Scour Risk Assessment of the O. O. Madsen Bridge During Flood

Ferriday, Daniel Goward (2022) Scour Risk Assessment of the O. O. Madsen Bridge During Flood. [USQ Project]

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The O.O. Madsen Bridge in Warwick experiences severe debris blockage when submerged by floodwaters. The impact of debris blocked guardrail was investigated during the Condamine River Flood Study in 2012. In 2014, USQ engineering student Russell Knipe developed a Computational Fluid Dynamics (CFD) model to assess the impact of debris-blocked guardrail on flood depths upstream of the O.O. Madsen Bridge in Warwick, QLD. Though not the focus of the study, he concluded that debris blocked guardrail increased the stagnation streamline by 0.7m adding an excess pressure head to the water travelling under the bridge, increasing bed shear stress experienced on the river bed by 25%. As such, a recommendation for future research was to modify the CFD model with a transportable channel bed under clear water conditions to determine the effect of scour around the piers. An initial scour assessment of the bridge was conducted to understand channel characteristics and other key parameters for the CFD simulation. Boundary conditions under peak flow conditions were obtained from separate 2D flood models including the Condamine River Flood Study (Jacobs 2012) and Warwick Heavy Vehicle Bypass – Madsen Bridge (TMR 2019). FLOW-3D Hydro was used to solve the unsteady non-hydrostatic NavierStokes equations for the free surface 3D hydraulic model. The hydraulic model was then coupled with the 3D mobile bed sediment transport model to calculate rate of transport and bed erosion. CFD simulations found there was a good representation of scour development due to the processes of local scour and vertical contraction scour for the submerged bridge. The maximum depth of scour was found to be 1.45m below the initial datum, with a confidence limit of ±0.125m. The maximum deposition was 0.35m (± 0.125m) above the datum. The CFD model successfully simulated local scour immediately around the base of the pier, and vertical contraction scour due to flows being forced being the deck. Full development of the scour hole was found to enlarge cross-sectional area by 35%. Velocities beneath the bridge were not found to decrease but occurred further downstream. A flood level drop across the structure was observed to decrease, reducing from 0.33m for the hydrodynamic solution to 0.25m for the sediment transport model.

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Item Type: USQ Project
Item Status: Live Archive
Faculty/School / Institute/Centre: Current – Faculty of Health, Engineering and Sciences - School of Engineering (1 Jan 2022 -)
Supervisors: Wandel, Andrew
Qualification: Bachelor of Engineering (Civil)
Date Deposited: 19 Jun 2023 04:22
Last Modified: 20 Jun 2023 01:11
Uncontrolled Keywords: debris blocked guardrail; impact; scour risk assessment

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