WATER QUALITY

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Desired Future Condition for Water Quality

Water quality with regards to dissolved oxygen, nutrient concentrations and cycling, turbidity, temperature, etc., is sufficient to support natural ecosystem functions, visitor safety and visitor experience to the extent feasible and consistent with the life history requirements of focal aquatic species.
• Ecosystem-sustaining nutrient distribution, flux, and cycling.
• Hydro-physical conditions and characteristics of the CRE necessary to sustain aquatic biota.
• Acceptable water quality for human health and visitor experience.

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Updates

The combination of the record five-year drought (1999-2004) and above average runoff into Lake Powell during the spring and summer of 2005 put large amounts of sediment and organic matter from the reservoir's delta into the lake. These substances consumed oxygen as they decay which, in turn, resulted in declining dissolved oxygen concentrations in the Colorado River immediately below the dam. While this phenomenon occurs to some degree every summer and fall, oxygen levels in 2005 reached a level that caused concern for the health of the trout fishery in the river below the dam.

As the river moves downstream, the water cascades through rapids, quickly raising the dissolved oxygen levels, so there is less impact or concern for endangered native fish in the reaches of the Grand Canyon. However, there may be some impact to the non-native trout fishery as fish remaining near the dam become lethargic or temporarily move downstream to more oxygen-rich waters.

Reclamation conducted short-term experiments to evaluate the relationship between dam operations and dissolved oxygen concentrations. Researchers from the Grand Canyon Monitoring and Research Center determined if low releases spread among varying numbers of generating units will inject more oxygen into the water. The turbines draw some air during operation, especially when operated at very low output levels. Various operational combinations of three to five units were tested.

While some changes in dissolved oxygen were been noted as a result of the experiments, a concern also has emerged. Operating the units at very low levels is both inefficient and damaging. Because the generating units were designed to operate efficiently only at higher releases, normal operations for low flows would be met by using fewer units. If the units are operated at too low a level, the risk of damage to the turbines increases significantly. While units have been operated that low in the past for various system and emergency reasons, every effort possible has been made to minimize the length of such operations to protect the generating units. Additionally, such "rough operation" also is inefficient in both the generation of power and the use of water.

The results of these studies indicate the turbines can contribute to improved dissolved oxygen concentrations in the water being released from the reservoir. The studies remain inconclusive concerning the best balance of turbine operations, or whether other alternatives should be developed.

The issue of declining dissolved oxygen becomes less of an issue by October or early November when the water in Lake Powell "turns over." This happens when the cooling air temperatures and seasonal winds mix reservoir waters, essentially causing the upper, better oxygenated water to mix with the lower level water that contains low oxygen. [1]


Water Quality Gages

Papers and presentations

2017

2016

2015

2014

2012

2010

2006

2005

Modifying releases at Glen Canyon Dam to improve water quality in the Lees Ferry reach

Rough operation of the turbines

Increases the oxygenation of water going through the power plant Is damaging to the turbines

Oxygenation of the tailwater using the bypass tubes

The Basin States have maintained that according to Sec 602a of the Colorado River Basin Project Act (1968), the bypass tubes at Glen Canyon Dam can only be used to avoid anticipated spills from Lake Powell. The Basin States have agreed to bypass at Glen Canyon Dam for HFEs on the condition that it be done as part of an experiment and not a management action or operational decision. Costs associated with any release that bypasses the powerplant for reasons other than to avoid a spill or for experimentation relating to HFEs would have to be borne by the GCDAMP (see DOI determination for costs of the 2004 BHBF).

Adding power generation to the bypass tubes

Allows for drawing water from deeper in Lake Powell: colder and more oxygenated water

Other Stuff