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<br />!'J~'~ ~).,~ <br />i. ~'.J,...' W~ <br /> <br />39 <br /> <br />" <br /> <br />improved water would be saved for other users, ,that conclusion should <br />be reser-i,ed for a hydrologic analysis of effect on the total. For <br />example, the recycl ing system described above has some important <br />benefits., The delay in subsurface return flow to the river produces <br />increased' flows late in the season that would otherwise not occur. <br />Further, the flow increases are felt in the downstream section where <br />water shortage is generally most severe. <br />Forty percent of the state's agricultural production occurs in the <br />basin. A total of approximately 2.6 million acres is devoted to agri- <br />cul tural c;rop production with about 1.3 million acres used for irrigated <br />agricultute and nearly 1.3 million acres used for dry land crops (1). <br />The Pepartment of Interior estimated in 1974 that total of basin <br />consumptNe uses average 1.5 million acre-feet annually. This estimate <br />was disaQgregatedin 1980 by the Colorado Department of Natural <br />Resources (CDNR) as: irrigation, 1.25 MAF; Municipal including domes- <br />tic and industrial (WI), 0.164MAF; other, 0.058 MAF, for a total of <br />1.473 MAF(2). This total suggests that the estimated consumptive use <br />of water is approximately the same as the estimated native annual supply. <br />The CDNR 'estimates average annual native supply,at 1.441 MAF. With <br />imports 01' 0.426, the total average annual supply is 1.867 MAF (2). <br />The :South Platte River, mainstem and its tributaries exhibit <br />substantial variations in stream flow from season to season and from <br />year to year. Around 70 percent of the runoff of the tributary mountain <br />streams, as noted previously, occurs during the months of May through <br />July. On. the other hand, summer thunderstorms over tributaries in the <br />Plains zone may produce large streamflows during July through September. <br />Pronounce~ seasonal and locational variations in runoff suggest the need <br /> <br />-,) <br /> <br />~ _ i 0: -' <br /> <br /> <br />,,~ <br />