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<br />
<br />CHRONOLOGY OF THE 1976-77 DROUGHT
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<br />Figure 24. Water content of the snowpack in
<br />California as a percentage of the April 1
<br />average.
<br />
<br />for 1976 are compared with the average and
<br />with data for 1948 and 1963, two other years
<br />with below average water content. In both
<br />1948 and 1963, above normal increases in
<br />water content occurred in March and April to
<br />relieve the potentially severe water shortage.
<br />This did not happen in 1976; in fact, the water
<br />content of the snow in the San Joaquin Valley
<br />area decreased in March, and the increase in
<br />the Sacramento Valley area was less than
<br />normal.
<br />Precipitation over the State during April
<br />1977 was only 10 percent of average, and April
<br />was the seventh consecutive month of below
<br />average precipitation, The precipitation for
<br />the 7-month period, October through April,
<br />was 30 percent of average statewide. The
<br />most severe deficiencies occurred in a band
<br />
<br />across the center of the State where many new
<br />minimum records were set for seasonal pre-
<br />cipitation.
<br />The water content of the 1977 snowpack is
<br />also shown in figure 24, It is less than that in
<br />1976 after January 1 in the Sacramento Valley
<br />watershed and after February 1 in the San
<br />Joaquin Valley watershed. The water content
<br />was also less than the previous minimum for
<br />the date in both watersheds on March 1 and
<br />April 1. About 75 percent of all snow courses
<br />visited on May 1, 1977 were bare.
<br />Not only was runoff in 1976 below normal,
<br />but the usual distribution in time of the runoff
<br />from the Sierra Nevada was distorted. Ac-
<br />cording to the California Department of Water
<br />Resources, (1977b), the snowmelt started
<br />about mid-March and was virtually over in
<br />many basins by May 15; whereas, snowmelt
<br />often extends through much of July. Runoff in
<br />the Central Valley ranged from 43 percent of
<br />normal for the Feather River to 16 percent of
<br />normal for the Cosumnes River. The head-
<br />waters of the latter stream do not extend to
<br />the higher elevations of the Sierra Nevada,
<br />Most coastal streams in the central part of the
<br />State had about 10 percent of normal runoff
<br />though the Russian River did have 15 percent
<br />of normal runoff.
<br />In 1977, the record low snow pack in the
<br />Sierra Nevada was almost gone by mid-April,
<br />but the above normal precipitation in May
<br />which added some snow, and thunderstorms in
<br />June extended the runoff period into early
<br />June, The April-July runoff for all major river
<br />basins in the Central Valley between the
<br />Feather River and the Kaweah River was at
<br />record low levels, less than 24 percent of the
<br />normal runoff. Though new low records were
<br />not set on the Tule and Kern Rivers, the 1977
<br />runoff barely exceeded the record lows. The
<br />runoff of the Sacramento River at Shasta Dam
<br />exceeded the previous low, which occurred in
<br />1924, by only 72,000 acre-ft or 10 percent.
<br />The annual unimpaired runoff to the Delta
<br />from the Sacramento and San Joaquin Rivers
<br />was only 28 percent of normal,
<br />Figure 25 is a plot of the monthly mean
<br />discharges of the North Fork American River
<br />at North Fork Dam, Calif., for the 1976 and
<br />1977 water years plus those for two previous
<br />drought years. The distributions of flows in
<br />1931 and 1976 are generally similar; all four
<br />years had abnormally low flows during the
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