Geologic Publications for Mount Rainier

Patterns, mechanics and geomorphic effects of wood debris accumulations in a forest river system

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Author(s): Timothy B. Abbe

Category: PUBLICATION
Document Type: Ph.D Thesis
Publisher: University of Washington
Published Year: 2000
Volume:
Number:
Pages: 248
DOI Identifier:
ISBN Identifier:
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Abstract:
Field surveys in the forested Queets River basin of Northwestern Washington revealed that wood debris (WD) entering the fluvial system accumulates in distinctive patterns dependent on the physical characteristics of the WD, recruitment mechanisms, and channel morphology. Eleven fundamental types of WD accumulation or jams are identified based on patterns of WD deposition and it geomorphic effects. WD jams decrease channel radius of curvature and increase pool and forested island frequency. WD jams can persist for centuries within migration zones that are recycled in less than 88 years, thereby creating hard points within the floodplain that allow patches of old-growth forest to develop despite frequent disturbance. Accumulations of WD can also be a principal mechanism for forming terrace-like surfaces by episodically raising the channel and floodplain over 10 meters. Stable WD jams influenced both channel reach and floodplain terrace morphology throughout the Queets River system. Abstract: Field surveys in the forested Queets River basin of northwestern Washington, revealed that wood debris (WD) entering the fluvial system accumulates in distinctive patterns dependent on the physical characteristics of the WD, recruitment mechanisms, and channel morphology. Eleven fundamental types of WD accumulation or jams are identified based on patterns of WD deposition and it geomorphic effects. WD jams decrease channel radius of curvature and increase pool and forested island frequency. WD jams can persist for centuries within migration zones that are recycled in less than 88 years, thereby creating hard points within the floodplain that allow patches of old-growth forest to develop despite frequent disturbance. Accumulations of WD can also be a principal mechanism for forming terrace-like surfaces by episodically raising the channel and floodplain over 10 meters. Stable WD jams influenced both channel reach and floodplain terrace morphology throughout the Queets River system. Two basic models were developed to investigate the principal factors controlling the stability of individual WD or logs. Where resistance is primarily provided by pre-existing boundary conditions, such as headwater channels where log length equals or exceeds channel width, stability is linked to material-strength. In large alluvial channels, where log length tends to be less than the channel width, the principal source of resistence is attributed to how the log itself alters boundary conditions, which is primarily as a function of the log's shape. Both models and empirical data indicate both that rootwads are critical to log stability large channels and that log diameter affects stability and longevity throughout a channel network. This study demonstrates that WD can result in spatially and temporally complex fluvial land forms unique to forest regions.

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In Text Citation:
Abbe (2000) or (Abbe, 2000)

References Citation:
Abbe, T.B., 2000, Patterns, mechanics and geomorphic effects of wood debris accumulations in a forest river system: Ph.D Thesis, University of Washington, 248 p..