Difference between revisions of "SEIS Bypass Releases"

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.

Cool Mix Alternative (Preferred Alternative)

The Cool Mix Alternative aims to maintain a daily average water temperature below 15.5 degrees Celsius (C) (60 degrees Fahrenheit [F]) at the target river mile locations below Glen Canyon Dam where smallmouth bass could spawn. It would involve strategic water releases from both the penstocks and river outlet works, with quantities determined by predicted temperatures. Flows would be triggered when temperatures rise above 15.5C (60F), with variations based on monthly water volumes and conditions.

Cool Mix with Flow Spike Alternative

The Cool Mix with Flow Spike Alternative would maintain daily average water temperatures below 15.5C (60F) at the target river mile locations below Glen Canyon Dam. It would include up to three 8-hour flow spikes, with a maximum flow of up to 45,000 cubic feet per second (cfs), to disrupt spawning in margin habitats. HFE releases could replace flow spikes to maximize sediment benefits. Water releases would vary monthly based on predicted temperatures. Flow spikes and HFE releases would be similar but triggered differently. During a flow spike, peak discharge would be up to 32,000 cfs, moving about 133,000 acre-feet of water over 3 days.

Cold Shock Alternative

The Cold Shock Alternative aims to induce short-duration cold shocks, lowering temperatures to 130C (55.4F) at the target river mile locations below Glen Canyon Dam to disrupt smallmouth bass spawning and rearing. Flows would be activated when temperatures rise above 15.50 (60 F), with cold shocks potentially occurring every weekend for up to 12 weekends, lasting 48 hours each. The goal would be to achieve rapid and sustained cooling of the river to disrupt spawning behavior. Actual release capacities may vary slightly based on operational constraints, and hydropower releases are assumed to be 2,000 cfs. Extreme high-temperature scenarios may limit reaching the target temperatures.

Cold Shock with Flow Spike Alternative

The Cold Shock with Flow Spike Alternative would involve releasing water through the river outlet works for 48 hours to induce a cold shock downstream to the targeted river mile. Up to three 8- hour flow spikes may also be implemented if enough water is available to disrupt spawning in warmer margin habitats. The release quantity would be based on predicted temperatures and operational constraints, which would vary' throughout the year. This alternative would start when daily water temperatures at the Little Colorado River reach 15.5C (60F), with weekly 48-hour cold- shock releases and at least one 8-hour flow spike, lasting up to 12 weeks.

Non-Bypass Alternative

The Non-Bypass Alternative would involve strategic river stage changes along the Lees Ferry reach to disrupt smallmouth bass nests and spawning activities below Glen Canyon Dam. It would include a once-weekly, short-duration, low-flow release followed by a short-duration, high-flow release. The low-flow release would target shallow nesting areas, while the high-flow release would increase water velocities in deeper habitats. These releases would be designed to attenuate by the time they reach the Little Colorado River confluence. Flows would start on Sunday nights, peak on Monday morning, and return to normal by Monday afternoon. The treatment would be repeated weekly based on water temperature projections. This alternative aims to disrupt spawning at river mile 61, with adjustments possible during implementation.

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.” (2024 SMB Flow Offramp - Decision Memo)

Potential off-ramps would be considered based on monitoring data. Off-ramps will occur if any unacceptable adverse impacts on the resources listed in Section 1.3 of the 2016 LTEMP ROD's Attachment B are anticipated. Off-ramps would also occur if the experiments prove to be inefficient at disrupting smallmouth bass spawning and meeting the purpose and need. (ROD)

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.” (2024 SMB Flow Offramp - Decision Memo)

• 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

• 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

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