Water used for hydroelectric power generation is classified as an instream use and refers to the water used in the generation of electricity at plants where the turbine generators are driven by falling water. Estimates of water used for hydroelectric power generation may vary because of the way individual estimates are made of the quantities of water passed through the plants. If the water is passed through the plants only one time, then accurate estimates of water use can be obtained by streamflow measurements and gate openings. However, it is difficult to define and obtain net water use at pumped-storage hydroelectric plants because the same water is recycled a number of times. Pumped-storage plants usually generate electric energy during peak-load periods by using water previously pumped into an elevated storage reservoir during off-peak periods when excess generating capacity is available to do so. When additional generating capacity is needed, the water can be released from the pumped-storage reservoir through a conduit to turbine generators located in a power plant at a lower level.
Estimates of hydroelectric power water use and power generation, as with the thermoelectric power category, are based on more information and fewer extrapolations than for the other water-use categories. Most of the information was obtained from hydroelectric utility companies. If information was not available from utilities, then records of the power generated were obtained from the U.S. Department of Energy's Energy Information Administration (1991). The power-generation data were multiplied by water-use coefficients to obtain estimates of hydroelectric power water use. In this report, it is assumed that none of the water used for hydroelectric power generation is consumptively used. Although the quantity of water evaporated in the actual generation of hydroelectric power (consumptive use) is very small, considerable depletion of the available water supply for hydroelectric power generation occurs as an indirect result of evaporation from reservoirs and repeated reuse of water within a pumped-storage power facility.
Water used for hydroelectric power generation during 1990 was an estimated 3,290,000 Mgal/d (by water-resources region: tables 27, and by State: table 28), or 8 percent more than during 1985. This total is 2.6 times the average annual runoff in the conterminous United States. (Graczyk and others, 1988). It is possible for the hydroelectric power water use to exceed average annual runoff because some water is used several times as it passes through several hydroelectric dams on a river.
Fresh surface water provides virtually all water for hydroelectric power generation. The Pacific Northwest water-resources region had by far the largest use of water for hydroelectric power generation during 1990, more than double the use in the Great Lakes region (figure 29 (GIF file), or as a PostScript file (620Kb)) and accounted for about 38 percent of the water used for hydroelectric power generation in the Nation. Almost one half of the water used for hydroelectric power generation in the United States occurred in Washington, Oregon (figure 30 (GIF file), or as a PostScript file (508Kb)) primarily on the Columbia River system, and New York on the Niagara and the St. Lawrence River systems.
Last updated Friday, 11-Jan-2013 12:45:35 EST
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