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McDowell, Conor

University of British Columbia

In order to predict the response of mountain streams to perturbations caused by climate and land use changes, a better understanding of the sediment transport processes that drive channel morphodynamics is required. Rivers deform systematically, with zones of erosion and deposition related to units of channel morphology (e.g., bars, pools, riffles). Changes in bed topography that build and maintain this morphology are caused by the aggregated displacements of individual particles, either though their entrainment or deposition. Previous studies aiming to link individual particle displacements to channel morphology and topographic change only provide qualitative descriptions of these dynamics. This thesis uses bedload tracing and topographic surveys across a range of laboratory and field settings to link the motions of individual particles to resulting topographic change. First, we apply Bayesian statistics to quantify along-channel trapping probabilities, a measure of the depositional influence of channel segments. These trapping probabilities are used as inputs into a survival model which successfully reconstructs particle travel distances. The results from this model demonstrate that some segments of the channel preferentially trap particles and that these traps are a major control on particle path lengths. Second, we compare trapping probabilities estimated using tracers and topographic differencing across four fluvial environments. In doing so, we demonstrate how the displacements of individual particles scale to create depositional zones along the channel. Finally, we monitor the response of a small mountain stream to a large episodic sediment pulse. We compare stream morphodynamics before and after the pulse to demonstrate how the historical trapping behavior of a river guides the river's response.

Text

2022-11-29

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/83320

Geography

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/