SEIS Bypass Releases

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Purpose and Need The purpose of the 2024 LTEMP SEIS is for Reclamation to analyze additional flow options at Glen Canyon Dam in response to nonnative, invasive smallmouth bass and other warmwater, nonnative species recently detected directly below the dam. The recent detection of large numbers of young-of-year smallmouth bass suggests spawning is occurring for the first time directly below the dam. The need is to disrupt the establishment of smallmouth bass below Glen Canyon Dam by limiting additional recruitment, which could threaten populations of the threatened humpback chub below the dam. Alternatives Triggers The ROD states that in 2024, “The Cool Mix Alternative would be implemented until the mean daily water temperature (without bypass) falls below 15.5°C (60°F) at river mile 61.” Furthermore, it states that in any given year for each alternative, “The trigger location for the 15.5°C (60°F) threshold could be anywhere upstream of river mile 61, depending on the smallmouth bass distribution and size class, frequency and efficacy of sampling, or other considerations as determined through the planning and implementation process.” Offramps The expert panel information was provided to the PI Leadership Team who provided the following recommendation for 2024: “Continue Cool Mix-flow to cool to River Mile 61. Stop Cool Mix flows when Glen Canyon Dam penstocks release water temperatures are observed to be at or below 15.5 and anticipated to remain below that threshold as measured by the sonde (NWIS #09379901) immediately below Glen Canyon Dam.”

Links 2023 Invasive Fish Species Below Glen Canyon Dam: A Strategic Plan to Prevent, Detect and Respond 2019 National Park Service Expanded Non-native Aquatic Species Management Plan 2016 Long-term Experimental and Management_Plan (LTEMP) Page 2013 National Park Service Comprehensive Fisheries Management Plan Nonnative Invasive Aquatic Species Page Smallmouth Bass Page The Temperature Control Page Documents 2024 Glen Canyon Dam Long-Term Experimental and Management Plan Final Supplemental Environmental Impact Statement (SEIS) 2024 Record of Decision for the Glen Canyon Dam Long-Term Experimental and Management Plan (LTEMP) Final Supplemental Environmental Impact Statement (SEIS) 2023 Glen Canyon Dam/ Smallmouth Bass Flow Options Draft Environmental Assessment Presentations and Papers 2024 2024 Off Ramp Memo Final 2024 SMB Flow Offramp - Decision Memo Science Panel Recommendation Regarding Smallmouth Bass Flow Offramps Risk Assessment Panel Summary GCMRC Panel Response AGFD Panel Response WAPA Panel Response WAPA 2024 bypass spawning model NPS Panel Response FWS Panel Response Arizona Republic: Cold water shots into the Colorado River slow a bass invasion in the Grand Canyon WAPA navigates costs of countering smallmouth bass Reclamation begins cold water flows to disrupt spawning of nonnative fish below Glen Canyon Dam Reclamation finalizes environmental process to combat nonnative fish below Glen Canyon Dam 2023 Glen Canyon Dam/Smallmouth Bass Environmental Assessment Update Other Stuff