The U.S. Army Corps of Engineers, Walla Walla District, marked a decade of safe fish passage over Ice Harbor’s spillway July 15, 2015 during a commemorative event to celebrate the tenth anniversary of the installation of a spillway weir at the dam.
Federal and industry officials representing fish-management, hydro-power and navigation in the Pacific Northwest joined Corps leaders, including the Corps’ Deputy Commanding General Maj. Gen. Richard L. Stevens, to observe the spillway weir in operation and get the latest information about the Federal Action Agencies’ efforts to improve ESA-listed fish survival and productivity.
Representatives from the Corps, Bureau of Reclamation, Bonneville Power Administration, Columbia Towboaters Association and Northwest River Partners provided informational presentations and interviews with regional news media who attended the event.
In 2005, the first full production spillway weir was installed at Ice Harbor Dam. The era of surface passage began, revolutionizing fish passage and providing one more tool to improve juvenile fish survival at the dams. Testing at Ice Harbor noted about 98-percent survival for fish passing the dams via the spillway weir.
By 2010, all eight Corps dams on the lower Columbia and lower Snake rivers put surface passage modifications in place for out-migrating juvenile fish, providing an effective and safe route past the dams on their way to the Pacific Ocean. Spillway weirs and smart spill operations benefit juvenile salmon and steelhead by providing safe passage, faster migration, higher in-river survival rates and better water quality.
As the largest fish-conservation initiative in the nation, results are evident by improved fish survival and productivity. Each of the Snake River stocks have shown marked improvements since aggressive efforts to overhaul the Federal Columbia River Power System began in the mid-1990s. Fish runs in the Columbia Basin, including on the Snake River, have seen record returns in recent years. 2014 noted the highest rate of adult fish returning past Bonneville Lock and Dam for chinook, coho and sockeye, and the 12th-highest returns for steelhead, since Bonneville was constructed in 1938.
Background
Most Columbia River Basin juvenile anadromous salmon and steelhead tend to stay in the upper 10 to 20 feet of the water column as they migrate downstream to the ocean. Because of the dams’ original configurations, juvenile fish passage routes at the Corps’ lower Columbia and Snake river dams caused the juvenile fish to dive to depths of 50 to 60 feet to find their way over the spillways. In the late-1990s, engineers and biologists collaboratively developed new technologies that provide a surface-oriented, less stressful, fish-passage route over the spillways. As of 2009, all mainstem lower Snake and lower Columbia rivers dams are equipped with a surface passage route.
There are three different types of surface bypass structures are currently used at all eight Corps dams on the lower Columbia and lower Snake rivers – removable spillway weirs, second-generation spillway weirs and surface bypass channels.
Removable Spillway Weirs (RSWs) were installed at Lower Granite, Lower Monumental and Ice Harbor dams on the lower Snake River. The RSW is attached to the upstream side of the dam and fitted into a spillbay, raising the spillway opening to the salmon’s preferred depth. Juvenile salmon and steelhead are safely passed over a raised spillway crest, similar to a waterslide, more efficiently than with conventional spill while reducing migration delays at the dam.
The first RSW was installed at Lower Granite Dam in 2001. The Corps installed an RSW at Ice Harbor Dam in 2005 and another at Lower Monumental Dam during 2008. Testing at Lower Granite and Ice Harbor noted a range of survival rates between 95-100 percent.
Second-Generation Spillway Weirs are based on design elements of an RSW to create a surface-oriented passage route over the spillway. Fitted into a spillway gate slot, the structure creates an elevated spillway crest, allowing water about 10-15 feet in depth to flow over the spillway. It can be fitted into any one of multiple spillway bays at a particular dam. It is shipped in sections and assembled during installation. The structure has a low relative cost, is easier to implement and allows for flexible biological testing. These spillway weirs do not have the pump-operated ballast system used in RSWs to lower the structure during flood operations, but can be removed using the dam’s gantry crane to accommodate increased spill operations.
These spillway weirs were installed in 2007 at McNary Dam and in 2008 at John Day Dam on the Columbia River. Another was installed at Little Goose Dam on the Snake River in 2009.
Surface Bypass Channels are used at two dams on the lower Columbia River to safely pass outmigrating juvenile fish.
Bonneville Dam’s corner collector, completed in 2004, provides effective surface bypass – the ice and trash chute at the second powerhouse was modified for safer passage, and a 2,800-foot-long transport channel and 500-foot-long outfall channel were constructed to guide fish around the dam. Tests indicate a nearly 100 percent survival rate for spring Chinook, steelhead and fall Chinook through the Comer Collector, and a 94 -99 percent survival rate, depending on the species, through all passage routes combined at this dam. The ice and trash sluiceway at The Dalles Dam is also used by outmigrating fish as a surface bypass route with similar survival rates. Additionally, an extended spillwall was construction, designed to move juvenile fish more quickly and safely downstream once they passed through the spillway with a two to four percent survival improvement.
For more information about federal fish recovery efforts in the region, visit www.salmonrecovery.gov