A weakly turbulent flow through a rectangular channel with a wall protrusion at its one side (which makes the model of a flow device with a vertical barrier) was analysed. Using a Laser Doppler Anemometry (LDA) method local velocities (averaged and fluctuation) were measured in characteristic flow zones near the wall protrusion and the results obtained were compared with qualitative visualisation studies. On this basis the flow structures, which develop near the protrusion, were evaluated as well as the reach of recirculation zones downstream the protrusions and the degree of velocity fluctuation.