Pilchuck Dam Removal and River Restoration

Pilchuck River, Washington

To reconnect 37 river miles of upstream habitat and address dwindling salmon stocks, Anchor QEA joined a community of partners to deconstruct the aging and obsolete 15-foot-high concrete Pilchuck Dam.

The Pilchuck Dam Removal and River Restoration project was listed as a priority in the Puget Sound Steelhead Recovery Plan and in the recommendations of the Southern Resident Orca Task Force.

Challenges and Solutions

Located on the Pilchuck River just 45 miles northeast of Seattle, the Pilchuck Dam was an aging and obsolete concrete structure that, along with its associated upstream wooden crib dam, required removal.

To deconstruct the dam without negatively impacting the environment, a thorough analysis of the geomorphology, hydrodynamics, and sediment transport was conducted to assess the upstream and downstream effects of its removal. The outcome of these analyses was that allowing the Pilchuck River to naturally transport the full volume of sediment behind the dam would have minimal disturbance to the surrounding ecosystem. Therefore, full removal of the dam structure while leaving the upstream sediment in place could occur in one summer construction season.

When concern arose regarding potential water quality impacts due to increased pH during the removal process, a rigorous step-by-step method of reducing or eliminating potential impacts went into place. The Pilchuck Dam removal required comprehensive water control plans to isolate and treat high pH water from contacting active concrete demolition activities.

Anchor QEA experts prepared preliminary designs and cost estimates for funding solicitation and support while utilizing site-specific technical evaluations to fill key data gaps.

Project Impact

In summer 2020, Pilchuck Dam and its upstream crib dam were successfully removed. With the dam removal complete and river connectivity restored, it was only a month before the first salmon were spotted.

Anchor QEA provided the following services for the Pilchuck Dam Removal and River Restoration project:

• Conceptual final designs and bid documents
• A channel grading and habitat restoration plan
• Multiphase demolition and water control plan
• Water quality monitoring plan
• Inspection of fish rescue, water quality monitoring, and construction for the duration of the dam removal and restoration