Lower Monumental Dam Removable Spillway Weir

Prime Contractor: Advanced American Construction
Owner: US Army Corps of Engineers

Kahlotus, WA
June 2006 - March 2008
« Previous ProjectNext Project »Back to Projects

Project Details

In an effort to find safer, less stressful passage routes for juvenile salmon and steelhead as they pass through the Columbia and Snake Rivers, the U.S. Army Corps of Engineers & AAC collaborated to construct a Removable Spillway Weir (RSW) designed to attach to the Lower Monumental Dam Spillway #8.

One of only three in the world, the Removable Spillway Weir (RSW) consisted of a 2 million pound, 120 feet high, 80 feet wide and 70 feet deep, high-performance coated structure delivered and attached to the Lower Monumental Dam Spillway #8. Construction included 500 each undercut anchors installed underwater; 60 rock bolts; 16 each rock anchors that were 53-feet in length and installed in 120 feet of water; mechanical building; and a complex ballasting and anchoring system to install the RSW with significant mechanical and electrical work.

AAC’s dive crews were also used to install hinge frame components; underwater concrete placement; seismic restraint bracket installation; RSW seal and bearing pad installation; underwater mechanical piping installation; and deployment and installation of the RSW itself. 

Project Highlights

  • 2 million pounds of structural steel fabrication for floating structure.
  • Underwater cast in place concrete placement.
  • Over 800 underwater dives to depths of 120 feet to support installation.
  • 500 undercut anchors installed underwater.
  • 16 each, 53-foot long rock anchors were installed in 120-feet of water.
  • Highly technical ballasting and anchoring of the RSW.
  • Installed controls & control room.

Project Photos


  • 2009 Awards

    • Award
      AGC/AON 2009 Build America Award
      AGC/AON 2009 Build America Award
      AAC's Lower Monumental Dam Removable Spillway Weir won the 2009 Aon Build America Award in the Federal and Heavy New construction category.  The Build America awards recognize AGC member companies who build the country's most impressive construction projects in transportation, utility infrastructure and federal and heavy divisions.  

      View PDF

Stay Informed / Subscribe to our newsletter for the latest news, event invitations, and more!