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<br />On average, California has an aouilable <br />water supply of about 77 million acre-feet <br />per year. <br /> <br />California as a whole is not short of <br />water, but. to meet the state's demands <br />water must be stored and transported <br />large distances. <br /> <br />California's Water Supply <br />California's surface water comes from an average annual statewide <br />precipitation of almost two feet. This precipitation ranges from almost <br />nothing in desert areas to more than 100 inches in the mountainous <br />regions along the northern coast. <br />Sixty percent of this precipitation is evaporated or transpired <br />hy trees and other natural vegetation. The other forty percent is <br />equal to about 71 million acre-feet of stream flow. (An acre-foot is <br />the amount of water needed to cover an acre ofland to the depth of <br />one foot. It is also usually considered to be the approximate amount <br />of water used over two years by a household of four people.) Flows <br />from the Colorado River currently supply another 4.8 million acre- <br />feet, and inflow from streams in Oregon adds an additional 1.4 million <br />acre-feet to this supply. In an average year, California has available <br />slightly more than 78 million acre-feet. <br />California as a whole is not short on water, but the supply is <br />difficult to utilize fully because of its distribution and variability. <br />Almost 29 million acre-feet, approximately 40 percent ofthe average <br />statewide runoff, occurs in the north coast region, the least popu- <br />lated part of the state. Annual runoff has also varied between a low <br />of. 15 million acre-feet in 1977 and a high of more than 135 million <br />in 1983. In 1986, nearly 8 million acre-feet flowed past the City of <br />Sacramento in the Sacramento River and the Yolo Bypass in just ten <br />consecutive days. This is more water than is used by all the cities in <br />the state in a year. Water developers in California have focused on <br />compensating for this variability by storing high winter and spring <br />flows for later use in the summer and early fall.2 <br />Many of the reservoirs that have been built in California in the <br />last 50 years were designed to maintain deliveries through a repeat <br />of a 7-year dry period equivalent to that of 1928 to 1934. However, <br />various constraints on the use of facilities, and the failure to complete <br />planned projects, saw California suffer severe shortages during the <br />6 dry years from 1987 to 1992. <br />California has some 450 groundwater basins that store approx- <br />imately 850 million acre-feet of water. By comparison, California's <br />surface reservoirs hold 43 million acre-feet of water. However, the <br />total amount of groundwater storage is deceptive because much less <br />than 50 percent of California's groundwater is close enough to the <br />surface to be economically pumped. Another constraint is that a <br /> <br />2 "California "Vater Plan Update," State Department of Water Resource, <br />Bulletin No. 160-93, volnme 1, pages 49-51. <br /> <br />2 CALIFORNIA WATER <br />