California statewide water storage is more than 9 million acre-feet (MAF) less than it was a year ago, according to the Department of Water Resources (DWR).
That sounds a bit ominous; however, the 2006-2007 season was very wet. This season has been one of the driest.
Nevertheless, statewide water storage was at 20.4 million acre-feet at the end of August, which is about 84 percent of the average for that date.
Last year, storage was at 29.2 MAF at the end of August.
Lake Oroville, the State Water Project’s principal storage reservoir, has 1,568,221 million acre-feet in storage, or 70 percent of average for the date. Lake Oroville, 70 miles north of Sacramento, has a capacity of 3.5 million acre-feet.
Lake Shasta, principal storage reservoir for the federal Central Valley Project, today has 1,879,144 acre-feet of water in storage, or 67 percent of average for the date. Lake Shasta, north of Redding, has a capacity of 4.5 million acre-feet.
An acre-foot is 325,851 gallons.
Those are not particularly encouraging figures. With normal or above normal winter snow and rain, those reservoirs could be recharged.
However, as the state begins its 2007-2008 water year, growers and cities are concerned about a possible “judicial drought” in the wake of a court ruling last month, which could severely limit pumping water through the Sacramento-San Joaquin Delta to save Delta smelt.
All of those major reservoirs are north of the Delta and water from them for use by 25 million people and 3 million acres of farmland south of the Delta must be moved down-state by two banks of large pumps on the south end of the Delta.
The 2007-2008 winter and summer smelt management plan is being written, but water users are expecting it to be a moving management plan, subject to weekly decisions which could shut down those vital pumps if the judge so orders.
During this water year, hydrologists and meteorologists will measure precipitation (the combination of rain and snow) and runoff in the Northern Sierra and other key watersheds and produce runoff forecasts.
The northern Sierra and southern Cascades are of particular importance because that's where most of the state's water supply accumulates.
Measurements are taken in the watersheds of the major rivers, including the Sacramento, Feather, Yuba and American. Snow surveys are conducted throughout the Sierra range and other mountains to measure water content. The first snow survey will be around the first of December.
The data that is gathered is evaluated to forecast water supply for the spring and summer, the heaviest months of water use by farms and homes.
For the Sacramento River basin the past 2006-2007 water year finished as the 18th driest in the 102-year record of stream flow measurements.
The San Joaquin River region was drier, finishing up as 8th driest, based on preliminary information.
The northern Sierra snow pack was measured at 40 percent of normal on April 1 2007, which was the lowest since 1988. Early melting reduced the snow pack to only 25 percent of average by May.
Snowmelt, which normally continues through June, had virtually ended by June 1 this year. Overall precipitation for the state ended at 60 percent to 65 percent of average. The dry year may impact water deliveries further, but as of now, State Water Project Contractors are scheduled to receive 60 percent of requested deliveries.
National Weather Service (NWS) long-range forecasts indicate a somewhat above average chance of wetter than normal precipitation in Northern California through the coming fall and winter months, but show a good chance that dry conditions will persist in Southern California.
Storage for the four largest reservoir on the Lower Colorado River is now about 51 percent of capacity, down from 53 percent last year. California's allocation from the Colorado River is 4.4 million acre-feet.
Precipitation in the Sacramento River Basin is the source of much of California's water supply, and was about 62 percent of normal during the 2007 water year, compared with 150 percent of average the previous year. In the San Joaquin Basin, precipitation ended at 60 percent of average compared to 145 percent of average during the 2006 water year. As a result, water supply conditions have been designated as dry in the Sacramento Valley, and critical in the San Joaquin Valley.