New system expected to eliminate a thermal barrier to migrating lower Snake River adult salmon and steelhead
POMEROY, Wash. – 2015 was the hottest year on record, and fish perished in rivers throughout the West, in reaches with and without dams due to elevated water temperatures.
The unusually hot weather last summer extended throughout the Columbia-Snake river basin and raised temperatures in the tailwater just below Lower Granite dam to above 68 degrees Fahrenheit and promoted development of a thermal barrier to adult salmon and steelhead (salmonids) migrating upstream to their spawning grounds.
To prepare for potential high water temperatures this summer and help migrating salmon and steelhead pass Lower Granite Dam, biologists and engineers from the U.S. Army Corps of Engineers’ Walla Walla District completed installing a permanent adult fish ladder water cooling system in February, which is expected to help fish migrate up the ladder and past the dam. This system also provides cooler water to the adult fish trap, a component of the fish ladder.
To build the permanent cooling system, the Corps constructed two permanent “intake chimneys,” which are large vertical structures bolted to the upstream face of the dam—a “supplemental water intake chimney” and a “pump intake extension chimney.”
Seasonal cool water releases or “flow augmentation” from Dworshak Dam’s large reservoir on the North Fork of the Clearwater River are used to cool the lower Snake River to benefit fish. This cooler water stratifies or settles in the lower elevations of Lower Granite reservoir. To access this cooler water, both chimneys draw cooler water from about 70 feet down in the Lower Granite Dam “forebay,” the water in the reservoir just upstream of the dam.
The supplemental water intake chimney provides cooler water to the fish ladder at “Diffuser 14” starting about 150 feet downstream from the top of the ladder. Diffuser 14 is located below the fish ladder control section and is meant to supply auxiliary water as needed to keep the ladder within acceptable passage criteria. The piping that feeds Diffuser 14 also routes water to the adult fish trap, where returning adults are captured for research or transport to fish hatcheries.
The pump intake extension chimney provides water to the upstream end of the fish ladder by spraying cooler water in a circular pattern to cool both the immediate forebay area at the upstream end of the fish ladder, plus the fish ladder itself. This chimney extended previously existing pump infrastructure to access cooler water deeper in the reservoir.
Prior to this year’s permanent system installation, in 2014 and 2015 the Corps initiated temporary water cooling measures. The Corps used temporary pumps during the summer months to bring cooler flow augmentation water up from about 60 feet deep in the Lower Granite forebay to provide cooler water to both the fish ladder and the adult trap.
Background
As part of the construction of four dams on the lower Snake River between the 1950s and 1980s, the U.S. Army Corps of Engineers (Corps) built adult fish ladders to allow passage of upstream-migrating adult salmon and steelhead (salmonids) on their way to their natal spawning areas. Since construction, the Corps has made both facility and operational improvements to assist adult salmon and steelhead migration as needed.
Beginning in summer of 2013, longer-duration high water temperatures began to occur in Columbia-Snake basin river reaches with and without dams due to unusually hot weather. At the Lower Granite Lock and Dam adult fish ladder, warmer water temperatures began to form a “thermal barrier” to upstream migrating salmon and steelhead, slowing and/or stopping adult fish migrating upstream to their natal spawning grounds. Salmon and steelhead are coldwater fish species and therefore prefer cooler water. Sockeye salmon are most susceptible to warmer water temperatures due to the timing of their upstream migration.
In 2015, a total of 510,705 sockeye that originated in numerous watersheds passed Bonneville Dam on the lower Columbia River. Snake River-born sockeye comprised about 4,069 of the more-than-510,000 sockeye run, or less than one percent, as confirmed by Passive Integrated Transponder (PIT) tag analysis.
By the time the survivors of those initial 4,069 Snake River sockeye reached Ice Harbor Dam, the first dam encountered on the lower Snake River, 74.1 percent had perished in the lower Columbia River, and their numbers were reduced to 1,052 Snake River sockeye to migrate up the Snake River. Survivors of those 1,052 Snake River sockeye reaching Lower Granite Dam totaled 440, or 41.8 percent of the Snake River sockeye first counted at Ice Harbor Dam.
More information about the new permanent fish ladder water cooling system to help migrating adult fish is available on the district website at http://www.nww.usace.army.mil/Missions/LowerSnakeRiverDams.aspx.
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U.S. ARMY CORPS OF ENGINEERS – WALLA WALLA DISTRICT
509-527-7020 cenww-pa@usace.army.mil www.nww.usace.army.mil