The energy in falling water was recognized long before the discovery of electricity. For centuries, small natural waterfalls have been used to power waterwheels, which in turn rotate grindstones for milling wheat, corn, and other grains. The first use of water for generating electricity in the United States was in 1879 at Niagara Falls, New York, where the power was used to illuminate the falls with large lamps at night. 1 Although its share of total electrical energy production reached a peak of about 40 percent in the 1930s and has declined since, hydropower remains a critical element in the overall energy balance in the United States, reaching 63.3 million kilowatts of installed capacity by 1980. 2 In 1980, hydropower contributed 12.1 percent of net electricity generation by electric utilities, while the rest came from several other sources such as fossil-fuel steam-electric plants (75. 7 percent), nuclear steam-electric plants (11.0 percent), gas turbine electric plants (1.1 percent), and internal combustion plants (0.2 percent). 3
Existing hydropower has some advantages over electricity generation from other sources. First, water is a renewable resource. Rivers run year after year, replenished by the hydrological cycle within some natural variation. One unit of water generates hydropower cumulatively by passing through the turbines of many dams along the descent of a river. A second advantage of water for hydropower is that it produces ""clean" electricity, whereas the combustion of fossil fuels results in air pollution, and oil, natural gas, and coal exploration and production result in environmental damages. Finally, a hydropower facility requires little maintenance, has infrequent shutdowns, and operates with a large degree of flexibility; in other words, it can respond quickly to peak load demands.