WIT Press

A Depth-averaged Mathematical Model Of A River Flow Around Bridge Piers


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WIT Press


M. Cetina & M. Krzyk


The main aim of the flow computation presented in the paper was to assess the influence of the designed new road-bridge on the flood situation in the area of the River Savinja in central part of Slovenia. Since the piers of the new bridge are to be situated in a river bend just upstream of the existed railway-bridge, detailed hydraulic investigations were necessary. The two-dimensional depth-averaged mathematical model PCFLOW2D was applied locally to 600 m long stretch of the river. Basic equations of continuity, momentum conservation, transport of turbulent kinetic energy per unit mass k and its rate of dissipation E are solved numerically by using the finite volume approach proposed by Patankar. Its main characteristics are staggered grid, hybrid scheme and iterative procedure of the depth corrections. For the preparation of the input topographic data (preprocessing) and graphical presentation of the final results of the model (postprocessing) the AutoCAD and Quick Surf graphic packages are used. During the calibration process, water surface elevations have been compared with field measurements and results of the one-dimensional mathematical model MIKE 11 and satisfactory agreement has been found. Finally, for different flood discharges ranging from Q100 = 1412 m3/s to Q2 = 612 m3/s, changes in velocity fields and free surface elevations due to the designed piers of the new bridge have been investigated. Some local flow details such as the rise of the water level just upstream and the increased velocities between the piers were well predicted.