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<br />. <br /> <br />\VATER SUPPLY <br /> <br />Stream Depletions <br /> <br />Annual man-made depletions in the Upper Colorado River Basin from <br />e;;isting developments and developmente authorized prior to 1949, the year <br />the Upper Colorado River Basin Compact became effective, are estimated to <br />average about 2,550,000 acre-feet. A number of years will be required <br />for full development of projects authorized prior to 1949. The 2,550,000- <br />acre-foot depletion is therefore used in this report as also applying to <br />Fiscal Year 1963 when initial operation of the storage project is sched- <br />uled and is also referred to as the present depletion. On the basis of <br />the ar.nual depletion of 2,550,000 acre-feet, the upper basin is utilizing <br />only about one-third of the consumptive use apportioned to it by the Colo- <br />r~o River Compact. <br /> <br />. <br /> <br />As a basis for evaluating the Colorado River Storage project and <br />participating projects, a projection was made of future stream depletions <br />estimated to occur in the upper basin during the 100-year period from <br />Fiscal Year 1963 through Fiscal Year 2062. It was estimated that the <br />depletions by 2062 would total about 6,191,000 acre-feet annually, con- <br />sisting of 2,550,000 acre-feet from existing developments, 691,000 acre- <br />feet from evaporation from the authorized storage units, and 2,950,000 <br />acre-feet from new projects including the authorized participating proj- <br />ects and other future Federal and non-Federal developments. The 2,950,000- <br />acre-foot depletion from new projects expressed as a weighted average <br />amount over the 100-year period approximates 1,800,000 acre-feet, a <br />fibure used hereinafter in the project economic analysis. Assumed aver- <br />age depletions are summarized in the table below. <br /> <br />Fiscal <br />year <br />1963 <br />19'70 <br />2020 <br />2062 <br /> <br />Projected depletio~s!l <br />(Unit--l,OOO acre-feet) <br />Depletion <br />from exist- Average <br />ing and new evaporation <br />projects in losses from <br />upper basin storage unitsSl <br />2,550 negligible <br />3,150 691 <br />4,750 691 <br />5,500 691 <br />!/ Based on averages for runoff period 1914~45, inclusive. <br />g; Estimated average stream depletions due to evaporation from <br />Canyon, Flaming Gorge, Navajo, and Curecanti storage units. <br /> <br />Total <br />2,550 <br />3,841 <br />5,441 <br />6,191 <br /> <br />Glen <br /> <br />Replacement Storage <br /> <br />. <br /> <br />The holdover reservoire in the Upper Colorado River Basin are <br />designed to impound water in years of high runoff and release such water <br />during prolonged dry periods to permit the upper basin to increase its <br /> <br />17 <br />