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Installing vertical rebar embeds to support the concrete pools.
The Portland Water Bureau's engineers and construction managers were put to the test this past summer with the implementation of the Alder Creek Fish Passage project, which was the construction of a fish ladder.
Alder Creek, one of the larger tributaries to the middle Sandy River, currently supports steelhead and coho salmon, both of which are threatened species listed under the federal Endangered Species Act. The fish passage project modified an existing waterfall under the Highway 26 Bridge east of Sandy in order to improve passage for adult steelhead during their winter migration to spawning grounds. This project is one of the required fish passage improvement projects for Alder Creek in the Bull Run Water Supply Habitat Conservation Plan (HCP), and was developed by Water Bureau Environmental Compliance Group Manager Steve Kucas.
Concrete wood forms were built in place after rebar was drilled into the basalt bedrock.
The fish ladder involved the construction of three stepped pools designed to meet the swimming and jumping requirements of adult steelhead. The pools were created utilizing existing topography, so the bottom and the upslope sides were carved into the native basalt. The lower sides of the pools are cast-in-place concrete with a vertical slot in the downstream side. The fish ladder concrete was dyed to match the color of the surrounding basalt and the ladder was designed to withstand a 100-year flood event.
Project Manager Tim Collins views the completed fish ladder from the top of the falls.
Construction ingenuity was required to work in a steep, narrow slot under the bridge with a swift flowing creek. Elaborate scaffolding staircases and landings were erected to get workers down the steep banks and safely to the site. The pools were excavated into bedrock by hand and hauled up in buckets from the bridge. The creek was dammed with sandbags, rerouted through a 24-inch pipe and released past the work site.
Tim Collins was the Project Manager, Kevin Larson was the Construction Manager and Rick Aune was the Inspector. Baseline Industrial was the contractor for the project.
The fish ladder is working as designed and is doing well during its first winter. The Environmental Compliance group will be monitoring the river to determine how well the fish ladder operates over time.
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