River Mill Hydroelectric Project – Trash Rack Replacement

Prime Contractor: Advanced American Construction
Owner: Portland General Electric
Location: Estacada, OR | January 2025 – October 2025

Advanced American Construction (AAC) was contracted by Portland General Electric (PGE) to perform a full in-kind replacement of the trash racks and support structures serving four hydroelectric generating units at the historic River Mill Dam. Commissioned in 1911, the facility is one of four dams on the Clackamas River supplying power to the Portland metropolitan area.

AAC’s scope included demolition, fabrication, and installation of a new galvanized steel trash rack structure measuring approximately 37 feet tall by 119 feet long. Nearly 75 percent of the work was performed underwater by divers, requiring specialized marine construction techniques to maintain safety, quality, and uninterrupted power generation.

All in-water work was limited to a strict 45-day construction window to avoid impacts to hydroelectric operations. To meet this schedule, AAC developed a fully marine-based construction plan, utilizing modular floats to assemble a 50-foot by 90-foot crane barge. This eliminated the need for cofferdams or temporary work bridges, minimized sediment disturbance, and allowed crews to work continuously from the water.

Prior to mobilization, AAC completed a full-scale mockup of the trash rack at its facility to verify fit-up, resolve fabrication issues, and reduce risk during installation. The structure was then disassembled into larger modular sections for rapid onsite reassembly. Once construction began, AAC coordinated dredging and debris removal before its in-house dive team completed underwater demolition of the existing trash rack.

The new structure was preassembled on the barge in four modular sections, each weighing approximately 30,000 pounds, allowing most bolting and inspection to be completed in dry conditions. Each section was then lifted, tilted, and installed underwater with diver assistance. Final installation was completed in just one week.