A Scientific Paradigm for Shaping Seasonal Flows to Favor Salmon and Energy

The Natural Flow (NF) paradigm asserts that a natural flow regime is best for aquatic communities because populations evolved to deal with historical conditions.  By emphasizing the importance of flow variability, the NF paradigm shifted the emphasis from moderate, stable flow regimes and within-channel habitat-flow relationships typically explored under the in-stream flow (IFIM) paradigm to more dynamic flow regimes and habitats.  The NF paradigm is a useful management tool because it provides a shortcut for designing flows based on statistical assessment of unimpaired historical conditions.  As scientists, however, we seek to understand why different aspects of flow-timing and periodicity are important to aquatic communities.  In this study, I developed a quantile recruitment model for fall Chinook salmon that represented benefits of floodplain inundation on salmon bioenergetics and flow-mediated temperature effects on survival.  Using this model, I optimized seasonal pulse flows to maximize salmon production and minimize spill (flow releases not used to generate hydropower).  Results demonstrate the ability to quantify benefits of alternative flow regimes for salmon, including the value of extreme flows.  Simulated results also highlighted the importance of indirect effects of flow, which were mediated by temperature and access to productive floodplain habitat.