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Engineered log jams: Recent developments in their design and placement, with examples from the Pacific Northwest, U.S.A.

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Author(s): Timothy B. Abbe, Mike Hrachovec, Steve Winter

Document Type:
Publisher: Reference Module in Earth Systems and Environmental Sciences
Published Year: 2018
Pages: 20
DOI Identifier: 10.1016/B978-0-12-409548-9.11031-0
ISBN Identifier:

Wood has been well-established as a material constituent of fluvial systems capable of altering channel morphology and fluvial processes. The published literature partially reflects humanity's relationship with wood. It was widely acknowledged that in-stream wood, even in large rivers, was a serious threat to navigation and capable of influencing fluvial systems. In his treatise on geology, Thomas Lyell (1830) describes logjams creating impoundments 50 km long in the Red River in the southern United States. Several major human activities were largely responsible for the disappearance of wood from fluvial systems of North America, beginning with the decimation of beaver populations. This was followed by massive efforts to clear snags and logjams from large rivers to allow navigation for land development (e.g., Guardia, 1933). Channel clearing and splash damming were widespread practices to transport the immense quantities of timber harvested during the industrial revolution. Homesteading and land development channelized and cleared channels to improve drainage. Wood was even removed under perceptions that it impeded fish passage. Dam construction has reduced downstream wood supply and altered flow regimes can reduce wood recruitment by reducing peak flows capable of erosion. The clearing of riparian and floodplain forests had a lasting impact on in-stream wood by eliminating the sources of functional wood. In many areas, it will take centuries to recover the natural quantities of wood that once existed.

With the disappearance of wood, so went the evidence of its key role influencing fluvial geomorphology and ecology. It wasn't until late in the 20th century that the influence of wood began to be studied in more detail, and over the last three decades wood research grew exponentially (Wohl, 2013; Montgomery et al., 2003). Evidence of wood's role in creating salmonid habitat became a major element of stream restoration programs (USBR and ERDC, 2016). Research has demonstrated that in-stream wood in many montane drainages was singularly responsible to gravel retention and limiting incision (e.g., Montgomery et al., 1996). By partitioning basal shear stress, wood reduces the sediment transport capacity of a stream (e,g., Manga and Kirchner, 2000). Wood removal increases sediment transport capacity which can lead to evacuation of alluvium and channel incision e.g., (Stock et al., 2005; USBR and ERDC, 2016).

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In Text Citation:
Abbe and others (2018) or (Abbe et al., 2018)

References Citation:
Abbe, T.B., M. Hrachovec, and S. Winter, 2018, Engineered log jams: Recent developments in their design and placement, with examples from the Pacific Northwest, U.S.A.: Reference Module in Earth Systems and Environmental Sciences, 20 p., doi: 10.1016/B978-0-12-409548-9.11031-0.