: Weirs are a type of hydraulic structures that are used in water supply systems and irrigation networks for different purposes such as; increasing the upstream water depth, measuring the flow discharge, deviating or evacuating the excess water from the reservoirs and canals. Weirs are categorized as different types. They must be selected in respect to the hydraulic conditions and to satisfy all the objectives of a project. The present study subjects to investigate the hydraulic characteristics of flow over the streamlined weirs, based on model experimentation, analytical modeling and numerical simulation. The streamlined weirs are a special type of weirs, designed based on the airfoil theory. This kind of weirs have some merits compared to the other types of weirs. They have high discharge coefficient, stability and fewer fluctuations of water free surface. According to the objectives of the present study, primarily, an experimental investigation was performed, applying different experimental models of streamlined weirs, designed according to the Joukowsky transform function. Applying this transformation, the weir pattern generated on the destination coordinate plain is a function of the radius and the coordinate of the center of a circle on the source coordinate plain. Experimental results inferred that for a constant flow discharge, the upstream flow heads over the streamlined weirs with different relative eccentricities are almost constant, showing an approximately constant discharge coefficient by the variation of flow head. Furthermore, adding a downstream sloped face does not change the flow discharge coefficients. However, increasing the weir height, results in the increase of the flow head and the decrease of the flow discharge coefficient, especially, for the higher heads and the lower relative eccentricities. Numerical simulations were performed using an open source software namely OpenFoam, leading to an extended data set. Moreover, details of the flow structure over, up- and downstream of these weirs were investigated. Analyzing the results of different turbulence models including; standard k - ? model, realized k - ? model, RNG k - ? model, k - ? SST model, and Reynolds stress LRR model, indicated that all the aforementioned models accurately estimate the flow field and hydraulic parameters. Accordingly, based on the convergence criteria and recommendations of the former studies, the k - ? SST turbulence model was chosen as the best turbulence model for analyzing flow over the streamlined weirs. Numerical results for different flow discharges as well as different relative eccentricities showed that, by increasing the flow discharge and the relative eccentricity, the flow velocity over the crest of weirs increases and accordingly the hydrodynamic pressure in such section decreases. For a constant flow head upstream of different types of the streamlined weirs, the lowest bed pressure and the most probable potential of cavitation belongs to the circular-crested weir (streamlined weir with a relative eccentricity of unity). Furthermore, the greatest bed shear stresses and the compressive forces occur downstream of the circular-crested weirs. Thus, downstream of the circular-crested weirs is responsible to larger potential of bed erosion. This is partly due to the formation of shock waves, reduction of the flow depth, and enhancement of the flow velocity downstream of the circular-crested weirs. Furthermore, the lowest bed shear stresses were observed upstream of the circular-crested weirs. Therefore, upstream of the circular-crested weirs shows the greatest potential of sedimentation. Finally, Applying the streamlined weirs with an appropriate curvature, tends to diminish the unfavorable flow conditions, as observed in the circular-crested weirs, leading to the most safe and economic hydraulic structures. Keywords: Streamlined weir, Joukowsky transform, Potential Flow, OpenFoam software, Discharge coefficient, Water Surface profile, Velocity and pressure distribution, Bed shear stress.