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<br />EIS Update: <br />Why Modify the Flows in the Preferred Alternative? <br />By: WiUiam C. Leibfried, EIS Team Member <br />Hualapai Tribe <br /> <br />As discussed in the Fall 1994 issue of the CRSO <br />newsletter, the preferred alternative for the Glen <br />Canyon Dam draft environmental impact statement <br />(EIS) was modified for the final EIS. In addition to the <br />operational changes in maximum flows and upramp <br />rates, the Adaptive Management Program will include <br />endangered fish research flows as requested by the u.s. <br />Fish and Wildlife Service in its biological opinion. The <br />biological opinion also identified temperature modifica- <br />tion as a critical factor affecting endangered fish in the <br />Grand Canyon. Reclamation will be requesting funds to <br />expeditiously complete the needed studies to move <br />forward with selective withdrawal structures at Glen <br />Canyon Dam. <br /> <br />The flow modifications to the preferred alternative <br />. include an increase from 20,000 to 25,000 cubic feet per <br />second (cfs) maximum flow and an upramp increase <br />from 2,500 to 4,000 cfs per hour. These changes were <br />reviewed and agreed upon by the cooperating agencies, <br />other interested parties, and the GCES senior scientist <br />and his advisory panel, made up of experts from each <br />discipline currently conducting research in the Grand <br />Canyon. <br /> <br />On March 1, 1993, the GCES senior scientist and the <br />advisory group met to determine the potential impacts <br />from these modifications. Their goal was to evaluate <br />the original interim operating criteria recommendations <br />made in April 1991, current interim operating criteria, <br />data from the research period of June 1990 to July 1991, <br />and other pertinent data collected during monitoring of <br />the interim operations of Glen Canyon Dam. Their <br />findings determined that there would be no significant <br />impact to downstream resources if the maximum flow <br />was raised to 25,000 cfs and the upramp to 4,000 cfs per <br />hour. <br /> <br />A consultation meeting, as required by the Grand <br />Canyon Protection Act, was held on August 26, 1993, to <br />discUss the proposal to change operations. This meeting <br />was open to the cooperating agencies, power interests, <br />recreation and environmental groups, and the general <br />public. An entire morning session was dedicated to the <br />discussion of impacts to natural resources, economic <br /> <br />resources, and compliance with the National Environ- <br />mental Policy Act. The GCES senior scientist presented <br />data concluding that resource impacts to aquatic <br />resources would be minimal to none below the Lees <br />Ferry reach, and there may be some slight impacts <br />during maximum flow releases above Lees Ferry. <br /> <br />The scientists concluded that increasing the maximum <br />releases to 25,000 cfs may provide for benefits to some <br />Grand Canyon resources. .. Riparian vegetation would <br />likely benefit from the infrequent inundation by the <br />25,000 cfs maximums. This flooding may encourage <br />growth of mature vegetation and may also benefit young <br />seedlings. During moderate and high volume months, <br />the more frequent higher maximum flows would rebuild <br />beaches to higher elevations, create and maintain <br />backwater habitats for young native fishes, and reduce <br />financial impacts to power consumers. <br /> <br />The maximum flows under this new preferred alternative <br />will rarely be used because of monthly release volumes <br />dictated by the Annual Operating Plan and maximum <br />daily fluctuating constraints. During minimum release <br />years (8.23 million acre-feet), flows are expected to <br />exceed 20,000 cfs less than 1 percent of the time. These <br />minimum release years may occur 50 percent of the <br />time. Only during months with release volumes between <br />.9 and 1.5 miIlion acre-feet will the maximum release <br />exceed 20,000 cfs. With monthly release volumes <br />greater than 1.5 miIlion acre-feet, the flows would be <br />steady at 25,000 cfs or more, regardless of the <br />alternative chosen. Simply put, in only 3 of the past 38 <br />months of interim operations have the flows exceeded .9 <br />million acre.feet, with no months over .925 miIlion acre- <br />feet. <br /> <br />With the small amount of time that the maximum flows <br />would actually be released under the preferred alterna- <br />tive, no measurable difference in impacts would be <br />realized from the original preferred alternative in the <br />draft EIS which did not contain these increases. <br /> <br />No impacts from increasing upramps to 4,000 cfs per <br />hour have been identified by the researchers working in <br />the Grand Canyon. <br /> <br />5 <br />