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<br />38 <br /> <br />extended to the entire basin with the aid of advanced technologies now <br />available. The continuing stresses on the basin's water resources <br />dictate that this be done. It is more important now than ever before <br />that water right owners be able to project ahead the likely scenarios <br />of water demands and the basinwide impacts of local management changes. <br />It is precisely forthh purpose that high technology products of <br />research are needed. <br /> <br />I <br /> <br />" <br />" <br />H <br />! <br /> <br />4.2 Basin Water System <br />The South Platte basin is laced with a complex system of man-made <br />streams, ditches, canals, reservoirs. Below the land surface is an <br />underground aqui fer containing about 8' mill ion acre-feet of water in <br />storage. The annual native supply for' the basin due to precipitation <br />and snowmelt runoff ~s previously noted is about 1.44 million acre- <br />feet (2). Streamflow withdrawn in the upper reaches of the basin is <br />applied to land for irrigation for the most part. Part of that water <br />is used by crops in ev~potranspiration;part of it percolates downward <br />into the groundwater th~ough which it eventually returns to the stream. <br />Downstream water right owners in turn withdraw their entitl ed flow and <br />the cycle repeats Hself. Because of this recycle system, the total <br />annual volume of water withdrawn for uSe i~ the basin rang~s from 2 to <br />2.5 times the annual native supply (4). <br />The basinwide use of the native supply available is "efficient" in <br />the physical sense. On the other hand, considering. a single (local) <br />withdrawal, say" for irrigation, the "local" physical efficiency might <br />be very low. While many feel that if such "local" efficiilncy were <br /> <br />~ <br />I <br />. <br /> <br />, <br /> <br />, <br /> <br />" <br />