For 96 years of the 20th century [1900-1995], the Truckee River flowed an average of 579,000 acre-feet (at Vista near the Truckee Meadows Waste Water Plant). That average number represents a continuous flow of 800 cubic feet per second (CFS).  Our measurements of flow during the last century, of course, were made after many changes had already taken place in the Truckee River watershed.  A dam was already in place at Lake Tahoe and a large network of ditches, dikes, and diversions from the river were already in place throughout the Truckee Meadows and Washoe Valley.  And the nation’s first reclamation project was constructed between 1905 and 1917.

Today, however, the changes that are occurring to our river may go well beyond ditches, dams, and diversions.  The watershed is seeing an increase in temperature that may be unprecedented in thousands of years.  Higher temperatures will very likely lead to greater evaporation and less snow.  That leads us to ask: What is the chance that we’ll see an average Truckee River flow of 579,000 acre-feet in the  remaining 86 years of the 21st century?

The Nettie, an expedition boat on the Truckee River, western Nevada, in 1867. Photo: Timothy O’Sullivan

Some studies are saying that the entire west – not just the far southwest dependent on the Colorado River – are facing a moderate to serious drop in precipitation coupled with increasing temperatures that may result in streamflows dropping by as much as 25%.

What worries many is that the decrease in river flows may have already started.  The Truckee River has already seen 14 years of “abnormal” dry conditions with only 2 years in that time frame seeing above average precipitation.  Drier than average conditions mean that water for Truckee River flows into Pyramid Lake are inadequate to keep up with natural evaporation rates.

Much of the worry about dry conditions has focused on the Colorado River and more recently on California.  In an article in “The Week” (theweek.com) the headline reads “The unprecedented water crisis in the American Southwest”, which focuses on the Colorado River.  Scientists are increasingly sounding the alarm of drying conditions affecting all who depend on the Colorado River.

“We can’t depend on history to project the future anymore,” said Carly Jerla, a geological hydrologist who closely monitors the Colorado. The river’s wet 20th century may have been an anomaly; in the 13 centuries before the 1900s, its flow was actually 15 percent lower. The current drought may also be the product of a wider pattern of climate change, signifying a barren future: Several global-warming studies predict that rising temperatures will reduce the river’s flow by up to 35 percent by 2050.

The articles on the continuing drought focus on the impacts to agriculture and the residents

The Derby Dam diverts Truckee River water from its natural course which goes to Pyramid Lake. Instead water flows into the Truckee Canal to the Carson River.

who reside in the west’s Mega-cities like Las Vegas, Los Angeles, and Phoenix.  But every westerner faces an uncertain future if there is a shift even half as great as 25-35% declines in stream flow.  The Truckee River is critical to the Truckee Meadows and a decline of such proportion would be devastating to the people and wildlife of the entire region.  Can we conserve 35% of all water use?  Agriculture?  Urban?  Industrial? Can natural systems at Lake Tahoe and Pyramid Lake and the length of the Truckee River survive with a smaller fraction of our left-over water?

That question was just fielded by the Sacramento Bee in a recent question and answer column.  And it’s not for the first time either.  Lake Tahoe, because of its immense size and depth, has been a target of water interests in California since the 19th century when tunnels through the Sierra were considered to tap the Lake and its water.  The Sacramento Bee does a credible job of answering the question (forget it, basically), but the large population in California (38 million people and rising) is a constant threat to water resources statewide.  Today, waters of the Truckee River (which includes all of the Lake Tahoe basin), are used in both California and Nevada.

Lake Tahoe is over 1,600 feet deep and contains a vast amount of fresh water, but has a very small watershed.

Most folks don’t realize that water from the Lake Tahoe basin already goes into a river that flows west to the Sacramento and eventually to the Pacific Ocean.  Late in the 19th and early 20th century, diversions of streams flowing to Lake Tahoe or to the Truckee River directly were constructed and still operate today.

Echo Lake Water is diverted to the American River by PG&E.

One of the diversions most everyone eventually drives past if they live anywhere in northern Nevada or California is at Echo Lakes at Echo Pass on US Highway 50. (Click on the map to see a larger version).  A dam on the lake provides 12 feet of storage that PG&E sends through a tunnel and pipeline to the American River to the west.  If the water followed its natural course it would flow to the Upper Truckee River, Lake Tahoe, and to the Truckee River.

The other diversion sends water from Independence Creek to irrigators in Sierra Valley.  The Sierra Valley Water Company owns the water.  Once the water is diverted it flows away from its natural course down the Little Truckee River (a major tributary to the Truckee River) and instead heads to Sierra Valley to the north.  There the water irrigates ranches and continues on to the west flowing Feather River.  A fly fishing website (http://www.flyline.com/places/little_truckee/) writes on its page:

“Much of the Little Truckee is diverted to Sierra Valley farmers at Hennese Pass and between the diversion and Stampede Reservoir the river is unable to support much trout life during the hot summer months.”

Independence Lake itself is a natural lake, but has a small dam.  Some of the water stored by the dam is owned by the Truckee Meadows Water Authority to supply the Reno-Sparks area during long-term drought.  So, in most conditions less water flows into the Truckee River because of the diversion to the Feather River and the storage of water in Independence Lake.

Map of Independence Lake in the Sierra showing Land Ownership (click for larger version)

The Nature Conservancy manages the private land surrounding Independence Lake.  (Click the link to see how the Nature Conservancy is protecting native Lahontan Cutthroat Trout at Independence Lake.)

These two diversions to California have operated for so long that most people don’t realize that water from both Lake Tahoe and the Truckee River already flows into west flowing American and Feather Rivers, through Sacramento and on to the Pacific Ocean.  Each takes water permanently away from the much smaller Truckee River.