The interaction between a dam-break bore and a vertical square cylinder is studied by using a Reynolds Averaged Navier-Stokes (RANS) model with a k - ε turbulence closure, a large-eddy simulation (LES) model, and direct numerical simulation (DNS). In all three numerical models the free-surface is tracked by the volume-of-fluid (VOF) method. Numerical results are compared with laboratory measurements in terms of the total force acting on the cylinder and the time history of velocity measured at a fixed point upstream of the cylinder. Overall, all three numerical models predict the force and velocity reasonably well, while the RANS model and LES appear to provide more accurate prediction during the period when strong turbulence is present. Based on the RANS model results, the turbulent intensity (TI), defined as the velocity fluctuation divided by the mean velocity, is in the range of 0.2 ∼ 0.4 in the wake zone behind the cylinder and 0.4 ∼ 0.8 in the plunging waves reflected from the end wall. The results from the RANS model and LES are compared with each other. The LES results reveal finer structure compared to the RANS results in terms of free-surface profiles and vorticities. The distribution of the vorticity field is similar to TI indicating that they are strongly correlated. The thin layer of water in front of the dam initially prevents the direct interaction between the bore and the bed. However, a series of vortexes generated by the edge of the square cylinder transports the water from the near bed region to the free surface.