In this study, the influence of Darcy and non-Darcy drag on the formation of channel segregation during columnar solidification inside a 3D rectangular cavity is investigated numerically. The contribution of non-Darcy drag is included in the model by introducing Forchheimer correction term in momentum conservation equation. A solver module is developed in OpenFOAM for solving the coupled transport equations of mass, momentum, energy and species. Subsequently, the simulations are performed to predict the flow field, temperature, species and solid fraction distribution including the morphology of channel segregates for Darcy and non-Darcy drag models. This study reveals that non-Darcy drag has a significant influence over the natural convection flow near the liquidus region. It strongly affects the species transport and hence the advancement of mushy zone. The most prominent consequence of this additional drag is that it affects the morphology of channel segregates and reduces the number of predicted channels.