Graduate Thesis Or Dissertation
 

Physical Modeling of the Feedbacks Between a Reed Canarygrass (Phalaris arundinacea) Patch, Hydraulics, and Bedform Evolution

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/w9505354t

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  • Reed Canarygrass (RCG) is an aggressive invader in aquatic ecosystems that swiftly modifies the environment and decreases biodiversity. A physical model was used to investigate the mechanisms by which RCG spreads. Experimental trials were implemented to examine feedbacks between a mid-channel patch of the flexible RCG, hydraulics, and bedform evolution as level of submergence increases and plant deflection occurred. The objectives of the study were (1) to examine feedbacks in wake and turbulence length scales and depositional patterns as plant submergence changes, (2) to investigate how the wake characteristics vary with depth and (3) to identify possible mechanisms for RCG expansion in the channel based on the observed positive and negative feedbacks and frontal area analysis. It was found that streamlined patch expansion is promoted at low submergence levels through the positive feedbacks of greater wake zone deposition and a long wake length scale. At low submergence depth, greater lateral scour served as a negative feedback for lateral patch expansion, inhibiting growth next to the patch. As submergence increases, stem deflection begins to occur and vertical shear turbulence is introduced in the wake zone in the upper portion of the water column. This turbulence shortens wake length scales and diminishes wake zone deposition, resulting in a negative feedback for streamlined patch expansion. However, a positive feedback for lateral patch expansion was seen at medium submergence due to diminished lateral velocities and near-bed stem deflection near the bed. Understanding of these feedbacks helps to inform management priorities and anticipate the geomorphic invasion-induced impacts such as diminished habitat diversity, decreased flood conveyance and channel incision.
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