Beavers are key agents of riparian-wetland succession because the dams they build act as hydrologic modifiers. When a beaver dam is constructed, a flowing stream can be changed overnight to an aquatic pond. This in turn can lead to aggradation of the channel, establishment of floodplains, and raising groundwater levels. Elevated water levels also help to keep water in areas that would be otherwise dry during summer months and also during times of drought. This helps to sustain plant and animal life. The key to whether or not a beaver dam is beneficial is its stability. Beaver dams built with the correct, stabilizing woody vegetation, where there is enough additional woody vegetation to maintain the dam once built, are considered stable. Some beavers, known as “mudders,” also pack their dams with mud. The mudders' construction technique creates a better basis for vegetation to capture a dam, thus helping to stabilize it.
Although beaver dams can be a benefit, they can also be a hazard. Beaver dams that are not stable unleash tremendous energies when they fail that often results in degradation and stream adjustments, including channel widening, lowering, and lateral migration. For this reason, it is important to note when evaluating riparian health whether beaver dams that are present are being actively maintained. A dam that isn't being maintained, or has not used mud in the construction, or is not captured by vegetation will breach at some point.
Some warning signs that present beaver dams are unstable, which may lead to a breach and subsequent decline in health, or “unraveling” of riparian areas include:
Riparian Health - Evaluating the Health of Riparian Areas - An Overview
Riparian Health - Understanding the Function of Floodplains
Riparian Health - Understanding if the Channel is in Balance with the Landscape
Riparian Health - Riparian Areas and Water Storage
Riparian Health - Understanding How Uplands Contribute to Riparian Health
Riparian Health - Understanding Riparian Vegetation Age-Class and its Role in Health
Riparian Health - Understanding Species Diversity
Riparian Health - Understanding the Relationship between Vegetation and Soil Moisture Characteristics
Riparian Health - Understanding Root Masses and Bank Stability
Riparian Health - Understanding Plant Vigor
Riparian Health - Understanding if you have Adequate Vegetation
Riparian Health - Understanding the Role of Large Woody Material in Riparian Areas
Riparian Health - Understanding a Channels Ability to Dissipate Energy
Riparian Health - Point Bars
Riparian Health - Understanding Lateral Stability in Riparian Areas
Riparian Health - Understanding Vertical Stability in Riparian Areas
Riparian Health - Understanding if the Channel is in Balance with the Soil and Water Being Supplied
American Geophysical Union. "Beaver Dams Create Healthy Downstream Ecosystems." ScienceDaily 6 June 2006. 21 June 2010 <http://www.sciencedaily.com/releases/2006/06/060605120417.htm>.
University of Alberta. "Busy Beavers Can Help Ease Drought." ScienceDaily 26 February 2008. 21 June 2010 <http://www.sciencedaily.com/releases/2008/02/080220130511.htm>.
USDI Bureau of Land Management. 1998. Riparian Area Management: A User Guide to Assessing Proper Functioning Condition and the Supporting Science for Lotic Areas. Technical Reference TR 1737-15. 124 pp. More Information available at: http://www.blm.gov/or/programs/nrst/index.php