Adult Salmon Passage (Tech Recommend 9)

Problem Statement

The construction and operation of mainstem hydroelectric projects has impaired adult salmon migrations in the Columbia River Basin. Direct and indirect adult passage losses range from 5 to 10% per project (Gibson et al. 1979; Northwest Power Planning Council 1986, 1989; Kacyzinski and Palmisano 1992). Cumulative impacts of multiple hydroelectric projects on adult salmon result from changes in water temperature conditions altered by impoundment of the Columbia and Snake rivers and the physical barriers to upstream migration at each dam. A minimum estimate of the cumulative losses of fall chinook adult salmon due to passage through eight hydroelectric projects is 39% (NMFS 1995). State and tribal fishery managers estimate that the loss was approximately 50% on average from 1988 to 1993.

Water temperature: Columbia and Snake river mainstem temperatures are detrimental to adult migrants. Impoundments have altered the water temperature conditions of the mainstem Snake and Columbia rivers (Jaske and Goebel 1967). Mainstem water temperatures mainstem often exceed state water quality standards. Water temperatures in the Columbia River often exceed 21°C during August (Columbia River Water Management Group Reports 1975-1994). Water temperatures in the Snake River can exceed 24°C (Karr et al. 1992). These levels equal or exceed lethal temperatures for Columbia River steelhead and chinook stocks (McCullough 1995). High water temperatures often lead to delay in migration.

Fishways and attraction flows: Adult fishways are not operated for maximum effectiveness for adult salmon passage much of the time (Beck et al. 1992; Basham 1993-4). Previous adult passage studies (Turner et al. 1983; Bjornn & Peery 1992) documented a need for additional fish ladders at Lower Granite and Little Goose dams and for additional attraction water at fishways at all projects. This need is particularly evident during average to high runoff years, when water volumes passed through powerhouses and spillways are many times more than those from ladder and powerhouse entrances. Because fishway attraction flows are insufficient, adults are delayed in collection channels and dam tailraces. Adult salmon often “fall out” from ladder and powerhouse entrances, especially during high flows (Stuehrenberg et al. 1994). Attraction flows, which are generated by electric pumps dependent on turbine power production and conveyance systems, are at risk in the event of system failure. Large numbers of shad also impede salmon passage through adult fishways.

Fish Counts: The majority of adult salmon are counted at dams by real-time human observations, which are prone to errors. The current objective of the Corps of Engineers is to count only 80% of the adult run, with the majority of counts occurring during daytime hours. This does not account for stocks such as the listed Snake River sockeye, which often pass in significant numbers at night (Hatch et al. 1993).


Water temperature: Reducing water temperatures in the mainstem during adult salmon migrations will improve salmon survival to completion of spawning. Snake River water temperatures can be lowered substantially by releasing cool water from Dworshak Reservoir (Karr et al. 1992). Releases during September 1992 stimulated passage of adult fall chinook over Lower Granite Dam; conversely, upstream migration slowed substantially when augmentation flows ended (Heinith 1994). This finding corroborated the work of Stabler (1981) and Stabler et al. (1976).

Fishways and attraction flows: Fishway modification and attraction flow measures will contribute substantially to timely passage through dams, adequate escapement, minimum prespawning mortality, and adult spawning success.

Fish Counts: By accounting for adult passage losses through more accurate dam and spawning ground counts, the effectiveness of the measures in this plan may be evaluated through a comprehensive monitoring and evaluation program.

Recommended Actions/Tests

Water temperature: Provide at least 400 kaf of 1000 kaf of Dworshak storage for use during July, August, and September to provide cool water flow augmentation for adult Snake River fall chinook and steelhead. Continue monitoring the effects of cool water releases, development of the COLTEMP model (Karr et al. 1992), and analyzing the correlation between cool water flow augmentation and reductions in migration time, interdam losses, and increases in spawning success.

Fishways and attraction flows: Correct operations of all adult fishways so that they conform to 1994 Detailed Fishery Operating Plan criteria. Provide funding through the Corps and PUD’s to the tribes and fishery agencies for frequent, independent inspection and monitoring of adult fishways.

The Corps and the Mid-Columbia PUDs, with fishery agency and tribal consultation and approval, finish ongoing structural analyses of all mainstem fishways and take corrective actions, including:

  • Improve extant fishway attraction flows, install additional pumps, gravity-flow systems, automated systems, install additional ladders and modify ladder exits to reduce occurrence of adult fallback;
  • Identify and implement structural remedies to reduce the incidence of adult shad in fishways;
  • Evaluate and implement new ladder designs including modifications to weirs, baffles and pools. Emphasize designs that integrate fish swimming and leaping abilities with fluid mechanics and designs that are based on fish responses rather than stimuli, as recommended by Orsborn (1987); and
  • Implement hydraulic evaluations of all fishways, make operational and structural corrections, and combine these evaluations with limited radio-telemetry studies that can provide focus on specific problem areas.

Fish Counts: Employ more accurate and precise counting methods, such as video counting, as well as 24-hour counting at each dam and selected tributaries during the entire upstream migration of listed species.

Expected Results

These measures should increase the numbers of adult salmon successfully completing their upstream migration and reduce delay through the mainstem hydroelectric projects. The measures should also decrease pre-spawning mortality, contribute to increased spawning distribution with appropriate timing and increase spawner success.

Institutional/Decision Structure

The success of these measures depends on the cooperation of the Corps of Engineers, operators of non-federal dams, and tribal, state, and federal fishery managers. Implementation of institutional recommendations related to mainstem passage research and dispute resolution processes is essential for successful implementation of this proposal.


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