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<br />O[)243:~ <br /> <br />D R AFT Federal Register Notice <br />5/13/98 <br /> <br />DEPARTMENT OF THE INTERIOR <br />Bureau of Reclamation <br /> <br />4.5 Foot Spillway Gate Extensions, Glen Canyon Dam <br /> <br />AGENCY: <br />Bureau of Reclamation, Interior <br /> <br />ACTION: <br />Decision to Postpone Installation <br /> <br />SUMMARY: The purpose of this action is to notify the public that the Secretary of the Interior, <br />based upon recommendations from the Adaptive Management Work Group (AMWG), has <br />decided not to install the 4.5 spillway gate extensions on Glen Canyon Dam for an indefinite <br />period oftime. During this indefinite period, operation of the dam, as stated in the Record of <br />Becision, shall be in accordance with The Annual Operating Plan process and shall not include <br />reservation of storage to compensate for that space that would have been created by the gate <br />extensions. <br /> <br />SUPPLEMENTARY INFORMATION: Since large dam releases have significant impacts on <br />downstream resources, the Glen Canyon Dam Environmentallmpact Statement (GeDEIS) <br />contained recommendations on restricting the frequency oflarge releases above powerplant. <br />capacity, citing two options for controlling such releases. The Record Of Decision (ROD) for <br />the GCDEIS selected the option of installing spillway gate extensions rather than the option of <br />providing a greater vacant storage space buffer to reduce the frequency of powerplant bypasses. <br /> <br />GCDEIS and Grand Canyon Protection Act (GCPA) Conclusions Regarding Powerplant <br />Bypasses <br /> <br />The majority of the Glen Canyon Environmental Studies (GeES) Phase I research work took <br />place in the mid-1980's, when the releases from Glen Canyon Dam were at an all time high since <br />the construction of the dam. These flood flows were so different than historic releases and caused <br />such large effects downstream that they had a great influence on GeES recommendations. <br /> <br />On page 83 of the final GeES Phase I report, the first and foremost conclusion was that <br />"Adverse downstream consequences are caused primarily by sustained flood releases significantly <br />greater than powerplant capacity and by fluctuating releases", noting the erosive effect of floods <br />on sand deposits and vegetation. Generally, these conclusions suggested the elimination or <br />reduction of flood flows. <br /> <br />In the committee report accompanying the GeP A legislation, the Congress continued this <br />thinking of adverse impacts by stating that "Flood releases from the dam erode beaches used by <br />