Design for culvert calls for additional $80,000 in project cost

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The design developed for a new culvert along Percival Creek under Sapp Road calls for an additional $80,753 in the project’s design cost, raising it from $143,000 to $223,753.

Tumwater’s Public Works Committee agreed to recommend the city council for Mayor Debbie Sullivan to sign an amended contract detailing the additional design work to be done by PBS Engineering and Environmental during their September 21 meeting. The contract was added as a consent item which the city council will likely approve at their next meeting.

Due to its slope, the culvert has been identified as a fish passage barrier. Tumwater plans to construct a larger culvert to allow fish to pass through it.

The new culvert features two 11-foot travel lanes on the road above it with a six-foot bike lane and five-foot sidewalks. These features increase the culvert’s impervious area to the extent that it now needs to be taken into account the additional stormwater management requirements.

The area of impervious surfaces proposed in the 60% design is large enough that it triggers the Drainage Design and Erosion Control Manual minimum requirements 1 through 11, which include runoff treatment and flow control facility design,” read the amended contract.

The original contract assumed that such requirements were not needed based on preliminary designs.

According to city administrator John Doan, the additional $80,000 will be covered by stormwater utility reserves. Project consultant Meredith Greer added that they had intended it this way as grants already cover the construction cost.

“For the construction of this project, we've applied for two grants to help cover that cost. One that would cover 85% and the other that would cover the other 15%.  We're really trying to line this up so that grants are covering almost all of the construction costs… which is why we're able to put a little bit more funding into the design work,” Greer said.

The 60% design also calls for retaining walls on either side of the 19-foot box-shaped culvert. Around five large wooden structures will be installed downstream, with 135 feet of the stream to be regraded. The wooden structures aim to replicate natural conditions – specifically when trees fall into creeks, thus providing additional habitat and steam complexity.

“They're really awesome for salmon to be able to hide behind from predators, but also to just take a rest as we have slower moving water there,” Greer said as she explained the benefit of fallen trees on riparian ecosystems.

Greer also gave updates on the overall status of the project. Tumwater is hoping to secure all environmental permits by the end of November. Greer added that PBS Engineering would complete 90% of the design by the end of the year.

Tumwater aims to open bidding for the project by the fall of 2023 and begin construction by the summer of 2024.

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  • sunshine39

    At the rate all these culvert improvements are happening I fear the salmon will become extinct.

    Where's the urgency?

    Saturday, September 24 Report this

  • Kruz81

    Looks like they are improving it for salmon. Read much?

    Monday, September 26 Report this