The “atmospheric river” resulted in rain throughout the central Sierra and the Reno area for most of Saturday, Dec 10, 2016. Rain was heavy in the mountains with snow confined to higher elevations. Consequently, runoff from the storm quickly entered the Truckee River below Lake Tahoe and sent flows approaching 5,000 cubic-feet-per-second through Reno and Sparks. That flow rate amounts to 2.2 million gallons of water per hour. The Truckee River hasn’t seen this rate of flow since 2012.
Graphic from USGS Lake Tahoe Gauge (Red annotations are mine)
Lake Tahoe as of today is just a little more than 1/2″ from its rim. Water from Lake Tahoe begins to flow into the Truckee River once its elevation reaches 6,223 feet. Lake Tahoe dropped below its rim this summer after rising above its rim in the spring, but has been mostly below its rim since October 2014. (Click graph for full size)
The National Weather Service in Reno is forecasting more rain should begin Tuesday. It could be an exciting week for the Truckee River if we get a repeat of mountain rains. High flows are important to move sediment and create new places for trees, grasses and shrubs to grow and create habitat for fish and wildlife. Floods are damaging to infrastructure built in the flood plain of the river, but flooding helps keep rivers healthy. Keeping buildings out of the floodplain and away from the river is the best approach to protecting our property and limits damage from flooding without expensive flood “control” structures – flood walls, levees, and dams.
Now that the rain has ended (hopefully, more snow and rain is on the way), the river is dropping rapidly. At 10 pm on Sunday, Dec 11 the flow rate through Reno is less than 1,500 CFS.
Truckee River in downtown Reno just above the Arlington Street bridge looking west at Whitewater Park.
Truckee River at 4,000 CFS December 10, 2016 during Sierra rains.
Truckee River at about 200 CFS on December 4, 2016 during dry weather.
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
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.]
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.
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
Will this year produce snow and rain that will finally raise Pyramid Lake’s level again and restore the flows to the Truckee River?
Click the either of the images below to see them full size.