How do dams impact rivers?
This fact sheet contains information from many sources and is a general reference sheet
explaining how non-hydropower dams impact our water resources. For more information
on dams in Alabama, please contact the Alabama Rivers Alliance at (205) 322-6395 or
toll free at (877) 862-5260 or at www.AlabamaRivers.org.
Unhealthy Water
Dams affect the health of the water both above and below the dam. They change the
qualities of the water that are important to the health of the river: the level of oxygen, the
temperature, the clarity, the amount of dirt and nutrients, and the accumulation of
pollutants. All of these factors are directly linked to human health, fish and wildlife
habitat, and Alabama’s natural beauty.
Trapped Fish and Aquatic Animals
Dams block the passage of fish and other aquatic animals,
preventing their movement up and down the river and into
the small streams that feed the rivers. As a result, fish
migration and reproduction are impacted. Many species of
aquatic animals cannot survive unless they are able to reach
certain areas of the river for reproduction, finding food, and hiding from predators. This
causes groups of species to be “trapped” in a certain areas and causes the gene pool to be
diminished, leading to weaker and fewer species.
Low Flows Below the Dam
Dams greatly change the amount of water (flow) in the river below the dam. Even if
water is released from the dam, the natural flow patterns of water in the stream will never
be the same. Maintaining a natural stream flow is critical for wildlife. Changing flows of
water released from a dam can also change the stability of stream banks, leading to
erosion, decreased property values, loss of land, and fewer opportunities for outdoor
recreation.
Changes to Habitat
Dams pool water behind them and cause the water to slow down, changing the type and
amount of space available for animals to live around the river. This even impacts landbased wildlife, such as deer, raccoons, and birds. Many species require clean, moving
water to survive. The deep, slow-moving water found in reservoirs behind dams is
drastically different from the natural habitat of many native animals that now exist in
Alabama streams.
Blocking Vital Nutrients and Storing Pollution
Dams block the flow of essential life elements (nutrients, plants, debris, and sediment) to
parts of the river below the dam. These naturally-occurring materials are essential for the
survival of native species. When these materials are not allowed to pass downstream,
they accumulate behind the dam, leading to problems with unhealthy water and build up
Updated June 2008
of deposits damaging the health of the river and reducing the life span of the dam. As an
example, sediment can build up in slow-moving water, smothering organisms such as
mussels and crawfish and creatures that live on the floor of the river.
Loss of Recreation
Dams can actually reduce the amount of fishing, swimming, and
boating opportunities available, especially below the dam. Hiking
and bird watching are also affected by the loss of water in the
streams and reduced food sources.
Destruction of Wetlands
When the flow of the river is disrupted, water can be cut off from natural wetlands that
are vital for wildlife, plants, fish reproductive cycles, and filtering and storage of flood
water and pollutants. As water backs up behind the dam and floods wetlands near the
river or stream, many wetlands and the wildlife dependant upon them could perish.
Wetlands are nature’s nurseries for fish and wildlife. Without the wetlands to act as
sponges the likelihood of flash flooding increases.
What are alternatives to a dam?
If the need for a new water supply or flood management project exists, there are many
other, less damaging options to consider instead of a dam.
In a recent publication, “Beyond Dams: Options and Alternatives,” from American
Rivers and International River Network, a number of viable alternatives are discussed
and include:
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Infiltration galleries and seasonal dams to divert and store water
Rainwater harvesting and recycling water for new sources of water
Water conservation programs and conservation pricing, reducing the
demand for water
Prior to planning for construction of a dam, alternatives should be considered for their
suitability.
The American Rivers report confirms that dams are not the only solution for water supply
and flooding problems. The publication is available at www.americanrivers.org. A copy
of the report is also available at the Alabama Rivers Alliance office in Birmingham.
Alabama Rivers Alliance
2027 Second Avenue North, Suite A
Birmingham, Alabama 35203
(205) 322-6395
www.AlabamaRivers.org
Updated June 2008