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<br />,111 I, <br /> <br />after year 2006 as the critical period extends out to 20 years and the average use over the <br />20 year critical period increases. <br /> <br />Reclamation allowed the surplus threshold storage requirement to increase up to the Flood <br />Control Surplus capacity of Lake Mead. From then on, the surplus threshold was held at <br />Flood Control Surplus, and the shortage threshold was assumed to be set at elevation <br />1120 feet to protect elevation 1050 feet. <br /> <br />Surolus lruidelines. Based on the surplus determination studies described above, and <br />consistent with the Law of the River, Reclamation recommends that: <br /> <br />Surplus conditions exist on the Colorado River System when the storage <br />in Lake Mead at the beginning of the water year exceeds the surplus <br />threshold storage requirement, and when there is a need for the use of <br />surplus water. <br /> <br />ComDarisoDS to earlier surolus stratel!ies. <br /> <br />Several runs were made to compare this methodology with the more familiar percent capacity <br />threshold strategies, and the percent assurance of avoidance strategies. The Critical Period <br />Method was compared with the Flood Control Surplus Strategy, the 70 Percent Assurance of <br />Avoidance Strategy, the 80 Percent Capacity Surplus Threshold Strategy and with the <br />70 Percent Capacity to 90 Percent Capacity Trended Strategy. Figures displaying these <br />comparisons can be found in the attached Draft Appendix Surplus Determination Studies. <br /> <br />The Critical Period Strategy provides more surplus opportunities during the early years of <br />lower development than do the 70 Percent Assurance of Avoidance, 80 Percent Capacity, and <br />70 Percent to 90 Percent Capacity Trended By Use strategies. <br /> <br />Regardless of the assumed protection level (this proposal uses elevation 1050 feet), the <br />surplus threshold storage requirement will rise sharply, after use exceeds 11.8 maf and the <br />critical period of record extends out to 20 years. <br /> <br />Lower protection levels would extend out the time when the surplus capacity would reach the <br />Flood Control Surplus conditi0P. However, the Critical Period Strategy would determine <br />surplus conditions for the next several years for protection levels less than or equal to <br />elevation 1050 feet. The analysis assumed shortages would be determined based on an <br />elevation of 1120 feet, in order to protect elevation 1050 feet. Other shortage strategies and <br />protection levels can be analyzed and considered. The Critical Period Strategy for <br />determining surplus would remain intact regardless of the shortage strategy selected. <br />Adopting this Critical Period strategy provides a technical basis from which other guidelines <br />can be analyzed and develop. <br /> <br />6 <br />