Hydroelectric projects potentially affect many aspects of water quality, as outlined in the Project Effects Matrix (Part I). The Clean Water Act of 1972 (33 USC ยง 1251 et seq), originally adopted in Public Law 92-500, requires each state to develop criteria protective of water quality. To do this, the Environmental Protection Agency and states examine the effects of specific pollutants on plankton, fish, shellfish, wildlife, plants and recreational activities and determine the levels of pollutants that can exist without harming human and aquatic life. The states then determine the most beneficial designated use(s) of a particular water body (most often aquatic species and drinking water supply), and adopt water quality criteria designed to protect these uses as well as more general provisions that protect against water quality degradation.
Dams, turbines, power lines, roads, and operations and maintenance all have some potential impact on water quality. Although watershed land uses and the potential impacts of past and ongoing discharges of anthropogenic contaminants must be taken into consideration in the development of any water quality sampling plan, the most common effects of hydroelectric projects are changes in the physical structure of the aquatic ecosystem. The most pronounced effects associated with hydroelectric operations are related to dams, such as increased sediment accumulation, alterations in temperature regimes in bypass reaches and the tailraces of powerhouses, reductions in dissolved oxygen, and increases in some pollutants such as hydrogen sulfide, nutrients, and manganese. A variety of approaches are discussed below to evaluate specific effects of hydroelectric projects on water quality, including:
- Instream water temperatures
- Reservoir temperature and chemical structure
- Nutrient exchanges and reservoir eutrophication
- Dissolved gasses
These are not all of the potential effects of hydroelectric projects on water quality, and the methods to evaluate them by no means cover all the potential approaches that could be used to study the effects. Rather, this discussion focuses on those effects where a nexus to project effects is most distinct and where approaches to evaluate effects are not necessarily standardized. The following references are recommended for additional information on general water quality and limnological monitoring techniques that may be employed to assess both existing water quality problems related to hydroelectric project operations, or possibly to identify emerging trends towards future degradation.
2.1.1 Selected references
Allan, J. D. 1995. Stream ecology: structure and function of running waters. First edition Chapman and Hall. New York.
Barbour, M. T., J. Gerritsen, B. D. Snyder, and J.B. Stribling. 1999. Rapid bioassessment protocols for use in streams and wadeable rivers: periphyton, benthic macroinvertebrates, and fish. Second edition. EPA 841-B-99-002. U. S. Environmental Protection Agency, Office of Water, Washington, D. C.
Wetzel, R. G. 2001. Limnology: lake and river ecosystems. Academic Press, San Diego,California.
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