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Large Wood Placement
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Large wood is the biological legacy driving stream processes
Historically, pieces of wood (e.g. whole trees, branches, etc.) were considered a potential source of “logjams” that could block river navigation, water-based log transport, and very importantly, the upstream passage of salmon and trout on their way to spawning grounds. As a result, many of these key pieces of wood were removed from rivers and streams in the western U.S.
But, now we know that large wood plays a crucial role in creating the habitat for salmon to spawn (laying eggs) and rear (grow up). More to the point, salmon and trout can effectively navigate through, under, and sometimes, over, these complex gatherings of wood.
Large wood plays a significant role in creating channel and hydraulic complexity, in part by raising the water level in a stream and facilitating its connection to the floodplain. This connection increases nutrient exchange (which means healthier forests) and helps promote the recharge and storage of ground waters that can be naturally released longer into the hot summer months.
Large wood plays a substantial role in creating channel and hydraulic complexity, in part by raising the water level in a stream and facilitating its connection to the floodplain. This connection increases nutrient exchange (which means healthier forests) and helps promote the recharge and storage of ground waters that can be naturally released longer into the hot summer months.
Substrate (rocks, gravel, sand, and sediments) move downstream just as water does, but at a much slower pace. When these substrate components collide with large wood structures, they are retained and sorted, creating the necessary spawning habitat for fish and gravel bars within the stream.
During high winter flows, large wood accumulations create secondary/side channels which help decrease single-channel stream velocity, creating refuges for small fish and wildlife, while also reducing unnatural erosion.
Large Wood Impacts
Large wood placement has lasting effects on improving stream processes, aquatic and terrestrial habitats, and water quality. As water flows over and around large wood structures, the force of the flow begins to scour (or dig) pools which offer cold water refuge for native aquatic organisms and increase stream channel complexity. Large wood structures also provide crucial habitat for every group of animals, from fish to insects to mammals to birds. These structures also raise the water level in streams and facilitate hyporheic flow. This process reduces water temperature when water cools as it flows through the substrate within the streambed.
Wild
Salmon
Center
Wildlife habitat
Creation of
pool habitats
Rearing habitat
for fish
Floodplain
connection and
hyporheic flow
See Large Wood in Action
The Placement Process
Placing engineered configurations of logs to mimic naturally occurring accumulations is a common restoration practice, and scientific research has long shown the importance of having large wood in a riverine system. Experienced RRWC staff and professional stream engineers work together to design these detailed configuration plans to determine the specific locations and types of large wood structures. These plans are developed using calculations of how the large wood structures will respond to various high-flow events (including floods) based on collected stream survey data and flow modeling. Safety measures are incorporated into the plan through this process.
The engineered designs are used by RRWC Project Managers and construction contractors to determine how and where large wood will be placed in the creek. These structures are either strategically woven among live trees or partially buried in the ground with large ballast boulders to add stability and security during floods. After the construction process is done, reseeding of the site occurs to counteract the disturbance of large machinery in the streamside areas.
Minutes after the large wood is installed, fish begin to explore the structures. Over time, as the wood assists with restoring the stream process and collects additional pieces of wood flowing downstream, more habitat will be created and enhanced for these fish and other wildlife. Post-restoration surveys have shown diverse large wood structure-use by reptiles, birds, insects, amphibians, mammals, and even live plants.
Fish aren't the only ones who benefit from large wood
Eiko
Jones
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