Engineered Log Jams
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Engineered log jams are structures created in streams, rivers and floodplains designed to simulate the function of naturally occuring log jams. Due to logging practices, large 'key peices' of old growth trees with attached root wads are no longer common in rivers and streams. Log jams create forage and refuge opportunities for young and spawning salmon. While engineered log jams are temporary, they provdie habitat services, until riparian forests can grow the large trees to allow for natural formation of log jams.
Rationale & Conceptual Strategy
- Collins et al 2002 describes the historical role of large wood in Puget Sound river habitats.
- Collins & Montgomery 2002 proposes a strategic view of river wood restoration, including short term construction of ELJs.
- Abbe & Montgomery 2003 completed a detailed assessment of wood patterns in the Queets River to describe the role of wood in river habitat structure.
- Montgomery et al 2003 summarizes the geomorphic effects of wood in rivers, pulling from Coastal Pacific NW research.
- Abbe et al 2003 in a book chapter, develops a comprehensive view of to role of ELJs in Puget Sound river restoration.
- Leonetti et al 2015 describes long term monitoring of natural and constructed wood jams in the Stillaguamish, showing a general decline in jams, only partly offset by ELJ construction.
- Roni et al 2015 provides and a historical and future direction assessment for wood placement in streams.
- Roni et al 2015 recommends basin scale strategies for evaluating river restoration including wood jams
Engineered Log Jams are a common component of river habitat enhancement and channel reconstruction projects in the Salish Sea.
- Larson's Reach Floodplain Restoration was a two phase project by the Lummi Nation that constructed a set of jams to attempt bed aggradation in the South Fork Nooksack Floodplain.
- Recovery of Nooksack River salmon includes large scale ELJ placement along both North Fork Nooksack Floodplain and South Fork Nooksack Floodplain. A summary of efforts is described at Nooksack Floodplain Restoration with Engineered Log Jams
Site Strategy & Design
- Aldrich & DeVries 2015 describes a unusual wood installation effort that uses roughness to guide sediment routing and river migration.
- Abbe et al 2018 summarizes over 20 years of experience with log jam construction by staff at Natural Systems Design including strategies for affecting river geomorphology.
- It appears that we only have conceptual evidence that the observed concentration of fish at ELJ sites (higher density) has an effect on populations (through increased growth and survival).
- We have no specific examples where predictions about the effects of ELJ placement based on modelling or best professional judgement have been verified by monitoring floodplain structure over time.
- McHenry et al 2007 describes observed changes from ELJ installation in the Elwha River between 1999 and 2006, reporting increased sediment storage and reduces size, pool formation, spawning in associated gravels, higher primary productivity and invertebrate density, and some preferential use by rearing juveniles.
- Pess et al 2011 provides evidence of higher salmonid concentrations associated with log jams.
- Maudlin & Coe 2011 provides observations of effects of ELJs on the South Fork Nooksack Floodplain