Development of simplified tools for erosion assessment and prediction in semi-alluvial clay-bed rivers

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An alluvial river has bed and banks composed of sediment transported by the flow, thus is free to adjust its shape to convey best its incoming flow and sediment. Rivers in much of eastern Canada flow through regions comprised of cohesive glacial sediments, including glaciomarine clays. These rivers are semi-alluvial, in that they are incising into these non-alluvial substrates, yet portions of the channel bed may be covered with a surficial veneer of alluvial material. Given the glacial history of Canada, many if not most of its rivers can be characterized as semi-alluvial. Management of these rivers is a difficult challenge, because relatively little is known about erodibility of their cohesive bed sediments or their stable channel geometry. The proposed research will 1) improve and compare methods for measurement of the critical bed shear stress required to mobilize a cohesive clay bed material, and 2) develop a simplified approach to account for erodibility of clay bed material when defining stable river geometry for channel design purposes. In the first stage of the research, cohesive bed sediments from Feedmill Creek, Ottawa will be tested for critical shear stress using three different methods: fluvial shear stress in a piston flume, normal stress using an industry standard jet tester, and by surface shear strength using a novel device developed at the University of Ottawa. In the second stage of the research, the one-dimensional hydraulic model SWMHYMO will be adapted to predict equilibrium cohesive-bed channel dimensions subject to unsteady continuous full year discharge hydrographs. This project is a collaboration with JF Sabourin and Associates Ltd, who will utilize the research results to improve management of semi-alluvial rivers in Eastern Canada.