Instream Flow Needs Below Peaking Hydroelectric Projectsby Robert T. Milhous, U.S. Fish and Wildlife Service, Fort Collins, United States,
Abstract: A method has been developed to assist in the determination of instream flow needs below hydroelectric projects operated in a peaking mode. Peaking hydroelectric projects significantly change streamflow over a short period of time; consequently, any instream flow methodology must consider the dual flows associated with peaking projects. The dual flows are the lowest flow and the maximum generation flow of a peaking cycle. The methodology is based on elements of the Physical Habitat Simulation System of the U.S. Fish and Wildlife Service and uses habitat, rather than fish numbers or biomass, as at basic response variable. All aquatic animals are subject to the rapid changes in streamflow which cause rapid swings in habitat quality. Some aquatic organisms are relatively fixed in location in the stream while others can move when flows change. The habitat available from a project operated in peaking mode is considered to be the minimum habitat occurring during a cycle of habitat change. The methodology takes in to consideration that some aquatic animals can move and others cannot move during a peaking cycle. Also considered is the stranding of aquatic animals as a result of a rapid decrease in streamflows. Dual flow analysis is useful for indentification of an instream flow requirement for a project, a study of the effect on the habitat of operations criteria for a project, and the development of a time series of habitats for in an instream flow study.
Subject Headings: Instream flow | Hydro power | Streamflow | Flow duration | Aquatic habitats | Animals | Fish management | Rivers and streams
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