CGRG Bibliography of Canadian Geomorphology
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Author : Gardner, J.T.; and Ashmore, P.E.;
Date : 2007.
Title : Bed elevation and grain size changes in a gravel-bed braided river physical model.
Publication : CANQUA Ottawa 2007. Canadian Quaternary Association Conference, June 4-8, 2007. Carleton University, Ottawa, Ontario, Canada.
Issue :
Page(s) :
Abstract
Digital elevation models are now routinely used to map elevation and elevation change in river channels. Data have been acquired from a variety of techniques including interpolation of ground survey points, terrestrial and aerial photogrammetry and remote sensing of flow depth. Repeat surveys can then be used to produce difference maps depicting areas and volumes of scour and fill of the river bed from which river bed dynamics and transport rates can be calculated. At the same time there have also been developments in automated grain size estimation from image analysis at a variety of scales. This can overcome the spatial constraints of traditional point sampling and lead to the prospect of simultaneous, high resolution mapping of elevation and grain size (roughness) and their mutual variation over time. Data of this type could also be used to infer the 3D structure and texture of fluvial deposits as they develop. However, grain size estimation is limited by the physical (pixel size) and radiometric resolution of the images. With field data there also are problems with variations in environmental conditions such as lighting, water depth and water clarity. Furthermore, field data can seldom be acquired for a long enough time or with sufficient frequency to connect the fluvial processes to the developing morphology and sedimentology. In contrast, physical models in a laboratory have none of these constraints. We have modeled gravel bed braided rivers in a flume and used photogrammetry and digital image analysis to produce high resolution, continuous DEMs with textural information at the grain scale over an extended period of time. The results can be used to associate spatial patterns of grain size with particular features and processes and with topography and topographic change. Compilation of a series of DEMs with textural information makes it possible to assemble a 3D picture of the fluvial sedimentology and relate this to particular morphological features and processes. Here we demonstrate the utility of these techniques in monitoring the evolution of a confluence in a braided river model. We are able to deliver high resolution statistical information regarding bed elevation and link that information with grain size at the confluence as it develops through time.
Bibliography of Canadian Geomorphology