Results 
The trend in fluctuations in natural runoff reflects 
climatic cycles and their variations over large regions and is 
not radically modified by man's activities (Figure 2). Analysis 
of natural runoff cycles (11-15 years as described by L'vovich, 
1979) in both the San Francisco Bay and Sea of Azov drainage 
basins indicates the two are almost in phase, and therefore 
suggests that any changes detected in regulated runoff are the 
result of human modification rather than climatological factors. 
An unusual feature of these variations is that the deviations of 
mean runoff in each cycle vary within 25 percent of the average 
perennial volume regardless of the magnitude of the annual mean 
or seasonal discharges into either drainage basin. 
Since the late 1950s, water withdrawals from the San 
Francisco Bay watershed have increased from 20-30 percent of the 
natural annual runoff to as much as 63 percent in 1977 (Figure 
3A), and for the spring months of April, May, and June, they 
have grown from 30-35 percent to 60-85 percent. For the Sea of 
Azov, diversions have grown to as high as 46 percent (1974; 
Figure 3B). This radical reduction of runoff superimposed on 
natural cycles has diminished the water supply of the Delta and 
Bay to levels below those observed for natural fluctuations for 
annual or spring runoffs. 
The deviations (for running averages of any 5-year period) 
of regulated water supply to the Delta and Bay from "normal" 
runoff have predominant ranges of -35 percent to -60 percent 
(annual), and -40 percent to -85 percent for spring 
(April-June). Deviation for both natural, annual, and spring 
5-year running means of Delta outflow, on the other hand, 
generally vary around 15-25 percent of the mean (Figure 4 A-D). 
This indicates that such extreme negative deviations did not 
occur in the natural state of this estuarine system and have 
only been seen since the onset of major human regulation. 
Between 1955 and 1978, the period after the completion of 
the Central Valley Project (CVP) and State Water Project (SWP), 
major water storage and transport facilities, diversions 
amounted to a total of 296 km 3 of freshwater (240 MAF; Figure 
5B), equivalent to 40 times the volume of the San Francisco 
Bay. Of this, 202 km 3 , or 164 million acre-feet (MAF), was 
diverted from the rivers for irrigation and domestic water 
supply and 94 km 3 (76 MAF) was removed from Delta outflow for 
agricultural and other needs. In other words, for 2 3 years, an 
average of 8.8 km 3 (7.1 MAF)/year was withdrawn from river 
inflow to the Delta and 4.0 km 3 (3.3 MAF) was removed from 
Delta outflow to the Bay, yielding a total of 12.8 km 3 (10.4 
MAF) per year that never reached San Francisco Bay. For the 
same period, (Figure 5A) the total losses of freshwater supply 
to the Sea of Azov accounted for almost 250 km 3 , or about 11 
km 3 /year. 
41 
