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<br />24 <br /> <br />(The above figures are not as exact as the number of significant figures <br /> <br />implies. Figures are subject to error as they are based on estimates of division <br /> <br />of ownership of water in the river below Falcon. However, the figures do give a <br /> <br />good picture of river operations within reasonable limits.) <br /> <br />Water Use Efficiency With a given water supply and increasing competition, <br /> <br />~ irrigator must increase water use efficiency or suffer. Thus competition should <br /> <br />be expected to result in increased water use efficiency. Overall efficiency is <br /> <br />the product of farm efficiency and canal (or distribution) efficienc~. <br /> <br />Farm efficiency is expressed ~s the percentage of water delivered to land <br /> <br />that is used by crops, or consumptive use divided by water supplied; the difference <br /> <br />represents farm waste and deep percolation. Canal efficiency is the percent of <br /> <br />total river diversion that is delivered to farms. The Select Committee on National <br /> <br />Water Resources decided that assumptions shown in table 15 were generally applicable <br /> <br />to Texas (from Chas. B. Thompson IIIrrigation Water Requirements in Texasll; ASCE <br /> <br />Jar. Irr. & Drain Div., Vol. 90, No. IR3, pt. 1, Sept. 1964; p. 17). <br /> <br />Table 15.- Water use efficiency. <br /> <br /> Item 1954 1980 2000 <br />Farm efficiency, in percent. . . . .. . ..... 50.0 59.2 68.4 <br />Canal efficiency, in percent........... 60.6 64.7 70.5 <br />Overall efficiency, in percent. . . . . . .. . 30.3 38.3 48.2 <br /> <br />As the trend must be towards greater efficiency, ~t would not be too much to <br /> <br />expect that in the near future an overall efficiency of 38.3 percent could be <br /> <br />attained; this level is assumed to be possible by 1980. <br /> <br />Sunnnary <br /> <br />During the next few years the domestic needs for Rio Grande water <br /> <br />will be about 60,000 acre-feet per year. <br /> <br />Irrigation requirements have been estimated as 1.75 acre-feet per acre per <br /> <br />year; this figure agrees very well with average requirements ,for a combination of <br /> <br />- ~ ,. r '", t'*, <br />...) 'J " .J l V <br />