Understanding and Improving Temperature Control at Shasta Dam
For years, dam managers at Shasta Dam have relied on the Temperature Control Device (TCD) to keep the Sacramento River cold enough to support endangered winter-run Chinook salmon. These fish depend on carefully managed water temperatures—especially during spawning and early life stages—when even small increases in temperature can significantly reduce survival.
The TCD was designed to help meet this need by allowing managers to draw water from different depths in Lake Shasta and blend colder and warmer water to achieve target temperatures downstream. However, in practice, managers observed that river temperatures were not always responding as expected, even when the system was operated according to plan. This raised an important question: Why weren’t temperature outcomes matching operational expectations?
To answer this, dam managers partnered with TERC researchers to better understand how the system functions under real-world conditions.
What the Research Revealed
Using a combination of field measurements, temperature monitoring, flow data, and advanced computer modeling, researchers developed a much more detailed picture of how water moves into and through the Temperature Control Device.
The study confirmed that the TCD operates as a complex intake structure. Water enters not only through the intended gate openings but also through internal flow pathways within the device, which can influence the temperature of the released water. These internal dynamics vary with reservoir conditions, gate configurations, and seasonal changes in the lake's temperature structure.
This finding helped explain why observed river temperatures sometimes differed from expectations: the source water contributing to releases was more dynamic and interconnected than previously understood.
Improving How the TCD Is Operated
With this new understanding, dam managers now have better tools to operate the TCD more effectively:
- Incorporating real flow behavior into decision-making
Managers can move beyond relying solely on which gates are open and instead account for how water actually moves through the structure. - Refining seasonal operations
By better understanding how different depths contribute to releases, managers can more strategically shift water withdrawals through the season to conserve cold water. - Improving forecasting and planning
Enhanced monitoring and modeling allow for more accurate predictions of downstream temperatures, especially during challenging drought and warm-weather conditions. - Adapting in real time
Combining field data with models supports a more responsive, science-based approach to managing water temperature year-round.
What This Means for Salmon
This research directly improves the ability to protect winter-run Chinook salmon by helping maintain river temperatures within the narrow range they need to survive and reproduce. More precise temperature control reduces the risk of harmful warming during critical periods, particularly late in the season when cold-water supplies are most limited.
Ultimately, this work enables dam managers to make smarter, more informed decisions about how to use the Temperature Control Device—ensuring that available cold water is used as effectively as possible to support salmon populations now and into the future.
For more information email Alex Forrest @ UC Davis.