Difference between revisions of "Entrainment"
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==Entrainment of warmwater nonnative fish through Glen Canyon Dam== | ==Entrainment of warmwater nonnative fish through Glen Canyon Dam== | ||
| − | + | The rate of entrainment is dependent on the season, reservoir elevation, and thermocline depth. <br> | |
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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> | |
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| − | + | 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> | |
| + | 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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*At elevations of 3621 ft, the risk of entrainment occurs in only 5% 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 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] |
Revision as of 12:39, 31 October 2025
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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 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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