Corrugated-steel culvert aids fish passage

February 2013 » Features » PROJECT NOTES

Lush valleys between tree-covered mountains with clear streams are abundant throughout the 1.1 million-acre Colville National Forest in the northeastern corner of Washington State. The Colville is part of the Rocky Mountain foothills and sits just south of the Canadian border – an hour's drive north of Spokane. In the Kettle Falls area, an undersized fish passage was in need of replacement.

The project consisted of removing the existing undersized culvert and replacing it with a new 21-foot, 6-inch-span by 7-foot, 3-inch-rise bottomless arch culvert. The U.S. Forest Service and Boulder Creek Contracting worked with Contech Engineered Solutions to develop a solution. In reviewing structural plate options, Contech's new BridgeCor corrugated-steel box culvert was selected.

A 21-foot, 6-inch-span by 7-foot, 3-inch-rise bottomless BridgeCor arch culvert was used to restore Pierre Creek's fish habitat and provide a safe crossing for the heavy-load log trucks travelling to local mills.
Photo: Conservation Northwest/David Heflick

BridgeCor uses a new, more robust corrugation pattern compared with traditional corrugated steel. This results in nearly doubling the structural stiffness to allow for longer spans of 18 to 35 feet standard range and as long as 65 feet for a custom configuration, higher fills, and high live load capacity, while reducing material thickness. Since the total structure weight is less, a cost savings also is realized when compared with traditional plate structures. These advantages make the BridgeCor box culvert a perfect solution for wetland and wildlife crossings like the Pierre Creek fish passage.

The 56-foot, 3-inch-long BridgeCor structure was used to restore Pierre Creek's fish habitat inside the structure, as well as provide a safe crossing for the heavy-load log trucks travelling to local mills. The box culvert is a 3-gage, hot-dip galvanized steel structure built for HL-93 loading.

"The new culvert replaces a long-standing fish-blocking culvert, restoring habitat connectivity between Pierre Lake – a popular fishing spot in northeast Washington State containing a variety of trout, kokanee, and large-mouth bass – and more than five miles of stream north of the lake," said Conservation Northwest Conservation Associate David Heflick.

"This product was a great solution for the low road fill of the site, and provided an ample span to achieve connectivity of the stream and riparian habitat, as well as the ability to easily handle the design flow," said Colville National Forest Civil Engineer Lucy Reeves, EIT.

The project was completed in August 2012. The U.S. Forest Service utilized precast concrete pedestal spread footing foundations to speed the construction process and eliminate the majority of concrete that otherwise would have been placed onsite. The first three BridgeCor rings were assembled and backfilled within just five hours.

During installation, the contractor reshaped the channel inside and outside of the structure. The stream bed was built up inside the structure as the plates were being set, making the crossing fish friendly. The new stream bed consisted of placing 3 feet of granular materials and boulders inside the structure with additional rip-rap added at both the inlet and outlet ends to stabilize the slope during periods of high runoff.

After the BridgeCor box culvert was fully backfilled and compacted and the road above repaved, heavy-load log trucks can now safely journey to local mills.

A Collaborative Forest Landscape Restoration Program grant that the Colville National Forest received in 2012 provided funding for the culvert. The Northeast Washington Forestry Coalition is a collaboration of Conservation Northwest, the Colville National Forest, local timber industry representatives, and other partners to focus on restoration projects that restore wildlife and fish habitats while boosting the local timber economy.
Information provided by Contech Engineered Solutions LLC

Submit news and photos of planned, ongoing, or recently completed projects to Bob Drake at bdrake@zweigwhite.com. In April, "Project Notes" will highlight mining/energy projects and geotechnology; in June, stormwater and site planning are the focus.


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