Entrainment - Revision history

Cellsworth at 20:23, 13 October 2026

2026-10-13T20:23:59Z

Cellsworth at 20:22, 13 October 2026

2026-10-13T20:22:39Z

Cellsworth at 20:18, 13 October 2026

2026-10-13T20:18:58Z

Cellsworth at 21:59, 18 June 2026

2026-06-18T21:59:43Z

Cellsworth at 19:02, 31 October 2025

2025-10-31T19:02:36Z

Cellsworth at 17:49, 31 October 2025

2025-10-31T17:49:04Z

Cellsworth at 17:39, 31 October 2025

2025-10-31T17:39:55Z

Cellsworth at 17:05, 31 October 2025

2025-10-31T17:05:59Z

Cellsworth at 18:35, 27 February 2025

2025-02-27T18:35:12Z

Cellsworth at 18:00, 27 February 2025

2025-02-27T18:00:15Z

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 '''2022'''
-*[https://www.usbr.gov/uc/progact/amp/twg/2022-10-13-twg-meeting/20221013-HydroacousticFishDistribution-508-UCRO.pdf Hydroacoustic Fish Distribution ]
+*[https://www.usbr.gov/uc/progact/amp/twg/2022-10-13-twg-meeting/20221013-GlenCanyonDamFishEscapementOptions-508-UCRO.pdf Svoboda. 2022. Glen Canyon Dam Fish Escapement Report (Final)]
 *[https://www.usbr.gov/uc/progact/amp/amwg/2022-08-18-amwg-meeting/20220818-GlenCanyonDamFishEscapementOptions-508-UCRO.pdf Glen Canyon Dam Fish Escapement Options ]
-*[https://www.usbr.gov/uc/progact/amp/twg/2022-10-13-twg-meeting/20221013-GlenCanyonDamFishEscapementOptions-508-UCRO.pdf Glen Canyon Dam Fish Escapement Report]
+*[https://www.usbr.gov/uc/progact/amp/twg/2022-10-13-twg-meeting/20221013-HydroacousticFishDistribution-508-UCRO.pdf Hydroacoustic Fish Distribution ]
 *[https://www.usbr.gov/uc/progact/amp/twg/2022-06-16-twg-meeting/20220616-CharacterizingFishAssemblageLakePowellForebay-508-UCRO.pdf Characterizing the fish assemblage of the Lake Powell forebay: identifying the potential for nonnative fish escapement through Glen Canyon Dam and into the lower Colorado River ]
 *[https://www.usbr.gov/uc/progact/amp/twg/2022-04-13-twg-meeting/20220413-HydroacousticFishDistributionLakePowell2022-Presentation-508-UCRO.pdf Hydroacoustic Fish Distribution - Lake Powell 2022 ]

@@ Line 114: / Line 114: @@
 '''2024'''
-*[[Media:Glen_Canyon_Fish_Escapement_Appraisal_Report_05.2024_FINAL.pdf | Glen Canyon Fish Escapement Appraisal Report (Final)]]
+*[[Media:Glen_Canyon_Fish_Escapement_Appraisal_Report_05.2024_FINAL.pdf | Wagner and Svoboda. 2024. Glen Canyon Fish Escapement Appraisal Report (Final)]]
 *[[Media:2024_GCD_Turbine_Outflow_Progress_Report.docx|Glen Canyon Dam Turbine Outflow Tucker Trawl Netting - 2024 Progress Report ]]
 *[https://www.usbr.gov/uc/progact/amp/twg/2024-01-25-twg-meeting/20240125-TWGMeeting-HydroacousticMonitoring-508-UCRO.pdf Hydroacoustic Monitoring ]

@@ Line 114: / Line 114: @@
 '''2024'''
 *[[Media:2024_GCD_Turbine_Outflow_Progress_Report.docx|Glen Canyon Dam Turbine Outflow Tucker Trawl Netting - 2024 Progress Report ]]
 *[https://www.usbr.gov/uc/progact/amp/twg/2024-01-25-twg-meeting/20240125-TWGMeeting-HydroacousticMonitoring-508-UCRO.pdf Hydroacoustic Monitoring ]

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 '''2024'''

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-The entrainment risk is reduced in the winter because smallmouth bass are located in shallower warmer water like in Wahweap Bay. <br>
+The entrainment risk is reduced in the winter because smallmouth bass are located in shallower warmer water like in Wahweap Bay. The entrainment risk is higher in the summer because smallmouth bass are located in the forebay. <br>
 The entrainment risk is higher in the summer because smallmouth bass are located in the forebay. <br>
 Lower reservoir elevations result in a higher entrainment risk because smallmouth bass are found nearer to the penstock withdrawals.

