Carson River Basin

General Description

The Carson River Basin covers about 4,000 square miles in west-central Nevada and eastern California, flowing from its headwaters in the Sierra Nevada to the terminus at Carson Sink, 236 river miles downstream. The upper watershed is divided into two main drainages, the East Fork Carson River and the West Fork Carson River, both originating in Alpine County, Calif. The highest headwater altitudes are at about 9,000 feet for the West Fork and about 11,000 feet for the East Fork. The East and West Forks join in Carson Valley near the town of Genoa, Nev., where the average altitude of the valley floor is about 4,700 feet above sea level. The Carson River continues downstream passing through Eagle Valley on the east side of Carson City, traversing Brunswick Canyon (a narrow canyon between the Virginia Range to the north and the Pine Nut Mountains to the south), before entering Dayton Valley.

On leaving Dayton Valley, the Carson River bends eastward around Churchill Butte and Fort Churchill State Park. After this point, the Carson River enters Lahontan Reservoir with a capacity of 314,000 acre-feet of storage—the only significant reservoir on the river. Prior to construction of Lahontan Reservoir, the Carson River terminated in an area known as the Carson Desert, the Basin’s lowest point and a “closed” basin with no outflow or discharge except through evaporation. The Newlands Project, the Nation’s first project under the Reclamation Act of 1902, constructed the Lahontan Reservoir to provide storage of water for irrigating thousands of acres of agricultural land in the Fallon area. The reservoir also stores supplemental water received from the Truckee Canal, a diversion of the Truckee River to the north. The terminus of the Carson River is known as the Carson Sink which includes the original Carson Desert as well as the drainage basin in the general area of the city of Fallon (the Carson River drainage area below Lahontan Reservoir is about 1,800 square miles, a little under half of the total basin area). More descriptive information on the Carson River Basin can be found in the Carson River Atlas available from the State of California, Department of Water Resources (http://www.publicaffairs.water.ca.gov/information/pubs.cfm).

Precipitation
Annual precipitation amounts vary from more than 55 inches at the upper altitudes to less than 5 inches in the Fallon area. Most of the precipitation falling in the eastern Sierra Nevada is stored as snow during the months of December through March and snow-melt induced runoff provides most of the tributary and main-stem Carson River streamflow.

Total annual precipitation from Ebbetts Pass SNOTEL. Click on image for full-size graph.	Total annual precipitation from Fallon Experimental Station. Click on image for full-size graph.

For more information on the Natural Resources Conservation Service SNOTEL sites, visit the SNOTEL web site at <http://www.wcc.nrcs.usda.gov/snow>

To access climate data from the National Oceanic and Atmospheric Administration's National Climatic Data Center, visit their web site at <http://cdo.ncdc.noaa.gov/CDO/cdo>

For historic climate information as well as current observations, visit the Desert Research Institute Western Regional Climate Center at <http://www.wrcc.dri.edu>

Flood Events
Most of the floods in the Basin are the result of rain-on-snow events caused by warm, moisture-laden air from the Pacific Ocean bringing rain to the mountain snowpack which contributes to rapid snowmelt. This scenario of snow followed by rain on the snow has been repeated time and again, as the narrative flood accounts provided in this web site show and have caused (as recently as January 2006) widespread flooding and subsequent damage throughout the Carson River Basin. Summer thunderstorms, while local in extent, nevertheless are frequent, and can cause severe localized flash flooding, as well as mud and debris flows. As areas prone to flash flooding are developed (for example, alluvial fans and piedmont areas), the risk of flooding developed areas from summer storms is increased.