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<br />UJJ383 <br /> <br />80% ASSURANCE SHORTAGE/SURPLUS METHODS <br /> <br />I. Define 80% assurance trigger as the Lake Mead trigger <br />elevation to reduce use so that 200 out of 1000 stochastic <br />traces will have at least one occurrence of Mead being below <br />the protection elevation or shortage elevation before the <br />trace rises above the trigger elevation. <br /> <br />II. Select Mead elevation to protect, i.e. 1050 ft. <br /> <br />III. Assume a constant use over a 56 year period in the Upper and <br />Lower Basin from the depletion schedule. The following 7 uses <br />were examined: <br />Year Use <br />1994 10636 kaf <br />2000 11092 <br />2010 11789 <br />2020 12006 <br />2030 12169 <br />2040 12358 <br />2050 12761 <br /> <br />~ <br /> <br />IV. For a given constant use iteratively select system starting <br />contents until 20% of the 1000 traces using CRSSez go below <br />1050 ft by: <br />1.--Select a constant Upper and Lower Basin use from above. <br />2.--Assume a Mead starting contents. <br />3.--Set Powell contents equal to Mead. <br />4.--Set Upper Reservoirs equal to Powell percent capacity. <br />5.--Using the stochastic hydrology, make a 1000-trace CRSSez <br />run for the period 1995 to 2050. <br />6.--Terminate each trace if: <br />a.--Mead elevation is greater than starting elevation. <br />b.--Year is greater than 2050. <br />7.--Rank the 1000 traces by minimum Mead elevation. <br />8. --Did exactly 20% or 200 traces have minimum elevations <br />below elevation 1050 ft? <br />a. --No: Select new system starting conditions and rerun. <br />b.--Yes: Note the drawdown volume difference between <br />Mead starting contents and contents at elevation <br />1050 ft. Also note the length of the drawdown <br />period as measured from starting year to year of <br />minimum elevation for the 200th trace. <br />9.--Repeat steps 2-8 for each of the 7 uses above and plot <br />Drawdown vs Use and plot Drawdown Period vs use. Note <br />that these plots are only valid for protecting elevation <br />1050 ft. <br /> <br />I <br /> <br />V. Application of resulting Drawdown vs Use for shortage: <br />1.--For AOP you could make a CRSSez run where: <br />a. --Use scheduled uses out to 2050 assuming shortage will <br />occur for all years following the first year. <br />b.--Set starting conditions to current elevations. <br />c.--Run 1000 traces and terminate if Mead greater than <br />