Lower Monumental Dam JBS Outfall Relocation

Owner: US Army Corps of Engineers - Walla Walla District

Kahlotus, WA
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October 2011 - April 2012
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Project Details

The Lower Monumental Dam Juvenile Bypass System Outfall Pipe Relocation was a fast paced project to remove and replace an existing juvenile bypass system outfall pipe. The project was 6 months from notice to proceed until project completion and included the installation of 3,000 feet of new outfall pipeline, with 500 feet placed in the Snake River.

The outfall portion of the project included the installation of 8 each, 60-inch diameter drill shafts placed in the river. AAC constructed a special barge to facilitate the over water drilling. Special anchoring devices were developed to hold both the barge and drilling casing in place against the fast moving current.

The upland work included 2,000 feet of buried-on-grade HDPE pipe. Sections of the pipe were placed 15 feet below final grade, a large amount of earthwork was required to facilitate the installation. The pipe conveys live salmon smolt, so grade and internal smoothness of the finished HDPE pipe were critical. 

Project Highlights

  • Installed 3,000 feet of new outfall pipe, 500 feet over water
  • Installed 8 each, 60-inch diameter drilled shafts up to 90 feet deep
  • Installed 2 each, 15-foot deep cast-in-place vaults for pipeline access
  • Installed bird deterrent sprinkler system
  • Mechanical and electrical upgrades at existing juvenile fish facility
  • Landscaping and site restoration

Project Photos