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 Smallmouth bass are less susceptible to entrainment in the winter because they are largely absent from the forebay at that time of year. As Lake Powell warms in the spring and summer, smallmouth bass move from the shallow bays into the mainstem areas of the reservoir [https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=1304&context=etd2023 (1)]. Additionally, as the reservoir elevations decline and the thermocline reaches penstock elevation, fish are brought into closer proximity to the intakes of the dam which increases the risk of entrainment [https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=1304&context=etd2023 (2)]. Also, in years with large inflows, the thermocline can reach deeper into the reservoir which also brings fish into closer proximity to the intakes and increases the risk of entrainment [https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=1304&context=etd2023 (3)], [[Media:Eppehimer_etal_2025_Declining_res_elevations_non-native_fish_passage_CJFAS.pdf|(4)]].  <br>
-How do you know if you are entraining smallmouth bass through the dam? Since smallmouth bass typically stay above the thermocline, any release when the thermocline is at or below penstock level is likely to be entraining bass and the warmer the release the higher the rate of entrainment. <br>
+How do you know if you are entraining smallmouth bass through the dam? Since smallmouth bass typically stay above the thermocline, any release when the thermocline is at or below penstock level is likely to be entraining bass and, as a gage, the warmer the release the higher the rate of entrainment. <br>
 Recommendation: Keep reservoir elevations higher during the spring, summer, and fall when smallmouth bass are more susceptible to entrainment or find some way to cool the forebay to keep smallmouth bass away from the dam (see the [https://gcdamp.com/index.php/TCD_Learning_Page Temperature Control page]). <br>

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 ==Entrainment of warmwater nonnative fish through Glen Canyon Dam==
-Winter: reduced entrainment risk, bass are in shallower warmer water like in Wahweap Bay. <br>
+The rate of entrainment is dependent on the season, reservoir elevation, and thermocline depth. <br>
-Summer: higher entrainment risk, bass are found in the forebay
-Lower reservoir elevations: higher entrainment risk, bass are found nearer to the penstock withdrawals
+Smallmouth bass are less susceptible to entrainment in the winter because they are largely absent from the forebay at that time of year. As Lake Powell warms in the spring and summer, smallmouth bass move from the shallow bays into the mainstem areas of the reservoir [https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=1304&context=etd2023 (1)]. Additionally, as the reservoir elevations decline and the thermocline reaches penstock elevation, fish are brought into closer proximity to the intakes of the dam which increases the risk of entrainment [https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=1304&context=etd2023 (2)]. Also, in years with large inflows, the thermocline can reach deeper into the reservoir which also brings fish into closer proximity to the intakes and increases the risk of entrainment [https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=1304&context=etd2023 (3)], [[Media:Eppehimer_etal_2025_Declining_res_elevations_non-native_fish_passage_CJFAS.pdf|(4)]].  <br>
-*3543 ft at the 5th percentile
-*3621 ft at the 95th percentile
-Recommendation: Keep reservoir elevations higher during the summer when bass are more susceptible to entrainment [https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=1304&context=etd2023]
+How do you know if you are entraining smallmouth bass through the dam? Since smallmouth bass typically stay above the thermocline, any release when the thermocline is at or below penstock level is likely to be entraining bass and the warmer the release the higher the rate of entrainment. <br>
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 *At elevations of 3621 ft, the risk of entrainment occurs in only 5% of the traces evaluated
-Recommendation: Keep reservoir elevations higher during the summer when smallmouth bass are more susceptible to entrainment with a minimum target of 3543 ft and and an optimal target above 3621 ft. [https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=1304&context=etd2023]
+Recommendation: Keep reservoir elevations higher during the spring, summer, and fall when smallmouth bass are more susceptible to entrainment with a minimum target of 3543 ft and and an optimal target above 3621 ft. [https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=1304&context=etd2023]

