Seismic Upgrade: City Gets $1.4 Million to Strengthen Forbes Creek Bridge

The City of Kirkland is planning to retrofit the Forbes Creek Bridge on 98th Avenue in Juanita to strengthen it against earthquakes, using a $1.4 million federal highways grant recently approved by the Washington Department of Transportation (WSDOT).

The bridge was built decades ago by King County to replace an older one that now serves as a walkway at Juanita Bay Park. It now fails to meet newer standards based on the potential for catastrophic earthquakes in the seismically active Pacific Northwest.

“A few years ago we did an assessment of our bridges for seismic integrity,” said Ray Steiger, Kirkland Public Works director. “The type of design used (on the Forbes Creek Bridge) is not what we would use today. It’s built in a wetlands area, and in an earthquake those sediments can act like jelly, a process called liquefaction.”

A consultant recommended the bridge be completely replaced, at a cost of some $10 million. A cheaper alternative is to strengthen it structurally, so the city applied for a Federal Highway Fund Grant through WSDOT. The state agency late last month selected 70 projects to repair or replace aging bridges around Washington with $130 million in federal funds, and one was Kirkland’s Forbes Creek proposal.

“We’re excited,” said Steiger. “The challenge will be that it’s in a stream.”

A design consultant will likely be selected early in 2012 for the project, which will include work on the bridge’s deck. “My sense is that the actual project will be sometime in 2014,” Steiger said.