A Report on California’s Water Supply
Although the beginning of the water year, which runs October 1 to September 30, was dry, the state’s hydrology has changed significantly within the last month. There is now a more promising outlook for California’s water supply. With the latest storms, the federal Drought Monitor Map shows only 3.5% of the state as “abnormally dry” and almost every state reservoir is at or above the historical average.
Precipitation and Snowpack
As of the third week in December, accumulated precipitation is trailing the long-term average for the Tulare Basin, San Joaquin Basin and Northern Sierra Station Precipitation Indices; however, snow water content for the North and Central Sierra regions are tracking near average. Because much of the water that flows through the Central Valley Project (CVP) for urban, environmental, and agricultural uses originates in the form of snowpack in the North and Central Sierra, it is crucial for healthy snowpack to continue to accumulate.
According to the United States Department of Agriculture, “California continues to be pounded by storms with heavy rain and mountain snow. Over the last two weeks precipitation totals topped 10 inches in much of the Sierra Nevada as snow, and over 15 inches in some areas along the coastal mountains.”
The C.W. “Bill” Jones Pumping Plant pumped at about 25% of capacity during November to comply with 2008 Delta smelt Biological Opinion fall X2 requirement – which regulates the level and location of salinity in the Bay-Delta. CVP exports have increased since November, and recently increased to the maximum capacity that can be conveyed by the Delta Mendota Canal.
The Harvey O. Banks Pumping Plant pumping was about twice the CVP rate during November with about 50 thousand acre-feet (TAF) of Banks’ pumping provided to the CVP as pay back in accordance with the Coordinated Operation Agreement accounting. Banks pumping is now at permitted capacity as Delta inflow has nearly doubled since the first of the month.
Shasta Reservoir Conditions
Water levels in reservoirs servicing the CVP are an important indicator of current water resources potentially available for delivery through the system. Currently, Shasta is at 73% of its capacity and 118% of its historical average. The storage capacity of Shasta reservoir is presently limited to about 3.3 million acre-feet per flood control requirements. The amount of water flowing into the reservoir increased slightly early December, after recent storms.
San Luis Reservoir Conditions
Prior to the latest storms, dry fall conditions, fall X2 compliance requirements and high demands were all factors that delayed the refill cycle of the CVP portion of San Luis Reservoir in November. The CVP portion of San Luis Reservoir refilled only once during the past 20 years when storage on December 1 was near or below the 2019 level of 250 TAF. As such, the CVP portion of San Luis is not expected to fill unless hydrology during the next few months is above average and Jones Pumping Plant export pumping is near the maximum rate allowed under the 2008 Biological Opinions.
New Biological Opinions
New Biological Opinions for federally listed species were published by the Fish and Wildlife Service (FWS) and the National Marine Fisheries Services (NMFS) on October 21, 2019. Additional factsheets on the Biological Opinions can be found here. Rather than relying on outdated science from the existing Biological Opinions, the new Biological Opinions are based upon the best available science that has been developed over the past ten years. The Bureau of Reclamation is expected to issue a final environmental impact statement for the new Biological Opinions in the latter part of December and issue a Record of Decision in late January. Until that occurs, Reclamation will continue to operate the CVP per the biological opinions issued in 2008 and 2009.
With the rain and snow that fell at the end of November and so far in December, as well as reservoir levels tracking at or above average, the allocation outlook has improved; however, it is critical for the rain and snow to continue to accumulate in the Sierra in order to receive a robust, adequate and timely allocation for South-of-Delta CVP contractors come February 2020.
To learn more about how allocation is determined, and water supply is distributed, watch our “Let’s Talk About Our Water Supply” featuring Westlands Water District COO Jose Gutierrez.
Status update from Westlands Water Resources Engineer, Tom Boardman