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consideration in the 602(a) determination through the year 2016. Under the Proposed Action <br />Alternative, water vear releases from Lake Powell would be the minimum objective release of <br />8. 3 million acre -feet when Lake Powell is projected to be below 14.85 million acre -feet <br />(elevation 3,630 feet- on September 30. <br />The Bureau of Reclamation has historically utilized a modeling algorithm for calculating 602(a) <br />storage volumes in the Colorado River Simulation System to determine when storage <br />equalization releases from Lake Powell should be made. This algorithm incorporates the <br />relevant factors listed in Article Il (1) of the Long -Range Operating Criteria. The 602(a) storage <br />algorithm has been utilized for over 20 years in modeling studies that involve simulation of the <br />Colorado River. The 602(a) storage algorithm is also considered each year in the preparation of <br />the Colorado River Annual Operating Plan. This modeling algorithm serves as the basis for the <br />No Action Alternative. <br />Adoption of the Proposed Action Alternative could affect the operation of the Colorado River <br />system (i.e., reservoir levels and river flow volumes) as a result of changes in the frequency and <br />volume of storage equalization releases from Lake Powell to Lake Mead. The potentially <br />affected environment includes the Colorado River and associated resources from Lake Powell to <br />the Southerly International Boundary between the United States and Mexico. To determine the <br />potential effects of the Proposed Action Alternative, simulation modeling of the Colorado River <br />system was conducted. Modeling provides projections of potential future Colorado River system <br />conditions (i.e., reservoir surface elevations, river flows, etc.). The modeling results allow a <br />comparison of potential future conditions. <br />Model simulations of the Colorado River show that there is a low probAtiti1y that the Pro osed <br />Action Alternative would result in -any chanize in the o eration of Colorado Rive_ r reservoirs. <br />Modem results showed t t there ' 12 ercent robabilit that the Pro osed Action <br />lternative would modify any stora e� equalization releases from Lake Powell to Lake Mead. <br />Within this 12 percent probability range, effects were enerally minimal. The Proposed Action <br />Alternative resulted in no long -term effects and there were no effects observed beyond the year <br />2016. <br />Within the identified 12 percent probability that the Proposed Action Alternative could result in a <br />modification of Lake Powell releases, the result would be a temporary increase in water storage <br />at Lake Powell of 0.01 to 6.4 feet of water surface elevation, an increase of up to 407,000 acre - <br />feet of storage (an increase of 2.8 percent). At Lake Mead there is a 12 percent probability that <br />the Proposed Action Alternative could result in a temporary decrease in water surface elevation <br />of 0.01 to 4.1 feet, a decrease of up to 413,000 acre -feet of storage (a decrease of 2.9 percent). <br />There is a 12 percent probability that there could be some minor changes in river flows in the <br />Colorado River between Lake Powell and Lake Mead (through the Grand Canyon). However, <br />changes to equalization releases would be made over multi -month time spans with the resulting <br />flow regimes remaining well within the range of normal operating parameters of Glen Canyon <br />Dam. <br />kIIV <br />