Lake Tahoe likely to fall below natural rim by mid-October
TRUCKEE, Calif. — Chief Deputy Water Master Dave Wathen provided an update on the state of the region’s water supplies during this week’s First Tuesday Breakfast Club forum.
The amount of water in Lake Tahoe will likely drop below the natural rim sometime in mid October, according to Wathen. The lake’s elevation on Thursday was 6,224.01, which is similar to this time last year before a historic amount of precipitation fell in October. The lake’s natural rim elevation is 6,223 feet.
A record 9.86 inches of precipitation, most of which was rain, was recorded in Tahoe City last October. The region was then hit with a December that was 226% of the average amount of precipitation with Tahoe City recording 12.69 inches. April brought another above average month with 4.36 inches of precipitation.
“Although it looks like we had a really average year for precipitation the way it came and when it came really impacted our runoff,” said Wathen. “We didn’t come close to seeing an average runoff. It was well below average.”
Wathen’s department is responsible for managing and operating the Truckee River and federal reservoirs in the system. And while a new Truckee River Operating Agreement, put into place in 2015, provides additional flexibility for releases and drought storage, balancing needed flow rates downstream while maintaining reservoir levels is a complicated order.
Lake Tahoe has a volume of around 122,000 million-acre feet, and while water is released into the Truckee River via the Lake Tahoe Dam, Wathen said most of the water lost from the lake is due to evaporation. Water is released from Tahoe and the area’s reservoirs to meet established Floriston Rates at the Farad Gauge.
Due to the loss of water through evaporation and other factors, there are rules specifying when water can be released from Tahoe or nearby Boca Reservoir. If the lake’s elevation is above 6,225.2 feet, water will be released from Boca. If it’s below that amount, water will be released from Tahoe.
“The reasoning behind that is because evaporation is so dominant at Lake Tahoe,” said Wathen. “It’s a way to maximize what storage we have in Tahoe to meet our demands because it’s just going to evaporate. It’s going to go up in the air. So, use it while it’s there.”
The maximum lake level, agreed to in 1917, is 6,229.10 feet.
“We’ll release water as much as we can to prevent it from going over that limit,” said Wathen.
Lake Tahoe hasn’t exceeded its upper limit since 1917 aside for a short time following a flood in 1997. The lake has, however, dropped below its natural rim many times.
“It’s very cyclical,” said Wathen. “We have periods of wet, periods of dry. Usually when we’re up, we’re up for a few years. When we’re down we’re down for a few years. It comes back pretty dramatically. We recover from these droughts as a result of flood-type years. Those are our saving grace.”
The Truckee River Operating Agreement includes management of nine reservoirs, 19 stream gages, and 35 water users.
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