U.S. Army Corps of Engineers approves a planned major deviation at Truckee dams
CARSON CITY, Nev. – The U.S. Army Corps of Engineers South Pacific Division recently approved a Bureau of Reclamation request to temporarily change operations at Prosser Creek, Stampede, and Boca dams this spring through a planned major deviation from the 1985 Truckee Basin Water Control Manual. The deviation will allow the reservoirs to begin refilling in late-March, almost a month earlier than the 1985 Water Control Manual would allow.
The reservoirs are currently operating below the required flood control levels, and the earlier refill will allow the capture of spring runoff without increasing flood risk based on current conditions. Further, Stampede Reservoir is more likely to remain at a higher elevation for longer under the deviation, with more water flowing through the powerplant, resulting in greater hydropower production.
The 40-year-old Water Control Manual that guides flood control operations in the Truckee Basin prohibits reservoir refill in the spring until snowpack has decreased to a level that some reservoirs do not reach full capacity, even in large water years. In the fall, the manual requires dam operators to evacuate flood space to keep the reservoirs at low levels throughout the winter, even during low water years. This prevents carrying over water storage from wet periods to dry periods to help manage the variability in the basin.
This deviation request resulted from a Reclamation cost-share study designed to evaluate the identified issues. The study identified an approach to improve future basin operations that includes updating the Truckee reservoirs’ guide curves, as well as using Forecast Informed Reservoir Operations to increase operational flexibility. These actions will result in improvements in the water supply, environmental flow, and flood risk management objectives.
The U.S. Army Corps of Engineers has begun the process to formally update the manual, but it will take several years to complete. Planned deviations may occur in the interim to test and evaluate the proposed operational changes.
More information on efforts to update operations at Reclamation’s Truckee Basin reservoirs is available as part of the Truckee Water Management Option Pilot Viability Assessment at https://www.usbr.gov/watersmart/bsp/completed.html.
