The California Department of Water Resources will conduct this winter's second snow survey on Tuesday, Jan. 29.

The second snow survey each season is the first comprehensive look at the snowpack in which all snow courses active in the statewide network, approximately 250, are measured manually.

In comparison, just 15 to 20 courses typically are manually measured in the initial surveys. The manual surveys – conducted on or about the first of the month from January through May – supplement and check the accuracy of real-time electronic sensors up and down the state’s mountain ranges.

One focus of attention on Jan. 29 will be the manual survey conducted near Echo Summit. This combined with the information gathered from all the manual surveys and the electronic sensors will give a comprehensive picture of statewide snowpack conditions.

Electronic readings on Thursday indicated that water content in the statewide snowpack is 97 percent of normal for the date and 53 percent of the average April 1 reading, when the snowpack is normally at its peak before the spring melt.

The snowpack normally provides about a third of California’s water supply as it slowly melts into streams, reservoirs and aquifers in spring and early summer.  

Lake Oroville in Butte County, the State Water Project's principal storage reservoir, is at 113 percent of its average level for the date, 75 percent of its 3.5 million acre-foot capacity.  

Lake Shasta north of Redding, the federal Central Valley Project’s largest reservoir with a capacity of 4.5 million acre-feet, is at 112 percent of its normal storage level for the date, 75 percent of capacity.

However, San Luis Reservoir in Merced County, an important storage reservoir south of the Delta, is at only 77 percent of average for the date, 60 percent of its capacity of 2,027,840 acre-feet.

San Luis is a critically important source of water for both the State Water Project and Central Valley Project, the Department of Water Resources said.

An acre-foot is 325,851 gallons, enough to cover one acre to a depth of one foot.

Conditions between now and early spring will determine the amount of State Water Project water the Department of Water Resources will be able to deliver this calendar year.

The current estimate is that Department of Water Resources will be able to deliver 40 percent of the slightly more than 4 million acre-feet of water requested by the 29 public agencies that distribute State Water Project water to more than 25 million Californians and nearly a million acres of irrigated farmland.

The final State Water Project 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 State Water Project 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.