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Modeling Results for <br />Colorado River Basin States' Modeling of <br />Colorado River and Reservoir Management Strategies <br />1,200 <br />1,180 <br />1,160 <br />1,140 <br />d <br />,t'0 1,120 <br />C <br />0 <br />1,100 <br />w <br />W <br />y 1,080 <br />0 <br />a <br />Y 1,060 <br />R <br />J <br />1,040 <br />Figure 4 -9 <br />Lake Mead Elevation Percentiles <br />75th Percentiles <br />50th Percentiles <br />1,020 � —9—Normal <br />1,000 <br />980 4- <br />2005 <br />10th Percentiles <br />--A-- Hybrid <br />— B— Hybrid - ISG Extended <br />2010 2015 2020 2025 <br />Calendar Year <br />Figure 4 -9 shows the 10th, 50th and 75th percentile elevations at Mead. <br />Extending the ISG does not affect Mead at the 10th percentile and has minor <br />effects at the 50th percentile, an average 5 ft decrease occurring in 2 years. As <br />with Powell, at the 75th percentile there is a slight decrease after 2017 from <br />extending the ISG. <br />4.4 Absolute Protect 1000 Sensitivity <br />The Step Shortage strategies that have been examined do not include the absolute <br />protection of 1000 ft at Mead. Under the Step Shortage strategies, the maximum <br />shortage ever taken is 600 KAF and Mead can drop below 1000 ft. An analysis <br />was performed to determine the effects of adding a second level shortage <br />(Absolute Protect 1000) to a Step Shortage strategy. Of specific interest was the <br />maximum shortage that would be required to protect 1000 ft at Mead and how <br />often a shortage of that magnitude would occur. The analysis was performed by <br />comparing the Hybrid revl and Step Shortage rev-2 strategy with the same <br />combination but with the addition of the Absolute Protect 1000 strategy. All other <br />parameters were unchanged. <br />26 <br />