Gabions have existed for a variety of uses as far back as the Egyptians and Romans. But it was in the 20th century that they were increasingly used for erosion control. Even today, some areas seem to make use of gabions more commonly than others do. Riprap is still in wide use where space is not a premium and stone is readily available. Yet, as many in the erosion control business seem to agree, for a vertical wall, nothing beats gabions for strength, ease of application, and durability.
Gabions Save the Day at Wastewater Facility
Nestled in an Appalachian valley on the Virginia border, Wardensville, WV, is a little hamlet of 258 that has resisted time, says engineer Fred Hypes of Dunn Engineers Inc., who has worked extensively with the town in the past few years. Once a farming community, its leaders now travel as far as Washington, DC, to earn a living. “The town of Wardensville has been a special client for us. They are very involved and forward looking, receptive to new ideas, and motivated to provide top-flight services for their people,” Hypes says.
In November 1985, Hurricane Juan brought the worst flooding in West Virginia’s history. The worst hit areas were the Cheat River and South Branch Potomac River basins. Constructed in 1980, Wardensville’s wastewater lagoons have been damaged four more times in succeeding floods. Because the site is adjacent to the Cacapon River, a Potomac tributary whose waters lead ultimately to the Atlantic Ocean’s Chesapeake Bay, more was at stake than the 325 households served by the facility.
The 120,000 gallon-per-day wastewater treatment facility consisted of two 3.5-acre lagoons and a small chlorine contact basin; dikes built up from ground level serve as wastewater containment. Each time the site flooded, repairs were done, with riprap installed around the lagoon. The dikes themselves were rebuilt several times, according to Hypes. “Then, in 2005, the town sought and received funds to raise the dikes 4 feet,” he says. “The project stalled because there was not enough suitable fill dirt available near the project site. This is an archeologically sensitive area requiring investigation before digging, and the project needed over 20,000 cubic yards of fill.”
In 2007, responding to directives from the state and from the Federal Emergency Management Agency (FEMA) regarding an imminent catastrophe if remediation failed to occur, the town hired Dunn Engineers Inc. of Charleston, WV, which suggested the town take a different direction entirely. “The Army Corps of Engineers had done extensive floodwater projects using gabion mattresses to armor floodwalls in the South Branch Valley,” Hypes says. “They are commonly used here due to the terrain, and they work around the waterways.”
Using funds from several sources, the town embarked on the $1.6 million Wastewater Upgrade Lagoon Project in late spring 2010, with an expected completion date in the fall. “A HUD Small City Block Grant provided $1.15 million, and $460,000 came from the state revolving fund, administered by the DEP, with a portion of it coming from ARRA stimulus money,” Hypes says. In addition to the gabion mattresses, a mechanical screen, lagoon baffles, and floating aerators were installed to improve the facility’s treatment efficiency.
Hypes says he had seen gabion mattresses at work in the neighboring city of Petersburg, where a water treatment plant project designed by Dunn Engineers is being built. Flood control levees protected by the gabions border the site, and Hypes has observed their performance for 10 years.
For this project, Dunn Engineers chose the Reno mattress manufactured by Maccaferri Inc. of Williamsport, MD. The base section of the Reno mattress is divided into compartments and filled with stones at the project site. With lids secured, Reno mattresses form flexible, permeable, monolithic structures. Hypes says he was impressed with Maccaferri’s product and especially with the company’s service. “The product is reliable and predictable. It is also user friendly, with technical assistance on final decisions and a willingness to incorporate their mattress into our project concepts.”
The vision for the Wastewater Lagoon project was to let grass grow over the gabion mattresses and leave it unmowed for up to 3 feet, Hypes says. “The vegetation atop the dikes, in addition to the mattresses, should give a relatively high degree of protection against future flood damage.”
Project manager John Billmyer of Snyder Environmental Services in Kearneysville, WV, describes the site: “It is a lagoon system with two large ponds, one incoming pond where the waste settles out the solids, and a clearing pond. The water then goes to a chlorinator and finally into the Cacapon River.”To rebuild the area, workers first removed 6 inches of topsoil from the dikes before installing gabion mattresses filled with 3- to 4-inch rocks, which were placed by hand and machine. The mattresses, when stapled together, are hooked and immovable, unlike riprap, which can move about. While more labor-intensive and with a cost of 70 cents per square foot as opposed to five cents for riprap, the mattresses are deemed to be worth the extra cost. “Once they’re in, they are sandwiched together,” Billmyer says, adding that the installation should last at least 50 years.
