Pringle Creek Project Restores Waterway and Increases Fish Passage
Otak has recently completed the design and structural and civil engineering work on the Pringle Creek Demolition and Stream Restoration project in Salem, Oregon. The project is just one of several that continue to advance the City’s vision, which has been on-going since the 1980s, to turn its waterfront from previous industrial use to public space and an area for economic redevelopment.
The City of Salem hired Otak to complete design on the project within a short timeframe. Otak relied on many of its skilled employees to complete the required work including Kevin Timmins, PE – Principal; Scott Nettleton, PE – Structural Lead; Greg Mines, PE – Structural Engineering; Nick Cook, EI, PhD – Stream Reconstruction Design; Gary Wolff, PE, D.WRE – Hydraulic Modeling; Scott Banker, RLA, CESCL – Construction Observation; and Mandy Flett – Construction Assistant. Suulutaaq Inc. won the construction bid and performed well as the Prime Contractor on a challenging site.
The site of this project had been home to a mill, most recently a paper mill, for more than 100 years. After the mill closed the City partnered with the owner to have the building removed. Removing the building was fairly straightforward. The challenge was to demolish the building’s substructure that sat within the 100-year floodplain of the Willamette River in the waterway known as Pringle Creek and then reconstruct the creek to a more naturally functioning stream for fish passage.
Sequencing plans were prepared to incrementally remove the building, construct the embankment, and maintain a stable wall configuration during and after construction. A carefully crafted staging plan for demolition and stream reconstruction was required to maintain the existing fish ladder, convey stream flows through the site, and protect the stream from sediment and falling demolition debris.
Otak used ground-penetrating radar to scan the old concrete for the presence of rebar reinforcement and then designed an embankment fill to buttress the remaining wall and, once graded, to provide a location for a future trail connection and space to incorporate urban furnishings and fixtures.
Otak was originally contracted to provide riprap stabilization of Pringle Creek, however, hydraulic conditions made riprap a questionable solution, as the use of riprap was found to require as much effort and expense as reconstructing the stream. The team needed to engineer and construct a natural feature to make it look like it had always been there. A combination of large boulders, trees with root wads intact, riparian plantings, and channel topography were introduced to create habitat complexity and hydraulic diversity to provide fish passage, and access to the remaining 15-square miles of the Pringle Creek Watershed for migratory salmon.
The size and scope of the project necessitated coordination among several firms including
Pacific Habitat Services who was key in obtaining environmental permits, and Geo Design Inc. who assisted with the management of contaminated soils. The prime contractor relied on two key subcontractors; Cascade Shoring and Abiqua Landscape.
While the goal of the project was to remove a run-down and unsafe structure over the stream, the end result was improved water quality, increased fish passage, and a desirable gateway and future multi-use trail connection between downtown Salem and Riverfront Park. Otak looks forward to an opportunity to help complete the associated trail project in the future, and to continue it’s working relationship with the City of Salem.