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29 <br />Two-dimensional hydraulic modeling <br />The River 2D two-dimensional (depth-averaged) model developed at the <br />University of Alberta (Ghanem et. al. 1994; 1995; 1996) was used to simulate depths and <br />water velocities at unmeasured flows. This model uses a Petrov-Galerkin upwinding <br />scheme for stability and jump capturing. It can therefore predict, without intervention, <br />regions of supercritical flow and associated transitions. The model also incorporates a <br />highly simplified groundwater flow model for flow in dry (water surface below ground <br />surface) areas. A continuous water surface elevation over the entire domain is predicted. <br />The groundwater component does not attempt to accurately represent subsurface flow <br />fields, but is used merely as a convenient way to handle the lateral wetting/drying <br />boundaries of the surface flow. As such, the groundwater parameters of storativity and <br />permeability are set to arbitrary but small values over the entire solution domain to <br />minimize the groundwater discharge. The model uses a physical description for lateral <br />eddy diffusivity, limited to 0.14 times the bed shear velocity and depth (Fischer, et al. <br />1979). <br />A two-dimensional finite element computational mesh consisting of linear <br />triangular elements was generated for each site. The mesh was created in an unstructured <br />fashion with the primary criteria for refinement being topographic matching. For both <br />study sites the pre-runoff channel geometry was used to define bed elevations. <br />Topographic matching was assessed visually by overlaying contour maps in the mesh <br />generation program. At each node the bed elevation and roughness height were <br />specified. Following the model's discretization scheme, these parameters were assumed <br />to vary linearly over each triangle. The computational domain was extended about 120 m