Developing Operational Criteria Information for Temperature Control Device (TCD) Installation at Reclamation Facilities Through the Use of Real-Time Integrated Entrainment Monitoring Systems to Improve Reliability of Water And Power Delivery
* What is the potential for entrainment of piscivorous fishes from Lake Powell into the Colorado River?
* Can entrainment quantification technologies be integrated to provide real-time decision data to managers who are trying to avoid the taking of species that are detrimental to the recovery of the endangered humpback chub (_Gila cypha_) at Glen Canyon Dam, Arizona?
Currently, fish exclusion facilities and water diversions associated with Reclamation operations do not have real-time ability to improve operations to avoid taking of piscivorous species harmful to threatened and endangered species. TCDs are proposed for installation at this facility and could potentially entrain large numbers of species harmful to recovery efforts. Integration of entrainment quantification technologies with proposed TCDs may help ameliorate the potential problem of entraining and passing fish that will adversely impact humpback-chub recovery efforts downstream.
Need and Benefit
Reclamation currently spends eight million dollars annually on recovery efforts associated with the federally endangered humpback chub. The current foci of these efforts are the flow manipulations from Glenn Canyon Dam and mechanical removal of non-native fish in the Grand Canyon near the Little Colorado River confluence.
Concomitant with this research, Reclamation is considering the installation of TCDs on 2 of 8 turbines at Glenn Canyon Dam (units #4 and #6). A TCD is a device that can selectively withdraw water from different depths, so that desired downstream temperatures can be attained while still generating power. Proposed cost of this installation is estimated at seventy-one million dollars. The TCDs will be used to withdraw water from warmer reservoir strata above the thermocline. This warmer water will more closely mimic preimpoundment water temperatures in the Grand Canyon with the intent to:
* Improve optimum spawning conditions for humpback chub
* Adversely impact cold-water, piscivorous salmonids that are implicated in the decline of chub populations
Proposed water withdrawals from the warmer epilimnion layers of Lake Powell has potential to complicate recovery of the humpback chub in the following manner: the majority of this reservoir's pelagic species are piscivorous (e.g. striped bass, walleye, carp) and are generally associated with this water strata for a majority of the year. It has been speculated (based on limited data from a 1996 acoustic survey near the Glenn Canyon Dam) that water withdrawals from the epilimnion could entrain 250, 000 fish (many of these fish being striped bass) per week (Mueller and Horn 1999). Further, Arizona Game and Fish studies have proven that these piscivorous species can be passed alive through the dam's turbines. Currently, water withdrawal at Lake Powell occurs in the reservoirs hypolimnion (deep, cold, oxygen poor water with very low fish densities) to maintain downstream trout fisheries at Lee's Ferry and below. This, coupled with poor survival through facility turbines has likely been responsible for the absence of piscivors (other that trout) in the reservoir's tailrace. Water withdrawal from Lake Powell's epilimnion has potential to add many more predators into a river that will be warmer and much more suitable to their survival and reproduction. Humpback chub densities (believed to be less than 4, 000 fish over 150 millimeters) would undoubtedly be impacted, and these impacts would in effect prolong non-native eradication efforts indefinitely, with little hope of de-listing this species. The long-term costs to Reclamation and its stakeholders could be enormous (over and above the eight million dollar annual outlay of resources currently allocated.)
This proposal seeks to establish base-line data on distribution and density of pelagic fish proximate to Glenn Canyon Dam, monthly. This will determine the potential, if any, for fish entrainment. Further, the proposal seeks to pursue methodologies to provide real-time fish distribution and density information to Glenn-Canyon Dam operators should the TCDs be installed. This would provide decision-support that would allow a desired water temperature strata to be accessed at a time and/or depth when these potential predators have low probability of being entrained.
Mueller, G., and M. J. Horn. 1999. Description of the pelagic zooplankton and fish communities of Lakes Powell and Mead. Open File Report 99-109. U.S. Department of the Interior, U.S. Geological Survey, and Bureau of Reclamation. Prepared in Cooperation with Glenn Canyon National Recreation Area. Lake Mead National Recreation Area, Utah Department of Wildlife Resources, Arizona Game and Fish and Nevada Department of Wildlife.
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