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How Streams Work

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  Dams  
   
A dam is an artificial barrier designed to divert a river to create a lake or reservoir. Dams have their good points. Dams may benefit humans in two ways: they generate electricity with the pressure of the water that is dammed and the reservoir stores water for future use.

Unfortunately, they also create problems.		  

 





 

The areas that surround a stream or river have a large diversity of plant and animal supported by the river, riverbanks, and flood plains.

When a dam is created, vast areas of land surrounding the river are flooded. The loss of habitat is considerable and as a result, the diversity of the area is reduced.

Dams change the sediment load in a stream. As the dam stops the water, sediment settles to the bottom and gets trapped. When water is released from the dam, it is very clear without sediments. In order to maintain a balance, the riverbed erodes to make sure there is enough sediment for the stream to carry. The stream eventually becomes narrower and deeper resulting in a reduction in the diversity of animal and plant life it can support.
 
Dams also are barriers to fish and other aquatic life that can no longer migrate or move freely along the river. An example of altering dams is the building of fish ladders in the Pacific Northwest to allow migrating salmon to pass on their migratory routes up and down rivers.

As dams capture sediments, these sediments may be contaminated with toxins. Dam removal or even the possibility of a dam failing could lead these contaminated sediments to be re-suspended in the water and to travel downstream.


 
   
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