Planned upgrades to a county bridge in Brush Prairie have at least one family worried that the job ignores the real problem of flooding, and could make it worse.
The county plans to spend $787,000 — all federally funded — for a seismic retrofit and erosion-related work on Brush Prairie bridge No. 201. The span carries Northeast 156th Street across Salmon Creek near its intersection with Northeast 102nd Avenue.
The area includes the property of Amy Bice and her family, who have lived there for about 15 years. Bice has watched Salmon Creek routinely flood during that time, its floodway squeezed by the narrow path under the bridge.
The creek rose high enough to spill over the road in 2011 and 2009, she said, and has a long history of high flows in the area.
Bice said the new supports planned as part of the bridge’s rebuild will do nothing to address the creek’s frequent flooding, and may further constrict flows. She’s not convinced by the county’s assertion that the project would result in a “no rise” impact.
“They can probably achieve that on paper,” Bice said. “I do not believe they can achieve that with the flooding that actually occurs.”
As for the erosion work, the county has proposed removing and adding fill around the bridge in a stabilization process known as “scour mitigation.” Bice worries what impact the end result will have upstream of the bridge.
“This is our property,” Bice said. “If it would really fix the flooding, then great.”
The seismic retrofit would cost $402,000, according to the county. The scour mitigation would cost $385,000. The Brush Prairie span is one of eight bridges countywide selected by the Washington State Department of Transportation for replacement funding from the federal government; most of the projects are expected to be constructed next year.
The projects are intended to add to the lifespan of the bridges. Of the county’s 74 vehicle spans, 18 are functionally obsolete, according to the county’s annual bridge report. One bridge is considered structurally deficient.
Those designations resulted from a total of 52 bridge inspections that were conducted in late 2013 and early 2014. The National Bridge Inspection Standards mandate that public agencies inspect and report on their bridges once every two years.
Jean Singer, the county’s capital project manager, said the typical lifespan for the county’s bridges is between 50 and 100 years. With upkeep, they can last longer, however.
The county can realign functionally obsolete bridges to meet modern transportation needs, Singer said, and they don’t pose a danger of collapsing.
This summer, the county will start the work on its first seismic retrofit at the Blair-Zeek Bridge on Northeast Blair Road across the Little Washougal River. Work on the Brush Prairie Bridge will take place next summer.
Of the county’s eight bridge projects, only one, the Fifth Plain Creek Bridge, will build a new bridge at a price tag of $2.3 million.
Most of the county’s bridges are what’s known as “simple spans,” where the superstructure extends from one vertical support to the other. They tend to be the easiest for engineers to repair, Singer said.
A challenge for engineers is that shifting waterways caused by scouring — when streambed material shifts under a bridge — were not considered when the bridges were built.
Since the collapse of the Schoharie Creek Bridge in New York in 1987, there has been significant effort to monitor and mitigate for bridges that are vulnerable to scour, said Carolyn Heniges, the county’s bridge program manager.
But for Bice, there are concerns that information provided by public works is possibly faulty or incomplete.
Bice outlined her concerns in a lengthy letter this month, and in previous emails to public works. She’s also spoken directly with county officials and other neighbors she says recognize the same problem.
Heath Henderson, the county’s public works director, said the Brush Prairie Bridge project was designed to address scour deficiencies and not the concerns about flooding.
“The project will not affect the federally designated floodplain and will comply with applicable Federal Emergency Management Administration regulations,” Henderson said in an email.
Bice said she’s hoping the county can still install a larger culvert or otherwise change its plans to alleviate flooding at the site.
