Hydroelectric energy

What is hydroelectric energy?
Flowing rivers have kinetic energy. This energy can be collected and used. Hydroelectric power is generated by the falling of water through a turbine.
How is hydroelectric energy collected?
If a dam is built across the river, water can be allowed to flow in a controlled way through turbines that generate electricity.

A dam across a river can provide a cheap, constant source of hydroelectric power for large communities.

 
Where is hydroelectric energy used?
Hydroelectric power schemes exist in many countries. They can be built in areas where there are fast-flowing rivers. These are often hilly or mountainous regions where rivers flow down steep slopes.

On flatter land rivers flow more slowly, so very large artificial dams have to be built to create reservoirs. The reservoir then provides a 'head' of water that can be directed through a turbine.

Most people live on flatter land, so most hydroelectric schemes require large dams and flood a lot of land. Advantages
The river flows continually and provides a constant source of energy. Once built, the supply of electricity is relatively cheap.
Disadvantages
A good site for a hydroelectric scheme, such as a mountainous region, is not always near towns. The building of large dams floods large areas and causes damage to existing habitats.

Changing the flow of a river will affect the water supply to lands nearer the sea. This may cause problems of irrigation for crops.