Swift Spillway Bulkheads

The Swift Dam spillway was not designed with the need to maintain water levels to repair or replace the spillway gates. To facilitate the upgrade of the spillway gates and maintain minimum water levels, PacifiCorp made the decision to add stoplogs upstream of the spillway gates.

As the prime contractor, we designed and fabricated stoplogs (bulkheads) that integrated into the existing structure. Each gate required 15 52-foot-wide stoplogs weighing 20,000 to 35,000 pounds each to seal the spillway. The onsite modifications to the existing spillway structure included cutting slots in the side of the spillway for the stoplogs to bear, modifications to the bridge over the spillway to lower the stoplogs through, and an offset installation method due to the geometry of the spillway walls and the bridge.

We partnerted with Morrison-Maierle as our structural designer and Thompson Metal Fab as our fabricator. This partnership was instrumental during the design and fabrication phase of the project to ensure all project constraints were met and the stoplog installation and removal procedure was optimized.

Project challenges included the design of the bottom stoplog to seal on a radiused ogee on a curve, designing an offset stoplog slot on the inner walls of the spillway bays to accommodate lowering the stoplogs down past the bridge structure and then rotating them parallel with the spillway walls to lower into their final location, and managing temporary cofferdams due to fluctuating inflows during construction.