While the top of the dikes and the outside slope of the lagoon were fitted with baskets, riprap on filter fabric was used from the top down into the ponds, Billmyer says.
Once the mattresses were in place, the topsoil was laid over the top, and then seeded by tractor with tall fescue. Reusing the topsoil eliminated the need for fill dirt from elsewhere.
Reinventing on the Links Is Par for the Course
In Raleigh, NC, the name Cheviot Hills once invariably evoked the 18-hole public golf course. Located off US-1, it was a popular destination for years. Then the owner died, and after keeping the facility going for a couple of years, the heirs placed it on the market. Enter an entrepreneur, who, seeing a big tract of land in a depressed economy, purchased the 100-acre site and decided to turn part of it into an auto park conglomerate. Only one problem: How to get the cars get over the knolls and onto the flat putting greens.
It was just a matter of moving an immense amount of dirt, according to Staci Smith, P.E., regional engineer for Atlantic Construction Fabrics (ACF) Environmental and technical consultant on a job that required both brain and person power to accomplish.
Starting at the beginning of July 2009 and finishing in September, the transformation was fast, if dirty. “The wall needed to be built quickly to bring up the grade and use the excess soil from the property,” Smith says. “Erosion control was a constant issue on the site, as it was being constructed during the summer with the invariable stray thundershower.”
Because the parcel faced a main road, the owner wanted to even out the road frontage so that each car brand got equal billing when drivers passed. This involved building a wall with a 101,000-square-foot of wall face and an average height of 30 feet. “We built a wire basket earth retaining wall with Huesker’s high-strength fabric,” says project manager Mike Sciortino of S.T. Wooten Corp. in Raleigh, NC. “A wall this size is usually an eyesore, but this eco-friendly green wall has excellent aesthetic qualities. There is no issue of settlement either. Raleigh loved it, and now they’re using it as a model.”
The now-green wall, at 100,000 square feet and 3,400 linear feet, is not to be missed by drivers, a plus when the goal is to sell cars perched atop it. “It’s a showpiece project,” Smith says. “People drive by and are impressed with S.T. Wooten’s project and give it accolades.”
One of the major pluses on this site was the ability to use onsite soil. “It was a green alternative to a modular concrete-block retaining wall,” Smith says.
Sciortino says the fabric wall sped production, because it was faster than a block wall to erect. The wall was seeded with Virginia creeper, honeysuckle, and magnolia.
However, since the area had hosted a rolling turf golf course, there was more going on than just wall building. With a natural stream running through the site, dividing it essentially in half, workers built a pond along the side of it, draining a previously existing pond and “moving it over” by constructing a dam and spillway. On the other side, they created a wetland. Of the eight basins acting as Neuse River buffers, three became permanent wetland structures or ponds.
An access road was built, allowing entrance on US-1, with a special lane and signal and tying into two other side streets.
Backyard for a Lucky Homeowner
For some, a backyard remodeling entails a few perennials and perhaps even a deck or a new patio. For others, it is considerably more complicated.
Steve Valero, chief operating officer for Pinnacle Design and Building Group, based in Cumming, GA, in July 2010 was working on an unusual challenge in MacLean, VA, where a homeowner needed to actually create a backyard in order to build a pool and other amenities.
“The site’s backyard is located on the Potomac River, and there are areas, or buffer zones that can’t be disturbed,” Valero says. “We couldn’t create a stable slope in that area, so we had to build vertically.”
The choice was to use C.E. Shepherd’s gabion baskets as the face of a dirt wall. Instead of vegetation, the owner specified natural stone veneer to match the residence. Natural stone veneer and boulders were hand-placed atop the gabion-faced structure, Valero says. “It is a mechanically stabilized earth wall with gabion baskets as facing and an earth-reinforced wall behind.”
