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Climate Change Impacts Suggest Snake River
Fish Passage Facilities Need 'Thermal/Hydraulic' Features

by Staff
Columbia Basin Bulletin, January 10, 2014

Modifications that could improve fish passage at Snake River hydro projects such as Lower Granite Dam will be necessary as apparent global warming moves the interior Pacific Northwest toward a future with higher summer temperatures, lower winter snowpack, longer, warmer summers with reduced river discharge, and stressful thermal conditions that stall spawning salmon and add unhealthy stress.

Such projections of climate change "suggest that management of the Columbia-Snake hydrosystem thermal regime will become increasingly important to the recovery and persistence of Snake River salmon and steelhead, particularly late spring and summer runs (e.g., summer chinook salmon, sockeye salmon) and early fall-run populations that currently experience the highest water temperatures," according to a recently published research paper produced by University of Idaho and federal researchers.

"Beyond the Snake River, dams worldwide have reservoirs that layer or stratify and potentially create thermal gradients inside downstream fishways," the researchers say. That stratification at four lower Snake River dams, and lower Granite in particular, can perplex the upward bound fish.

As summers progress, that stratification can play out with relatively cool, inviting water in the tailrace of the dams where fish enter fish ladders, and warmer water at the top of the ladder where the fish are expected to exit.

As that temperature differential from top to bottom increased, "migrants were consistently more likely to move down fish ladders and exit into dam tailraces, resulting in upstream passage delays that ranged from hours to days," according to the report, which includes analysis of data retrieved from radio tags implanted in spring/summer and fall chinook salmon and steelhead migrating up through the system in 2000-2003.

"Fish body temperatures equilibrated to ladder temperatures and often exceeded 20 degrees C, indicating potential negative physiological and fitness effects," the report says. That equilibration means that the fishes' body temperature warmed to match the temperature of the water.

"Collectively, the results suggest that gradients in fishway water temperatures present a migration obstacle to many anadromous migrants. Unfavorable temperature gradients may be common at reservoir-fed fish passage facilities, especially those with seasonal thermal layering or stratification. Understanding and managing thermal heterogeneity at such sites may be important for ensuring efficient upstream passage and minimizing stress for migratory, temperature-sensitive species.

". . . consideration of both thermal and hydraulic features should be integral to new fish passage design."

The paper, "Indirect Effects of Impoundment on Migrating Fish: Temperature Gradients in Fish Ladders Slow Dam Passage by Adult Chinook Salmon and Steelhead," was published in the Dec. 31 edition of the scientific journal PLOS One. It can be found at:

Lead author is Christopher C. Caudill of the University of Idaho's Department of Fish and Wildlife Sciences. Co-authors include Matthew L. Keefer, Tami S. Clabough and George P. Naughton of the UI's Department of Fish and Wildlife Sciences; Brian J. Burke of NOAA Fisheries' Northwest Fisheries Science Center in Seattle and Christopher A. Peery, Idaho Fisheries Resource Office, U.S. Fish and Wildlife Service, Ahsahka, Idaho.

This study was funded by the U.S. Army Corps of Engineers, Walla Walla District, with assistance provided by M. Shutters and K. Zelch. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

According to the research paper "at most run-of-river Columbia and Snake River dams (Washington-Oregon), well-mixed water from dam tailraces is pumped into lower fishway segments, but upper sections of ladders are gravity-fed from seasonally warmer surface water in dam forebays."

"In all four lower Snake River reservoirs, increased water residence times and solar heating cause additional thermal layering, especially in dam forebays. Prevailing upstream summer winds reinforce the layering by further slowing the movement of surface water masses," the research paper says. "Such wind setup events can result in stratification and net transport of warm masses upstream over a deeper water mass moving downstream.

"The strongest stratification has been observed at Lower Granite Dam in summer, where forebay surface waters are often several degrees warmer than relatively well-mixed tailrace water. This pattern repeats at the dams farther downstream, but generally with smaller thermal gradients between the forebay and tailrace," the paper says.

The thermal issues were evident this past summer, when warmer than normal summer temperatures and relatively low flows caused hesitations in both sockeye and fall chinook runs. Both stocks are protected under the Endangered Species Act. A variety of operational actions were taken at the dam by the U.S. Army Corps of Engineers in an attempt to prompt fish movement. But those efforts had limited success.

Related Sites:
"TMT Lessons Learned: Keeping Fish Moving During Hot Times At Lower Granite Fish Ladder" CBB, Dec. 20, 2013
"Warm Weather Has Fall Chinook Passing Over Little Goose Dam Then Stalling At Lower Granite Ladders" CBB, Sept. 6, 2013
"Endangered Adult Sockeye Passing Little Goose Dam Then Hitting Lower Granite's ‘Thermal Barrier

Climate Change Impacts Suggest Snake River Fish Passage Facilities Need 'Thermal/Hydraulic' Features
Columbia Basin Bulletin, January 10, 2014

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