This blog post analyzes long term changes in the Sacramento Four River runoff using a 10 year and 30 year running mean. Sacramento River runoff was lower during the Dust Bowl era drought of 1928-34, and the current 30 year mean runoff is close to the mean for the historic record. However, the current 10 year mean runoff is significantly lower than the long-term mean. The data also shows that the Water Board’s Decision 1641 was adopted during a wetter period in the historic record.
The Sacramento Four River runoff is calculated by the Department of Water Resources’ division of Cooperative Snow Surveys, and is used to determine the Water Year classification under Decision 1641. It is the sum of the unimpaired flow at the Sacramento River at Bend Bridge, Feather River inflow to Lake Oroville, Yuba River at Smartville, and American River inflow to Folsom Lake.
The mean runoff for the historic record is 17.8 MAF. The 30 year running mean for 1992-2021 is 17.6 MAF. The minimum 30 year running mean runoff was 15.3 MAF for 1918-1947.
California Department of Water Resources. 2022. Chronological Reconstructed Sacramento and San Joaquin Valley Water Year Hydrologic Classification Indices. Web page, accessed August 22, 2022.
California Department of Water Resources. 2015. California’s Most Significant Droughts: Comparing Historical and Recent Conditions. February 2015.
US Geological Survey, 2022. 2012-2016 California Drought: Historical Perspective. Web page, accessed August 22, 2022.
Related blog posts
The State Water Project was originally designed for a six year drought. April 26, 2021.
2 thoughts on “Water Board’s Decision 1641 adopted in wetter period”
This work should prove useful to hydrologists, especially those concerned with Sacramento-San Joaquin Delta ecology.
Super helpful history.