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'Thinking Outside the Channel: Optimal Flow Regimes that Favor Salmon Populations and Energy Value'
Henriette Jager (jagerhi@ornl.gov), Oak Ridge National Laboratory

Two common assumptions are 1) that seasonal flow releases from reservoirs requires compromise between fish and energy producers and 2) that natural flows are best for fish. This study identified exceptions to these rules while optimizing seasonal flows for salmon and energy value in a tributary of the San Joaquin River in California. I developed a quantile recruitment model in which flow influences on salmon were mediated by temperature and prey availability. Cohorts of salmon from nests constructed in the same space-time quantile were tracked by the model until they exited the tributary. One feature of this study was the explicit consideration of the benefits of higher, floodplain-inundating flows on salmon growth, permitting faster rearing and out-migration with the same amount of flow. Using this quantile model, I sought a Pareto-optimal frontier, where the magnitude, timing, and duration of seasonal pulse flows maximized salmon production and the value of energy from hydropower. Solutions that shaped flows to favor salmon highlighted the importance of indirect effects of flow, mediated by temperature and access to productive floodplain habitat during late winter and early spring. However, they deviated from the natural flow regime in this river. Solutions that shaped flows to favor energy value were timed to meet demand during extreme temperatures. Optimal flow regimes were similar to those favoring salmon production in that both called for pulse flows in late spring. However, solutions favoring energy production shifted the second pulse to winter and the magnitude of pulse flows for energy was sensitive to the maximum generation capacity. This analysis revealed areas where economic and salmon objectives were aligned and where they differed.