Sources of Pollution: Flow Alteration


Flow alteration occurs when the normal flow of a waterbody is changed. This can happen through clearing of vegetation from a stream, removing natural debris, making a stream straight so that boats or water can move through more quickly, or lining a channel with concrete to move floodwater through more quickly. This phenomenon is also referred to as hydrological modification.


How does this cause Non-Point Source Pollution?

When a stream is straightened or vegetation is removed from the stream, it can cause more pollutants to be carried into the stream at a faster rate. Why? Because the water is removed faster from a straighter channel. Similarly, a stream without trees holds back less water, and the trees are not there to "drink up" part of the water moving into the stream. More pollutants washed into the stream, such as nutrients and organic debris, mean that dissolved oxygen will be used and will drop.

Drainage, filling and loss of wetlands are also ways that flow alteration can occur. Similar to the removal of trees. the removal of wetlands means the removal of places for the water to go for storage. Wetlands hold back water, nutrients, sediments, and other pollutants. They play a large role in the way that water is held within a watershed. They release the water slowly over a long period of time. If wetlands are filled in or removed, the water is released all at once, causing it to flood streams and bayous.


What can you do to prevent this pollution?

  • Best Management Practices for Flow Alteration
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