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Large wood structures recreate the natural channel complexity historically found in many Oregon rivers. Large woody debris – root wads, limbs and whole trunks – in rivers or side channels helps to control flow hydraulics as well as regulate the transport of sediment, gravels and organic matter through the river system. Logs that span the entire width of the channel raise the elevation of the mainstem water level and divert the water the nearby floodplains. Large wood added to a streambank increases roughness and enhances riparian resilience. Large wood structures also provide desirable habitat for fish. The structures create pools and create a hydraulic shadow where gravel deposits on a streambed, producing ideal conditions for spawning. The pools also provide a refuge from predators or during periods when water levels are low. By mitigating flow, the structures can provide safe shelters for fish during high-flow periods.
From 2012 to 2015, the Sandy River Basin Partners have treated over 2.5 miles of mainstem river with 1,344 pieces of large wood that in return restored over 90 acres of riparian habitat with 4.1 miles of off-channel habitat including side channels, alcoves, and beaver ponds.
To construct new large wood structures in a straightened channel, trees can be felled on site or flown to the project areas. Trees are often obtained and reused from other areas. We get them from road and development projects, those that have blown down or timber sales. Each structure that is installed can contain between 15 and 40 pieces of wood. The wood structures can be anchored to existing trees, the streambank or streambed.
Invasive species often crowd out native species and change the characteristics of habitat for native wildlife. In certain circumstances, they can also be thirstier than native plants.
At the most fundamental level, restoring and reopening side channels means fish have more spawning and juvenile rearing habitat. Side channels provide low velocity areas where juvenile fish can rear year round and also provide refuge during higher winter flows.
Physical pre- and post-restoration monitoring has included cross-section and longitudinal (lengthwise) profile measurements of the stream channel, streambed pebble counts, stream habitat surveys, and photo point documentation completed cooperatively by the Bureau of Land Management, The Freshwater Trust, Sandy River Basin Watershed Council and the Forest Service.
Pre- and post-restoration biological monitoring has included over 20 years of continuous smolt (young salmon or trout) out-migration monitoring and spawning surveys completed cooperatively by the Bureau of Land Management, the Forest Service, Oregon Department of Fish and Wildlife, and Portland Water Bureau.
On-going post-project effectiveness monitoring occurs following construction to establish as-built conditions. Physical habitat surveys are repeated following construction and after events such as flooding.
In Salmon River project areas, fish response was immediate and was assessed via spring Chinook, coho and winter steelhead spawning surveys and juvenile fish surveys and visual observations made by project partners. Additional snorkeling surveys have confirmed the use of large wood structures in side channels and in the mainstem river by adult and juvenile salmon and steelhead. Winter steelhead, coho and spring Chinook salmon have been observed spawning and rearing in restored side channels.
In year-over-year monitoring, from 2012 to 2015, the Bureau of Land Management-Salem District found significantly more winter steelhead and Chinook salmon spawned in gravel patches associated with the Salmon River large wood projects. During 2009 to 2015, an average of 10 coho salmon redds per mile were located in reconnected side channels within the restored reach.
The number of coho redds in reconnected side channels tracked yearly coho abundance in the Sandy River Basin, based on Oregon Department of Fish and Wildlife estimates of coho population. The number of redds in side channels (19 per mile) was greatest in 2014, with 9 redds per mile in restored side channels in 2015.
The Sandy River Basin Partners formed a coalition in response to the federal listing of threatened species for Chinook, steelhead and coho. The Partner’s vision is to restore the rivers and streams of the basin for fish and for people though a coordinated basin-wide strategy built from a solid scientific foundation.
From 2001 to 2006, the Partners worked collaboratively to develop a fish habitat database and model to help assess conditions for Chinook, steelhead and coho within the Sandy River Basin. Water temperature data was added to the dataset. These assessments identified approximately 150 restoration opportunities targeted to address limiting factors for the fish, all of which were then compared to a set of anchor habitats for four fish species. Finally, the Partners completed a habitat and conservation restoration strategy that zeroes in on the priority locations in the watershed and the priority restoration actions needed to achieve results.
This strategy ensures the appropriate types of restoration actions are identified and implemented in priority sequence to address the primary changes and alterations in watershed processes responsible for the factors limiting salmon and steelhead production. Restoration actions identified for treating the root causes of impaired habitat conditions are considered higher priority in order to ensure the achievement of greatest long-term restoration benefits. This is in contrast to implementing short-term actions that treat only the symptoms of aquatic habitat impairment.
The main priority actions and their outcomes include: reconnecting isolated habitats such as redesigning bridges for improved fish passage and reconnecting side channels; restoring natural watershed processes such as decommissioning forest roads and replanting native vegetation; and restoring natural instream processes such as reintroducing large woody debris.
The 12 collaborative partners include: Association of Northwest Steelheaders, Bureau of Land Management, City of Portland Water Bureau, Clackamas County Department of Transportation and Development, East Multnomah County Soil and Water Conservation District, National Marine Fisheries Service, Oregon Department of Fish and Wildlife, The Freshwater Trust (formerly Oregon Trout), Sandy River Basin Watershed Council, The Nature Conservancy, U.S. Fish and Wildlife Service, and U.S. Forest Service.