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66 .........' ". . ~ . , HYDROLOGIC AND HUMAN ASPECTS OF THE 1976-77 DROUGHT The largest accumulated deficiencies were equivalent to the normal runoff for periods ranging from 1.1 to 2.0 years, The shortest period is fOl: the Salmon River at Somes Bar, a tributary of the Klamath River on the north coast, and reflects a smaller effect in 1976. This is compatible with the nondrought con- ditions in the Pacific Northwest in 1976, The longest period is for the Napa River near St. Helena, a northern tributary to San Francisco Bay, where the Palmer index indicated the most severe drought conditions in the State. See figures 6 and 7, Except for the Salmon River where the accumulated deficiency in 1976 was 24 percent of that for the 2-year period, the accumulated deficiencies at the other five sites were almost equally divided between the two years, This relation does not hold for regulated streams where releases from storage were used to augment the flow, and the graphs in figure 26 should not be inter- preted to indicate that the graph must rise to zero deficiency before the basin is back to normal. The very poor snowpack in 1977 was bad enough by itself, but its damaging effects were compounded because it was the seond year in a row with a snowpack having a water content much below normal, This sequence was the reason that the water withdrawn from reser- voirs in 1975 and 1976 to meet agricultural and other demands was not replaced in 1976 or 1977; therefore, reservoir levels reached all- time lows in the fall of 1977. The April-July 1976 runoff into major re- ser-voirs between the Am,erican and San Joa- quin Rivers was either the lowest of record or nearly so, Storage in six reservoirs in the Cen- tral Valley Was depleted to dead storage levels by September 30, 1976, The total capacity of 79 reservoirs in the Central Valley is 27.0 million acre-ft, but on September 30, 1976 there was only 9,8 million acre-ft in storage or 58 percent of average. Comparable figures for 74 other reservoirs in California are 7.4 mil- lion acre-ft total capacity, 3.8 million in storage or 84 percent of average, The depleted condition of water in storage in two reservoirs is illustrated in figure 27, Figure 27ashows the intake tower at Pardee Reservoir n,ear Valley Springs, on the Moke- lumne River southeast of Sacramento, when it was out of water on March 26, 1977. The contents was 47,300 acre-ft, only 23 percent of capacity, and the water level was 112.3 ft below the spillway elevation which is just be- low the walkway to the tower, 'The old U,S. Highway 99 bridge across the Sacramento River is shown in figure 27b. The bridge was submerged during the filling of Shasta Lake three decades ago, and it reap- peared for the first time since then in 1977. The picture was taken on September 5, 1977 wh~n the contents was 572,900 acre-ft or 13 percent of capacity and when the water surface was 229 ft below the top of the gates on the spillway of Shasta Dam, Several good storms brought precipitation to northern California in September and No- vember 1977; but even so, on December 1, 1977 the Central Valley reservoirs contained only 5.8 million acre-ft which is just 22 percent of the total capacity and 38 percent of the average for that date. Storage in the other major reservoirs in the State dropped to 1.8 million acre-ft which is 24 percent of the total capacity and 43 percent of average for December 1. Ground-water Conditions Ground-water levels in a large part of Cali- fornia were lower in the spring of 1976 than they were in the spring of 1975, and, in some places, they were even lower than those in the fall of 1975. A few wells located where water levels remained nearly the same had lower yields in 1976 than in 1975, and a few wells less than 50 feet deep went dry, Declines in water levels from the spring of 1975 to the spring of 1976 were mainly in the 1- to 6-foot range; but wells in Yolo County west of Sacramento averaged about 7 ft lower, the' Madera, Tulare, and lower Kaweah and Tule River areas of the San Joaquin Valley reported declines of 7 to 8 feet, and there wer,e declines of 23 ft in the Shafter-Wasco area northwest of Bakersfield, and 25 ft near Chowchilla northwest of Madera. The average decline in Santa Clara County at the south end of San Francisco Bay was 15 ft, but wells in the southern part of the county dropped as much as 30 ft (California Department of Water Resources, 1976), Water levels declined an additional 15 ft by August 1976 in the northern Sacramento Val- ley, but they recovered about 6 ft when rain fell' in the late summer and pumping was