Difference between revisions of "Entrainment"

Latest revision as of 15:23, 13 October 2026

Entrainment of warmwater nonnative fish through Glen Canyon Dam

The 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).

--	--	--

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

Maintaining Lake Powell elevations above 3590 ft would likely minimize entrainment from the reservoir and create downstream conditions that minimize smallmouth bass population growth.

Smallmouth bass entrainment is predicted to increase with decreasing reservoir elevation until 3490 ft (minimum power pool), after which the dam switches to deeper river outlets which will lower entrainment. The rate of entrainment increases dramatically as reservoir elevation declines below 3530 ft.

Recommendation: Keep reservoir elevations above 3530 ft with an optimal target above 3590 ft. (1)

Friesen, Barrett T., 2024, "Invasion Potential of Nonnative Fishes Through a Large Western Dam Into a Prized and Vulnerable Ecosystem" .

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.

Lower reservoir elevations result in a higher entrainment risk because smallmouth bass are found nearer to the penstock withdrawals.

At elevations of 3543 ft, the risk of entrainment occurs in 95% of the traces evaluated
At elevations of 3621 ft, the risk of entrainment occurs in only 5% of the traces evaluated

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. [1]

Links
Temperature Control Page Smallmouth Bass Page Green Sunfish Page Striped Bass Page
Projects
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 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
Presentations and Papers
2026 Temperature Control and Entrainment Prevention 2024 Wagner and Svoboda. 2024. Glen Canyon Fish Escapement Appraisal Report (Final) Glen Canyon Dam Turbine Outflow Tucker Trawl Netting - 2024 Progress Report Hydroacoustic Monitoring 2023 Characterizing the fish assemblage in the Lake Powell forebay and identifying the potential for nonnative fish escapement into the Lower Colorado River Hydroacoustic Fish Distribution Characterizing the fish assemblage in the Lake Powell forebay and identifying the potential for nonnative fish escapement into the Lower Colorado River Glen Canyon Dam Fish Exclusion: Project Overview 2022 Svoboda. 2022. Glen Canyon Dam Fish Escapement Report (Final) Glen Canyon Dam Fish Escapement Options Hydroacoustic Fish Distribution 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 Hydroacoustic Fish Distribution - Lake Powell 2022 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 Glen Canyon Fish Escapement Options 2021 Existing and Planned Monitoring of Non-Native Aquatic Species in Lake Powell and Below Glen Canyon Dam Lake Powell Fish Monitoring Study 2021 -2024
Other Stuff

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-[[Image:Entrainment.png|thumb|center|500px| ]]
+[[Image:Entrainment.png|center|600px| ]]
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 ==Entrainment of warmwater nonnative fish through Glen Canyon Dam==
-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.
+The rate of entrainment is dependent on the season, reservoir elevation, and thermocline depth. <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>
-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.
+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>
-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]
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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]]
+</h2>
 |-
 |style="color:#000;"|
-[[Image:Forebay_telemetry.png|thumb|center|500px| ]]
+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 entrainment is predicted to increase with decreasing reservoir elevation until 3490 ft (minimum power pool), after which the dam switches to deeper river outlets which will lower entrainment. The rate of entrainment increases dramatically as reservoir elevation declines below 3530 ft.
-[[Image:Forebay sonor.png|thumb|center|500px| ]]
+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)]]
+[[Image:EntrainmentRate.jpg|center|600px| ]]
+|-
+! <h2 style="margin:0; background:#cedff2; font-size:120%; font-weight:bold; border:1px solid #a3b0bf; text-align:left; color:#000; padding:0.2em 0.4em;"> [https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=1304&context=etd2023 Friesen, Barrett T., 2024, "Invasion Potential of Nonnative Fishes Through a Large Western Dam Into a Prized and Vulnerable Ecosystem" . ]</h2>
+|-
+|style="color:#000;"|
+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>
+Lower reservoir elevations result in a higher entrainment risk because smallmouth bass are found nearer to the penstock withdrawals.
+*At elevations of 3543 ft, the risk of entrainment occurs in 95% of the traces evaluated
+*At elevations of 3621 ft, the risk of entrainment occurs in only 5% of the traces evaluated
+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]
+[[Image:Forebay_telemetry.png|center|600px| ]]
+[[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]]
+*[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 ]
 |-
@@ Line 83: / Line 110: @@
 |style="color:#000;"|
+'''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'''
+*[[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 ]
+'''2023'''
 *[https://www.usbr.gov/uc/progact/amp/twg/2023-11-08-twg-meeting/20231108-NonnativeFishDistributionLakePowellForebay-508-UCRO.pdf Characterizing the fish assemblage in the Lake Powell forebay and identifying the potential for nonnative fish escapement into the Lower Colorado River ]
 *[https://www.usbr.gov/uc/progact/amp/twg/2023-04-13-twg-meeting/20230413-HydroacousticFishDistributionLakePowell-508-UCRO.pdf Hydroacoustic Fish Distribution]
 *[https://www.usbr.gov/uc/progact/amp/twg/2023-04-13-twg-meeting/20230413-CharacterizingFishAssemblageLakePowellForebay-508-UCRO.pdf Characterizing the fish assemblage in the Lake Powell forebay and identifying the potential for nonnative fish escapement into the Lower Colorado River]
 *[https://www.usbr.gov/uc/progact/amp/amwg/2023-02-16-amwg-meeting/20230216-GlenCanyonDamFishExclusionProjectOverview-508-UCRO.pdf Glen Canyon Dam Fish Exclusion: Project Overview]
-*[https://www.usbr.gov/uc/progact/amp/twg/2022-10-13-twg-meeting/20221013-HydroacousticFishDistribution-508-UCRO.pdf Hydroacoustic Fish Distribution ]
+'''2022'''
+*[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 ]
 *[https://www.usbr.gov/uc/progact/amp/twg/2022-04-13-twg-meeting/20220413-CharacterizinFishAssemblageLakePowellForebay-Presentation-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-TWGMeeting-FinalMinutes-508-UCRO.pdf Glen Canyon Fish Escapement Options ]
+'''2021'''
 *[https://www.usbr.gov/uc/progact/amp/twg/2021-10-14-twg-meeting/20211014-ExistingPlannedMonitoringNon-NativeAquaticSpeciesLakePowellBelowGlenCanyonDam-Presentation-508-UCRO.pdf Existing and Planned Monitoring of Non-Native Aquatic Species in Lake Powell and Below Glen Canyon Dam]
 *[https://www.usbr.gov/uc/progact/amp/twg/2021-10-14-twg-meeting/20211014-LakePowellFishMonitoringStudy2021-2024-Presentation-508-UCRO.pdf Lake Powell Fish Monitoring Study 2021 -2024 ]

Difference between revisions of "Entrainment"

Latest revision as of 15:23, 13 October 2026

Entrainment of warmwater nonnative fish through Glen Canyon Dam

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

Friesen, Barrett T., 2024, "Invasion Potential of Nonnative Fishes Through a Large Western Dam Into a Prized and Vulnerable Ecosystem" .

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