U.S. delays Lower Monumental weir work for salmon migration

The Corps of Engineers has postponed until fall the installation of a removable spillway weir at its 810-MW Lower Monumental Dam, to avoid affecting the safety of juvenile salmon migrating downstream.

The weir had been scheduled for installation by April 13, before migration. However, Advanced American Construction Inc., Oregon City, Ore., the general contractor, informed the Corps it was unable to install the weir by that date. The Corps said it would implement traditional spill at the dam, on the lower Snake River near Kahlotus, Wash., to provide for safe fish passage.

In the fall, once the juvenile migration season passes, the weir will be installed, the Corps said. In the meantime, the Corps will monitor progress on construction, delivery, and installation of the weir, being fabricated at Portland Shipyard.

The Corps awarded a $15 million contract in 2006 to Advanced American Construction for work on the weir. Oregon Iron Works, a subcontractor, is manufacturing the structure. Once installed, it will be the Walla Walla District’s third removable spillway weir to improve passage conditions for migrating juvenile salmon and steelhead in the lower Snake River. (HNN 1/9/07)

The Corps’ 810-MW Lower Granite and 603-MW Ice Harbor dams feature the other two removable spillway weirs, considered removable by controlled descent to the bottom of the dam forebay. Testing at Lower Granite and Ice Harbor identified an average 98 percent survival for fish using the weirs to pass the dams.

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