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Overview 13 certain critical modules of the model could not even reliably predict the general direction of ecosystem response, such as response of native fishes to warmer water conditions through implementation of a proposed temperature control device. \Vhile water could be routed through the ecosystem with confidence, there was considerably less confidence about the longer term relationship of flows to fine-sediment flux and beaches on the basis of remain- ing downstream sand supplies alone. Although the inability of the GCM to accurately simulate higher level trophic (e.g., fishes) responses in critical areas was cause for concern among managers, the goal of systematically identifying gaps in data and knowledge so that future research (including eXperimentation) and monitoring could be designed and implemented to fill the gaps was an acknowledged objective of the modeling effort. In a sense, the largest contribution made by the conceptual modeling project was the identification of vari- ous experimental /1ow and nonflow treatments that would need to be tested (presumably, within some longer term design) to provide managers with scientifically based options for most effectively meeting the proposed management goals. Experimentation has long been identified as a sign of "active" adaptive management and has been shown to be an efficient means of resolving the uncertainty associated with various alternative management policies ('Valters and Holling, 1990). Simultaneously, the modeling project helped identify additional monitoring data that would be required to more fully evaluate the influence of the modified low fluctuating flow policy on downstream resources of concern. Although evaluation of all the resources outlined in the EIS has not been possible because of pro- gram funding limitations, the GCM identified the general linkages between the varied resources as related to dam operation. The experimental designs proposed and implemented in the Glen Canyon Dam Adaptive Management Program have been a direct and logical outcome of conceptual modeling activities. Though still not complete, to date, the experimental results have greatly advanced ecosystem understanding. Ultimately, the knowledge gained through these scientific activities in the Colorado River ecosystem should lead to improved management options for Glen Canyon Dam that will benefit society. . . . . . 1992 Grand Canyon Protection Act of 1992 passed " , ,~~..;:. ,,"" ~-i~~ !~L - t.".~ ~:.,. f~~' ~,,: \ .-...,.' . . .'" ~. . 1995 Operation of Glen Canyon Dam Final Environmental Impact Statement completed; Transition Work Group and Grand Canyon Monitoring and Research Center begin formulating strategic plan; southwestern willow flycatcher (Empidonax trail/ii extimus) federally listed as endangered; Department of the Interior constitutes the Grand Canyon Monitoring and Research Center and locates it in Flagstaff, Arizona 1994 Programmatic Agreement on Cultural Resources signed between the State of Arizona, Department of the Interior agencies, and six tribes over protection of cultural resources in the river corridor below Glen Canyon Dam; U.S. Fish and Wildlife Service designates critical habitat for four species of endangered Colorado River fish and completes Biological Opinion outlining reasonable and prudent alternatives that must be evaluated for dam operation