A 2022 Fall HFE

High Flow Experiment- 2022

2022 Fall High Flow Experiment Snapshot

Recommendation Summary

Based on the LTEMP Record of Decision (ROD), the Glen Canyon Dam technical implementation/planning team (PI Team) has worked over the past several weeks to evaluate existing information and data in determining this recommendation regarding a HFE at Glen Canyon Dam. The PI Team’s recommendation regarding implementation of a fall 2022 HFE is based on a careful assessment of resources and best available science. By consensus, the PI Team does not recommend that the Department implement any duration of HFE in fall 2022.

Purpose of the Recommendation Memo

The purpose of this memorandum is to transmit a recommendation to the Glen Canyon Leadership Team (Leadership Team) and to the Department of Interior (Department) in accordance with the LTEMP ROD. The PI Team includes technical representatives from the National Park Service (NPS), U.S. Fish and Wildlife Service (FWS), Bureau of Indian Affairs (BIA), U.S. Geological Survey (USGS) Grand Canyon Monitoring and Research Center (GCMRC), Bureau of Reclamation (Reclamation), Western Area Power Administration (WAPA), Arizona Game and Fish Department (AZGFD), seven Colorado River Basin States (Basin States), and the Upper Colorado River Commission (UCRC).

As noted above, the PI Team has worked over the past several weeks to evaluate existing data and coordinate the potential implementation of an HFE. The PI Team evaluated the latest data from agency experts and considered multiple issues in making its recommendation, as summarized below. The PI Team arrived at this recommendation after several weeks of PI Team conference calls and after receiving feedback from Adaptive Management Program stakeholders. The Secretary of the Interior and/or her Designee will consider the recommendation of the PI Team but retains sole discretion to decide how best to accomplish operations and experiments in any given year pursuant to the LTEMP ROD and other binding obligations for Glen Canyon Dam. The PI Team incorporated the most current science and data and considered multiple issues with agency experts, as summarized below, in making this final recommendation.

24-hour, 48-hr, 96-hour, 144-hour, and 192-hour Fall HFE

The PI Team arrived at this recommendation after several weeks of PI Team conference calls, and after receiving feedback from Adaptive Management Program stakeholders. By consensus, the PI Team is opposed to implementation of any duration (24-hour to 192-hour) HFE in fall 2022. The PI Team identified the following resource concerns associated with any duration of a fall HFE: 1) the increased risks to non-native fish, including the potential to transport juvenile smallmouth bass downstream; 2) challenges and risks associated with reallocating large volumes of water for longer duration HFEs; uncertainties and risks associated with exacerbating low reservoir elevations (e.g. lower annual minimum and risk of falling below minimum power pool); 3) impacts to hydropower production; and 4) increased risk of fish entrainment at lower reservoir elevations.

They also noted that in LTEMP, fall HFEs were predicted to be conducted frequently (~3 out of every 4 years) and it has been four years since the most recent HFE (fall 2018) was triggered and implemented, such that this HFE would rebuild some of the beaches that were lost during this time. GMCRC noted that sandbar benefits from even a 24-hour HFE would likely provide a good learning opportunity and likely have some measure of sediment benefits. It was noted that maintaining camping beaches is important for the LTEMP sediment resource goal. Also noted is the potential for improved legacy of sandbar increases resulting from a fall HFE (predicted +20% sandbar size in April 2022 relative to October 2021) due to relatively low winter flows consistent with the 7.0 maf annual release pattern planned for Lake Powell in Water Year (WY) 2023. The GCMRC highlighted the learning value of implementing an HFE in November 2022 in that it would contribute to addressing, 1) the long-term question about the cumulative effect of multiple HFEs over the 20-year period of the LTEMP, and 2) questions about the effects of shorter duration and lower magnitude HFEs. Although the best available science indicates a fall HFE could result in some unknown level of increased to undesired non-native species (smallmouth bass and green sunfish), the consequences to humpback chub of dispersing new young-of-year non-native smallmouth bass is very high. Thus, expert opinion among fishery biologists was that even a 24-hour fall HFE could substantively increase the risk to endangered and native fishes in Grand Canyon. [1]

Sediment Conditions

Fall Accounting Period

• Paria input (Jul 1 to Nov 30): 1,600,000 mt
• Accumulated in Upper Marble Canyon (Jul 1 to Nov 30, lower bound) = 970,000 mt
• Accumulated in Lower Marble Canyon (Jul 1 to Nov 30, lower bound) = 270,000 mt
• Available for Fall HFE: 1,240,000 mt

SUPPORTING DOCUMENTS

• Fall 2022 HFE - Decision Memo
• Tech Team Report - Fall 2022 HFE Recommendation
• Evaluation of High-Flow Experiments under conditions of low flows and low reservoir elevations

