Low-Tech, Nature-Based Stream Restoration

Post-Assisted Log Structures (PALS) and Beaver Dam Analogues (BDAs) are nature-based, beaver mimicry techniques that can restore badly eroded streams.

Unfortunately, centuries ago unregulated trapping eliminated most of the beavers and their dams across North America. Without beaver dams to slow, sink and store stream water, our waterways were degraded and many of our streams became badly eroded, incised and damaged.

As erosion cuts a stream channel deeper and deeper into the ground, the surrounding water table also drops. Once the water table drops too low for the roots of nearby plants to reach, the lush native vegetation dies off resulting in a barren, arid landscape with a loss of biodiversity. Without beaver dams, a lowland teeming with life can become a desolate dust bowl and a fire risk.

Some incised streambanks are so steep, and the vegetation so sparse and inaccessible, that beavers cannot live there. Fortunately though, we can undo some of this damage and entice beavers back to these severely damaged streams by building Beaver Dam Analogs (BDA’s) and Post-Assisted Log Structures (PALS). The use of BDA’s, PAL’s and similar structures to heal incised stream is often called low-tech, process-based restoration (LTPBR). Research has shown that these manmade in-stream structures promote sediment deposition. An excellent LTPBR manual from Utah State Restoration Consortium can be downloaded HERE.

Similar to natural beaver dams, nature-based BDA’s and PAL’s slow water velocity, allowing suspended particles to settle. As sediment accumulates, the stream bottom rises resulting in corresponding elevations of the surrounding water table. Stream banks become less steep the stream eventually becomes hydrologically reconnected to the floodplain. Once the area can support beavers, the beavers build dams on top of the these manmade structures that continue the stream restoration process. The riparian corridor once again becomes a lush and healthy ecosystem with a multitude of species. Biodiversity flourishes, and the stream restoration process is complete.

The beauty and increasing popularity of using low-tech, process-based restoration for streams includes their low cost and high success rate. BDA’s and beavers effectively restore severely damaged stream corridors, and they do it at a much lower cost and higher success rate than we humans could accomplish alone.

Beaver Restoration Guidebook v. 2.0

The definitive reference for beavers and stream restoration.

Beaver Restoration Guidebook v. 2.0

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