California snow surveyors reported that water content in California’s snowpack is only 52 percent of normal, with the spring melt season already under way.
“With most of the wet season behind us, this is more gloomy news for our summer water supply,” said DWR Director Mark Cowin.
After a record dry January and February in much of the state, DWR on Friday decreased its water delivery estimate, or allocation, from 40 to 35 percent of requested amounts from the State Water Project (SWP).
The 29 public agencies that purchase SWP water requested just over four million acre-feet of water for this calendar year. Collectively, the agencies supply more than 25 million Californians and nearly a million acres of irrigated agriculture.
Pumping restrictions imposed this winter to protect Delta smelt and salmon are another reason for the low water delivery estimate.
November and December were unusually wet, but between November 1 and February 28, fishery agency restrictions prevented DWR from pumping more than 550,000 acre-feet of water from the Sacramento-San Joaquin Delta to store in San Luis Reservoir. Today San Luis – a summer supply pool for both the State Water Project and the federal Central Valley Project – is 63 percent full.
“This is the kind of conflict we are working to resolve through the Bay Delta Conservation Plan,” said Cowin.
The Bay Delta Conservation Plan would reduce harm to fish from altered stream flows caused by the south Delta pumps serving the SWP and Central Valley Project. Pumping there at times causes reverse flows which may disorient or entrain fish. The comprehensive plan's large-scale habitat restoration would also improve Delta conditions for fish and wildlife.
The November and December storms built California’s snowpack water content to 134 percent of normal by January 2, when DWR and cooperating agencies conducted this season’s first manual survey. Manual surveys and electronic readings have recorded the water content decline since dry weather set in. Statewide, the season’s second manual survey on January 29 found the snowpack water content at 93 percent of normal for the date. On February 28, the season’s third manual survey found the snowpack water content at 66 percent of average
The survey – finding snowpack water content at only 52 percent of normal -- is particularly significant because this is the time of year the snowpack normally is at its peak before slowly melting with warming weather. The season’s final survey on or about the first of May will check the rate at which the snowpack is melting. Snow normally provides about a third of the water for California’s homes and farms as it melts into streams, reservoirs and aquifers.
Electronic readings indicate that water content in the northern mountains is 55 percent of normal for the date, and 55 percent of the April 1 seasonal average. Electronic readings for the central Sierra show 57 percent of normal water content for the date and 57 percent of the April 1 average. The numbers for the southern Sierra are 40 percent of average for the date and 40 percent of the April 1, full-season average.
DWR and cooperating agencies conduct manual snow surveys around the first of the month from January through May. The manual measurements supplement and check the accuracy of the real-time electronic readings from sensors up and down the state.
Despite the dwindling snowpack, most key storage reservoirs are above or near historic levels for the date thanks to November and December storms.
Lake Oroville in Butte County, the State Water Project’s principal storage reservoir, is at 108 percent of its average level for the date (83 percent of its 3.5 million acre-foot capacity). Shasta Lake north of Redding, the federal Central Valley Project’s largest reservoir with a capacity of 4.5 million acre-feet, is at 102 percent of its normal storage level for the date (82 percent of capacity).
(An acre-foot is 325,851 gallons, enough to cover one acre to a depth of one foot.)
Reservoir storage will meet much of the state’s water demand this year, but successive dry years would create drought conditions in some areas.
Today’s conditions, including the State Water Project allocation, could change with April storms.
The final SWP allocation for calendar year 2012 was 65 percent of requested deliveries. The initial delivery estimate for calendar year 2011 was only 25 percent of requested SWP water. However, as winter took hold, 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 pumping restrictions to protect Delta fish -- was in 2006.
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