Anticipating winter snows for Truckee River flows

Despite the rains of October in the central Sierra, Tahoe today is still 3.6″ below its rim and no water flows to the Truckee River from the Lake.  Most of the Truckee River flow comes from tributaries downstream of Lake Tahoe’s outlet including the Little Truckee River, its largest tributary. It is, however, likely that Tahoe will rise above its rim in the coming weeks as winter weather approaches. Filling Lake Tahoe to its maximum elevation would raise the current level more than 6 feet and require at least a 200 percent water year or double the long-term average annual precipitation of snow and rain.

Lake Tahoe elevation week ending 12-05-2016

Lake Tahoe elevation week ending 12-05-2016

October was a wet month in Reno with two storms that each produced over an inch of rain. It was extremely welcome after a long and very dry summer and early autumn. The storms resulted in record October rainfall for some places in the central Sierra and Lake Tahoe. Temperatures remained warmer than “normal”, however, until late November when it finally cooled off. Mt Rose Ski area on the Mt Rose Highway is reporting 13″ of snow at the lodge of natural and artificial snow and 25″ at the 9,800 foot level as I write this. Squaw Valley-Alpine Meadows Ski Resort in California reports a base of 28″ and anticipates up to 2 feet of snow from a series of storms predicted to arrive Wednesday a stay into Saturday. News of the wet October have made a hoped for wet winter in the central Sierra after last year’s dismal “El Niño” palpable. [Find an SFGATE report on the October rainfall/snowfall here.]

Nov 16-Feb 17-precipitation-outlook

Nov 16-Feb 17-precipitation-outlook

NOAA forecasts Northern California and Nevada will see a 50-50 chance of average precipitation under the “La Niña” conditions in the central Pacific Ocean. However, southern California and Nevada as well as most of the southwest and southeast US are forecast to see dry conditions during the “La Niña” winter. Some are saying that there is a good chance for more snow this year around Lake Tahoe northward to the Cascades.

US Drought Monitor Map 2016 11 29

US Drought Monitor Map 2016 11 29

The US Drought Monitor is still showing Reno in the Moderate to Severe drought category despite the recent rains, but soil moisture conditions have improved as you go north toward Oregon. California mostly remains in drought with a large portion of central and southern California in the most severe drought categories. Drought conditions in Nevada have moderated with western and southern Nevada remaining in the drought categories (click map for full size).

Truckee River flow through Reno is running around 200 cubic-feet-per-second (CFS).  Most of the water in the river, however, is not making it to Pyramid Lake, captured instead at Derby Dam and sent to Lahontan Reservoir through a canal.

Unfortunately, Pyramid Lake’s elevation continues to fall due significantly to the diversion of Truckee River water into the canal built by the Bureau of Reclamation in 1905 as its very first project. Water is taken out of the Truckee and sent through an unlined canal from Derby diversion dam on the Truckee all the way to Lahontan Dam on the Carson River. Since the beginning of the drought in 2000, Pyramid Lake has fallen approximately 27 feet in elevation exposing large land areas previously covered by water including shrinking the Lake on its south end to puddles near the mouth of the river. Most of the loss of water to Pyramid Lake is due to diversions to the Newlands Project, however, rather than the drought itself. (More on this later)

Derby Dam on the Truckee River diverts Truckee River water to the Carson River for the Newlands Irrigation Project starting in 1905.

Derby Dam on the Truckee River diverts Truckee River water to the Carson River for the Newlands Irrigation Project starting in 1905.

The Truckee Canal diversions have resulted in the loss of Winnemucca Lake in the valley adjacent to Pyramid Lake and the approximately 80 foot drop in elevation of Pyramid Lake itself since the early 1900s. This amounts to an approximately 8 million acre-foot water deficit for Pyramid Lake, the largest body of water entirely within Nevada or, in other words, represents nearly two decades worth of the average flow of the Truckee River that Pyramid Lake never received.

Pyramid Lake benefits from high precipitation years because of reduced diversions from the river when flows are high. During the drought starting in 2000 there have only been two periods of significant flows to Pyramid Lake which raised its level over the previous year. (click to see photo comparison at full size)

Pyramid at Pyramid Lake changes over recent decade and a half are dramatic

Pyramid at Pyramid Lake changes over recent decade and a half are dramatic

Will this year produce snow and rain that will finally raise Pyramid Lake’s level again and restore the flows to the Truckee River?

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Click the either of the images below to see them full size.

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This entry was posted in Conserve, Drought, Keep it flowing on by .

About Dennis Ghiglieri

My concern for the Truckee River grew over the years. It started with picking up trash and supporting better water quality. I helped create the "living river"plan with other citizens on the Community Flood Coalition; a plan to reduce flood impacts to infrastructure through river restoration and protection of the floodplain. I understand how critical the Truckee River is to the environment – and economy – of our entire region. I'm hoping that through these pages we can all understand our connection to the Truckee River and why we need to protect it.

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