Drift Creek cutthroat trout rearing capacity analysis

The purpose of this study was twofold: First, we aimed to assess baseline conditions for cutthroat trout rearing capacity in a reach of Drift Creek, below the proposed dam. Second, we aimed to assess potential changes in rearing capacity that would result from alternative reservoir management scenarios.

Our approach included environmental sampling and a modeling effort that estimated cutthroat trout rearing capacity within the study reach. Our survey measurements including an assessment of in-stream habitat, including stream channel geometry, flow, and water temperature. We collected baseline condition measurements for seven habitat units on three dates, which represented a range of flow and habitat conditions that approximate those anticipated to result from the alternative reservoir management strategies. Next, we combined these environmental data with modeled stream temperatures from a previous effort to generate estimates of rearing capacity associated with the reservoir management strategies.

Briefly, we found that substantial rearing habitat exists below the proposed dam, but this habitat is strongly limited by temperature. The impacts of reservoir management on downstream rearing habitat are generally favorable, although there are considerable differences among the alternative options. In general, it appears that rearing capacity associated with the management strategies involving piped delivery of water are less favorable than rearing capacity associated with the management strategies involving in-stream delivery of water.