The experimental investigations were carried out in order to have detailed information on the flow structure around perforated cylinders using high-image density Particle Image Velocimetry technique in shallow water flow. The depth-averaged free-stream velocity was kept constant as U-infinity=100 mm/s corresponding to the Reynolds number of Re=10000 based on the perforated cylinder diameter. In order to analyze the effect of porosity, beta on the flow structure, the porosities in the range of 0.1 <= beta <= 0.8 with an increment of 0.1 were used and the results were compared with the bare cylinder case by means of velocity and vorticity contours, turbulent kinetic energy, Reynolds shear stress and streamline topologies. It was concluded that the porosity, beta had a substantial effect on the control of large-scale vortical structures downstream of the cylinder in which the shear layers were elongated, fluctuations were significantly attenuated and formation of Karman Vortex Street was successfully prevented by the use of perforated cylinders. (C) 2015 Elsevier Ltd. All rights reserved.