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<br />, <br /> <br />MEMO TO FILE <br /> <br />Date: October 24, 1997 <br /> <br />From: Anthony G. Morton, Environmental Compliance Specialist, UC-333 <br /> <br />Subje~t: Proposed Fall 1997 Release from Glen Canyon Dam <br /> <br />The foUowing questions and answers pertain to a proposal to make a special test release from <br />GCD in October 1997, the reasons for the proposal, and the anticipated impacts. <br /> <br />Q: What is the proposed action? <br /> <br />A: The Bureau of Reclamation proposes to do a test release of water from Glen Canyon Dam, at <br />powerplant capacity, for 2 days, beginning at noon on November 3, 1997 and concluding at noon <br />on November 5, 1997. The maximum rated powerplant capacity is 33,200 cfs, but due to the <br />current status of the generating units, the maximum achievable during this event is expected to be <br />only about 3 1,000 cfs. <br /> <br />Q: What is the purpose for this release? <br /> <br />A: The release is viewed as an opportunity to test the whether a designed release can move fine <br />sediments that came down the Paria River, and other ungaged tributaries to the Colorado River in <br />Grand Canyon, AZ, this past August, and deposit it at higher levels on beaches along select <br />reaches of the Colorado River. <br /> <br />Q: Why is the Bow needed? <br /> <br />A: Previously accumulated sediment deposits in the channel of the Colorado River appear to have <br />been depleted by high-constant flows between 21,000 and 27,000 cfs during Water Year 1997. <br />The volume of channel-stored sand in the system is now near those that existed after 1986, the <br />end of the last high-Bow period. The intent of this proposed flow is to attempt and establish a <br />reserve of fine sediment along shorelines and in eddies for use in a possible subsequent spring <br />1998 beachfhabitat building flow. The high August inflows to the Paria and other tributaries has <br />temporarily made more sediment available. Because a release of this particular magnitude, timin:g <br />and duration hu not been Slleciftcally planned and observed in the past, the event is also viewed <br />as a test, with the objective of determining if sediment can be deposited in such a way as to be <br />subsequently available to move during a higher flow event. <br /> <br />Q: Are there other alternatives to accomplishing the desired objective? <br /> <br />A: No. This specific action is unique because it's based on existing sediment conditions due to <br />the August runoff from the Paria and other tributaries and the fact that there is enough water <br />available in the system due to high inflows to attempt and move the sediment onto the banks, In <br />fact, that available water must be moved downstream anyway, in anticipation of continuing high <br />