Evaluating Patterns of Juvenile Chinook Salmon Out‐Migration During Pulse Flow Events in California's Sacramento River to Inform Operations of a Newly Proposed Water Infrastructure Project

Large‐scale water infrastructure projects (i.e., dams and water conveyance structures) are necessary for human development but often come at the expense of native fish species. A new water infrastructure project has been proposed in California's Sacramento River (a tributary of the San Francisco Estuary) which has the potential to affect threatened and endangered Chinook Salmon ( Oncorhynchus tshawytscha ) populations by exporting water during juvenile out‐migration, thereby, exposing juvenile salmon to an increased risk of impacts associated with intake structures. We use a Bayesian mixed effects hurdle model to evaluate whether out‐migrating juvenile Chinook Salmon catch at monitoring sites near the proposed location of the Delta Conveyance Project intakes differs on the ascending or descending limb of pulse flow events to inform future water infrastructure practices. We determined that Chinook Salmon catch increases with proximity to peak flow (i.e., increases throughout the ascending limb of the hydrograph and decreases throughout the descending limb of the hydrograph) with significantly higher catch in the descending limb relative to the ascending limb. Our results indicate increasing water exports during any period of pulse flow events, particularly during the descending limb, will increase risks to Chinook Salmon and highlight the need to protect pulse flow events to maximize species and ecosystem protections.