Meandering compound channels, consisting of a main channel flanked by floodplains, are fundamental components of riverine landscapes, playing vital roles in flood management and ecological processes. Accurately predicting the velocity distribution within these channels during overbank flow scenarios is a persistent challenge due to inherent three-dimensional (3D) flow complexities. These complexities include the development of significant secondary currents within the main channel bends and strong momentum exchange phenomena occurring at the interface between the main channel and the adjacent floodplains. Precise velocity field characterization is paramount for reliable flood inundation mapping, sediment transport modeling, and the design of river engineering works. Computational Fluid Dynamics (CFD) is a vital tool for studying these complicated flows in detail. However, it’s important to understand how well different turbulence models work within the common Reynolds-Averaged Navier–Stokes (RANS) framework, especially in capturing the details of flow patterns at the channel-floodplain boundary and in sharp bends. While standard models like k-ε are widely applied, studies suggest limitations in their ability to accurately predict secondary flows driven by turbulence anisotropy. This study uses the ANSYS Fluent CFD software to evaluate the Shear Stress Transport (SST) k-ω turbulence model. A 3D numerical model simulating flow in a representative meandering compound channel geometry is developed. The Primary focus is comparing the SST k-ω model’s predictions of velocity distribution and secondary flow structures against the standard k-ε model across different relative flow depths. This research confirms that more advanced RANS models, such as the SST k-ω model, are useful tools for real-world computer simulations of how water flows in complex river channels.