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Turley, Mike

University of British Columbia

It is becoming increasingly important to understand how mountain regions will respond to accelerated glacier retreat and land use changes. Long-term records that capture the inherent variability of these systems and document past landscape responses and recovery from glaciation are essential for contextualizing contemporary changes and enabling future predictions. Sediment storage landforms are useful archives of past landscape response and are important for linking onsite erosion to sediment yield at the outlet. This thesis employs a spatially and temporally nested approach to provide a long-term record of sediment dynamics and yield while linking insights across different scales. In particular, we investigate Holocene sediment dynamics, focusing on the controls, variability, and interactions of sediment supply, storage, and yield in glacierized mountain catchments. First, we construct a contemporary bed material sediment budget for the 94 km² Fitzsimmons Creek watershed using field surveys, net-change lidar analysis, and geomorphic mapping. Active channel, floodplain, and landslide sources each contributed roughly one-third of the total sediment yield at the outlet. Historical sediment yield, quantified through field surveys and air photo analysis, varied by a factor of 17 over 76 years, driven primarily by a large landslide-flood event and gravel extraction activities. Second, we explore the inter- and intra-catchment variability in sediment dynamics for tributaries of the 875 km² Green River watershed throughout the Holocene. We approach this through geomorphic mapping, geochronology, postglacial erosion and storage estimates, and longitudinal analyses of channel and valley characteristics. We propose a conceptual model linking geology, glacial history, and postglacial history as controls on sediment dynamics, explaining the observed longitudinal patterns in postglacial mountain watersheds. Finally, we synthesize the Holocene history of the 3,765 km² Lillooet River watershed focusing on controls on sediment dynamics, sediment supply, and yield. In line with our conceptual model, we demonstrate how topographic steps result in a unique hypsometry of sediment storage and fragment the sediment cascade. Our findings reveal that specific sediment yield varies by more than five orders of magnitude across space and time within the same watershed, underscoring the importance of considering landscape organization and its’ control on sediment dynamics.

Text

2025-02-20

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/90398

Geography

University of British Columbia

UBCV

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