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<br />002431 <br /> <br />DRAFT <br /> <br />TWG POSmON PAPER <br /> <br />Glen Canyon Dam Spillway Gate Extensions <br /> <br />, <br /> <br />Background: The preferred alternative in the final environmental impact statement on the <br />operations of Glen Canyon Dam allowed two options for decreasing the frequency of spills <br />greater than 45,000 cfs. When the Secretary of the Interior signed the Record of Decision he <br />chose the option of permanently installing 4.5 foot extensions on both sets of spillway gates at <br />Glen Canyon Dam. The purpose of this provision was to increase Reclamation's ability to safely <br />control high runoff years and not spill large volumes of water downstream through Glen and <br />Grand Canyons. This was selected as the means to accomplish this objective instead of the <br />alternative of increasing the storage buffer currently used as a protection against unexpected late <br />spring forecast increases. The Basin States opposed the storage buffer concept due to the <br />negative impact it would have on the Upper Basin yield. <br /> <br />At the January 1998 AMWG meeting a position paper was presented recommending the TWG be <br />tasked with analyzing the implications of not installing the extensions. Some members of the <br />TWG were charged with addressing the issue and provided the attached analysis to the TWG for <br />review and comment. <br /> <br />Recommendation: Based upon the analysis and comments received from TWG members, the <br />TWG recommends that the AMWG advise the Secretary of the Interior to indefinitely postpone <br />permanent installation of the 4.5 foot spillway gate extensions. During this indefinite period, <br />operation of the dam, as stated in the Record of Decision, shall be in accordance with the Annual <br />Operating Plan process and shall not include reservation of storage to compensate for that space <br />that would have been created by the gate extensions. The decision to indefinitely postpone <br />installation of the gate extensions would be documented in the form of a Federal Register Notice. <br /> <br />Attachment: Analysis Paper on Spillway Gate Extensions <br />