CONCERNS

Humpback chub

The adult humpback chub population in the Little Colorado River aggregation is currently above the Tier-1 threshold of 9,000 adults identified in the Biological Opinion for the LTEMP (GCMRC unpublished data, FWS unpublished data). Past HFEs have had no measurable direct effects, positive or negative, on humpback chub or other native fish. Their populations in the Little Colorado River aggregation remained relatively stable over the decade from 2009-2019, a period that included HFEs in 2012, 2013, 2014, and 2016 and increased water temperatures (Kennedy and Ralston 2011, GCMRC unpublished data). However, populations are now declining in the Little Colorado River aggregation and are expected to continue to decline over the next few years. The three-year average (2018-2020) of large sub-adult humpback chub in the Colorado River mainstem from river mile 63.45 to 65.2 (juvenile chub monitoring reach) was estimated at 600 fish, which is below the 810 fish required to prevent initiation of a Tier 1 fish management action trigger. Fish biologists are working to identify factors that may have led to poor recruitment, assess the current outlook for humpback chub populations in the Grand Canyon, and evaluate early intervention actions that can be taken to reverse the decline. HFEs may indirectly affect humpback chub through increased risk of dispersal of warmwater nonnative fish which inhabit Lees Ferry, such as smallmouth bass, which are discussed below. Based on provisional unpublished data, humpback chub were not directly affected by the 2012, 2013, 2014, 2016, or 2018 HFEs, with adult populations appearing stable over the period of these HFEs and juvenile populations fluctuating in response to variable recruitment in the Little Colorado River. A fall 2022 HFE poses unacceptable risks to humpback chub because of the increased risk of distributing smallmouth bass downstream.

Hydropower and Energy

WAPA estimated the financial cost of implementing a 2022 fall HFE is between $0.56 million and $6.13 million, depending on duration and which months water is moved from to provide volume for the HFE (Table 2). Total loss in energy production due to bypass flows and losses in efficiency range from -12,872 MWh to -74,490 MWh depending on the flow duration and month of water exchanges.

WAPA estimates that the balance of the Upper Colorado River Basin Fund (Basin Fund) will be approximately $115 million at the end of fiscal year 2022. This increase from last year is the result of temporary mitigation efforts including Reclamation’s use of miscellaneous receipts and carryover funds ($34 million), appropriations received by Reclamation to fund the environmental programs ($21.4 million), utilization of funds from the Bipartisan Infrastructure Law (BIL) ($29.8 million), and deferrals of O&M expenses and capital projects. WAPA also implemented a new rate, which increased the rate of energy and also significantly reduced the amount of hydropower being delivered to CRSP customers. This action mitigated $98 million of purchase power O&M expense in FY22. Many of these mitigation efforts will not be available to WAPA in the future. As a result, WAPA projects significant reductions in the Basin Fund balance over the next two years. The project is facing reduced reservoir levels (hydraulic head), low annual releases from Glen Canyon Dam (7.0 maf in WY 2023) and has further concerns about the risk of going below minimum power pool at Glen Canyon Dam. Multiple PI Team members cited the current status of the Basin Fund and the hydropower resource as cause for concern regarding implementation of a Fall 2022 HFE without considerable risk of adverse impacts and exacerbation of the system.

Other Native Fishes

In addition, if an HFE led to dispersal of smallmouth bass, it could then lead to indirect impacts on native fish such as humpback chub through future predation. Nonetheless, this potential indirect effect depends on factors driving turbidity that are less certain, such as additional tributary sediment inputs. Thus, no direct unacceptable negative response would be expected among native fishes to a fall HFE this year, based on current monitoring results and previous HFEs. However, indirect effects from potential expansion of smallmouth bass create an unacceptable risk to native fish.

Sediment

Sandbar monitoring data collected in October 2021 show erosion of sandbars since the fall 2018 HFE caused both by normal dam operations and extensive gully erosion at many sandbars in Marble Canyon and Grand Canyon caused by thunderstorms in summer 2021. Additional gully erosion has occurred in the summer 2022 monsoon season.

Nonnative Invasive Species

Though there are several locations of green sunfish in Grand Canyon, an HFE would still present an elevated risk of dispersal if a fall HFE pushed a large number of green sunfish downstream from Lees Ferry. Fall HFEs do pose an unacceptable risk to humpback chub recovery when there are high numbers of green sunfish and other warmwater nonnative fish found in Glen Canyon that could be dispersed downstream.

Although a November 2022 HFE may trigger additional immigration of adult brown trout into Lees Ferry, brown trout populations in Lees Ferry are large enough at this point that additional immigration arising from a fall HFE is not anticipated to substantively increase the risk to endangered and native fishes that are downstream in Grand Canyon above the existing level of risk.

It is not known what the response of smallmouth bass might be to a high flow event. There is some evidence that smaller fish (<25 mm TL) are more susceptible to being displaced by higher flows compared to larger fish (Harvey 1987). The HFE could displace them further downstream, or it may not have any effect. Smallmouth bass prefer water velocities of < 0.2 meters per second (m/s) (Todd and Rabeni 1989) and during a HFE one could assume that they would be actively searching for areas of low water velocity. A fall 2022 HFE poses unacceptable risk to endangered and native fishes due to the potential for increasing downstream movement of smallmouth bass.

With low lake elevations, increased risk of fish entrainment through Glen Canyon Dam and increased river temperatures conducive to warm water invasive fishes exists. At reservoir elevations below ~3,530 ft, surface levels are less than 20 m away from the penstock centerline and fish entrainment risk increases, as recent monitoring has revealed that the majority of pelagic fish are located in the top 20 m of the water column (Utah State University, unpublished data). A November 2022 fall HFE may pose unacceptable risks to endangered and native fishes from non-native fish that may be entrained through the penstocks during a fall HFE.

Water Delivery - Monthly, Daily, and Hourly Releases

A fall 2022 HFE poses progressive risk to critical Lake Powell elevations with increasing duration HFE alternatives. (http://gcdamp.com/images_gcdamp_com/7/75/2022.09.30_-_FINAL_TechReport_-_Fall_2022_HFE_Recommendation_dist.pdf)

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