Going with the (Fish) Flow: Contrasting Implementation of Additional Environmental Fish Flows and Natural Flows in Select Reservoirs of the Upper Colorado River Basin

The Green River is the Colorado River’s largest tributary, contributing a substantial volume of water to the Colorado River Basin that may be retained in reservoirs and utilized to generate hydroelectric power while maintaining important riparian and ecological habitat. Recently, two environmental fish flows for Flaming Gorge Dam along the Upper Green River have been proposed. The primary objective of this study was to assess the effect of these proposed environmental fish flows, in addition to a “run-of-the-river" alternative, on reservoir storage and hydropower generation at Fontenelle, Flaming Gorge, and Lake Powell Reseroirs. Results obtained from Colorado River Simulation Software (CRSS) multi-run simulation models reveal that, for the years 2020-2060, implementation of both proposed environmental fish flows at Flaming Gorge Dam will decrease average monthly storage by 1.6% and increase annual hydropower generation by 0.1%. The environmental fish flow promoting elevated summer baseflows to advantage native Colorado pikeminnow had greater influence on these findings than did the environmental fish flow aimed to disadvantage non-native smallmouth bass. Over the same time period, the “run-of-the-river” alternative will decrease average monthly storage 2.2% and decrease annual hydropower generation 2.7%. These results provide Colorado River Basin water managers, scientists, and stakeholders with additional context regarding the potential future implementation these alternatives.

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