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<br />
<br />CHRONOLOGY OF THE 1976-77 DROUGHT
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<br />67
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<br />reduced. All time record low levels were
<br />reached in the lower Sacramento Valley where
<br />wells are the major source of water. In Yolo
<br />County, declines were in the 10- to 20-ft
<br />range. Outside the Sacramento Valley, water
<br />levels in northern California were near normal.
<br />The depletion of ground-water storage in
<br />the San Joaquin Valley during 1976 has been
<br />estimated as between 3 and 3.5 million acre-
<br />ft. This is about two to three times the
<br />normal annual extraction of 1.2 million acre-
<br />ft,
<br />The additional pumping in California during
<br />1977 increased the overdraft to n.5 million
<br />acre-ft and caused an Average lowering of
<br />ground-water levels of 13 to 20 ft. One con-
<br />sequence of the heaviel' pumping was that land
<br />subsidence resumed in the San Joaquin Valley
<br />after a 2- to 3-year cessation. Figure 28
<br />shows the ground-water level changes from
<br />1975 to 1977. Because diversions of Sacra-
<br />mento River water were restricted in the
<br />sum mer of 1977, irrigators drilled new wells;
<br />and some of these were close enough to the
<br />river that they probably drew water from the
<br />river. The relative amounts drawn from the
<br />river and from the ground-water body have not
<br />been determined (California Department of
<br />Water Hesources, 1978).
<br />The dl'ought affected runoff in the Owens
<br />Valley area in the eastern Siet'rus where the
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<br />Figure 27. Depleted conditions of water in
<br />storage in two reservoirs.
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<br />intake to the Owens Valley aqueduct of the
<br />city of Los Angeles is located. Los Angeles
<br />sought permission to about double its pumping
<br />from the Owens Valley ground-water basin, but
<br />pumping was limited by a court injunction until
<br />the effectiveness of the water rationing pro-
<br />gram was demonstrated. This was done, and
<br />increased pumping from deep wells started on
<br />August 1, 1977 and provided an additional
<br />10,000 acre-ft per month for 8 months.
<br />The decreased use of surface water was
<br />partly offset by increased use of ground water,
<br />The cooperative way that water managers
<br />operated ground-water basins throughout
<br />southern California was beneficial to all of
<br />southern California as well as the entire State.
<br />However, the managers are now concerned
<br />over significantly lower water levels, many of
<br />them being at all-time lows. The 2-year over-
<br />draft is estimated as 500,000 acre-ft (E. L,
<br />Griffith, 1978).
<br />The number of reports received by the
<br />State of wells put into operation was 8,300 in
<br />1975,11,200 in 1976, and 20,000 in 1977. Be-
<br />cause all wells drilled are not reported, the
<br />total for 1977 has been estimated as 28,000
<br />wells.
<br />
<br />Water Quulity
<br />
<br />The reduced inflow into the Sacramento-
<br />San Joaquin River Delta allowed the saltwater
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