Water power: Falling water

Dams and greenhouse gases

While water power may seem like a squeaky clean way to make electricity, dams are not. Building a dam creates large carbon dioxide emissions through:

• heavy machinery and huge excavations of stone to shape the valley ready to take the dam;
  
• vast quantities of concrete to build them;
  
  • which must be transported along using machines;
  • which releases CO₂ while the concrete sets;
     
    

Once completed, all dam reservoirs release large amounts of methane, which is 25 times more powerful as a greenhouse gas than CO₂. As water sits still in the reservoir for a while, organic matter flowing in via incoming rivers falls to the bottom. This rots and releases methane into the air.

In northern latitudes, dams can produce 5% of the volume of greenhouse gases that would be produced by a conventional power station. In hot countries, they can produce up to 25% of this volume. In future though, it may be possible to reduce or remove much of this methane.
 

Dams and risk