CGRG Bibliography of Canadian Geomorphology
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Author : Gardner, J.T.; and Ashmore, P.
Date : 2008.
Title : Confluence evolution and river deposit geometry in a braided river model.
Publication : Joint Annual Meeting of the Canadian Geophysical Union and the Canadian Geomorphology Research Group. May 11-14, Banff, Alberta.
Issue :
Page(s) :
Abstract
Confluence zones in braided streams and associated bed scour are ephemeral and laterally unstable in keeping with the overall instability of braided river morphology. Although individual confluences may exist for relatively short periods, they are significant to the river morphology and sedimentology because the local bed scour is often greater than that in individual anabranches and therefore confluences define the intrinsic maximum scour depth and scour surface in braided rivers and their deposits. In this way, there is a fundamental connection between confluence morphology and development and the overall geometry of the braided river deposits. In fluvial sedimentology research, confluence movement and sedimentation patterns have been inferred from outcrop or inference from observations of physical models, or based on theoretical analysis. Analysis of the connection between confluence morpho-dynamics and bed geometry requires data on confluence dimensions and migration patterns in order to characterize the spatial extent of the scour surface and the associated lateral migration deposits. This connection between confluence zones and bed thickness has not been fully addressed in part because of a lack of the necessary data. To this end, we used small-scale physical models of braided rivers in a flume understand the connection between confluence migrations and their control on deposit geometry. Digital photogrammetry was used to create a series of high-resolution DEMs of bed topography over a period of 22 hours in the flume. Based on these DEMs we present an analysis of the morpho-dynamics and dimensions of multiple confluences and their migration zones, and compare this with previous analyses of confluence deposits in ancient and modern river deposits. This geometric connection between confluence behaviour and the confluence deposits supports the idea that confluence migration has a significant impact on braided river deposit geometry. Finally, we present an assessment of the evolution of the scour surface of the deposit and the role of confluences in defining that surface.
Bibliography of Canadian Geomorphology