By Chris Marr

In 2003 the Wyoming Department of Transportation (WYDOT) was faced with the challenge of maintaining roads along a pristine section of the Popo Agie River, in the vicinity of Sinks Canyon State Park, while at the same time protecting water quality in the river. Rough terrain and large boulder fields made it difficult to prevent concentrated water flows, sediment, and rock from being deposited into the river during road construction. Traditional silt fence could not be properly installed due to the topography, and large rock and boulders prevented trenching and silt fence stake placement.

The solution was a geotextile berm that would conform to the surface. This would prevent undercutting by concentrated water flows and keep rocks and boulders from disturbing post-construction revegetation. Four years after the construction, the area was reevaluated to determine the degree of success of the geotextile berm, compared to conventional silt fence.

Background of Sinks Canyon State Park
Sinks Canyon State Park is located 6 miles southwest of Lander, WY, on Highway 131, where the Popo Agie River flows out of the Wind River Mountains. It is home to abundance of wildlife such as bighorn sheep, golden eagles, and black bear. Major habitats include heavily forested north slopes that accumulate heavy snowfalls, south-facing slopes where snow melts quickly due to increased sunshine, and the riparian zone where there are large aspen groves and abundant wildflowers. Average annual rainfall is 13 inches, with an average snowfall of nearly 100 inches. In recent years, though, the Lander area has been under drought conditions, with currently only 42% of average precipitation.

Photos: John Samson, WYDOT

Over 8,000 feet of berm bag were installed at Sinks Canyon.

Sinks Canyon is so named because the middle fork of the Popo Agie River, a fast-running mountain river, flows from the mountains and through a limestone canyon, where the river “sinks” into fissures and cracks in the limestone. Here the river runs underground for about 0.25 mile and emerges down the canyon in an area called “The Rise,” where it continues down the canyon into the valley below. The river flows at 150 cubic feet per second on average and up to 500 cubic feet per second during spring runoff.

Project Overview
In the summer of 2003, WYDOT was conducting road maintenance and construction directly along the Popo Agie River near Sinks Canyon. Preventing gravel and sediment from running off into the river and adjacent riparian zones was turning into a major challenge. Sinks Canyon is an environmentally sensitive area, and the municipal drinking-water intake was downstream of construction activities. National Pollutant Discharge Elimination System (NPDES), EPA, and US Army Corps of Engineers regulations mandated that sediment and turbid runoff be prevented from entering the river and especially the drinking-water intake. The area was large contours with fields of 16-inch-diameter or larger river cobble and boulders. The boulder field would not allow silt fence trenching or proper burial techniques, and traditional burlap tube installation would be prone to rupture. There were fresh-cut slopes, and the road design included a 4% to 5% gradient that allowed concentrated runoff to flow through the material. There were also super-elevated curves that increased the concentrated flows from the road. A material was needed to contain heavy mudflows, sediment, gravel, and rocks during normal construction and rain, as well as during storm events. A high-flow, porous barrier material was needed to handle these heavy flows.

Project Solution
WYDOT decided to use a geotextile berm instead of other traditional methods of sediment control. The bag chosen was the California Anaconda Berm Bag, a 10- to 12-inch-diameter geotextile berm bag 750 feet long, which can be cut to appropriate lengths to fit site installations. The bags, constructed of UV-resistant geotextile, are filled onsite with gravel and rock fill and conform to the terrain.

WYDOT had previously used 12-inch-diameter burlap tubes, but they lasted only one or two seasons before breaking down and becoming ineffective for sediment control.

John Samson, an agronomist with WYDOT, believed the California Anaconda Berm Bags were a better solution for several reasons:

• The geotextile lets water filter through while retaining sediment in runoff; it has a flow rate of more than 200 gallons per square foot per minute.
• The fabric molds to fit the terrain and has a high tensile strength to hold heavy gravel and rock.
• The seams are woven together, which means that the seams are not welded, glued, or sewn, making the seams as strong as the material itself.
• The geotextile has a high UV rating (five years) whereas most existing woven geotextile has only a 70% to 80% rating after 500 hours.
• The green color blends into the surroundings and gives a more natural look.
• The berm has minimal environmental impact and is suitable for use in sensitive areas such as wetlands and riverbanks or streambanks (Leshchinsky et al. 1996; Fowler, Sprague, and Toups 1994).

