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.