Photo: Toulumne Meadows in Yosemite National Park on March 13, 2020. Source: National Park Service.
Ninety percent of the annual water flow in the Colorado River comes from the river’s upper basin — Colorado, southern Wyoming and eastern Utah. Much of this area is 7,000 feet or higher in elevation, and the winter snowpack in the Rockies, Wasatch and Uinta ranges feeds the Colorado River and its tributaries, including the Yampa, Gunnison, Green and Duchesne.
On April 1, the snow water equivalent in the upper basin (the amount of water in the snow) is 91 – 130 percent of the median.
The following diagrams from the U.S. Bureau of Reclamation show that Lake Powell and Lake Mead, the two largest water storage reservoirs on the Colorado River, remain less than 50 percent full. These reservoir levels are the outcome of an extended dry period in the Colorado River Basin that began in 2000.
Lower Colorado River Drainage Basin
State Water Project
For California’s water resources managers, April 1 marks the end of the state’s wet season and the start of the warm, dry part of the year.
According to the California Department of Water Resources (DWR), “75 percent of California’s annual, statewide precipitation occurs from November through March”. In April, DWR officials look at Sierra snowpack levels, the amount of water in the snow (this is called the snow water equivalent) and the amount of water stored in reservoirs, and they decide how much water to deliver to farms and cities through the State Water Project.
DWR’s map below shows the April 1, 2020 snowpack levels in the Sierra, and a snowpack in the northern Sierra that is just 57 percent of average. This is important to agriculture and cities because the northern Sierra snowpack is the water supply for the State Water Project.
Sierra Snowpack on April 1, 2020
While California’s snowpack is below average, the state’s water supply outlook for 2020 is favorable because State Water Project reservoirs are at or near average.
Lake Cuyamaca received just over 26 inches of precipitation this fall and winter and we collected 2,567 acre feet of local water supply in El Capitan Reservoir.
Just under 422 acre feet of the water we collected this spring in El Capitan Reservoir is from Lake Cuyamaca, and there is adequate water in Lake Cuyamaca to release another 400 acre feet if needed.
San Diego River & Creeks
Just over 2,146 acre feet of the water we collected in El Capitan Reservoir is water collected from the San Diego River at our diverting dam, and from local creeks.