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<br />0022186 <br /> <br />4 <br /> <br />INTRODUCTION <br /> <br />Many of the physical, biological and cultural resources and processes of the Colorado <br />River ecosystem affected by Glen Canyon Dam are dynamic, and although most changes do <br />not normally occur abruptly, resources may change considerably through time. Some <br />resources do change in a punctuated fashion, rapidly responding to changes in flow regimes. <br />For example, sand bars rejuvenated by the 1996 Beach/Habitat-building Flow began to erode <br />immediately after the event. Other resources shift more gradually; for example, the aquatic <br />foodbase in the Glen Canyon reach changed more gradually during Interim Flows (1991 to <br />1995). <br /> <br />Assessment, use. management and effective protection of ecosystem products and <br />services requires a clear definition of the desired future condition of resources and processes, <br />and must be based on knowledge of antecedent conditions and trends through time. <br /> <br />Monitoring and science programs are critical in providing appropriate knowledge of <br />resource change resulting from differing dam operations. Effectively managed flow regimes <br />can enhance many resources in this ecosystem, and a science-based adaptive management <br />process is the best approach to assure effective management that optimizes stakeholder <br />concerns while affording appropriate protection, management and use of the river ecosystem. <br /> <br />Colorado River ecosystem stakeholders have requested from the GCMRC an annual <br />evaluation of state of the river ecosystem resources. This report also fulfills part of the <br />requirements of Section 1804, subsections (c) and (d) of the 1992 Grand Canyon Protection <br />Act (GCP A), as well as some requirements of the 1995 Glen Canyon Dam Environmental <br />Impact Statement (GCDEIS) and 1996 Record of Decision (ROD). This evaluation. <br />combined with information on predictions of future reservoir storage and weather, can be <br />used as resources to discuss potential flow regimes to protect and/or enhance the Colorado <br />River ecosystem. This report presents the 1997 state of the Colorado River ecosystem in <br />relation to the March/April 1996 Experimental Flow (45,000 cfs for 7 days. hereafter referred <br />to as the 1996 Test Flow), and subsequent high sustained flows (20,000-27,000 cfs) in 1996 <br />and 1997 <br /> <br />FLOW HISTORY <br /> <br />Discharge from Glen Canyon Dam in 1996 and 1997 reflected the transition from <br />Interim Flows to ROD management strategies, and a transition from a relatively normal year <br />to a high inflow year (Figure 1). Dam releases in 1996 generally varied between 8,000 cfs and <br />19,000 cfs, with high end fluctuating flows predominating prior to, and after the Beach <br />Habitat Building Flow During the late March/early April 1996 Test Flow. discharge was <br />maintained at 45,000 cfs for 7 days. Lower fluctuations in flows occurred in the autumn of <br />1996. <br /> <br />Final Draft - 12/12/97 - For AMWG Review <br />