USING HYDRAULIC CHARACTERISTICS OF SOCKEYE SALMON SPAWNING AREAS IN DESIGNING THE OKANAGAN RIVER RESTORATION PROJECT

Riffles and rapids may be added to uniform channels for a variety of purposes, for example stabilizing mobile bed streams, backflooding perched culverts or restoring preferred fish habitats. The riffles are designed as fish-passable hydraulic structures, often replacing traditional fixed drop structures and low dams. The aquatic habitats created are beyond design equations and rely on mimicking preferences observed in natural streams. The hydraulics of spawning grounds used by sockeye salmon (Oncorhynchus nerka) in the Okanagan River, a tributary of the Columbia River in Canada, were studied to provide guidelines for improving spawning in channelized reaches. The hydraulic characteristics: depth, velocity, and the Froude number were determined at redd sites in natural and channelized reaches. Froude numbers (Fr = 0.315 ± 0.10) were found to be statistically similar between the two hydraulically different reaches suggesting that this flow characteristic was selected for by spawning sockeye salmon. The natural reach contained a wider range of Froude numbers in both years sampled than did the channelized reach. The greater Froude number diversity has the ability to create greater salmon population stability because preferred Froude numbers would subsist regardless of fluctuating discharge levels. Consequently, riffles and spawning ramps with the preferred Froude numbers are being added to a 1 kilometre channelized reach in an ongoing habitat restoration project near Oliver, BC.