Stabilizing the earth behind the baskets allowed the project to save on stone, which is in limited local supply and is very expensive due to transportation into the Washington, DC, metro area, Valero says.
It took a crew of five about a month to complete the first phase of the project at a cost of $250,000. The first part of the wall was built to create an access road for heavy equipment to come. The wall’s extension was expected to cost another $400,000.
Valero says his company has a long-standing relationship with C.E. Shepherd. “We like their welded gabions; they are easy to install.”
Soil Bags Preserve History
Pat Dixon is co-owner with his wife Colleen of Dixon Shoreline LLC in Portage, WI, a family business he inherited after his father died in 1994. “I kept getting telephone calls, so we started up again,” he says.
With an emphasis on water quality and erosion and sediment control, the company tries to stay ahead of the curve on new regulations and products, Dixon says, adding that it was among the first to install soil bags. “We use bioengineered soil stabilization for erosion and sediment control on hillsides and shorelines. I have done thousands of installations.”
Veteran Gil Layton, who acted as technical advisor to the project, spent 38 years with the Wisconsin Department of Transportation and has been involved in erosion control and stormwater programs for 44 years.
In an August 2009 project, Dixon and Layton used Agrecol’s Envirolok geotextile fabric bags. “They grab and have good bursting strength,” Dixon says. The site, on Lake Mendota north of Madison, WI, involved a 50-foot cliff where the hillside had started to wash out and the homeowner’s backyard had started to collapse. “We used earth anchors, geogrid, and Envirolok soil bags with permeable drain tiles behind them.”
A residential lakeside property, the site was home to a 1,200-year-old Native American effigy mound in the shape of an eagle. With a 60-foot body, the entire mound covered 100 feet of the owner’s backyard. According to authorities, about 10,000 such mounds once existed in Wisconsin. Only a small fraction of these earthworks remain today, and most of those were tampered with at one time or another. The failure of this cliff had already started to affect the effigy mound, which prompted the homeowner to proceed with the project.
To prepare the site, workers removed 20 cubic yards of soil by hand, using a pulley system and buckets to move it uphill. “It took eight hours a day, with many men, for several days,” Dixon says. “We laid the first soil bags at the base, then went up 2 feet, wrapped the next course in geogrid, and put in earth anchors to connect the two and tie the system back into the cliff. We did the whole thing in 2-foot stages, putting drain tiles behind to alleviate hydrostatic pressure. The hillside was so steep that we had to use rock-climbing harnesses for safety.” Dixon says placing the bags is more than a mechanical process. “You have to work with the contour of the slope. It’s all handwork, and you have to feel the hill. It’s almost like artwork.”
The next step involved hydroseeding the site with a native mix. “We brought in a hydroseeding tank on a 26-foot work barge so we could work from the water and more easily access the site,” Dixon says. “We applied the mix of seed, tackifier, and hydroseed mulch as a cover crop for germination. Then we harnessed up and planted 2,800 plant plugs by hand.”
Layton says Wisconsin regulatory agencies are reluctant to allow hard armor along a waterway above the ordinary high water mark. “Therefore, we were telling the owner that a “˜green’ system was our only alternative.”
Dixon says the cliff, a one-quarter-to-1 slope, was the steepest project he had ever done: “Probably the steepest anywhere.” He praised the Envirolok bags. “They are individual units, so they add strength to the hillside; they are much better than sediment logs on steep slopes. We used 2,500 individual bags.”
Why did the hillside fail in the first place? “There’s usually a reason for shoreline erosion,” Dixon says. “It can be due to bottom, groundwater flow, or overland stormwater runoff flow at the top. In this case it was mainly overland flow. We redirected the downspouts and tiled them in to flow away from the slopes. We also directed the runoff from the yard to a catch basin on the site and redirected it toward the lake with an underdrain system.”
As a retired journeyman lineman, Dixon has traveled the country, always dealing with nature. Wherever there is a problem, there is a way to fix it. This is Dixon’s mantra. “You can always find a solution. We work with Mother Nature, not against her. Rock is not always the answer. Much of our erosion is caused by man. From the DNR to the counties with their zoning administration, good regulations are doing their job. We need to value native plants and clean water and become less dependent on foreign energy.”
