Effects of Beaver Dams on Riparian Areas

The Question: What is the role of beaver dams on hydrological processes in montane riparian areas?

Understanding the hydrological processes such as inundation and recharge of alluvial aquifers in riparian areas is key to proper management of rivers and watersheds. For example these processes can influence biodiversity by providing wildlife habitat for a disproportionally large number of wildlife species (i.e. birds, butterflies, small mammals, insects, and amphibians). Biologists have long assumed that beaver (Castor canadensis) may influence hydrologic processes in riparian areas of rivers through the building of dams. Researchers conducted this study in order to test the assumption that beaver dams play an integral role in creating and maintaining healthy montane riparian areas.

The Project: Measure ground water flow patterns and levels before and after the breach/construction of two beaver dams.

During the summers of 2002-2004, Cherie Westbrook and David Cooper (Colorado State University) and Bruce Baker (USGS) used 95 pipe wells to measure subsurface water fl ow patterns and water table fluctuations along a one-mile reach of the Colorado River containing two beaver dams. One of the dams was constructed in October 2003, and the other dam breached in May 2004 allowing researchers to take surface and subsurface hydrologic data in the study area in the presence and absence of beaver dams.

The Results: Beaver can influence hydrological processes in streams and valleys and thus create flow patterns suitable for the formation and persistence of wetlands.

This study found that beaver dams strongly aff ect the hydrologic processes of the Colorado River and its floodplain and terraces near its headwaters. The beaver dams and ponds greatly enhance the depth, extent, and duration of inundation associated with fl oods. Additionally the investigators found that beaver dams elevate the water table during both high and low river flows and slow the decline of the water table during dry months. Unlike previous studies the researchers found that the main eff ects of beaver dams occur below the dam and not just at the pond created by the dam. Overall this study confirms that beavers and their associated dams play an important role in the formation, function, and persistence of riparian wetlands.