Dry winter means low water levels
After a dry winter, lake levels in the Truckee-Tahoe area will be dipping by the end of the summer.
Balancing the water needs downstream with the lake levels at Tahoe, Boca, Stampede, Prosser, and Donner lakes, officials are already letting water out of local dams to maintain a minimum flow on the Truckee River.
Combined with evaporation, the discharge has already outstripped the inflow from streams and snowmelt.
“Tahoe can carry us for a couple of years, but Prosser will get pretty low and Boca will get down near its minimum,” said Chief Hydrologist Chad Blanchard with the U.S. District Court Water Masters Office.
The required outflow from Tahoe, Prosser, and Boca is used to maintain the minimum “Floriston Rate,” which is 500 cubic feet of water per second in the Truckee River below the Town of Truckee and near Floriston, he said.
Currently, the Truckee River is flowing at 100 cfs, meaning Tahoe, Prosser, and Boca have to make up the missing 400 cfs, he said.
Blanchard predicted that natural flow would drop further by the end of the summer, possibly down to 60 or 70 cfs, putting more pressure on the local lakes and reservoirs.
In contrast, this time of year last year, the Truckee was running at 800 cfs naturally, needing no help from dam releases, Blanchard said.
For Tahoe, this means a potential drop of 2 feet before inflow picks up again in the early winter, he said, with 0.6 foot being released, and 1.5 feet evaporating.
“For Tahoe, the difference means there will be more beaches, maybe some more rocks exposed,” Blanchard said.
Boca Reservoir, which never filled enough to reach the boat ramp this year, will require boaters to launch off of gravel bars to access the lake, he said.
Stampede Lake releases, on the other hand, aren’t used to achieve the Floriston Rate – the water is instead earmarked as “fish water” for the propagation of threatened and endangered species in Pyramid Lake, Blanchard said.
Donner Lake, a drought reservoir, has to maintain a certain level during the summer as part of an operational agreement, said Bill Hauck, the water supply coordinator for the Truckee Meadows Water Authority.
While authorities started filling the lake early this spring after a dry winter, Hauck said with the closing of the dams in March, the required level was reached and the lake should be open for recreational business as usual for the summer.
He said Donner Lake, like other lakes in the area, is losing more to evaporation than any remaining inflow.
Overall, Blanchard said there are no concerns about the water supply this year, but said if the coming winter is also dry, the flow could fall below the minimum rate.
“It happens every so often, normally late in the year; it’s why we have these reservoirs,” Blanchard said.