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The systematic and widespread removal of large woody debris (LWD) and beaver has resulted in simplified and degraded riverscapes. Historically, large woody debris and beaver dams were ubiquitous throughout North American riverscapes. Beaver dams and large woody debris have been shown to influence hydrologic and geomorphic processes in similar ways, creating fish habitat and spawning areas and promoting sediment and nutrient retention The introduction of habitat structures has been practiced for at least a century, with restoration focused on the creation of discrete habitat features, often pools for fish, rather than emphasizing how structures could enable and promote processes.
However, to address the scope of degraded streams region-wide, cost-effective and scalable restoration methods are critical. The approach to restoration, the design of low-tech process-based restoration projects, described here is informed by the vision of physically complex valley bottoms and multi-thread channels described as ‘Stage 0’. We describe the design process for two types of low-tech structures, post-assisted log structures (PALS) and beaver dam analogues (BDAs). PALS are woody material of various sizes pinned together with untreated wooden posts driven into the substrate to simulate natural wood accumulations. BDAs are channel-spanning, permeable structures, with a uniform crest elevation, constructed using woody debris and fill material, to form a pond and mimic natural beaver dams. Both structure types are designed as complexes, or a group of low-tech restoration structures designed to achieve specific objectives. A complex may be composed of a single type of structure, or a mix of structure types, and consist of 2 – 15 structures.
Dr. Chris Jordan, Research Fisheries Biologist with NOAA/NMFS’s Northwest Fisheries Science Center and Program Manager for the Mathematical Biology and Systems Monitoring Program
Trained as a mathematical biologist, Dr. Jordan has worked on a wide range of biological topics, all with an emphasis on the development or application of quantitative methods. Recent work has focused on the design and implementation of large-scale monitoring programs to assess anadromous salmonid freshwater habitat and population status as well as the watershed-scale effect of management actions on salmonid habitat and population processes.
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