Waiting for winter
Heading into fall Lake Tahoe and other area lakes and reservoirs are dipping, and may leave the Truckee River a comparative trickle before snow recharges the water supply again.
Two slow winters in a row ” feeding 31 percent and 32 percent of normal runoff into Tahoe ” mean the lake could drop below its natural rim unless precipitation shows up this fall. This means the top of the Truckee River could go dry, and other water stores will have to be leaned on more heavily to supply the Reno/Sparks area.
“At this point it looks like we will get very close to Tahoe’s natural rim,” said Chad Blanchard, chief hydrologist for the U.S. District Court Water Masters Office.
Currently the lake is within 11 inches of the natural rim, down to just 15 percent of the dam’s total storage capacity, he said.
“As the lake drops the amount going over the dam drops and the amount going down river drops, so we have to supplement that with others. We’re using Boca right now,” Blanchard said. “By the end of the year Boca could be very low also.”
Bill Hauck, the water supply coordinator for the Truckee Meadows Water Authority, said Boca could empty to 5 percent of its top capacity.
Prosser Lake will dip down to about one-third its total capacity, and Stampede will be about half its normal volume, Blanchard said.
Donner Lake is being drawn down as usual this fall, emptying the top 9 feet of the lake into Donner Creek, Hauck said.
Windy weather has played a major role in lake levels, especially on the enormous surface area of Tahoe, Blanchard said.
“If it is windy it creates huge amounts of evaporation off the lake,” Blanchard said.
Right now, the Truckee is meeting the minimum required rate of 500 cubic feet of water per second, called the Floriston rate, Blanchard said.
Blanchard said the flow could slow beyond that minimum rate, but said water demand in Reno and Sparks also drops significantly in the winter, so supplies should be all right.
“We’re hoping for a great winter, but even if we don’t have a great winter we have adequate drought supplies in place,” Hauck said.
And as for predicting what winter will bring, Blanchard said it’s too early to make any meaningful predictions.
The real forecasting for water supply happens when precipitation is actually on the ground, he said.
“I talk to the weather service and the California Nevada River Forecast Center regularly,” Blanchard said. “There’s nothing concrete but we’re hoping for a wet winter.”
Making weather projections for the winter this far out is difficult, especially in the Tahoe region, said Jim Ashby, Service Climatologist with the Western Regional Climate Center.
“Take these with a grain of salt ” looking to December, January, and February, there is a slight chance of above-normal temperatures,” Ashby said. “And equal chances on precipitation, which means they have no idea.”
There are no strong signals being sent by the ocean either, Ashby said, as no El Nino patterns are emerging.
“Really winter could go either way,” Ashby said.