Floating vegetation (Water hyacinth) causes many problems in waterways where it retards flow movement and changes flow structure. In this study the impact of water hyacinth on flow behavior in open channels was investigated in a laboratory flume. Water hyacinth was harvested from natural streams. Four different vegetation densities, three different vegetation root depths and three different vegetation zone lengths were used for smooth and rough channel bed. The case without water hyacinth was considered as comparative case. The water surface profiles for all cases were investigated. Results show that in the presence of water hyacinth water surface profile rises before vegetation zone then goes down until reaches to normal water surface. Results also show that water surface profile influenced by vegetation density, vegetation root depth, and vegetation zone length and bed roughness. Also the effect of vegetation parameters (density, root depth, zone length) on heading up, discharge and equivalent Manning's roughness coefficient was investigated and it is found that these parameters have a great effect on it. Multiple regression equations based on the dimensional analysis theory were deduced to calculate heading up, discharge and equivalent Manning's roughness coefficient.