Numerical Investigation of the Effect of River Modeling Parameters on Bed Shear Stress

In the design of stream restorations, boundary shear stress (shear stress) during high flow events is one of the key parameters in the assessment of the risk of morphological failure associated with channel bed and bank erosion and sediment transport. The use of two-dimensional hydrodynamic models (2D models) is becoming more common to estimate shear stress for stream restorations. These models can provide detailed distribution of shear stress over channels and floodplain surfaces. Obtaining accurate and reliable estimates of stress requires an accurate digital terrain model, estimates of input flows, and surface roughness coefficients. Impediments to the use of these models include the cost associated with extensively detailed terrain surveys, distributed information about the roughness coefficients, and the determination of appropriate flow conditions that must be modeled to identify erosion susceptible components. In the present research, the two-dimensional hydrodynamic model TUFLOW is employed to assess the sensitivity of shear stress to flow magnitude, upstream extent of the model, and roughness coefficients. Topography and hydraulic data obtained from monitoring efforts of the restored channel and floodplain of Slabcamp Creek located in Rowan County, Kentucky, was used to develop and calibrate the 2D model. Flow magnitude, the location of the upstream inflow boundary condition, and the roughness coefficients were varied to determine the sensitivity of the shear stress at a critical location in the restoration. The shear stress analysis was conducted along cross sections located in areas identified as being potentially at risk for high shear stress. The shear stress distribution was found to be relatively insensitive to the location of the upstream boundary condition and most sensitive to the flow and roughness coefficients of the floodplain. An interesting observation was that the shear stress in the channel decreased with the increased roughness of the floodplain.