16-034 Corps improving fish passage at Lower Granite Dam Two new construction projects expected to increase fish survival as they pass the dam

Published June 2, 2016
POMEROY, Wash. – The Walla Walla District of the U.S. Army Corps of Engineers is improving both adult and juvenile fish passage at Lower Granite Lock and Dam to help endangered salmon and steelhead migrate in the lower Snake River. Two significant new fish passage improvements are in progress:

First, to prepare for potential high water temperatures this summer and help upstream-migrating adult salmon and steelhead pass Lower Granite Dam, the Corps completed installing a permanent adult fish ladder water cooling system in February. This new Adult Fish Ladder Temperature Improvement System was built in response to unusually hot weather the past several years throughout the Columbia-Snake river basin. Hot weather raised temperatures in the “tailwater” just below Lower Granite Dam in summer to more 68 degrees Fahrenheit, which is above acceptable limits. Hotter water promoted development of a “thermal barrier” in the adult fish ladder, hindering upstream migration of adult salmon and steelhead to their spawning grounds. Sockeye salmon were most affected in summer 2015, though the Corps used temporary pumps to cool the fish ladder in 2014 and 2015. This permanent system will cool fish ladder water starting this summer.

Secondly, the Corps is constructing a Juvenile Bypass System (JBS) upgrade including “daylighting” juvenile fish passage by reconfiguring the juvenile transportation channel to a large elevated bypass flume leading to the Juvenile Fish Facility (JFF) just downstream of the dam, plus other related fish bypass improvements. This upgrade is anticipated to increase survival of juvenile fish migrating downstream, and will also increase operational reliability of the bypass system. The Corps previously upgraded its other lower Snake River juvenile bypass systems at three other dams downstream during the past several decades. These improvements contributed to increased juvenile fish survival, which supports the ultimate goal of improved adult fish returns when those juveniles return from the ocean as adults several years later.

“These fish passage improvements are part the Corps’ mission to protect salmon and other endangered fish species as we continue to provide value to the Nation with our dams in the Snake River basin,” said Lt. Col. Timothy Vail, Walla Walla District Commander. “We continue to upgrade our older dam infrastructure as planned and to respond to unusually hot weather conditions as we help fish migrate.” 

More information about each fish passage improvement project, plus downloadable photos, are available on the Walla Walla District website. Adult Fish Ladder Temperature Improvement System information is at  http://www.nww.usace.army.mil/Missions/FishPrograms/LowerGraniteFishLadderTemperatureImprovement.aspx. Juvenile Bypass System Improvements information is at http://www.nww.usace.army.mil/Missions/FishPrograms/LowerGraniteJuvenileBypassSystemImprovements.aspx.  

Background: Adult Fish Ladder Temperature Improvement System
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. 

To build the permanent adult fish ladder 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.” This system also provides cooler water to the adult fish trap, a component of the fish ladder. 

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, plus routing water to the adult fish trap. 

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. 

Beginning in summer 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 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.

See fact sheet at http://www.nww.usace.army.mil/Missions/FishPrograms/LowerGraniteFishLadderTemperatureImprovement.aspx for more details.

Background: Juvenile Bypass System Improvements
As millions of juvenile fish pass over, around or through Lower Granite Dam each year, with an average juvenile survival rate of about 93 to 96 percent passing the dam, Juvenile Bypass System improvements to increase the survival of juveniles migrating downstream are significant. Current construction of the JBS and future Primary Bypass Outfall Pipe are divided into two phases, termed “Phase 1a” and “Phase 1b.” 

Phase 1a construction of an elevated transportation flume started in the fall of 2014 and is expected to be complete by March 2017. Phase 1a construction includes reconfiguring the juvenile fish transportation bypass channel to transition to an elevated flume outside the dam; enlarging the fish collection channel within the dam; enlarging fish passages or “gatewell orifice” openings within the dam; installing new passive integrated transponder (PIT) tag detection to provide fish research and monitoring data, and more.

Phase 1b Primary Bypass Outfall Pipe design is anticipated to be completed mid-2016 and construction completed by March 2017. The bypass outfall design and construction is being managed separate from Phase 1a due to additional time needed for design efforts. This primary bypass outfall pipe will transport juvenile fish from the new elevated transportation flume system to a better release location in the river below the dam. Similar to other bypass outfalls recently constructed by the Corps, this new primary bypass structure will contain various bird deterrent and access walkway structures.

See fact sheet at http://www.nww.usace.army.mil/Missions/FishPrograms/LowerGraniteJuvenileBypassSystemImprovements.aspx for more details.


Release no. 16-034