Doctor of Philosophy
Marco Van De Wiel
Despite that many places around the world in general, and North America in particular, were glaciated during the last ice age, relatively little is known about rivers that evolved over these landscapes once they deglaciated. These rivers are commonly categorized as alluvial with a glacial legacy, and often described as plain gravel-bed or sand-bed rivers. Alternatively, they are considered to be bedrock rivers when the glacial deposits were eroded and underlying rock was exposed. However, ignoring the glacial history of these rivers is scientifically wrong and they should be termed "semi-alluvial". This work shows that classification is important, not only for scientific accuracy but for river management that must be based on a sound understanding of river form and process. Poor understanding can be costly, leading to wasted resources and inefficient functioning of the river.
Two major geomorphologic phases can be discerned in formerly glaciated terrains:
1. Deglaciation which exposed the landscape to erosion when ponded meltwater was abundant and led to outburst flooding. These catastrophic floods cannot occur under the modern climate of southern Ontario. Evidence for glacial lakes is found in lacustrine deposits upstream, and on top of moraines while spillways indicate where glacial lakes drained and carved deep valleys into the subdued terrain. Spillways reveal outburst flooding with boulder lags, terraces, flow scars and possibly mounds and berms away from the modern misfit channel.
2. Postglacial incision and deposition during a single flood event or a single hydrological year. Human disturbance over the past two centuries, includes agriculture, channelization, millponds and weirs.
The dissertation has two parallel paradigms in fluvial geomorphology: Which processes are responsible for most geomorphic work that shapes the landscape - catastrophic flood(s) or smallscale erosion and deposition that bit by bit give the channel and valley its present morphology. My work will show that the outburst flooding of Glacial Lake London (paper 1) sets the stage for the postglacial morphology and small-scale processes we see today (paper 2). The third paper attempts to explain these small-scale processes using a 1D hydraulic model that can answer dynamic questions like bankfull discharge, water surface slopes of discharges, and velocity reversal hypothesis.
Bergman, Nathaniel, "Channel Form and Processes in a Formerly Glaciated Terrain" (2016). Electronic Thesis and Dissertation Repository. 4332.
Available for download on Monday, December 31, 2018
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