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<br />19 <br /> <br />that in any year the flow will exceed or will fall short of 1,500,000 acre-feet. <br /> <br />The long-time "record" of discharge may be misleading due to changed condi- <br /> <br />tions in the basin. The short-time "record" indicates. considerably less water may <br /> <br />be available in the future. <br /> <br />Knowing the chance of occurrence of a range of flows, the next question is: <br /> <br />What flow should be selected as a future dependable supply? It is helpful to <br /> <br />remember that when the river supplies more water than the selected amount, the <br /> <br />surplus may be held in storage and used to supplement low-supply years. Critical <br /> <br />periods will be when several low-supply years follow each other; there seems to be <br /> <br />no way to avoid this situation when nature so performs. <br /> <br />It should be remembered that figures used here are annual averages, and as <br /> <br />such may not give a completely true picture so far as irrigation needs are con- <br /> <br />cerned. Crops require water throughout the year, but nature supplies it in an <br /> <br />erratic manner. As an example, the 1964 annual discharge of 1,750,000 acre-feet <br /> <br />came mostly in late September and early October, and water was not available for <br /> <br />needs during most of the year; even though the annual supply was adequate, poor <br /> <br />time distribution made a poor supply for crop production. Also, it should be <br /> <br />remembered that figures used here are for calendar years; other water years would <br /> <br />give a different picture, although for the relative long period studied (65 years) <br /> <br />and considering carry-over from one year to the next, no significant difference <br /> <br />wuuld result. <br /> <br />Water Use <br /> <br />Domestic Requirements <br /> <br />Future domestic, municipal, and industrial require- <br /> <br />ments in the Valley have been estimated by TWC (Bul. 6413) as: <br /> <br />1965----------------------------------------------------- <br />1975----------------------------------------------------- <br />2000----------------------------------------------------- <br /> <br />51,649 acre-feet <br />68,404 acre-feet <br />126,516 acre-feet <br /> <br />Part of this water will be supplied from wells. <br /> <br />For purpose of computations, it is assumed that 60,000 acre-feet of river water <br /> <br />'-. ~ " I" ~ <br />U'JG...t.J <br />