This study was conducted to evaluate the effect of the transverse troughs on hydrodynamic behavior within a full-scale sedimentation basin (flow rate/one basin: 10,000 m3/d) using CFD (Computational Fluid Dynamics) simulation and ADV (Acoustic Doppler Velocimetry) technique. In order to verify the CFD simulation, we measured the factual velocity at 36 points in the full-scale sedimentation basin, whose outlet structure is inadequate, with ADV. Both the CFD simulation and the ADV measurement results were in good accordance with each other. From the CFD simulation results of the existing basin, it was found that extreme upward flow occurs in the near of two transverse troughs. It was suspected that, since the transverse troughs converted the open channel flow into the local closed pipe flow, the increased pressure in this local closed pipe flow region made the extreme upward flow. To solve this problem, it was suggested changing a transverse typed into a finger typed launder and building a longitudinal baffle at the central plain in this study. The CFD simulation results of all retrofitting suggestions told us that the extreme upward flow had occurred especially beneath the transverse troughs, and was much less in the case of a finger-typed launder basin than that in the existing basin. Also, it was predicted that installing a longitudinal baffle made the fully developed flow which is more effective for sedimentation.