Abstarct: Side weirs are extensively used in hydraulic engineering, irrigation, and environmental engineering applications which involve flow measurement and regulation. Flows through side weirs are typical examples of spatially varied flow (SVF) with decreasing discharge. The flow emerging out from the side weir is three-dimensional due to variations in the water surface profile. The present study is confined to the rectangular side weir located in a horizontal rectangular channel having zero sill height. In this research side weirs are simulated using the CFD software Ansys Fluent and turbulence models k-ε, RNG k-ε, and k-ω have been used in the simulation. Volume of fluid multiphase flow simulation model is used to analyze the flow’s free surface. The goal of this research is determining flow’s various parameters including distribution of velocity vectors, free surface profile, separation zone in the flow, stagnation zone, and separation plane, using the aforementioned turbulence models, and deciding the optimum turbulence model. Results of numerical models were compared with the lab model of Concordia University for validation. All the turbulence models gave acceptable results for most of the side weir’s flow parameters. The discrepancy in these model’s results were mostly apparent in determining the separation zone of the flow. The k-ε model could not do this task at all and the RNG k-ε turbulence model could only determine the starting point and width of the separation zone of the flow. But the k-ω model could simulate the flow’s separation zone well enough and in comparison with the lab model gave acceptable results.