To study flows in man-made or natural channels, the identification of the roughness caused by vegetation is important. The roughness parameters used in several equations such as Manning, Chezy, and Darcy-Weisbach are the experimental coefficients that represent mostly sidewall characteristics. In open channel flows having natural or man-made vegetation to control the flow sections, the knowledge of flow velocities, flow depths and/or flow rates are crucial for planning and management studies. For such studies, the quantification of the roughness caused by the vegetation becomes vital. In this study, roughness caused by vegetation in open channel flows is investigated experimentally and a non-linear regression equation relating Manning roughness coefficient to flow and vegetation characteristics is proposed.