Hydroelectric power: the effects of damming

The containment of water by a dam and subsequent constant flow can be utilised to create a constant supply of electricity by channelling flow through a turbine. Naturally, as populations grow, the demand for water and electricity grows with them. And the world's largest renewable energy source is found in flowing water. Hydroelectric power plants convert the kinetic energy contained in falling water into electricity. In 1993 hydroelectric power provided 15% of the world's electricity, filling 6% of the world's energy needs.

However altering flow of water with dams does have consequences for aquatic life in the rivers.

• Fish that transverse downstream are often killed in the turbines of hydroelectric power stations. At Snake River, east coast USA, direct mortality from hydropower turbines eliminates 25 to 73 % of juveniles and adults. After direct mortality, Snake River fish may then experience 37 to 68 % "additional mortality," i.e. delayed mortality.
• Transversing upstream is also near impossible without the aide of fish ladders.
• Also as flow downstream is slowed by the dam suspended particles in the water are deposited on the reservoir bed. This sediment build up decreases the amount of water that can be stored in the reservoir and thus used to create electricity.
• And there are localised effects of increased water temperature.

The Niagara Power Project (left) is one of the world's largest hydroelectric power plants, located 4 miles from Niagara Falls. Hoover Dam Power Plant has 17 large generators and has a rated capacity of more then 2,000 megawatts; it generates more than 4 billion kilowatt-hours a year, enough to serve 1.3 million people. Photo Courtesy of NOAA

Impacts caused by other more polluting energy supplies, such as fossil fuel power stations, are the only alternative. And these dams will provide hydroelectricity and both irrigation and drinking water to large areas and populations of people.