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Beaver Dam Analogs
"Beaver dam analogs 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
According to the company Symbiotic Restoration, located in Fall River Mills, California, "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 anchor brush and sod."
BDA Materials and Equipment
Materials similar to beaver dams: willow branches, herbaceous vegetation, rocks, mud, and wood posts (non-treated)
Equipment needed: chainsaw (to cut and sharpen posts), hand saws to cut willow, post pounder/power source (hydraulic or pneumatic)
Material cost and labor averages $500-$5,000 per structure, depending on size of structure (length), size of stream (depth of posts), source distance of building materials, and labor costs
Because our hydrology is different in the Midwest than on the West Coast, best practices for BDA building may differ in Illinois. For example, in Iowa, which has flashy rivers, Chris Sorflaten of Leave It to Beavers reports the need to use living willow in the BDAs that his company builds. He carves the willow into a 5’ stick and drive it into the creek bed with a spike. Because beavers would show up and eat the living willow stick right away, he learned that he needed to paint the willow stick with sandy paint, which creates a texture that deters beavers.
Anabranch Solutions offers "recipes" for BDAs, cautioning, "you can substitute ingredients to better match what you might have available in the cupboard (i.e. onsite), and find efficiencies an improvements that work better in your situation." In general, BDAs should be strategically installed in groups, with a large primary BDA and secondary dams to extend forage access for beaver. That way, if one BDA fails, there is other backup. BDAs do not need to last forever, especially if beavers colonize and start to maintain the site.at deters beavers.
CLICK HERE to view the BDA recipes in "Low-Tech Process-Based Restoration of Riverscapes Design Manual."
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