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-[[Image:Entrainment.png|thumb|center|550px| ]]
+[[Image:Entrainment.png|center|600px| ]]
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-! <h2 style="margin:0; background:#cedff2; font-size:120%; font-weight:bold; border:1px solid #a3bfb1; text-align:left; color:#000; padding:0.2em 0.4em;">Updates</h2>
+! <h2 style="margin:0; background:#cedff2; font-size:120%; font-weight:bold; border:1px solid #a3bfb1; text-align:left; color:#000; padding:0.2em 0.4em;">[[Media:Eppehimer_etal_2025_Declining_res_elevations_non-native_fish_passage_CJFAS.pdf|Eppehimer et al., 2025, Declining reservoir elevations following a two-decade drought increase water temperatures and non-native fish passage facilitating a downstream invasion: Canadian Journal of Fisheries and Aquatic Sciences]]
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-When the reservoir was cold (<10 °C) and well-mixed, most fishes selected gently sloping habitat such as that found in Wahweap Bay (5 km from GCD), and thus winter entrainment risk is low for most species. When the reservoir was stratified (>20 °C surface temp.) fish were active in the forebay epilimnion within meters of the dam, increasing entrainment when the dam penstock is positioned within the epilimnion, as it was during our study, rather than below the thermocline when the reservoir water level is higher.
+Maintaining Lake Powell elevations above 3590 ft would likely minimize entrainment from the reservoir and create downstream conditions that minimize smallmouth bass population growth. <br>
-Smallmouth Bass Micropterus dolomieu) may survive entrainment at rates above 50% at low water levels, with survival expected to decrease as the water level rises, but remaining problematically high across all water levels where entrainment is expected. Other fishes may survive entrainment at higher rates, depending on physiology.
+Recommendation: Keep reservoir elevations above 3530 ft with an optimal target above 3590 ft. [[Media:Eppehimer_etal_2025_Declining_res_elevations_non-native_fish_passage_CJFAS.pdf|(1)]]
-Minimizing successful nonnative fish passage through GCD is best achieved through maintenance of water levels higher than those in 2022 and 2023, which would decrease both entrainment and survival of entrainment. [https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=1304&context=etd2023]
+[[Image:EntrainmentRate.jpg|center|600px| ]]
-The depth of the epilimnion in the Forebay varies annually as a function of spring runoff, a suite of environmental factors (e.g., Boehrer and Schultze 2008), and water management. Consequently, the minimum reservoir elevation necessary to prevent entrainment of epilimnetic water and associated biota will vary among years and will likely require an adaptive management framework (Williams 2011).  Based on this study, minimum reservoir elevations necessary to limit epilimnetic entrainment in 2022 and 2023 were 1083 m (3552 ft) and 1096 m (3594 ft), respectively.
+Recommendation: Keep reservoir elevations higher during the summer when smallmouth bass are more susceptible to entrainment with a minimum target of 3543 ft and and an optimal target above 3621 ft. [https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=1304&context=etd2023]
-Considering the full likely range of depth to thermocline (5th to 95th percentiles of USGS historical time series), we suggest avoiding epilimnetic entrainment requires a reservoir water level between 1080 m (3543 ft) at the 5th percentile and 1104 m (3621 ft) at the 95th percentile (note: as this range is based on historical context, it is valid for a stationary climate, and may shift or expand under nonstationarity).  These elevations translate to a substantial difference in water storage, with storage of 10.1 km3 (8.2 M acre-ft) at 1080 m elevation, increasing roughly 75% to 17.9 km3 (14.5 M acre-ft) at 1104 m elevation (Jones and Root 2022).  The degree of water storage required to maintain higher water elevations and limit epilimnetic entrainment has broadscale implications with respect to water supply and hydropower generation in the Colorado River Basin that are beyond the scope of this study. [https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=1304&context=etd2023]
+[[Image:Forebay_telemetry.png|center|600px| ]]
-[[Image:Forebay sonor.png|thumb|center|500px| ]]
+[[Image:Forebay sonor.png|center|600px| ]]
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-[https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=1304&context=etd2023 Friesen, Barrett T., "Invasion Potential of Nonnative Fishes Through a Large Western Dam Into a Prized and Vulnerable Ecosystem" (2024). All Graduate Theses and Dissertations, Fall 2023 to Present. 288. https://digitalcommons.usu.edu/etd2023/288 ]
+*[[Media:Eppehimer_etal_2025_Declining_res_elevations_non-native_fish_passage_CJFAS.pdf|Eppehimer et al., 2025, Declining reservoir elevations following a two-decade drought increase water temperatures and non-native fish passage facilitating a downstream invasion: Canadian Journal of Fisheries and Aquatic Sciences]]
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