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January 27, 2020

Best in state: Gold award
Social, Economic and Sustainable Design

Mead & Hunt

Photo provided by Mead & Hunt
This culvert replacement project in Roslyn had an in-water work window of just one-and-a-half months

Project: Roslyn fish passage and culvert
Client: City of Roslyn

The city of Roslyn’s fish passage and culvert project started primarily as a flood-control project, but new mandates from stakeholders for fish passage ended up driving much of the design and transitioning it into a successful habitat-restoration project.

Mead & Hunt oversaw engineering design and project management of the project, which not only alleviated flooding but also enabled fish passage upstream in Crystal Creek through what was previously a fish barrier.

The South A Street culvert had been identified as one of the highest-priority projects in the city of Roslyn’s Stormwater Comprehensive Plan, and was also an identified project in the Kittitas County Hazard Mitigation Plan. Residents and businesses in Roslyn were tiring of repeated flooding at this location during high-intensity storm events.

A number of challenges arose during the design phase of the project. Extremely poor bearing capacity in the soils required a detailed alternatives analysis to find a constructible option. The team considered six options — from metal free-span bridges to aluminum culverts — before deciding on a solution. Geometrically, the skewed box wall angle of the box culvert sections was a unique design consideration, but necessary due to the stream alignment and space constraints with adjacent utilities.

Low clearance between the stream bed and road grade as well as a tight in-water work window of just one-and-a-half months complicated the project even further.

Numerous stakeholders and review agencies were involved in the project, from city and state agencies to the Confederated Tribes and Bands of the Yakama Nation and the U.S. Army Corps of Engineers.

The completion of the flood-mitigation project not only brings stability to the city’s stormwater infrastructure, reduces flooding and potentially reduces homeowners’ flood insurance premiums in the long run, but it also provides habitat connectivity for fish and aquatic species within the Crystal Creek watershed.


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