Dakota Creek bridge will get seismic retrofits

Published on Wed, Feb 12, 2014 by Quinn Welsch

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While significant earthquakes don’t happen very often in Whatcom County, the Washington State Department of Transportation (WSDOT) is making sure that if one does occur the Dakota Creek Bridge on Peace Portal Drive will be ready to rock and roll. 

On February 11, Whatcom County Council approved funding for a seismic upgrade project in the amount of $2,718,268 in a 7–0 vote at the council’s regular meeting that will allow engineers to begin work on making the bridge earthquake-ready. The upgrade project is funded through federal money awarded to the state. Whatcom County will foot the initial bill, but be reimbursed, said assistant public works director Joe Rutan. 

“That bridge has been there 90 years,” said Steve Dillon, a county engineer. “We’re thinking we can get another 30 years out of it at a reasonable cost.”

To ensure that extended lifespan, significant changes will have to be made. A structural assessment of the bridge in 2010 found serious deficiencies that could lead to a collapse during an earthquake, according to the public works department.

The spans between each of the bridge’s support columns move independently, causing movement of the entire bridge. Since the bridge’s construction in 1928, the bridge has shifted sideways by about one-fourth to one-half of an inch, Dillon said. The concrete and rebar around the bridge’s footings have also deteriorated.

The upgrade includes plans to stabilize corrosion on the bridge’s footings by protecting them with steel casings and installing seismic cable restrainers – cables connecting the girders and the piers – to reduce the likelihood of collapse due to unseating. When the bridge was originally built there was no seismic consideration at all, Dillon said. Despite the deficiencies, the new upgrades aren’t due to a serious risk of failure, he said. 

“It’s not unsafe, or we would have closed it,” Dillon said.

WSDOT lists 496 bridges in the state that need retrofitting and 134 that are partially retrofitted. There are 278 bridges that have been retrofitted already. WSDOT has invested about $100 million in upgrading bridges throughout the state since WSDOT began its seismic retrofit program in 1991.

Though most areas in the Pacific Northwest have a high seismic rating, Whatcom County is more protected in some respects, said Western Washington University geology professor Jackie Caplan-Auerbach. 

The county is farther away from the “megathrust,” an area where tectonic plates overlap and can cause destructive earthquakes, she said. The faults in the county are also much shallower, she added.

Three active faults were discovered in Birch Bay and Blaine in 2012, according to the U.S. Geological Survey. The faults lie northwest to southeast and run through Drayton Harbor, Birch Bay and Sandy Point.

Work on the bridge is set to begin in spring 2015 and end in late October of that year. Dillon said there will be some traffic impact, but no road closures have been established. Partial road closures on Peace Portal Drive and an I-5 detour have been discussed, he said.

NWPRD2 name change

At the council’s regular meeting, the council approved a request by Northwest Parks and Recreation District 2 (NWPRD2) to change its name to Blaine-Birch Bay Park and Recreation District.

The district, which serves Birch Bay and Blaine and is funded by taxpayers within the Blaine School District’s boundaries (except Point Roberts), has been facilitating and organizing recreational activities in the area since 2007. However, many residents were unfamiliar with the district and its facilities because of the vague and nondescript moniker, according to the district.

The name change will help residents identify what area the district serves, said NWPRD2 program manager Heidi Holmes.

The district’s board of commissioners decided to change the name with a 5–0 vote in December 2013. The county council voted 7–0 to approve the name change.