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- Title
Discharge‐Mediated Temperature Management in a Large, Regulated River, With Implications for Management of Endangered Fish.
- Authors
Michel, C. J.; Daniels, M. E.; Danner, E. M.
- Abstract
For large, regulated rivers, operators can impact abiotic conditions for the benefit of the ecosystem, primarily by controlling the volume of discharge from upstream reservoirs. Understanding the decision space around discharge is necessary for evaluating tradeoffs between environmental and other objectives. As a result of climate change, warming water temperatures are increasingly becoming a concern for thermally‐sensitive fauna. In California's largest river, the Sacramento, extinction risk of salmon populations is linked to high water temperatures. Yet, little is known about how much water temperature in lower reaches can be affected by reservoir discharge operations, and the potential benefits to salmon. We used a process‐based water temperature model to estimate the ability of reservoir discharge to mediate river temperature heating processes impacting downstream locations (discharge‐mediated temperature management). To bound this analysis, we used historical forcings over a recent 29‐year span. Results indicate reservoir discharge increases of up to 340 cms over the historical record could have decreased water temperature in the lower reaches by up to 3.6°C. Salmon require water below 20°C during most stages of their lifecycle, and we found that normative water operations could ensure 20°C was rarely exceeded for two potential management seasons, in late‐spring and early‐fall. These periods coincide with important rearing and migratory periods for salmon, during which they frequently experience excessive temperatures under the management status‐quo. This analysis provides stakeholders tools to manage conditions for native fauna in the face of a warming climate, and a framework for developing similar tools in other large, regulated rivers. Plain Language Summary: High river water temperatures have long been known to have lethal effects on juvenile and adult salmon in California's Sacramento River. While water temperatures are managed in the upper 30 km for winter‐run Chinook salmon eggs, no effort is made to manage water temperatures in the remaining 450 km of the Sacramento River. We use a water temperature model to estimate water temperatures as a result of hypothetical river flow simulations to demonstrate that reservoir discharge management can effectively reduce water temperatures throughout the non‐tidal portions of the Sacramento River during key times of the year for migrating salmon. We suggest, and give examples for how, discharge‐mediated temperature management can be used as a tool to mitigate against excessively warm temperatures in the Sacramento River. Key Points: Discharge‐mediated temperature management can be used as a tool to mitigate against excessively warm temperatures in the Sacramento River
- Subjects
CALIFORNIA; RARE fishes; CHINOOK salmon; FISHERY management; WATER temperature; GLOBAL warming; LOW temperatures; STREAMFLOW
- Publication
Water Resources Research, 2023, Vol 59, Issue 9, p1
- ISSN
0043-1397
- Publication type
Article
- DOI
10.1029/2023WR035077