DUVALL — Steelhead, coho and other fish may soon enjoy more room to swim Loutsis Creek, where Washington state just built its first bridge using composite fibers.

The new kind of structure, nicknamed bridge-in-a-backpack, can be assembled faster than concrete or steel, especially in deep ravines.

It’s an innovation that could benefit the state’s long-term effort, costing at least $3.5 billion, to rescue endangered and blocked fish species by opening hundreds of streams, from Quillayute to Asotin. An estimated 1,526 road crossings remain in need of “significant habitat gain” by replacing clogged or narrow culverts by wider spans, says the 2020 Fish Passage Annual Report.

25,000 cubic yards of dirt were removed to quickly build a bridge using concrete-filled fiberglass arches, widening a salmon culvert in Duvall. (Ken Lambert/The Seattle Times)

Contractors installed the $8.2 million Duvall span along Highway 203 during dry August while the fish were away, and the creek flowed through a diversion pipe. The 13,000 daily drivers there also detoured for five weeks.

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Composite tubes are easily delivered to streams where there’s no place to park heavy cranes, or where the stream runs in a deep cut below the road, said Mark Gaines, bridge engineer for the Washington State Department of Transportation (WSDOT).

Workers can set them into place within hours and then pump them full of concrete to harden the fiber-covered ribs of a bridge arch.

The technique is best suited for 50- to 70-foot crossings, where contractors may find the lightweight material economical compared to concrete I-beams, Gaines said. Shorter crossings of around 20 to 40 feet would remain easier with precast-concrete structures, he said.

The Loutsis Creek culvert opens three miles of fish passage from the Snoqualmie River to the upstream Loutsis Dam reservoir, and feeder streams behind it, said Tom Pearce, WSDOT spokesperson.

The new 51-foot-wide opening replaced a concrete pipe, just south of Duvall. Though the creek flows merely 6 feet wide, the new bridge allows space for a rainstorm surge, along with hundreds of evergreens, deciduous seedlings and broken logs along the banks.

“Coho will spawn in these tributaries,” said Colin Wahl, environmental scientist for Tulalip Tribes. “Their young do really well in these backwater habitats.” Last year about 38,000 coho spawned in the Snohomish River system that includes the Snoqualmie, down from a 250,000 in 2001, he said.

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Threatened chinook and steelhead may benefit too, Wahl said, because a longer stream habitat provides more places for juvenile fish to grow in Snoqualmie Valley floodplains and tributaries, before they migrate downriver to the sea.

On a drizzly Sunday morning, frogs croaked and running water chattered like marbles as Colby Kohn, marketer for Maine-based AIT Bridges, walked under the bridge.

Workers needed only four hours, he said, to raise a dozen 300-pound fiberglass tubes and insert them into preformed circles within twin concrete foundations, creating an arch over the stream bed. Next they attached a layer of charcoal-colored sheets over the arch. Workers drilled through the apex of the 12 tubes, so concrete could be pumped in. Finally, prime contractor Goodfellow Brothers covered the arch with soil sandwiched between concrete sidewalls, restoring the highway to level.

AIT says it has supplied 30 fiber and carbon-fiber beamed bridges in eastern states. Composites are familiar in aircraft, automobiles and boats, so extending them to culverts and bridges is mainly a matter of persuading engineers, Kohn said.

“We’ve been through the Bronze Age, the steel age, the concrete age,” he said. “We’re entering the composite age.”

While the fiber method didn’t save much money or time, contractors lifted them easily using a forklift and straps, instead of bringing heavy cranes to the creek, which would have taken an extra day, said Mike Jacobs, project manager for Goodfellow Brothers.

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Jacobs said engineering and materials procurement are quicker with fiber. Concrete beams need to be custom-built and the backlog from suppliers can be as long as eight months, he said.

Two smaller culvert projects within the town of Duvall, where concrete boxes were installed near utility lines, each took more than 60 days, so the composite method may shorten future traffic blockages, said Steven Lenizewski, Duvall public-works director.

The U.S. District Court in 2013 ordered Washington to improve streams and tributaries that flow into the Salish Sea and Pacific Ocean, where 73 passages have been improved so far. WSDOT is also reopening streams east of the mountains and along the lower Columbia River.

Motorists have a stake in keeping fish projects affordable, because of competition between salmon and highways for gas-tax revenue. Current budgets show a $2.8 billion allotment to replace fish barriers from 2017-31, which could be scaled up to $3.5 billion in the $16.6 billion Forward Washington transportation plan released last year by House Transportation Committee Chairman Steve Hobbs, D-Lake Stevens.

State agencies have rebuilt 352 culverts and bridges since 1955, to reopen 1,170 miles of habitat. Another 14 projects are scheduled this year.

“We’re satisfied with the structure,” Gaines said of the Highway 203 rebuild. “We think it’s going to provide a 75-year service.” He expects the state to order more composite fiber bridges.