Heavy rains have filled the Snohomish River and its tributaries to the point that cranes have had to park on the U.S. 2 trestle three times since October to clear flood debris that butted up against the bridge’s piers in Ebey Slough. The most recent trip was Feb. 5.
Reader Paul Kelly, of Snohomish, worries that this has to be done each time the river swells and wonders if there was a bridge design flaw. “Why was it designed that way? Is it too low, or did someone mess up the water flow design under it where the posts go directly into the water? What caused this problem, and is there ever going to be a fix?”
Design standards were different when the bridge was built, Washington State Department of Transportation spokesman Tom Pearce said. “At the time … piers were the required method for construction. Materials and designs developed since that bridge was built would allow a bridge to be built without piers today,” he said.
If not removed, the flood flotsam increases pressure on the trestle’s support columns and adds to upstream flooding.
“The space for water to flow past the bridge piers is restricted. This can force the current down under the pier, eroding the support. We call this erosion ‘scour,’” Pearce said. “Left unchecked, extreme cases of scour can destabilize a bridge pier, which could end up requiring a weight limit on a bridge or even a closure.”
It costs about $35,000 each time the crane needs to be brought to clear debris.
“Depending on the season, we may not have to do it all; the most we’ve had to do in a season was eight,” Pearce said.
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