Vegetation plays a fundamental role in river ecosystems and flow structure. Vegetation patch are placed in the cross section or edge of river that would influence on flow structure and make turbulent and complex flow. Also for small aspect ratio (W/H 5), the velocity profiles and shear stress distribution is different from the ). The bottom of the flume was covered by gravel having a median size d 50 =17.2 mm similar to Kaj River in the Chaharmahal and Bakhtiari city. Data were measured for different vegetation densities and the results were compare whit bare bed runs (gravel without vegetation patch). Then straws were placed as patch near the right wall of flume in five densities and measured data whit ADV. Reynolds stress, turbulence intensity, degree of turbulence, Quadrant analysis, drag coefficient, Manning's roughness coefficient and vegetation blockage ratio were calculated and analyzed. Results showed that in the presence of emergent vegetation, the velocity profile exhibits a two-layer pattern and when the vegetation density increased, the profile showed a three-layer pattern in which Reynolds stress and the degree of turbulence distributions have a different trend. Velocity profile has Three-layer and S-shape distribution, and degree of turbulence has three-layer and Z-shapes distribution. Due to direct relation between drag coefficient with Reynolds stress and inverse relation between drag coefficients with the square of velocity, non-uniform distribution of resistance coefficient emphasizes on considering flow structure in hydraulic models rather than a constant value for a whole of flow depth. In this study, Manning's equation and drag coefficient equation were combined and was proposed an equation, which is independent on vegetation properties to estimate the Manning coefficient. Traditional Manning equation is not suitable and underestimates roughness coefficient that is why it is necessary to use roughness distribution rather than a constant value. Keywords: Emergent vegetation, drag coefficient, Manning's coefficient, turbulence flow structure, blockage ratio
