Journal of Energy Engineering

In 1987 the Government of Canada, the Province of British Columbia, and Alcan Aluminium Ltd. entered into a tripartite agreement establishing a program of measures to conserve chinook ( Oncorhynchus tshawytscha ) and sockeye ( Oncorhynchus nerka ) salmon stocks in the Nechako River. Large-scale applications of habitat measures are planned to manage the risks caused to chinook salmon by potential reductions in habitat quality associated with the reduction of flows. The reduction of flows result from the planned diversion of an additional portion of the upper Nechako River drainage. Experimental placements of debris structures and channel modifications were conducted from 1988 to 1993. Juvenile chinook salmon highly colonized debris structures, particularly the sweepers and rail-debris catchers installed in 1991, and fry density was similar to sparse natural debris cover. Channel modifications, point bars, and a side channel were durable, but were not as well utilized by young chinook. Physical assessment indicated that durability was medium to high where debris catchers and bundles withstood peak flows of 250–283 m ³ /s.

Alcan Smelters & Chemicals Ltd. initiated construction of the final phase of the Kemano Completion Project in north-central British Columbia to divert additional water from the Nechako Reservoir to the existing powerhouse. The Nechako Reservoir was created by the construction of the Kenney Dam in Nechako Canyon, a natural barrier to salmon migration. The Nechako River downstream of Nechako Canyon supports important runs of sockeye and chinook salmon. This additional diversion of Nechako River flow creates the potential of high water temperatures and increased thermal stress to migrating sockeye salmon enroute to their spawning grounds in Nechako River tributaries. To achieve specific downstream water temperature objectives during sockeye salmon migration each summer, a two-level outlet facility adjacent to Kenney Dam is to be constructed to release cooling water at 10°C to the Nechako River. Results of mathematical modelling of Nechako River water temperatures show that, based on specified design criteria, a maximum Kenney Dam release of 167 m ³ /s at 10°C would be required to meet the downstream water temperature objectives.

Utility companies release water to mitigate the effects of hydroelectric projects on fish habitats. Utility companies, government agencies, and research communities in Canada, the United States, Europe, New Zealand, and Australia were surveyed as part of a Canadian Electrical Association study to evaluate the effectiveness of water release as a mitigation. Respondents identified only 28 projects in which water was released specifically to protect fish habitats. Fewer than half of these projects (12) were judged as being effective. Six case histories with preimpact assessment and postimpact monitoring were reviewed. In four cases fish habitat or fish populations or both were maintained; in two cases they were not. The effectiveness of water release differed among rivers and fish species, and was greatest when designed to meet the habitat requirements of each life-history stage. A review of the literature did not support the theory that a particular fraction of the mean annual flow provides the best fish habitat. Although smaller changes in the flow regime had smaller effects, increasing minimum flows above those historically observed did not necessarily increase fish production.

Salmon populations in the Columbia River Basin have declined, and several species are now protected under the Endangered Species Act. Many factors have contributed to the decline, including overharvest, loss of habitat, degradation of water quality, and construction of dams. Many measures have been implemented to reduce the impact of the dams, but additional measures are being considered. Lowering water-surface elevations behind four lower Snake River dams has been proposed as a measure to improve juvenile salmonid survival. The Corps of Engineers has determined preliminary costs, schedules, and required modifications for several drawdown alternatives. Initial estimates of the ability of this type of operation to improve salmonid survival are controversial.