ANALYSES OF FLOW MODIFICATION ON WATER-QUALITY IN NECHAKO RIVER

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 degrees 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 degrees C would be required to meet the downstream water temperature objectives.