When dealing with flood issues, compound channels flows are often encountered in the field. This paper investigates the errors that can be expected when using 2-D modelling for compound channel flows, comparing the simulations with experiments. Three flow configurations are analyzed: uniform, gradually varied and rapidly varied flows. The last configuration is obtained by setting a transverse embankment on the flood plain. Errors are estimated on the sub-section mean velocity, discharge andwater depth, on the mixing layer width and on the depth-averaged stream-wise velocity and lateral shear stress. Depending on the flow configuration and on the studied parameter, relative errors significantly vary from nearly zero to 50%. The influence of the 0th order turbulence closure on the mean flow and the dimensions of the recirculation zone behind the embankment is also investigated, using either constant eddy viscosity or Elder’s model.