More than 8,000 linear feet of berm bags were installed in the toe of fill locations above the Popo Agie River and near campgrounds within Sinks Canyon State Park. High Country Construction, of Lander, installed the bags. Where terrain was too steep to fill the berms in place, High Country Construction filled the berm laid in half of a concrete pier form. Crews then used an excavator to move the form to the desired location and then rolled the berm from the form into place. To fill the berms in place, the berm bags were filled using a modified dump truck with a 6-foot-long, 10-inch-diameter metal filling auger. The tube was filled with 1-inch-minus rock filling the tube to one-half to two-thirds full. The cross section of the berm was therefore more like a dome than a cylinder, which conforms better to the terrain and gives better contact to the surface, preventing undercutting by runoff.

Although the 10- to 12-inch-diameter California Anaconda Berm Bag was originally specified, as a result of a communication misunderstanding, the delivered berm bags were 18 to 20 inches in diameter; crews referred to them as the “Wyoming Super-Sized Berm Bags.” As it turned out, these larger bags were much more efficient in fitting the contours created by the large river cobble and boulders, which exceeded 16 inches in diameter.

“This material is the only material I would recommend for this kind of installation,” says Chad Connell of High Country Construction. “In the past, burlap was used but did not last as long and could not handle the weight of fill material put into the tube.”

Project Results After Four Years
Monitoring and review of the installation project area has been ongoing for four years. John Samson took pictures in April 2005 and again a month later after a major spring storm hit the area. Visible inspections were taken over the four-year period. WYDOT recently noted that the bags continue to provide good boulder and sediment retention and estimated that they still have a half-life remaining.

“These longer-life geo-bags have been useful since severe drought has enveloped Sinks Canyon since construction,” says Samson. “This has allowed extended grow-in for the native, permanent vegetation to establish itself. In comparison, silt fence has long ago deteriorated and has been removed from select areas of the Sinks Canyon job.”

Samson also notes an unexpected benefit of the Wyoming Super-Sized Berm Bags was that their extra mass of gravel and rock fill allowed for topsoil slope fill, or toe berm, reinforcement where silt fence was never successful before. The large berm size provides an important “fill avoidance” function, as the Army Corps of Engineers terms its mandate to keep fill material out of riparian zones. The bags have retained boulders of more than 12 inches in diameter.

Conclusion
The four-year conclusion is that the Wyoming Super-Sized Berm Bag was the right decision for the rough terrain and boulder fields of the Sinks Canyon area and is substantially better than silt fence or burlap berms. Based on this success, WYDOT has since elected to use the California Anaconda bags on two other projects in sensitive national parks. The Brooks Lake WYDOT project, east of Grand Teton National Park, used the smaller-diameter California Anaconda Berm Bag in many locations for easier filling and placement, while the larger Wyoming Super-Sized Berm Bag was used near stream crossings. The Buffalo Fork WYDOT project in the Grand Teton National Park area provided the opportunity to test durability of the Super-Sized Berm Bag in bridge construction wheeled traffic, as well as a direct comparison with non-reinforced silt fence in the Grand Teton National Park. As was demonstrated in the Sinks Canyon, standard silt fence is unable to retain significant fill, while the large berm bag retains even 12-inch rock. In the bridge construction area, the bags have held up to everyday wheeled traffic.

These projects have demonstrated that trenchless geotextile berms, whether standard or “super-sized,” have great potential for controlling runoff and erosion, even of large cobbles and boulders, under the most challenging topography.

References
Leshchinsky, D., O. Leshchinsky, H.I. Ling, and P.A. Gilbert. 1996. “Geosynthetics Tubes for Confining Pressurized Slurry: Some Design Aspects.” Journal of Geotechnical Engineering 122(8): 682–690. American Society of Civil Engineers.

Fowler, J., C.J. Sprague, and D. Toups. 1994. “Dredged Material-Filled Geotextile Containers, Environmental Effects of Dredging Technical Notes.” Case history. Geotechnical Fabrics Report 12(8): 42–54. Industrial Fabrics Association International.

Chris Marr, CPESC, works for ProTech GCS and is a newly elected board member of the Western Chapter of IECA.

EC - January/February 2008