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Removable Spillway Weirs, Snake River Dams

The purpose of a removable spillway weir (RSW) is to pass juvenile salmon and steelhead downstream over a "raised" spillway crest, similar to a waterfall. This new passage system is a more efficient and less stressful passage route for the juvenile fish. The weir is installed in an existing dam spillway and must be removable to return the spillway to full flow capacity in the event of severe flood conditions.


The RSW´s themselves are 2.5 million pound hollow steel structures that are pinned underwater at the base of the dam. To remove the weir, the buoyancy of the structure is changed pneumatically such that the large structure rotates safely away from the dam to a final position resting on the river floor.

Lund Engineering, working with Jacobs Civil for the Army Corps of Engineers, designed the pneumatic and electrical controls for this project as well as the seals, above water attachment points and the underwater hinges. Lund Engineering was involved in the initial concept, design, construction and initial operation phases of the project. The initial RSW at Lower Granite Dam won the 2003 Grand Conceptor Award from the American Council of Engineering Companies in national competition. RSW’s have since been added to Ice Harbor Dam (2005) and Lower Monumental Dam (2008).