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Environmental Impact Statements and Records of Decision

The Glen Canyon Dam Final EIS analyzed baseline impacts of dam operations on downstream environmental and cultural resources from 1963 to 1990, and compared those baseline impacts to possible alternative operations of Glen Canyon Dam, including three alternatives that would provide steady flows from the dam and six alternatives that would provide various levels of fluctuating flows. The EIS team and the cooperating agencies identified a preferred alternative called: the Modified Low Fluctuating Flow Alternative. This EIS served as the culmination of the Glen Canyon Environmental Studies launched in the early 1980s to document the effects of Glen Canyon Dam on downstream resources, fulfilling one of the mandates of the Grand Canyon Protection Act of 1992.

The 1996 RoD formally adopted the preferred alternative from the 1995 EIS stipulating the Modified Low Fluctuating Flow Alternative for operating Glen Canyon Dam. It also initiated the Glen Canyon Dam Adaptive Management Program (GCDAMP) by establishing the Adaptive Management Work Group (AMWG) under the Federal Advisory Committee Act (FACA). AMWG’s stipulated purpose was to develop “a long-term monitoring, research, and experimental program” to evaluate the continuing effects of dam operations and to propose additional modifications when warranted.