Laserfiche WebLink
<br />OD2282 <br /> <br />normal pool level in July of 1983. Because of the need for increased releases from Glen Canyon <br /> <br /> <br />Dam, the spillway structures and hollow jet bypass tubes were operated on several occasions. <br /> <br /> <br />This allowed significant amounts of water to be released from levels above and below the <br /> <br /> <br />penst.Q~k zoneo_Thesefactors,combined to cause nearly complete mixing of the reservoir in 1985, <br /> <br /> <br />due to the high volume of reservoir throughput and the operation of the alternative release <br /> <br /> <br />structures. In the late 1980's, drought conditions returned to the upper basin and resulted in <br /> <br />decreasing reservoir levels and the return of strong chemical stratification below the penstock <br /> <br />level. <br /> <br />1990-1997 The period from 1990 to 1997 was marked by a series of manipulations to the <br /> <br />operation of Glen Canyon Dam for scientific and environmental purposes. Before this time, the <br /> <br /> <br />dam was operated primarily for peaking power generation and water delivery to the Lower Basin <br /> <br /> <br />States. In 1990, Phase II of the Glen Canyon Envirorunental Studies and the development of the <br /> <br /> <br />Glen ganyon Dam EIS began. As part of the GCES Phase II Integrated Research Plan (USBR <br /> <br /> <br />1990), a series of research flows was initiated from June 1990 to August 1991. These flows <br /> <br /> <br />ranged widely in daily fluctuations and ramping rates, interspersed with periods of steady flow. In <br /> <br /> <br />November 1991, following the research flow period, the Secretary of the Interior implemented the <br /> <br /> <br />Interim Operation Criteria, which set limits on minimum and maximum discharge, daily range of <br /> <br /> <br />discharge, and hourly ramping rates. These criteria remained in place until October 1996, when <br /> <br /> <br />the Secretary signed the Record of Decision for the preferred alternative of the Glen Canyon <br /> <br /> <br />DAM EIS (U.S. Bureau of RecIamation 1995 and 1996). <br /> <br /> <br />Of significance during this latter period was the experimental beachlhabitat building flow in <br /> <br /> <br />March and April 1996. This 7-day discharge of 45,000 cfs included a release of 15,000 cfs from <br /> <br /> <br />the river outlet works of Glen Canyon Dam. The operation of this structure released water from <br /> <br />03/06/98 <br /> <br />DRAFT <br /> <br />Page 6 of 62 <br />