Tahoe, Donner Lake levels: A successful water year
This year has shown immense promise for both Tahoe and Donner. Lake Tahoe’s current elevation is 6227.8 feet above sea level, just shy of the maximum legal limit of 6,229.10. With a natural rim at 6,223.00 feet above sea level, this allows for 6.1 feet of reservoir storage from the natural rim to the top of the dam in Tahoe City.
While it’s encouraging that the lake has recovered from being below the natural rim in December, Heather M. Segale, Education and Outreach Director at the UC Davis Tahoe Environmental Research Center, notes that higher water levels, devastatingly enough, lead to reduced beach areas. Visit Tahoe.ucdavis.edu for hours and reservation/ticketing.
The lake level fluctuates annually, rising from high stream, groundwater, and precipitation inputs, and falling due to evaporation, withdrawals, groundwater outflows, and outflow via the Truckee River at Tahoe City. The Lake Tahoe Dam releases approximately 70 cubic feet per second.
Each year, approximately 40 inches of water evaporates from the surface, accounting for roughly 55% of the total reservoir portion of the lake.
“More water goes into the atmosphere than we release,” Lake Tahoe’s water master Chad Blanchard said.
During summer, Lake Tahoe absorbs heat energy. When the air temperature is notably lower than the water temperature, substantial evaporation events occur, particularly during cold fronts. Some of the most significant evaporation incidents have been observed in October. For instance, when fog blankets the lake, it signifies water vapor – or heat energy – being released back into the atmosphere. Essentially, the cooler air temperature extracts heat, carrying water vapor with it.
According to Laura Patten, senior policy analyst at the League to Save Lake Tahoe, elevated water levels and cooler temperatures result in fewer algal blooms. In drought years, when the lake is at lower depths and temperatures are higher, the algae can transform into harmful blooms, posing a threat to both pets and humans. The most severe drought in Blanchard’s 124-year records occurred in 1992, with the lake level dropping two and three-quarters feet below the rim. The algal blooms must have been having a field day.
To contribute to the well-being of Lake Tahoe, you can utilize the Citizen Science Lake Tahoe app provided by Keep Tahoe Blue. This app allows citizens to share their observations about the lake, helping to monitor its condition.
So what about Donner? Kara Steeland, Senior Hydrologist for the Truckee Meadows Water Authority, a not-for-profit, community-owned water utility responsible for the ownership and operation of the Donner Lake Dam, says strict monitoring is in place. The dam’s gates are deliberately kept slightly ajar to accommodate the needs of fish and wildlife. Donner Lake is maintained at 5,932 feet as a precaution for drought emergencies, with a maximum fill elevation of 5,935.8 feet. Presently, the lake stands at 5,935.05 feet. During autumn, Donner Lake levels typically decrease due to the controlled release of water into the Truckee River, a measure taken to mitigate potential flood risks.
October 1 signals the commencement of the new water year, and experts are unanimous in their assessment that this year’s water patterns remain entirely uncertain. It’s impossible to determine whether it will ultimately be the driest or wettest year on record.
Zoe Meyer is a reporter for the Sierra Sun, a sister publication for Tahoe Daily Tribune. She can be reached at email@example.com.
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