In spite of mid-January storms, there is only a 10% chance of a normal runoff of water into the Northern California dams that defend much of the state from drought, the Department of Water Resources said in its latest forecast of runoff that could be expected in the Sacramento River watershed. Most of California's reserve water supply is stored in three large dams on the Sacramento and its tributaries. They are Shasta Dam on the Sacramento near Redding, Oroville Dam on the Feather River and Folsom Dam on the American River near Sacramento. The long-term average on runoff of water into the Sacramento River basin has been 18.9 million acre-feet a year. The chances of normal rainfall have not looked good since Jan. 17, when the last storm died out, officials said.