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Manual and electronic readings on Tuesday record the snowpack’s statewide water content at 19 percent of the Jan. 3 average. That is only 7 percent of the average April 1 measurement, when the snowpack is normally at its peak before the spring melt, according to the California Department of Water Resources.
Despite the dry conditions, water managers remain cautiously optimistic about this year’s water supply.
“Fortunately, we have most of winter ahead of us, and our reservoir storage is good,” said Department of Water Resources Director Mark Cowin.
Electronic readings indicate that water content in the northern mountains is 21 percent of normal for the date and 8 percent of the April 1 seasonal average; 13 percent of normal for the date and 5 percent of the April 1 average for the central Sierra; and the southern Sierra’s results are 26 percent of average for the date and 9 percent of the April 1 average.
Statewide, the snowpack water content is 19 percent of normal for today’s date and 7 percent of April 1, the agency reported.
The Department of Water Resources cooperating agencies conduct manual snow surveys around the first of the month from January to May. The manual surveys supplement and check the accuracy of real-time electronic readings from sensors up and down the state.
The agency’s initial estimate is that the State Water Project (SWP) will be able to deliver 60 percent of the slightly more than 4 million acre-feet of water requested by the 29 public agencies that supply more than 25 million Californians and nearly a million acres of irrigated farmland.
The 60 percent delivery estimate is largely based on the known quantify of carryover reservoir storage. Unknown is how much snow and rain the state will get the rest of this winter, the state said.
Calendar year 2011 illustrates how weather-driven water supply conditions can dramatically change. The initial 2011 estimate was that the SWP would be able to deliver 25 percent of the slightly more than 4 million acre-feet requested. As winter took hold and storms swept the state, a near-record snowpack and heavy rains resulted in deliveries of 80 percent of requests in 2011. The final allocation was 50 percent in 2010, 40 percent in 2009, 35 percent in 2008, and 60 percent in 2007.
The last 100 percent allocation – difficult to achieve even in wet years because of Delta pumping restrictions to protect threatened and endangered fish – was in 2006, officials reported.
Lake Oroville in Butte County, the SWP’s principal storage reservoir with a capacity of 3.5 million acre-feet, is still 72 percent full thanks to last winter’s heavy storms. That is 114 percent of average for the date.
Lake Shasta north of Redding, the federal Central Valley Project’s (CVP) largest reservoir with a capacity of 4.5 million acre-feet, is 68 percent full (106 percent of average).
San Luis Reservoir in Merced County, an important reservoir south of the Delta, is 95 percent full (137 percent of average for the date). San Luis, with a capacity of 2, 027,840 acre-feet, is an important source of water for both the SWP and the CVP when pumping from the Delta is restricted or interrupted.
An acre-foot is 325,851 gallons, enough to cover one acre to a depth of one foot.
Mountain snow that melts into reservoirs, streams and aquifers in the spring and summer provides approximately one-third of the water for California’s households, farms and industries.
Statewide snowpack water content readings are available at http://cdec.water.ca.gov/cgi-progs/snow/DLYSWEQ.
Electronic reservoir level readings may be found at http://cdec4gov.water.ca.gov/cdecapp/resapp/getResGraphsMain.action.
Historic readings from snowpack sensors are posted at these sites:
http://cdec.water.ca.gov/cgi-progs/rpts1/DLYSWEQ
http://cdec.water.ca.gov/cgi-progs/rpts_archived1/DLYSWEQ
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