Difference between revisions of "Entrainment"
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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> | 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> | 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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| − | 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 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. | Lower reservoir elevations result in a higher entrainment risk because smallmouth bass are found nearer to the penstock withdrawals. | ||
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| + | '''2026''' | ||
| + | *[https://www.usbr.gov/uc/progact/amp/amwg/2026-02-26-amwg-meeting/uc-gcdamp-amwg-temperaturecontrol-508-20260226.pdf Temperature Control and Entrainment Prevention] | ||
'''2024''' | '''2024''' | ||
| + | *[[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 ]] | *[[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 ] | *[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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'''2022''' | '''2022''' | ||
| − | *[https://www.usbr.gov/uc/progact/amp/twg/2022-10-13-twg-meeting/20221013- | + | *[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/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- | + | *[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/2022-06-16-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 ] | *[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 ] | ||
Latest revision as of 15:23, 13 October 2026
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Entrainment of warmwater nonnative fish through Glen Canyon DamThe rate of entrainment is dependent on the season, reservoir elevation, and thermocline depth. 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 (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 (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 (3), (4). 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. 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 Temperature Control page).
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