What is a BDA?
Beaver dam analogues (BDAs) are channel-spanning structures that mimic or reinforce natural beaver dams. As such, they are semi-porous to water, sediment, fish and other water-borne materials. Like natural beaver dams, BDAs are biodegradable, temporary features on the landscape with functions that change in response to the effects of flowing water, sediment, and beaver activity (Pollock 2012). Also like natural beaver dams, BDAs function best when constructed in sequence, such that the structures work in concert with each other. Beaver dam analogues are the latest iteration in a long history of constructing channel spanning structures for the purposes of restoring stream habitat. -The Beaver Restoration Guidebook
Why are we building them? Shouldn't we leave it to beavers?
To answer the second question first, ideally yes. Beaver are incredible engineers and stay on site to repair dams as needed.
But here's the issue-- beavers and the healthy habitat needed to support beavers are not in the same abundance they once were.
Why you may ask?
Past overuse during the fur trade
Landowner conflict with beavers flooding property
Degraded wetland ecosystems from channel erosion & loss of riparian trees that beavers need to eat and build their lodges and dams. Channels may start to erode in excess from land manipulation or over grazing.
Benefits of beaver dams and BDAs:
Provide habitat for wildlife (including sensitive and endangered aquatic and terrestrial species)
Help prevent flooding downstream by slowing and spreading out the force of the water.
Hold water longer for a slow release throughout the season
Promote wetland vegetation cycling through an increased wetland footprint (organic carbon storage)
Can help mitigate the effects of forest fire by protecting riparian areas and allowing those areas to act as refuge for wildlife.
How do we build them?
Each BDA is designed to be site specific. Locally sourced materials are ideal for future repairs and allow us to build more structures on the site efficiently. Some common natural materials used are; willow, cottonwood, juniper, sage, and sod. Untreated wooden posts at least 2" in diameter are driven into the channel from one edge of the floodplain to the other. From there, longer materials are woven in and out of the post to create strength and to anker brush and sod.
Example BDA Illustrations. Not all structures are the same.
Click on the above manual and pocket field guide to be directed to Utah State University for more information and to download them for free. Click on the guidebook to be directed to online .pdf