Open channels and rivers often have vegetation patches of finite length and width. The flow over these patches is in the transition region which significantly influences the prediction of roughness coefficient. This study investigates the interaction of patches with turbulent flow structures in the transition region and evaluates the application of different roughness coefficients in the presence of vegetation patches. Since most of the studies in the area of flow structure interaction with vegetation have been for the extended vegetation on the all open channel bed; therefore the purpose of this research is to investigated the atchy vegetation effect on the flow structure (distributions of velocity components, stress tensor, Reynolds stress), and identification of relation between flow resistance and factors affecting it. Experiments were conducted in an 8 m length, 40 cm width and 60 cm depth flume, contains rectangular cross section, located at Water Research Center of Isfahan University of Technology. The bed flume is covered by gravel with grain median diameter equal to 16.63 mm. Placed natural vegetation at the bed was selected from aquatic plants from Characeae family, that there are in small streams, which its height chaned that in the range 1-3 cm. Research, in order to measure the instantaneous three-dimensional velocity components, Acoustic Doppler Velocimeter (ADV) was used. Experiments were performed in three runs, contain in gravel bed as witness bed, gravel bed with two patches at the right and left bank, and gravel bed with three patches at the right and left bank and at the center of channel. Spectral analysis revealed that the power law of -5/3 Kolmogorove was satisfied in the inertial subrange at the leading edge and over the patch, but did not work at the trailing edge due to the variation in roughness scale and flow conditions. Results showed that the spectral distributions of velocity, Reynolds stress and turbulent kinematic energy at the trailing edge of vegetation patch were significantly different from those at the leading edge and over the patches. By plotting the stress tensor components, it could be found that for the most cases the normal stress (u’u’) and the shear stress (u’w’) have the maximum and minimum magnitudes, respectively. Also it was observed, by going forward from the leading edge to the end of the patch, the distribution of stress components, especially for the normal stress, comes from the linear state to the divergent state, however at the leading edge was shown the convergent shape, which this state is more visible for the near bank patches. Investigating of the relation between different parameters of patch and flow resistance coefficients, indicated that L c W c /LW ratio have the maximum correlation with Darcy-Weisbach coefficient. Keywords: Patchy vegetation, Turbulent flow structure, Stress tensor, Reynold stress, Roughness coefficient