Beaver Dam Analogs: Building Beaver-Style Dams to Heal Great Basin's Streams

Beavers are among the best stream engineers there are: their small dams slow water, raise it, and create habitat. Where there are no beavers, Great Basin National Park builds the dams for them. Beaver dam analogs (BDAs) are human-made, but they use the same materials a North American beaver would — willow, aspen, sticks and mud found on site — and they do much the same job.

Packing mud onto a line of vegetation laid across the stream. Credit: NPS photo/Emily Luberto.

What a slowed stream does

Both BDAs and real beaver dams back up short stretches of flowing water, slowing it and raising its level. That partial, temporary pooling:

• creates backwaters — resting and winter habitat for fish such as the native Bonneville cutthroat trout — in the steep, uniform mountain streams of eastern Nevada;
• raises the water table, keeping wet meadows and streamside vegetation, and the life they support, connected to the water;
• makes the channel more complex and traps sediment.

For several years the park and the Nevada Department of Wildlife have been installing BDAs and similar structures to offset damage from recent fires.

Fighting incision

Fast water cuts down through land, carving a narrow channel where it flows faster and deeper. In an incised stream, the water sits below the surrounding land. After fire the effect can be severe: on Strawberry Creek in the park, incision reaches as much as 12 feet in places. Slowing the water weakens its cutting force and lets new banks form where streamside plants can re-establish. This takes longer than making backwaters, and depends on maintaining and monitoring the structures.

How to build one

1. Pick the site — one with logs, brush and plenty of mud, and with suitable biological, physical and water conditions.
2. Lay the base — large sticks and logs placed parallel to the flow, their upstream ends forming an even line from bank to bank, packed over with silty clay mud into a low mound across the stream.
3. Layer up — brush laid bank to bank just downstream, covered with mud, and repeated until the structure reaches the right height, often level with the bank. Ideally, water flows slowly and evenly over the top.
4. Pin it — untreated wooden posts driven in with a hydraulic post pounder, "one tool humans have that beavers do not."

A pool forming upstream of a beaver dam analog. Credit: NPS photo/Emily Luberto.

The alternatives

Where a stream lacks the materials or conditions for a BDA, crews build post-assisted log structures (PALS): looser, messier piles of logs, stumps and branches that imitate natural log jams, slow the water, add wood to wood-starved streams and catch debris. And the best option of all is the real thing: beavers, who keep maintaining and improving their dams without being asked.

Sources

Based on "Leave it to Beaver… Dam Analogs" by Emily Luberto, Biological Science Technician, first published in The Midden (Great Basin National Park, Winter 2023), from the National Park Service; a work of the United States government in the public domain.