streambed stabilization and channel repair a thriving business for both government and private enterprise.
Mary Ellen Hare is a writer residing in Granville, OH.
EC - May 2008
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