The idea of partitioning a flow has been widely used by hydraulic researchers and engineers as a mathematical treatment to simplify complex flows. Although the flow partitioning argument is intensive, no specially designed experiments have been conducted to verify them or the models, or to determine whether the existence of division lines can be inferred from mean velocity profiles. The aim of this paper is to examine the existence of division lines in smooth channel flow by analyzing the mean velocity distribution in a flume with a smooth flat or curved bed. The newly discovered division lines from experiments were compared with the existing models. It is found that some proposed models proposed have good agreement with the derived division lines obtained from the mean velocity distributions.