Difference between revisions of "Entrainment"
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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. | ||
Revision as of 14:02, 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, 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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