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<br />seeding in the San Juan Mountains of southern Colorado began in 1970 and continued through <br />1982. then from 1990-1991 and 2000-prescnt. Similarly. the secdcd pcriods for a program over <br />the Grand Mesa area of west em Colorado arc; 1975. 1979. 1990-1995 and 1999-present. For the <br />Gunnison area of western Colorado. programs have been eonductcd from 2002 to the present. <br />For a Denver Board of Water Commissioners program in the upper Colorado River Basin west <br />of Denver. secding was conducted from 2002 to 2004. The only program in Utah modeled by the <br />Rivcr Forccast Center that would contribute to llows of the Colorado River would be the south <br />slope of the Uinta Mountains program. This program has only been operated from 2002-prcsent. <br />Anothcr complication is that some of the seeding during thesc "sceded years" on some <br />programs \....as conducted for only one or two months. not the cntire winter season. The point is <br />that enn though there has been some seeding in some areas of the uPI,er Colurado River <br />drainage during the base period. this seeding has not been l'onducted on an ongoing, <br />systematic basis for long time periods. Since the Rinr Forecast Center used a base period <br />of 1975-2002 to provide nerage eslimales of increases in streamflow. the question then <br />becomes: would Ihert~ be significant contributions to these streamflow a,,:erages due 10 the <br />amount of cloud secding that has actually been eonductcd'! It is beyond the seopc of this <br />study to quantify what the effects of sel'{ling from these "existing" programs may have been <br />during the historical base period of 1975-2002. We estimated that the impact of the seeding <br />during the historical period could be accounted for by appl)'ing a 5% reduction to the <br />streamflow increases calculated by the Ri\'(~r Forecast Cenler. In reality, the 5% reduction <br />probabl)' onrstates the magnitude of the sel.ding effects during the historical period. <br /> <br />Tablc 5 provides the resulting estimates of averagc increases in inflow to Lake Powcll for <br />both cxisting and ncw programs in the Upper Colorado Rivcr nasin. assuming full <br />implcmcntation in all areas. based on the historical basc pcriod of 1975-2002. Thc calculated <br />increases are provided for 5.10. and 15% increases in October through March prccipitation. The <br />estimated anra~e April through December increase in inflow 10 Lake Powell from a 10% <br />increase in precipitation in existing and new areas located in the upper Hasin States of <br />Colorado. Utah and W)'ollling would be 1.227,00" acre feet. The contributions to this tot;11 <br />from the existin~ and new areas would be 576.50" and 650.500 acre feel, respectinly. April <br />through December \.alues were used since water year amoun's ''''ere not a".ailable from fhe <br />Ri\-"er Forecast Center. <br /> <br />Table 5 Eslimated Anrage Increases in April thmugh December Streamflow for Upper <br />Basin States plus Arizona frum Existing and New Programs for 5. 10. and 150/0 increases in <br />October through March Precipitation for the 1975-2002 Base Period (Acre Fect) <br /> <br />Seeded Area 5% 10% 15% <br />Existin2. 284,700 576,504 875,808 <br />New 325,000 650,500 741,127 <br />Arizona + 15...000. + <br />Totals 609,700 1.381,004 1,616,935 <br /> <br />* Annual runofTamount based upon results from thc carlier 12 Basin Study <br />+ No estimate available <br />