Description of the Low Summer Flow Experiment
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Low summer flows (minimum daily mean 5,000 to 8,000 cfs) for three months (Jul.–Sep.) to target ≥ 14°C at Little Colorado River confluence.
The experiment would not be conducted if:
- release temperatures were too low to reach 14°C at Little Colorado River confluence even with going to a minimum flow of 5,000 to 8,000 cfs, or
- release temperature were predicted to be high enough in July, August, or September to reach 14°C at Little Colorado River confluence under normal operations.
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Objectives
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Increase humpback chub growth
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Trigger
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Initial experiment: in the second 10 years of the LTEMP period (2026-2036) when target temperature of ≥14°C can be achieved only with low summer flow
Subsequent experimental use if:
- initial test was successful,
- humpback chub population concerns warrant their use,
- water temperature appears to be limiting recruitment, and
- target temperature of ≥14°C could be achieved only with low summer flow.
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Offramps
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- Low summer flows do not increase growth and recruitment of humpback chub
- Increase in warmwater nonnative species or trout at the Little Colorado River
- Longterm unacceptable adverse impacts on the resources listed in Section 1.3 are observed
- Or sufficient warming does not occur as predicted
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Risks
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- Reduce food availability to humpback chub by
- desiccating the nearshore environment with the reduction in flow between June and July, and
- reducing drift with the reduction in daily fluctuation.
- Increasing bioenergetic demands of humpback chub via warmer water while decreasing food supply and availability.
- Increasing sediment transport during the high releases in the months prior to the LFS test in order to get the annual volume commitment to the Lower Basin.
- Increasing the potential for nonnative fish and parasites to proliferate throughout the Grand Canyon.
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Implementation Issues
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- Modeling release temperatures far enough in advance to start making releases to meet annual release requirements
- Scheduling monthly releases in order to meet annual release requirements while dealing with uncertanties in inflow forcasts.
- Science planning to monitor affects
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Links
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Papers and Publications
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Other Stuff
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