UPDATE, Sunday, 9 a.m. | WSDOT officials say they’ll have “hours” to close bridges (I-5, SR9, SR530) if the debris dam breaks.
ORIGINAL POST | Besides the threat of a surge of debris damaging bridges, state transportation officials are preparing for the chances that bridge supports could be scoured and weakened by heavy water flow.
One of the two Interstate 5 spans over the river was built in the 1930s, when bridge piers were shallower than used in current construction.
About 10 years ago, the base of the piers under that bridge was reinforced with rock, which was used to fill in gaps caused by past river scouring, said Bart Treece, of the Washington State Department of Transportation (WSDOT).
After a surge, Bridge Preservation Office engineers will examine the bridge supports to ensure they are safe. Whether that causes highway closures would depend on what the river carries with it, Treece said.
Saturday night, WSDOT incident-response trucks were stationed next to bridges on Highway 9 and Interstate 5 in case a closure is needed.
“We don’t know what’s going to happen when the blockage breaks loose, so why take the risk of having traffic on the bridges? That’s a preventable thing,” Treece said.