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<br />. <br /> <br />.. <br /> <br />. <br /> <br />r,,. Q ,,') <br />.:iiJu,..J <br /> <br />The effect of these discrepancies ~ould be to increase the demand <br />for project ~ater from the 178,000 acre-feet shown in the operation <br />studies to 182,800 acre-feet. This error is insignificant ~ith <br />regard to reservoir sizing analyses or project benefits and <br />therefore the operation study was not revised. <br /> <br />WATER illILIZATION <br /> <br />A reservoir operation study was made to determine the yield <br />~hich could be realized from the storage of surplus flo~s and <br />subsequent release of this ~ater to meet the computed supplemental <br />water requirements of the 23 major ditch systems in the Lo~er South <br />Platte Water Conservancy District. Estimates of storable flo\ol ~ere <br />based on actual flo~ coruii tions for ~he 19lj. T -1961 st,.",dy period. The <br />study ~as based on a re,servoir capacity of 430,000 acre-feet <br />(373,000 acre-feet conservation capacity and 75,000 acre-feet <br />joint-use capacity, less 18,000 acre-feet to reflect sediment <br />encroachment at the end of 50 years). All requirements for <br />supplemental ~ater were met as long as project water was available. <br />Supplemental ~ater was not provided class 6w lands. <br /> <br />Since the South Platte River acts as a natural drain for the <br />basin, the return flo~ from irrigation continuously accrues to the <br />stream. Of the total return flow from project deliveries, 2l+ per <br />cent can be reused. This factor ~as used in reducing reservoir <br />releases to meet downstream requirements. The balance is not <br />available for diversion, because of the time at ~hich the returns <br />occur or the location of return. The return flow from the project <br />deliveries averaged 21,300 acre-feet per year. <br /> <br />The plan of development includes the transfer of the existing <br />Jackson Lake function into the Narro~s Reservoir. Under project <br />conditions, the agricultural fUnction will be carried on from <br />Narro~s Reservoir in the same manner as it has been from Jackson <br />Lake historically. <br /> <br />Thrmlgh transfer of the irrigation function, the existing <br />Jackson Lake could become available for fish and wildlife and <br />recreation uses. Historically the reservoir content fluctuated <br />yearly from full to empty. With a fish and wildlife pool, the <br />content is maintained at a relatively constant 25,400 acre-feet. <br />The only drawdown of the pool occurs from evaporation which averaged <br />7,800 acre-feet and from seepage which averaged 11,100 acre-feet <br />per year. A gross supply of only 7,800 acre-feet of evaporation <br />loss from the pool would become available to the project if the lake <br />was abandoned because the seepage loss returns to Narrows Reservoir. <br />Replacement of losses will be accomplished by exchanging into <br />Jackson Lake from Narro\ols Reservoir. <br /> <br />7 <br />