A dam is a wall across a river. A dam has built to control water through placement of a blockage of earth, rock and/or concrete across a stream or river. Dams have constructed to store water in a reservoir, which has then used for a variety of applications such as irrigation and municipal water supplies.
Dams are important because they help people have water
- to drink,
- for industrial purpose,
- for irrigation,
- for fishing and recreation,
- for hydroelectric power production,
- for navigation in rivers,
- reducing or preventing floods,
- for hydroelectricity
Dams have Bad Effects
1) Dams reduce river levels, block rivers, and slow rivers.
2) Dams decrease oxygen levels in reservoir waters, When oxygen-deprived water is released from behind the dam, it kills fish downstream.
3) They don't spread the nutrients needed for the soil, which is carried by flood waters.
4) In flat basins large dams cause flooding of large tracts of land, destroying local animals and habitats.
5) Large amounts of plant life are submerged and decay anaerobically (in the absence of oxygen) generating greenhouse gases like methane. It is estimated that a hydroelectric power plant produces 3.5 times the amount of greenhouse gases as a thermal power plant burning fossil fuels.
6) The building of a dam generally has a major impact on fish populations: migrations and other fish movements can be stopped or delayed, the quality, quantity and accessibility of their habitat, which plays an important role in population sustainability, can be affected.