River Mill Fish Ladder & Spillway Modifications

Location: Estacada, Oregon
Project Cost: $14.7 million
Completion Date: June 30, 2007
Owner: Portland General Electric
Engineer: Washington Group International

Originally built in 1911, River Mill Dam in Estacada is a major component of Portland General Electric’s Clackamas River Hydroelectric Project. River Mill consists of a dam, powerhouse, fish ladder and spillway. When PGE applied for a new Federal Energy Regulatory Commission license in 2003, however, federal guidelines required a complete removal and replacement of River Mill’s fish passage facility, which were determined to be outdated. The spillway needed to be demolished and a new one built to help improve downstream passage for juvenile fish. The existing fish ladder, a hollow-interior design called an Ambursen structure, also needed to be partially demolished to make room for a new dual-sided fish entrance and a state-of-the-art, 1,000-foot-long fish ladder. The new fish ladder would snake up a right abutment and into an upstream reservoir via an opening cut through the existing dam. The new plan would solve the challenges that stood between PGE and its new license, but it would also require the project team of Natt McDougall Company and the Washington Group International and a list of subcontractors to tap into a full scope of its total industry experience.

One of the first hurdles that needed to be cleared was the problem of getting workers where they needed to be in order to work on the project. Walkways, work decks, catwalks, and stair towers had to be hand-built in order to provide safe access to upper spillway and powerhouse draft tube areas. A lower spillway and a center island area were initially only accessible by a small barge and shore-mounted drum hoist, and a right abutment with an extreme vertical drop had to be surveyed and scaled using a crane and man basket.

Getting materials to all of the work locations also served as an exercise in thinking outside the traditional envelope. A combination of floating barges, cranes, winches and work boats were employed to clear construction debris and bring in new materials for many hard-to-reach locations.

Despite those challenges and other that arose throughout the project, work was completed in a manner that met reasonable budget and time requirements, preserved the scenic aspect of the Clackamas River and protected the historic aspect of River Mill – all while ensuring the future safe passage of fish.

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