79 River Power-Mid

River Power FOCUS Question How does hydroelectric power affect people and the environment?

There's Energy in That Water Have you ever raced through rapids in a raft or watched waves crash on a beach? If so, you know that moving water has power. People harness that power to make energy. Electricity produced from moving water is called hydroelectric power. You might also know it as hydropower or hydroelectricity. Moving water is a very useful energy resource. Not only is it abundant and renewable, but it's also right where people need it most. Many towns and cities are located near an ocean or river. People use ocean waves and tides to make electricity. But most hydroelectric power in the world is generated using rivers. Wowser! For thousands of years, people used the energy of moving water to turn wheels and grind grains such as wheat. Some still do today!

It Starts with Gravity Hydroelectric power production begins with the force that gets water moving— gravity. Earth's gravity pulls water downhill. Water flows from higher to lower land as runoff. Runoff collects in streams that flow into rivers and eventually flow into oceans. Fast-flowing water in a large river with a large drop in elevation has a lot of kinetic energy from the motion of the water. That's why hydroelectric power plants are often built on such rivers. To harness all that energy, people build a dam to control how the river flows. The dam blocks the river and forms a lake for storing water called a reservoir. Do You Know? Most dams are not built for generating electricity. They are built to control floods and irrigate crops.

Gravity pulls water from the reservoir into a large pipe inside the dam. At the end of the pipe is a turbine— a fan-shaped machine with large blades. The water turns the turbine blades, which turn the shaft of a generator. The generator uses strong magnets to convert this motion into electricity. After flowing through the turbine, the water moves through another pipe, exits the dam, and continues down the river. What happens to the electricity after it leaves a hydroelectric power plant? It travels through a system of stations, machines, and power lines. The lines bring electricity to communities near and far. They supply homes and businesses with energy to power appliances, computers, and lights.

Pros and Cons There's a lot to like about hydroelectric power. It uses water, an abundant renewable resource that won't run out. It can be used in most parts of the world— anywhere rivers flow. It creates reservoirs that provide water for drinking, irrigation, and recreation. Reservoirs help protect against dangerous floods. They also store water for use during droughts. Hydroelectric power plants are "cleaner" than power plants that burn fossil fuels such as coal, oil, or gas to produce electricity. Burning these fuels releases greenhouse gases and other air pollutants. These pollutants contribute to global warming, smog, and acid rain. Hydroelectric power is produced without releasing greenhouse gases and other air pollutants. Hydroelectric power does have some drawbacks, however. Dams cost a lot to build, and they change the land and water above and below them.

Constructing dams and creating reservoirs cover land with water. These actions destroy natural habitats. Sometimes reservoirs cover towns, farms, and archaeological sites. People lose their homes, food, and heritage. Drowned vegetation can rot and release methane, a greenhouse gas. Less flooding happens on farmlands along rivers. Floods no longer deposit silt, which contains nutrients needed to help crops grow. Fish populations decline when dams block fish from swimming upstream to reproduce. Turbines injure or kill fish that swim through them. Dams also block water flow downstream. This can harm habitats by changing the water temperature and quality. Wowser! Some dams have elevators for fish! The elevators lift salmon and other migrating fish up and over the dams so they can spawn upstream.