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<br />26
<br />
<br />this risk might be acceptable, a larger quantity should be selected if excessive
<br />
<br />storage and consequent evaporation is to be avoided during those consecutive years
<br />
<br />of plenty.
<br />
<br />There is a 50-50 chance (based on the 1900-64 "record") that 1,500,000 acre-
<br />
<br />feet will be available in any year in the future. Considering that 95 percent of
<br />
<br />this amount will be diverted by river pumps and that 60,000 acre-feet will be the
<br />
<br />domestic requirement, a net of 1,365,000 acre-feet will be available for allocation
<br />
<br />to the land.
<br />
<br />To supply 1,500,000 acre-feet of water to the pumps each year will require
<br />
<br />1,640,000 acre-feet of water from the source of supply. The chance of the flow
<br />
<br />being this large is 43 (34) percent, or, in only 4 (3) years out of 10 will the
<br />
<br />flow be this much. The number of years the flow will be equal to or above given
<br />
<br />amounts, amounts available at pumps, and amounts available for irrigation is shown
<br />
<br />in table 16; data from table were plotted to define curves of figure 9 (p. 46).
<br />
<br />Table 16.- Time annual flow above selected amount.
<br />
<br /> Total 95 percent Less
<br /> Time flow of total domestic
<br /> (acre-feet) (acre- feet) (-60,000)
<br />1 year out of :JlO 2,750,000 2,610,000 2,550,000
<br />2 years out of 10 2,250,000 2,140,000 2,080,000
<br />3 " 10 1,920,000 1,820,000 1,760,000
<br />4 " 10 1,680,000 1,600,000 1,540,000
<br />5 " 10 1,500,000 1,420,000 1,360,000
<br />6 " 10 1,350,000 1,280,000 1,220,000
<br />7 " 10 1,200,000 1,140,000 1,080,000
<br />8 " 10 1,000,000 950,000 890,000
<br />9 " 10 800,000 760,000 700,000
<br />10 " 10 444,000 422,000 362,000
<br />
<br />Figure 9 shows, for example, that if it is desired to have 1,500,000 acre-feet
<br />
<br />of water for irrigation use, 1,640,000 acre-feet must be supplied. Experience, on
<br />
<br />the average, will be as follows:
<br />
<br />c_'" (. "
<br />,'" ,
<br />,,' ....4_ ,"'"
<br />
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