About Envirolok, a product of Agrecol Corp. headquartered in southern Wisconsin, Layton says,” There’s a right place and a wrong place for every product out there. In this case, we were not allowed hard armor and there is nothing comparable to the Envirolok wall system when a vegetated or “˜green’ system is required. The bags are filled with 80% sand and 20% topsoil. The sand, or mineral-type soil, prevents settlement of the system, which is a common cause of failure with compost-filled systems when used on steep slopes. This was erodible clay soil, so we also tied the system back into the native soil as deep as possible using geogrid and earth anchors. This was a unique site; we used native plants with their deep roots, 10 to 15 feet, to enhance the structural value of the wall as they grow.”
In Maine, Fish Matter
Mark Brown is vice president of Brex Corp., a construction company in Kennebunk, ME. In late fall 2009, he worked on a project for the coastal village of Kennebunk. The project’s goal was to add 2,000 feet of rear access roads behind commercial developments in order to ease traffic on US Route 1, Maine’s busy coastal highway, which runs down the main street of this town.
“Part of the road had to cross Wonder Brook, and the local Conservation Commission was concerned about the impact on the wetland area,” Brown says.
Wonder Brook is part of a 27-acre preserve area adjacent to the town’s 45-acre Wonder Brook Park. Together, these lands offer a wooded 3-mile hike close to the center of town with views of Wonder Brook and the Kennebunk River, which empties into the Atlantic.
“We set 96-inch reinforced concrete pipe for the brook to travel through. We set the pipe invert elevation 4 feet below the existing channel grade to make a natural riverbed through the culvert to allow for natural passage of fish. To lessen the wetland impact, we kept the culvert length to 75 feet; therefore we used gabion baskets to build head walls and wing walls on either side to hold the slopes.”
The Terra Aqua gabion baskets provided by A.H. Harris of Portland, ME, were not new to Brown, who says he had used gabions extensively when he worked in Arizona. This is the first time in 12 years that he has constructed gabions as part of a project in Maine. “Gabions worked extremely well to hold back the slopes and minimize the wetland impact as well as eliminate erosion issues. An added bonus is that they are relatively easy to construct and they look good aesthetically,” Brown says.
In all, 96 baskets of varying sizes were used to create a wall that was wide at the base and staggered back for a slope that was 10 feet at its highest. Once the area was graded and prepped, the baskets were assembled and set in by hand, Brown says, and then filled with 4- to- 8-inch crushed rock from an excavator.
On the remainder of the slopes, Brown used riprap and fabric or loam and hydroseed. But for the vertical wall near the culvert, gabions worked well, he says.
Seventeen Years Later, His Wall Still Stands
David Grant, owner of Gabion Contracting Services Inc. in Katy, TX, has been using gabions since 1993, when they were a relatively new concept for him and others in his area. “They’re standard now,” he says. “The basket is superior to the old technology; its ease of application is appealing.”
In that first project with gabions, Grant says, the specifications called for gabions. “There was no option; it was a space consideration. We couldn’t use riprap, because there wasn’t room to lay back soil.”
The project involved a creek that was losing its banks near Tupelo, MS, and property owners adjacent to the creek were losing chunks of their property along a three-quarter mile strip on both sides of Bird Creek.
“We widened the channel and stabilized the creek bottom with gabion mattresses; then we did the sides with gabion walls,” Grant says. “Gabions were new at that time; we used C.E. Shepherd’s Modular Gabion CES. In this case we couldn’t lay the switchback far enough, so we had to build a vertical wall.”
Stone to fill the gabions had to be trucked from a site about an hour and a half away. Crews used 3-inch stone in the mattresses and 3- to 5-inch stone for the walls.
“We excavated 200 feet, then placed the mattresses with fabric underneath and filled it using an excavator. We put in the stones by hand in order to manipulate them on the face of the basket. The baskets used spirals then; now we use pneumatic guns,” Grant says.
While the disturbed areas were revegetated, the baskets were laid over with topsoil, leaving the seeding to nature. “It’s a natural process,” Grant says.
Has the wall held up after all these years?
“It’s perfect,” Grant says.
